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MICROTECHNOLOGIES:
Past, Present and future
Further presentations:
www.symbaloo.com/mix/manufacturingtechnology
Dr. Endika...
MICROTECHNOLOGIES: Past, Present and Future
AUTHOR
by E. Gandarias
Dr. ENDIKA GANDARIAS MINTEGI
Mechanical and Manufacturi...
MICROTECHNOLOGIES: Past, Present and Future
INDEX
1. INTRODUCTION__________________________________ 2
2. HISTORICAL BACKGR...
MICROTECHNOLOGIES: Past, Present and Future
by E. Gandarias
MICROTECHNOLOGIES: Past, Present and Future
1. INTRODUCTION
As Dr. Richard Feynman stated in the late 1950s, world’s minia...
a b
Fig. 2.1 The first transistor: (a) invented in 1947 at Bell Labs [2
]; (b) transistor
inventors William Shockley (seat...
• Energy and materials consumption during manufacturing;
• Lightness and portability;
• Increase of selectivity and sensit...
Etymologically, the term MEMS places limitations on the technology and, therefore,
MEMS should more rightly be considered ...
products that need to be “small” to reach a more compact and portable version, and
those products whose functionality is a...
lithography based micromachine, it is noticed that both are approximately the same.
The optimum level in relative accuraci...
4.1. Research policy in Asia
Activity in Asia is basically focused on Japan, Korea, Singapore and Taiwan. The
effort reali...
seem to have invested heavily in micromanufacturing technologies continuously over
the last fifteen or so years [12
].
Reg...
Historically, in the European Union there were no dedicated programs targeting the
specific needs and requirements of micr...
“Fraunhofer System”, which is a splendid case, is a major driving force for
micromanufacturing research, technology develo...
The major boost to the growing market will be the consumer electronics segment,
which is forecast to almost quadruple its ...
Concerning the total amount expected to be invested in MST and MET, MET are far
behind MST because they are emerging techn...
Fig. 2.10 Transistors Per IC Trends [Error: Reference source not found].
The IT field depends strongly on miniaturization ...
applications for micro machined components could be divided in the following fields
(see Fig. 2.11):
• Automotive & transp...
Fig. 2.11 Principal micromanufacturing industrial application fields.
6.1 Automotive & Transport means
Automotive applicat...
a
b c d
Fig. 2.12 Automotive and transport mean applications; (a) Some micromachining
applications in automotive sensing [...
A b c
d e
Fig. 2.13 IT & Telecommunication applications; (a) Toshiba's 0.85 inch hard disk drive
can store 4 GB of data [2...
A b c
d e f
Fig. 2.14 Health & biotechnology applications; (a) In Vivo Magnetically guided Micro-
Robots ETH Zurich [Error...
Sensors take a large relevancy in this field since they make feasible the detection,
determination or measurement of physi...
Similarly, many other classifications for micromanufaturing technologies have been
reported. Mazusawa [Error: Reference so...
Miniaturization methods (Fundamentals of Microfabrication)
Traditional techniques
(not involving
photolithography-
defined...
Fig. 2.17 shows graphically the Brinksmeier´s classification although it should be
mentioned that groups are not fully ind...
noticeable, e.g. stereo-lithography, in which the possibility to build truly 3D
microstructures is present (see Fig. 2.19a...
Thin film deposition
(additive processes)
Etching
(material removal)
CVD
• Atmospheric pressure
• Low pressure
• Plasma en...
electroplating. The resulting metal structure can be used as a tool for ceramic
sintering or plastic replication (hot embo...
Energy assisted processes, similarly called electro-thermal processes, comprise
Laser Beam Machining (LBM), Focused Ion Be...
as small as 5 µm are reported with aspect ratios in the interval of 10-20 [47
-48
],
micro grooves and even complex formed...
7.2.5. Plasma Beam Machining (PBM)
Plasma spraying is a particle method adapted towards fast deposition of thick
films (>3...
along defined paths; eventually leading to removal of the useless part of the
workpiece in the form of chips. In order to ...
Fig. 2.23 Diamond milling processes for the fabrication of microstructured
surfaces [Error: Reference source not found].
D...
a b
Fig. 2.25 Polishing of structures: (a) pin-type tool; (b) wheel-type tool
[Error: Reference source not found].
Polishi...
a b c
d e f
Fig. 2.26 Mechanical processes applications: (a) Micro-car (L =7 mm, W=2.3 mm &
H=3 mm) and rice grains by dia...
The process of hot embossing of thermoplastic polymers involves the plastic
flow of material around a tool that has a shap...
d e f
Fig. 2.27 Replication techniques applications: (a) MIM piezosensor [72
] ; (b) Replicated
sol-gel micro-optical elem...
Standardization in the field of micro technology is required if some sort of unified
language has to be developed. Input f...
Standardization. If a higher acceptance of microsystems is sought, costs and
development time should be reduced. Standardi...
1 [] IC Knowledge, Website: www.icknowledge.com, 2002.
2 [] Bell laboratories, Website: www.bell-labs.com
3 [] IEEE-virtua...
32 [] P. Althainz, J. Goschnick, S. Ehrmann, H. J. Ache, Multisensor microsystem for
contaminants in air, Karlsruhe Micron...
58 [] Acceleron, Inc, Website: www.acceleron-enbeam.com
59 [] Norsam Technologies, Inc., Website: www.norsam.com
60 [] TWI...
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Microtechnologies: Past, present and future

  1. 1. MICROTECHNOLOGIES: Past, Present and future Further presentations: www.symbaloo.com/mix/manufacturingtechnology Dr. Endika Gandarias Mintegi
  2. 2. MICROTECHNOLOGIES: Past, Present and Future AUTHOR by E. Gandarias Dr. ENDIKA GANDARIAS MINTEGI Mechanical and Manufacturing department Mondragon Unibertsitatea - www.mondragon.edu (Basque Country) www.linkedin.com/in/endika-gandarias-mintegi-91174653
  3. 3. MICROTECHNOLOGIES: Past, Present and Future INDEX 1. INTRODUCTION__________________________________ 2 2. HISTORICAL BACKGROUND________________________ 2 3. TERMINOLOGY __________________________________ 4 3.1. MicroStructures or MicroSystems Technologies/ MicroElectroMechanicalSystems (MST/MEMS) 3.2. MicroEngineering Technologies (MET) 4. MICROMANUFACTURING RESEARCH & DEVELOPMENT_ 7 4.1. Research policy in Asia 4.2. Research policy in USA 4.3. Research policy in Europe 5. MARKET EXPECTATIONS__________________________11 6. MICROMANUFACTURING APPLICATIONS____________ 14 6.1. Automotive & Transport means 6.2. Information technology & Telecommunications 6.3. Health & Biotechnologies 6.4. Instrumentation 7. MICROMANUFACTURING TECHNOLOGY CLASSIFICATION__________________________________ 19 7.1. MEMS processes 7.2. Energy assisted processes 7.3. Mechanical processes 7.4. Replication techniques 7.5. Handling, assembly, packaging, quality assurance & metrology 8. FUTURE CHALLENGES___________________________ 34 9. BIBLIOGRAPHICAL REFERENCES __________________ 36 by E. Gandarias 3
  4. 4. MICROTECHNOLOGIES: Past, Present and Future by E. Gandarias
  5. 5. MICROTECHNOLOGIES: Past, Present and Future 1. INTRODUCTION As Dr. Richard Feynman stated in the late 1950s, world’s miniaturization technology has advanced at an astonishing pace. The forerunner of this technology was mostly the electronics industry with its need for manufacturing processes for electronic components, like printed circuit boards and Integrated Circuits (IC). However, currently the market of miniature technologies supports in general, a very fast growing market in a broad field of applications, especially in the medical, biotechnology, telecommunications and energy fields. This chapter represents a general review of the microtechnologies and many illustrations have been included in order to provide a better understanding. Aspects such as the historical background, terminology, research & development efforts in various countries, market expectations & future trends, technology classification and application and future trends will be analysed. 2. HISTORICAL BACKGROUND Since the forties and through the next decade, many important advances were made in the field of microtechnologies; a significant one was the invention of transistors by Bardeen, Brattain and Shockley that fetched them the Nobel Prize in Physics in 1956 (see Fig. 2.1). Transistor had a tremendous impact on computer design, replacing costly, energy-inefficient and unreliable vacuum tubes, as a device that could act as an electric switch. Another important advancement, upon which the current IC industry was built, was the oxide-masking process developed at Bell Labs in 1954 [1 ]. Not long after these inventions, the idea to extend this technology to more sophisticated geometries arose. In fact, miniaturised devices were already invented, but their dimensions were too large to be considered micro-devices. Inspired by the performance of biological systems and their ability to perform functions and store information within their microscopic volumes, R. Feynman discussed the possibilities of making miniaturised mechanical devices. Although he
  6. 6. a b Fig. 2.1 The first transistor: (a) invented in 1947 at Bell Labs [2 ]; (b) transistor inventors William Shockley (seated), John Bardeen (in glasses), and Walter Brattain [3 ]. Fig. 2.2 The first IC, invented in 1958 by Jack Kilby, Texas Instruments, contained a total of five components (transistors, resistors and capacitors) [Error: Reference source not found]. Today's Pentium-IV processor contains over 125 million transistors on it. [4 ]. was building on the techniques available during his time, Feynman made spectacular speculations about the development of the miniaturization industry in terms of both manufacturing and potential processing and operating problems [5 , 6 ]. By the 1970s, the IC industry had made considerable progress since its first appearance at Texas Instruments in the late fifties (see Fig. 2.2). In a few decades the continuous advances involved a considerable improvement of productivity and quality of life through proliferation of computers, electronic communication and consumer electronics. Most frequently cited trend in this development is probably the integration level achieved in the circuits, usually expressed as Moore’s Law, which states that the number of components per chip doubles every 2 years. Other principal trends are shown in Table 2.1. Nowadays, society demands that the success achieved in the miniaturization of microelectronics should be extended to other fields. This miniaturization involves many improvements, mentioned as follows.
  7. 7. • Energy and materials consumption during manufacturing; • Lightness and portability; • Increase of selectivity and sensitivity; • Use of more intelligent materials with structures at the nanoscale; • Taking advantage of scaling when scaling works in the micro domain (e.g. improved thermal management, etc.); • Minimally invasive techniques; • Exploitation of new effects through the breakdown of continuum theory in the micro domain; • Cost/performance advantages. TREND EXAMPLE Integration level Components/chip, Moore’s Law Cost Cost per function Speed Microprocessor clock rate, GHz Power Laptop or cell phone battery life Compactness Small and light-weight products Functionality Non-volatile memory, imager Table 2.1 Improvement trends for ICs enabled by feature scaling [7 ]. These technologies integrated into Micromanufacturing Technologies present an important role for the current and future industry. They bridge the gap between the nano and macro worlds and they are completely changing the thinking as to how, when or where products should be manufactured (e.g. on-site, on-demand, in the hospital operating room or on-board a warship). 3. TERMINOLOGY 3.1. MicroStructures or MicroSystems Technologies/ MicroElectroMechanicalSystems (MST/MEMS) Micromachining techniques were developed over thirty years ago as a result of semiconductor technology. It was found that, through selective doping and etching, one could produce three-dimensional elements on a silicon wafer. This technology became known worldwide as MST (MicroStructures or MicroSystems Technology). Somewhat more recently, companies in the United States adopted the term MEMS (MicroElectroMechanical Systems) as the descriptor of choice, whereas the rest of the world chose to stay with the original term MST. The difference in nomenclature has created substantial confusion in this emerging industry, and may actually have inhibited its growth.
  8. 8. Etymologically, the term MEMS places limitations on the technology and, therefore, MEMS should more rightly be considered a subset of MST rather than a broad-based descriptor. A true MEMS device must include both electrical and mechanical components which, consequently imply that there must be at least one moving or deformable part and that electricity must enter into its operation in some fashion. 3.2 MicroEngineering Technologies (MET) While micro-scale technologies were well established in the semiconductor and microelectronics fields, the same cannot be said for manufacturing micro features and products in materials different from silicon. These technologies are generally classified as MicroEngineering Technologies (MET) and refer to the creation of high-precision three-dimensional (3D) products using a variety of materials and possessing features with sizes ranging from tens of microns to a few millimetres (See Fig. 2.3). Fig. 2.3 Dimensional size for the micro-mechanical machining [8 ]. There is no clear agreement either defining the micro engineering or what a micro product or micro component is considered. Most authors talk about micro engineering simply in terms of size but L. Alting et al. [9 ] gave a more general view that has been accepted in this thesis. Micro engineering is closely related to the whole process of conception, design and manufacture of micro products and thus, cannot be totally expressed without a definition of the concept of micro product itself. It is difficult to give an exact definition of a term that seems to be only size-related in a rapidly changing era. The definition should, therefore, contain the philosophy and characteristics of a micro product. Of course a micro product is characterised by small dimensions, either of the product itself, or of functional features or structures of the product. From a geometrical point of view, micro products can be classified as two- dimensional structures (2D) (optical gratings), 2D-structures with a third dimension (2½D) (fluid sensors) and real three-dimensional structures (3D) (components for hearing aids). The geometry affects the possible manufacturing methods and the associated production support in terms of handling, assembly and metrology. Another important characteristic of micro products is integration. The reason for miniaturization has to be taken into account in order to distinguish between those
  9. 9. products that need to be “small” to reach a more compact and portable version, and those products whose functionality is achievable only by virtue of their small dimensions. Finally, a micro product is usually constituted by several components. Thus it is apparent to distinguish between a micro product and a micro component. Thus, the definition of micro engineering accepted is as follows: Micro engineering deals with development and manufacture of products, whose functional features, or at least one dimension, are in the order of μm. The products are usually characterised by a high-degree of integration of functionalities and components. The creation of truly three-dimensional miniature parts with a high aspect ratio is always a challenge in micromachining in terms of achievable accuracy and relative accuracies. Whereas the absolute accuracy (feature size) that can be reached in micromachining is excellent from millimetres range down to less than 1 µm, the relative accuracy is rather bad. In traditional manufacturing of precision parts; relative accuracies of 10-6 can be attained, but these relative accuracies cannot be reached in micromachining [10 ]. Fig. 2.4 shows habitual range of sizes to clarify about the range of sizes, accuracies, and relative accuracies one talks in micromachining. Fig. 2.4 Precision machining in terms of absolute sizes and absolute & relative tolerances [Error: Reference source not found]. With some processes, surface finishes as good as 1 nm can be created, which are approximately ten times the size of an atom. If the relative accuracy of a house, which is not considered to be a precision part is compared with the relative accuracy of a
  10. 10. lithography based micromachine, it is noticed that both are approximately the same. The optimum level in relative accuracies is usually achieved at sizes that are bigger than micromachined features. In general, it is seen that the smaller the micromachined part is, the more difficult it is to achieve a good relative accuracy. Other challenges that need to be considered in micromachining are the assembly and handling of the small parts, and the strict requirements for the alignment and positioning accuracy of the tools. 4. MICROMANUFACTURING RESEARCH & DEVELOPMENT In general, R&D infrastructures and governmental support are key factors for promoting technological and industrial competitiveness of a country. In the case of microtechnologies, this is even truer when considering the deeply rooted risk in this sector and the need for basic research. Considering the three main world economic regions Europe, USA and Japan with respect to microtechnologies, they differ considerably in the areas of research policy, application level and market penetration. USA and Japan appear to have recognised ahead of Europe the importance of micro and nano technologies as the engine for the growth of their industrial system. In the case of nanotechnologies in particular, the efforts of USA and Japan have been significantly more intense, especially in the USA leading various fields of application. However, emphasis on micromanufacturing R&D is lagging far behind in USA compared with the rest of the world despite the previously realised vast investment. This will undoubtedly have serious long-term implications, since it is well-recognised that micromanufacturing will be a critical enabling technology in bridging the gap between nano-science and technology developments, and their realization in useful products and processes. Table 2.2 reports all trends that micromanufacturing technologies are supporting. Table 2.2 Summary of the relative status of international micromanufacturing technology development (2005) [].
  11. 11. 4.1. Research policy in Asia Activity in Asia is basically focused on Japan, Korea, Singapore and Taiwan. The effort realised in Australia and Hong Kong is remarkable as well although, the activities in these countries have been mostly pushed by universities. Both Japan and Korea support large, multi-year country-wide programs in micromanufacturing and micro-factories, although in Korea this has been a very recent phenomenon. In Japan, the 10-Year Micromachine Program (1991-2001) constituted a major government investment that started a number of initiatives with industry that continue even today. Major successes include micromanufacturing and assembly systems at Olympus, Seiko, Hitachi, Fanuc, and Mitsubishi. In Korea, the Korean Institute of Machinery and Metals (KIMM) was awarded a major government contract for micro-factory development (saving energy, saving space and saving resources) [Error: Reference source not found] (see Fig. 2.5). Fig. 2.5 Micro-factory project [11 ]. In Japan, both the National Institute for Advanced Industrial Science & Technology and The Institute of Physical & Chemical Research (RIKEN) have missions heavily oriented towards R&D for industrial application, and both make major efforts directed towards micromanufacturing with very impressive results. In both laboratories, the R&D programs are producing very sophisticated, complex, and highly innovative processing methods. It is interesting to note that most of the micromanufacturing equipment developed could be classified as somewhat exotic in nature, directed toward sophisticated, low-volume, high-precision needs of specific products and devices, and requiring a significant investment costing between several $100K to $1 million. The companies that have been strong over the past two to three decades in manufacturing leadership, e.g. FANUC (controls), Matsushita Electric (consumer products), Mitsubishi Electric (electronic products, devices) and Olympus (optics),
  12. 12. seem to have invested heavily in micromanufacturing technologies continuously over the last fifteen or so years [12 ]. Regarding the relationship between the universities and companies in Japan, companies expect universities to teach fundamental principles and provide broad scientific education, whereas they provide focused and application-oriented special training during the early years of employment. The government policy related to intellectual property (IP) provides a favourable situation for industry regarding university-based innovations and inventor-ship under government funding. Companies can purchase licenses from the government, that owns all such funded IP, to commercialize university-based inventions. In Taiwan, there is some institutional government investment, but it is mostly through large corporations with strong product focus, typical of Japan’s “branding” strategy. The Industrial Technology Research Institute (ITRI) is the major government- supported laboratory conducting research in support of Taiwan’s high-technology industries, with a large segment being devoted to micromanufacturing research and development. Another government facility, the Metal Industries Research Institute (MIRI) is initiating a program in micro/meso-scale manufacturing methods (M4 ) [13 ]. 4.2 Research policy in USA The USA is surely the leading country for microtechnologies in many application fields due to the vast efforts realised in the development of IC since the late sixties, and the impulse given to the evolution of the silicon microfabrication technologies. This allowed American companies, especially in California (Silicon Valley) a relatively quick access to such sophisticated processing technologies that are essential for the development of microsystems. Over the last 20 years, the USA emphasised MEMS, and many start-up companies were promoted; thanks to the positive conditions to produce low volume-price rates. Public support policies started slowly in MEMS field were principally pushed by the National Science Foundation (NSF) with less than $1million per year. However, the Defence Department is currently the biggest investor with funds exceeding $50 millions per year. Nevertheless, the effort devoted to R&D is limited at present with respect to the effort in production due to a change in the USA government’s investment policy. The USA government regards nanotechnologies as a national priority, emphasising the impact of such technologies mainly on structural (mechanical) properties of new materials, on diagnosis and therapy, and on storing, processing and transmitting data. This matter has relegated all investments in micromanufacturing technologies aside, which is allowing Asian and European countries to gradually reduce the difference in the state of the art micromanufacturing technologies with USA [Error: Reference source not found]. 4.3. Research policy in Europe
  13. 13. Historically, in the European Union there were no dedicated programs targeting the specific needs and requirements of microtechnologies, and its development has been strongly linked to research centres and universities. During the past few years, there has been an increase in government investment in institutions. The emphasis seems to be on creating an enabling infrastructure to support the conversion of research results into technologies to the point that they are attractive to companies for application and commercialization [Error: Reference source not found]. Opportunities for micro systems can also be found in EURIMUS II program, an industrial initiative inside the EUREKA programme to support the development of products and systems exploiting microtechnologies as well as enabling technologies, manufacturing and equipment for all application domains [14 ]. Additional support is provided by two other initiatives: NEXUS (Network of Excellence in Multifunctional Microsystems) and EUROPRACTICE. Established in 1992 with European Community support, NEXUS aims to promote R&D and commercialisation of MEMS and microsystems through the creation of a set of co- ordinated forums for discussion and exchange of information among researchers and workers in the MST field. EUROPRACTICE, which links together several European competence centres (also includes non European Union (EU) participants), provides support in designing, prototyping and manufacturing of micro systems [15 ]. More recently, inside the VI EU´s Framework Programme, the Multi-Material Micro Manufacture (4M) Network of Excellence has been created. Its main aim is to improve research collaboration in the development of Micro and Nano Technology (MNT) for the batch-manufacture of micro-components and devices in a variety of materials for future microsystem products. Furthermore, many projects related to microtechnologies have been approved, like LAUNCH-MICRO (MicroTechnologies for Re-launching European Machine Manufacturing SMEs), PROFORM (an innovative manufacture process concept for a flexible and cost effective production of the vehicle body in white: Profile forming), MASMICRO (integration of manufacturing systems for mass-manufacture of miniature/micro products bulk forming), Nano-CMM (universal and flexible 3D coordinate metrology for micro and nano components production), PHODYE (new photonic systems on a chip based on dyes for sensor applications scalable at wafer fabrication) or Production4micro (production technologies for micro systems). It is clear that Europe, inside and outside the EU, is stepping up its effort to increase its competitiveness in this field with respect to USA and Japan. However, the situation of the development varies from country to country mainly due to a bigger investment in recent years in micromanufacturing R&D; Germany, France, UK, Switzerland and some of the Scandinavian countries seem to be already better placed than others in this effort. The great investments realised in the field of microtechnologies by Germany has led it to the third position in the world, just behind the USA and Japan. There is a mix of government and private/industry funding and projects tend to be long-term. Emphasis is on refining and fine-tuning technologies to make them commercially attractive and easily adapted. Links with universities seem to be very important to success. The
  14. 14. “Fraunhofer System”, which is a splendid case, is a major driving force for micromanufacturing research, technology development and commercialization with strong ties with the university system and industry obtaining impressive results. On the other hand, there is abundant evidence of the desire to commercialize smaller micromanufacturing machine tools and accessories on a commodity basis, examples include Kugler’s Flycutter and MicroTURN machines, the Carl Zeiss F25 small-scale CMM, the Klocke Nanotechnik microscale robotic systems, etc. [Error: Reference source not found]. 5. MARKET EXPECTATIONS According to a study of the European NEXUS organization (Network of Excellence in Multifunctional Microsystems), the worldwide market for Microsystems (including MEMS/MST) technologies is growing at an average rate of 11% per year from $36 billion in 2005 to $52 billion in 2009. This analysis includes a break-out of the market for 1st level package MEMS/MST, e.g. the inkjet head of an inkjet printer, from $11.5 billion in 2004 to $25 billion in 2009 [Error: Reference source not found]. Fig. 2.6 offers a broad view of the current market segmentation along MNT functionality and maturity. Fig. 2.6 Typology of microsystems markets [Error: Reference source not found]. NEXUS “Market Analysis for MEMS and Microsystems III, 2005-2009” report states that MST/MEMS sensors and actuators consolidate their position in established Information Technology (IT) peripheral markets for read/write heads and inkjet heads, in addition to creating new opportunities in areas such as microphones, memories, micro energy sources and chip coolers (see Fig. 2.7) [Error: Reference source not found]. EnablingMNT market researchers (an international team of experts in the business of micro and nano technologies) expect the automotive sector to remain a major application field with several high-volume safety products including air bags and tire pressure monitoring systems.
  15. 15. The major boost to the growing market will be the consumer electronics segment, which is forecast to almost quadruple its share from 6% of the MST/MEMS market in 2004 to 22% in 2009. Experts see rear and front projection TVs for home theatre, as well as HDDs serving the increasing storage requirements of digital equipment such as DVD recorders, digital cameras, camcorders and portable MP3 players. A big driving force is the mobile phone, which already features motion sensors and is amenable to a variety of additional sensors and functions like liquid lenses for camera zoom, fingerprint sensors, micro-fuel cell power sources, gas sensors and weather barometers (see Fig. 2.8). Fig. 2.7 Total market for 26 MST/MEMS products, 2004-2009 [Error: Reference source not found]. Fig. 2.8 Market Analysis for MEMS and Microsystems III 2004 – 2009 [Error: Reference source not found].
  16. 16. Concerning the total amount expected to be invested in MST and MET, MET are far behind MST because they are emerging technologies. However, regarding expansion percentage expectations, MET present a sharp promising growth and extension to many applications and fields. Microsystems have experienced a strong evolution since the appearance of the initial read/write and inkjet heads and the first micro acceleration sensors used in airbags. Existing microsystem markets worth a few billion euros (e.g. inkjet heads) attest the economical interest of microsystems. It should be noted that the overall microsystem market growth depends equally on established (e.g. pressure sensor, inkjet) and new (e.g. displays) applications. These trends are summarised in Fig. 2.9. Automotive remains a driving force for microsystem innovation by offering high volume applications with only a few major customers. Microsystem supply chain for automotive shows that it can innovate on all levels (materials, components, systems, usage). The biomedical and telecommunications sectors are also major drivers for current and future microsystems development. In this field, for example, in-vitro diagnostics (mostly biochips, bio arrays and micro plates) are expected to become a very strong large-volume market. Fig. 2.9 Microtechnologies Timeline [Error: Reference source not found].
  17. 17. Fig. 2.10 Transistors Per IC Trends [Error: Reference source not found]. The IT field depends strongly on miniaturization capabilities. The engine that powers the computer revolution is micromanufacturing. Micromanufacturing packs more and more devices into each chip devices that switch faster and consume less energy. In 1945, computers used vacuum tubes with the size of a thumb. As shown in Fig. 2.10, today they use transistors so small that a hundred of them could sit on the tiny, round, transversal section of a cut off hair. All signs point to a revolution that advances to the limits set by natural law and the molecular graininess of matter. Trends in miniaturization point to remarkable results around 2015; device sizes will shrink to molecular dimensions and switching energies will reduce to the scale of molecular vibrations. With devices like these, a million modern supercomputers could fit in a pocket. Although detailed studies already show how such devices can work and how they can be made, using molecules as building blocks, will require vast efforts before results are obtained. 6. MICROMANUFACTURING APPLICATIONS Miniaturization was first conceived for military applications in the 1960s. However, information technology and communications were the first sectors to use the techniques, developed and paid by the military for industrial and consumer products. Without such investments in miniaturization, PCs, mobile phones and the Internet would not have been possible these days. In forecasting the trend, it is expected that the progress of society will be tightly connected with technological evolution, affecting both the available products and the services offered. The most spectacular results in the progress of miniaturization will probably be seen in the increase of processing power of mainframe computers and PCs [Error: Reference source not found]. There is an increasing demand to make existing products smaller, producing microcomponents with tolerances in the submicron range. The broad range of industrial
  18. 18. applications for micro machined components could be divided in the following fields (see Fig. 2.11): • Automotive & transport means; • Information technologies (IT) & Telecommunications; • Health and biotechnologies; • Instrumentation & sensors. Many of these applications will have a drastic increase in the world market in the upcoming years. IT and Health/Biotech, with around 60% and 30% respectively of the total, have majority of the market. However, Telecommunication that somewhere between 5% and 7% of the total at present, is showing one of the highest rates of growth, and in the future, it will be one of the main driving forces for micro and especially, nano technologies [Error: Reference source not found]. Applications in the Automotive and Telecommunication sectors have gained increasing ground during the last few years and their share of the market continues to expand. Instrumentation, namely sensors, has a high degree of overlap with the other three sectors considered. There are also other rather interesting applications for these miniaturised systems, such as, sensors for environmental control or in domotics that justifies separate treatment. The situation and trends in the four specified application fields is illustrated in more detail in the following sections. Some of the products listed below have been in the market for quite a substantial length of time, but many did not even exist until recently.
  19. 19. Fig. 2.11 Principal micromanufacturing industrial application fields. 6.1 Automotive & Transport means Automotive applications for microtechnologies address problems mainly related to the increase in safety, quality and reliability requirements. There is a strong demand for better economy of operation as well as more comfortable transport means and the production of environmentally sustainable components. The present range of commercial products refers to micro system technology (MST) products and to miniaturised electronics and systems (see Fig. 2.12). However, microtechnologies will also find their way in other fields such as new types of paints, new catalysts and new materials, all of which could greatly influence the characteristics and the use of the next generation cars. In a complex electronic/electro-mechanical system such as the modern car, the need for effective, accurate, reliable and low-cost electronics and sensors are pressing. Whereas in 1980, electronics accounted for merely 2% of the total cost of the car, today it has reached almost 30% [Error: Reference source not found]. There are 20 to 100 sensors installed in a modern automobile depending on the make and model. Some of the most demanding sensors positioned currently in cars are accelerometers (airbag release), micro-nozzle systems (injection system), pressure sensors (gas recirculation), gyroscopes (navigation), level, light & temperature sensors (oil/gas indicator, turn on lights and outside/inside temperature measurement), parking sensors (collision avoidance) and air flow sensors (air/flow ratio control) [16 ]. AUTOMOTIVE & TRANSPORT MEANS INFORMATION TECHNOLOGIES & TELECOMMUNICATIONS HEALTH & BIOTECHNOLOGIESINSTRUMENTATION & SENSORS
  20. 20. a b c d Fig. 2.12 Automotive and transport mean applications; (a) Some micromachining applications in automotive sensing [17 ]; (b) MS7000 Series accelerometer [18 ]; (c) Diesel fuel injection nozzle [19 ]; (d) Silicon Micro Ring Gyro [20 ]. 6.2 Information technology & Telecommunications It is hard to deny that our society evolves towards an information society. As a matter of fact, today every citizen, at least in the developed countries, is in position to receive, store, process and transmit a huge quantity of information, much more than even few years ago, and this quantity of information will steadily increase in the next years. Microtechnology has been one of the driving forces pushing this trend, since each progress in information storage, processing and sharing is accompanied by a progress in reduction of the geometrical features of the used devices. Besides this, demand for increasing the performance and for reducing the costs have been main factors in this trend.
  21. 21. A b c d e Fig. 2.13 IT & Telecommunication applications; (a) Toshiba's 0.85 inch hard disk drive can store 4 GB of data [21 ]; (b) Single nozzle (diameter 5 µm) [22 ]; (c) Micro- mirrors fabricated on the surface of a silicon wafer for an image projector [23 ]; (d) Virtual keyboard [24 ]; (e) Acceleration Sensing Glove [25 ]. This application area today also constitutes the largest micromanufacturing technologies market dominated principally by two products, namely, the hard disk drive heads (HDD) and ink-jet print heads. Other important applications involve magneto- optical heads, projection displays, electronic papers, gyroscopes, optical switches, attenuators, gain equalizers, micro-relays, RF components, etc. [Error: Reference source not found] (see Fig. 2.13). 6.3. Health & Biotechnologies Many promising expectative claim that health & biotechnologies field will have a pervasive and profound impact on the future of microtechnologies. Demand to address problems like miniaturization of existing devices, increasing in biocompatibility and functionality, or decreasing in time for measuring and analysis are needed. Medical and biomedical markets show promise in a wide variety of applications as shown in Fig. 2.14 [Error: Reference source not found]. They could be grouped as: • Implantable systems: cardiac pacemakers, implantable hearing aids; • Diagnostic systems: blood pressure sensors, glucose sensors; • Minimal-invasive surgery or non-invasive surgery: endoscopy, tools for minimally invasive surgery (see Fig. 2.15); • Pharmaceutical applications: intelligent drug delivery systems and smart pharmaceuticals; • Biotechnical applications: biochip/lab-on a chip technology, nano particles in gene technology and therapy; • Biofunctional devices: tissue engineering for bioartificial organs and skin.
  22. 22. A b c d e f Fig. 2.14 Health & biotechnology applications; (a) In Vivo Magnetically guided Micro- Robots ETH Zurich [Error: Reference source not found]; (b) Hearing aid device [26 ]; (c) Microfluidic cytological tool, for cell counting and separation [27 ]; (d) Bucal Tubes and brackets for dental applications [28 ]; (e) Lilliput chip for microbiological diagnostic system [29 ]; (f) Micro-gripper for surgery [30 ]. Fig. 2.15 World Market Share of Minimally Invasive Surgery Products [Error: Reference source not found]. 6.4. Instrumentation The term instrumentation can be referred to a wide range of products and microtechnologies can have a profound impact. The pursued goals are broad due to the variety in products; large-scale miniaturization, user’s comfort increase, reduction of energy & raw material consumption & product’s final cost, autonomous and remote control, easy maintenance, improvement of environment quality, etc.
  23. 23. Sensors take a large relevancy in this field since they make feasible the detection, determination or measurement of physical and chemical parameters in sectors like ambient conditions control, industrial automation, house control and domotics, agro- industrial production control or metrology (see Fig. 2.16). Today, the market for sensors is segmented into pressure, temperature, acceleration, flow and force where pressure and temperature sensors cover practically two thirds of the market [Error: Reference source not found]. 7. MICROMANUFACTURING TECHNOLOGY CLASSIFICATION The number and diversity of technologies to produce microcomponents and microproducts is enormous. Those could be classified first as top-down manufacturing methods; starting from bigger building blocks and reducing them into smaller pieces. Second as bottom-up manufacturing methods, in which small particles such as atoms/molecules are added for the construction of bigger functional structures. And third as either the development of entirely new technologies or combination of existing technologies. a b c d e f Fig. 2.16 Instrumentation applications; (a) Silicon micromechanical microphone for a mobile telephone or a hearing aid [31 ]; (b) Gas sensor microchip [32 ]; (c) Wireless micro-weather station (size of a film canister) [33 ]; (d) Micro-spectrometer [34 ]; (e) Biometric device [35 ]; (f) Gas sensor with oil isolation [Error: Reference source not found].
  24. 24. Similarly, many other classifications for micromanufaturing technologies have been reported. Mazusawa [Error: Reference source not found] for instance, classified micromachining technologies according to their working principle or phenomena giving the advantages and disadvantages of each of them. Table 2.3 depicts these considerations combined with a description of the process/material interaction. Madou listed most popular miniaturization techniques with their respective characteristics organising as traditional or non-traditional methods and lithographic or non-lithographic method and gave an extensive overview of the existing microfabrication technologies [2] (see Table 2.4). Some other authors divided the micromanufacturing technologies in removal, deposition and molding [36 ], others from University Nebraska-Lincoln made a classification considering technologies which used tools (solid or image) or masks (anisotropic and isotropic) [37 ], etc. Working Principle Material interaction Subtractive Mass containing Additive Joining Mechanical force Cutting Grinding Blasting Ultrasonic machining Rolling Deep drawing Forging Punching Ultrasound Cold pressure welding Melting/Vaporization (Thermal) EDM LBM EBM CVD PVD Welding Soldering Bonding Ablation LBM Dissolution ECM Isot.& anisot. etching Reactive ion etching Solidification Casting Injection moulding Recomposition Electroforming Chemical deposition Polymerisation/Lamination Stereo-lithography Photo-forming Polymer deposition Gluing Sintering Combination of mechanical and thermal principles Table 2.3 Overview of technologies for manufacturing of micro products by Mazusawa [38 ].
  25. 25. Miniaturization methods (Fundamentals of Microfabrication) Traditional techniques (not involving photolithography- defined mask) Non traditional techniques (involving photolithography- defined mask) Non traditional techniques (not using photolithography- defined mask) AFM, STM (A,S), (Se) Self-assembled monolayers LIGA (S/A) UV transparent resists (S/A) Molded polysilicon HEXSIL (S/A) Erect polysilicon (S/A) Micromolding (A), (Ba) Photofabrication (S) Photochemical milling (S) Wet etching of anisotropic material (S) Dry etching (S) Polysilicon surface micromach. (S/A) SOI (S) LBM (S/A), (Se) PBM (S/A), (Se/Ba) Stereolithography (A), (Se) Ultraprecision mechanical mach. (S), (Se) Microdispensing (A), (Se/Ba) Injection molding, hot embossing (A), (Ba) Power blasting (S), (Se) Abrasive water jet (S), (Se) Chemical Milling (S), (Ba) Electrochemical machining (S/A), (Ba) EDM (S), (Se) EDWC (S), (Se) EBM (S/A), (Se) Continuous deposition (A), (C) FIB (S/A), (Se) Hybrid thick film (A), (Ba) A=Additive C=ContinuousS=SerialBa=BatchS=Subtractive Table 2.4 Classification of miniaturization methods by Madou [Error: Reference source not found]. However, Brinksmeier’s classification [Error: Reference source not found] (see Fig. 2.17) is currently one of the most widespread and it is the accepted one in this thesis. The machining of precision parts and micro structures is subdivided into two general types of technologies having different origins; MicroSystem Technologies (MST) and MicroEngineering Technologies (MET). MST are qualified for the manufacture of products of Micro Electro Mechanical Systems (MEMS) and Micro Opto Electro Mechanical Systems (MOEMS). MET comprise the production of highly precise mechanical components, moulds and microstructured surfaces. Next, regardless of its origin, Brinksmeier classifies the micromanufacturing technologies in four groups: • MEMS processes, like UV-lithography, silicon-micromachining and LIGA. • Energy assisted processes like Laser Beam Machining, Focused Ion Beam Machining, Electron Beam Machining and Micro Electro Discharge Machining. • Mechanical processes like diamond machining (e.g. turning, milling, drilling and polishing), micromilling or microgrinding. • Replication techniques like forming, injection moulding or casting. These technologies are suggested in a class on their own, although they require a previous micromanufacturing step to achieve the moulds. • In addition to these four groups, Brinksmeier includes an additional group where important steps for micromanufacturing such as handling, assembly and metrology appear.
  26. 26. Fig. 2.17 shows graphically the Brinksmeier´s classification although it should be mentioned that groups are not fully independent among themselves and that, there can be an overlapping between the categories. The size of the arrows indicates how frequently each group of processes are employed in the MST and MET technologies. In the following sections most widespread processes and production systems used in micromanufacturing will be exposed briefly. 7.1 MEMS processes The manufacturing processes related to the Micro Electro Mechanical Systems (MEMS) and microelectronics fields are based on 2D or planar technologies. This implies the construction of components or products is on or in flat wafers. MEMS products take their starting point in a prepared wafer (usually silicon) cleaned and oxidised. Then, they are formed by creating patterns in the various layers of the wafer. Pattern transfer consists of a photographical transfer of the desired pattern to a photosensitive film covering the wafer, followed by a chemical or physical process to remove or add material in order to create the pattern [Error: Reference source not found]. This basic flow of MEMS micromachining is depicted in Fig. 2.18. Photo-lithography is the basic technique used in pattern transferring between many others like X-ray lithography, charged particle beam lithography, extreme ultra violet lithography, etc. Besides these, the potential of the emerging lithography methods is Microsystem Technologies (MST) Microengineering Technologies (MET) MEMS processes Replication techniques Mechanical processes Energy assisted processes Handling, assembly, packaging, quality assurance and metrology T e c h n o l o g i e s Origin Micro Product Micro Product Fig. 2.17 Process technologies for machining of precision parts and microstructures by Brinksmeier [Error: Reference source not found].
  27. 27. noticeable, e.g. stereo-lithography, in which the possibility to build truly 3D microstructures is present (see Fig. 2.19a). Most usual chemical or physical processes mentioned above are listed in Table 2.5. Fig. 2.18 Basic flow of MEMS micromachining. The microfabrication by MEMS processes is currently accomplished by three major technologies, namely, bulk micromachining, surface micromachining and micromolding (LIGA). These techniques group different processes mentioned before. 7.1.1 Bulk Micromachining In bulk micromachining processes, a portion of the substrate (bulk) is removed in order to create free-standing mechanical structures (such as beams and membranes) or unique three-dimensional features (such as cavities, through wafer holes) by orientation dependent (isotropic) and/or orientation independent (anisotropic) etchants (see Fig. 2.19b-c). Bulk micromachining can be applied to silicon, glass, gallium arsenide and other materials of interests [39 ]. This technique was the conventional one utilised in the IC industry; therefore, it was also adapted and utilised, in microfabrication of MEMS, first among other techniques from the IC industry [Error: Reference source not found].
  28. 28. Thin film deposition (additive processes) Etching (material removal) CVD • Atmospheric pressure • Low pressure • Plasma enhanced • Vapour phase epitaxy PVD • Vacuum evaporation • Molecular beam epitaxy • Sputtering Electrochemical deposition • Electroplating • Electroless plating Spin-on deposition Wet etching • Isotropic wet etching • Anisotropic wet etching (single crystal) Dry etching • Vapour etching • Plasma etching • Reactive ion etching Table 2.5 Thin film deposition techniques and etching techniques [Error: Reference source not found]. 7.1.2. Surface Micromachining At first glance, surface micromachining may look similar to bulk micromachining. However, some sharp differences exist between the two techniques. In bulk micromachining, the three dimensional structure is built by etching the substrate (e.g. polysilicon or single crystal silicon), whereas in surface micromachining, the structure is built through layer by layer deposition (See Fig. 2.19d). Besides this, in surface micromachining, shapes in the XY- plane are not restricted by crystallography as is the case for bulk processes. Table 2.6 compares bulk and surface micromachining. Some of the limitations associated with surface micromachining, as outlined in Table 2.6, have been overcome by process modification and/or alternative designs. 7.1.3. LIGA & Micromolding LIGA is a combination of processes used to manufacture high aspect ratio microstructures with height in the millimetre range, lateral submicronic precision and very smooth walls (See Fig. 2.19e-f). Components made of a large variety of materials can be manufactured; polymers, metals, alloys and ceramics. LIGA was developed by the Forschungszentrum Karlsruhe. It stands for LIthographie (lithography), Galvanoformung (electroplating) and Abformung (moulding), which are the main steps of the process. The original LIGA process starts with an X-ray lithography on a conductive substrate coated with PMMA. The cavities are then filled with metal by
  29. 29. electroplating. The resulting metal structure can be used as a tool for ceramic sintering or plastic replication (hot embossing or injection moulding). Bulk Micromachining Surface Micromachining z-dimension restricted by wafer thickness No annealing needed Devices can be built from single crystal Si Can use crystallography for dimensional control Stiction is not a concern z-dimension restricted by deposition technique used Annealing at high temperatures needed Only Polysilicon can be used Crystallography dimensional control at possible Surface stiction possibility Table 2.6 Comparison between bulk and surface micromachining techniques [Error: Reference source not found]. a b c d e f Fig. 2.19 LIGA & micromolding applications: (a) 3D Micro stereo-lithography components [40 ]; (b) V-grooves by bulk micromachining (anisotropic) [Error: Reference source not found]; (c) Silicon micro air turbine by bulk micromachining [41 ]; (d) Micro-gripper by surface micromachining [42 ]; (e) SU-8 with aspect ratio  60:1 wall by LIGA [Error: Reference source not found]; (f) SU-8 micro gear by UV LIGA [Error: Reference source not found]. 7.2. Energy assisted processes
  30. 30. Energy assisted processes, similarly called electro-thermal processes, comprise Laser Beam Machining (LBM), Focused Ion Beam (FIB), Electron Beam Machining (EBM), Micro Electro Discharge Machining (MicroEDM) and Plasma Beam Machining. 7.2.1. Laser Beam Machining (LBM) The use of laser technology in processing of materials for micro products has been reported over the last decade [43 ]-[Error: Reference source not found], and is now used routinely in many industries. Laser beams are used both to remove material and to join components (heat treatment, welding, ablation, deposition, etching, lithography, photo-polymerization, etc.) [Error: Reference source not found]. The use of lasers in micromanufacturing is closely connected to the characteristics of the laser and depending on that, lasers can be used for a broad range of materials [44 ]. Metals, ceramics, glass, polymers and semiconductors are the most widely used materials for micro products, and all of these materials can be processed by one or more laser technologies (see Fig. 2.21a) [45 ]. The parameters such as wavelength, power, pulse duration and pulse repetition rates are the main ones to be chosen and controlled. 7.2.2. Micro Electro Discharge Machining (MEDM) Electrical discharge machining (EDM) is a relatively slow manufacturing process which has traditionally been used to machine unusual designs in hard and brittle metals. Material is removed (melting and partly vaporization) by high frequency electrical sparks, which are generated by pulsing a high voltage between the cathode tool and a workpiece anode. The workpiece and the tool are submerged in a dielectric fluid [Error: Reference source not found]. The process requires the workpiece material to be conductive and the hardness is not critical. Electrodes are usually made from graphite, copper, or even silver (see Fig. 2.21b). Typical machining technologies for MEDM are Wire-EDM (WEDM), Sinking- EDM (SEDM), EDM-drilling, EDM milling and WEDG (Wire Electro Discharge Grinding). WEDM and SEDM are two major types of EDM. In the wire EDM process, thin wires with diameters as small as 20µm are used as electrodes (see Fig. 2.21c). This process is primarily used for producing 2D structures and for manufacturing electrodes [Error: Reference source not found]. Regarding the SEDM, the manufacture of the electrode is an essential step since it determines the resulting quality of the manufactured feature. The electrode tool is shaped in the form of the desired cavity or simple shaped, in order to avoid the significant wear suffered while machining [46 ]. Holes diameters
  31. 31. as small as 5 µm are reported with aspect ratios in the interval of 10-20 [47 -48 ], micro grooves and even complex formed 3D structures [Error: Reference source not found]. 7.2.3. Electron Beam Machining (EBM) Electron-beam removal of materials is another fast-growing thermal technique. Instead of electrical sparks, this method uses a stream of focused, high-velocity electrons from an electron gun to melt and vaporize the workpiece material. The electron beam is used to write on an electron-sensitive film or create surface modifications of materials (see Fig. 2.21d). The basic techniques are highly developed for IC mask production and are particularly useful for the production of structured surfaces such as binary optics [49 ]. A typical cross- sectional diameter of the beam is 10 to 200 µm at the point of impact on the workpiece [Error: Reference source not found]. 7.2.4. Focused Ion Beam (FIB) Some authors classify Focused Ion Beam (FIB) as a pure mechanical machining technique in which the drill bit is replaced with a stream of energetic ions though it is not very extended yet. A liquid metal ion source (e.g. gallium) is used rather than an argon beam, and the ion beam is focused down to a submicron diameter [Error: Reference source not found]. A principal capability of the dual beam FIB is either the removal or addition of material (see Fig. 2.20). These processes are assisted through several gas micro-nozzle injectors with a gaseous material for a locally reactive environment. Focused ion beam machining is an alternative way of machining Fig. 2.20 Focused Ion Beam dual beam capability [50 ]. fine structures and extremely fine details, even 3D structures with spot sizes down to 10-50 nm [51 ]-[52 ], [53 ] (see Fig. 2.21e) [54 ].
  32. 32. 7.2.5. Plasma Beam Machining (PBM) Plasma spraying is a particle method adapted towards fast deposition of thick films (>30µm) and in terms of future micromachining applications, the method might enable the batch fabrication of solid state gas sensors. However, the technique is currently of marginal use in micromachining (see Fig. 2.21f). a b c d e f Fig. 2.21 Energy assisted processes applications: (a) Micro gearwheel made of sapphire machined by UV LBM [55 ]; (b) Rod, machined by WEDG, diameter: 12 μm [56 ]; (c) Die to extrude polymer for fishing line production using 30 m wire by WEDM [57 ]; (d) Filter body with Ø100 m 3,5 million micro-holes in 316 S/S by EBM [58 ]; (e) Bull sculpture machined in diamond by FIB [59 ]; (f) Aero-engine turbine with a thermal barrier coating by PBM [60 ]. 7.3. Mechanical processes Mechanical processes are mainly employed for the direct manufacture of small numbers of precision parts. These processes comprise micro-cutting processes, microgrinding and ultrasonic machining. In mechanical machining, various factors such as deformation of the workpiece and tool, vibration, thermal deformation, inaccuracies of machine tools, etc., are major concerns regarding attainable machining accuracy [Error: Reference source not found]. 7.3.1. Micro-cutting processes Micro-cutting processes are characterised by mechanical interaction of a sharp tool with the workpiece material causing breakage inside the material
  33. 33. along defined paths; eventually leading to removal of the useless part of the workpiece in the form of chips. In order to realize such a process, the tool material must be harder than the workpiece material, and no thermally activated diffusion has to take place between tool and workpiece material [Error: Reference source not found]. Most common micro-cutting technologies are diamond turning, diamond milling, micromilling, diamond drilling and diamond polishing of structures. Micro-cutting has the advantage that the tools in these processes contact the workpiece during machining leading to a strong geometric correlation of tool path and generated surface. The major drawback of processes of this type is that the machining force may influence machining accuracy and the limit of machinable size because of elastic deformation of the micro tool and/or the workpiece [Error: Reference source not found]. Diamond turning Micro machining is gaining popularity and micro diamond turning is one of the most suitable machining processes for micro-optical device fabrication [61 ]. This process is also known as Single-Point Diamond Turning (SPDT). The process of diamond turning is widely used to manufacture high-quality aspheric optical elements from glass, crystals, metals, acrylic and other materials (see Fig. 2.22). Optical elements produced by the means of diamond turning are used in optical assemblies in telescopes, TV projectors, missile guidance systems, scientific research instruments, and numerous other systems and devices. Tool alignment is an essential pre-condition for achieving the desired quality in diamond turning (tilt errors in X-Y, X-Z and Y-Z planes). Fig. 2.22 Diamond turning [62 ].
  34. 34. Fig. 2.23 Diamond milling processes for the fabrication of microstructured surfaces [Error: Reference source not found]. Diamond milling In diamond milling, mainly two different types of processes for the generation of microstructures can be found; circumferential milling, so called fly-cutting (V- shaped monocrystalline diamond tool), and ball-end milling (Fig. 2.23). Typical applications of fly cutting are micro prisms and reflective arrays, and embossing rollers for circumferential milling (see Fig. 2.26a-b). Micromilling The micro-cutting of traditionally used materials in manufacturing such as steel, aluminium, brass, etc. with tungsten carbide tools can meet many of the demands of miniaturised components (see Fig. 2.26c). Many micromanufacturing processes lack the ability to structure different materials from silicon or polymer, and they are not suitable to generate three- dimensional geometries for small and medium lot sizes. Micromilling is a promising approach to overcome these limits of common microfabrication technologies and it will be analysed in detail in Chapter 3. Diamond drilling For special applications, diamond turning and milling processes applying mono-crystalline diamond tools may not be useful due to their geometric and cinematic limitations. Therefore, diamond contour boring has been developed for the manufacture of micro structured optical moulds (see Fig. 2.24). Fig. 2.24 Contour boring with half-arc monocrystalline diamond tools [Error: Reference source not found].
  35. 35. a b Fig. 2.25 Polishing of structures: (a) pin-type tool; (b) wheel-type tool [Error: Reference source not found]. Polishing If surface quality of structured high-precision molds for the replication of optical components is not sufficient to meet the increasing demands concerning surface roughness, form and accuracy, subsequent polishing of the structured molds may be necessary (see Fig. 2.25). The feasibility for polishing of structures has been demonstrated [63 ]. 7.3.2. Microgrinding Microgrinding is applied for the manufacture of precision parts made of hard materials; glass lenses, silicon, ceramic, etc. (see Fig. 2.26d). It can be used for the fabrication of pins, grooves and micro-cavities with dimensions in the micrometer range. Microgrinding has some constraints in wheel size and shape that limits achievable quality and geometry of micro parts and structured surfaces. Moreover, difficulty in grinding tool-making and preparation including truing and dressing also hampers the widespread application of diamond grinding into micro fabrication significantly. 7.3.3. Ultrasonic Machining (USM) USM, also called ultrasonic impact grinding, is a method in which a tool and free abrasives are used. The tool that is vibrated at ultrasonic frequency drives the abrasive to create a brittle breakage on the workpiece surface. The shape and dimensions of the workpiece depend on those of the tool. Since material removal is based on brittle breakage, this method is suitable for machining brittle materials such as glass, ceramics, silicon and graphite (almost any hard material) [64 -65 ] (see Fig. 2.26e-f). The major problems are the accuracy of the setup and the dynamics of the equipment. Ultrasonic vibration of the machining head makes accurate tool holding difficult [Error: Reference source not found].
  36. 36. a b c d e f Fig. 2.26 Mechanical processes applications: (a) Micro-car (L =7 mm, W=2.3 mm & H=3 mm) and rice grains by diamond machining [66 ]; (b) Plastic fresnel lens replicated from diamond machined moulds for photovoltaic panel [Error: Reference source not found]; (c) Mould for gearwheel milled in steel by micromilling [Error: Reference source not found]; (d) Ra<5nm component by microgrinding [67 ]; (e) A micro-hole in quartz glass machined by USM [68 ]; (f) Micro-devices produced by USM [69 ]. 7.4. Replication techniques In many manufacturing cases, the final objective is mass production. The economic mass production of microparts and microstructures is achieved mainly by replication techniques like Micro-Injection Moulding, hot embossing and micro-casting; though other forming processes in an incipient stage (cold forging, bending, punching, deep drawing, extrusion, etc.) are growing rapidly [70 ]. 7.4.1. Micro-injection moulding Micro injection moulding is based on heating a thermoplastic material until it melts, thermostatting the moulds’ parts, injecting the melt with a controlled injection pressure into the micromould cavity, and cooling the manufactured goods. Micro injection compression moulding and thin-wall injection moulding are two good Micro Injection Moulding candidates for microfabrication [Error: Reference source not found] (see Fig. 2.27a). 7.4.2. Hot embossing 10mm
  37. 37. The process of hot embossing of thermoplastic polymers involves the plastic flow of material around a tool that has a shape inverse of the desired part shape. The material is first heated to a point between the glass transition temperature (Tg) and the melting temperature (Tl) and then, the tool is pressed into the material uniaxially [71 ]. It takes place in a machine frame similar to that of a press. The frame delivers the embossing force of the order of 5 to 20 tons. Hot embossing provides several advantages as compared with micro injection moulding, such as relatively low costs for embossing tools, a simple process, and a high replication accuracy for small features. However, it has the inconvenient with regards to the micro injection moulding of elevated residual stresses on moulded parts and the capability only for low aspect ratio [Error: Reference source not found] (see Fig. 2.27b). 7.4.3. Casting For new product development, an attractive way of rapid prototyping is casting. This method called soft lithography has been used by many researchers because of its simplicity (see Fig. 2.27c). However, the long cycle time and polymerization shrinkage make it difficult for mass production in most industrial applications [Error: Reference source not found]. 7.4.4. Microforming The term microforming refers to the shaping technologies (cold forging, bending, punching, deep drawing, extrusion, etc.), with at least two dimensions under the millimetre range, particularly appropriate for mass production of metallic parts. In this field, metal forming takes up quite a special position due to its well-known advantages of high production rates, minimised or zero material loss, excellent mechanical properties of the final product and close tolerances making it suitable for near net shape or even net shape production. Considering sheet metal working as well as bulk metal forming, the large potential of this technology to be applied in the microworld is opened up. Typical examples are the production of leadframes and connector pins (see Fig. 2.27d-e-f). a b c
  38. 38. d e f Fig. 2.27 Replication techniques applications: (a) MIM piezosensor [72 ] ; (b) Replicated sol-gel micro-optical elements by hot embossing [73 ]; (c) Aluminium casting [74 ]; (d) Micro springs and filaments [75 ] ;(e) Micro extrusion part in comparison with an ant (diameter 500 µm / 300 µm, wall thickness of the cup 50 µm) [76 ]; (f)Pins used for IC carriers [Error: Reference source not found]. 7.5. Handling, assembly, packaging, quality assurance & metrology Manipulation and assembly of micro parts is an issue facing new problems (small joining tolerances, surface forces dominating effect or even micro-device breakage for excessive force, positioning errors due to changes in temperature, vibrations or contamination [56]) that there were not encountered in conventional size production. Besides this, handling and packaging of micro components is crucial to their application, and currently makes more than even 80% of the total costs in some applications [Error: Reference source not found] (see Fig. 2.28a-b). Regarding quality assurance and metrology, process control is the key to the successful manufacture of micro scale devices and products. Functional tests of micro a B c Fig. 2.28 Handling, assembly, packaging, quality assurance & metrology applications: (a) Surgical microtool microgripper with a size of two grains of salt [77 ]; (b) Electro Microfluidic Packaging [78 ]; (c) 3D Zeiss F-25 CMM 7.5nm resolution & 250nm uncertainty for 1cm3 volume [79 ]. products are important to determine product performance. This implies dynamic testing under various operating conditions, and the simultaneous monitoring of product performance.
  39. 39. Standardization in the field of micro technology is required if some sort of unified language has to be developed. Input from both the MEMS and the precision- engineering world are necessary in order to define common guidelines regarding tolerances, measuring instruments as well as measurement and calibration methods [80 ]. Moreover, in the case of small product dimensions, the ratio between surface area and dimensions causes metrological problems. As product dimensions become smaller, the ability to distinguish between surface and linear dimension becomes more difficult. There is a need for instruments capable of measuring real 3D micro products though a few attempts have been made in this direction (see Fig. 2.28c). 8. FUTURE CHALLENGES Currently existing idea that microfabrication technologies and microproducts will have an excellent industrial and commercial acceptance is generalised, and market expectations reveal an enormous potential. However, there are some challenges to be faced if more rapid spread, and an improved acceptance are sought [81 -82 ]: Production capacity. A massive implementation of the microtechnologies in industry requires the possibility to obtain large batch production of microcomponents at a reduced cost. In consequence, new manufacturing processes, new machines and other production means should be developed, or current microtechnologies should be adapted as well. Packaging and assembly techniques. The packaging and assembly techniques allow microsystems to connect with external applications. Existing techniques involve a significant increase of the final microsystems prices. Thus, more economical and novel techniques with an easy connection and suitability for aggressive environmental conditions are required. New materials. Microsystems requirements vary depending on their application. Satisfying these needs means using one or another type of material. Generally, the need to reduce fabrication costs and large batch production of microcomponents, materials’ biocompatibility, the possibility to work within aggressive environments, special behaviour over certain physical properties, and other factors demand using alternative materials to silicon, like polymers, metals, ceramics, composites, etc. or the development of new materials modifying the internal structure at nanometric scale. Specific engineering tools. An adequate microsystem design and simulation helps to reduce errors and save time and money. The design and simulation tools should be specific for each fabrication technology and adapted to work with high precisions and reduced dimensions including appropriate material libraries for microcomponents considering the scale effect.
  40. 40. Standardization. If a higher acceptance of microsystems is sought, costs and development time should be reduced. Standardization results in an effective way to reduce them, increasing the demand to produce microcomponents, overcoming the economies of scale, and making possible the construction of microsystems by means of the integration of modular blocks. Industry needs to be active and aware of standardization matters as well as being effective in getting its standards accepted in the markets. Qualified workforce and multidisciplinary teams. An education system capable of delivering the required diversity and multidisciplinarity in a skilled research, design and production workforce is needed. It is imperative to note that the increasing complexity of the technology requires significant multidisciplinary education and training programmes. Demand is already outstripping the supply of talent. Infrastructure creation. A research environment and adequate infrastructure capable of supporting visionary and industrially relevant advanced pre-production research activities, including validation processes (such as pilot lines), that facilitate the rapid introduction of innovative technologies into manufacturing systems, products and services to deliver world-class results in a timely manner should be constructed. Financial and institutional support. A favourable legal and financial environment (including fast-responding regulatory support) would speed-up participation from the major actors of the critical value chains for the huge and ever-increasing investments required in the competitive globalised market. Strategic public-private partnerships should be rewarded, in which strong user industries share their long-term visions with research partners, and a critical mass of resources is mobilised in the most coherent possible way. 9. BIBLIOGRAPHICAL REFERENCES
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Microtechnologies description: past, present and future Mikroteknologien deskribapena: lehena, oraina eta geroa Descripción de las Microtecnologías: pasado, presente y futuro

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