Nanotechnology

1. begin
A g r e at e r m e a s u r e o f c o n f i d e n c e
Introduction 2 | Nanotech Testing Challenges 2 | Electrical Measurement Considerations 5 | Electrical Noise 6 | Source-Measure Instruments 7
Pulsing Technologies 8 | Avoiding Self-Heating Problems 9 | Application Example: Graphene 10 | Summary 12 | Glossary 13 | Selector Guide 16 | For More Information 17

2. previous home next
Introduction. .....................................................2
.
Nanotech Testing Challenges.......................2
Electrical Measurement Considerations....5
Electrical Noise.................................................6
Nanotech Testing Challenges Source-Measure Instruments. ......................7
.
Pulsing Technologies......................................8
Avoiding Self-Heating Problems.................9 .
Application Example: Graphene................ 10
The nature of nanotech materials requires some As a substance is reduced to nanoscopic dimensions, Summary.......................................................... 12
novel testing techniques. Because these materials both the bandgap and the distance between
Introduction are built at the atomic or molecular level, quantum adjacent energy levels within the material’s electron
Glossary............................................................ 13
Selector Guide................................................ 16
Nanotechnology has the potential to improve mechanics come into play. As a result of small energy bands are altered. These changes, along For More Information.....................................17
our quality of life in diverse ways, such as faster particle sizes, the atoms and molecules of these with a particle’s nanoscopic size with respect to the
electronics, huge memory/storage capacities new materials may bond differently than they material’s mean free path (the average distance an
for PCs, cheaper energy through more efficient might otherwise in bulk substances. There may be electron travels between scattering events), directly Want to Explore Further?
energy conversion, and improved security new electronic structures, crystalline shapes, and affect the electrical resistance of a nanoparticle.
through the development of nanoscale bio- More generally, a material’s bandgap directly Featured Resources
material behavior. Nanoparticles with these new
and chemical-detection systems. influences whether a particle is a conductor, an • Standards Will Help
properties can be used individually or as building Ensure Order in Nano-
blocks for bulk material. Although the discovery of insulator, or a semiconductor. These influential Enabled Industries
bulk properties remains important, measurements electronic properties allow, for example, a carbon
also need to uncover the characteristics unique to nanotube (CNT) to be used to create a transistor
nanoscale structures. switch.2 One way to do this is by connecting a
semiconducting CNT between two electrodes that • Discover Today’s
With nanoelectronic materials, sensitive electrical Particle size and structure have a major influence function as a drain and source. A third electrode (the Solutions for
measurement tools are essential. They provide on the measurement techniques used to investigate gate) is placed directly under the entire length of the Tomorrow’s Nano
the data needed to understand the electrical a material. The material’s chemical and electrical carbon nanotube channel. For a semiconducting Characterization
properties of new materials fully and the electrical characteristics change as particle sizes are reduced CNT, the introduction of an electric field through the Challenges
performance of new nanoelectronic devices and to nanometer dimensions. This even applies to channel (via the insulated gate placed in proximity
components. Instrument sensitivity must be much biological materials. Therefore, most of these to the CNT channel) can be used to change the CNT
higher because electrical currents are much lower materials require chemical and electrical testing to from its semiconducting state to its insulating state
and many nanoscale materials exhibit significantly characterize them for practical product applications. by increasing the gate voltage. Decreasing the gate
improved properties, such as conductivity. The For many of them, the actual quantity being voltage will transition the device into a conducting Additional Resources
magnitude of measured currents may be in the measured is a low level current or voltage that was state. This conduction mechanism is analogous to • The Emerging Challenges of
femtoamp range and resistances as low as micro- translated from another physical quantity.1 Direct the operation of a silicon MOSFET transistor switch, Nanotechnology Testing
ohms. Therefore, measurement techniques and electrical measurements are possible on many which is created by doping silicon with either an • Climbing the Commercialization Hill
instruments must minimize noise and other sources substances with the probing instruments and nano- electron acceptor or donor to alter the material’s
of error that might interfere with the signal. manipulators now available. electronic conductivity in specific localities.
Ask Us Your Application Or Product Question.
2
E n s u r i n g t h e Ac c u r ac y o f N an o sca l e E l ect r ica l M eas u r ements A g r e at e r m e a s u r e o f c o n f i d e n c e

3. previous home next
Introduction. .....................................................2
.
Nanotech Testing Challenges.......................2
Nanotech Testing Challenges (continued) Electrical Measurement Considerations....5
Electrical Noise.................................................6
For macroscopic particles, electrons take on Because the density of states can be used to predict Source-Measure Instruments. ......................7
.
discrete quanta of energy that lie within energy the electrical behavior of materials, it is also possible Pulsing Technologies......................................8
bands, with each band consisting of many energy to use electrical impedance measurements to derive Avoiding Self-Heating Problems.................9 .
levels that electrons can share through their density of states information. The density of states Application Example: Graphene................ 10
thermal energies. For a conducting material, is found by plotting differential conductance vs. Summary.......................................................... 12
electrons can be thermally excited into the applied voltage. Differential conductance is simply Glossary............................................................ 13
conduction band (i.e., electrons are present in (di/dv). When this conductance is plotted against Selector Guide................................................ 16
the valence as well as in the conduction band). voltage, the graph indicates the material’s density For More Information.....................................17
For an insulator (bandgap > thermal energy of of states. Highly conductive materials possess an
the electron), enormous energy is required for abundance of free energy levels in the conduction
an electron to transition from the valence to Figure 1. As material is reduced from band, i.e., greater density of states (more individual
the conduction band separated by the material macroscopic dimensions to nanoscopic size, allowed energy levels per unit energy). Insulating
its continuous energy bands (a) separate into
bandgap. If a suitable amount of energy is absorbed discrete energy levels within the band (b) and materials have an electronic structure with a dearth
(> bandgap), then electrons can jump bands. the bandgap increases. of occupied energy levels in the conduction band.
Because density of states corresponds to the density
As a particle’s size is reduced to nanoscopic Characterizing the density of states is a fundamental of these energy levels, a plot of conduction vs.
dimensions, the allowable energies within the activity in nanoscopic material research. Density of voltage provides a direct measure of the electronic
continuous bands separate into discrete levels states (3D dimensionality) as a function of energy density of states at each energy level (voltage across
(because there are far fewer atoms in the mix). This can be expressed as: the device).
occurs when the separation between energy levels
approaches the thermal energy of the electrons One approach to this technique is to use a nano-
(Figure 1). With fewer energy levels within the This represents the number of electron states per manipulator that makes low resistance contacts
specific energy band, the density of states of the unit volume per unit energy at energy E, where: to the nanoparticle. Such an arrangement
material changes. allows charge transport and density of states
m = the effective mass of the particle,
measurements. This works well into the conduction
The density of states is a measure of the number h = Planck’s constant, and region thanks to the low resistance direct
of energy options available to an electron as it falls E = the energy (electron orbital location) in connections of the nano-probes on the material
into a lower energy level by giving up energy or as electron volts. (particle) being tested.
it ascends to a higher energy level after absorbing
energy. A corollary is that if the density of states is Although the result is independent of volume
known, the size of the particle can be deduced. (can be applied to any size particle), this equation
is of limited value if the particle size/structure is
unknown. However, other ways are available to
determine the density of states experimentally, from
which the particle size can be found.
Ask Us Your Application Or Product Question.
3
E n s u r i n g t h e Ac c u r ac y o f N an o sca l e E l ect r ica l M eas u r ements A g r e at e r m e a s u r e o f c o n f i d e n c e

4. previous home next
Introduction. .....................................................2
.
Nanotech Testing Challenges.......................2
Nanotech Testing Challenges (continued) Electrical Measurement Considerations....5
Photos courtesy of Zyvex Corporation Electrical Noise.................................................6
The nano-manipulator and its probes, along Source-Measure Instruments. ......................7
.
with a source-measure unit (SMU), are used to Pulsing Technologies......................................8
apply a current or voltage stimulus directly to the Avoiding Self-Heating Problems.................9 .
nanoparticle and measure its corresponding voltage Application Example: Graphene................ 10
or current response (Figure 2). The advantage Summary.......................................................... 12
of electrical source-measure testing is rooted in Glossary............................................................ 13
the fact that a specific SMU measurement mode Selector Guide................................................ 16
(source current/measure voltage or vice versa) can For More Information.....................................17
be chosen based on the relative impedance of the
material or device under test (DUT). Furthermore, Want to Explore Further?
the measurement mode can change dynamically Featured Resources
as the impedance changes, such as occurs in CNTs • Give Your Microscope a
acting as semiconductor switches. This allows a Hand: Characterization of
much wider dynamic range of voltage and current Nano Structures
stimuli and measurements, thereby optimizing Kleindiek Nanotechnik
parametric test precision and accuracy. SMU voltage Figure 2. Nano-manipulator probing of nanoscale structures: Microscopic view of low impedance probe
and current sensitivity can be as good as 1 microvolt contact to a CNT for direct electrical measurements. Photo of a nano-manipulator head assembly. • Electrical Character-
and 100 atto-amps. ization of Carbon
Nanotube Transistors
Electrical measurements on nanoscopic materials Particle self-assembly can be accomplished measurements through the volume as well as over (CNT FETs) with the
place stringent requirements on the instrumentation. from silicon to silicon, where conventional the surface, using appropriately placed macroscopic Model 4200-SCS
In order to measure conductivity, impedance, photolithographic techniques are used to make test pads formed on the material surface. For
or other electrical properties, and relate those electrical connection pads for probing. Particles thatconductive materials, separate pads for source and
measurements to the density of states, a galvanic are long enough to straddle such pads (for example, measure can be deposited to create a Kelvin (4-wire) Additional Resources
connection must be made to the nanoscopic DUT.3 carbon nanowires) can be connected to the pads connection.4 This type of circuit eliminates test lead • Nanoscale Device and Material Electrical
This represents one of the major hurdles to be through externally generated electrostatic fields. resistance from the measurement and improves Measurements
overcome in the field of nanotechnology testing. accuracy. In any case, a quantum well (nano-film) • Advanced Particle Beam Methods For
Although the properties of quantum wells, wires, Nano-characterization And Analysis
There are only a few tools available and few device can be tested like any other bulk material.
and dots differ, it’s possible that information about • Optimizing Low Current Measurements
constructs that facilitate connections of this type. with the Model 4200-SCS Semiconductor
a particular material in the form of a quantum dot Bioimpedance Bioelectricity Basics, Wiley 2003.
1
can be inferred by examining the same material Applied Physics Letters, Single and Multiwalled Carbon Nanotube Field Effect Characterization System
2
fashioned as a quantum wire or well (nano-film). Transistors, volume 17, number 73, October 26, 1998, IBM Research Division. • I-V Measurements of Nanoscale Wires
Nano-films are particularly easy to measure because I-V Measurements of Nanoscale Wires and Tubes with the Model 4200-SCS and Zyvex
3 and Tubes with the Model 4200-SCS and
S100 Nanomanipulator, Application Note #2481, Keithley Instruments, 2004. Zyvex S100 Nanomanipulator
only one dimension is small. Such a film might
• Tips for Electrical Characterization of
be deposited on a conductive substrate, allowing Four-Probe Note #2475,and Hall Voltage Measurements with the Model 4200-SCS,
Resistivity
4
Application Keithley Instruments, 2004. Carbon Nanotubes and Low Power
Nanoscale Devices
4
E n s u r i n g t h e Ac c u r ac y o f N an o sca l e E l ect r ica l M eas u r ements A g r e at e r m e a s u r e o f c o n f i d e n c e

5. previous home next
Introduction. .....................................................2
.
Nanotech Testing Challenges.......................2
Electrical Measurement Considerations....5
Electrical Noise.................................................6
Electrical Measurement Considerations Source-Measure Instruments. ......................7
.
Pulsing Technologies......................................8
Avoiding Self-Heating Problems.................9 .
Application Example: Graphene................ 10
Electrical measurements on passive devices (any n Nanoscopic particles will not hold off as much The switching speed of a source-measure test Summary.......................................................... 12
device that is not a source of energy) are made by voltage from adjacent devices as a conventional circuit may be limited by the instrumentation used Glossary............................................................ 13
following a simple procedure: stimulate the sample electronic component or material (such as a to follow the state of the device. This is especially Selector Guide................................................ 16
in some way and measure its response to the transistor). This is because smaller devices true if a non-optimal measurement topology is For More Information.....................................17
stimulus. This method also works for devices that can be and are placed closer together. Smaller used to observe the device. The two possible
have both passive and active properties with linear devices also have less mass and may be affected topologies are source current/measure voltage or
or non-linear transfer functions. With appropriate by the forces associated with large fields. In source voltage/measure current. Want to Explore Further?
techniques, a source-measure algorithm can be addition, internal electric fields associated with
When considering the measurement of low imped- Featured Resources
useful for characterizing sources of energy. nanoscopic particles can be very high, requiring
ance (<1000 ohms) devices, the source current/ • Measurement Needs in
careful attention to applied voltages.
For nanoscopic particles, this general method measure voltage technique will generally yield Nano-Architectonics
takes the form of source-measure testing to n Given that nanoscopic devices are so small, the best results. Current sources are stable when
quantify impedance, conductance, and resistance, they typically have lower parasitic (stray) applied to lower impedances, and a good signal-to- Dr. Kang Wang
Director of the Center on Functional
which reveal critical material properties. This test inductance and capacitance. This is especially noise ratio can be achieved without great difficulty. Engineered Nano Architectonics
methodology is useful even if the end application is useful when they are used in an electronic This allows for accurate low voltage response University of California, Los Angeles
not an electronic circuit. circuit, enabling faster switching speeds and measurements.
• Improving Low
lower power consumption than comparable Current Measurements
Several considerations are important in the When measuring high impedance (>10,000 ohms)
macroscopic devices. However, this also means on Nanoelectronic and
characterization of nanoscopic particles: devices, the source voltage/measure current
that instrumentation for characterizing their I-V Molecular Electronic
n Nanoscopic
technique is best. Stable voltage sources to drive Devices
particles will not support the curves must measure low currents while tracking
high impedances are easily constructed. When
magnitude of currents that macroscopic device the short reaction time.
a well-designed voltage source is placed across a
can carry (unless they are superconducting).
Because nanoscopic test applications often high impedance, it will quickly charge the stray
This means that when a device is interrogated,
require low current sourcing and measurement, capacitance of the DUT and test cables and rapidly Additional Resources
the magnitude of a current stimulus must be
appropriate instrument selection and use is critical settle to its final output value. The small current • Electrical Measurements on
carefully controlled.
for accurate electrical characterization. In addition response of the DUT can be accurately measured Nanoscale Materials
to being highly sensitive, the instrumentation must with an appropriate ammeter. • Four-Probe Resistivity and Hall Voltage
have a short response time (sometimes referred to Measurements with the Model 4200-SCS
as high bandwidth), which is related to a DUT’s low • Guide to Measuring New Materials
capacitance and ability to change state rapidly at and Devices
low currents.
Ask Us Your Application Or Product Question.
5
E n s u r i n g t h e Ac c u r ac y o f N an o sca l e E l ect r ica l M eas u r ements A g r e at e r m e a s u r e o f c o n f i d e n c e

6. previous home next
Introduction. .....................................................2
.
Nanotech Testing Challenges.......................2
Electrical Measurement Considerations....5
Electrical Noise.................................................6
Electrical Noise Source-Measure Instruments. ......................7
.
Pulsing Technologies......................................8
Avoiding Self-Heating Problems.................9 .
Application Example: Graphene................ 10
Summary.......................................................... 12
Glossary............................................................ 13
Selector Guide................................................ 16
For More Information.....................................17
Measurement topology also has an impact on
electrical noise, which is the ultimate limitation
on measurement sensitivity and accuracy. For low
impedance voltage measurements with a current Want to Explore Further?
source, the measurement circuits will be sensitive to Featured Resources
DUT voltage noise and impedance. For macroscopic • Electronic Properties of
devices, such as a resistor, the Johnson noise voltage Zinc-Blende Wurtzite
at room temperature (270K) is expressed as: Biphasic Gallium Nitride
Vn = √(4kTBR)
Nanowires and NanoFETs
(a) (b) Dr. Virginia Ayers
Head, The Electronic and Biological
Nanostructures Laboratory
where k = Boltzmann’s constant Figure 3. (a) Circuit model for the source voltage/measure current technique; (b) Modified Michigan State University
model illustrating the noise gain (op-amp noise “gained up”) when the DUT impedance is low
T = Absolute temperature of the source compared to the measurement impedance.
in degrees Kelvin • Making Ultra-Low Current
B = Noise bandwidth in Hertz The Johnson current noise of a resistor at 270K is: the correct measurement topology is chosen. Measurements with the
For example, consider a source voltage/measure Low-Noise Model 4200-SCS
R = Resistance of the source in ohms
current topology. An operational amplifier is used
which can be further simplified to: in many current measurement (ammeter) circuits,
as shown in Figure 3.
indicating that the noise goes down as DUT resis-
tance increases. To minimize noise gain, the ammeter circuit must
This equation shows that as DUT resistance (R) operate at a low gain with respect to its non-inverting Additional Resources
For all particle sizes, in addition to Johnson
decreases, the Johnson voltage noise generated by input terminal. • Low Level Measurements Handbook
noise, there could be a noise gain associated with
the DUT also decreases. Conversely, high impedance the measurement topology chosen. Noise gain
devices stimulated with a voltage source are limited is a parasitic amplification of the noise of the
by current measurement noise. measurement system that is not present when
Ask Us Your Application Or Product Question.
6
E n s u r i n g t h e Ac c u r ac y o f N an o sca l e E l ect r ica l M eas u r ements A g r e at e r m e a s u r e o f c o n f i d e n c e

7. previous home next
Introduction. .....................................................2
.
Nanotech Testing Challenges.......................2
Electrical Measurement Considerations....5
Electrical Noise.................................................6
Source-Measure Instruments Source-Measure Instruments. ......................7
.
Pulsing Technologies......................................8
Avoiding Self-Heating Problems.................9 .
Application Example: Graphene................ 10
A commercial DC source-measure unit (SMU) is a When using the compliance function, an SMU will Summary.......................................................... 12
convenient test tool for many nanoscopic material satisfy the source value unless the user’s compliance Glossary............................................................ 13
and device measurements. SMUs change measure- value is exceeded. For example, when an SMU is Selector Guide................................................ 16
ment topology automatically (that is, they can rapidly configured to source voltage with a preset current For More Information.....................................17
switch between sourcing voltage/measuring current compliance, if that compliance value is exceeded, the
and sourcing current/measuring voltage). This SMU automatically starts acting as a constant current
makes it easier to minimize measurement noise source. Its output level then will be the compliance Want to Explore Further?
while maximizing measurement speed and accuracy. current value. Alternately, if the SMU is set to source
current with a compliance voltage, it will automati- Featured Resources
Some nanoparticles can change state with the • Test System is Key to
cally switch to sourcing voltage (the compliance
application of an external field. When investigating Practical Applications
voltage) if the DUT impedance and the current it
such materials, an SMU can be configured to source of Nanotechnology
draws begin to drive the voltage higher than the
voltage and measure current for a nanoparticle in its
compliance value.
high impedance state. When the material is in its low
impedance state, more accurate results are achieved Although a nanoscopic device, such as a CNT switch, • In-situ Correlation of
by sourcing current and measuring voltage. can change states rapidly, the change in instrument Mechanical Properties,
Furthermore, the SMU has a current compliance state is not instantaneous. Depending on the SMU Deformation Behavior,
function that can automatically limit the DC current model, the switching time can range from 100 and Electrical
Characteristics of
level to prevent damage to the material or device nanoseconds to 100 microseconds. Although such Materials Using
under test (DUT). Similarly, there is a voltage switching speeds are not fast enough to track a Conductive
compliance function when voltage is being sourced. nanoparticle as it changes state, the time is short Nanoindentation
enough to allow accurate measurements of both Ryan Major
states while limiting DUT power dissipation to R&D Project Manager
Hysitron, Inc.
acceptable levels.
Additional Resources
• Model 4200-SCS Semiconductor
Characterization System
• Series 2600A System SourceMeter®
Instruments
Ask Us Your Application Or Product Question.
7
E n s u r i n g t h e Ac c u r ac y o f N an o sca l e E l ect r ica l M eas u r ements A g r e at e r m e a s u r e o f c o n f i d e n c e

8. previous home next
Introduction. .....................................................2
.
Nanotech Testing Challenges.......................2
Electrical Measurement Considerations....5
Electrical Noise.................................................6
Pulsing Techniques Source-Measure Instruments. ......................7
.
Pulsing Technologies......................................8
Avoiding Self-Heating Problems.................9 .
Application Example: Graphene................ 10
Choosing the correct measurement topology to Low power pulsing techniques may offer a partial Summary.......................................................... 12
improve measurement speed and minimize noise solution to this problem and are available in some Glossary............................................................ 13
may still be insufficient to the test needs for some SMU designs. The idea is to use a much higher test Selector Guide................................................ 16
nanoscopic materials. For example, it appears current or test voltage and apply this large stimulus For More Information.....................................17
that some CNTs can switch 1000 times faster than for a short sourcing cycle. The larger stimulus will
conventional CMOS transistor switches. This is lower the sourcing noise (by improving the signal-
too fast for the nano-amp ranges of commercial to-noise ratio) and improve the rise or settle time Want to Explore Further?
picoammeters. Demanding devices like these may for a voltage pulse or current pulse, respectively.
require other techniques to improve the speed of Quieter sources require less filtering and permit a Featured Resources
impedance measurements. shorter sourcing cycle time (narrower pulse width). • Low-Level Pulsed
A larger source stimulus also increases the response Electrical Characteri-
zation with the Model
current or voltage so that higher instrument ranges 6221/2182A Combination
can be used, further minimizing the effects of
noise. Because there is less noise, the measurement
acquisition time (integration period) can be
shortened, allowing for faster measurements.
• Ultra-Fast I-V Applications
for the Model 4225-PMU
Ultra-Fast I-V Module
Additional Resources
• Pulse Testing for Nanoscale Devices
• Keithley Pulse Solutions
DC offsets due to thermal voltages and meter Performing a 2-point delta measurement cancels An optional third measurement point can help
offsets can give significant errors in the mea- offset error. The measured delta voltage gives cancel moving offsets.
sured voltage. correct voltage response to the current pulse.
Ask Us Your Application Or Product Question.
8
E n s u r i n g t h e Ac c u r ac y o f N an o sca l e E l ect r ica l M eas u r ements A g r e at e r m e a s u r e o f c o n f i d e n c e

9. previous home next
Introduction. .....................................................2
.
Nanotech Testing Challenges.......................2
Electrical Measurement Considerations....5
Electrical Noise.................................................6
Avoiding Self-Heating Problems Source-Measure Instruments. ......................7
.
Pulsing Technologies......................................8
Avoiding Self-Heating Problems.................9 .
Application Example: Graphene................ 10
A possible source of error in nano research is The following equation illustrates how duty cycle Summary.......................................................... 12
self-heating due to excessive electrical current and measurement time in pulse mode affect DUT Glossary............................................................ 13
through the DUT. Such currents may even lead power dissipation. To calculate power dissipation Selector Guide................................................ 16
to catastrophic failure of the sample. Therefore, in pulse mode, multiply the apparent power For More Information.....................................17
instrumentation must automatically limit source dissipation (V·I) by the test stimulus time and
current during device testing. Programmable divide by the test repetition rate:
P = P × Tt / Tr
current and voltage compliance circuits are Want to Explore Further?
standard features of most SMU-based test
systems with pulsed current capabilities and may p a Featured Resources
be required to avoid self-heating of some low
resistance structures. • How to Avoid
where: Pp = Pulse power dissipation Self-Heating Effects on
When an elevated test current is required, it must Pa = Apparent power (i.e., V·I) Nanoscale Devices
be short enough so that it does not introduce Tt = Test time
enough energy to heat the DUT to destructive T = Test repetition rate
r
temperatures. (Nanoscopic devices tolerate very
little heat, so the total energy dissipated in them Pulse mode is also useful for density of state Jonathan Tucker
must be maintained at low levels.) In addition, measurements using a low impedance connection, Senior Marketer, Nanotechnology
care must be taken that the magnitude of the test such as through a nano-manipulator. Pulsing allows Keithley Instruments, Inc.
current is low enough that the DUT’s nanoscopic measurements at I/V locations that were previously
channel does not become saturated. (For instance, uncharacterizable due to particle self-heating.
a current channel that’s 1.5 nanometers in diameter
severely limits the number of electrons that can
pass through it per unit of time.) Some nanoscopic
devices can support only a few hundred nano-amps
of current in their conductive state. Thus, a device’s
saturation current may define the maximum test
current, even in pulsed applications.
Ask Us Your Application Or Product Question.
9
E n s u r i n g t h e Ac c u r ac y o f N an o sca l e E l ect r ica l M eas u r ements A g r e at e r m e a s u r e o f c o n f i d e n c e

10. previous home next
Introduction. .....................................................2
.
Nanotech Testing Challenges.......................2
Graphene: The Semiconductor Industry’s
Electrical Measurement Considerations....5
Electrical Noise.................................................6
Replacement for Silicon? Source-Measure Instruments. ......................7
.
Pulsing Technologies......................................8
Avoiding Self-Heating Problems.................9 .
Nanovoltmeter Vxx = Longitudinal
Application Example: Graphene................ 10
Graphene, the single-atom-thick crystal of carbon, Researchers characterizing graphene and V xx
Voltage
Summary.......................................................... 12
Vxx
has outstanding electrical conductivity. It also has graphene-based materials use Hall effect V = Transversal Voltage,
xy I
= R xx
Glossary............................................................ 13
extremely strong, yet flexible bonds. Its hardness is measurements and study longitudinal Hall Voltage with
applied B
Selector Guide................................................ 16
greater than the hardness of diamond. Until relatively resistance to assess carrier mobility and look For More Information.....................................17
recently, physicists did not believe that a solid crystal for evidence of the quantum Hall effect,
just a single atom thick could exist. Professors whereby longitudinal resistivity decreases to Vxy Graphene
Novoselov and Geim proved otherwise with the near 0Ω-cm. These measurements require Nanovoltmeter
discovery of graphene in 2004; for their achievement, very low current, precision sourcing, on
they won the 2010 Nobel Prize in Physics. the order of nano-amps. However, the
most important aspect of tight control over
For the semiconductor industry, the exciting
sourcing is ensuring that excessive power
thing about graphene is that electrons travel DC Current Source
does not develop across the graphene sample
through it unimpeded, and these electrons behave
in order to avoid destroying it. Furthermore, Configuration for simultaneous measurement of
according to quantum electrodynamic principles.
at nano-amp source current levels, the Hall effect voltage and longitudinal resistance of a
Carrier mobilities through graphene are on the
resulting voltages developed across the graphene sample in a Hall bar configuration.
order of 10,000cm 2/V-s at room temperature,
sample are extremely small, on the order
and mobility values as high as 200,000 cm2/V-s
of ten to hundreds of nanovolts. These type of nanovolt-level measurements require special
on suspended samples of graphene have been
instrumentation with sufficient resolution and
reported. Graphene’s high mobility has
extremely high sensitivity.
already led to the development of very
high frequency (100GHz and higher) RF In nanovolt-level measurements, thermoelectric
transistors. Unfortunately, graphene does voltages and noise sources can significantly impact
not have a natural bandgap, so many measurement accuracy, so it’s important to employ
researchers are investigating methods techniques designed to minimize these effects.
to create one so graphene’s high speed For example, using a current source that allows
properties and nano scale size could reversing the polarity of its signal can eliminate
replace silicon in next-generation FETs measurement errors due to thermal voltage
for digital circuitry, thereby extending the offsets. Furthermore, a current source that can
life of Moore’s Law. output low duty cycle, narrow pulses will minimize
measurement errors due to resistivity changes
resulting from self-heating of the graphene sample.
A graphene single electron transistor (SET). Ask Us Your Application Or Product Question.
10
E n s u r i n g t h e Ac c u r ac y o f N an o sca l e E l ect r ica l M eas u r ements A g r e at e r m e a s u r e o f c o n f i d e n c e