Nanoscale materials and devices, such as graphene and carbon nanotubes (CNTs), hold enormous promise for the development of new electronic devices. Graphene is particularly attractive because it is a high quality, flawless crystalline lattice of carbon, without atomic defects; itís transparent; it has high affinity for other elements; and it forms strong yet highly flexible bonds and can handle substantial deformation.
Graphene also exhibits very high electrical conductivity and thermal conductivity. Electrons travel through it unimpeded and behave according to quantum electro-dynamic principles, with carrier mobility of ~10,000cm2/V*s at room temperature and mobility values as high as 200,000cm2/V*s on suspended samples.
As a result of these characteristics, researchers are exploring myriad applications for graphene, including high frequency transistors and single electron transistors (SETs) for use in ICs, high efficiency solar cells, flexible displays, touchscreens, printable electronics, and a wide range of chemical sensors. Researchers at IBM have already reported creating graphene-based RF transistors with high bandwidths.
Graphene and other nano materials undoubtedly offer enormous potential for innovation for the designers and manufacturers of electronic devices, but they also represent an enormous testing challenge. For example, for characterizing delicate samples, the instrumentation used must be able to source sub-microamp currents with high precision in order to limit total power dissipated in the sample. The current source must also provide a constant output so the exact value forced to the material is known with a high level of accuracy. It should also have an adjustable voltage compliance to prevent overvoltages and device damage. Ideally, it would have a bipolar output to eliminate voltage offsets and reduce noise.
When characterizing low resistance samples, these low-level sourced currents will generate low voltages, demanding the use of a nanovoltmeter with low internal noise and excellent ability to reject external AC noise.
About the author: Robert Green is a senior market development manager at Keithley Instruments, Cleveland, Ohio, which is part of the Tektronix test and measurement portfolio. During his career at Keithley, Green has been involved in the definition and introduction of a wide range of instrumentation. He holds a BS in electrical engineering from Cornell University and an MS in electrical engineering from Washington University in St. Louis, Missouri.
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