Keithley University Classroom

Nanoscience research labs

· Overview	· Measurement Example	· Test Solution
· Major Benefits To The Nanoscience Researcher	· Nano Alliance Partner Resources	· Products Commonly Used
· Related Materials	· Other Customer Types

Overview

Nanotechnology is seen with increasing confidence as a key science and technology trend going forward, just as are the digital revolution and modern biology. Nanoscale science and engineering will lead to advances in fundamental research and education, advances in electronic and optoelectronic devices, and significant changes to semiconductor fabrication, biotechnology, alternative energies, and industrial manufacturing.

3-Terminal Nanowire Transistor
(Image courtesy of The University of Texas at Dallas)

Keithley Model 6430 Sub-Femtoamp Remote SourceMeter^® Measures currents with 400aA (400X10^-18A) Sensitivity

Fabricating nanoscale materials and devices typically starts in the chemistry, biology, or semiconductor device/microelectronics laboratory. Electrical measurements on nano-scale materials and devices reveal not only electronic characteristics, but also general properties like a nanoscopic particle’s density of states. These fundamental properties can be used to predict and manipulate physical characteristics, such as tensile strength, color, and electrical and thermal conductivity. However, making meaningful measurements requires highly sensitive instruments and sophisticated probing techniques. Instrumentation designed specifically for nanotechnology research is increasingly available, but users must understand the types of measurement needed, and which test system features will enhance speed and accuracy.

For many of the nanoscale materials and devices studied in the lab, the most common electrical characterization methodology is the current vs. voltage (I V) test. A current-voltage characteristic is a chart showing the relationship between the DC current through an electronic device and the DC voltage across its terminals. Electrical engineers use these charts to determine basic parameters of a device and to model its behavior in an electrical circuit. Engineers commonly refer to characteristic charts as I-V curves, referring to the standard symbols for current and voltage. A typical carbon nanotube MOSFET I-V drain voltage vs. drain current I-V curve might look like the curves on the left.

Measurement Example

New Materials Research

A four-wire connection to a carbon nanotube.
(Image reproduced courtesy of Zyvex Corporation.)

During device development, structures like nanowires, carbon nanotubes, and nanocrystals often display unique properties. Characterizing these properties without damaging one-of-a-kind structures requires systems that provide tight control over sourcing to prevent device self-heating. Keithley instrumentation combines this tight control with exceptional measurement speed and sensitivity in flexible, modular architectures that make it easy to adapt to changing test requirements.

One of the most common measurement techniques for measuring these materials is to use the four-wire or “Kelvin” measurement. With Kelvin measurements, a second set of probes is used for sensing. Negligible current flows in these probes; therefore, only the voltage drop across the DUT is measured, as shown in the figure below. As a result, resistance measurement or I-V curve generation is more accurate.

Keithley Interactive Test Environment (KITE) in Model 4200-SCS

The Keithley Interactive Test Environment (KITE) in the Keithley Model 4200-SCS Semiconductor Characterization System allows the researcher from any nanoscience discipline the ability to easily and quickly configure measurement tests. KITE is an application program designed and developed for characterizing nanoscale materials, devices, as well as semiconductor devices. Source and measurement functions for a test are provided by Source-Measure Units (electronic instruments that source and measure DC voltages and currents). Test capabilities are extended with support from a variety of external components. Here’s an example setup for a carbon nanotube I-V test and the resulting I-V sweep on a Single Walled Carbon Nanotube:

This figure illustrates an I-V curve on a carbon nanotube using the Keithley 4200-SCS and KITE
(Courtesy of Zyvex Corporation)

Experimental Device Development

A device formed by an array of gold nanoparticles. Photo courtesy of K. Elteto and X.M. Lin, the University of Chicago.

During device development, structures like single electron transistors (SETs), sensors, and other experimental devices often display unique properties. Characterizing these properties without damaging one-of-a-kind structures requires systems that provide tight control over sourcing to prevent device self-heating. Keithley instrumentation combines this tight control with exceptional measurement speed and sensitivity in flexible, modular architectures that make it easy to adapt to changing test requirements.

Low-level pulsed measurements involve sourcing a pulse of current and measuring the resulting voltage. Because the Model 6221/2182A combination is intended for pulse characterization at low signal levels, low-level noise issues will be of concern. However, the 6221/2182A combination differs from all previous test configurations in some important ways. One of the differences is that all of the pulse measurements are difference (or relative) measurements. This means that background voltages that would add error to the measured signal, such as offsets, drift, noise, and thermoelectric EMFs, are cancelled.

DC offsets due to thermal voltage and meter offsets can give significant errors in the measured voltage.

Offsets are cancelled using a delta-mode measuring technique.

Performing relative measurements cancels offset error.
The measured delta voltage gives correct voltage response to the current pulse.

A two-point delta mode measurement works by sourcing current pulses and taking one measurement before and one during each pulse. Taking the difference between these two measurements cancels out any constant thermoelectric offsets, which leaves the true value of the voltage. However, the two-point method cannot cancel thermoelectric offsets that drift over time. Using a third measuring point in the delta method cancels drifting offsets.

An optional third measurement point can help cancel moving offsets.

The third measurement is optional but it is not preferable. For instance, depending on the device timing characteristic, if the sourced current pulse has long-lasting effects on the device, the third measured point, which is intended for canceling the moving offset, may include errors due to the heat from the pulse of the DUT and, therefore, do more harm than good.

To learn more about different measurement techniques for Nanoscience, be sure and obtain our latest edition of the Nanotechology Measurement Handbook and the Low Level Measurements Handbook

Test Solution

Keithley Instrumentation is being used in a growing list of nanotechnology research and development settings. The applications shown here are only a sampling of the nanotechnology test and measurement tasks for which our instruments and systems are suitable. If your tests require sourcing or measuring low level signals, Keithley instrumentation can help you perform them more accurately and cost-effectively."
with the attached diagram.

For specific measurements on Nanowire, Nanotubes and other NanoMaterials, the following selector guide will direct you to the best solutions.

Resistance Measurements on Nanotubes, Nanowires, or Nanofibers

For specific Current versus Voltage measurements on Nanoelectronics, the following selector guide will direct you to the best solutions.

For specific measurements where pulse characterization is required to reduce Joule-Heating effects on Nanowire, Nanotubes, NanoMaterials, and Nanoelectronics, the following selector guide will direct you to the best solutions.

Model 4200-SCS Semiconductor Characterization System

Features:

Conforms to IEEE 1650-2005 standard

Easy-to-use, Windows-based operation

A complete, integrated solution

Unmatched flexibility and adaptability

Product Page

Product Specs

Product Demo

Product Brochure

At the heart of the nanoscience device research lab is the Model 4200 Semiconductor Characterization System. Keithley originally developed the Model 4200-SCS for the semiconductor industry, but nanotechnology researchers soon discovered its effectiveness for developing and studying nano-scale materials and devices. Today, this powerful characterization system is the industry-standard tool used in nanotechnology research and education labs around the world in applications ranging from materials research and nanostructure development to I-V characterization of nanoelectronic devices. The system's popularity is due in part to our commitment to enhancing its hardware and software to meet emerging test needs. Our ongoing commitment to the Model 4200-SCS ensures we'll continue to provide you with a cost-effective system upgrade path to new measurement capabilities.

Major Benefits To The Nanoscience Researcher

The ability to characterize nanomaterials and experimental devices electrically with precision and confidence

DC, pulse, RF testing: Expand your capabilities, expand the potential for discovery

Configurable, scalable, upgradeable: Works now, grows later

Pulse testing to minimize joule-heating effects

The Model 4200-SCS conforms to and supports the IEEE 1650-2005 Standard: "IEEE Standard Test Methods for Measurement of Electrical Properties of Carbon Nanotubes," the world's first electrical measurement standard for carbon nanotubes.

Keithley’s solutions are designed for speed and simplicity, allowing the biologist, chemist, physicist, or any other researcher the ability to make complex measurements with ease.

Keithley’s products are widely used and cited by your peers in prestigious nanoscience research journals such as: