Enabling researchers to chase electrons and measure PΩ
The materials science field is poised for significant advancement as researchers investigate graphene, polymers, nanomaterials such as carbon nanotubes, and exotic dielectrics, according to Alan Wadsworth, market development manager for the Hachioji Semiconductor Test Division of Keysight Technologies. He cited Yole Développement predictions that the market value for graphene materials for opto and electronic applications will increase at an 18.5% CAGR through 2018 and then at a 35.7% CAGR through 2024.
“New materials science applications are growing, and investment is ramping up quickly,” he said. Researchers involved in such applications, he said, typically need to measure extremely small currents and extremely large resistances.
A DMM can make current measurements down to 10 nA or so, but you need a picoammeter to go lower. Similarly, you’ll need an electrometer, which Wadsworth defines as a high-performance DMM, to make resistance measurements beyond a gigaohm and up into the petaohm range—as well as low-current measurements. An electrometer, he said, can serve as an ohmmeter, voltmeter, and charge meter as well as an ammeter. He added that most picoammeters do not include voltage sources; most electrometers do.
|B2987A electrometer with histogram display
Courtesy of Keysight Technologies
Wadsworth cited several test challenges in making low-level measurements. The numeric displays found on most meters do not give you control of when to take data when measuring a transient signal, for example. “You don’t always get the same measurement every time you push the button,” he said. In addition, the least significant digits are unstable. Eliminating noise also is challenging, as is verifying the integrity of measurement cabling.
Keysight aims to help meet these challenges with the addition of the B2980A series of femto/picoammeters and electrometers to its B2900 family of instruments, which includes the B2900A SMU series and the B2960A series of low-noise sources. Wadsworth described the B2980A as a graphical picoammeter/electrometer that lets you confidently make measurements down to 0.01 fA and up to 10 PΩ. He added that 0.01 fA is just 62 electrons per second.
The B2980A addresses the transient-signal challenge by adding a time-domain view with 100-kHz sampling that enables transient data capture so you can select the desired measurement data. And rather than presenting unstable numerical least significant digits, the instrument can display a real-time histogram to present an instant statistical analysis of measured data, allowing you to check mean and standard deviation and compare accumulated data with instantaneous numeric data. Double peaks in a histogram, Wadsworth said, could indicate measurement problems.
To deal with noise, Wadsworth said, the instruments feature an “innate low-noise measurement capability.” And battery-operated models are available to eliminate AC powerline noise. The instruments also include a test-setup integrity checking function that can help you measure and compare the noise levels of different cables and fixtures.
In addition, the instruments each feature measurement assist functions that help you find the optimal measurement and speed (aperture time) settings. Optional accessories include a high-resistance-measurement universal adapter, a component test fixture, a high-resistance meter fixture adapter, a resistivity cell, and test leads. The instruments have inputs for temperature and humidity sensors as well, Wadsworth said.
Although the instruments don’t require an external PC for time-domain and statistical analysis, they do come with free PC measurement software called Quick IV. They also have LXI as well as USB and GPIB interfaces. All the instruments feature 6½-digit measurement resolution and support 0.01-fA to 20-mA current measurements with a 2-pA minimum range. Reading rate is 20,000 per second.
Offering better than 200-TΩ input resistance, the electrometer versions can source up to ±1,000 V (with 700-µV minimum resolution) and measure up to 10 PΩ. They can measure voltage from 1 µV to 20 V and charge from 1 fC to 2 µC.
Prices for the picoammeter start at $6,198; the battery-operated version costs $8,264. Prices for the electrometer start at $8,987; the battery-operated version costs $11,032.