How to Compare FETs: NIST Releases a Guide to FET Benchmarking
At last, researchers and companies will have a standardized method to evaluate and benchmark new transistors.
While benchmarking electronic devices and components is a long-held practice in the world of electrical engineering, the process is far from perfect. Namely, it can be difficult to equally compare two devices with several subjectivities, such as different benchmarking techniques, setups, and measurement methods.
One component that is historically difficult to benchmark in a consistent manner is the field-effect transistor (FET). On July 29, experts at the National Institute of Standards and Technology (NIST) announced a new set of guidelines to help unify FET benchmarking.
Flowchart showing the many different branches of FETs. Image used courtesy of Octopart
In this article, we’ll talk about the shortcomings of current benchmarking techniques and what NIST is proposing with its new guidelines.
The Challenges of Benchmarking
Despite the waves of research devoted to new FET technologies, the semiconductor industry lacks a way to accurately and uniformly compare these different research prototypes. According to the experts at NIST, this is particularly challenging for field-effect transistors because there is a high level of interdependence between multiple FET device parameters. Further, the performance of a FET often depends on unique aspects of the device's structure.
Device parameters of a FET can be intertwined with one another. Image used courtesy of Cheng et al.
Some of these structural parameters include channel lengths, contact lengths, gate insulator thickness and permittivity, contact metal types, the thickness of channel material, and gating scheme. Each of these variables is somewhat intertwined with other relevant variables, making it hard to discern the impact of a single change or design decision.
Industry leaders have also struggled to compare FETs because of a lack of consistent reporting and benchmarking guidelines. One reason for this is that the research community consists of engineers from various disciplines, including electrical engineering, chemistry, materials science, and physics. Different fields often come with unique perspectives and reporting styles, not all of which are compatible with one another.
NIST Releases New FET Standards
To help create cohesion in the reporting and benchmarking of field-effect transistors, a group of experts from NIST recently released a series of suggested standards.
Born from a collaboration of more than a dozen experts across industry, academia, and government labs, the standards were recently published in Nature. In the paper, the researchers describe what they consider to be the most important device parameters and performance metrics that should be considered and reported in all studies on the subject.
Key FET Parameters
According to the guidelines, the most representative FET parameters include:
- Structural parameters, including contact length, channel length, channel width, insulator thickness, and channel thickness
- Insulator capacitance
- Threshold voltage and hysteresis
- Drain current in the saturation region
- Contact resistance
- Conductivity mobility
- Subthreshold swing
The paper also suggests a list of benchmarking plots to help evaluate device parameters and performance metrics. These plots evaluate:
- Maximum and minimum current of the device (Imin vs Imax)
- Saturation current (Isat vs. ns)
- Drain current (ID vs. Lch)
- Contact resistance (RC vs. ns)
- ucon (ucon vs. tch)
A New Measuring Stick to Compare FETs
At the heart of it all, the guidelines stress the importance of completely describing the device geometry, collecting and reporting current-voltage characteristics, and detailing the procedures in experiments. Through these suggested guidelines, NIST and its industry partners hope to contextualize key performance metrics, so researchers can accurately evaluate and compare their FET prototypes.