Reviewed by Alex SmithAug 1 2022
The industry is profoundly focused on identifying promising next-generation designs and materials for the key components of modern electronics: the tiny electrical on–off switches known as field-effect transistors (FETs). This means that smartphones, laptops, and other devices can be made that are more powerful and energy efficient.
Typical design for an emerging field-effect transistor made with nanomaterials. The movement of current from the source electrode (gold, left top) across an ultrathin channel (blue) to the drain electrode (gold, top right) is controlled by the source voltage and the electric field produced by the gate electrode (gold, top center) that is separated from the channel by an insulating layer (light gray). At left: Atomic-thickness channel materials can be one-dimensional, such as carbon nanotubes, or two-dimensional layers. Image Credit: Z. Cheng/ National Institute of Standards and Technology.
When it comes to deciding where to invest billions of funding dollars for next-generation transistors, investors will base many of their decisions on published research results.
However, an alarming amount of research on FETs is currently plagued by inconsistent results reporting and benchmarking, increasing the likelihood of incorrect conclusions and claims that create unwarranted expectations for the field. An international group of top semiconductor device experts published an article outlining this issue and potential solutions.
Industry is trying to determine the right materials and designs to use. They want to know exactly what to make and how to make it. But the industry is getting terribly frustrated, they tell us, because they see a promising piece of information in one publication and another promising piece in another publication, but they’re incompatible. They have no way to compare them.
Curt Richter, Study Co-Author and Physicist, National Institute of Standards and Technology
Richter further adds, “Given the enormous cost of adopting design innovations, the industry can’t afford to make a mistake. What they want is uniform benchmarking.”
An effort is being led by Richter, former NIST associate Zhihui Cheng (now at Intel), and Duke University’s Aaron Franklin to develop and promote standards for uniform test procedures and reporting. The researchers, along with more than a dozen other colleagues from business, academia, and government labs, outline their recommendations in a study that was published in the journal Nature Electronics.
The paper offers a detailed evaluation and description criteria for eight significant parameters that are essential to new field-effect transistor designs.
Physicists, chemists, materials scientists, electrical engineers, and others are among the researchers working on cutting-edge FET designs; each one is approaching the issue differently.
Cheng adds, “At present, each group frequently has its own techniques and measurement methods. There are no uniform guidelines or metrics about how to measure and report a particular parameter. So it is often very difficult to evaluate the significance of a reported result, and it is hard to tell whether the results are biased or incomplete.”
The inaccuracies that occur in reporting are “not necessarily intentional,” said Franklin, the Addy Professor of Electrical and Computer Engineering at Duke.
But the impact that misreporting has on the field cannot be overstated. In addition to the negative effect on industry, it also affects the decisions made by funding agencies, program managers and others who influence research direction in academic and government labs. Properly extracting and then keeping new findings in the proper context is critical to making true progress.
Aaron D. Franklin, Addy Professor, Electrical and Computer Engineering, Duke University
“It’s really a matter of providing education that is currently lacking. There’s no textbook out there about how to properly extract these parameters for emerging devices. You could think of our paper as a sort of abstract for such a textbook,” added Franklin.
The researchers assert that in the absence of general guidelines, false results are too easily produced. For instance, the relationship between the ramp-up of applied voltage required to turn the transistor “on”—that is, to get current flowing through the channel between the source electrode and the drain electrode and the amount of increase in current from the ramped-up voltage—is one of the important parameters to a device’s performance.
There is a transition voltage as the current goes up from the lowest to the maximum and it’s not a straight line. It has little variations in curvature. You want the slope of that curve to be as steep as possible so that you can work with smaller voltages to turn the current on. Some researchers will report the one spot where the slope is steep instead of reporting the entire voltage span. That misleads people into believing that you can operate at lower power.
Curt Richter, Study Co-Author and Physicist, National Institute of Standards and Technology
Cheng remarks, “It’s like you’re running a 100-meter race and you only report the last 10 meters where you run the fastest.”
A positive outcome could also be attributed by researchers to novel channel characteristics “when in fact it is actually determined by the geometry of the transistor and the non-semiconducting materials. Reporting must be done in the proper context of the dimensions and materials of the transistor, rather than simply attributing everything, by default, to the semiconductor channel,” Franklin says.
The results could be misleading if the researchers do not conduct enough tests with enough variations to account for all factors, and this presents challenges for numerous labs. Making one or two samples of a novel material or developing a design can take several months. So, it takes a lot of time and effort to create enough variations of a device to allow for accurate comparisons.
The authors argue that efforts must be made to prevent the negative effects of false reporting. “It’s often the case that once a paper is published, everybody believes it. It becomes gospel. And if your research gets a different answer, you have to work ten times harder to overcome the effect of the first publication,” stated Richter.
A “gold rush” mentality can result from too many inaccurate or misleading reports, as was the case with carbon nanotubes (CNTs) in the late 1990s and early 2000s. Many people believed they would replace silicon semiconductor elements in microelectronics based on the wildly optimistic early reports. However, interest and funding dried up when it turned out that the initial claims were exaggerated.
Franklin elaborates, “CNTs are a hugely instructive example. So much hype and overstated claims led to disillusionment and frustration rather than steady, collaborative and accurate progress. An entire field of research was negatively impacted by overstated claims. After a frenzy of activity, the eventual distaste resulted in a massive shift of research funding and attention going to other materials.”
“It has taken a decade to bring deserved attention back to CNTs, and even then many feel it is not enough,” added Franklin.
These kinds of convulsive effects can be reduced by uniform benchmarking and reporting, which can also assist researchers in persuading their peers that they have made real progress. “By using these guidelines. It should be possible to comprehensively and consistently reveal, highlight, discuss, compare, and evaluate device performance,” the authors concluded.
Journal Reference:
Cheng, Z., et al. (2022) How to report and benchmark emerging field-effect transistors. Nature Electronics. doi.org/10.1038/s41928-022-00798-8.