Domestic researchers revealed that there is a serious error hidden in a performance evaluation index that has served as a compass for researchers in the semiconductor development process.
Professors Kim Jeong-hwan and Jeong Chang-uk and their team at the Graduate School of Semiconductor Materials and Components of Ulsan National Institute of Science and Technology (UNIST) said on the 3rd that they identified that "field-effect mobility," a key performance index for semiconductor devices, can be measured up to 30 times higher than in reality depending on device structure, and presented a standard for semiconductor device structure design to solve this problem. The study was published on Oct. 21 (local time) in ACS Nano, an international nanoscience journal issued by the American Chemical Society (ACS).
Charge mobility is an indicator of how fast and efficiently charge (current) moves inside a semiconductor. The larger this value, the faster the device operates and the less power it consumes, so it is considered an important yardstick for gauging the success or failure of developing high-performance semiconductor chips.
According to the study, charge mobility can be overmeasured by more than a factor of 30 depending on the geometric structure of oxide thin-film transistor (Thin-Film Transistor) semiconductor devices.
The team pointed to fringe current flowing through a "side road" as the cause. In thin-film transistor devices, current enters through the "source electrode," passes through the official path, the "channel," and exits to the "drain electrode." However, when the channel width is much wider than the electrodes, "fringe current" occurs, in which current spreads and flows not only through the original path directly under the electrode but also through the wide surrounding area (side road) outside the electrode. Because measuring instruments add up all of this current to calculate performance, the results are inflated compared with reality.
If charge mobility is compared to the average speed of cars on a heavily congested expressway, fringe current has the effect of creating the illusion that the overall average speed is much faster than it really is by adding in cars recklessly speeding along the shoulder.
The researchers also presented a design standard for thin-film transistor devices to solve this problem. They said the channel width should be designed narrower than the electrode width, or if unavoidable, the electrode width should be designed to be at least 12 times larger than the overall device length. When this criterion was followed, the influence of fringe current almost disappeared, eliminating the difference between actual mobility and measured mobility and enabling accurate performance measurement.
The team also recommended cross-checking field-effect mobility by measuring an index called Hall mobility together. Hall mobility measures the inherent electrical properties of the semiconductor thin film material itself, not a finished device, and is free from errors caused by the geometric structure of semiconductor devices.
Kim Jeong-hwan said, "Errors in device performance measurement can lead to wasted research capabilities by causing materials with overestimated performance to be mistaken for promising next-generation technologies, or hinder the development of the entire semiconductor industry by making objective technology comparisons impossible," adding, "It is a meaningful study in that it proposes a global standard that can solve this."
References
ACS Nano (2025), DOI: https://doi.org/10.1021/acsnano.5c11904