Next-Generation Transistor Technology: A Study Reveals Overestimated Performance
For nearly two decades, the world of semiconductor technology has been abuzz with the potential of 2D semiconductors as a promising successor to silicon transistors. These 2D materials, only a few atoms thick, have been hailed as the future of smaller, faster, and more energy-efficient processors. But a recent study by electrical engineers at Duke University has cast a shadow of doubt over these claims, revealing a critical oversight in the way these transistors are tested and benchmarked.
The study, led by Aaron Franklin, the Edmund T. Pratt, Jr. Distinguished Professor of Electrical and Computer Engineering, highlights a phenomenon called 'contact gating' that significantly inflates the performance of 2D transistors in laboratory settings. This approach, widely used in the field, has led to overestimating the potential of these transistors for commercial applications.
Transistors, the fundamental building blocks of computers, are responsible for rapidly turning electrical currents on and off, forming the 1s and 0s of digital programming. To improve processing performance, transistors must be made smaller, faster, and more efficient, or all three. Silicon has long been the semiconductor of choice for transistor manufacturing, but modern technology is pushing the material's intrinsic limitations.
To explore alternative materials, researchers often rely on a simple 'back-gated' architecture, where all transistor components are built on a single piece of silicon for easier fabrication and rapid experimentation. In this setup, an ultrathin 2D semiconductor like molybdenum disulfide (MoS₂) sits between two metal contact electrodes, with the current flow controlled by the silicon substrate acting as the gate.
However, the gate doesn't just modulate the 2D semiconductor channel; it also influences the portion of the semiconductor below the metal contacts, creating the 'contact gating' effect. This amplifies the transistor's performance by lowering contact resistance using the gate, which sounds like a good thing. But Franklin points out that while this architecture is great for basic testing, it has physical limitations like speed and current leakage that prevent it from being used in actual device technologies.
To uncover this underlying factor, Victoria Ravel, a PhD student in Franklin's lab, spent a year fabricating a new device architecture that allows direct measurement of how much contact gating alters performance. She built a symmetric dual-gate transistor with gates above and below the same 2D semiconductor channel, contacts, and materials, enabling a one-to-one comparison between the presence and absence of contact gating.
The results were striking. In larger devices, contact gating roughly doubled performance. As Ravel scaled devices down to tiny dimensions relevant for future technologies, the contact gating effect increased. At a channel length of 50 nanometers and contact lengths of 30 nanometers, contact gating boosted performance by up to six times.
As devices shrink, Franklin explains, the contacts dominate overall performance. Any mechanism that alters contact behavior becomes increasingly important. Because most 2D transistor results reported over the years have used back-gated architectures, the findings from Franklin and Ravel have broad implications. The team plans to push scaling further, with contact lengths down to 15 nanometers, and investigate alternative contact metals to reduce contact resistance, aiming to establish clearer design rules for integrating 2D semiconductors into future transistor technologies.
This research, supported by the National Science Foundation, emphasizes the importance of honest evaluation of device architecture in shaping performance measurements. As 2D materials aspire to replace silicon channels, this work sets the foundation for a more accurate understanding of their potential.
CITATION: "Impact of Contact Gating on Scaling of Monolayer 2D Transistors Using a Symmetric Dual-Gate Structure." Victoria M. Ravel, Sarah R. Evans, Samantha K. Holmes, James L. Doherty, Md Sazzadur Rahman, Tania Roy, and Aaron D. Franklin. ACS Nano, 2026. DOI: 10.1021/acsnano.5c19797
