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One of the greatest challenges in the evolution of electronics has been to reduce power consumption during transistor switching operation. In a study recently reported in Nature, engineers at University of California, Santa Barbara, in collaboration with Rice University, have demonstrated a new transistor that switches at only 0.1 volts and reduces power dissipation by over 90% compared to state-of-the-art silicon transistors (MOSFETs).
MOSFETs have been the building blocks of everyday electronic products since the 1970s. However, to sustain the ever-growing need for increased transistor densities, miniaturization of MOSFETs has given rise to a power dissipation challenge due to the fundamental limitations of their turn-on characteristics.
"The steepness of a transistor's turn-on is characterized by a parameter known as the subthreshold swing, which cannot be lowered below a certain level in MOSFETs," explained Kaustav Banerjee, Professor of Electrical and Computer Engineering at UC Santa Barbara. A minimum gate voltage change of 60 millivolts at room temperature is required to change the current by a factor of ten in MOSFETs. In essence, the existing state of transistor technology limits the energy efficiency potential of digital circuits in general.
The research group of Professor Kaustav Banerjee at UC Santa Barbara took a new approach to subverting this fundamental limitation. They employed the quantum mechanical phenomenon of band-to-band tunneling to design a tunnel field effect transistor (TFET) with sub-60mV per decade of subthreshold swing.
"We restructured the transistor's source to channel junction to filter out high energy electrons that can diffuse over the source/channel barrier even in the off state, thereby making the off state current negligibly small," explained Banerjee. At UCSB, Banerjee's Nanoelectronics Research Lab includes Deblina Sarkar, Xuejun Xie, Wei Liu, Wei Cao, Jiahao Kang, and Stephan Kraemer, as well as Yongji Gong and Pulickel Ajayan of Rice University.
Banerjee and his colleagues are motivated by a global electronics industry that loses billions of dollars each year to the impact of power dissipation on chip cost and reliability. "This translates into lower battery lifetime in personal devices like cell phones and laptops, and massive power consumption of servers in large data centers," adds Banerjee, pointing out the global scale of this energy demand.
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