LONDON—A transistor designed with a molybdenum disulfide single atomic layer as its channel has been shown to switch at voltages down to 0.1 volt with the prospect of reducing power dissipation by 90 percent compared with state-of-the-art silicon transistors.
Engineering researchers at the University of California Santa Barbara and Rice University performed the work and a paper written by the team has been published recently in journal Nature.
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," said Kaustav Banerjee, Professor of Electrical and Computer Engineering at UC Santa Barbara. For MOSFETs that steepness is 60mV/decade and is an effective limit on the energy efficiency of digital circuits in general.
To get around these problems in silicon, the team built a transistor with germanium as the source and MoS2 as the channel that is capable of band-to-band tunneling. This tunnel field effect transistor (TFET) has sub-threshold swing of less than 60mV/decade.
The source to channel is designed to filter out high-energy electrons that could otherwise make it past the source/channel energy barrier even in the off-state. This keeps the off-state current negligible the research team said in a statement.
Top: A schematic cross-sectional view of the ATLAS-TFET showing the Ge source/substrate, MoS2 channel, and the band-to-band (BTBT) tunneling direction. Lower: A schematic view of the fabricated device showing Ge source/substrate along with a native GeOx layer, the MoS2 channel with a gate dielectric on top. Note that sections of the source and drain electrodes as well as the Ge substrate around the MoS2 are fully covered by a dielectric (SiO2) to prevent them from influencing the gate electrode. (Image & caption: Jiahao Kang, UCSB)
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.
The approach is superior to TFETs built with silicon or III-V compound semiconductors as the channel materials because these materials have a high density of surface states that increase leakage current. The paper reports a subthermionic sub-threshold swing of approximately 30 millivolts/decade at room temperature over four decades of drain current and at operating at 0.1V.
"The use of 2D materials in tunneling transistors started only recently, and this paper gives the whole field yet another strong boost in improving the characteristics of such devices even further," commented Konstantin Novoselov, a professor of physics at the University of Manchester who was a co-recipient of the 2010 Nobel Prize in Physics, awarded for the discovery of graphene.
Article originally posted on EE Times Europe.
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