Wednesday, October 07, 2015
A new tunnel field-effect transistor (TFET) with an atomically thin current-carrying channel that operates at ultralow supply voltages has been unveiled by a team of researchers at the University of California, Santa Barbara, and Rice University in Texas. The new device, which is made from a 2D semiconducting crystal and a bulk germanium substrate, can be switched on at just 0.1 V. It could be used in ultradense and lower-power integrated circuits and to make ultrasensitive bio- and gas sensors.
The size of silicon-based metal-oxide FETs (which make up the bulk of modern-day electronics devices) has been decreasing steadily over the last few decades, but this scaling down cannot continue forever without running into major difficulties. For one, FET switching is limited by a theoretical thermionic quantity known as subthreshold swing that cannot be lower than 60 mV per decade of drain current at room temperature.
Now, a team of researchers led by Kaustav Banerjee of the University of California at Santa Barbara, has developed TFETs made from bilayer molybdenum disulphide and bulk germanium that has a very steep subthreshold swing (of 31.1 mV per decade of current for over four decades of drain current at room temperature). This makes them one of the best material combinations for switches that could operate with supply voltages as low as 0.1 V, which means they would require 90% less power to run compared with conventional FETs.
The researchers made their TFET by using highly doped germanium as the source electrode and atomically thin molybdenum sulphide (just 1.3 nm thick) as the current-carrying channel. The resulting vertical heterostructure has a strain-free interface, a low barrier for current-carrying electrons to tunnel through, and a large tunnelling area.
“Our atomically and layered semiconducting channel tunnel FET (or ATLAS-TFET) is the only planar architecture TFET to achieve subthermionic subthreshold swing over four decades of drain current, and the only one in any architecture that can be switched on using an ultra-low drain–source voltage of 0.1 V,” say the researchers, “and at present is the thinnest-channel sub-thermionic transistor ever made.”
The International Technology Roadmap for Semiconductors (ITRS) says that the average subthreshold swing should be lower than 60 mV per decade over four decades of current. The only experimental TFET made so far to have achieved this metric is one that relies on one-dimensional (nanowire) based structures, which are difficult to produce and manipulate. “Our ATLAS-TFET is the first TFET with in-planar architecture to satisfy the ITRS prescription and, as such, might be used in the development of next-generation ultralow-power integrated electronics and ultrasensitive sensors,” say Banerjee and colleagues.
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