UAlberta electrical engineering PhD student Gem Shoute (second from right) is the lead author on a research paper demonstrating a powerful new flexible transistor. The team: electrical engineering professor Doug Barlage, Triranta Muneshwar, Shoute and materials engineering professor Ken Cadien, published its work in Nature Communications. Credit: Image courtesy of University of Alberta
Engineering first with applications in displays to medical imaging and renewable energy production.The transistor is easily scaled and has power-handling capabilities at least 10X greater than commercially produced thin film transistors. The team was exploring new uses for thin film transistors (TFT), which are most commonly found in low-power, low-frequency devices like the display screen you’re reading from now. Efforts to improve the performance of the transistors have been slowed by the challenges of developing new materials or slowly improving existing ones for use in traditional thin film transistor architecture, known technically as the metal oxide semiconductor field effect transistor (MOSFET).
They improved performance by designing a new transistor architecture that takes advantage of a bipolar action. In other words, instead of using one type of charge carrier, as most thin film transistors do, it uses electrons and the absence of electrons (referred to as “holes”) to contribute to electrical output. Their first breakthrough was forming an ‘inversion’ hole layer in a ‘wide-bandgap’ semiconductor, a great challenge in the solid-state electronics field.
DC characteristics as a three terminal device. (a) The cross-section of the TJT based on the HCAP; (b) the measured family curves in common-emitter mode from VBE=0 to 3 V; (c) the transconductance of the TJT in the common-emitter mode; and (d) the forward current gain between emitter and base current (βE).
Once this was achieved, “we were able to construct a unique combination of semiconductor and insulating layers that allowed us to inject “holes” at the MOS interface,” said Gem Shoute. Adding holes at the interface increased the chances of an electron “tunneling” across a dielectric barrier. Through this phenomenon, a type of quantum tunnelling, “we were finally able to achieve a transistor that behaves like a bipolar transistor.” “It’s actually the best performing [TFT] device of its kind-ever,” said Prof. Ken Cadien. “This kind of device is normally limited by the non-crystalline nature of the material that they are made of”
“Our goal was to make a thin film transistor with the highest power handling and switching speed possible.” he said. “The high quality sub 30 nanometre (a human hair is 50 nanometres wide) layers of materials produced by Professor Cadien’s group enabled us to successfully try these difficult concepts” The team has filed a provisional patent on the transistor. The next step is to put the transistor to work “in a fully flexible medium and apply these devices to areas like biomedical imaging, or renewable energy.” http://www.engineering.ualberta.ca/NewsEvents/Engineering%20News/2016/February/Researchersengineeranelectronicsfirstopeningdoortoflexibleelectronics.aspx
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