Nitride-Based Transistors: The Power of Polarization
Speaker: Tomás Palacios , University of California – Santa Barbara
Date: April 20 2006
Time: 3:00PM to 4:00PM
Location: 34-401A (Grier Room A)
Host: Prof. Jesus del Alamo, MIT MTL
Contact: Cindy Gibbs, 3-4602, cindy@eecs.mit.edu
In the short span of 15 years, nitride-based semiconductors have evolved tremendously from almost the first material growth to commercial applications. These materials have a unique set of properties that makes them the most complete semiconductor family. Their tunable direct bandgap from infrared to deep ultraviolet, very high electron velocity, polarization, piezoelectricity, chemical and thermal stability, ferromagnetism and biocompatibility allow applications spanning from LEDs and laser emitters to surface acoustic wave filters, photodetectors, advanced physical and bio- sensors and transistors.
This seminar will focus on AlGaN/GaN high electron mobility transistors, which have demonstrated outstanding performance in recent years in the area of power amplification in X band (8-12 GHz). One of the new challenges for these transistors is to increase their operating frequency to Ka-band (26-40 GHz) and beyond, with the aim to replace or complement traveling wave tube amplifiers. Satellite transponders, broad-band wireless communications, highly efficient radars and many other applications would greatly benefit from the increased reliability, reduced size and low noise of these solid-state based amplifiers. However, three main problems need to be overcome to achieve these frequencies. First, these transistors suffer from a lower-than-expected current gain cut-off frequency. Second, their small signal performance strongly depends on the bias point. Third, deep submicron devices show important short channel effects due to the poor electron confinement typical of a single heterojunction device. This seminar will study how by engineering the unique properties of nitrides in combination with a new 50 nm technology all these three important problems can be solved to finally achieve unprecedented performance at 40 GHz and above.
In addition to the excellent results demonstrated by nitride-based transistors in the field of power amplification at high frequencies, there are many other areas where these devices can play a very important role. I will conclude my talk by discussing how the unique properties of nitride-based devices have the potential to revolutionize fields as diverse as biosensors, energy and power conversion, and even high speed digital electronics for a beyond-Si scenario.
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