Recent Seminars and Conferences



Nanowire Transistors for Thin-Film and Transparent Applications

Speaker:	David B. Janes, School of Electrical and Computer Engineering & Birck Nanotechnology Center, Purdue University
Seminar Details:	Semiconductor nanowires are interesting as transistor channel materials, offering the possibility of relatively high performance devices which can be integrated on a variety of substrates. One possible application involves thin-film transistors, which would enable large-area electronics operating at RF frequencies. We have demonstrated thin-film transistors in flexible and transparent formats and demonstrated basic circuits, including drive circuitry for organic light-emitting diode displays [1-2] While many reports have demonstrated specific I-V relationships, there is a lack of simple models for device operation in regimes where contact injection, e.g. by tunneling, dominates the I-V relationships. Low-frequency (1/f) noise studies have been reported, but generally describe the noise in terms of the bulk Hooge model, in which the Hooge parameter (aH) is typically quoted as a constant for a given device. In order to understand the effects of contacts and noise mechanisms and evaluate potential circuit performance, nanowire transistors employing several channel materials, including ZnO, In2O3 and InAs, have been studied [3-4]. The use of organic gate dielectrics and appropriate control of the interfaces, including contacts, yields on/off ratios of 107 and "on" currents as high as 10 uA per nanowire. The various channel materials, nanowire diameters and channel lengths allow tuning of both the device electrostatics, e.g. characteristic band bending lengths at the contacts, and the general transport parameters, e.g. tuning toward quasi-1-D density of states and quasi-ballistic transport. Although simple field-effect mobility models are typically used to evaluate nanowire transistors, the overall I-V characteristics can generally be understood in terms of injection across gated barriers at the contacts, rather than in terms of mobility.Low-frequency (1/f) noise has been studied as a function of bias point, in order to determine how the nanowire transistor noise compares to classical noise models. While the data generally fits the Hooge relationship (i.e. noise current power proportional to ID2 and inversely proportional to number of carriers), the Hooge parameter is a strong function of bias. Noise properties can be changed significantly both by control of the nanowire interfaces and by modification of the contacts. These relationships allow evaluation of the relative contributions of interface states and contacts to the overall noise properties, and provide insights into the conduction mechanisms within the devices.
Speaker Details:	David B. Janes received the B.A. degree in Physics from Augustana College in 1980 and the B.S.E.E., M.S.E.E. and Ph.D. degrees from the University of Illinois at Urbana-Champaign in 1980, 1981 and 1989, respectively. From 1981 to 1985, he worked as a research scientist at the Research Division of Raytheon Company, where he worked on microwave devices and integrated circuits. Since 1989, he has been at Purdue University, where he is a Professor of Electrical and Computer Engineering. From 2001-2003, he was Research Program Coordinator for the Birck Nanotechnology Center. From 2003-2007, he was Technical Director of the Institute for Nanoelectronics and Computing, a NASA-supported center. Current projects include development of molecular electronic components, nanowire/nanotube transistors, and chemical sensors.
Date and Time:	3 PM, 23rd August, 2010
Venue:	EE-105, EE Main Building