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Materials Science at Oregon State University

Multifuctional Thin Film Electronics by Plasma-Enhanced Atomic Layer Deposition

Date: Thursday, Oct 14th
Presenter: Devin Mourey, Hewlett-Packard

Abstract


The field of flexible electronics has garnered considerable interest for use in displays, imaging systems, RFID tags, and many other novel applications. However, high performance flexible electronics on plastic require a range of materials and processing developments to become a reality. In particular, low deposition temperature semiconductors and dielectrics are critical. Recently, oxide semiconductors have demonstrated exceptional performance even when deposited at low temperatures and provide clear opportunities for flexible electronics. We have used a novel, weak oxidant, plasma-enhanced atomic layer deposition (PEALD) process to fabricate stable, high mobility ZnO TFTs and fast circuits on glass and polyimide substrates at 200 °C. Weak oxidant PEALD provides a simple, fast deposition process which results in uniform, conformal coatings and highly crystalline dense ZnO thin films. Our PEALD ZnO TFTs have high field-effect mobility and devices with ALD Al2O3 passivation can have excellent bias stress stability. We have studied and will describe the effects of temperature and gamma radiation on our ZnO TFTs and circuits. A simple percolation model using a Gaussian distribution of near-conduction band barriers describes the temperature dependent mobility behavior well. We have utilized the linear shift in threshold voltage with temperature in our ZnO TFTs to form integrated temperature sensing arrays on non-planar substrates. Devices exposed to 1 MGy of gamma irradiation showed small threshold voltage shifts which were fully recoverable with short (1 min) low-temperature (200 °C) anneals. We have demonstrated a variety of simple ZnO circuits on glass and flexible substrates, and will describe the use of a backside exposure process to form gate-self-aligned structures with reduced parasitic capacitance. Finally, to combat some of the thermal and design challenges associated with unipolar circuits we have developed a simple 4 mask organic inorganic hybrid CMOS process.

Bio
Devin Mourey received a B.S. in materials science and engineering from Cornell University, Ithaca, NY in 2006 where he worked on small-molecule organic photovoltaic cells. He then received a Ph.D. degree in Materials Science and Engineering from Penn State University, University Park in 2010 as a Corning Fellow. At Penn State University, he developed new processes to deposit oxide and organic thin films for use in flexible electronics. Currently he is a research and development engineer at Hewlett Packard where he continues his work on oxide electronics.