Patrick Lenahan
The next generation of computers will hinge on the development of new materials for silicon-based transistors. A critical factor in reducing transistor size is the ability to make thin insulator layers. Presently, strong international research efforts to reduce the insulator thickness from the current 20 atom thickness are rapidly approaching the fundamental physical limits of oxide thickness. An alterative approach to maintain present gate oxide thickness levels is to explore new dielectric materials with higher dielectric constant than silicon dioxide. These new materials will allow for thicker gate oxide layers, which will allow the technology to advance a few more generations.
This figure illustrates two, now relatively well understood,
interface and near interface defects which play dominating
roles in limiting the performance of conventional
metal/oxide/silicon (MOS) devices. The role of silicon
"dangling bond" defects was identified through ESR studies
of MOS materials and devices. Current research on new
dielectrics is geared to identify the dominating
imperfections in new dielectric /silicon systems.
Dr. Patrick Lenahan's research group focuses on electronic and magnetic characterization of gate oxide materials. Currently Dr. Lenahan is characterizing hafnium oxide thin films, which are leading candidates to replace silicon oxide as a gate dielectric. He explores electronic states at the interface between the dielectric oxide and semiconductor materials systems and is presently collaborating with major semiconductor manufacturers and research institutes such as Intel, the Oregon Graduate Center, Sharp and Silicon Research Corporation.
Professor Lenahan collaborates with researchers at Sharp, the Oregon Graduate Center, and at Intel. This work is supported by Intel, through the Semiconductor Research Corporation and The Jet Propulsion Laboratory. In addition, he has some related work with NASA Glenn and the Army Research lab in Adelphi, MD. Other Penn State faculty that have research programs in this area are Darrell Schlom and Jerzy Ruzyllo.
Dr. Patrick Lenahan working with one of his students,
Greg Nallo, on Electron Spin Resonance
characterization of gate oxides. The operating
frequency of this ESR spectrometer is in the
X-band (10 Ghz) and the applied magnetic fields
can exceed one Tesla, though fields nearer a third
of that value are typically utilized. Prof. Lenahan has
made modifications to the ESR measurement technique
to carry out specialized measurements of deep trap state
defects in semiconductors and semiconductor devices.
The size and number of high-field magnets make an immediate impression on any visitor walking into Dr. Lenahan's laboratory. Professor Lenahan uses electron spin resonance (ESR) as a tool to characterize electronic states in dielectric films and at the dielectric/semiconductor interface. The ESR response of a material is measured in a microwave resonant cavity under high magnetic field (approx. 1/2 Tesla). From the response of the ESR signals to interface potential, the electronic density of trap states at an interface can be determined. From the response of ESR signals to the flooding of a dielectric with charge carriers, the relationship between specific point defects and various charge capture phenomena can be identified within the dielectrics. In some of his latest research he is exploring a silicon dioxide replacement hafnium oxide.
Dr. Patrick Lenahan is Professor of Engineering Science and Mechanics and he has been at Penn State for eighteen years. His research and teaching interests are primarily in materials for the semiconductor industry. In addition to his research, Dr. Lenahan teaches ESM 314 "Engineering Applications of Materials" which emphasizes the electrical and optical properties of semiconductors, dielectrics, and magnetic materials. He has taught several experimental graduate courses dealing with the electronic properties of semiconductors and insulators utilized in the semiconductor industry. Presently, he regularly teaches several undergraduate engineering mechanics courses in the Engineering Science and Mechanics Department.
