maboudianlab - W. Robert Ashurst

Alumnus - Ph.D.

Ph. D. in Chemical Engineering, University of California, Berkeley, 2003

B.S. in Chemical Engineering, Auburn University, Auburn, 1998

ashurbr (at) cal.berkeley.edu

Current Position:

Assistant Professor of Chemical Engineering

Auburn University

Personal Webpage

Surface Engineering for MEMS Reliability

As a postdoctoral fellow and graduate student at the University of California - Berkeley, my research has primarily focused on the surface engineering of semiconductor materials with the ultimate goal of improving the reliability of MicroElectroMechannical Systems (MEMS). These micromechanical devices are made by a variety of techniques, including surface micromachining, bulk micromachining, LIGA, HEXSIL, and many others. Irrespective of their fabrication process, these micro scale machines all have the common property that their surface area to volume ratios are very large. From a surface engineering point of view, this means that forces and interactions that are related to surface area will dominate forces and interactions that are related to volume. This is sometimes evidenced when microstructure surfaces spontaneously stick together, and remain adhered. Experimental evidence (and force calculations) show that the capillary force is usually the main surface force responsible for adhesion. When adhesive forces exceed restoring forces internal to the micromechanical structure, a phenomenon known as stiction is likely to occur. Stiction refers to unintentional adhesion of compliant micromechanical surfaces either to each other or their substrate. Additionally, in the microscale, friction is not independent of adhesion (or sticking), so the terms were combined to describe the phenomena. Stiction is a major factor which limits the reliability of MEMS.

Engineering approaches to avoid release stiction (stiction that occurs during the release step as a result of liquid capillary forces) include supercritical drying techniques, vapor release techniques, and freeze sublimation. However, these techniques are not capable of addressing the problem of in-use stiction (stiction that occurs after the release, i.e., while the device is in operation) and other approaches must be investigated. In fact, the most effective treatments to date involve chemical modification of the MEMS surfaces. This is where my research is focused.

Ph.D. Thesis

Surface Engineering for MEMS Reliability (2003)

Advisors: Prof.'s Roya Maboudian