MSE Colloquium: Fatima Alleyne, Precipitation Effects in Ion Implanted Aluminum Nitride

Abstract

One of the more attractive sources of green energy has roots in the popular recycling theme of other green technologies, now known as "energy scavenging."  In its most promising conformation, energy scavenging converts cyclic mechanical vibrations in the environment or random mechanical pressure pulses, caused by sources ranging from operating machinery to human footfalls, into electrical energy via piezoelectric transducers.  Commercial piezoelectrics have evolved to favor lead zirconate titanate (PZT) for its combination of superior properties; these materials, however, do not meet the criteria for “green” nanotechnology due to potential health implications.  Fortunately, the search for alternative piezoelectrics has been underway for several years, generating renewed interest in silica (SiO₂) and more recently aluminum nitride (AlN), the object of the present study.  Working on the hypothesis that buried conducting layers can both mitigate delamination problems and generate sufficient electric fields to engage the operation of resonator devices, we have undertaken a study of silver (Ag) ion implantation to experimentally assess their feasibility in AlN devices.  The ion-implanted sample is subjected to a thermal treatment, encouraging diffusion-assisted phase transformations. The objective of this study is to understand these phase transformations with the intent to ultimately control the electrical operation of AlN piezoelectric resonators in energy scavenging applications.  Data reveals that computer simulation models provide reliable predictions of silver dose and depth while microscopic analysis reveals the fate of the ion implanted Ag.  Sputtered AlN films are also found to grow epitaxially in a columnar morphology with acceptable crystalline quality of the epilayer.  It is concluded that the Ag implanted region does indeed have potential as a buried contact layer for piezoelectric based MEMS devices.

Bio

Fatima Alleyne is a doctoral candidate in the Materials Science and Engineering Department at the University of California, Berkeley and a Guest Scientist at the Lawrence Berkeley National Laboratory (LBNL).  Her research interests include structural characterization of ceramic materials for sensing and energy scavenging devices.  She previously served as Principal Investigator for Seguro, a UC Berkeley research team established to develop engineering solutions that protect and empower the farmworker communities of California.  In that capacity, she identified and evaluated chemical sensors for the detection of pesticides and other toxic chemicals, and both laboratory and in-field testing of protective apparel for farmworkers.  Fatima Alleyne’s prior research experiences include microstructural analysis of cis-isoprene thin films as effective barrier methods and magnetic resonance studies of chemically intercalated lithium vanadium oxide for rechargeable battery applications.  During her time at Berkeley, Alleyne supervised 10 undergraduate researchers and a high school student, and served as an Education Outreach Coordinator for a science research center founded at UC Berkeley.  She is a proud recipient of the UC Berkeley Dissertation-Year Fellowship.  She was also a recipient of the Founder Region Soroptimist Fellowship, National Science Foundation (NSF) Fellowship, National Collegiate Inventors and Innovators Alliance (NCIIA) Advanced E-Team Grant, Ford Foundation Fellowship and UC Berkeley Chancellor’s Opportunity Fellowship.  Fatima Alleyne is also a member of the Materials Research Society (MRS), Microscopy Society of America (MSA), and the American Chemical Society (ACS).