Abstract:

Controlled spalling of single-crystal semiconductors is an emerging technique which results in the rapid exfoliation of a thin, single-crystal layer by propagating fracture parallel to the wafer surface. Spalling fracture has been engineered to controllably and intentionally exfoliate thin film electronic devices from single-crystal semiconductors for the purposes of creating flexible devices or enabling substrate reuse to mitigate costs. The process uses an adhered stressor layer combined with an externally applied mechanical force to initiate and propagate a lateral fracture parallel to the substrate surface. Devices have been successfully removed from silicon, gallium arsenide, germanium, and gallium nitride substrates using this method. In this talk, examples will be drawn mainly from spalling (100)-oriented Ge and GaAs to illustrate the impact of cleavage system alignment on the resulting fracture morphology and spalling conditions. The spontaneous spalling model of Suo & Hutchinson has been used to model behavior in these systems, approximating spall depth and critical spalling conditions reasonably well. Fractography is used to understand morphological defects in spalled surfaces. Finally, we show that the fracture process does not generate extended defects that inhibit quality regrowth or degrade delaminated cell efficiency.

Biography:

Dr. Packard is an Associate Professor in the George S. Ansell Metallurgical and Materials Engineering Department at the Colorado School of Mines and holds a joint appointment at the National Renewable Energy Laboratory (NREL) in the National Center for Photovoltaics. She is the co-director of the International Center for Multiscale Characterization, a network of experts and state- of-the-art instruments at Mines and NREL that enable materials characterization and cross-correlation with functional properties and performance from the atomic- to macro-scales.   Prior to appointment at Mines, Packard earned her Ph.D. in Materials Science & Engineering from MIT. Her research program applies experimental techniques commonly used to characterize mechanical behavior and properties in structural materials to solve problems in ceramics in predominantly energy-related applications. She has focused on elucidating the principles and mechanisms of deformation behavior in ceramics at the micro- and nano-scales. In 2014, she received a National Science Foundation Faculty Early Career Development (CAREER) Award and was selected as a TMS Young Leader. In 2017, she received the AIME Robert Lansing Hardy Award. To date, she has more than 35 archival publications, 3 issued patents, and has given over 40 invited and contributed talks. She is currently on sabbatical at CoorsTek Research & Development.

Reception at 3:30 p.m. in the Georgia Tech Manufacturing Institute Atrium.

The Packard Research Group profile page.