— IEEE Orange County CPMT Chapter
Meeting Date: Tuesday May 16, 2017
Time: 6:30 PM Networking; 7:00 PM Presentation
Speaker: Dr. Shengke Zhang of Wispry Inc.
Location: Broadcom, Irvine
RSVP: Registration is appreciated, but not required. Everyone is invited. Dinner is provided at no cost.
Event Details: IEEE/vTools
Perovskite microwave ceramics are of significant practical importance for wireless communication systems due to their superior performance including ultra-low microwave loss and “low/no” frequency drift with respect to temperature variations. However, a first-principles understanding of what mechanisms are responsible for the microwave loss and temperature coefficient of resonant frequency (τf) have not been firmly established. In this talk, I will focus our discussions on transition-metal-doped Ba(Zn1/3Ta2/3)O3 (BZT) and Ba(Zn1/3Nb2/3)O3 (BZN) perovskite ceramics because they are the highest performers at room temperature that are commercially available and widely used in cellular base stations. The properties of commercial microwave ceramics are optimized by adding transition-metal dopants or alloying agents, such as Ni, Co, or Mn to adjust τf to near-zero. This occurs as a result of the temperature dependence of dielectric constant offsetting the thermal expansion. At cryogenic temperatures, we discover that microwave loss in these commercial materials is dominated by the spin-excitation process within the unpaired d-shell electronic spins existing in the transition-metal additives, a loss mechanism differing from the usual suspects. The temperature coefficient of resonant frequency (τf) of a microwave resonator is determined by three fundamental materials properties according to the following equation: τf = – (½ τε + ½ τμ + αL), where αL, τε and τμare defined as the linear temperature coefficients of the lattice constant, dielectric constant, and magnetic permeability, respectively. We have experimentally determined each of these three parameters for undoped and Ni-doped BZT materials. These results, in combination with density functional theory (DFT) calculations, have allowed us to quantitatively model the physical processes that determine τf with reasonable accuracy.
Bio: Shengke Zhang is currently a Senior RF-MEMS Reliability/Failure Analysis Engineer at Wispry Inc., an industrial leader in high-performance tunable radio frequency (RF) semiconductor products for the wireless industry. He earned his M.S. and Ph.D. degrees in Materials Science and Engineering from Arizona State University in 2012 and 2016. He received his B.S. degree in Materials Control and Engineering in 2011 at Huazhong University of Science and Technology in China. Dr. Zhang’s research focuses on developing high performance microwave dielectric resonators and superconducting resonators for wireless communication and quantum computing applications. He has 4 peer-reviewed publications (3 first-authored) in the top journals of the field such as Journal of the American Ceramic Society and Applied Physics Letter, and more than 20 presentations/invited talks in leading international conferences.