| PhD Viva

Name of the Speaker: Mr. Bijay J (EE16D414)
Guide: Prof. Deleep R Nair
Online meeting link: https://meet.google.com/ene-ssgu-xyh
Date/Time: 22nd February 2024 (Thursday), 9:00 AM
Title: Performance improvement of thin film piezoelectric on silicon MEMS resonator for timing applications.

Abstract

Demand for CMOS-compatible and small-footprint devices in modern-day wireless communication systems has forced a shift in focus from high-quality factor (Q) off-chip passives like Quartz resonators and SAW filters towards MEMS resonators. Crystal resonators were widely used due to their high Q and temperature-stable properties. Thin Piezoelectric on Silicon (TPoS) resonators, consisting of a piezoelectric thin film sandwiched between top and bottom electrodes deposited on a high energy density material like Silicon, have low motional resistance, high coupling coefficient and relatively higher Q. An analysis of various losses that brings down the Quality factor (Q) of TPoS resonators are presented. A semi-analytical model is derived to calculate the Q of these resonators. Various predictions to improve the performance of the resonators based on the model are also presented. The results are validated with experimental data. Design and simulation of Phononic Crystals (PnCs) with a wide Acoustic Band Gap (ABG) are also presented.

The fabrication and characterization of the resonators with the resonant frequency of around 1 GHz with optimized design improvements from the model are presented. The fabrication process flow, along with the challenges, are also discussed. The results of the experiments are then compared with the model predictions and validated. Another significant loss occurs due to the isotropic etch used to release the resonators. This additional loss is modeled and validated with measured experimental data found in the literature. The electrical modeling of the resonator for the oscillator design is also discussed.