Keywords
Temperature stability, MEMS resonators, Lithium tantalate, X-cut, Turnover temperature, Oscillators
Abstract
All radio devices require a highly accurate frequency reference with superb temperature stability. While quartz-based oscillators meet accuracy demands, they cannot be easily miniaturized for higher frequencies. Silicon-based MEMS resonators offer a promising alternative due to their small size, and low power consumption, though they suffer from significant temperature drift.
This research proposes a silicon-based MEMS device that exhibits low-frequency variations across wide temperature ranges, high-quality factors, and low insertion loss, meeting modern communication system requirements. Two main research avenues are explored.
Firstly, the thermal behavior of S0 Lamb wave X-cut Lithium Tantalate (LT) resonators is investigated, demonstrating a zero-temperature coefficient of frequency (i.e., turnover temperature) numerically. These resonators are optimized to achieve high electromechanical coupling and high turnover temperature, crucial for designing micro-oven-controlled oscillators with excellent stability. Experimental fabrication confirms their high-quality factor (~2000 at 200 MHz), high turnover temperature (>80°C), and moderately large effective electromechanical coupling (~5% at 200 MHz). This unique characteristic of S0 Lamb wave X-cut LT resonators is utilized to propose a novel passive temperature compensation method, potentially canceling both first and second-order temperature coefficients of frequency (TCF) in silicon-based resonators. The combined heterostructure of highly doped silicon and rotated X-cut LT resonators, each with opposing quadratic TCF curves, provides near-perfect compensation for temperature-induced frequency fluctuations. Implementing this design with a thin LT film on an SOI wafer resulted in a frequency drift as low as 70 ppm over a temperature range of 20°C to 100°C at a 313 MHz operation frequency, significantly improving over conventional silicon-based resonators.
Secondly, the phase noise and temperature dependency of the oscillation frequency are studied. The relationship between thermally-induced frequency fluctuations and phase noise of thin-film Piezoelectric-on-silicon (TPOS) resonators is examined, providing experimental validation for the suppression of overall oscillator circuit noise through operation at the resonator's turnover temperature.
Completion Date
2024
Semester
Fall
Committee Chair
Reza Abdolvand
Degree
Doctor of Philosophy (Ph.D.)
College
College of Engineering and Computer Science
Department
Electrical and Computer Engineering
Degree Program
Electrical Engineering
Format
Identifier
DP0029009
Language
English
Release Date
12-15-2024
Access Status
Dissertation
Campus Location
Orlando (Main) Campus
STARS Citation
Majd, Yasaman, "Design and Optimization of Temperature-Stable MEMS Resonators for Timing Applications Based on Thin-Film Lithium Tantalate" (2024). Graduate Thesis and Dissertation post-2024. 45.
https://stars.library.ucf.edu/etd2024/45
Accessibility Status
PDF accessibility verified using Adobe Acrobat Pro Accessibility Checker