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Published on: October 6, 2020
Electrostatically tunable piezoelectric-on-silicon micromechanical resonator for real-time clock
Diego Serrano1, Roozbeh Tabrizian, Farrokh Ayazi
1School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, USA. diego.serrano@ece.gatech.edu
Summary
This study presents a tiny, tunable micromechanical resonator for real-time clocks. It achieves stable frequency over temperature using minimal voltage, ideal for compact electronic devices.
Area of Science:
- Microelectromechanical Systems (MEMS)
- Solid-State Physics
- Electrical Engineering
Background:
- Traditional quartz crystal oscillators face limitations in miniaturization and power consumption for modern electronics.
- Real-time clock (RTC) applications require stable, low-frequency timing references with minimal power usage.
- Piezoelectric resonators offer potential for miniaturized timing solutions but require careful design for stability and tunability.
Purpose of the Study:
- To design, fabricate, and characterize a small-form-factor, piezoelectrically transduced, tunable micromechanical resonator for 32.768 kHz RTC applications.
- To achieve low-frequency operation and reduced motional resistance in a compact die area.
- To demonstrate sufficient frequency tuning range for temperature compensation.
Main Methods:
- Utilized finite element simulations for optimizing resonator size, insertion loss, spurious-mode rejection, and frequency tuning.
- Fabricated microresonators on a thin-film aluminum nitride (AlN) on silicon-on-insulator (SOI) substrate.
- Characterized the device performance, including frequency tuning range and motional impedance, using discrete electronics for oscillator implementation.
Main Results:
- Developed a microresonator with a 350 × 350 μm die area using AlN on SOI.
- Achieved a frequency tuning range of 3100 ppm with DC voltages below 4 V, sufficient for -20°C to 100°C temperature compensation.
- Demonstrated low motional impedance, independent of frequency tuning, and verified functionality as a timing reference in an oscillator circuit.
Conclusions:
- The developed micromechanical resonator is suitable for RTC applications due to its small size, tunable frequency, and stable operation over temperature.
- The design successfully balances low-frequency operation, reduced motional resistance, and miniaturization.
- This work provides a viable alternative to traditional timing components for power-sensitive and space-constrained electronic systems.
