Quality factor tuning and power consumption optimization of thermal piezoresistive micromechanical self-oscillating resonators

Abstract

Over the past decades, capacitive transduction and piezoelectric transduction have been the most common mechanisms for both actuation and sensing in the micro-electro-mechanical resonator domain. However, the relatively small coupling coefficient of capacitive transduction and the relative large loss of the piezoelectric material, as well as its low compatibility with the traditional complementary metal-oxide-semiconductor (CMOS) process limit their performance in resonators. Thermally-actuated piezoresistive sensed resonators show simple and compatible fabrication with the traditional CMOS process. Additionally, due to the thermal piezoresistive pumping effect, the quality factor of thermally-actuated and piezoresistive-sensed micro-resonators can be tuned by biasing a constant voltage source or constant current source. In this research, a p-type [110] oriented silicon in-plane resonator is designed, fabricated and measured. Under a voltage bias source, the quality factor of this micro-resonator is tuned from 208 to 448 in air ambient. Additionally, a feedthrough reduction configuration is implemented, causing an improvement of the signal to noise level from 1.5 dB to 15 dB. Implementing this resonator to work as a mass sensor, a silver droplet is deposited onto the center mass with inkjet printing, and it is shown that the frequency sensitivity of this device is 55.4 Hz/pg. When the biasing source keeps increasing until it is over a critical value, the thermal piezoresistive micro-resonator starts to resonate and obtains critical power consumption. In order to improve the tuning effect, an analytical model for the pseudo-bimorph resonator is presented and verified. Then, the thermal piezoresistive micro-resonator is designed, fabricated and tested. By tuning the design geometries, the critical power consumption is well tuned and it finds out that the smaller actuation beam length and width, and an optimal separation distance of actuation beam and support beam is the optimal design.

Date of Award	2020
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology