Effect of Doping Concentration on the Performance of a Thermally Actuated MEMS Resonator using Piezoresistive Readout

Background/Objective: Thermally actuated dog-bone actuators with an in-plane extensional mode of operation and integrated piezoresistive sensing have found versatile applications especially in realizing miniaturized precision oscillators. In this paper, we present a systematic investigation on the impact of dimensional scaling of the resonator structure and the surface doping concentration of the piezoresistor on the performance of a joules heating driven thermal actuator. Methods/Statistical Analysis: To enhance the performance, the dependence of the in-plane resonant frequency and piezoresistive sensing mechanism on the electrical and mechanical design parameters of the actuator has been investigated. Especially, an in-depth analysis of the effect of the dimensional scaling and the surface doping concentration of the piezoresistor on the electromechanical response of the actuator were performed. The resonator structure and the joules heating induced actuation mechanism were efficiently modeled using a Finite Element Model (FEM) software simulation tool IntelliSuite®. Findings: Here, we devise a modified version of the thermally actuated dog-bone resonator with enhanced performance compared to the traditional designs reported in the literature. The simulation results show that the modified version of the thermally actuated resonator with an additional central beam depicts an improved in-plane extensional mode of resonant frequency by a factor of 2.55. It has been shown that the surface doping concentration of the piezoresistor plays a crucial role in determining the resonant frequency and the equivalent electrical signal by directly influencing the rate of heat generation by varying the drive current of the actuator. In addition, it has been also demonstrated that the doping concentration also plays an important role in determining the resultant magnitude of ΔR/R of the thermally driven actuator. Conclusion/Improvements: It has been demonstrated that the performance of the thermally actuated resonators improve with dimensional scaling. Moreover, the performance metrics of the thermally driven resonator with piezoresistive readout has been shown to have a strong dependence on the surface doping concentration of the piezoresistor.