Design of temperature compensated radio frequency free-free beam MEMS resonators using a commercial process

We present the design and simulation of temperature compensated Radio-Frequency (RF) Free-Free (FF) beam MEMS resonators that are developed using PolyMUMPS, which is a commercial multi-user process available from MEMSCAP. The proposed devices, which operate at 10MHz and 20MHz, are designed using CoventorWare finite element modeling software. We present a novel and effective temperature compensation strategy that is achieved using structural layer of gold (Au) that is patterned on the resonator devices. Au is a standard layer available in PolyMUMPS, thus allowing the compensated devices to be fabricated in the standard process. The performance of Au layer temperature compensated composite devices were evaluated and compared with uncompensated devices and with devices compensated with silicon dioxide (SiO2). For example, considering the 20MHz resonator, devices compensated with Au layer gave the best temperature coefficient of frequency (TCF) of -1.66ppm/°C compared with SiO₂ (-6.38ppm/oC) and uncompensated (-8.48ppm/°C) devices between the temperature range of -50°C to +125°C.