Quasi-linear frequency tuning for CMOS-MEMS resonators

A voltage-dependent quasi-linear frequency tuning mechanism with zero dc power consumption for CMOS-MEMS resonators has been demonstrated with total tuning range of 5,000 ppm and sensitivity of 83.3 ppm/V at 11.5 MHz. Such frequency tuning is realized by a combination of “nonlinear” voltage-controlled electrode-to-resonator gap modulation and electrical stiffness of capacitive transduction to effect a desirable (i.e., linear) frequency dependence versus modulated dc voltage for temperature compensation of capacitive resonators which often exhibit a negative linear temperature coefficient of frequency (TC_f). To alleviate inferior temperature coefficients of Young´s Modulus (TC_E´s) of CMOS metal materials, a composite metal-SiO₂ resonator is utilized with TC_f 6X better than that of mere-metal structures, allowing the proposed frequency tuning to compensate resonator frequencies over temperature range of 80°C. This tuning capability has potential to benefit low power temperature compensation targeted for timing reference and RF synthesizing applications.