Enhanced temperature sensitivity of a single CMOS-MEMS resonator via resonant modes in orthogonal axes

A novel CMOS-MEMS composite ring resonator capable of a dual-mode operation has been proposed to enable self-temperature sensing in a single device. To maximize the temperature sensitivity between the dual modes, two resonant modes of a single resonator vibrating in orthogonal axes (i.e., inplane and out-of-plane) are chosen due to the large difference of their temperature coefficients of frequency (TCf's). By adjusting the constituent ratio and the position of metals and dielectrics through CAD layouts, different TCf's have been successfully demonstrated in a single CMOS-MEMS resonator. By measuring the TCf's of the in-plane (INP) and out-of-plane (OOP) mode concurrently, a beat frequency with a temperature coefficient of 72 ppm/°C was characterized. By employing a divider-based scaling concept, an estimated maximum beat frequency sensitivity of 3,244 ppm/°C can be obtained under proper scaling numbers.