Reduced TCF, High Frequency, Piezoelectric Contour-Mode Resonators with Silicon-on-Nothing

This paper describes microelectromechanical systems (MEMS) contour mode resonators (CMRs) with 900MHz resonant frequencies suitable for radio frequency (RF) applications, using a ~2µm thick degenerately doped n-type silicon (Si) layer. The Silicon-on-Nothing (SON) process has been used to fabricate monocrystalline thin pre-released Si membranes over cavities with well-controlled thickness across the wafer. A thin layer of 15% scandium (Sc)-doped aluminum nitride (AIN) has been incorporated in the vertical stack of the CMRs for piezoelectric transduction. The CMRs were aligned to the <100> crystal orientation of a (100) Si substrate to obtain a reduced temperature coefficient of frequency (TCF) of - 7.4ppm/°C.