Stress-Modulated Control of TCF and Frequency Shift in 4H-SiC Beam Resonators for Enhanced Thermal Stability

Abstract

Precision time and frequency references are critical components in electronic devices, impacting sectors such as wireless communications, global positioning systems, and network synchronization. While quartz-based oscillators have historically dominated the market, micro-electromechanical systems (MEMS) resonators are emerging as potential successors, albeit with challenges related to thermal frequency drifts. This paper presents doubly-clamped beam resonators in monocrystalline 4H-silicon carbide (4H-SiC), showcasing a tunable local zero Temperature Coefficient of Frequency (TCF) across a wide temperature range. Our novel approach employs axial stress to counteract temperature-induced softening in the 4H-SiC beam, leveraging the unique attributes of a 4H-SiC on insulator (SiCOI) substrate with a silicon handle layer. By manipulating the beam’s geometrical dimensions, we demonstrate the capability to define the TCF turnover point from -20°C to 100°C and tailor the overall frequency shift. The fabrication process ensures strong covalent interlayer bonds in the 4H-SiCOI substrate, eliminating frequency hysteresis and enhancing yield and stability metrics. We conducted comprehensive short- and long-term stability tests, showing that our resonators exhibit negligible frequency hysteresis across temperature cycles and exceptional long-term stability. Our findings enrich the current understanding of 4H-SiC MEMS resonator thermal stability and pave the way for future innovations in timekeeping and frequency reference technologies. This study underscores the potential of stress-modulated 4H-SiC resonators as reliable, efficient, and versatile instruments for advanced precision timing applications.