A Low Phase Jitter MEMS Oscillator With Centrally Anchored Piezoelectric Resonator for Wide Temperature Range Real-Time Clock Applications

Abstract

This article describes prototype temperature compensated piezoelectric MEMS oscillators operating in the wide temperature range from $- 40~^{\circ }$ C to $85~^{\circ }$ C for real-time clock (RTC) applications. The AlN-on-Si resonator is centrally anchored at one point and designed for low power operation with a wide frequency tuning range of 5000 ppm. The oscillators exhibit a stable sinusoidal output at about 497-kHz frequency for time keeping applications with an integrated phase jitter (IPJ) being $10\times $ better than the best commercially available MEMS RTC oscillators for supplementary use in portable devices for clocking audio circuits. The measured oscillator performance remains relatively unchanged when comparing the wafer-level packaged (WLP) capped MEMS resonator with the uncapped one, showing great potential for a high-performance low-power RTC oscillator.Index Terms—Automatic gain control (AGC), frequency compensation, low phase jitter, low phase noise, MEMS oscillator, piezoelectric MEMS, real-time clock (RTC), wafer-level packaging, wide temperature range.