A Tunable Low-Power Oscillator Based on High- $Q$ Lithium Niobate MEMS Resonators and 65-nm CMOS

This paper presents a comprehensive guide to codesign piezoelectric RF-micro-electromechanical system (MEMS) resonators and CMOS for enabling voltage-controlled MEMS oscillators (VCMOs) that harness the best benefits out of both platforms. The analysis, focusing on understanding different tradeoffs among the tuning range, power consumption, gain, and phase noise, is generic to any kind of piezoelectric resonators and specific for Colpitts VCMOs. As a result of this paper, the first VCMO based on the heterogeneous integration of a high-Q lithium niobate (LiNbO3) micromechanical resonator and CMOS has been demonstrated. A LiNbO3resonator array with a series resonance at 171.1 MHz, a Q of 410, and an electromechanically coupling factor of 12.7% is adopted, while the TSMC 65-nm RF LP CMOS technology is used to implement the feedback and tuning circuitry with an active area of 220 × 70 μm2. The frequency tuning of the VCMO is achieved by programming a binary weighted digital capacitor bank and a varactor that are both connected in series to the resonator. The best measured phase noise performance of the VCMO is -72 and -153 dBc/Hz at 1 kHz and 10-MHz offsets from 178.23and 175.83-MHz carriers, respectively. The VCMO consumes a dc current of 60 μA from a 1.2-V supply while realizing a tuning range of 2.4 MHz (~1.4% fractional tuning range). Such VCMOs can be applied to enable ultralow power, low phase noise, and wideband RF signal synthesis for emerging applications in Internet of Things.