Frequency stability of RF oscillator with MEMS-based encapsulated resonator

This paper presents a RF MEMS oscillator with high frequency stability and low phase noise. The oscillator consists of MEMS disk resonator and low noise feedback circuits. The two-port radial-contour-mode silicon resonator was fabricated with high Q-factor and hermetically encapsulated using Sn-rich Au-Sn solder bonding, which significantly improves the frequency stability. A PCB-based oscillator circuit was designed for low phase noise of the oscillator. The two-stage amplifying architecture with automatic gain control (AGC) loop and impedance matching network was utilized to improve phase noise performance. The measured phase noise is as low as -96 dBc/Hz at 1 kHz offset and -128 dBc/Hz at far-from-carrier offsets. The short-term, medium-term frequency stability and Allan deviation of the oscillator are ±0.5 ppm, ±4 ppm, and 10 ppb, respectively.