A Novel Miniature OCXO Using Hermetically Sealed Ceramic Package

This work presents an ultra-miniature oven controlled crystal oscillator (OCXO) using a hermetically sealed ceramic package with the size of $7.0\ \text{mm} \times 5.0\ \text{mm}$. The oven structure combined within a heater-embedded ceramic package and a low thermal conductivity bonding adhesive provides excellent thermal performance, achieving temperature stability within ±10 ppb across −40 to 95°C. Hermeticity is accomplished with a seam-welded lid to a kovar ring on the ceramic substrate. In addition, a $2.5\ \text{mm} \times 2.0\ \text{mm}$ SC-cut crystal is utilized to further improve the temperature stability, aging, gravity sensitivity, and phase noise performance that can be compliance with Stratum 3E specifications. The proposed ultra-miniature OCXO provides more robust and smaller package alternative for 5G outdoor applications, such as remote radio heads (RRHs), active antenna unit (AAU), and small cells.