Commercial Crystal and MEMS Oscillators Characterized at Deep-Cryogenic Temperatures

Electronics, from basic sub-micron MOSFETS to large-scale FPGAs, has been shown to operate at deep-cryogenic temperatures. Any digital system relies on an accurate clock for operation. While a clock signal can be provided from room temperature into the cryogenic environment, a clock generated at low temperatures features both smaller system size and tighter integration with the remainder of the electronics. While custom integrated cryogenic oscillator architectures have been proposed, mainly for the generation of radio-frequency signals, no commercial devices have been shown to operate at temperatures as low as 4 K. In this work, we focus on cryogenic frequency generation with commercially available oscillators. Eight commercial crystal and MEMS oscillators, generating 50 or 100 MHz signals, were tested over a wide temperature range from 300 K down to 4 K. Although MEMS devices suffered from apparent ageing effects after several cooling cycles, the majority of crystal oscillators were fully functional even at such low temperatures. The oscillation frequency of crystal-based devices decreased by roughly 0.1%, while power consumption and signal amplitude were slightly higher at cryogenic temperatures. The phase noise and corresponding phase jitter were elevated mainly due to increased flicker noise; the best device shows a phase jitter increase from 350 fs at 300 K to 620 fs at 4 K.