[ARC5] Crystal aging

[Bruce Long]

It urns out if you take a 10 MHZ quartz crystal and remove one atomic lattice layer you will move the frequency something like 50 ppm.  Twenty years ago I had designed in production for 10 MHz SC-cut ovenized oscillators that where meeting 20 ppb maximum first year aging specs.

So we are talking absolute manufacturing cleanliness and consistency at the  atomic level

Also at this level of aging performance crystal mechanical stress is a big factor.  If you place the crystal blank under mechanical stress as you might when you insert the crystal blank into the mechanical crystal holder- ie the structure that holds the crystal inside the evacuated enclosure  that stress will slowly relax over weeks months and years creating crystal agging at the parts per billion area.