[time-nuts] Quartz crystal aging and applied voltage

[Bob Camp]

Hi

Ummm…. errrr…. not so much.

Ions in the lattice are part of the crystal structure. When you "move" them by sweeping you put stress on the quartz. That stress may take a *long* time to relax out. Since there is now a defect in the lattice (where the ion was) the stress may be relieved by an ion moving back to that location. 

Quartz is swept to reduce it's radiation sensitivity. That's a big deal if you are going to put the oscillator in outer space or if you expect to need to use it when unexpected bright lights appear in the sky. Neither one is likely to be of interest in a typical basement lab. The levels involved also would drive you to radiation harden the rest of the oscillator circuit, not just the crystal.

There have been a series of papers on various influences on crystals. If the blank is an SC, it can be tuned by an applied DC voltage. Many precision parts have a DC short across the resonator for this reason. In that case, you would not see anything to drive an ion anyway. 

If you have electrodes on the crystal, diffusion of plating into the quartz will move far more material around than trapped ions. How much more depends a lot on the exact plating materials and plating process.

Bob

On Jun 30, 2013, at 11:47 AM, Attila Kinali <attila at kinali.ch> wrote:

> Moin,
> 
> While looking at various crystal oscillator circuits and a paper on
> stability of quartz oscillators i stumbled over a small detail that
> doesn't seem to be mentioned anywhere, at least i couldnt find anything:
> 
> All quartz crystals contain some amount of ions that move within the
> lattice over time. Good crystals are "swept" using an high electric
> field prior to sawing the crystal slabs.
> 
> Most of the oscillator circuits out there place a small, but constant
> DC voltage on the crystal, which has the same effect on the ions as
> sweeping does, albeit much slower. But i couldn't find any resource
> on how this DC voltage affects aging of quartz crystals.
> 
> Does anyone know any paper/book/webpage that has a discussion of this
> topic?
> 
> 			Attila Kinali
> 
> -- 
> The people on 4chan are like brilliant psychologists
> who also happen to be insane and gross.
> 		-- unknown
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