buried (subsurface) Zener diodes, and so their LF noise time-drift should be inline with anything else you can buy with one of these type of diodes.
I have a doubt about it, if the process would be so simple, then anyone can reproduce it. But problems to grow a prefect semiconductor lay in millions layers. starting with a regular process parameters, and quality of raw materials, and finish with fancy problems like unwanted injection of atoms that disrupting a structure, or metal atoms diffusion from conductor that connecting atoms to output legs .... So it not soo simple ....
The variation of crystals may indirectly indicate an overall quality - that means a significant effort for selection, and even this doesn't guarantee a long term stability for a simply reason, during manufacturer process crystal was contaminated, and defects slowly spreading ....
Go to
http://translate.google.com (or use the chrome or chromium browser), and then type in this URL:
http://bbs.38hot.net/thread-120731-1-1.html(
>>>HERE<<< is an "all in one" link if you are lazy ).
About 3/4 the way down in the page, we have a post by user Archwang:
"The discussion Ni originally "high power stability," page 68, PN zener diode emitting end portion work described herein to a breakdown occurs; surface Breakdown causes the device to be noisy. This is the case with the first two samples.
The new 2DW234 does not emit light when it is working, suggesting that the device is likely to have a buried structure. Moreover, according to the longshort altar friend's previous reminder, the two PN junction directions in this device are exactly opposite to other products, indicating that the production process has undergone major changes. The buried Zener in the literature report is also the formation of P-type impurity diffusion, which may be related to this change."