Stability Studies on Crystal Units

Abstract

One hundred quartz crystal 16.25 mc resonators of type CR 19-U have been obtained from each of s i x manufacturers. One t h i r d of each group were stored at025OC, 85OC, and l25OC respectively. The frequencies of t h o s e s t o r e d a t 85 C were measured periodically at that temperature whereas those stored a t 25OC and l25OC were brought t o 55OC every 14 days for measurement. The b e t t e r units exhibited both positive and negative drifts of 1 ppm in periods of 60 t o 150 days a t 25OC 2 ppm a t 85Oc and 5 ppm a t l25OC; however, the bulk of the units exhibited f a r greater drifts than these. Fifty-four of t h e u n i t s s t o r e d a t 85Oc were leak tested. Six were shown t o l e a k by a helium leak t e s t b u t 49 were shown t o l e a k b y ' t h e vacuum oil technique. Leaks through the m e t a l t o g l a s s s e a l s of the base were the predominant type of leak. The r e s u l t s of the vacuum o i l leak t e s t were more nearly in agreement with aging data. Positive frequency drifts observed appeared t o be associated with s t r e ssed electroplated nickel films or inadherence; and negative d r i f t s w i t h leaking, corrosion, or bimetal diffusion of the nickel and s i l v e r films commonly used f o r p l a t i n g . One hundred 16.25 mc aluminum plated resonators have been f a b r i c a t e d i n glass containers and s t o r e d a t 85Oc. Conditions of fabrication changed were substrate temperature during deposition, post deposition heating, vacuum bakeout and the atmosphere of the container--either vacuum or dry argon. The b e t t e r units, 40 of t h e 100, exhibited only small random s h i f t s of 0.5 ppm. The aluminum plating of t h e b e t t e r u n i t s was deposited on the quartz surface a f t e r t h e surface was heated t o 45OoC and cooled t o 250°C i n vacuo. Subsequently the units were vacuum baked a t 1 8 0 O c for three hours before sealing i n vacuo.

Temperature dependence of Ohmic contacts of In0.83Ga0.17As photodiodes and its correlation with interface microstructure

“…According to the relationship between kT and the tunneling parameter E 00 in the traditional current transport mechanisms [18,21], thermionic field emission (TFE) model is supported by the estimated maximum (E 00 /kT) of 1.56. However, the specific contact resistivity of TFE model decreases with an increase in the measurement temperature, which is in contradiction with our results, obviously.…”

“…Figure 2b shows the I-V-T characteristics of sample A with 22 lm gap spacing at different temperatures. Note that the I-V curves keep linear in the measurement temperature range, but the current decrease anomalously with increasing temperature, which does not conform to the typical feature of MS contact [18]. On the basis of the I-V-T characteristics of samples, the specific contact resistivity q sc as a function of measurement temperature is obtained, as shown in Fig.…”