The temperature coetlicients of resistance (TCR) of films of sputtered Au, Ir, Mo, Ni, Pd, Pt, Rh, Ta, and W, of evaporated AI, Cr, Ti, and Zr, and of the alloy films Pt-Au, Pt-Ir, and Pt-Ni have been measured in vacuo over the temperature range 25° to 600°C; the film thickness range was 75 to 2oooA. The TCR values of films of the substantially pure metals were in the range i to i those of the respective bulk metals whether deposited on glass, Vycor, or Stupalith substrates. The departure of the conditions of growth of the film from those usual for the bulk metal, i.e., rapid cooling effects and impurities present, contributed imperfections which reduced the TCR of the film. The TCR values of alloy films were low, 0.0004 per °C for Au-Pt, and resistivities were 3 to 4 times that of either constituent. The TCR values of sputtered films of Mo, W, and Ta and of evaporated Cr, Zr, and Ti were generally less than 0.0001 per °C. Electron diffraction examination of films of these latter metals revealed oxide inclusions in the films. The presence of the oxide of the metal reduced the TCR and increased the R/sq of the film as compared to those of the pure metal. Only films of gold, platinum, and iridium were corrosion resistant in air near 600°C. Overcoats of evaporated SiO provided partial protection for the others. Powers up to 15 watts were dissipated by refractory metal films only i2 by ! in. and about 750 A thick. These high values contrasted with less than l w for a gold film of similar dimensions.*
Articles you may be interested inMethod and a simple apparatus for rapid simultaneous measurement of resonance frequency and Q factor of a quartz crystal Rev.
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.
Approximately 100 quartz resonators have been fabricated, stored a t 8 5 "~, and measured a t the fundamental, third, and f i f t h overtone modes. Resonators were fabricated of natural, synthetic, swept natural, and swept synthetic quartz.A l l were base plated with aluminum. Some were given an overcoat of evaporated aluminum or gold. Units were mounted i n the glass T-5-l/2 bulb or i n t h e HC-6/U glass holder.Overtone modes of operation often showed aging patterns different from the fundamental, and the percentage aging at the higher overtones was f r e q u e n t l y l e s s t h a n t h a t a t t h e fundamental f o r t h e same resonator. Studie of t h e s a t u r a t i o n e f f e c t s of gamma i r r a d i a t i o n a t adosage of 1.4 x 10 8 rad/sec for periods up t o 24 hours indicated that quartz resonators irradiated for the longer periods usually exhibit positive frequency s h i f t s . Subsequent aging rates a t 85"c following the saturat i o n i r r a d i a t i o n were small compared t o those obtained subsequent t o irradiation periods of a few minutes a t the same dose l e v e l . 'The freq u e n c i e s o f t h e i r r a d i a t e d r e s o n a t o r s t e n d t o s t a b i l i z e a f t e r s t o r a g e f o r a few days a t 85°C.
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