Design of Low Power Crystal Oven

Abstract

Two new m i n i a t u r e c r y s t a l ovens f o r u s e w i t h HC-t/U and HC-l8/U o r e q u i v a l e n t c r y s t a l h o l d e r s and f o r o p e r a t i o n a t 85 +3 C have been designed, constructed and tested. Each oven f i t s i n t o a thre6-cubic-inch envelope and i s composed of two d i s t i n c t p a r t s , t h e c o r e a n d t h e i n s u l a t i o n . The c o r e i s canposed of c r y s t a l and c r y s t a l h o l d e r , a h e a t e r , a mercury-inglass thermostat, and a c o n t r o l c i r c u i t f o r i n v e r t i n g t h e s w i t c h i n g a c t i o n of t h e t h e r m o s t a t . I n one oven t h e c r y s t a l i s a c c e s s i b l e and replaceable. The avegage power consumption i s 500 milliwatts a t an ambient temperature of -55 C. The i n s u l a t i o n c o n s i s t s of a p a r t i a l l y -s i l v e r e d p y r e x dewar of 0.015-inch walls, which has been evacuaged t o 1 x 10-4 xnm Hg o r b e t t e r .Over a n ambie n t t e m p e r a t u r e r a n g e of -52 C t o +80 C t h i s oven m a i n t a i n s c r y s t a l t e mp e r a t u r e s t a b l e w i t h i n i-0.1 C . 0 -I n t h e s e c o n d oven t h e c o r e , a n d t h e r e f o r e t h e c r y s t a l , i s permanently s e a l e d w i t h i n t h e i n s u l a t i o n . The average power consumption i s approximately 70 m i l l i w a t t s a t an ambient temperature of -55OC. The i n s u l a t i o n i s composed of a l t e r n a t i n g l a y e r s of h i g h -e m i s s i v i t y h e a t r a d i a t i o n s h i e l d s (aluminum) and low t h e r m a l c o n d u c t i v i t y s p a c e r s ( f i b e r g l a s s m a t t paper). The a s s e m b l e d m u l t i p l e -l a y e r i n s u l a t i o n i s enclosed i n a s t e e l s h e l l , e v a cu a t e d t o 1 x mrn Hg o r b e t t e r and s e a l e d from the atmosphere. Over a n ambient temperature range of -55OC t o +8Oog t h i s oven m a i n t a i n s c r y s t a l t e m p e r a t u r e s t a b l e w i t h i n b e t t e r t h a n +1.0 C . -I n t r o d u c t i o n I n common c r y s t a l ovens minimization of the effect of the frequencyt e m p e r a t u r e c o e f f i c i e n t of a s i n g l e q u a r t z c r y s t a l b l a n k r e q u i r e s powers ranging from about 3 watts t o 50 watts depending upon t h e c o n t r o l r e q u i r e d and t h e e f f i c i e n c y of t h e c o n t r o l d e v i c e . T h e r e are a number of examples of u n i t s a s small as three-cubic-inches volume w i t h c r y s t a l t e m p e r a t u r g s t a b i l i t y w i t h i n +l.O°C over an ambient temperature range of about -50 C t o +5OoC; a few 0 ; t h e l a r g e r a n d / o r h i g h e r powered ovens are s t a b l e w i t h i n +0.1 C o r b e t t e r . T e m p e r a t u r e c o n t r o l f o r t h e s e ovens has g e n e r a l l y been r e s t r i c t e d t o e i t h e r ON-OFF t h e r m o s t a t i c c o n t r o l o r c o n t i n u o u s c o n t r o l i n v o l v i n g e l e c t r o n i c a m p l i f i e r s . Because of t h e i n c o m p a t i b i l i t y of req u i r...

Low-Stress CMOS-Compatible Silicon Carbide Surface-Micromachining Technology—Part II: Beam Resonators for MEMS Above IC

“…To mitigate these limitations, resonators can be thermally tuned. This is analogous to the thermal control used to enhance the stability of crystals [33]. The resonant frequency can be rewritten from (10) including the temperature dependence as [27] …”