The history of ceramic filters is surveyed. Included is the history of piezoelectric ceramics. Ceramic filters were developed using technology similar to that of quartz crystal and electro-mechanical filters. However, the key to this development involved the theoretical analysis of vibration modes and material improvements of piezoelectric ceramics. The primary application of ceramic filters has been for consumer-market use. Accordingly, a major emphasis has involved mass production technology, leading to low-priced devices. A typical ceramic filter includes monolithic resonators and capacitors packaged in unique configurations.

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A b s t r a c t P i e z o e l e c t r i c materials f o r SAW d e v i c e s w i l l be reviewed. A l l m a t e r i a l s have some d i s t r i b u t i o n o f m a t e r i a l c o n s t a n t s . The t y p i c a l r e s u l t s o f t h e d i s t r i b u t i o n of LSAW v e l o c i t y i n a s u b s t r a t e as measured by t h e Line-Focus-Beam u l t r a s o n i c microscope w i l l be r e p o r t e d . The d e s i g n s of o s c i l l a t o r c i r c u i t s u s i n g bulk wave and s u r f a c e a c o u s t i c wave r e s o n a t o r s a r e analyzed. Maximum i n p u t power f o r SAW d e v i c e s i s l i m i t e d by electrode m i g r a t i o n , which depends on t h e maximum stress a t I D T e l e c t r o d e s . S t r e s s d i s t r i b u t i o n i n a S A W s u b s t r a t e can be c a l c u l a t e d and shown g r a p h i c a l l y by t h e F i n i t e Element Method. The use of t h e o r i e n t e d A 1 e l e ct r o d e s , i n s t e a d of t h e o r d i n a r y amorphous A 1 e l e c t r o d e s , can i n c r e a s e t h e l i f e o f q u a r t z c r y s t a l S A W r e s o n a t o r s o v e r one thousand times. F i n a l l y , t h e r e l i a b i l i t y o f dipped r e s i n packages f o r TV VIF SAW f i l t e r s w i l l be r e p o r t e d . 1. I n t r o d u c t i o n S i n c e 1975, w e i n Japan have developed S A W d e v i c e s p r i m a r i l y f o r t h e consumer m a r k e t . [ l ] 2 . M a t e r i a l s I n J a p a n , p i e z o e l e c t r i c m a t e r i a l s f o r SAW r e s o n a t o r s and f i l t e r s a r e d i v i d e d i n t o c a t e g o r i e s o f s i n g l e c r y s t a l s , t h i n f i l m s and p i e z o e l e c t r i c ceramics. [ 31 Quartz c r y s t a l i s t h e b e s t m a t e r i a l f o r SAW r e s o n a t o r s , b u t LiTaOg and L&B407 a r e a l s o u s e f u l f o r v o l t a g e contro*d oscill a t o r s (VCO). Many kind o f t h i n f i l m m a t e r i a l s have been developed, b u t ZnO/IDT/glass i s t h e most popular f i l m f o r TV VIF i n mass p r o d u c t i o n o f more t h a n 30 m i l l i o n p i e c e s p e r y e a r . PZT modified by Sn and Sb i s developed t o have non p o r o s i t y , low d i e l e c t r i c cons t a n t s and low t e m p e r a t u r e c o e f f i c i e n t of SAW d e l a y time. Table 1 shows c o n s t a n t s o f each b a s i c m a t e r i a l f o r SAW d e v i c e s i n Japan. Fig.1 shows r e l a t i o n s of t h e SAW c o u p l i n g c o e f f i c i e n t t o t h e a b s o l u t e t e m p e r a t u r e c o e f f i c i e n t of d e l a y t i m e . A z e r o temper a t u r e c o e f f i c i e n t o f d e l a y t i m e and a h i g h c o u p l i n g c o e f f i c i e n t a r e i d e a l f o r SAW d e v i c e m a t e r i a l s , b u t s u c h m a t e r i a l s have n o t been d i s c o v e r e d y e t . I n p r a c t i c e , every s u b s t r a t e has some d i s t r i b u t i o n o f m a t e r i a l c o n s t a n t s . Fig.2 shows an example o f LSAW v e l o c i t y d i s t r i b u t i o n on a PZT 2 i n c h w a f e r poled i n t h e ...

Piezoelectric ceramics are widely used for filter and resonator applications in the audio to UHF frequency range. The most suitable vibration mode differs for each frequency range mainly by the spurious frequency response and fabrication techniques. Many examples of filters and resonators using PZT and PbTiO3 ceramics are described hereafter. It should be noted that a ZnO thin-film is not ferroelectric but piezoelectric ceramics, and components utilizing this technique are available for transducers of LF to UHF range resonators. Also, ZnO thin-film on glass is a suitable structure for SAW filters. Using a high sonic velocity substrate, ZnO thin-film has a high SAW coupling coefficient at the third overtone.

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