A planar-processed PI-FET accelerometer

Abstract

Excel lent experimental performance has been observed on in tegra ted acce lerometer s t ruc tures t h a t were fab r i ca t ed us ing capac i t i ve PI-FET t r a n s d u c e r s ( l ) t o d e t e c t s t r a i n s i n m i n i a t u r e c a n t i l e v e r beams. The beams are composite struct u r e s c o n s i s t i n g of s i l i c o n , s i l i c o n d i o x i d e , z i n c oxide, metal and pass iva t ing oxide (F igure 1). They a r e formed by a n i s o t r o p i c a l l y e t c h i n g t h e s i l i con f rom undernea th the l aye red s t ruc tu res using EDP e t c h a n t i n t h e manner desc r ibed by P e t e r s e n , ( Z ) o r e l s e by a combination of backside and f r o n t s i d e e t c h i n g of t he wafe r w i th EDP so lu t i on . The p i e z o e l e c t r i c s t r a i n s e n s i n g l a y e r s are direct ly coupled to deplet ion-type, p-channel MOS t r a n s i s t o r s . Dependent on the fabrication procedures employed, the total beam t h i c k n e s s e s a r e e i t h e r below 5 pm ( f o r t o p s u r f a c e e t c h i n g ) , o r else range to about 50 pm ( for e tch ing f rom both s i d e s of t he wafe r ) . S ix sets of beam wid th l l eng th rat ios have been designed: 701235, 2001225, 2751510, 4101505, 5001570, and 950/1240 pm i n o r d e r t o a c h i e v e s e n s i t i v i t i e s t o a wide range of g values and to de te rmine process ing cons t ra in ts . The a c c e l e r o m e t e r s t r u c t u r e s a r e p a r t i a l l y t e m p e r a ture compensated by t h e a d d i t i o n o f a n u n s t r a i n e d z inc -ox ide capac i to r t o ba l ance ou t t he vo l t age produced by t h e p y r o e l e c t r i c i t y o f t h e ZnO. An i n v e s t i g a t i o n of t e m p e r a t u r e s e n s i t i v i t y i s prese n t l y underway.