Thin film ultrasound transducer

Abstract

The present invention relates to a transducer ( 11 ) comprising a membrane ( 31 ) configured to change shape in response to a force, the membrane ( 31 ) having a first major surface ( 16 ) and a second major surface ( 17 ), a piezoelectric layer ( 18 ) formed over the first major surface ( 16 ) of the membrane ( 31 ), the piezoelectric layer ( 18 ) having an active portion, first and second electrodes ( 19 ) in contact with the piezoelectric layer ( 18 ), wherein an electric field between the first and second electrodes ( 19 ) determines the mechanical movement of the piezoelectric layer ( 18 ), support structures ( 40 ) at the second major surface ( 17 ) of the membrane ( 15 ) on adjacent sides of the active portion of the piezoelectric layer ( 18 ), at least part of the support structures ( 40 ) forming walls perpendicular, or at least not parallel, to the second major surface ( 17 ) of the membrane ( 31 ), so as to form a trench ( 41 ) of any shape underlying the active portion, so that an ultrasound transducer is obtained with a high output pressure at the support side than at the opposite side. The invention also relates to a method of forming such a transducer, and an array comprising at least one transducer of the like.

1 . A method of forming a transducer ( 11 ), the method comprising:
 obtaining a substrate ( 30 ) having a front side and a back side,   forming a membrane ( 31 ) over the front side of the substrate ( 30 ),   forming a piezoelectric layer ( 18 ) over the membrane ( 31 ),   forming at least one patterned conductive layer including first and second electrodes ( 19 ) in contact with an active portion of the piezoelectric layer ( 18 ),   patterning the substrate ( 30 ) from the back side such that supports ( 40 ) partly comprising walls perpendicular or at least not parallel to the membrane ( 31 ) are obtained on adjacent sides of the active portion of the piezoelectric layer ( 18 ) and a trench ( 41 ) is provided underlying the active portion, wherein patterning the substrate ( 30 ) comprises dimensioning the trench ( 41 ) to achieve a higher ultrasound output on the support side than on the opposite side; optionally, forming a protection layer on top of the patterned conductive layer.   
     
     
         2 . A method according to  claim 1 , furthermore comprising forming a barrier layer ( 32 ) on top of the membrane ( 31 ). 
     
     
         3 . A method according to  claim 1 , furthermore comprising patterning the piezoelectric layer to realize the active portion. 
     
     
         4 . A method according to  claim 1 , furthermore comprising thinning the substrate before patterning it from the backside.