Composite passive materials for ultrasound transducers

Abstract

Provided herein are composite passive layers for ultrasound transducers having acoustic properties that can be easily tailored to the needs of the transducer application using current microfabrication techniques. In an embodiment, a passive layer comprises metal posts embedded in a polymer matrix or other material. The acoustic properties of the passive layer depend on the metal/polymer volume fraction of the passive layer, which can be easily controlled using current microfabrication techniques, e.g., integrated circuit (IC) fabrication techniques. Further, the embedded metal posts provide electrical conduction through the passive layer allowing electrical connections to be made to an active element, e.g., piezoelectric element, of the transducer through the passive layer. Because the embedded metal posts conduct along one line of direction, they can be used to provide separate electrical connections to different active elements in a transducer array through the passive layer.

1 . A method of fabricating a transducer, comprising:
 coating a photoresist layer on an active acoustic element;   exposing the photoresist layer to light through a mask to transfer a pattern from the mask to the photoresist layer;   removing portions of the photoresist layer based on the transferred pattern to create a plurality of voids in the photoresist layer; and   depositing conductive material in the voids to form conductive posts embedded in the photoresist layer, wherein the patterned photoresist layer and conductive posts form a passive layer attached to the active acoustic element.   
     
     
         2 . The method of  claim 1 , further comprising curing the photoresist layer after the conductive posts are formed. 
     
     
         3 . The method of  claim 1 , wherein the active acoustic element comprises a piezoelectric element. 
     
     
         4 . The method of  claim 1 , wherein removing portions of the photoresist layer comprises removing portions of the photoresist layer that are oriented substantially perpendicular to an acoustic emitting face of the active acoustic element. 
     
     
         5 . The method of  claim 1 , wherein depositing conductive material comprises depositing a metal material in the voids to form conductive metal posts. 
     
     
         6 . The method of  claim 5 , wherein depositing a metal material comprises depositing a silver or nickel material in the voids to form the conductive metal posts. 
     
     
         7 . The method of  claim 1 , wherein at least one of the conductive posts extends across a thickness of the passive layer. 
     
     
         8 . The method of  claim 1 , wherein the passive layer forms a matching layer that acoustically couples ultrasound energy from the active acoustic element. 
     
     
         9 . The method of  claim 1 , further comprising depositing an electrode on a surface of the passive layer, wherein the electrode is electrically coupled to the active acoustic element through at least one of the conductive posts. 
     
     
         10 . The method of  claim 1 , wherein coating a photoresist layer on an active acoustic element comprises coating the photoresist layer on a plurality of active acoustic elements. 
     
     
         11 . The method of  claim 10 , further comprising depositing a plurality of electrodes on a surface of the passive layer; and electrically coupling each of the electrodes to one of the active acoustic elements through at least one of the conductive posts. 
     
     
         12 . The method of  claim 12 , wherein electrically coupling each of the electrodes comprises electrically coupling each of the electrodes to a different one of the active acoustic elements. 
     
     
         13 . The method of  claim 10 , further comprising electrically coupling an integrated circuit (IC) chip to at least one of the active acoustic elements through at least one of the conductive posts. 
     
     
         14 . The method of  claim 13 , further comprising bonding the IC chip to the passive layer. 
     
     
         15 . The method of  claim 14 , further comprising disposing the passive layer and plurality of acoustic elements on the IC chip. 
     
     
         16 . The method of  claim 13 , wherein the IC chip comprises a plurality of electrical contacts, and wherein electrically coupling the IC chip to at least one of the active acoustic elements comprises electrically coupling each one of the electrical contacts of the IC chip to a different one of the active acoustic elements in the transducer array through at least one of the conductive posts. 
     
     
         17 . The method of  claim 10 , further comprising disposing a first array of electrodes between the passive layer and the plurality of acoustic elements, wherein the first array of electrodes are electrically coupled to the conductive posts of the passive layer. 
     
     
         18 . The method of  claim 17 , further comprising disposing a second array of electrodes on an opposite surface of the passive layer from the first array of electrodes, wherein the second array of electrodes are electrically coupled to the first array of electrodes through the conductive posts of the passive layer. 
     
     
         19 . The method of  claim 1 , further comprising disposing a first electrode between the passive layer and the active acoustic element and electrically coupling the first electrode to the conductive posts of the passive layer. 
     
     
         20 . The method of  claim 19 , further comprising disposing a second electrode on an opposite surface of the passive layer from the first electrode and electrically coupling the second electrode to the first of electrode through the conductive posts of the passive layer.