Ultrasonic transducer and method for using same

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment of the present invention is now described with reference to the figures, wherein like numbers represent like parts throughout the figures.
While specific techniques for producing etch stop layers, depositing dielectric layers, and etching materials are presented here, for the most part these will be recognized by those skilled in the art as standard microelectronic processing techniques, for which other equivalent techniques may be substituted.
Moreover, any low-temperature technique (<80.
degree.
c.
) may be used to deposit the metal conducting layers or layers of any other suitable conductor.
It is required only that the conductor deposition method not adversely affect previously processed electronic circuitry on the semiconductor substrate, if any such circuitry exists, and that the deposition method not seriously degrade the PVDF-TrFE piezoelectric film.
An example of a preferred embodiment of an ultrasonic transducer 10 on a semiconductor base in accordance with the invention is depicted in FIG.
1.
The illustrated transducer may be fabricated on a base layer 20 of lightly doped (p-) silicon substrate having a top layer 26 of heavily doped (p+) silicon, a polished top side 19, and an unpolished bottom side 21.
The p+ silicon layer 26 is preferably formed by diffusing boron into the polished side 19 of the p- silicon base layer 20 to a depth of 5 microns.
A dielectric layer 18 is deposited on top of the p+ silicon layer 26 and also on the unpolished side 21.
Dielectric layer 18 may be any depositable, insulating dielectric substance such as an oxide or nitride, e.
g.
, silicon dioxide, silicon nitride, or a layered combination of both silicon nitride and silicon dioxide known as a compound dielectric structure.
It is preferred that the dielectric layer 18 disposed over the p+ silicon layer 26 be about 4000 Angstroms thick, while the dielectric layer over the bottom side 21 be about 3000 Angstroms thick.
Silicon nitride may be deposited using plasma-enhanced chemical vapor deposition (PECVD)