Ultrasonic image sensing array and method

• US 5,160,870 A
• Filed: 06/25/1990
• Issued: 11/03/1992
• Est. Priority Date: 06/25/1990
• Status: Expired due to Fees

• Current Assignee: Andrew L. Robinson, Dale W. Fitting, Fred L. Terry, Paul L. Carson
• Original Assignee: Andrew L. Robinson, Dale W. Fitting, Fred L. Terry Jr, Paul L. Carson
• Inventors: Robinson, Andrew L., Carson, Paul L., Terry, Fred L. Jr., Fitting, Dale W.
• Primary Examiner(s): Budd, Mark O.
• Application Number:
  US07/543,267
• Time in Patent Office: 862 Days
• Field of Search: 310/311, 310/324, 310/334, 310/338, 310/339, 310/366, 310/800
• US Class Current: 310/339
• CPC Class Codes: B06B 1/0629 Square array
• CPC Class Codes: Y10S 310/80 Piezoelectric polymers, e.g. PVDF

Abstract

An ultrasonic sensing array having ultrasonic transducer elements formed on a micromachined single-crystal semiconductor wafer provided with a deep recess under each transducer. Etch-altering dopants are diffused into the water to form rimmed support structures for dielectric stress-balanced elements. Composite dielectric layers are grown on both surfaces of the wafer. One composite layer serves as a diaphragm underlying the transducer elements. The other composite layer serves as a mask for etching away the substrate under each transducer element to form the deep recess while leaving the support structures and diaphragm layer. The resulting hollow or recess under each transducer element reduces the parasitic capacitance between the transducer and support substrate. The transducer elements are made by forming conductive bottom plates on the dielectric diaphragm layer, adding a piezoelectric polymer layer and thereafter forming the conductive top plates. The resulting ultrasonic sensors are capable of operation over a wide variety of frequencies with improved sensitivity and decreased acoustic crosstalk between sensor elements. Switching transistors may also be fabricated as part of the patterned semiconductor substrate.

Claims

1. A micromachined ultrasonic sensing array having a plurality of piezoelectric transducers, each of which generates an electric signal corresponding to a mechanical force acoustically applied thereto, the array comprising:

a patterned micromachined support substrate;

a composite dielectric diaphragm layer formed on the substrate;

a first plurality of electrically conductive plates spaced from one another and connectable to an external bonding pad and resting on the diaphragm layer, each such plate forming a first plate of a distinct one of the transducers;

a plurality of patterned piezoelectric polymer film layers spaced from one another and bonded to the diaphragm layer and the first plurality of electrically conductive plates, said layers of piezoelectric film being responsive to ultrasonic acoustically applied forces;

a second plurality of electrically conductive plates spaced from one another and resting on the piezoelectric polymer film layer, each such plate forming a second plate of a distinct one of the transducers; and

electronic circuit means for detecting analog values of said electric signal generated by said piezoelectric layer in response to an ultrasonic acoustically applied mechanical force.

5. An ultrasonic sensing array as in claim 1 wherein:

the patterned substrate is provided with a plurality of holes which pass entirely through the substrate and extend to the dielectric layer, and wherein each of the holes is substantially similar in area to the first plurality of conductive plates, thereby reducing parasitic capacitance between the plates and the substrate.

2. A micromachined ultrasonic sensing array having a plurality of piezoelectric transducers, each of which generates an electric signal corresponding to a mechanical force acoustically applied thereto, the array comprising:

a patterned support substrate;

a composite dielectric diaphragm layer formed on the substrate;

the composite dielectric diaphragm layer being composed of at least three layers;

the first such layer generally being silicon oxide;

the second such layer generally being deposited silicon nitride; and

the third layer generally being deposited silicon oxide;

a first plurality of electrically conductive plates spaced from one another and connectable to an external bonding pad and resting on the diaphragm layer, each such plate forming first plate of a distinct one of the transducers;

a plurality of patterned piezoelectric polymer film layers spaced from one another and bonded to the diaphragm layer and the first plurality of electrically conductive plates; and

a second plurality of electrically conductive plates spaced from one another and resting on the piezoelectric polymer film layer, each such plate forming a second plate of a distinct one of the transducers.

3. A micromachined ultrasonic sensing array having a plurality of piezoelectric transducers, each of which generates an electric signal corresponding to a mechanical force acoustically applied thereto, the array comprising:

a patterned support substrate which is a single crystal semiconductor material that is primarily silicon.

a composite dielectric diaphragm layer formed on the substrate;

a first plurality of electrically conductive plates spaced from one another and connectable to an external bonding pad and resting on the diaphragm layer, each such plate forming a first plate of a distinct one of the transducers;

a plurality of patterned piezoelectric polymer film layers spaced from one another and bonded to the diaphragm layer and the first plurality of electrically conductive plates; and

a second plurality of electrically conductive plates spaced from one another and resting on the piezoelectric polymer film layer, each such plate forming a second plate of a distinct one of the transducers.

4. A micromachined ultrasonic sensing array having a plurality of piezoelectric transducers, each of which generates an electric signal corresponding to a mechanical force acoustically applied thereto, the array comprising:

a patterned substrate which is doped to render it at least moderately electrically conductive;

a composite dielectric diaphragm layer formed on the substrate;

a first plurality of electrically conductive plates spaced from one another and connectable to an external bonding pad and resting on the diaphragm layer, each such plate forming a first plate of a distinct one of the transducers;

a plurality of patterned piezoelectric polymer film layers spaced from one another and bonded to the diaphragm layer and the first plurality of electrically conductive plates; and

a second plurality of electrically conductive plates spaced from one another and resting on the piezoelectric polymer film layer, each such plate forming a second plate of a distinct one of the transducers.

6. An ultrasonic sensor array having a plurality of piezoelectric transducers, each of which is responsive to ultrasonic forces applied thereto, the array comprising:

a micromachined support substrate;

a diaphragm layer formed on one side of the substrate;

a first plurality of electrically conductive plates laterally spaced from one another on a side of the diaphragm layer opposite the substrate, each such plate being associated with a distinct one of the transducers;

at least one layer of piezoelectric material bonded to the first plurality of electrically conductive plates said layer of piezoelectric material being responsive to acoustically applied forces;

a second plurality of electrically conductive plates spaced from one another and located on a side of the layer of piezoelectric material opposite the first plurality of electrically conductive plates, each such plate of the second plurality of plates being associated with a distinct one of the transducers; and

electronic circuit means for detecting analog values of said electric signal generated by said piezoelectric layer in response to an ultrasonic acoustically applied mechanical force.

7. An ultrasonic sensing array as in claim 6 wherein:

the piezoelectric material is a polymer material.

8. An ultrasonic sensing array as in claim 6 wherein:

the piezoelectric material is polyvinylidene difluoride (PVDF).

9. An ultrasonic sensing array as in claim 6 wherein:

the piezoelectric material is a copolymer including vinylidene fluoride and trifluoroethylene.

10. An ultrasonic sensor array having a plurality of piezoelectric transducers, each of which is electrically responsive to an ultrasonic force applied thereto, the array comprising:

a patterned support substrate made of single-crystal silicon semiconductor material and having a plurality of deep recesses therein, one for each transducer;

a diaphragm layer formed on one side of the substrate and overlying at least the deep recesses in the support substrate;

a plurality of ultrasonic transducers, spaced from one another, each being electrically responsive to an ultrasonic force applied thereto transducer including;

a first electrically conductive plate resting on the diaphragm layer and overlying a distinct one of the deep recesses in the substrate;

a piezoelectric film layer bonded to the first electrically conductive plate; and

a second electrically conductive plate bonded to the piezoelectric film layer on a side thereof opposite the first electrically conductive plate of the transducer.

11. An ultrasonic sensor array having a plurality of piezoelectric transducers, each of which is electrically responsive to an ultrasonic force applied thereto, the array comprising:

a patterned support substrate made of single-crystal semiconductor material and having a plurality of deep recesses therein, one for each transducer;

a diaphragm layer formed on one side of the substrate and overlying at least the deep recesses in the support substrate;

a plurality of ultrasonic transducers, spaced from one another, each transducer including;

a first electrically conductive plate resting on the diaphragm layer and overlying a distinct one of the deep recesses in the substrate;

a piezoelectric film layer bonded to the first electrically conductive plate;

a second electrically conductive plate bonded to the piezoelectric film layer on a side thereof opposite the first electrically conductive plate of the transducer; and

a backing material substantially filling the deep recesses of the substrate for reflecting a major portion of the ultrasonic energy in a predetermined frequency range that passes through the plates of the transducers back toward the transducers, thereby increasing transducer sensitivity.

12. An ultrasonic sensor array having a plurality of piezoelectric transducers, each of which is electrically responsive to an ultrasonic force applied thereto, the array comprising:

a patterned support substrate made of single-crystal semiconductor material and having a plurality of deep recesses therein, one for each transducer;

a diaphragm layer formed on one side of the substrate and overlying at least the deep recesses in the support substrate;

a plurality of ultrasonic transducers, spaced from one another, each transducer including;

a first electrically conductive plate resting on the diaphragm layer and overlying a distinct one of the deep recesses in the substrate;

a piezoelectric film layer bonded to the first electrically conductive plate;

a second electrically conductive plate bonded to the piezoelectric film layer on a side thereof opposite the first electrically conductive plate of the transducer; and

a backing material substantially filling the deep recesses of the substrate, the backing material having an impedance that substantially matches that of the piezoelectric film layer, thereby helping make the transducers of the array responsive to a broad range of frequencies.

13. A micromachined ultrasonic sensing array having a plurality of piezoelectric transducers, each of which generates an electric signal corresponding to a mechanical force acoustically applied thereto, the array comprising:

a patterned micromachined support substrate, the patterned substrate being provided with a plurality of holes which pass entirely through the substrate and extend to the dielectric layer, and wherein each of the holes is substantially similar in area to the first plurality of conductive plates, thereby reducing acoustic coupling between the transducers;

a composite dielectric diaphragm layer formed on the substrate;

a first plurality of electrically conductive plates spaced from one another and connectable to an external bonding pad and resting on the diaphragm layer, each such plate forming a first plate of a distinct one of the transducers;

a plurality of patterned piezoelectric polymer film layers spaced from one another and bonded to the diaphragm layer and the first plurality of electrically conductive plates, said layers of piezoelectric film being responsive to ultrasonic acoustically applied forces;

a second plurality of electrically conductive plates spaced from one another and resting on the piezoelectric polymer film layer, each such plate forming a second plate of a distinct one of the transducers;

electronic circuit means for detecting analog values of said electric signal generated by said piezoelectric layer in response to an ultrasonic acoustically applied mechanical force.

14. A micromachined ultrasonic sensing array having a plurality of piezoelectric transducers, each of which generates an electric signal corresponding to a mechanical force acoustically applied thereto, the array comprising:

a patterned micromachined support substrate, said substrate having a surface with alternating regions of two distinct levels;

a composite dielectric diaphragm layer formed on the substrate;

a first plurality of electrically conductive plates spaced from one another and connectable to an external bonding pad an resting on the diaphragm layer, each such plate forming a first plate of a distinct one of the transducers adjacent plates of each adjacent transducer being formed on said alternating regions of two distinct levels;

a plurality of patterned piezoelectric polymer film layers spaced from one another and bonded to the diaphragm layer and the first plurality of electrically conductive plates, said layers of piezoelectric film being responsive to ultrasonic acoustically applied forces;

a second plurality of electrically conductive plates spaced from one another and resting on the piezoelectric polymer film layer, each such plate forming a second plate of a distinct one of the transducers; and

electronic circuit means for detecting analog values of said electric signal generated by said piezoelectric layer in response to an ultrasonic acoustically applied mechanical force.