Method for fabricating a focal plane array for thermal imaging system

• US 5,743,006 A
• Filed: 06/07/1995
• Issued: 04/28/1998
• Est. Priority Date: 01/03/1995
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Texas Instruments, Inc.
• Inventors: Beratan, Howard R.
• Primary Examiner(s): VO, PETER DUNG BA
• Application Number:
  US08/485,957
• Time in Patent Office: 1,056 Days
• Field of Search: 29/25.35, 29/595, 29/832, 29/840, 29/846, 29/847, 216/62, 228/180.1, 228/180.21, 228/180.22, 250/338.1, 250/338.2, 250/338.3, 250/338.4, 250/332, 348/165, 427/100, 427/126.3, 430/313, 430/314, 430/327, 430/329, 430/330, 430/349
• US Class Current: 29/840
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20
• CPC Class Codes: H10N 15/10 Thermoelectric devices using thermal change of the dielectric constant, e.g. working above and below the Curie point
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/4913 Assembling to base an electrical component, e.g., capacitor, etc.
• CPC Class Codes: Y10T 29/49144 by metal fusion
• CPC Class Codes: Y10T 29/49156 with selective destruction of conductive paths

Abstract

A hybrid thermal imaging system (20, 120) often includes a focal plane array (30, 130), a thermal isolation structure (50, 150) and an integrated circuit substrate (60, 160). The focal plane array (30, 130) includes thermal sensitive elements (42, 142) formed from a pyroelectric film layer (82), such as barium strontium titanate (BST). One side of the thermal sensitive elements (42, 142) may be coupled to a contact pad (62, 162) disposed on the integrated circuit substrate (60, 160) through a mesa strip conductor (56, 150) of the thermal isolation structure (50, 150). The other side of the thermal sensitive elements (42, 142) may be coupled to an electrode (36, 136). The various components of the focal plane array (30, 130) may be fabricated from multiple heterogeneous layers (74, 34, 36, 82, 84) formed on a carrier substrate (70).

Claims

1. A method of fabricating a focal plane array having a plurality of thermal sensors for use with a hybrid thermal imaging system comprising the steps of:

forming a layer of optical coating on a carrier substrate;

depositing a first layer of electrically conducting material on the optical coating layer;

forming a film layer of pyroelectric material on the first layer of electrically conductive material by mixing particles with liquid pyroelectric material to provide nucleation sites for growing the film layer, wherein the pyroelectric material is selected from the group consisting of lead titanate, lead lanthanum titanate, lead zirconate titanate, lead strontium titanate, lead scandium tantalate, barium strontium titanate, and lead lanthanum zirconate titanate;

forming a second layer of electrically conducting material on the pyroelectric film layer opposite from the first layer of electrically conducting material; and

patterning the pyroelectric film layer to correspond with the desired location and configuration of the associated thermal sensors.

2. The method of claim 1 wherein the step of forming the pyroelectric film layer further comprises the steps of:

using metal organic deposition and spin coating techniques to deposit liquid pyroelectric material on the first layer of electrically conductive material;

mixing particles of a selected material with the liquid pyroelectric material to provide nucleation sites for grain growth of the pyroelectric material; and

spinning the mixture of liquid and nucleation sites onto the carrier substrate to form the pyroelectric film layer.

3. The method of claim 1 further comprising the steps of:

forming a separation layer of calcium oxide on the carrier substrate;

forming the layer of optical coating from material sensitive to infrared radiation on the separation layer;

forming a first layer of platinum on the optical coating layer;

forming a film layer of barium strontium titanate on the first layer of platinum; and

forming a second layer of platinum on the barium strontium titanate layer opposite from the first layer of platinum.

4. The method of claim 1 wherein the carrier substrate comprises ceramic alumina.

5. The method of claim 1 wherein forming the film layer of pyroelectric material further comprises the step of spin coating a liquid solution of barium strontium titanate having small granules of barium strontium titanate to provide nucleation sites to form the film layer.

6. A method of fabricating a hybrid thermal imaging system having a focal plane array with a plurality of thermal sensors mounted on a thermal isolation structure projecting from an integrated circuit substrate, comprising the steps of:

forming a separation layer of refractory material on a carrier substrate;

forming a layer of optical coating material on the separation layer;

forming a first layer of electrically conductive material on the optical coating layer;

forming a film layer of pyroelectric material on the optical coating layer from a solution of liquid pyroelectric material and powder nucleation sites by sol/gel and spin coating;

forming a second layer of electrically conductive material on the pyroelectric film layer opposite from the first layer of electrically conductive material; and

patterning the pyroelectric film layer and the second layer of electrically conductive material to correspond with the desired location and configuration of the respective thermal sensors.

7. The method of fabricating a hybrid thermal imaging system as defined in claim 6 wherein the step of forming the film layer of pyroelectric material further comprises placing a liquid solution of the pyroelectrical material having small granules between approximately 0.5 micron and 2.0 microns in diameter on the first layer of electrically conductive material.

8. The method of fabricating a thermal imaging system as defined in claim 6 further comprising the steps of:

removing portions of the second layer of electrically conductive material to form sensor signal electrodes for each of the respective thermal sensors;

reticulating the pyroelectric film layer to form the desired pattern of thermal sensors; and

separating the focal plane array from the carrier substrate.

9. The method of fabricating a thermal imaging system as defined in claim 6 further comprising the steps of:

forming a layer of bump bonding material on the second layer of electrically conductive material;

removing portions of the bump bonding layer and the second layer of electrically conductive material to form sensor signal electrodes with bump bonding material disposed thereon for each of the respective thermal sensors;

reticulating the pyroelectric film layer to form the desired pattern of thermal sensors; and

bonding the focal plane array with the thermal isolation structure projecting from the integrated circuit substrate using the bump bonding material on the sensor signal electrodes.

10. The method of fabricating a thermal imaging system as defined in claim 6 wherein the first layer and the second layer of electrically conductive material are selected from the group consisting of platinum, nickel chrome, ruthenium oxide and lanthanum strontium cobalt oxide.

11. The method of fabricating a thermal imaging system as defined in claim 6 further comprising the steps of:

forming the separation layer from calcium oxide;

forming the first layer of electrically conductive material and the second layer of electrically conductive material from paltinum;

removing portions of the second platinum layer to form sensor signal electrodes for each of the respective thermal sensors;

reticulating the film layer of pyroelectric material to form the desired pattern of thermal sensors; and

separating the focal plane array from the carrier substrate.

12. The method of fabricating a thermal imaging system as defined in claim 6 further comprising the step of:

forming the separation layer from silicon dioxide;

removing portions of the second layer of electrically conductive material to form sensor signal electrodes for each of the respective thermal sensors;

reticulating the film layer of pyroelectric material to form the desired pattern of thermal sensors;

mounting the focal plane array on the thermal isolation structure projecting from the integrated circuit substrate; and

separating the focal plane array from the carrier substrate.

13. A method of fabricating an array of thermal sensitive elements for use with a hybrid thermal imaging system, the method comprising the steps of:

forming a film layer of pyroelectric material on a carrier substrate by mixing particles with liquid pyroelectric material to provide nucleation sites for growing the film layer;

annealing the film layer at a temperature between 300 and 800 degrees C.; and

patterning the pyroelectric film layer to form thermal sensitive elements.

14. A method of fabricating an array of thermal sensitive elements for use with a hybrid thermal imaging system, the method comprising the steps of:

forming a film layer of pyroelectric material on a carrier substrate from a solution of liquid pyroelectric material and powder nucleation sites;

annealing the film layer at a temperature between 300° and

800°

C.; and

patterning the pyroelectric film layer to form thermal sensitive elements.

15. The method of claim 14, wherein the patterning step occurs before the annealing step.

16. The method of claim 14, further comprising at least one heat treatment step before the annealing step;

wherein the temperature of the heat treatment step is between 50 degrees C. and 500 degrees C.