Monolithic thermal detector with pyroelectric film and method

• US 5,602,043 A
• Filed: 01/03/1995
• Issued: 02/11/1997
• Est. Priority Date: 01/03/1995
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Hanson, Charles M., Beratan, Howard R.
• Primary Examiner(s): Thomas, Tom
• Assistant Examiner(s): MULPURI, SAVITRI
• Application Number:
  US08/368,067
• Time in Patent Office: 770 Days
• Field of Search: 437/2, 437/3, 437/4, 437/247, 437/902, 148/DIG. 3, 148/DIG. 80, 156/655.1, 156/643.1, 156/651.1, 250/370.08, 250/338.3, 250/338.4, 250/330, 250/332, 257/467, 257/470
• US Class Current: 438/54
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors
• CPC Class Codes: H01L 27/1465 of the hybrid type
• CPC Class Codes: H10N 15/10 Thermoelectric devices using thermal change of the dielectric constant, e.g. working above and below the Curie point

Abstract

One or more thin film layers of material may be formed on an integrated circuit substrate and anisotropically etched to produce a monolithic thermal detector. A first layer of material may be placed on the integrated circuit substrate and anisotropically etched to form a plurality of supporting structures for the thermal sensors of the associated focal plane array. The thermal sensors of the focal plane array may be provided by anisotropically etching one or more thin film layers of material formed on the supporting structures. In an exemplary thermal detector, one of the thin film layers preferably includes pyroelectric material such as barium strontium titanate. A layer of thermal insulating material may be disposed between the integrated circuit substrate and the pyroelectric film layer to allow annealing of the pyroelectric film layer without causing damage to the associated integrated circuit substrate. In addition to the layer of insulating material, a heat sink may be disposed on the integrated circuit substrate opposite from the pyroelectric film layer to protect the integrated circuit substrate while annealing the pyroelectric film layer. Alternatively, a thermal isolation structure may be formed between the pyroelectric film layer and its associated supporting structures to allow annealing of the pyroelectric film layer without substantial heating of the underlying circuit substrate.

Claims

1. A method for fabricating a monolithic thermal detector having a focal plane array of thermal sensors disposed on an integrated circuit substrate comprising the steps of:

forming a first layer of electrically conductive material on one surface of the integrated circuit substrate;

anisotropically etching the first layer of electrically conductive material to form supporting structures for respective thermal sensors;

forming a second layer of thermal insulating material on the one surface of the integrated circuit substrate with the supporting structures disposed therein;

forming a third layer of electrically conductive material on the supporting structures and the layer of insulating material;

forming a thin film layer of thermal sensitive material on the third layer of electrically conductive material;

forming a fourth layer of electrically conductive material on the thin film layer;

etching the layer of thermal insulating material, the third and fourth layers of electrically conductive material and the thin film layer of thermal sensitive material to form the plurality of thermal sensors which comprise the focal plane array disposed on the integrated circuit substrate; and

applying heat to one side of the thin film layer of thermal sensitive material with the layer of thermal insulating material disposed between the one surface of the integrated circuit substrate and the thin film layer of thermal sensitive material to anneal the thin film layer.

2. The method of claim 1, wherein the second layer of thermal insulating material is formed from polyimide.

3. The method of claim 1, wherein the thin film layer is formed from material selected from the group consisting of barium strontium titanate, barium titanate, antimony sulfoiodide, vanadium oxide, lead titanate, lead lanthanum titanate, lead zirconate titanate, lead lanthanum zirconate titanate and amorphous silicon.

4. The method of claim 1, wherein the step of anisotropically etching is performed using an oxygen-based reactive ion etch.

5. The method of claim 1, wherein the step of forming the supporting structure is performed using a photolithographic process.

6. The method of claim 1, further comprising the step of placing a heat sink on the integrated circuit substrate opposite from the one surface of the integrated circuit substrate.

13. The method of claim 1, wherein the thin film layer is pyroelectric.

14. The method of claim 1, further comprising the step of:

removing the layer of thermal insulating material to form cavities between said integrated circuit substrate and each of said thermal sensors.

7. A method for fabricating a monolithic thermal detector having a focal plane array of thermal sensors disposed on one surface of an integrated substrate with an array of contact pads for respectively receiving signals from the thermal sensors, comprising the steps of:

forming a first layer of electrically conductive material on the one surface of the integrated circuit substrate;

anisotropically etching the first layer of electrically conductive material to form supporting structures for the respective thermal sensors with at least one of the supporting structures disposed adjacent to the contact pad for the respective thermal sensor;

forming a second layer of insulating material on the one surface of the integrated circuit substrate with the supporting structures disposed therein;

forming third layer of electrically conductive material on the supporting structures and the layer of insulating material;

forming a thin film layer of pyroelectric material on the third layer of electrically conductive material;

forming a fourth layer of electrically conductive material on the thin film layer;

etching the layer of insulating material, the third and fourth layers of electrically conductive material and the thin film layer of pyroelectric material to form the thermal sensors which comprise the focal plane array disposed on the integrated circuit substrate; and

annealing the thin film layer of pyroelectric material.

8. The method of claim 7, further comprising the steps of:

etching the thin film layer of pyroelectric material to form respective thermal isolation structures between the thermal sensors and their associated supporting structures; and

annealing the thin film layer of pyroelectric material after the thermal isolation structures have been formed.

9. The method of claim 7 wherein the second layer of insulating material is formed from silicon dioxide.

10. The method of claim 7, further comprising the steps of:

patterning the film layers formed on the supporting structures and the layer of insulating material to correspond with the desired thermal sensors; and

anisotropically etching the film layers and the layer of insulating material to form the thermal sensors which comprise the focal plane array disposed on the integrated circuit substrate.

11. The method of claim 7, wherein the insulating material is polyimide.

12. The method of claim 7, wherein the step of anisotropically etching is performed using an magnetically enhanced reactive ion etch.

15. The method of claim 7, further comprising the step of:

removing the layer of insulating material to form cavities between said integrated circuit substrate and each of said thermal sensors.