1. Micromachined Infrared Sensor Arrays on Flexible Polyimide Substrates
Aamer Mahmood, Shadi Dayeh, Donald P. Butler, and Zeynep Çelik-Butler
Dept. of Electrical Engineering,
University of Texas at Arlington
Arlington, TX USA

2. Outline
Why flexible substrates.
Microbolometers on flexible substrates.
Fabrication
Results
Conclusions.

3. Advantages of Flexible Substrates
Conform to underlying object.
Batch fabrication potential for low cost.
Enable applications on complex geometries.
Multilayer construction.
Integrated electronics in the future (TFTs).
Large area electronics, reel-to-reel processing.
TFT’s, OLE Displays, flexible keyboards, etc. have been demonstrated.

4. 1x10 array made of 60x60 mm2 microbolometers
Some Examples of Flexible Microsensors
Si islands containing micromachined pressure sensors and circuitry joined by a polyimide membrane: Y. Xu, Y.-C. Tai, A. Huang, and C.-M. Ho, “IC-Integrated flexible shear-stress sensor skin”, Solid State Sensor, Actuator and Microsystems Workshop, Hilton Head Island, South Carolina, June 2-6, 2002.
Bolometers Directly on Kapton and Spin-on Polyimide
1x10 array made of 60x60 mm2 microbolometers
Responsivity V/W
Detectivity cmHz1/2/W
A. Yaradanakul, Z. Celik-Butler, and D.P. Butler, IEEE Trans. on Electron Devices 49, 930 (2002).

5. Microbolometer Fabrication Trench Geometry
YBCO Au Ti Ti
Si3N4
PI2610 Al
SrTiO3
Si3N4
PI5878 Si

6. Microbolometer Fabrication Mesa Geometry
60x60 μm 2 after ashing sacrificial layer
40x40 μm 2 after ashing
sacrificial layer
YBCO
PI2737 Au Ti Al
SrTiO3
Si3N4
PI5878 Si

7. Micromachined Infrared Microsensors on a Flexible Substrate
A picture showing a part of our flexible skin and its silicon carrier. The flexible skin contains 384 infrared microsensors.
A picture showing a two die flexible skin applied to the little finger.

8. SEM Micrographs of 40x40 μm2 Microbolometers
1x10 array of infrared microbolometers (40x40 mm2)
3 micromachined
infrared microbolometers (40x40 mm2)
Coated with 40-nm-thick Au to eliminated charging

9. I-V Characteristics
DD7,10 (Mesa Geometry)

10. Temperature Coefficient of Resistance (TCR)
1b4 Trench Geometry W

11. Responsivity/Detectivity
1b4 (Trench Geometry)

12. Responsivity/Detectivity
DD15 (Mesa Geometry)

13. Area scans of bolometers Device 1b4 (Trench Geometry)

14. Area scans of bolometers Device DD15 (Mesa Geometry)

15. Future Work
Encapsulate microbolometers in a vacuum cavity on the no strain plane with polyimide superstrate.
Integrate flow sensors and pressure/strain sensors to form a “sensitive skin”.

16. Conclusions Acknowledgement
Can fabricate micromachined infrared sensors on flexible polyimide substrates with performance similar to those fabricated directly on rigid Si substrates.
Can bend flexible substrate containing microbolometers over a 1.5 mm radius of curvature without any apparent damage.
Successful fabrication requires an emphasis on low temperature processing.
Future work involves vacuum packaging the microbolometers with a superstrate.
Acknowledgement
This work is based in part upon work supported by the NSF under grant ECS