An uncooled infrared (IR) camera that is based on thermomechanical sensing and visible optical readout has been developed. The system contains a focal plane array (FPA) consisting of bimaterial cantilever beams made of silicon nitride (SiNx) and gold (Au) in each pixel. Absorption of incident IR radiation in the 8-14 μm wavelength range by SiNx in each cantilever beam raises its temperature, resulting in proportional deflection due to mismatch in thermal expansion of the two cantilever materials. To maximize the thermal performance, the conductance of each pixel was reduced to about five times of the radiation conductance. Based on thermomechanical analysis, the geometrical shape of the pixels were designed to maximize the cantilever sensitivity within the constraints of the pixel size and layout. Microfabrication of stress-balanced bimaterial cantilevers was achieved by varying the silicon concentration along the thickness of the SiNx films in order to balance the residual tensile stress in the Au film and the Cr adhesion layer between Au and SiNx. The optical design of each pixel was based on IR properties of the cantilever materials, IR absorption enhancement due to resonance cavity formation, as well as visible optics of deformable diffraction gratings. The latter formed the foundation for two different optical readout techniques that were both used for IR imaging. The results suggest that objects at temperatures as low as 30'C can be imaged with the best noise-equivalent temperature difference (NETD) in the range of 2-5 K. It is estimated that further improvements that are currently being pursued can improve NETD to about 10 mK.
|Title of host publication
|Micro-Electro-Mechanical Systems (MEMS)
|American Society of Mechanical Engineers (ASME)
|Number of pages
|Published - 1999
|ASME 1999 International Mechanical Engineering Congress and Exposition, IMECE 1999 - Nashville, United States
Duration: 1999 Nov 14 → 1999 Nov 19
|ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE)
|ASME 1999 International Mechanical Engineering Congress and Exposition, IMECE 1999
|99/11/14 → 99/11/19
Bibliographical noteFunding Information:
The devices were made in the Microlab, U.C. Berkeley. We are thankful for the support we received from the DARPA MEMS program under contract N66001-97-C-8621, as well as from our program monitors Drs. Elias Towe, Cindy Hanson, and Randy Shimabukuro. M. Ray and R. Anderson from SBRC must be acknowledged for their contributions in some of the microfabrication. Our thanks also to An Huynh of Virginia Tech, who helped in the diffraction calculations.
© 1999 American Society of Mechanical Engineers (ASME). All rights reserved.
ASJC Scopus subject areas
- Mechanical Engineering