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Abstract
A microbolometer structure including carbon nanotubes, a substrate (silicon, alumina, etc.) with an array of micromachined wells/holes/pockets, a weak thermal link (membrane or legs) at the base of each well/hole/pocket, a protection layer bonded to substrate over the wells for subsequent back side processing such that the carbon nanotubes are protected from contact/liquids, a thermistor (vanadium oxide, amorphous silicon, metal film, photonic sensor, etc.) array, a heater (metal film) array and methods for making the same.
patent description
The proposed invention is a microbolometer array utilizing vertically aligned carbon nanotubes
(V ACNTs) as broadband absorbing elements inside wells micromachined into a substrate. Membranes at the base of each well support the VACNTs and act as a weak thermal link. The VACNTs are grown to a height less than the depth of the well, allowing for a protection layer to be placed over·the well openings without contacting the delicate VACNT structure. This protection layer (polymer film, electrostatically bonded wafer, glued wafer) allows subsequent processing (photolithography, solvent cleans, metal deposition) not typically possible with exposed VACNTs due to their delicate nature. Backside arrays of thermistors and electrical substitution heaters (a single set per pixel) can be lithographically defined (using lift-off or etching). A readout integrated circuit (ROIC) can then be bump bonded to wiring associated with the thermistor and heater array.
Using VACNTs as broadband absorbers in micromachined wells allows for post-processing of the microbolometer after VACNT deposition or growth. VACNT growth is a high temperature process which is deleterious to thermistor technology (vanadium oxide, amorphous silicon) currently used in microbolometers. Use of wells and a protection layer allow for the use of state of the art thermistor technology not previously compatible with VACNT growth. In addition, electrical substitution calibration, typically used and proven in metrology standards, will see benefit in a commercial microbolometer.
Features
The proposed invention describes a method to manufacture a bolometer using VACNTs as a broadband low reflectance (approximately< 0.1% reflectance) absorbing element. A carbon nanotube microbolometer using VACNTs would be effective at SWIR, MWIR, and LWIR unlike current microbolometers which are spectrally limited due to the use of a'JJ4 cavity formed by an absorber above a reflector. In addition, electrical substitution at the pixel level will provide for internal calibration of the microbolometer array. Current microbolometers without electrical substitution require an external black body calibration target increasing overall system complexity.