A novel substrate-free uncooled IR detector based on an optical-readable method is presented and fabricated successfully. The detector is composed of a bi-material (BM) cantilever array, without a silicon substrate, which is eliminated in the fabrication process. Compared with the generally used sacrificial layer cantilever, the loss of incident IR energy caused by the reflection from and absorption by the silicon substrate is eliminated completely in the substrate-free structure. The IR radiation reaching the IR detector surface increases by over 80% in the case of the novel substrate-free detector array structure, compared to the sacrificial layer structure. Moreover, the substrate-free structure has less heat loss than the sacrificial layer structure. The results of thermal imaging of the human body show the detector is able to sense objects at room temperature. The experimental NETD was estimated to be 200 mK.
An optical readout platform using a knife-edge filter for detecting the bending of a bimaterial microcantilever array is established, and the influence of stress-induced micromirror deformation on the optical detection sensitivity is discussed. The influence of deformation is modeled theoretically and validated experimentally. Analysis shows that the optical detection sensitivity will decrease by 50% when the mirror has a deformation of lambda/5 (lambda is the wavelength of readout light). Finally, an infrared image is obtained by the platform.
An optical readout uncooled infrared (IR) imaging detector of bimaterial cantilever array using knife-edge filter operation (KEFO) is demonstrated. The angle change of each cantilever in a focal plane array (FPA) can be simultaneously detected with a resolution of 10 -5 degree. A deformation magnifying substrate-free micro-cantilever unit with multi-fold interval metallized legs is specially designed and modeled. A FPA with 160×160 pixels is fabricated and thermal images with noise equivalent temperature difference (NETD) of 400 mK are obtained by this imaging detector.CCL Numbers: TP206+.1 Document code: A Article ID: 1673-1905(2007)02-0119-04
DOICompared with cooled photon detectors, uncooled IR imaging detectors are playing a more significant role in many applications due to their improved performance and reduced cost. They operate on a simple principle that any temperature change in each pixel will be either electrically measured by detecting the change of resistance or capacitance [1] , or optically measured by detecting deflections of bimaterial cantilevers [2], [4] . Much attention has been attracted on optical readout uncooled IR detectors since they don't require any micro readout circuit connected to each pixel, which brings the following merits: (i) higher temperature rise of each pixel owing to better thermal isolation; (ii) eliminating the heat noise caused by readout current through the IR detector; (iii) reducing the fabrication complexity of FPA, which may reduce the cost of optical readout uncooled IR detectors for commercial applications. Using a single cantilever for temperature and radiation sensing has been demonstrated by several groups [5],[7] . Although the deflection of a single cantilever has been measured with sub-angstrom resolution using optical beam steering [8] , such far-field technique is susceptible to cross talk when applied to cantilever array. Sequential position readout from a micro-cantilever array by switching on/off prearranged micromode fibers connected to a sensor solves the problem of cross talk of optical readout [9] , but it is not suitable for large imaging array. Majumdar's group developed a few optical readout methods, and fabricated special FPA to obtain thermal images. A pin-hole array was mounted on the FPA to eliminate cross talk and thermal images at 250 were obtained [3] . Since the resolution of this method is limited by a short optical-lever, they tried diffraction grating filtering and optical interferometry methods to obtain higher resolution of detecting vertical displacement, and they got thermal images of objects at room temperature [4] . In the method of diffraction grating filtering, to get a thermal deformation map of the cantilever array, the change of the spectrum intensity of the first diffraction order of grating is measured, which changes with the relative vertical displacement of the deformable grating of cantilever unit. In this case, the grating limits the unit size and the utilization of the readout light is poor since only the first diffr...
The uncooled IR thermal imaging technology with its wide applications in military, medical and industrial areas has been an active topic in international research. Thermal imaging based on optical readout bi-material microcantilever array is a new concept in methodology. In this paper, a new kind of bi-material micro-cantilever unit with multi-fold legs and interval gild structure is designed and its thermal and thermo-mechanical performance are analylized. A 100×100 microcantilever array is fabricated as a FPA (focal plane array), and by using this FPA, a thermal image of a room-temperature body (human body) is successfully detected. The NETD (noise-equivalent temperature difference) is about 200mK.The experimental results are well accordant with the thermal analysis of the microcantilever unit.
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