Optical readout uncooled infrared imaging detector using knife-edge filter operation

Abstract

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...

Room temperature detector array technology for the terahertz to far-infrared.

“…The metamaterial enhanced cantilever detectors demonstrated in this effort are naturally fabricated in array form and are suitable for real-time 2D imaging by simultaneously measuring the deflection of all of the pixels using, for example, a visible CCD/CMOS camera to obtain an intensity map for parallel pixel readout [20][21] . Furthermore, it is possible to combine multiple SRRs with different resonant frequencies into a super pixel, thus enabling frequency-sensitive THz imaging/spectroscopy with a "multicolor" THz illumination source.…”

Bi-material terahertz sensors using metamaterial structures

“…The SiO x and top Al layers can be used for making the bi-material legs, simplifying the fabrication process. Additionally, the Al ground plane is an efficient mirror for optical readout of deformation of pixel under THz absorption [8,17,18]. The square metamaterial geometry is particularly attractive since the difference in Al coverage on both surfaces of the central absorber is less than 20%.…”

“…Although the fabricated sensor arrays do not have high spatial resolution, their imaging capabilities were probed by a CCD camera with coaxial illumination as schematically illustrated in Fig. 12(a) [17,18]. A real time video recording of the QCL beam, gated at 500 mHz, is shown in Fig.…”

“…The bimaterial legs undergo bimetallic deformation [13] due to the temperature rise upon absorption of incident radiation. The deformation can be probed by different approaches such as piezoresistive [14], capacitive [15,16] and optical readouts [8,12,17,18]. The latter requires a reflective surface, normally embedded into the absorber, and has the advantage of avoiding the complex on-chip integrated microelectronics necessary for other approaches.…”

Microelectromechanical systems bimaterial terahertz sensor with integrated metamaterial absorber

“…Although both approaches share the same detection principle, bimaterial sensors appear to be more attractive as a research platform due to the possibility of utilizing external optical readouts [5,6], eliminating the requirement of monolithic integration of readout electronics [7]. To achieve high sensitivity in the THz spectral range, it is necessary to design pixels featuring high THz absorbing materials and to optimize their size for the desired spatial resolution.…”