13 February 2016 Stray light suppression in InGaAs/GaAsSb type-II FPA
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Stray light in focal plane array (FPA) deteriorates the accuracy of hyper spectral imaging. Multiple reflections between FPA window and peripheral region of a sensor chip are considered to be the major sources of stray light. One idea for suppressing the stray light is to shield the incident light on the peripheral region of the sensor chip by narrowing the FPA window. However, it is limited by the tolerance of assembly. In this study we have examined an epoxy coating on the peripheral region such as ROIC contact pad area, AlN substrate and bonding wire. Sensor chip with InGaAs/GaAsSb type-II quantum well structures, which has the cut-off wavelength of 2.35 μm, 320×256 pixels were bonded to ROIC through indium bumps, assembled to AlN substrate and to a four stage TEC. To avoid the degradation by the stress to the chip and bonding wire, low elastic modulus epoxy was selected. Stray light suppression was confirmed by the sensor signal output of epoxy coated samples, 3% contrast improvement was achieved. Further, reliability test of 10,000 heat cycles between -75°C and 25°C was carried out. No degradations were found in sensor characteristics of the epoxy coated sample. These results suggest that the epoxy coating in SWIR FPA is effective in suppressing the stray light and suitable for hyper spectral imaging.
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Sundararajan Balasekaran, Sundararajan Balasekaran, Masaki Migita, Masaki Migita, Takahiko Kawahara, Takahiko Kawahara, Ken-ichi Machinaga, Ken-ichi Machinaga, Kouhei Miura, Kouhei Miura, Hiroshi Inada, Hiroshi Inada, Yasuhiro Iguchi, Yasuhiro Iguchi, Tsukuru Katsuyama, Tsukuru Katsuyama, } "Stray light suppression in InGaAs/GaAsSb type-II FPA", Proc. SPIE 9755, Quantum Sensing and Nano Electronics and Photonics XIII, 97551Z (13 February 2016); doi: 10.1117/12.2213971; https://doi.org/10.1117/12.2213971

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