Dark current is a critical index for Hg1-xCdxTe IRFPA(Infrared focal plane array) detectors, which is main limit for the application in the very long wave(≥12μm) spectral range. In this paper we reduced the dark current by using small pixel effective areas. And by fabricating in-situ integrated microlens on the illumination side of the detector, the disadvantage of the small pixel effective areas has been overcome.
Indium bumps are widely employed in high density interconnection between infrared focal plane arrays and Si read out integrated circuits by flip-chip bonding. Indium bump array formation is a critical step in the flip-chip fabrication process. Taller and higher uniformity indium bumps are necessary for high pixel density and low noise photodetectors. In this work, a new process of indium bumping through evaporation and ion etching was developed to produce ultrafine pitch indium bumps for assembly of large-area HgCdTe photodetector. Electron microscopy was used to analyze and evaluate the microstructure, height and uniformity of indium bumps. The results showed 7 μm height indium bumps with 10 μm pitch were easily achieved. The bump height and uniformity were significantly improved with our new developed indium bump fabrication method.
At present, HgCdTe arrays has been commonly used in photodetectors for infrared detection in space system, where they are exposed to the space radiation environment. For high radiation-tolerance and the optimum performance of the detector, surface-passivation technology that provides long-term stability is required. Double layer of ZnS/CdTe passivant is most recommendable, because ZnS/CdTe-passivated HgCdTe detectors could show great insulating and radiation-tolerant properties. However, the thickness ratio of ZnS and CdTe layers has not been optimized. In this study, the gamma radiation effects on ZnS/CdTe-passivated mid-wavelength HgCdTe arrays with different ZnS-layer thicknesses were investigated, by analyzing the current-voltage curves before and after gamma irradiation at a very low rate. To our surprise, increase of ZnS thickness from 300 nm to 700 nm dramatically improved the radiation tolerance, although ZnS is considered to be vulnerable to gamma irradiation. We hypothesized that gamma radiation could be strongly absorbed by ZnS with sufficient thickness and the transmitted intensity is harmless to the HgCdTe arrays. Therefore, increase of ZnS thickness could protect the HgCdTe arrays from gamma radiation damage. Here, we presented an efficient and easy processing method to increase radiation-tolerant properties of the high performance HgCdTe photodetectors.
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