31 May 2012 Study on optimizing the thickness of silicon window of WLP for IR sensor
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Abstract
Silicon is a promising material as an IR(Infrared Ray) transparent window platform for packaging MEMS( microelectro mechanical systems), especially, IR sensors with WLP(wafer level package), because silicon has advantages in price and CMOS process compatibility compared to Ge, although Ge exhibits higher IR transmittance than Si. This paper reports on optimizing the thickness of Si window in the range of 8 ~ 12 um, LW-IR(Long wave IR). Two of important things which have to be considered in window material of IR sensor are minimizing absorption of IR(maximizing transmittance) and minimizing deformation due to the pressure differences between outside and inside of the package. Because of trade-off between minimizing IR absorption and minimizing mechanical deformation, optimization of thickness is important. Infrared absorbance of silicon was measured as varying thickness from 100 um to 700 um of the Si window. Decreasing the thickness of silicon made the absorption smaller. Under 300 um, the difference of absorbance with decreasing thickness becomes negligible. Degree of deformation according to the thickness of the Si window was calculated by simulation varying pressure differences, and package area. Based on this analysis, we suggest the optimized thickness of silicon window for WLP of LW-IR sensor.
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Myeongho Song, Tae Hyun Kim, Moon Seop Hyun, Jae Hong Park, Hee Yeoun Kim, Gawon Lee, "Study on optimizing the thickness of silicon window of WLP for IR sensor", Proc. SPIE 8353, Infrared Technology and Applications XXXVIII, 83532B (31 May 2012); doi: 10.1117/12.918982; https://doi.org/10.1117/12.918982
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