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.