A medium wave (MW) 640×512 (25 μm) Mercury Cadmium Telluride (HgCdTe) polarimetric focal plane array (FPA) was demonstrated. The micro-polarizer arrays (MPA) has been carefully designed in terms of line grating structure optimization and crosstalk suppression. An on-chip micro-nano fabrication process with low damage was explored, which was verified to be compatible well with HgCdTe devices. After monolithic integration of MPA, NETD < 9.5 mK was still maintained. Furthermore, to figure out the underlying mechanism that dominates extinction ratio (ER), specialized MPA layouts were designed, and the crosstalk was experimentally validated as the major source that impacts ER. By expanding opaque regions at pixel edges to 4 μm, crosstalk rates from adjacent pixels can be effectively reduced to approximately 2%, and promising ERs ranging from 17.32 to 27.41 were implemented.