Development of a novel radially-distributed spiral bilayer thermopile infrared sensor with enhanced responsivity

Current trend of pursuing higher resolution in uncooled cost-effective infrared imagers demands thermopile sensing units with higher responsivity. Conventional designs often have limitations such as non-uniform temperature distribution among individual thermocouple legs or complex fabrication process, which limit further responsivity improvement. Here, a novel thermopile featuring a radially-distributed spiral structure with bilayer P-poly/Al thermocouples is proposed. The radially distributed legs along with the circular membrane effectively improve the temperature uniformity among individual thermocouples. Meanwhile, the spiral bilayer configuration decreases thermal conductance and increases the thermocouple number simultaneously, resulting in a significant enhancement of the responsivity. The spiral parameter was designed and optimized, and the fabricated sensors were characterized and compared with conventional non-spiral thermopiles. Experimental results demonstrate a responsivity of 52.53 V/W and a specific detectivity of 9.76 × 10⁷cm·Hz^1/2·W^-1 for the proposed sensor, representing a 39.35% and 17.81% enhancement over the 37.70 V/W and 8.29 × 10⁷cm·Hz^1/2·W^-1 achieved by the non-spiral counterpart. With its high responsivity and CMOS-compatible fabrication, the proposed thermopile offers a cost-effective solution for next-generation, high-resolution infrared imagers.