Low thermal mass long wave infrared metasurface absorber for small pixel microbolometer with fast response

We demonstrate a low thermal mass long wave infrared broadband metasurface absorber employed for a double-layer umbrella 8 mu m small pixel pitch microbolometer, which is achieved by depositing an array of metal patches on the thin dielectric slab and forming an optical resonator with a metal back-reflector. The absorber achieves near-unity optical absorptivity within the long wave infrared regime (8-14 mu m) due to its optical impedance exhbits a good matching characteristic with the free space impedance of 377 Omega, while reducing significantly the thermal mass and obtaining the time constant of 10.96 ms. Consequently, the thermal response speed of the microbolometer is increased by nearly 50% compared with the multilayer absorbing film. Furthermore, maximum thermal mass reduction of the device is performed, finding the optimal perforated diameter 0.75 mu m with the thickness of SiNx film 65nm, which reduces the absorbing area by 28.8%, lower the time constant to 9.7ms and further improve the response speed of the detector, while maintaining the average LWIR absorption as high as 96%.