MEMS AlN pyroelectric infrared sensor with medium to long wave IR absorber

Abstract

Polycrystalline Aluminum Nitride (AlN) thin films are of significant interest due to their pyroelectric properties for last few years. In this paper, study on development of a polycrystalline AlN thin film based bulk micromachned pyroelectric IR sensor is presented. Structural optimization of IR sensor has been carried out using 3D finite element modeling (FEM) and simulations. A 1.0 μm thick thermally grown SiO2 layer used for thermal isolation, also serves as a diaphragm to hold the fabricated IR sensor. Rate of temperature change (dT/dt) of the sensor under dynamic heating is 0.12–0.15°K/s, and agrees well with the simulated value of 0.1°K/s. High pressure, N2 ambient sputtered Au film of thickness 160 nm has been used to enhance the IR absorptivity. IR absorptivity of sensor on medium to long wave (2.5–25 μm) radiations is nearly 67%, and creates thermal gradient of 0.23°K between sensor and substrate. Developed pyroelectric IR sensor exhibits response time 8.0 ms, pyroelectric coefficient (ρ) 0.32 × 10−4 C/m2K, ρ/ε figure of merit (FOM) 3.0 μC/m2K, and pyroelectric current responsivity (Ri) of 2.5 × 10-6 A/W.