Fabrication and characterization of integrated uncooled infrared sensor arrays using a-Si thin-film transistors as active elements

In this paper, we report on the first realization and characterization of monolithic uncooled 8×8 infrared sensor arrays, based on amorphous silicon thin-film transistors (a-Si TFT). The a-Si TFT is employed as the active element of the sensor, because it possesses a high temperature coefficient of its drain current of 1.5%-6.5% K^-1 at room temperature. The improved porous silicon micromachining techniques described here enable the integration of the a-Si TFT-based sensor array with the MOS readout circuitry. The sacrificial material of porous silicon is prepared in the first step. It is then well protected all the time during the fabrication of MOSFETs and sensors before being released. Optical tests are performed to characterize the sensor. The influences of the gate voltage of a-Si TFT (V_g) and the voltage source of the circuitry (V_dd) on the sensor performance are investigated. The measurement indicates that the sensor has a maximum detectivity of 8.67×10⁸ cm Hz¹2/W^-1 at V_g=-15 V, V_dd=-12 V and a chopping frequency of 30 Hz. The noise equivalent power (NEP) of the sensor is less than 10^-10 W Hz^-12/, and the noise equivalent temperature difference (NETD) is as low as 67 mK at room temperature, which compares well with the recent results of some uncooled IR sensors developed by other groups. Primary imaging tests indicate that the 8×8 sensor array has potential for high performance imaging applications.