Integrated a-Si:B Microbolometer Arrays Based on Improved Porous Silicon Micromachining Techniques

A monolithic uncooled 8×8 microbolometer array with boron-doped a-Si (a-Si:B) thermistors as active elements is presented. The a-Si:B film was deposited by plasma enhanced chemical vapour deposition. To decrease the thermal conductance of the microbolometer, a-Si:B thermistor was formed on a four-leg suspended microbridge. The improved porous silicon micromachining techniques described here enable the integration of the sensor array with the metal--oxide--semiconductor 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 metal--oxide--semiconductor field effect transistors and microbolometers before being released. Measurements and calculations show that the uncorrected uniformity of the 8×8 microbolometer array is about 4.5%, and the detectivity of 2.17×10⁸cm Hz^1/2W^-1 is achieved at a chopping frequency of 30Hz and a bias voltage of 5V with a thermal response time of 12.4ms.