Study On The Material, Design, Fabrication And Measurement Of An Amorphous Silicon Microbolometer

The technology of uncooled infrared focal plane arrays (FPA) is a new developing way for wide military applications and civil domain because it owns the advantages of light weight, no need of cryogen, low cost and so on. The use of micromachining techniques has greatly increased the detectivity of bolometer as well as the other thermal infrared (IR) detetectors. A bolometer , as one of the most successful thermal detectors, has been actively researched for low cost systems.As a device with high performance, bolometer should be thermally isolated from the substrate effectively and presented ideal sensing material with both high TCR and low-resistivity at room temperature.Being the key materials in the formation of bolometer, amorphous silicon can be made with high TCR, low price and being compatiable of IC processes. It promotes greatly the utilization of infrared system in all fields. In the disseration, the properties of the material, as well as the design, fabrication and measurement for an amorphous silicon microbolometer is carefully studied.The microstructure and TCR of PECVD the hydrogenated amorphous silicon fabricated with different phosphor doping concentration were characterized after annealed at different temperature for different annealing time. Raman Scattering spectrum indicated that there is a mixture of amorphous as well as the micro-crystalline in the as-grown sample. When annealing temperature increased from 500°C to 700℃, the structure showed the tendency to amorphous phase at first and then to complete crystallization. While, the resistivity and the temperature coefficient resistance keep on decreasing. According to Lus model, the variation of the potential energy at the crystalline border caused by Si-P bonds is the fundamental reason for all the results.Performance of an uncooled microbolometer depends on geometrical design and properties of the sensitive materials. In this work, the voltage responsibility and thermal time have been investigated by the analytical theory. Based on the optimized structure, further thermal performances are simulated and confirmed by the Finite Element Method of ANSYS 8.0.For the compatibility with CMOS technology, a bolometer with front-cut design along the <110> direction is fabricate. The openings in absorbing area makes a fast etching on <100> planes and form a perfect suspended structure. The experimental result shows that the design of windows in IR absorbing area together with the dielectric thin film is characteristic of short releasing time and good IR adsorption. The typical measured responsivity of such a bolometer is 8.685×10³ V/W and the detectivity is 2.451×10⁷cmHz^1/2/W, which paves a way for a high yield low cost uncooled IR array.