Amorphous Silicon Microbolometer Technology

Abstract

Highly sensitive hydrogenated amorphous silicon (a-Si:H) microbolometer arrays have been developed that take advantage of the high temperature coefficient of resistance (TCR) of aSi:H and its relatively high optical absorption coefficient. TCR is an important design parameter and depends on material properties such as doping concentration. Ultra-thin (∼2000 Å) aSiNx:H/a-Si:H/ a-SiNx:H membranes with low thermal mass suspended over silicon readout integrated circuits are built using RF plasma enhanced chemical vapor deposition (PECVD) and surface micromachining techniques. The IR absorptance of the bolometer detectors is enhanced by using quarter-wave resonant cavity structures and thin-film metal absorber layers. To ensure high thermal isolation the microbolometer arrays are vacuum packaged using wafer level vacuum packaging. Imaging applications include a 120×160 a-Si:H bolometer pixel array IR camera operating at ambient temperature. Non-imaging applications are multi-channel detectors for gas sensing systems.

Un-Cooled Microbolometers with Amorphous Germanium-Silicon (a-GexSiy:H) Thermo-Sensing Films

“…The B doped a-Si:H films have a significant reduction in its resistivity, however a reduction in E a and TCR is obtained also, Ea ≈ 0.22 eV and TCR ≈ 0.028 K -1 (A. J. Syllaios, 2000). In our work (R. Ambrosio, 2004;A.…”

“…In general the a-Ge x Si y B z :H alloys have similar characteristics than those of the a-Si:H,B thermo-sensing film (A. J. Syllaios, 2000), but also have one order of magnitude shorter resistivity. The boron alloy planar structure microbolometers have a cell resistance, around R cell ≈ (1-3) x10 6 Ω, which is two orders of magnitude shorter than that of the planar structure devices with intrinsic film and one order of magnitude shorter than that of the a-Si:H,B commercial devices (A. J.…”

“…Hydrogenated amorphous silicon (a-Si:H) prepared by PECVD is very attractive to be used as thermo-sensing film in microbolometers, for room temperature operation (A. J. Syllaios, 2000). It is compatible with the IC technology, has a high activation energy, E a ≈ 0.8 -1 eV and high value of TCR, (T) ≈ 0.1 -0.13 K -1 , however it also has a very high undesirable resistivity, which often cause a mismatch with the input impedance of the read-out circuits.…”

“…Syllaios, 2000). Intrinsic a-Si:H is compatible with CMOS technology and has a very high TCR, around 0.1-0.13 K -1 ; however it is a highly resistive material, resulting in high resistive microbolometers which present a mismatch impedance with the readout circuits.…”

“…Tanaka, 1996), polycrystalline (S. Sedky, 1998) and amorphous semiconductors (A. J. Syllaios, 2000).…”