Thin film uncooled microbolometers based on plasma deposited materials

Abstract

We make a summary of our research and development efforts made about microbolometers (MBs) based on plasma-enhanced chemical vapor deposition (PECVD) materials, like noncrystalline semiconductors that provide high temperature coefficient of resistivity values, in conjunction with SiOx and SiNx dielectrics used for thermoisolation, which, together with micromachining, are paving new ways for fabrication of MBs, making them promising for 2D imagers in both infrared and tera-Hertz regions. We studied a-Si:H(B), a-Ge:H, a-GeSi:H, and polymorphous p-Ge:H, p-SiGe:H as thermosensing materials (TSMs) for MBs in “bridge” configuration with “planar” and “sandwich” electrodes. This allows placing the read-out circuitry under the bridge, improving use of pixel area. PECVD SiNx films were used as both a support layer and as a coating for improving the response for λ = 8–12 μm. 2D modeling revealed both linear and super linear response to IR intensity. Voltage responsivity RU = (1.2–7) × 105 V/W is observed in both “planar” and “sandwich” MBs. The latter shows current responsivity RI = 0.3–14 A/W higher by about three orders of magnitude than the former. A key issue for any detector is the detectivity. Different TSMs show different noise characteristics. Noise in “sandwich” MBs is several orders of magnitude higher than that in “planar” structures. The best parameters observed with TSM Ge-Si:H are: RU = 7.2 × 105 V/W, RI = 14 A/W voltage and current detectivities [Formula: see text] = 8 × 109 cm Hz1/2W−1 and [Formula: see text] = 4 × 109 cm Hz1/2W−1. Junction structures on top of the “bridge” are also discussed. Finally we describe some reported applications of MBs.