Uncooled microbolometers with hydrogenated amorphous germanium-silicon films: Different device configurations and improv
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Uncooled microbolometers with hydrogenated amorphous germanium-silicon films: Different device configurations and improvements on the thermosensing films Mario Moreno1, Alfonso Torres1, Roberto Ambrosio2, Pedro Rosales1, Andrey Kosarev1, Claudia Reyes1, Carlos Zuniga1, Wilfrido Calleja1, Francisco J. de la Hidalga Wade1, Miguel A. Dominguez1 1 National Institute for Astrophysics, Optics and Electronics, INAOE, Electronics Department, Tonatzintla, Puebla, Mexico 2 Universidad Autonoma de Ciudad Juarez, UACJ, Ciudad Juarez, Chihuahua, México. ABSTRACT We report our main results on the development of un-cooled microbolometers based on hydrogenated amorphous Germanium-Silicon (a-GexSiy:H) thermo-sensing films deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD). Our research has been conducted to improve both, the structure of the devices (pixels) and the performance characteristics of the amorphous Germanium-Silicon thermosensing films. Our motivation is to produce microbolometers with much better performance characteristics (larger thermal coefficient of resistance, larger conductivity and better stability) than those available in commercial microbolometer arrays, based on boron doped hydrogenated amorphous silicon (a-Si:H,B). As part of our latest research, we also report the study of what we believe is the next generation of thermosensing films based on Silicon and Geranium amorphous films with embedded nanocrystals in the amorphous matrix (polymorphous films). Those materials have several advantages over amorphous, as a lower defect density, better stability and better transport properties. INTRODUCTION Currently hydrogenated amorphous silicon (a-Si:H) is a mature material on the microelectronics industry. For infrared detectors (uncooled microbolometers) intrinsic a-Si:H deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) is very attractive to be used as thermo-sensing material, since intrinsic a-Si:H has a very large activation energy (Ea) of above 1 eV, and therefore, provide a very large thermal coefficient of resistance (TCR) of above -0.13 K-1. However a-Si:H has a very low room temperature conductivity (σRT ≤ 1x10-9 (Ωcm)-1), resulting in a very high pixel resistance when is used as thermo sensing material in microbolometers (Rpixel ≥ 109 Ω). Such high pixel resistance causes a mismatch with the input impedance of the CMOS Read Out circuit (ROIC). For commercial microbolometers, boron doping is commonly used in order to decrease the undesirable resistivity of intrinsic a-Si:H [1], to values of pixel resistance of around 30x106 Ω, however it also results on a reduction on the activation energy (Ea ≈ 0.22 eV) and on the TCR (0.028 K-1), and therefore in a decrement on the pixel sensitivity and performance. Our work has been conducted to investigate the electrical and optical properties of hydrogenated amorphous germanium-silicon (a-GexSiy:H) and amorphous germanium-silicon-boron (aGexSiyBz:H) thin films, deposited by plasma (PECVD) [2-6]. We believe this kind of films have several advantag
