Silicon Germanium Oxide (Si x Ge y O 1-x-y ) Infrared Sensitive Material for Uncooled Detectors
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Silicon Germanium Oxide (SixGeyO1-x-y) Infrared Sensitive Material for Uncooled Detectors R. Anvari1, Q. Cheng1, M. L. Hai1, T. Bui1, A. J. Syllaios2, S. Ajmera2 and M. Almasri1 1 Department of Electrical and Computer Engineering, University of Missouri, Columbia, MO, [email protected] 2 L-3 Communications Electro-Optical Systems, Dallas, TX, [email protected] ABSTRACT This paper presents the formation and the characterization of silicon germanium oxide (SixGeyO1-x-y) infrared sensitive material for uncooled microbolometers. RF magnetron sputtering was used to simultaneously deposit Si and Ge thin films in an Ar/O2 environment at room temperature. The effects of varying Si and O composition on the thin film’s electrical properties which include temperature coefficient of resistance (TCR) and resistivity were investigated. The highest achieved TCR and the corresponding resistivity at room temperature were -5.41 %/K and 3.16×103 Ω cm using Si0.039Ge0.875O0.086 for films deposited at room temperature. INTRODUCTION Infrared imaging cameras have a broad range of commercial and military applications. These cameras are developed by companies such as L-3 Communications [1], Raytheon [2], DRS [3] and BAE Systems [4], and are mainly based on vanadium oxide (VOx) or amorphous silicon (a-Si) technology. Several other materials have been used in uncooled infrared detection, including yittrium barium copper oxide (YBaCuO), silicon germanium (SiGe), silicon germanium oxide (Si-Ge-O), metals, and poly silicon (Poly: Si). A detailed TCR summary of common materials used in uncooled infrared imaging technology is shown in Table I. Table I. Temperature coefficient of resistance (TCR) of common uncooled infrared microbolometer materials. Infrared Materials VOx a:Si YBaCuO Si-Ge Si-Ge-O Metals
TCR (%/K) 2 - 2.4 2 - 3.2 2.88 - 3.5 2–3 See table II 0.2
References [5, 6] [1, 7-9] [10, 11] [12, 13] [14]
Other research groups have studied SixGeyO1-x-y compound as an infrared sensitive material. Clement et al. sputtered Ge-Si compound target (15% atomic Si) in argon/oxygen environment [15]. A similar deposition method was performed by Rana et al. [16] but instead of using Si-Ge target, they fixed a piece of silicon (cut from a silicon wafer) to a Ge target and deposited using one power source. A third group has deposited SixGeyO1-x-y using co-sputtering system in Ar/O2 environment [17, 18]. The three groups have achieved relatively high TCR. However, the
corresponding resistivities were too high to be compatible with microbolometer readout electronics. Table II. Recent results of TCR and resistivity of Si-Ge-O. TCR (%/K) - (2.27 - 8.69) -5 -5 - 6.43
Resistivity (Ω Ω.cm) 4.22×102 - 3.47×109 104 3.8×104 3.34×102
References [15] [19] [17, 18] [20, 21] Our group
This paper utilizes amorphous SixGeyO1-x-y as the infrared sensing layer because of its excellent infrared radiation absorption, and mechanical and electrical properties at room temperature. Si and Ge based compounds are standard materials in silicon integrate
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