Noise in Different Micro-bolometer Configurations with Silicon-Germanium Thermo-sensing Layer
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1066-A18-05
Noise in Different Micro-bolometer Configurations with Silicon-Germanium Thermosensing Layer Mario M Moreno, Andrey Kosarev, Alfonso J Torres, and Ismael Cosme Electronics, National Institute for Astrophysics, Optics and Electronics, L.E.Erro No. 1, col.Tonatzintla, Puebla, 72840, Mexico ABSTRACT We have studied noise in four configurations of un-cooled micro-bolometers: three of them were built in a planar structure with a) a-Six Ge y, y = 0.88, b) a-SixGeyBz:H, y = 0.67 and z = 0.26; c) y = 0.71, z = 0.23 and the fourth d) sandwich structure with y = 0.88. These samples were characterized by SIMS (composition), FTIR (H-bonding and H content), conductivity measurements (σ(T), activation energy, TCR), current-voltage characteristics in dark and under illumination enabling in this way the determination of responsivity. The power noise spectral density (PNSD) versus frequency S(f) was studied in the range of frequency f=1 to f=103 Hz under IR illumination and constant bias. The measurements were performed in a vacuum chamber with pressure P=10 mTorr. In general the S(f) measured on our devices, demonstrated three regions separated by two corner frequencies: fc1 and fc2. The regions are: 1) f ≤ fc1 S1 ~ f β and β = 0.1 to 0.3, 2) fc1 ≤ f ≤ fc2, S2 ~ f-γ and γ = 0.75 to 1.5 and 3) f ≥ fc2 and S3 – const (f). The different samples here studied showed different values of fc1, fc2, β, γ and S3 level. The noise characteristics experimentally observed experimentally are used for determining the detectivity D* of the devices and these data are analyzed and compared with the data reported in literature. INTRODUCTION A renewed recent interest in thermal detectors has resulted from to plasma deposited materials with large temperature coefficient of resistance (TCR), which in conjunction with micro-machining technology for thermal isolation, have provided a fabrication process compatible with the dominating Si CMOS technology that makes it possible the development of system -on-chip configurations. In our previous works we have reported on the study of fabrication and characterization of single cell micro-bolometers based on silicon-germanium thermo-sensing films deposited by low frequency plasma [1-3]. Noise measurements are very important part of device characterization, which have been poorly reported in literature with only a few publications [4-8]. In ref. [4] the spectral dependence of noise has been reported in GexSi1-xOy films deposited by sputtering. The currently proposed models for noise description in non-crystalline samples (either in films or in device structures) are still debated and no one can be considered as the only accepted [9]. The goal of this work is to study experimentally noise spectral density in several configurations of micro-bolometers built with silicon-germanium (a-SixGey:H) as thermo-sensing films. The power noise spectral density (PNSD) has been measured in four configurations of micro-bolometers: a) planar structure with a silicon-germanium intrinsic (a-SixGey:H, y =0.88) thermo-sen
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