Noise Spectra of Si x Ge y B z :H films for micro-bolometers
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1153-A19-05
Noise Spectra of Six Gey Bz:H films for micro-bolometers A.Kosarev, I.Cosme, A.Torres Electronics, National Institute for Astrophysics, Optics and Electronics, L.E. Erro 1, col. Tonantzintla, Puebla, 72840, Mexico ABSTRACT Noise spectra in plasma deposited SixGeyBz:H thermo-sensing films for micro-bolometers have been studied. The samples were characterized by SIMS (composition) and conductivity (room temperature conductivity, activation energy) measurements. The noise spectra were measured in the temperature range from T= 300 K to T=400 K and in the frequency range from f=2 Hz to f=2x104 Hz. The noise spectra SI(f) for the samples Si0.11Ge0.88:H and Si0.04Ge0.71B0.23 can be described by SI(f) ~ f – β with β = 1 and β = 0.4, respectively. For the sample Si0.05Ge0.67B0.26 two slopes were observed: in low frequency region f≤ 103 Hz β1= 0.7 and at higher frequencies f>103 Hz β2= 0.13. Increasing temperature resulted in an increase of noise magnitude and a change of β values. The latter depended on film composition. The correlation observed between noise and conductivity activation energies suggests that noise is due to bulk rather than interface processes. Noise spectrum of the thermo-sensing film Si0.11Ge0.88:H was compared with that for micro-bolometer structure with the same thermo-sensing film. The micro-bolometer structure showed higher noise value in entire frequency range that assumed additional processes inducing noise. INTRODUCTION Thermal detectors (bolometers) based on plasma deposited films have demonstrated many attractive advantages such as high responsivity, moderate resistance, compatibility of the fabrication process with standard silicon CMOS technology. Pioneering works with boron doped amorphous silicon in this field have been reported by “LETI” [1] and “Raytheon” [2] In our previous works we have reported on the study of fabrication and characterization of microbolometers with non doped silicon-germanium thermo-sensing films [3-5]. Noise measurements are of principal importance for performance characterization of the devices, because noise and responsivity determine detectivity that is a figure of merit based on signal-to-noise ratio enabling a comparison of different detectors (not only thermal ones). Another reason to study noise is related to its high sensitivity to fabrication and material parameters. So far noise in thermosensing materials and micro-bolometers has been poorly reported in literature. Only a few papers considered noise in plasma deposited non-crystalline materials [6 and references therein]. Noise related data for micro-bolometers can be found in refs. [7, 8]. The goal of this work is to study experimentally noise spectra in several plasma deposited thermo-sensing films used in micro-bolometers.
EXPERIMENT The SixGeyBz: H films were deposited by low frequency (LF) plasma enhanced chemical vapor deposition (PE CVD). Deposition parameters were as follows: substrate temperature
Ts= 300 oC, power W = 450 W, the discharge frequency f=110 kHz, pressure P= 0.6 Torr, a g
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