Study of a Fabrication Process and Characterization of One Dimensional Array of Un-cooled Micro-bolometers Based on Germ
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0989-A19-01
Study of a Fabrication Process and Characterization of One Dimensional Array of Uncooled Micro-bolometers Based on Germanium Films Deposited by Plasma Mario Moreno, Andrey Kosarev, Alfonso Torres, and Roberto Ambrosio Electronics, Institute National of Astrophysics, Optics and Electronics, L.E. No. 1 Tonanzintla., Puebla, 72840, Mexico ABSTRACT In our previous works, we have studied the fabrication process and characterization of single cell micro-bolometers based on germanium thin films deposited by low frequency (LF) PECVD technique at low temperature and fully compatible with the IC fabrication technology. We have demonstrated promising properties of those devices for further development of IR imaging systems [1-2]. In this work, we report the study and characterization of the fabrication process of a lineal array of 32 un-cooled micro-bolometers. We have used surface micro-machining techniques for the array fabrication onto a silicon wafer. The micro-bolometers in the array have a ìbridge typeî configuration. In this case, a SiNx supporting film is suspended 2.5 µm from the substrate by two legs, which form the bridge and provide sufficient thermo-isolation to the thermo-sensing layer. The thermo-sensing layer was deposited on the bridge by using LF PECVD. The a-GexSiy:H film used in this devices showed high activation energy Ea= 0.34 eV, providing high thermal coefficient of resistance, TCR=α=0.043 K-1and improved but still high resistance. We studied the effect of the addition of boron to the a-GexSiy:H film deposition process, for reducing its undesirable high resistance and, the resulting layer (a-GexBySiz:H) is used as thermo-sensing film in the micro-bolometers arrays. The active area of the cell in the array is Ab=70x66 µm2 and the area of the array including interconnection lines and pads is AA=1600x3120 µm2. The temperature dependence of conductivity σ(T), current-voltage characteristics I(U), and spectral noise density have been measured in the array and the main figures of merit such as, responsivity and detectivity have been obtained. INTRODUCTION The maturity of the MEMS structures fabrication process through the surface micromachining techniques, has allowed the development of low cost and reliable night vision systems based on thermal detectors [3-4]. Among the thermal detectors used for IR arrays, the microbolometer is one of them. The main requirements for the thermo-sensing materials used in micro-bolometers are: high value of the temperature coefficient of resistance, TCR (α(T)), defined as α (T) = (1/R)|dR/dT| = Ea/kT2, where Ea is the activation energy, moderated resistivity, low noise and compatibility with standard IC fabrication processes. Currently, it have been developed large arrays of un-cooled micro-bolometers that use different thermo-sensing materials. But none of them can be consider as the optimum one. Among the materials preferably used as thermo-sensing films are vanadium oxide, amorphous and polycrystalline semiconductors, and some metals [5-6]. Those materials ha
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