Study On Preparation Of Vanadium Oxide Thin Films With High TCR For Uncooled IR Detectors

Vanadium oxide thin films are widely used in the field of uncooled IR detecting and imaging for its high temperature coefficient of resistance (TCR). In this thesis, three vapour deposition techniques are adopted to prepare vanadium oxide thin films with high TCR for uncooled IR detectors. The gained preparation process has nice repetitivity, and can be compatible with semiconductor process. The prepared vanadium oxide thin films have moderate surface resistance values at room temperature (RRT), high TCR, nice thermal sensitivity, homogeneous surface and strong binding force with substrates. So the films completely meet the demands of IR detectors.The effects of deposition parameters on the performance of vanadium oxide thin films are analyzed by orthogonal experiments. The optimal deposition parameters by direct current facing targets sputtering are as follows: the flux of Ar and O2 is 48 and 0.4sccm, respectively; gas pressure is 2Pa; sputtering power is 210~240W; sputtering time is 30~60 minutes; annealing temperature is 400℃and time 3~7 hours. The vanadium oxide thin films prepared by these parameters have RRT less than 100 K?/□, TCR over -3%/K.In the study on deposition conditions, the effects of Ar/O2, sputtering power, gas pressure, vacuum annealing, substrate types and substrate temperature on the performance of vanadium oxide thin films are analyzed. Among these parameters, Ar/O2 is the key factor for preparation of perfect vanadium oxide thin films. Vacuum annealing facilitates deoxidizing V5+ to V3+ or V4+, forming homogeneous films, reducing RRT and transforming vanadium oxide thin films from amorphous to multicrystal.The results of studying on process of vacuum evaporation, radio frequency sputtering and direct current facing targets sputtering indicate it is difficult for traditional vacuum evaporation to prepare pure and high performance VOx thin films by vaporizing V2O5 powder. However, the films by sputtering techniques have much better performance, because incident particles have much more energy in sputtering. In the two sputtering techniques, direct current facing targets sputtering has more advantages: high ratio of utilizing targets, easy to gain high power, low cost and nicerepetitivity.The relations between TCR, RRT and composition of the VOx films are founded in the research on resistance versus temperature characteristic of VOx films. TCR becomes higher (lower) as RRT changes higher (lower). In the VOx films with high TCR and moderate RRT, the average valence of vanadium is about +4.The research on multi-layer structure indicates that if porous silicon is used as thermal insulator in the multi-layer structure, VOx thin films still keep high thermal sensitivity even when input power is very low, such as 20μW. This multi-layer structure provides a reference for thermal sensitive devices.