Sol-gel deposition and characterization of vanadium pentoxide thin films with high TCR

Vanadium pentoxide thin films have been deposited on quartz substrates via sol-gel synthesis and dip coating. The process was developed to establish a reliable and inexpensive method to produce thin films with a high temperature coefficient of resistance (TCR) for sensing applications. Sol-gel precursor concentration and post-deposition annealing conditions were varied to address their effects on film composition, morphology, structure, resistivity, and TCR response. The resulting thin films were structurally characterized by thin film profilometry, x-ray diffraction, scanning electron microscopy, and Raman spectroscopy. Resistivity and TCR measurements were carried out to determine their efficacy as sensor materials. Both low and high concentration alkoxide sol-gel precursors led to films of pure α-V2O5 composition but with characteristically different structural and electrical properties. Low concentration films showed a modest decrease in resistivity and TCR with increasing annealing temperature, consistent with the formation of increasing grain size and the coalescence of largely planar grains with common crystalline orientation. In contrast, films fabricated from higher alkoxide precursor concentration are characterized by a higher density of grains with a larger dispersion in orientation and better-developed grain boundaries, leading to a general increase in resistivity and TCR with annealing temperature. The TCR of the films lied in the range of -3%°C−1 to -4%°C−1, comparing favorably with films produced through conventional techniques such as DC magnetron sputtering, chemical vapor deposition, or pulsed laser deposition. Further, their TCR and resistivity characteristics can be controlled through sol-gel precursor concentration and post-deposition annealing temperature, indicating that sol-gel deposited vanadium pentoxide films are promising candidates for infrared sensor applications.