Nano-vanadium oxide thin films in mixed phase for microbolometer applications

Abstract

Among the several phases of vanadium oxide, mixed phases of VO2 and V2O5 are preferred for uncooled micro-bolometers with low noise. The aim of this investigation is to achieve mixed phase VO2 and V2O5 thin films with nanometre grain sizes and high temperature coefficient of resistance (TCR). Since the phase depends upon the oxygen reactivity, these vanadium oxide thin films are prepared by reactive electron beam evaporation at different oxygen flow rates and substrate temperatures. The mixed phases have been evaluated through x-ray diffraction and x-ray photo emission studies. The temperature dependence of resistance has shown that the films grown at 473 K with 2.8 × 10−5 mbar chamber pressure of oxygen (VO2 : V2O5 ratio of 36 : 64) have the highest TCR of −3.2 K−1 with a reasonable low resistance (120 Ω/square).

Influence of Post-Annealing on Resistivity of VO x Thin Film

“…The V 2 O 5 phase also has high TCR but its resistivity is too high (> 1 × 10 4 · cm). Thus, mixed VO x thin films may be suitable due to their big resistivity range (0.01∼10 · cm) and high TCR [4]. The relationship between resistivity and TCR is generally subject to the specific composition of the film, especially to the content of oxygen (O).…”

Group IV Materials for Low Cost and High Performance Bolometers

“…The typical phases are known as VO, V 2 O 3 , VO 2 (or V 2 O 4 ) and V 2 O 5 (or as a "mixed oxide) (Subrahmanyam et al, 2008 Thus, a mixed phase of VO 2 and V 2 O 5 may demonstrate an appropriate resistivity which is convenient and matches also with the readout electronics for high sensitive bolometers (Malyarov, 1999).…”

Adjustment of thermal hysteresis in epitaxial VO2 films by doping metal ions

“…In general, typical bolometer films using VO x film show semiconductor behaviors in electronic property and therefore TCR value was limited to around 3.0%/°C . 16), 17) In contrast, the TCR value was drastically improved by using the non-hysteretic MI transition region, which was induced by metal-ion-substitutive structural defects. It was revealed that Ti and Nb ions were appropriate ions for inducing structural defects in VO 2 because these ions did not affect the MI transition temperature significantly.…”