Nonhysteretic behavior inside the hysteresis loop of VO2 and its possible application in infrared imaging

Abstract

In the resistive phase transition in VO 2 , temperature excursions taken from points on the major hysteresis loop produce minor loops. For sufficiently small excursions these minor loops degenerate into single-valued, nonhysteretic branches ͑NHBs͒ linear in log͑͒ versus T and having essentially the same or even higher temperature coefficient of resistance ͑TCR͒ as the semiconducting phase at room temperature. We explain this behavior based on the microscopic picture of percolating phases. Similar short NHBs are found in otherwise hysteretic optical reflectivity. We discuss the opportunities NHBs present for infrared imaging technology based on resistive microbolometers. It is possible to choose a NHB with 10 2-10 3 times smaller resistivity than in a pure semiconducting phase, thus providing a microbolometer operating without hysteresis, with low tunable resistivity, and high TCR. Unique features of the proposed method and projected figures of merit are discussed in the context of uncooled focal plane array IR visualization technology.

Treating the Case of Incurable Hysteresis in VO 2

“…The larger is ΔR for a given ΔT, the greater is the sensitivity. At the same time, very large resistance R is detrimental because of bolometric sensor Joule heating during readout, difficulty of matching to the electronic readout circuit and higher noise, both Johnson and 1/f [1] . Thus a commonly-used measure of the bolometric material's sensitivity is the logarithmic derivative (1/R) ΔR/ΔT called temperature coefficient of resistance, or TCR.…”

“…5a. These features depend on the rate of temperature sweep; they are probably instrumental effects resulting from a lag between film surface and thermometer temperatures [1] .…”

“…The films used in these measurements were prepared on Si/SiO 2 substrates by Pulsed Laser Deposition; details of sample preparation and measurements can be found in Ref. 1. On the log(R) vs. T plot, starting from room temperature, with increasing T resistivity first follows the semiconducting S-phase slope, then falls sharply along the right (heating) branch of the transition reaching metallic M-phase; the decreasing temperature corresponds to values of R tracing the left (cooling) branch, eventually forming a closed loop between two transition-end points T S and T M .…”

“…We offer a way of operation which circumvents these problems. The applied aspects of IR visualization vis-à-vis our proposed approach are discussed in our recent publication [1] , and we will refer to it in a number of instances for further details and references. Here we want to explain the essence of the method and touch upon its physics fundamentals.…”

Metal-insulator transition in nanocomposite VOx films formed by anodic electrodeposition

“…4 MIT transitions in VO 2 exhibit a change in resistivity of about five order of magnitude in single crystals, 5 and about 3 orders of magnitude in thin films, 6 sufficient to enable in principle MIT-based electronics. 7 Amorphous VO 2 has also found application in bolometer devices for infrared detectors, 8 where a high temperature coefficient of resistance (TCR) 9 facilitates temperature determination from the measured resistance; values as high as À2%/ C have been obtained by physical vapor deposition (PVD) methods for amorphous VO x (x $ ¼ 1.8À2.0) films. [10][11][12] In this case, a gradual change in resistance, allowing operation over a large temperature range, is required.…”