Vanadium Dioxide Storage Material

Abstract

Vanadium dioxide undergoes a semiconductor-metal phase transi­ tion at temperature of 340 K. When prepared as a thin film on a suitable substrate, the transition exhibits hysteresis, i.e. the curve describing the state of the film versus temperature is double valued. Here the material is capable of existing in equilibrium in either of two states at the same temperature. Both high writing speed and high spatial resolution are possible, contrary to what one might normally expect from a thermal process. The writing speed is limited by the time taken to deliver the latent heat of transition, and the resolution is limited by the diffusion time during which written and unwritten adjacent areas are out of thermal equilibrium. Both of these times are connected, and they along with the latent heat dictate the exposure. Experiments thus far have produced writing times as small as 30 nanoseconds and stored spots of a few microns in size. They by no means represent limits, and writing times of a few nanoseconds and spot sizes down to a few thousand angstroms appear feasi­ ble. A discussion will be given detailing the material as a high density recording medium including laser beam writing requirements, spot sizes, stored contrast, and signal-to-noise ratio. In addition, information on optical constants, latent heat and other physical parameters will be given along with some past results concerning long term storage, cycling, lifetime, and reciprocity.