Vanadium dioxide (VO2) is also a ferroelectric: Properties from memory structures

This work claims that VO₂, of interest currently for its metal-insulator phase transition properties, is also a ferroelectric material. Using a VO₂ film sandwiched between two silicon dioxide layers, memory transistor structures with substantial and useful properties have been fabricated. Threshold voltage shifts are opposite of charge trapping phenomena and consistent with ferroelectric polarization switching phenomena. Hysteresis memory window of ~1 V is obtained in -4 to 4 V gate voltage cycling. We argue that the effects observed are due to the ferroelectricity of VO₂. Its remnant polarization of ~0.53 μC/cm² and coercive field of ~450 kV/cm are extracted from the saturation behavior of threshold voltage shift. Similar to other ferroelectric memory structures, depolarization effects are observed. The state of memory devices decays gradually and retention times of approximately 15 minutes are obtained at room temperature. These ferroelectric properties do not vanish above metal-insulator phase transition temperature.