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Phase Change Materials for RF Microsystems

In the past we have used vanadium dioxide (VO2) films to develop reconfigurable terahertz filters (known as frequency selective surfaces or metmaterial) operating in approximately 500GHz band. VO2 belong to a group known as insulator-to-metal (ITM) or phase change materials (PCM). This metal oxide group exhibits large change in electrical conductivity when excited with temperature, strain, or an electric field. The structure of the material changes between monoclinic (insulating state) and tetragonal rutile (metallic state) causing massive changes in electrical and optical properties. Unlike other PCMs such as germanium telluride (GeTe), the phase transition temperature of VO2 occurs at relatively a low temperature of 68°C making it attractive for device development. We have recently developed DC magnetron sputtering deposition technique for VO2 films on sapphire (Al2O3) substrate at the Ohio State University where we demonstrated 7×104 times change in electrical conductivity for 80-nm-thick VO2 film.

Example of VO2 film properties fabricated at OSU showing large change in resistivity with temperature.Example of VO2 film properties fabricated at OSU showing large change in resistivity with temperature [1,2].

Related papers:

1) V. Sanphuang, N. Ghalichechian, N. Nahar, J. Volakis, “Equivalent Circuit for VO2 Phase Change Material Film in Reconfigurable Frequency Selective Surfaces,” Applied Physics Letters, vol. 107, p.253106, 2015, http://dx.doi.org/10.1063/1.4938468

2) V. Sanphuang; N. Ghalichechian; N. K. Nahar; J. L. Volakis, "Reconfigurable THz Filters Using Phase-Change Material and Integrated Heater," in IEEE Transactions on Terahertz Science and Technology, doi:  http://dx.doi.org/10.1109/TTHZ.2016.2560175