Advanced microwave and optical switching devices based on reversible Metal-Insulator Transition (MIT) in VO2 thin films – ADMOS-VO2

The main objective of the proposed project is to develop new types of ultra-fast switches operating in the RF- microwave and optical domains by using a class of materials undergoing fast reversible transitions from a semiconducting state to a metallic one (Metal- Insulator Transition – MIT). The final goal is to realize commutation functions allowing to improve the current problems encountered in the communication systems (consumption, power handling, fast switching, integration). Currently, a lot of research effort is employed for studying the performances of reconfigurables millimeter-wave circuits integrated in advanced communication systems for space or defense applications (reconfigurable antennas, complex communication networks etc.). Presently, the switching microwave circuits are employing mainly semiconductor-based solution or, more recently, MEMS-based devices. On the other hand, the optical communication networks, with their high transmission capabilities, are perceived as key elements in the design of a communication system. They require ultra-fast switching elements (single switch or matrices) with outstanding performances (low insertion losses, low cross talk and consumption and increased lifetime operation). The functioning of the devices we proposed within this project is based on the reversible MIT transition of vanadium dioxide (VO2) thin films, which occurs very fast (within ps down to ~100 fs) and it is accompanied by an abrupt, remarkable modification of electrical and optical properties of the VO2 material. Thus, during the transition from semiconductor to the metal state the electrical resistively of the VO2 thin films can decrease by several orders of magnitude. From the optical point of view, the material is transparent at the semiconductor phase and highly reflective at metallic state for a large spectral domain (from 1 mm up to the THz frequencies). The reversible MIT transition can be triggered by different external excitations (temperature, optically or electrically by charge injection). Within the frame of this project we intend to use these remarkable properties of the VO2 material for switching on and off an incoming electromagnetic field propagating in a microwave coplanar waveguide integrating a thin VO2 film (on/ off switching during the fast changing of VO2 resistivity during an MIT transition). For the optical commutation applications we will employ the reflectivity change of a VO2 thin films undergoing an MIT transition in order to realize variable reflectivity micro-mirrors (rapid optical commutation) with a large application area (optical modulators for obtaining short laser-pulse in the Q-switching or mode-locking regime, optical switches etc.). The proposed devices will be realized using the micro fabrication technology and facilities available in our institute. The VO2 thin films will be obtained by using a conventional pulsed laser deposition (PLD) technique. After a preliminary stage concerning the deposition of VO2 films and the extensive characterization of the evolution of their properties (structure, morphology, MIT transition) with the experimental parameters (deposition conditions, type of substrates, thickness) we will realize simple devices for studying the rapid MIT transition triggered by different excitations (temperature, optical, charge injection). The next step will concern the simulation, design, fabrication and RF and optical characterization of more complex structures like RF switches integrated on a coplanar microwave line or optical switches. The final applications we aim to develop during the proposed research project concerns complex broadband devices employed in the telecommunication networks in the millimeter-wave domain (switches, filters, phase shifters etc.) and the design of optical devices for applications using miniature laser systems or optoelectronics (optical switches, filters, variables attenuators). The realization of these new types of switches widens a new and extremely rich activity in the field of device fabrication for millimeter-wave reconfigurable systems or for integrated optics and optical communication systems. The members of the team involved in the project possess all the necessary expertise, the technological means, as well as competencies that will allow, within the framework of a close cooperation, to pass through material synthesis to the fabrication of functional devices in the domain aimed by this project.