In our previous papers on Electro-Chromic (EC) materials, we have shown that standard inorganic EC structures in the form of EC film/electrolyte/Ion storage films (such as WO3/LiNbO3/NiO), in addition to possessing reconfigurable optical properties also exhibit a degree of electric field induce dielectric tunability at radio frequencies. The extent of dielectric tunability in those standard EC structures is commensurate with the tunability exhibited by more mature bulk-tuneable technologies, such as Liquid Crystals (LCs), being between 5% and 20% depending on the frequency of operation, the thickness of the individual EC layers (EC films, electrolyte and ion tank).
In the present paper, we report on a new, inorganic EC structure capable of achieving a high degree of dielectric tunability. In particular, this new structure has the same chemical composition as our previously examined EC structures, however, its constituent layers are perturbed: the EC film (WO3) is placed in the interior of the device, while the electrolyte (LiNbO3) is placed at the periphery of the cell, as shown in Fig. 1. The new structure, termed LiNbO3/WO3/LiNbO3, is capable of no less than three times higher dielectric tunability compared to the standard EC cell structure, WO3/LiNbO3/NiO, standing up to 65%, in the same frequency range, up to 20 GHz.
These are very important results as they point to new ways of increasing dielectric tunability, which will be useful in the enablement of flexible spectrum usage of new communications technologies, such as 6G.
Fig. 1 Structure of new, high dielectric tunability EC cell