title: A transparent electrochromic metal-insulator switching device with three-terminal transistor geometry.
abstract: Proton and hydroxyl ion play an essential role for tuning functionality of oxides because their electronic state can be controlled by modifying oxygen off-stoichiometry and/or protonation. Tungsten trioxide (WO3), a well-known electrochromic (EC) material for smart window, is a wide bandgap insulator, whereas it becomes a metallic conductor HxWO3 by protonation. Although one can utilize electrochromism together with metal-insulator (MI) switching for one device, such EC-MI switching cannot be utilized in current EC devices because of their two-terminal structure with parallel-plate configuration. Here we demonstrate a transparent EC-MI switchable device with three-terminal TFT-type structure using amorphous (a-) WO3 channel layer, which was fabricated on glass substrate at room temperature. We used water-infiltrated nano-porous glass, CAN (calcium aluminate with nano-pores), as a liquid-leakage-free solid gate insulator. At virgin state, the device was fully transparent in the visible-light region. For positive gate voltage, the active channel became dark blue, and electrical resistivity of the a-WO3 layer drastically decreased with protonation. For negative gate voltage, deprotonation occurred and the active channel returned to transparent insulator. Good cycleability of the present transparent EC-MI switching device would have potential for the development of advanced smart windows.
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, N20W10, Kita, Sapporo 001-0020, Japan.
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Katase
authors.affiliation: Graduate School of Information Science and Technology, Hokkaido University, N14W19, Kita, Sapporo 060-0814, Japan.
authors.forename: Takaki
authors.initials: T
authors.lastname: Onozato
authors.affiliation: School of Engineering, Hokkaido University, N13W8, Kita, Sapporo 060-8628, Japan.
authors.forename: Misako
authors.initials: M
authors.lastname: Hirono
authors.affiliation: Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan.
authors.forename: Taku
authors.initials: T
authors.lastname: Mizuno
authors.affiliation: Research Institute for Electronic Science, Hokkaido University, N20W10, Kita, Sapporo 001-0020, Japan.
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Ohta