Electrostatic and electrochemical charging mechanisms for electric-double-layer gating media based on a crystalline LaF3 solid electrolyte

The electric-double-layer, constituted on the interface between an electronic conductor and an ionic conductor, enables practical applications of electronic devices and electrochemistry. Specifically, the electric-double-layer interfaces have been widely reported to achieve the insulator–metal transition and interfacial superconductivity in field-effect transistors because of the large electric-double-layer capacitance and high carrier density accumulation. Recently, a crystalline LaF3 solid electrolyte has been shown to be an ideal gate medium candidate for realizing stable electric-double-layer transistors. However, the intrinsic electrostatic and electrochemical mechanisms about LaF3 electric-double-layer interfaces remain elusive. Here, by combining electrochemical-impedance-spectroscopy with low-temperature technology, we demonstrate the temperature–frequency mapping “phase diagram” for the capacitance and dielectric loss at the LaF3/metal interfaces. Two well-distinguished regions correspond to the electrostatic and electrochemical nature, providing a promising guideline for practical device applications based on the crystalline LaF3 solid electrolyte.