Bistable Electrical Switching Using a Crown Ether-Based Monolayer Electrolyte on WSe₂ Field-Effect Transistors with...

Bistable electrical switching using a crown-ether-based electrolyte on WSe₂ field-effect transistors (FETs) is measured for four salts: LiClO₄, NaClO₄, Ca(ClO₄)₂, and LiCl. The solid-state monolayer electrolyte comprises cobalt crown ether phthalocyanine in which cations are solvated by 15-crown-5 ethers. The switching mechanism is the toggling of cations through the crown ether cavity in response to an applied field, creating low and high resistance states in the WSe₂ channel. This work shows that bistability is not unique to Li⁺ and extends to other perchlorate-based salts with Na⁺ and Ca²⁺ cations. LiClO₄ induces the largest sheet density (2 × 10¹² cm^-2) followed by Ca(ClO₄)₂ (1 × 10¹² cm^-2) and NaClO₄ (0.8 × 10¹² cm^-2). The impact of the anion was evaluated by replacing LiClO₄ with LiI and LiCl. A homogeneous deposition of LiI could not be achieved, and LiCl only induced 0.2 × 10¹² cm^-2-an order of magnitude less charge than the perchlorate-based salts. Devices with LiCl required the largest voltages to achieve switching and had the smallest ON/OFF ratio in a 6 h state retention test. The results point to the anion playing a critical role in bistability, and Li⁺ as the best performing cation in terms of doping density, minimum switching voltage, and state retention.