Highly conducting leakage-free electrolyte for SrCoO_x-based non-volatile memory device

The electrochemical switching of SrCoO_x-based non-volatile memory with a thin-film-transistor structure was examined by using liquid-leakage-free electrolytes with different conductivities (σ) as the gate insulator. We first examined leakage-free water, which is incorporated in the amorphous (a-) 12CaO·7Al₂O₃ film with a nanoporous structure (Calcium Aluminate with Nanopore), but the electrochemical oxidation/reduction of the SrCoO_x layer required the application of a high gate voltage (V_g) up to 20 V for a very long current-flowing-time (t) ∼40 min, primarily due to the low σ [2.0 × 10⁻⁸S cm⁻¹ at room temperature (RT)] of leakage-free water. We then controlled the σ of the leakage-free electrolyte, infiltrated in the a-Na_xTaO₃ film with a nanopillar array structure, from 8.0 × 10⁻⁸S cm⁻¹ to 2.5 × 10⁻⁶S cm⁻¹ at RT by changing the x = 0.01–1.0. As the result, the t, required for the metallization of the SrCoO_x layer under small V_g = –3 V, becomes two orders of magnitude shorter with increase of the σ of the a-Na_xTaO₃ leakage-free electrolyte. These results indicate that the ion migration in the leakage-free electrolyte is the rate-determining step for the electrochemical switching, compared to the other electrochemical process, and the high σ of the leakage-free electrolyte is the key factor for the development of the non-volatile SrCoO_x-based electro-magnetic phase switching device.