Field Effect Control of in Y-Ba-Cu-O Electric Double Layer Transistors

Electric-double-layer field-effect-transistors (EDLFETs) were fabricated using 10.5-12.9 nm thick YBa₂Cu₃O₇ (YBCO) films and N, N-Diethyl-Nmethyl-N-(2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide (DEME-TFSI), and critical temperature (T_c) and vortex behavior were evaluated in the devices. Decrease in sheet resistance and increase in Tc were observed when negative gate voltage (V_G) was applied, and opposite variation was observed in the case of positive gate voltage. At V_G = 0 V, T_c^onset was ~70 K, and T_c0 was ~47 K. V_G = -5 V resulted in T_c^onset of 83.3 K and T_c0 of 61.8 K, and those in V_G = +2 V were 65.0 K and 40.0 K. To discuss carrier doping mechanism, activation energy for vortex motion and irreversibility temperature were measured at V_G = 0 V and -3 V. Activation energy and irreversibility temperature were improved by negative gate voltage. This shows that carrier doping was performed throughout thickness of film since vortices moved with length scale larger than coherence length. This suggests that electrochemical reaction such as oxygen ion injection strongly affected carrier density in the present devices.