  Recently, as a novel technique, electronic double-layer transistors (EDLTs)
with ionic liquids have shown strong potential for tuning the electronic states
of correlated systems. EDLT induced local carrier doping can always lead to
dramatic changes in physical properties when compared to parent materials,
e.g., insulating-superconducting transition. Generally, the modification of
gate voltage ($V_{\rm G}$) in EDLT devices produces a direct change on the
doping level, whereas the processing temperature ($T_{\rm G}$) at which $V_{\rm
G}$ is applied only assists the tuning process. Here, we report that the
processing temperature $T_{\rm G}$ plays a dominant role in the electric field
induced superconductivity in layered ZrNBr. When applying $V_{\rm G}$ at
$T_{\rm G}\geq$ 250 K, the induced superconducting (SC) state permanently
remains in the material, which is confirmed in the zero resistance and
diamagnetism after long-time relaxation at room temperature and/or by applying
reverse voltage, whereas the solid/liquid interface induced reversible
insulating-SC transition occurs at $T_{\rm G}\leq$ 235 K. These experimental
facts support another electrochemical mechanism that electric field induced
partial deintercalation of Br ions could cause permanent electron doping to the
system. Our findings in this study will extend the potential of electric fields
for tuning bulk electronic states in low-dimension systems.
