Selector is indispensable to suppress leakage current for crossbar array of resistive random access memory. According to the nonlinear requirement, electron tunneling mechanism is firstly attempted. However, earlier studies discovered drawbacks of insufficient current density. This work aims at exploring the idealized characteristic of selector based on Fowler-Nordheim tunneling mechanism by selecting various materials and structures. Thereinto, current density transforms to drive voltage according to corresponding current density standard. Simulation results indicate that metal/insulator barrier and insulator thickness play key roles in determining drive voltage and nonlinearity of the tunneling selectors. Specifically, metal/insulator barrier influence drive voltage and nonlinearity, while insulator thickness mainly influence drive voltage. Thus it can help comprehend restrictions of tunneling mechanism and attempt other improvement directions.