Nanogaps Mediated Field Effect-Controlled Field Emission Triode

Nanogaps can serve as electron transport channels in field emission devices, enabling scattering-free electron transport and high-performance nanoelectronics. Here, we demonstrate a field effect-controlled field emission triode that combines field-emission and ballistic electron transport in nanogaps. The device comprises three two-terminal nanogap structures formed by two symmetric metal-oxide-semiconductors (MOSs) that share the same n-Si substrate but are separated by a nanoscale etched trench. The device has three terminals because one nanogap is in the lateral direction between the top metal electrodes of the MOSs as Al/≈50 nm nanogap/Al and is connected to two nanogaps in the vertical direction as Al/≈100 nm nanogap/n-Si. By exploiting the benefit of a field-effect MOS capacitor in conjunction with the effects of field enhancement and a reduced potential barrier at the metal–air interface, the device exhibits a clear and well-defined triode feature with a back gate voltage controlling electron emission current in nanogaps. Due to an asymmetric cathode and anode, the vertical nanogap exhibits rectifying characteristics of an electron emission current with a transition from space-charge-limited emission at a low bias voltage (<0.5 V) to field emission (Fowler–Nordheim) current at a higher bias voltage (>0.5 V). In contrast, the lateral electron current between top metal electrodes is bidirectional with ballistic electron emission and transport that is independent of the gate field effect. The presented nanoscale vacuum triode combines two-electron emission sources, up to 104 A/cm2 from the vertical current and 103 A/cm2 from the lateral current. Thus, a nanogap device may facilitate the development of a low-power, high-speed vacuum logic technology.