Miniaturized large current GaN-based nanogap device for millimeter-wave systems

In the post-Moore era, conventional solid-state electronic devices face increasing limitations in high-frequency operation. Although traditional vacuum electronic devices offer excellent high-frequency and high-power capability, their large size makes them incompatible with modern requirements for miniaturization and integration. This work explores a micro-/nanoscale vacuum electronic device based on a gallium nitride vacuum field-emission diode with a vertical structure. A fabrication process compatible with conventional photolithography, plasma-enhanced atomic layer deposition, and reactive ion etching is developed, avoiding the use of costly electron-beam lithography. Electrical measurements under different ambient conditions demonstrate stable field-emission behavior. In atmospheric measurements, the device delivers current in the order of hundreds of μA at 5 V, while under high vacuum (10−5 Pa), the output current increases to about 10 mA at the same bias. To describe the device behavior, a symbolically defined device model and a small-signal equivalent circuit model are established. Based on the extracted nonlinear field-emission resistance and capacitance terms, the RF potential of the device is analyzed using an RC-based framework. The analysis further separates the intrinsic and extrinsic capacitance contributions, showing that the local emission region can in principle support a much higher intrinsic cutoff frequency limit than that of the present full device structure. The overall high-frequency performance is found to be mainly limited by parasitic capacitance associated with the surrounding macroscopic layout. These results provide both a device platform and a modeling framework for the further optimization of GaN-based vacuum nanoelectronic devices toward high-frequency applications.