Our previous work also precisely fabricated sub-30 nm aligned nanogap arrays with a well-controlled process. With superior on/off current ratio and low working voltages, the graphene NVCT are expected to be applied in severe environments such as electromagnetic radiation or extreme temperature. successfully fabricated a graphene-based vacuum transistor with better electrical performance than those graphene-based solid-state transistors. In order to enhance the gate controllability, they further fabricated a surround-gate NVCT consists of sub-50-nm vacuum channel, and the device was proven to stand against ionizing radiation (proton and Gamma ray) and high temperature (200 ☌). demonstrated a back-gate vacuum nano-channel transistor with standard silicon semiconductor processing, showing high-frequency switching characteristics with negligible leakage current. Recently, planar-type vacuum transistors with nanogap channel have been fabricated with traditional semiconductor processing. Compared with up–down structure, the planar NVCT are more prospective for future integration as the nanogap is variable with mask layout, including electron beam lithography (EBL), focused ion beam (FIB), or nanoimprinting. However, the vertical structure could hardly be compatible with CMOS process. Researchers have proposed different types of vertical NVCTs, where the electrons could emit directly out of plane, e.g., the slit-type vacuum transistor, or the Spindt-type NVCT. For instance, the vertical structure was widely utilized in the traditional vacuum electronic devices. The development of manufacturing technology can open up enormous opportunities for creating nanoscale vacuum channel, which might be compatible with modern integrated circuit (IC).Īs a result, many attempts have been made to downscale the vacuum channel into nanogap and construct three terminal junctions. More importantly, the NVCT is proved to retain the advantages of the traditional vacuum tubes that operate normally in the extreme conditions, like exposure of ionizing radiation or high temperature. Thus, the nanoscale vacuum channel transistors (NVCTs) may output high frequency, on/off ratio, or fast temporal response with low working voltage. And the vacuum nano-devices could be compatible with standard silicon process and combine the advantages of ballistic transport with miniaturization and integration. Intrinsically, electrons could ballistically travel through the nanoscale vacuum channel while suffering from collision or scattering in the semiconductors. Also, intrinsic graphene-based FETs were found to have an on–off current ratio less than 10 due to the lack of a bandgap, which are not suitable for modern integrated logic circuits. For conventional field effect transistors (FETs), the carriers may collide with the optical and acoustic phonons during the transport.
Distinct from the early vacuum tubes with high-power consumption and difficulty for high integration, the nanogap structures are more prospective for the modern nanoelectronics. Among these prominent issues, transistors composed of nanoscale vacuum channels or known as the nanogap have been steadily attracting attentions. As the traditional Si-based technology gradually reaches the minimize limitation, many efforts have been made in the novel nanostructures or low-dimensional materials.
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