![]() The cathode is bent downward so that the emitting surface is facing the gate. The gate, cathode and anode terminals are artificially colored for better view and contrast. 1b shows a TEM cross-sectional view of the fabricated device. ![]() While 120 nm SiO 2 was removed in the vertical direction, the same amount of SiO 2 underneath the cathode was also removed laterally because of the isotropic nature of wet etching.įig. The etch process was controlled by time to ensure exposing the bottom n + silicon surface. 10 : 1 diluted HF was used for isotopically etching the sacrificial SiO 2. Finally, the sacrificial SiO 2 was removed to complete the device fabrication (step iv). Then, the top electrode W was patterned over the rounded region (step iii) and as a result, the downward edge became sharp. At this point, the conformal film deposition makes the downward curved W over the n + polySi corner. Tungsten is the cathode and SiO 2 is in part the spacer between the cathode and the anode, and in part the sacrificial layer to create the vacuum channel. Silicon dioxide (SiO 2) and tungsten (W) were blanket deposited subsequently (step ii). The n + polySi is the anode and the SiN layer is the spacer between the gate and the anode. Silicon nitride (SiN) and in situ doped n + polySi films were subsequently deposited, followed by patterning (step i in Fig. The phosphorous was heavily doped ( N d = 1 × 10 20 cm −3) on the wafer and this wafer surface becomes the gate. A 150 mm p-type silicon wafer was used as the starting material. ![]() 1a shows the process steps for the fabrication of an umbrella type inverted vertical field emission gated diode (VFEGD). The fabrication details and the measured device characteristics are provided and complemented by multi-physics simulations to gain insight.įig. Second, the gate is separated from the source (or the cathode) farther than the drain (or the anode), which results in great reduction of the gate leakage. Inherent deposition and etching process steps alone allow producing the sharp cathode without any additional dedicated processes to sharpen the corner. First, an innovative fabrication approach makes the cathode have an umbrella-like shape with a sharp-edged rim. The device features an inverse vertical channel with two major distinctions. In this work, a gated diode structure with a 100 nm anode–cathode gap is experimentally demonstrated. 9–11 Their study showed an exponential increase in current as the gap is decreased without showing any signs of current saturation even down to 10 nm this information is valuable in the design of more complex VFETs. systematically studied the impact of the anode–cathode gap on anode current in the range of 10 to 200 nm for three cathode materials of SiC, VO 2 (A) and Cu. anode current, impact of material quality on field emission, emission uniformity over the cathode area and many other factors with minimal fabrication efforts. Besides having their own applications, vacuum diodes can be used to optimize several important design, operation and reliability criteria such as channel gaps vs. 8 There have been a large number of studies 4,9–13 focusing on vacuum diodes with nanoscale gaps as these are easier to fabricate and provide a preliminary understanding of the emission characteristics prior to undertaking complex VFET fabrication. 1–5 The nanoscale vacuum field emission transistors (VFETs) have been used for the construction of circuit elements including inverters 6 and adders 7 for various applications, and even complementary device operation has been proposed for the first time in vacuum electronics to enable low power logic circuits. Recently efforts have been made to aggressively miniaturize vacuum electronic devices at the nanoscale with the aid of conventional integrated circuit manufacturing practice. In addition, the operation voltage is 100s of volts and cannot be scaled down due to their large size. The devices in most of these applications are made by machining and not amenable for miniaturization. Vacuum electronic devices have a broad set of applications including traveling wave tubes, klystrons, X-ray generators, free electron lasers, field emission displays, radio frequency power sources, miniaturized mass spectrometers, vacuum gauges, and charge neutralizers.
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