Load line analysis showing AIE used to calculate the current sensitivity for field emitter tips with radius r 1 < r 2 < r 3 (blue lines) in series with (a) small or large resistor, (b) FET or nanowire, and (c) FET or nanowire with reduced tip radius distribution (red lines).
Silicon gated field emitter arrays have been used as a vacuum transistor to demonstrate a 152 kHz Colpitts oscillator. The transfer and output characteristics of the 1000 × 1000 silicon arrays were measured using a collector placed ≈ 1 mm away with a gate voltage up to 40 V and a collector voltage up to 200 V. The data were used to establish an LTspice transistor model based on a field emission tip model and a collector current model that fit the characteristics. Then, the LTspice model was used to design a low frequency Colpitts oscillator. Furthermore, experiments were carried out to successfully demonstrate the oscillation. Oscillation frequency was 152 kHz with a peak to peak voltage of 25 V for a tip to ground series resistance value of 10 kΩ at 50 V on the gate and 210 V on the collector. Further, the oscillator was also tested at 50, 100, 200, 300, and 400 °C. It was observed that frequency shifts for each temperature which is due to the change in the overall capacitance of the test setup. This type of device could be used as a temperature sensor in harsh environments.
Out-of-plane focusing is essential for electron beam collimation in gated field emission sources. The focus electrode redirects electrons emitted by the tip with a wide angle towards the central axis, resulting a small focal spot at the anode. Here, we demonstrate for the first time, very high density (108 emitters/cm2) arrays of double-gated field emission electron sources with self-aligned apertures and integrated nanowire current limiters. Release of the emitters after fabrication required the combination of a highly selective dry-etch and an isotropic wet-etch to avoid the loss of the insulator between the two gates. The aperture diameters are ∼360 nm and ∼570 nm for the extractor gate and focus gate, respectively. The turn-on voltage was low (15-20) V and anode currents of 400 nA were measured at 25 V. We compared devices with different extractor gate thicknesses resulting from planarization non-uniformity, and demonstrate the influence of the focus gate on anode current. The focal spot size was measured, using a low energy phosphor screen, to be around 700 µm for a 500 µm device when the ratio was 0.35.
Silicon field emitter arrays (Si FEAs) are being explored as an electron source for vacuum channel transistors for high temperature electronics. Arrays of 1000 × 1000 silicon tip based gated field emitters were studied by measuring their electrical characteristics up to 40 V of DC gate bias with a 1.3 mA emission current at different temperatures from 25 to 400 °C. At ∼350 °C, residual gas analyzer measurements show that water desorption and carbon dioxide partial pressures increase significantly, the gate to emitter leakage current decreases by more than ten times, and the collector current increases by more than ten times. These improvements remained after heat-treatment but were then lost once the device was exposed to the atmosphere for several days. The improvements could be recovered upon additional baking suggesting that adsorbates (primarily water) on the surface affected field emission and surface leakage. It was also found that after heat-treatment, the electrical characteristics of the devices exhibited <3% variation in collector current at 40 V, which (without exposure to the atmosphere) can be termed as a weak temperature dependence. These results suggest that Si FEAs could be viable as a high temperature transistor.
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