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.
Effects of gases on field emission performance were measured using silicon-gated field emitter arrays. Gas was injected into a vacuum chamber with a 1000 × 1000 tip array, which was driven by a DC gate and collector voltages. The collector voltage was fixed at 200 V while the gate voltage was swept to 40 V. For the gas exposure study, N2, He, and Ar were used. The sets of partial pressures, 5 × 10−6, 5 × 10−5, and 5 × 10−4 Torr, were used for the experiment. It was observed that N2 had the least effect and Ar had the worst effect on emission current performance. The degradation of collector current at 5 × 10−4 Torr pressure for Ar was ≈65% where for the N2, at the same level of pressure, the degradation was ≈41%. However, further experiments with high purity Ar gas showed that it was the water vapor present in the gas itself that was the primary cause of reduction in emission current and not the gas itself. The results expressed in reduction in emission current versus Langmuir exposure versus the current clearly showed the effect of water vapor. After the vacuum was recovered, the work function again restored partially to its original value. After ultraviolet light cleaning, the emission current was restored completely to the original state.
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