Silicon field emitter arrays with low capacitance and improved transconductance for microwave amplifier applications

Abstract

We report here on DC and RF measurements of electron field emission current obtained from silicon field emitter arrays (FEAs) containing more than 1000 tips. The field emitters in these FEAs have the form of 4 μm tall cylindrical columns where the tops of the columns were sharpened into points having radii of curvature estimated from TEM analysis of similar devices to be less than 100 Å. With a gate bias voltage of about 120 V DC, emission currents of approximately 2 mA have been collected at the anode. This collector current, corresponding to about 2 μA per tip, is in the acceptable range suggested in the literature for RF amplification in the GHz frequency range. RF modulation of the collected current at 1 GHz has been measured from these structures and the data are presented. As a result of placing the field emitters on tall columns, the parallel-plate capacitance between the cathode and gate electrodes of these FEAs has been decreased to under 2 fF per emitter tip. The magnitude of the input impedance at 1 GHz is about 30 Ω, which is a reasonable match to the commonly used 50 Ω instrument impedance. The RF measurements of collected current, input power, and device input impedance are consistent with the current and voltage measurements at DC, thereby giving credence to the design of vacuum microelectronic microwave amplifiers using this type of silicon FEA. From these results we believe that RF power gain in the GHz regime is attainable with vacuum microelectronic triode and tetrode structures by scaling up the size of these low-capacitance, high-transconductance silicon FEAs.