High-density gated field-emitter arrays

Summary form only given, as follows. We have developed a process based on laser interferometric lithography that can pattern an array of gated Mo cones having 0.32-/spl mu/m tip-tip spacings, 0.08-/spl mu/m gate-tip spacings, and tip radii of 5 nm. These are the smallest dimensions and highest density for such cone arrays reported. This geometry offers substantial advantages for achieving lower gate operating voltages, higher transconductance, and higher frequency operation. Numerical simulations of our cathodes operated in a microtriode configuration have shown that values of unity-current-gain frequency (f/sub T/) above 10 GHz can be obtained using refractory emitter materials such as Mo and ZrC which have work functions between 3.0 and 5.0 V. Lowering the effective work function to 1.0 V or below by using surface treatments of Cs or similar materials is predicted to provide f/sub T/ values above 100 GHz. Experimentally, our gated cone arrays have demonstrated record turn-on voltages as low as 17 V (uncesiated) and 6 V (cesiated). Cesiated devices have shown an emission current density as high as 1600 A/cm/sup 2/ averaged over the array. The gate voltage at this current density was 40 V. In addition, RF modulation of the emission current in these devices has been demonstrated at 1 GHz, an important milestone in transitioning this technology to microwave operation. At present, we are collaborating with a number of other organizations under the Vacuum Microelectronics Initiative to realize an X-band klystrode using gated field-emitter cathodes. Progress in this effort will be described.