Carbon Nanotube Metal Cathode for Microwave and mm Wave Device

Abstract

Summary form only given. Field Emission cathode possesses certain advantages over the rmionic emission cathode: smaller FWHM of emission energy, smaller size, no need for filament heating power supply, an d possibility of higher pulsed current. The small field emission energy spread and small size are particularly important as frequency goes up into mm, sub-mm or THz regime in devices like Clinotron or Orotron, where a sheet beam interacts with periodic grating at inclined or parallel trajectory. Carbon nanotube (CNT) has been known for its field emission property. We present a new method to make CNT cathode by hot-bonding CNT with BGA balls on metal surface. This method differs from the spray or print approach in the past, and delivers better adhesion capability in high field. Turn on field (at 1 muA/cm2) as low as 1 V/mum has been achieved, field enhancement factor beta reaches 3900, and dynamic resistance is about 1.28 MOmega at current below 1 mA. Four 0.5 mm2 emission sites emit 0.1 mA current at 400 V bias with 200 mum cathode-anode distance. Current increases as BGA density multiplies. This cathode can be made into various shapes, and defective ball can be repaired through reflow process. Spatial uniformity of emission sites can also be achieved with special emission site shielding structure at the expense of applied field.