Hardened Planar Nitride Based Cold Cathode Electron Emitter

Low threshold electron emission from planar AlN/Silicon heterostructures is reported. The surface emitting ballistic electron structure consisted of an undoped AlN layer grown on Silicon by Molecular Beam Epitaxy, a Ti/Au Ohmic contact, and a thin Pt Schottky contact fabricated by e-beam deposition. Tunnel-transparent Pt Schottky contact was deposited on a 1 mu m thick Silicon Dioxide (SiO2) layer and covered a 4 x 4 matrix of 50 mu m diameter via produced in the SiO2 layer using photolithography The measurements were performed in vacuum (similar to 10(-8) Torr) using a metal grid separated from the structure by a 60 micron thick Kapton (R) polyimide film having an opening aligned with the via. Bias voltages in the range of 0-130 V were applied across the Schottky diode, while currents were recorded across the structure for grid voltages ranging from 0 to 50 V. The field emission nature of the measured currents was confirmed by plotting the Fowler-Nordheim dependence. Current density of at least 2.5x10(-4) A/cm(2) was achieved for a grid voltage of 50 V and a bias of 130 V. Degradation of the structure performance was observed at bias voltages exceeding 90 V as a result of Schottky barrier modification under the elevated temperature and high electric field operation. The solid-state electron emitting structure indicated a threshold field as low as 0.2 V/mu m under applied grid voltage of 12 V.