Ballistic Electron Surface-Emitting Cold Cathode by Porous Polycrystalline Silicon Film Formed on Glass Substrate

It is demonstrated that a porous polycrystalline silicon (PPS) film is useful as a ballistic electron emitter for excitation source of a flat panel display. A 1.5 µ m polysilicon layer is deposited on a silicon substrate by Low Pressure Chemical Vapour Deposition (LPCVD) technique and subsequently anodised in an ethanoic HF solution and oxidised in a Rapid Thermal Oxidation (RTO) furnace. A thin Au film is deposited onto the RTO-treated PPS layer and used as a top electrode. The electron emission current Ie and the diode current Ips are measured as a function of the bias voltage Vps. Electron emission of which onset voltage is about 8 V rapidly increases with increasing Vps. The Ie value reaches about 2 mA/cm2 for Vps= 20 V at which the emission efficiency defined as Ie/Ips is about 1 %. The emission mechanism has also been investigated in terms of the correlation between the emitted electron energy and the structure of PPS layer. The observed energy distribution curve of output electrons suggests that the PPS layer acts as a ballistic transport medium and the emission occurs based on multiple tunnelling through silicon nanocrystallites. The PPS layer is also formed on the polysilicon layer deposited on a glass substrate by Plasma Enhanced Chemical Vapour Deposition (PCVD) technique. In this case, the film is treated by an electrochemical oxidation (ECO) in an H2SO4 solution. Similar emission characteristics are observed, although the emission current is lower than that formed on silicon substrate. We also demonstrate the 2.6 inches diagonal 53×40 pixels multicolour flat panel display. We name it ballistic electron surface-emitting display device (BSD). BSD shows the possible application to the future flat panel display.