Boron Nitride Emitters
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[email protected] tSarnoff Corporation, Princeton NJ, 08543 ABSTRACT New observations are presented on the emission of electrons from n-type boron nitride (BN) cold cathode films. These carbon-doped BN films demonstrate a significant improvement in the electron emission current, on the order of 1 to 3 orders of magnitude, as a function of the extraction field for many different materials and morphologies. These BN cold cathodes have yielded stable DC currents in excess of 4 mA at an extraction field of approximately 30 V/ýsm. INTRODUCTION Stable, reliable electron emitting materials are needed for a diverse collection of high and low current applications. Such applications include display products, microwave amplifiers, e-beam induced light sources, arrays for lithography, etc. At present, Spindt-type emitters fabricated from refractory metals and silicon are typically the emitters of choice. Such devices have been widely investigated [1]. In addition to such gated devices (triodes), planar emitters (diodes) fabricated from wide band gap semiconductors such as polycrystalline diamond and diamond-like films are increasingly being explored because of their potential for high electron emission, low cost, and large deposition area. Some of these cold cathode materials are considered to exhibit negative electron affinity (NEA). Such NEA materials will, at least in theory, prove to be the best electron emission sources. In addition to the diamond and diamond-like films, BN [2-4], CN [5-6], GaN [7], and others are NEA emitter candidates. It has been shown that laser ablated, laser annealed, carbon-doped BN deposited on n-type polycrystalline diamond forms a good cold electron emitter [8]. Current densities of >3A/cm2 have been obtained using a 0.5mm diameter flat tungsten extraction electrode and that emission was uniform to a pressure of about lxlO4 Torr. In comparison, refractory metal, gold, and silicon emitters start to degrade at about lx10'- Torr [9]. In this paper, the results of the comparative emission testing of carbon-doped BN films s ynthesized by this technique on several elementally and geometrically different substrates are presented. This type of BN film shows a consistent improvement in the emission current for all substrates explored thus far, independent of the material and the geometry. Reactive Magnetron Sputtered BN is also expected to be low cost and easy to scale for large area deposition. Cold Cathode Film Synthesis: Reactive Magnetron Sputtering (RMS) The technique used to synthesize these carbon-doped polycrystalline BN films on the various substrates was Reactive Magnetron Sputtering (RMS). The chosen substrates were loaded into the deposition system as shown below (Fig. 1). Once the synthesis chamber was evacuated and the substrates heated to temperature (-450 C), the substrates were exposed to an atomic hy113 Mat. Res. Soc. Symp. Proc. Vol. 509 ©1998 Materials Research Society
drogen plasma etch (-10 min.) to remove any residue that may have formed during the loading / pump-down / heat-up
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