Surface Treatment Effects on the Electron Emission Characteristics of Ultra Thin AIN Coated Molybdenum Tips
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ASTRACT Although plasma surface treatment has proven useful for both metal and diamond field emitters, there is at this time no study of the effect of plasma treatment on the field emission from a thin layer of AIN. In this study a 7 nm film of AIN deposited on a molybdenum emitter tip was treated with different plasmas (H 2, 02, and N 2). All surface treatments and measurements were carried out by using an in-situ technique inside the magnetron sputtering chamber. Changes in the measured I-V curves were not observed from the emitter after treatment with either hydrogen or nitrogen plasmas, but were observed after oxygen plasma treatment. In addition, it was found that a very thin coating of aluminum over the AIN further enhanced the emission characteristics. We propose that the lowering of the surface barrier is due to the electronegativity difference of the species forming the surface layer.
INTRODUCTION Since wide band gap materials generally have high melting points, high thermal conductivity, low electron affinity, and are chemically inert, they have been considered as coating materials for gated and ungated field emitter tip arrays'. When coating sharp emitters, major factors to be considered are the coating thickness, and the surface condition of the coating 2.3.4. However most of the previous studies are focused on diamond and carbon related materials 2 4.,5 6. There are only a few studies on AIN 7'8' 9,'0 , and these show emission characteristics similar to diamond. At this point, there is no study related to the effects of surface treatment on emission from AIN coatings. The purpose of this study is to investigate systematically surface treatment effects on electron emission from ultra thin AIN coated Mo tips. This is accomplished by using an in-situ I-V measurement technique that allows repeated deposition and measurement on the same metal tip without exposure to the atmosphere.
EMITTER TIP PREPARATION, AIN DEPOSITION AND CHARACTERIZATION Molybdenum field emitters were fabricated using an electrochemical method of polishing in KOH solution2 . The typical radius of curvature of the tips was approximately 100nm. Before AIN deposition Mo tips were treated with an argon plasma for a minute to remove any possible surface contamination. An ultra thin AIN layer was deposited by reactive sputtering at 200 'C in the N 2/(N2+Ar) ratio of 0.75 for 15 seconds. The base pressure of the system was 3.5 x10 7 Torr. These conditions result in a smooth and continuous layer of AIN approximately 7 nanometers thick, as measured by TEM. A schematic drawing of the experimental setup for in-situ measurement and plasma treatment is shown in Fig 1. Details of the system and procedures can be found in reference 3. The
563 Mat. Res. Soc. Symp. Proc. Vol. 558 ©2000 Materials Research Society
AIN coated emitters were treated sequentially with a hydrogen plasma, an oxygen plasma, and another hydrogen plasma within the deposition chamber. The effect of nitrogen plasma treatment was studied with another Mo emitter coated with AIN u
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