Study of Surface Conduction Electron Emission Devices for Flat Panel Display Technology

• Main Authors: Tsai, Chih-Hao, 蔡志豪
• Other Authors: Pan, Fu-Ming
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/86499395961816405633

博士 === 國立交通大學 === 材料科學與工程系所 === 97 === In this thesis, we present a simple, highly controllable, and scaleable method to produce nanogaps by palladium hydrogenation. Experimental results and theoretical analysis are conducted to investigate the field emission properties of the surface conduction electron emission (SCE) emitters, in terms of the I-V curve、field emission efficiency and field emission stability. We used undertake various approaches to improve field-emission characteristics of the Pd nanogap SCE device, including optimization of hydrogenation conditions, nanogap structure optimization and hydrogen plasma treatment. Nanometer-scale gaps in Pd strips were obtained by hydrogen absorption under high pressure treatment. The resulting lattice constant increase due to the Pd phase transformation from the α-phase to the β-phase after hydrogen absorption is accompanied by a volume expansion of ~ 12 %, resulting in a large compressive stress in the Pd thin film. With proper geometric arrangement of the Pd electrode within the SCE emitter structure, a single nanogap per SCE device was obtained at 25 oC. The large stress induced by phase transformation during the Pd hydrogenation resulted in a nanogap in the Pd line electrode at the step area over the Pt/Ti contact pad in the SCE structure. Electron conduction properties of the hydrogenated SCE device were studied, and a turn-on voltage of 41 V for the SCE emitter with a 25 nm nanogap was obtained. The gap width was a function of not only Pd hydrogenation conditions but also the dimension of the SCE structure. Finite element analysis was use to study the stress distribution in the SCE structure with the Pt/Ti contact pad of various thicknesses so that an SCE structure with a minimized gap width could be obtained. Among the SCE emitters under study, the optimal SCE structure, which was with a Pt/Ti contact pad thickness of 20 nm and had a Pd nanogap width of 18 nm, had the best field emission performance in terms of the field emission current and turn-on voltage (~30 V). For comparison, a focused ion beam (FIB) was used to prepare a single nanogap in a conventional SCE emitter which had smooth gap edges. Compared with the conventional SCE emitter, the hydrogenated SCE emitter demonstrated a much higher emission efficiency (~4%). We ascribed the better electron emission performance of the hydrogenated SCE emitter to that the cathode had a rugged and tilting protruding structure on the nanogap edge. The study demonstrates that the Pd hydrogenation is an ideal method to fabricate Pd nanogaps in SCE emitters for surface conduction electron emission display (SED) applications. To study the effect of the hydrogen plasma treatment on field emission properties of the nanogap emitter, a planar nanogap was also prepared on a Pd line electrode by FIB. After the hydrogen plasma treatment, the field-emission property of the Pd nanogap emitter was significantly enhanced. The improvement in the field-emission property was mainly attributed to formation of a ragged morphology on the nanogap emitter during the hydrogen plasma treatment. The ragged morphology provided more emitting sites with a high field enhancement factor. Aside from creating new emission sites, the increase in film roughness could significantly reduce the work function of Pd nanogap emitter, thereby improving field emission efficiency.