| A growing interest in vacuum microelectronic field emission device (FED) research continues to be fueled primarily by the promise of flat cathodoluminescent display applications exhibiting high resolution, brightness, and wide viewing angle. In order to take full advantage of the performance features of FEDs many of the proposed applications will employ an electrostatic focusing lens as an integral part of the electron emitter structure. Electrostatic aperture lens methods have been previously reported and some of the fundamental, symmetric lens systems have been characterized. However, it is suggested that there remains some opportunity to further improve FED performance through continued development and characterization of the aperture lens. In this work a number of electrostatic lens focusing systems employing the axially symmetric non-coplanar aperture lens technique with arrays of FEDs are described and studied. Dual-aperture and three-aperture lens systems are found to provide improved focusing performance with significantly reduced aberration. Considering practical fabrication constraints, simulations for multiple-aperture lens systems have been performed wherein each focusing element is realized with an aperture radius greater than that of the associated FED gate radius. Focusing performance is found to be least sensitive to process variation, while gate extraction voltage, emitter/gate geometry, and emitter current variations are each found to impact the electron beam profile more significantly than do process variations. Spindt-cathode FEDs with material properties associated with refractory metals such as molybdenum and tungsten are assumed in the simulation of the structures. However, the results obtained are, in general, applicable to other material systems such as silicon, diamond-like carbon, or compound semiconductor. For a typical dual-lens configuration, FEDs with gate aperture diameter of 1.0 μm and a lens diameter of approximately 1.75 μm, a collimated electron beam of approximately 2.0 μm cross-section was achieved. The three-aperture lens emitter system was shown, via simulation, to provide a collimated electron beam of approximately 1.2 μm cross-section. Based on our present work, we propose that the multiple aperture electrostatic lens may be suitable to achieve the demands of high resolution, cathodoluminescent display applications. |
