Microstructural control of aluminum/aluminum oxide electrochemistry: Aluminum/aluminum oxide photonic devices.

摘要

An electrochemical process which automatically patterns and forms ring electrodes and interconnects while simultaneously burying the electrodes in a thin sheet of aluminum oxide has been demonstrated. Without the assistance of photolithographic patterning or etching techniques, anodization (in 0.3 M oxalic acid at 50 V and 15°C) of aluminum foil (which has previously machined microcavities 50--250 microm in diameter), results in an aluminum oxide film in which an electrode encompasses each microcavity, and planar interconnects between adjacent microcavities are developed. Modulation of the geometry has been achieved by controlling the arrangement of microcavities and the anodization duration, and with in-situ monitoring of the anodic current. Growth stress in the vicinity of a microcavity plays an important role in developing this self-formed buried ring electrode and interconnect. A maximum growth stress of 10.8 GPa was evaluated from the measurement of the porosity of anodic aluminum oxide.;In addition, novel electrochemical fabrication techniques for large scale microcavity arrays and three dimensional microstructures have been developed. Modified anodization processes produce microcavity arrays with controlled cavity inner-wall shapes which are adjustable from vertical to parabolic on the patterned aluminum foil. Anodic current exhibiting unique characteristics is used not only as an in-situ monitor but also as a predictor of the resulting geometries. As an alternative electrochemical etching process, controlled, self-limiting electrochemical etching (in a perchloric acid and ethanol mixture at 30V and 0°C) has been developed. This renders not only control over microcavity geometries from linear (taper) to parabolic, resulting from the diffusion limiting process of electrolyte, but is also faster than the anodization initiated microcavity formation method. The controllability of structural dimensions (such as the top and bottom aperture diameter) with a uniformity of ∼ 3% has been obtained. Finally, a microchannel structure with complex electrode geometries has been fabricated with a high aspect ratio (depth/width) of 2. A minimum channel width and maximum depth have been observed at 40 microm and 80 microm, respectively, with a highly vertical sidewall.;Based on these electrochemical processes, several different types of microcavity plasma devices have been demonstrated for photonic applications, including the stress-free bridge type microcavity plasma devices, a fully addressable microcavity plasma device, and a microchannel plasma device with complex electrode geometries. These microplasma devices exhibit a uniform glow discharge in confined microcavities or microchannels with intense luminance in various rare gases, such as Ne and Ne/Xe mixtures. They produce emission spatially uniform within +/- 5%, an ignition response time of 10 micros for a 20 kHz sinusoidal excitation and 250 ns for a pulsed, unipolar excitation having a temporal width of 4 micros and a frequency of 100 kHz.;The fully addressable microcavity plasma device, fabricated by the combination of modified electrochemical etching and anodization, is the first to be demonstrated. Intense luminance and luminous efficacies approaching 1800 cd/m2 and 4 lm/W, respectively, have been observed for 50 x 50 to 320 x 160 arrays of microplasma devices with parabolic cross-sectional microcavities and conformal aluminum electrodes, operating in Ne/Xe gas mixtures. In addition, a microchannel plasma device with complex electrode geometries have been fabricated in a single sheet of aluminum foil with an active area of over 30 cm 2. Power consumption as low as 0.8 W with a luminance of 500 cd/m 2 has been observed in 600 Torr of Ne. These devices are promising for advanced displays and backlighting technology.