An Investigation of Anodic Aluminum Oxide for Electronic and MEMS Applications
In this dissertation, we have explored the use of a highly anisotropic film, porous anodic aluminum oxide (AAO) for electronic and MEMS applications. In the first part, AAO templates integrated with ferromagnetic material were studied for spiral inductors as a magnetic core. In the second part, the applications of AAO as a structure material, a mold for electroforming, and a sacrificial layer for MEMS applications were demonstrated.
There is a strong demand for high performance and quality spiral inductors for radio frequency integrated circuits (RFIC). For this purpose, ferromagnetic materials are integrated into the spiral inductors to improve their performance and miniaturize their size. However, spiral inductors with ferromagnetic cores suffer from poor performance at high frequencies due to ferromagnetic resonance effect and eddy current loss occurrence in the layer of ferromagnetic materials. Since AAO templates are self-laminated and patterned, these drawbacks are solved by integration of ferromagnetic materials into the nanopores of AAO templates. By using nickel electroplated AAO templates as a magnetic core, we presented 21% enhancement of inductance value at 5 GHz with a quality factor of 14.48.
High precision, high aspect ratio structures are needed for a variety of microelectromechanical systems (MEMS) applications. The most common technology for producing high aspect ratio structures for MEMS is deep reactive ion etching (DRIE). Despite the successes of the DRIE process for MEMS applications, it has several significant shortcomings which limit its adoption for many microstructure applications.
The DRIE process is expensive, time consuming, requiring expensive dedicated etching equipment, and primarily useful for etching structures in silicon, making it unlikely to be used for non-silicon applications. Other technologies, such as LIGA and SU-8 are highly specialized, and while they can be used for making simple structures, they are generally not useful for producing MEMS-like structures. Since AAO templates are highly anisotropic and can be prepared at various thicknesses, deep vertical structures with high aspect ratios can be formed by a simple low cost wet etching process. Various types of MEMS structures were fabricated by using this technique.