Electrochemical Deposition of Magnetics Based Sensors

Abstract

Within the context of this thesis, advancements in sensor technology are driven in three separate applications. In each application electrochemistry is used as one of the primary fabrication steps, and magnetic phenomena are sensed in order to convey information about the different systems. The medical device industry is an area where various sensors are seeing increased use. Electromagnetic catheter tracking is an application that depends on high-quality magnetic sensors. The size of the sensor is a significant design constraint in catheters. Investigation of a microfabricated inductive sensor is pursued in chapter 4 of this thesis. High shape anisotropy inductive structures utilizing etched aluminum oxide as electroplating templates are investigated through first-order modeling and fabrication process development. Results show that the AAO is capable of producing high aspect ratio inductive structures though further development would be needed to achieve the consistency in etching required for large scale device fabrication. Biomimetic devices are another area of scientific interest where magnetics can play a role. Electroplated magnetic nanowires can act like large arrays of cilia. In chapter 5, biomimetic nanowire arrays are fabricated into microfluidic channels, and their movement sensed via a magnetic sensor. The nanowires provide a magnetic field that bends as fluid flows through the channel which enables a simple flow measurement through microfluidic channels. Similarly, a low frequency (>10Hz) vibration sensor is demonstrated utilizing a nanowire array above a magnetic sensor. Vibration of the sensor imparts momentum on the nanowires, which bend and leads to a time-varying field. In chapter 6, electrodeposition of Galfenol on a cylindrical surface is demonstrated for the first time. Galfenol has a large magnetostriction constant up to ~400 ppm. Utilizing a rotating cylinder electrode, the parameters to deposit Fe1-xGax films in the x = 15 to 35 range were found. The film's magnetostriction was then demonstrated as part of a torque sensor where magnetic anisotropy was controlled through texturing of the cylinder surface. The effect of magnetic shape anisotropy can be seen to play a significant role in the sensor's output by increasing the sensitivity of the sensor nearly 6x that of the non-textured film.