Magnetic Sensors: From Ultrathin Film Growth to Sensor Integration in Unexpected Systems
Nanoelectronics combines physical principles of materials with the impressive capability of engineering ultra-small devices at the nanoscale. Magnetic field sensors—in particular, magnetoresistive (MR) sensors—were driven by the technological push from computers and information storage in the early 1990s. Currently, they have a mature and broad level of implementation in the market, from automotive to biomedical domains. In this talk, I will first introduce key concepts in spintronics and highlight the physical mechanisms defining sensor performance and the figures of merit for the classification of outstanding MR sensors. The impressive technological progress in thin film preparation and characterization, combined with nano- and microfabrication tools, offer a large spectrum for device design. The materials discussed include several varieties of thin films: oxide films as tunneling barriers, ultrathin amorphous and crystalline films, ultrathin textured layers with grain size control, magnetically soft layers, and antiferromagnetic films, all combined onto multilayer stacks, typically thinner than 60 nm in total. In addition, the noise mechanisms (the “killing factor” that limits MR sensor performance) will be discussed, and I will show successful strategies for improving the signal-to-noise ratio, which determines the ultimate field detectable by an MR sensor.
Examples where spintronic sensors are useful tools for precision sensing will be provided, including integration with microfluidics, optical, and micro-electromechanical micromachined actuators. Detection principles, sensor design, simulations, and experimental validation will be discussed for exciting applications where MR sensors bring added value over competing technologies. I will show how challenging applications have inspired creative solutions, requiring joint skills in physics, materials, electronics, and mechanical engineering. I hope that academics and engineers will be encouraged to propagate their expertise in magnetism to the young, talented people we see every day, and so promote innovation in future spintronic sensors.