Ion Beam Milling for Structuring of Tunnel-Magneto-Resistance Sensors

The tunnel-magneto-resistance effect (TMR) is used in modern high-precision sensors ranging from angular position sensors in the automotive industry to read-out sensors in the hard-disk-drive industry. Compared to standard giant-magnetoresistance (GMR) sensors, TMR sensors have higher thermal stability and higher signal output while reducing power consumption. These advantages lead to a rapidly growing market for TMR sensors. However, the multilayer composition of the TMR sensor causes issues regarding the necessary etching, which is essential for electrical contacting of the sensor. Classical dry-etching methods are limited due to the generally poor reactivity of magnetic materials, like CoFe, CoPt or NiFe. Additionally, required reactive gases, such as chlorine, can cause aftercorrosion of the sensor electrodes.

In this White Paper, the authors Robert Rückriem, Stefanie Rumbke, and Enrico Loos demonstrate that high-quality tunnel-magneto-resistance (TMR) sensors composed of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) can be produced by using ion beam etching to structure the layer stack with a scia Mill 200. You will also receive background information on MTJ functionality, sample preparation, and the ion beam etching process.