Student Name: Mr. Kumaran Narasimhan
Date/Time: 7th August 2025 / 02:30 PM-03:30 PM
Research Supervisor : Prof. Anil Kumar P S and Chair of IAP Prof. Sanjiv Sambandan
Venue: S V Narasaiah Auditorium, IAP Department
Title: Planar Hall Magneto-resistive Device for Angle Position Sensing
Abstract: This study investigates rotary position sensors, emphasizing the importance of core sensing technology for both performance and cost-effectiveness. While Giant Magnetoresistance (GMR) and Tunnel Magnetoresistance (TMR) technologies offer high sensitivity and compact designs, their long development cycles and calibration needs make them impractical for those with existing AMR manufacturing capabilities. Hall effect-based solutions meet most industry needs, but high-precision applications still require advanced magneto-resistive solutions. The present research proposes a fusion of Anisotropic Magnetoresistance (AMR) and Planar Hall Magneto-resistive (PHMR) technologies to balance performance and affordability. The AMR sensor provides robust, non-contact angle sensing but is limited by its uniaxial anisotropic nature, which hinders 360° angle detection. To address this, a bilayer PHE sensor incorporating ferromagnetic and antiferromagnetic layers is proposed, enabling pole sensing and reducing reliance on rare-earth magnets. This design lowers the operating field to around 100 Oe and allows monolithic integration into the CMOS substrate.
The thesis begins by differentiating magnetic sensors from other types, exploring various magnetic sensing technologies, their applications, and general signal conditioning circuits. It explains the differences between AMR and PHE in magnetic field sensing and the role of antiferromagnetic materials in achieving 360° angle sensing. The study covers material selection, existing device structures, and their capabilities.
A comprehensive overview of MEMS fabrication and characterization techniques is presented to develop and validate the AMR and PHMR sensor. The research highlights processes like lithography, ultra-thin film sputtering, ion-beam etching, e-beam evaporation, dicing, and wire bonding. Techniques for continuous film deposition and magnetic annealing of samples are discussed. A demo set-up for demonstrating sensor properties using a desktop oscilloscope has also been developed.
A custom-built rotating field generating test set-up for sensor performance verification is detailed, including components like two-axis field coils, power supplies, data acquisition hardware, and Python-based software for current control and sensor output reading. The design of the coil using FEM tools and the development of 3D printed fixtures for sample verification and calibration are explained.
The enhancement of exchange bias in bilayer NiFe/IrMn films is explored, focusing on material selection, thickness calibration, and magnetic characterization. The study defines the optimal combination of layers for higher exchange bias after magnetic annealing and compares observed properties with existing publications.
The final chapter discusses device development using ECAD software Clevin, detailing the four distinct layers: PHMR, AMR, Metallization, and encapsulation. The verification of device resistances, bridge performance, and characteristics with increasing field is presented. The transition from 2π to π periodicity and the PHMR characteristics are analyzed, concluding with sensitivity measurements at Earth’s magnetic fields compared to published results.
Further scope of studies and enhancements to the angle sensors are discussed at the end of the thesis.