June 26, 2022
Digital Tunneling Magnetoresistance (TMR) Sensors
Digital Tunneling Magnetoresistance (TMR) Sensors


TDK’s TMR sensors are a new type of magnetic sensors using a TMR element, which is a highly sensitive playback element of an HDD head. The read elements of HDD heads are based on the magnetoresistance effect, which refers to a resistance change induced by the application of an external magnetic field. Since the 1980s, they have promoted a significant improvement in the recording density of HDDs while evolving into AMR (anisotropic magnetoresistance effect) elements, GMR (giant magnetoresistance effect) elements, and TMR (tunneling magnetoresistance effect) elements.

Magnetic sensors based on tunnel magnetoresistance (TMR) effect feature high sensitivity, small size, and low power consumption. They have attracted a lot of attention and have potential applications in various fields. This study first presents the development history and the basic principles of TMR sensors. A comprehensive description of the linearization of TMR sensors and the Wheatstone bridge configuration is then presented. Two key performance parameters, field sensitivity and noise mechanisms, are considered. Finally, the emerging applications of TMR sensors are discussed.

In this thesis, the design and microfabrication of a tunnel magnetoresistive (TMR) electric current sensor is presented. After its physical and electrical characterization, a wattmeter is developed to determine the active power delivered to a load from the AC 50/60 Hz power line. Experimental results are shown up to a power load of 1000W. A relative uncertainty of less than 1.5% for resistive loads and less than 1% for capacitive loads was obtained. The application described is an example of how TMR sensor technology can play a relevant role in the management and control of electrical energy.