bservation on Magnetoresistive Sensor Elements

We investigate the domain behavior of different magnetoresistance sensor elements to optimize a sensor shape for high sensitivity applications. Some of the encountered re- manent domain patterns are analyzed using a novel quantitative magnetooptic observation technique. The center coercivity field and the saturation field of the elements were measured as a clue for stability and sensitivity of the sensor element. I. INTRODUCTION ENSOR elements based on the classical anisotropic magne- toresistive (AMR) effect are widely used in data recording, machine control, electric current measurement, and many other applications connected with the detection of small magnetic fields ( 11. They have a potential for extremely high sensitivity competing with flux gate sensors and even with SQUID detectors. The advantage of magnetoresistive sensors is their compact shape and the possibility to integrate the sensor and all evaluation electronics on a few silicon chips. To achieve high sensitivity the Permalloy sensor elements are coated with a barber pole (2) conductor pattern forming a Wheatstone-bridge. The magnetization of the elements is flipped periodically along the easy axis of the elements by a pulse current through an additional conductor stripe. In the design of IMO (3) the sensor strips consist of chains of small (elliptical) elements which are more sensitive to transverse applied fields and which can be easily switched by a meandering conductor. A typical AMR-sensor design of this kind is shown in Fig. 1. Focusing on high sensitivity and low noise we investigated the near remanence domain patterns and the magnetization behavior of different sensor element shapes with the goal of identifying shapes with the highest perpendicular penneabihty still undisturbed by domains in the operating state. Also important is the stability of the sensor elements with respect to external fields along the switching axis of the sensor. We performed quantitative measurements of this stability for various element shapes. )