Mark Lee Watson


Sensors have been fabricated, which are able to read the information stored on magnetic tape using the anisotropic magnetoresistance effect. These have major advantages over conventional replay heads in that they are multi-track devices, with very small trackwidths. To overcome the signal limitation imposed by the reduced trackwidth the sensor consists of two long magnetoresistive elements which are folded together. By differentially sensing the magnetoresistive signal in each of the elements second harmonic distortion can be removed. To improve the linearity of the magnetoresistive response, the sensors are arranged in such a way that the sensor signal current in each of the elements provides the field necessary to correctly bias the head. A theoretical evaluation of the bias field for all configurations of element has been performed, and was found to fit experimental data. Sixteen tracks are provided across the width of a compact cassette tape, and the design specifically allows the finished sensors to be packaged using standard components. Several performance related features have been considered, and various other fabrication aids included on the photomasks used to build the sensors. These photomasks are provided by the S.E.R.C. from an original computer program written in a graphics language, which defines the size and shape of the various elements making up the device. The heads are fabricated using photolithographic methods, from thin films of several materials all of which are R.F. sputtered. To improve the performance of the sensors, various electro-magnetic properties of the magnetoresistive layers have been measured using apparatus built especially for the purpose. These properties have been optimised by varying the bias potential used in the sputtering process. The finished heads have been tested, and have been found to compare well with the theory derived to describe their performance.

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