STABLE ENCAPSULATION STRUCTURES FOR PERMALLOY-FILMS

This paper presents a study Of the effects of annealing on the microma gnetic properties of encapsulated Permalloy films. The stress relaxati on during annealing causes observable changes in the micro-magnetic st ate of the permalloy. The amount of stress relaxation is highly sensit ive to the shape of the Permalloy film. and the encapsulation material . After Permalloy films with negative magnetostrictive coefficient are annealed, the easy axis of bar-shape yokes remains in the transversal direction while those of ring-shape yokes and heart-shape yokes rotat e so that the easy axis is normal to the film edge. The annealing prop erties of bar-shape Permalloy films in six different encapsulation str uctures are compared. Permalloy films encapsulated entirely in hardbak ed photoresist are consistently more stable. The uneven external stres s is absorbed by the relatively softer hardbaked photoresist buffer la yer and is re-distributed evenly to the Permalloy. A better control of the anisotropy of the Permalloy yoke can be obtained by placing a har dbaked photoresist buffer layer between the alumina overcoat and the P ermalloy.