Sputtered Permalloy Films Research Articles

Electrochemical Aspects of the Beveling of Sputtered Permalloy Films

For the production of thin film magnetic heads, beveled steps in sputtered Permalloy films have been made using a duplex layer chemical etching technique. In this work, special attention was paid to galvanic interaction between the Permalloy base layer and the top layer metal, titanium. By changing the concentration of the etchant, the beveling angle α could be varied between 6° and 40°. The fact that (i) the rest potential of the bimetallic system lies in a region of the anodic polarization curve for titanium, in which the metal dissolution rate is almost completely independent of potential but strongly dependent on concentration, and (ii) the etch rate of Permalloy is insensitive to concentration, is important in this application. Values of α calculated on the basis of electrochemical measurements agree favorably with values found in chemical etching experiments. Factors that influence the beveling process when, as in the present case, a metal is used as the top layer to etch another metal are discussed.

Prevention of Oxidation in a Glow Discharge Environment with Sputtered Permalloy Films as an Example

Problems associated with the elimination of significant amounts of oxygen inclusions in sputtered thin films grown in a plasma environment are discussed. In particular data are presented to show that a plasma environment can easily be produced in which the concentration of ground state, excited and ionic oxygen containing species is sufficiently low so that no discernible effects on the magnetic properties of sputtered Permalloy films due to antiferromagnetic inclusions can be detected. Experimental evidence is also given to show that neither the energy of bombarding ion species at the cathode nor the inevitable electron bombardment of the substrate need influence the inducement of a truly uniaxial anisotropy into the film provided independent temperature control of the film during its growth can be achieved. A comparison between d.c. and asymmetric a.c. as well as substrate biasing with respect to the plasma is made with particular reference to the substrate environment.

Factors Influencing Coercive Force Values in Sputtered Permalloy Films

Depending upon the experimental conditions used, the mean composition of a sputtered Permalloy film can change progressively with thickness or can be maintained almost constant. In the first case, the extent to which a homogeneous composition is achieved depends upon the ease with which diffusion and mixing can proceed during film growth. It appears that chemical inhomogeneity, resulting from incomplete mixing, leads to the appearance of an anomalous maximum in the plot of wall coercive force Hc versus thickness within the range 600–1000 A. This maximum is similar to that observed in evaporated films and has previously been identified with the transition from Néel to Bloch-type domain walls. The anisotropy coercive force Hk is found to be relatively insensitive to average film composition and homogeneity, but varies systematically with sputtering power and substrate temperature. A similar variation occurs for Hc in those films which are chemically homogeneous, i.e., in which the mean composition remains substantially constant during growth. The equilibrium temperature attained at the substrate after a few seconds and the resulting values of Hk and Hc can thus be effectively controlled by regulating the electrode potential V and current I.