Induced Magnetic Anisotropy of Sputter NiFe Thin Films on Thin Tantalum Nitride Underlayer
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233 Mat. Res. Soc. Symp. Proc. Vol. 384 01995 Materials Research Society
EXPERIMENT Samples of NiFe film with and without a thin tantalum nitride underlayer were RF sputter deposited on silicon wafers coated with thermally grow oxide. A 350A thick NiFe film was sputter deposited on the two different underlayers and then a 75A thick tantalum nitride layer was deposited on the NiFe film to prevent the surface of the NiFe film from oxidation. After the depositions the magnetic properties of the deposited films were characterized by a B-H loop; the sheet resistance of the films were measured by using a four-point probe, the anisotropic magnetoresistance effect of the sample films was characterized by a four point probe with 100 Oe applied magnetic field. Higher magnetic anisotropy fields were found when the NiFe film was sputter deposited on a thin tantalum nitride underlayer. In an attempt to study the manner in which the magnetic properties of NiFe films are affected by the thin tantalum nitride underlayers, the stress of the NiFe sample films were determined by a flexus stress gauge along both easy and hard axes. The magnetostriction of the sample films was also measured by optical interferometry method. X-ray diffractometry was used to characterize the crystalline structure of the sample films. X-ray diffration patterns obtained on all the NiFe sample films show a predominantly face-centeredcubic (111) peak. The preferred crystalline orientation of the NiFe films was measured by using A05o of X-ray rocking curve of the NiFe (111) diffraction peak. RESULTS AND DISCUSSION The averages of the magnetic properties of the NiFe films obtained from B-H looper measurement are summarized in the Table 1. The experiment results obtained show that the underlayers have a great effect on the magnetic properties of the NiFe thin films. Very low skew and dispersion measured on all the sample films is evidence of the unaxial anisotropy of the sample films. Figure 1 shows a typical hysteresis loop of the sample films measured along both easy and hard axes of the NiFe films. Table 1 Magnetic properties of the NiFe films deposited on both thermal oxide and thin tantalum nitride underlayers skew Dispersion! thermal
oxide
(dewe e)
(degree)
Bs (nW)
HK (Oe)
Hc[ (Oe)
R (Q)
AR/R (%)
0.4
2.3
2.78
8.2
2.29
6.00
2.72
-0.9
1.1
2.74
5.2
1.70
7.19
2.33
tantalum
nitride
One of the significant effects due to the different underlayers is that the magnetic anisotropy field HK of the sputter NiFe films increase from 5.2 Oe for the films deposited on thermal oxide to 8.2 Oe for the NiFe deposited on thin tantalum nitride. The sheet resistance was measured on the NiFe films to be 6.0 W9/1, and 7.19 Q/Q for the films deposited on thin tantalum nitride and thermal oxide, respectively. The magnetoresistance effect of 2.72% and 2.33% for the NiFe films deposited on thin tantalum nitride and thermal oxide respectively were obtained. Higher magnetoresistance effect was obtained on the NiFe films with lower sheet resistance. The Bs is
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