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Absorption Experiments of Ni-Zn Ferrite Thin Films forEMC Applications

F. GRÄBNERb), G. TEICHERTa), F. BLASCHDAa), CH. KNEDLIKa) 

a) Technische Universität Ilmenau, Institut für Werkstofftechnik 

Postfach 10 05 65, 98684 Ilmenau, Germany

b) Institut für Maschinen, Antriebe und elektronische Gerätetechnik gGmbH

An der Salza 8a, 99734 Nordhausen, Germany

Abstract - Ni-Zn-ferrite thin films were deposited on bariumsilicatglass-substrates by dc magnetron sputtering from a (Ni,Zn)Fe2O4-

target. The structure and texture of the Ni-Zn-ferrite thin films were investigated by x-ray diffractions measurements. To develop the

spinel structure a post-deposition heat treatment is required. The Ni-Zn-ferrite thin films are polycrystalline and show a weak texture.

The morphology of the thin films was studied by AFM. From the magnetization curves of the Ni-Zn-ferrite thin films a coercive field

HC with values in the range of 0.95 to 1.3 kOe were found. The HF losses of multilayer ( 4 layer ) thin films in the frequency range

900 MHz to 3800 MHz was measured with a stripline measurement arrangement connected with a network analyzer. The parameter

∆S11 describes the reflection loss.

I. INTRODUCTION

Soft ferrite thin films are promising materials for many

applications such as magnetic thin-film read heads [1],

microwave acoustic devices [2] and monolithic microwave

integradet circuits [3]. The deposition of thin layers of soft

ferrites such as Mn-Zn or Ni-Zn ferrite has been studied

recently by various groups [2, 4-8]. In this study we

investigated the influence of the processing parameters on

the structural and magnetic properties of Ni-Zn-ferrite

thin films deposited by dc magnetron sputtering. We will

show, that Ni-Zn-ferrite films are also promisingmaterials as HF-absorber for electromagnetic

compatibility components.

II. EXPERIMENTAL

The Ni-Zn-ferrite thin films were deposited with the dc

magnetron sputter system LA 440 S (VON ARDENNE

ANLAGENTECHNIK GMBH DRESDEN). Typical film

deposition conditions are listed in Table I.

Table I Film preparation conditions

Target Sintered (Ni,Zn)Fe2O4,

µ = 2000

Substrate Bariumsilicatglass

Sputtering gas Ar

Gas pressure 8.10

-3mbar

Substrate temperature 200 °C

Sputtering power 150 W – 200 W

Sputtering time 10 min – 15 min

The crystal structure of the thin films was investigated

by x-ray diffraction (XRD) with Cu-K radiation in grazing

incident geometry (GID – grazing incident diffraction).

The coercivity HC and saturation moment density were

determined by means of vibrating sample magnetometer

(VSM).

The HF-loss behaviour was investigated with a stripline

measurment arrangement connected with a network 

analyzer.

The increase the number of layer was taken as a criterion

for an rf loss increase.

The S-parameter S11 desribe the absorption loss of the Ni-

Zn-ferrite thin film ( multilayer of 4 layers ) in the

stripline, special ∆S11 the reflection loss.

The film thickness was measured by the x-ray

fluorescence method and by a thickness laserprofilometer.

The film composition was determined by energydispersive x-ray fluorescence spectroscopy.

The surface morphology and grain size of the Ni-Zn-

ferrite thin films were studied by atomic force microscopy

(AFM).

For a stable sputtering process we used a target, which

has the form of a disc with a hole (Fig. 1).

Fig. 1 Form of the Ni-Zn-ferrite sinter target

All films were deposited to a thickness of 200 nm to 300

nm with an avarage deposition rate of 0.3 nm/s. To

develop the spinel structure the films were annealed at

different temperatures in Argon or air.

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III. RESULTS AND DISCUSSION

Figure 2 shows the x-ray diffraction pattern of a Ni-Zn-

ferrite thin film after deposition. The diffraction pattern

shows weak diffraction peaks of the spinel ferrite

structure. Therefore the films are nanocrystalline andshow many crystal defects.

Fig. 2 X-ray diffraction pattern after deposition

Figure 3 shows the x-ray diffraction pattern of the Ni-Zn-

ferrite thin films after a postdeposition heat treatment at

500 °C in Ar for 30 min. Similar diffraction pattern were

found for a postdeposition heat treatment at 600 °C and

for a heat treatment in air at the same temperatures.

Fig. 3 X-ray diffraction pattern after heat treatment

The x-ray diffraction patterns show that the Ni,Zn-ferrite

films annealed at and above 500 °C in Ar or air are

polycrystalline with a single phase of the spinel structure.

The annealed films show a weak preferred crystallite

orientation. . It can´t be detected any x-ray diffraction

peak from polycrystalline copper for the grazing-incident

geometry.

Magnetic properties are determined at room temperature

by applying a magnetic field parallel to the surface of the

films. Remarkable is the very high coercive field HC of the

Ni-Zn-ferrite films in the range 0.95 to 1.3 kOe. This

results are reasonable because the effects of the annealing

temperature are increasing grain size and improving thinfilm crystallinity. All these effects contribute to the

increase of MS and decrease of in-plane coercivity HC. The

high values of in-plane coercivity HC indicate the presence

of crystallite shape anisotropy [10]. A first measurement

of the anisotropy constant k 1 with a torque magnetometer

gives a value of  -8.10-6 erg/cm³.

Figure 4 shows the stripline measurements for the

absorption experiments.

Fig.4 stripline measurements for the absorption

experiments ( 40 MHZ- 3800 MHZ )

The measurement of the absorption loss by means of the

S-parameter-method was carried out in the frequency

range 40 MHz – 3800 MHz. Figure 5 shows the ∆S11-

parameter.

Fig. 5 ∆ S11-parameter of Multilayer Ni-Zn-ferrite thin

films ( 40 MHZ – 3800 MHZ )

      C     p     s

200

300

400

500

600

2-Theta - Scale

20 30 40 50 60 70 80 90 100

 

      C     p     s

200

300

400

500

600

2-Theta - Scale

20 30 40 50 60 70 80 90 100

 

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The analysis of the S-parameter ∆S11 shows a average

reflection loss of 2 to 4 dB. 

IV. CONCLUSION

Spinel multilayer ( 4 layer ) Ni-Zn-ferrite thin films forelectro-magnetic- compatibility applications have been

successfully deposited on bariumsilicatglass subtrates at

relatively low temperatures by means of dc magnetron

sputtering. The temperature at the post-deposition heat

treatment is a important factor to control the structural

and magnetic properties of the sputtered Ni-Zn-ferrite

thin films.

ACKNOWLEDMENTS

The authors want to acknowledge the financial support of 

this study ba the BMBF under contract 03N1048.

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