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SiN]×n thin films
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 304 (2006) e709–e711 www.elsevier.com/locate/jmmm
The evolution of magnetic, electrical and structural properties of nanogranular [FeCoBN/SiN] n thin films M. Urse, H. Chiriac, M. Grigoras, M. Tibu National Institute of R & D for Technical Physics, 47 Mangeron Blvd., RO 700050 Iasi 3, Box 833, Romania Available online 20 March 2006
Abstract Some results concerning the magnetic, electrical and microstructural properties of multilayer [FeCoBN/Si3N4] n films in view of their utilization for manufacturing thin film magnetic inductors are presented. A comparison between the magnetic, electrical and structural properties of FeCoBN and [FeCoBN/Si3N4] n thin films is also reported. The [FeCoBN/Si3N4] n thin films with the thickness of the FeCoBN layers varied from 10 to 30 nm, exhibit good soft magnetic characteristics and high values for electrical resistivity such as Ms of 172–185 A m2/kg, Hc of 318–1433 A/m and r of 82–48 107 O m, respectively. These physical properties of the samples are discussed in relation with the microstructure of the multilayer system. r 2006 Elsevier B.V. All rights reserved. PACS: 03.75.Hh; 75.47.Pq Keywords: Thin films—multilayer; Magnetization; Coercive force; Electrical resistivity; Granular systems
The granular thin film systems with very high electrical resistivity and good soft magnetic properties are an excellent candidate for modern electromagnetic devices operating in GHz ranges, such magnetic recording heads, integrated inductors and machined motors. Recently, the (Fe7Co3)BN thin films have received much attention because of their high saturation magnetization and magnetic anisotropy that play an important role in improving the high frequency characteristics [1]. However, Fe59Co29B3N9 thin films have low values for the electrical resistivity (i.e. about 13.2 107 O m) [1]. At the same time, it was observed that the coercive force of these samples increased abruptly over a certain thickness [2]. The limitation due to thickness can be avoided by the utilization of multilayer structures such as magnetic material/non-magnetic materials. The magnetic metal/ insulator multilayer films exhibit high electrical resistivity and good soft magnetic properties attributed to finely dispersed metallic magnetic nanograins in an insulator matrix [3]. Corresponding authors. Tel.: +40 32 430 680; fax: +40 32 231 132.
E-mail address: [email protected] (M. Urse). 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.02.197
In this paper we report some results concerning the influence of the thickness for FeCoBN and Si3N4 layers and of the annealing temperature on the magnetic, microstructural and electrical properties of multilayer [FeCoBN/Si3N4] n thin films, in view of their utilization for manufacturing magnetic thin film inductors, which can operate at high frequencies. A comparison between the magnetic, structural and electrical properties of FeCoBN and multilayer [FeCoBN/Si3N4] n thin films is also reported. The [FeCoBN/Si3N4] n thin films were deposited on glass substrates at room temperature by sequential reactive sputtering, in an (Ar+N2) atmosphere, from two targets: a disc of Fe68Co32 alloy with chips of B on its surface and a disc of Si, mounted on two separate guns. The electrical resistivity of the samples was measured using the D.C four-probe technique and the magnetic characteristics were measured using a vibrating sample magnetometer (VSM). The crystallographic structure of the samples was investigated by X-ray diffraction (XRD) and electron diffraction analysis. The microstructure was analyzed by transmission electron microscopy (TEM).
ARTICLE IN PRESS M. Urse et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e709–e711
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The as-deposited samples were annealed in vacuum at temperatures between 300 and 400 1C, for 1 h. The electrical resistivity and magnetic characteristics of the [FeCoBN/Si3N4] n thin films are very sensitive to the thickness of FeCoBN and Si3N4 layers and to the microstructural changes caused by annealing. In our studies the thickness of FeCoBN layers were varied from 10 to 30 nm and of Si3N4 layers from 2 to 6 nm. In Table 1, the results concerning the dependence of the resistivity on the FeCoBN/Si3N4 number of the layers (n), for as-deposited and annealed [FeCoBN/Si3N4] n thin films are presented. One can see that the values of the resistivity increase with increasing the FeCoBN/Si3N4 number layers and decrease with increasing the annealing temperature. For all the samples there is a gradual decrease of the resistivity with increasing the annealing temperature up to 350 1C followed by a sharp decrease after annealing at 400 1C. The sharp decrease of the resistivity of samples annealed at temperature of 400 1C, is due to the beginning of the recrystallization process, a fact also suggested by the X-ray diffraction patterns. For a multilayer system it is possible that the recrystallization process to be associated with a diffusion process at FeCoBN/Si3N4 interfaces. The dependence of the saturation magnetization Ms and coercive force Hc values on the annealing temperature for FeCoBN and [FeCoBN/Si3N4] n thin films is presented in
Table 2. One can see that for multilayer samples the saturation magnetization values decrease by increasing of the FeCoBN/Si3N4 number of layers. For all the samples, the saturation magnetization values increase when increasing the annealing temperature from 300 to 400 1C. It can also be observed from Table 2 that the coercive force values decrease after annealing at 300 1C and then increase when increasing the annealing temperature up to 400 1C. The saturation magnetization and coercive force values abruptly increase after annealing at 400 1C caused by growth of the metallic grains. From the analysis of the thermal treatment data it results that [FeCoBN/Si3N4] 30 thin films present good soft magnetic properties after annealing at 300 1C. In Fig. 1 the XRD patterns of FeCoBN and [FeCoBN/ Si3N4] 30 thin films in as-deposited state and after annealing at 300 1C are presented. The XRD pattern of as-deposited FeCoBN thin film (curve a) shows a nanocrystalline structure. The XRD patterns of [FeCoBN/Si3N4] 30 thin film (curve b and c) show an amorphous or nanocrystalline structure, as follows: amorphous structure for as-deposited [FeCoBN/ Si3N4] 30 thin film (curve b); nanocrystalline structure for [FeCoBN/Si3N4] 30 films annealed at 300 1C (curve c), corresponding to the a-FeCo (1 1 0) reflection. Fig. 2 shows the electron micrographs and electron diffraction patterns of as-deposited FeCoBN (50 nm)
Table 1 Values of the resistivity for as-deposited (A-D) and annealed samples Samples
Resistivity (O m) A-D
FeCoB (300 nm) FeCoBN (300 nm) [FeCoBN(30 nm)/ Si3N4(6 nm)] 10 [FeCoBN(20 nm)/ Si3N4(4 nm)] 15 [FeCoBN(10 nm)/ Si3N4(2 nm)] 30
After annealing 300 1C
350 1C
400 1C
22 107 35 107 53 107
19 107 29 107 48 107
17 107 18 107 26 107
12 107 16 107 21 107
73 107
69 107
34 107
31 107
89 107
82 107
49 107
42 107 Fig. 1. XRD patterns of FeCoBN and [FeCoBN/Si3N4] 30 thin films.
Table 2 Values of the saturation magnetization and coercive force for as-deposited (A-D) and annealed samples Samples
FeCoBN (300 nm) [FeCoBN(30 nm)/Si3N4(6 nm)] 10 [FeCoBN(20 nm)/Si3N4(4 nm)] 15 [FeCoBN(10 nm)/Si3N4(2 nm)] 30
Saturation magnetization Ms (A m2/kg)
Coercive force Hc (A/m)
A-D
A-D
189 183 175 169
After annealing 300 1C
350 1C
400 1C
192 185 179 172
195 186 183 175
197 189 185 178
2149 2229 1274 557
After annealing 300 1C
350 1C
400 1C
1353 1433 796 318
1831 2070 1194 716
3025 3343 3662 4139
ARTICLE IN PRESS M. Urse et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e709–e711
Fig. 2. TEM micrographs and electron diffraction patterns of FeCoBN (50 nm) (a) and FeCoBN/ Si3N4 thin films (b).
(Fig. 2a) and [FeCoBN(10 nm)/Si3N4(2 nm)] 5 thin films (Fig. 2b). The micrograph of as-deposited FeCoBN thin film reveals an extremely fine crystalline structure evidentiated of the sharp electron diffraction rings (Fig. 2a). The electron micrograph of [FeCoBN/Si3N4] 5 thin film reveals a labyrinth structure consisted by short filamentary chains with interconnected metallic nearly equiaxed particles and the dispersed insulator material (Si3N4), filling in the free spaces. This aspect is evidentiated of the broad electron diffraction rings as compared with electron
e711
diffraction rings of the FeCoBN sample. By analyzing the presented results in Figs. 1 and 2, it can be seen that the structure of [FeCoBN/Si3N4] 30 films rather consist of a mixture of nanocrystalline grains embedded in a residual amorphous matrix. In conclusion, by controlling the layer thicknesses and annealing conditions in multilayer [FeCoBN/Si3N4] n films, a nanogranular structure and good resistive and soft magnetic properties are obtained. The [FeCoBN/ Si3N4] 30 films annealed at 300 1C, exhibit high electrical resistivity of about 82 107 O m, and good magnetic properties of saturation magnetization ffi172 A m2/kg and coercivity ffi318 A/m.
References [1] I. Kim, J. Kim, K.H. Kim, M. Yamaguchi, Phys. Status Solidi (a) 201 (2004) 1777–1780. [2] H.J. Jeon, I. Kim, J. Kim, K.H. Kim, M. Yamaguchi, J. Magn. Magn. Mater. 272–276 (2004) 382–384. [3] K. Ikeda, K. Kobayashi, K. Ohta, R. Kondo, T. Suzuki, M. Fujimoto, IEEE Trans. Magn. 5 (39) (2003) 3057–3061.
Journal of Magnetism and Magnetic Materials 304 (2006) e709–e711 www.elsevier.com/locate/jmmm
The evolution of magnetic, electrical and structural properties of nanogranular [FeCoBN/SiN] n thin films M. Urse, H. Chiriac, M. Grigoras, M. Tibu National Institute of R & D for Technical Physics, 47 Mangeron Blvd., RO 700050 Iasi 3, Box 833, Romania Available online 20 March 2006
Abstract Some results concerning the magnetic, electrical and microstructural properties of multilayer [FeCoBN/Si3N4] n films in view of their utilization for manufacturing thin film magnetic inductors are presented. A comparison between the magnetic, electrical and structural properties of FeCoBN and [FeCoBN/Si3N4] n thin films is also reported. The [FeCoBN/Si3N4] n thin films with the thickness of the FeCoBN layers varied from 10 to 30 nm, exhibit good soft magnetic characteristics and high values for electrical resistivity such as Ms of 172–185 A m2/kg, Hc of 318–1433 A/m and r of 82–48 107 O m, respectively. These physical properties of the samples are discussed in relation with the microstructure of the multilayer system. r 2006 Elsevier B.V. All rights reserved. PACS: 03.75.Hh; 75.47.Pq Keywords: Thin films—multilayer; Magnetization; Coercive force; Electrical resistivity; Granular systems
The granular thin film systems with very high electrical resistivity and good soft magnetic properties are an excellent candidate for modern electromagnetic devices operating in GHz ranges, such magnetic recording heads, integrated inductors and machined motors. Recently, the (Fe7Co3)BN thin films have received much attention because of their high saturation magnetization and magnetic anisotropy that play an important role in improving the high frequency characteristics [1]. However, Fe59Co29B3N9 thin films have low values for the electrical resistivity (i.e. about 13.2 107 O m) [1]. At the same time, it was observed that the coercive force of these samples increased abruptly over a certain thickness [2]. The limitation due to thickness can be avoided by the utilization of multilayer structures such as magnetic material/non-magnetic materials. The magnetic metal/ insulator multilayer films exhibit high electrical resistivity and good soft magnetic properties attributed to finely dispersed metallic magnetic nanograins in an insulator matrix [3]. Corresponding authors. Tel.: +40 32 430 680; fax: +40 32 231 132.
E-mail address: [email protected] (M. Urse). 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.02.197
In this paper we report some results concerning the influence of the thickness for FeCoBN and Si3N4 layers and of the annealing temperature on the magnetic, microstructural and electrical properties of multilayer [FeCoBN/Si3N4] n thin films, in view of their utilization for manufacturing magnetic thin film inductors, which can operate at high frequencies. A comparison between the magnetic, structural and electrical properties of FeCoBN and multilayer [FeCoBN/Si3N4] n thin films is also reported. The [FeCoBN/Si3N4] n thin films were deposited on glass substrates at room temperature by sequential reactive sputtering, in an (Ar+N2) atmosphere, from two targets: a disc of Fe68Co32 alloy with chips of B on its surface and a disc of Si, mounted on two separate guns. The electrical resistivity of the samples was measured using the D.C four-probe technique and the magnetic characteristics were measured using a vibrating sample magnetometer (VSM). The crystallographic structure of the samples was investigated by X-ray diffraction (XRD) and electron diffraction analysis. The microstructure was analyzed by transmission electron microscopy (TEM).
ARTICLE IN PRESS M. Urse et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e709–e711
e710
The as-deposited samples were annealed in vacuum at temperatures between 300 and 400 1C, for 1 h. The electrical resistivity and magnetic characteristics of the [FeCoBN/Si3N4] n thin films are very sensitive to the thickness of FeCoBN and Si3N4 layers and to the microstructural changes caused by annealing. In our studies the thickness of FeCoBN layers were varied from 10 to 30 nm and of Si3N4 layers from 2 to 6 nm. In Table 1, the results concerning the dependence of the resistivity on the FeCoBN/Si3N4 number of the layers (n), for as-deposited and annealed [FeCoBN/Si3N4] n thin films are presented. One can see that the values of the resistivity increase with increasing the FeCoBN/Si3N4 number layers and decrease with increasing the annealing temperature. For all the samples there is a gradual decrease of the resistivity with increasing the annealing temperature up to 350 1C followed by a sharp decrease after annealing at 400 1C. The sharp decrease of the resistivity of samples annealed at temperature of 400 1C, is due to the beginning of the recrystallization process, a fact also suggested by the X-ray diffraction patterns. For a multilayer system it is possible that the recrystallization process to be associated with a diffusion process at FeCoBN/Si3N4 interfaces. The dependence of the saturation magnetization Ms and coercive force Hc values on the annealing temperature for FeCoBN and [FeCoBN/Si3N4] n thin films is presented in
Table 2. One can see that for multilayer samples the saturation magnetization values decrease by increasing of the FeCoBN/Si3N4 number of layers. For all the samples, the saturation magnetization values increase when increasing the annealing temperature from 300 to 400 1C. It can also be observed from Table 2 that the coercive force values decrease after annealing at 300 1C and then increase when increasing the annealing temperature up to 400 1C. The saturation magnetization and coercive force values abruptly increase after annealing at 400 1C caused by growth of the metallic grains. From the analysis of the thermal treatment data it results that [FeCoBN/Si3N4] 30 thin films present good soft magnetic properties after annealing at 300 1C. In Fig. 1 the XRD patterns of FeCoBN and [FeCoBN/ Si3N4] 30 thin films in as-deposited state and after annealing at 300 1C are presented. The XRD pattern of as-deposited FeCoBN thin film (curve a) shows a nanocrystalline structure. The XRD patterns of [FeCoBN/Si3N4] 30 thin film (curve b and c) show an amorphous or nanocrystalline structure, as follows: amorphous structure for as-deposited [FeCoBN/ Si3N4] 30 thin film (curve b); nanocrystalline structure for [FeCoBN/Si3N4] 30 films annealed at 300 1C (curve c), corresponding to the a-FeCo (1 1 0) reflection. Fig. 2 shows the electron micrographs and electron diffraction patterns of as-deposited FeCoBN (50 nm)
Table 1 Values of the resistivity for as-deposited (A-D) and annealed samples Samples
Resistivity (O m) A-D
FeCoB (300 nm) FeCoBN (300 nm) [FeCoBN(30 nm)/ Si3N4(6 nm)] 10 [FeCoBN(20 nm)/ Si3N4(4 nm)] 15 [FeCoBN(10 nm)/ Si3N4(2 nm)] 30
After annealing 300 1C
350 1C
400 1C
22 107 35 107 53 107
19 107 29 107 48 107
17 107 18 107 26 107
12 107 16 107 21 107
73 107
69 107
34 107
31 107
89 107
82 107
49 107
42 107 Fig. 1. XRD patterns of FeCoBN and [FeCoBN/Si3N4] 30 thin films.
Table 2 Values of the saturation magnetization and coercive force for as-deposited (A-D) and annealed samples Samples
FeCoBN (300 nm) [FeCoBN(30 nm)/Si3N4(6 nm)] 10 [FeCoBN(20 nm)/Si3N4(4 nm)] 15 [FeCoBN(10 nm)/Si3N4(2 nm)] 30
Saturation magnetization Ms (A m2/kg)
Coercive force Hc (A/m)
A-D
A-D
189 183 175 169
After annealing 300 1C
350 1C
400 1C
192 185 179 172
195 186 183 175
197 189 185 178
2149 2229 1274 557
After annealing 300 1C
350 1C
400 1C
1353 1433 796 318
1831 2070 1194 716
3025 3343 3662 4139
ARTICLE IN PRESS M. Urse et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e709–e711
Fig. 2. TEM micrographs and electron diffraction patterns of FeCoBN (50 nm) (a) and FeCoBN/ Si3N4 thin films (b).
(Fig. 2a) and [FeCoBN(10 nm)/Si3N4(2 nm)] 5 thin films (Fig. 2b). The micrograph of as-deposited FeCoBN thin film reveals an extremely fine crystalline structure evidentiated of the sharp electron diffraction rings (Fig. 2a). The electron micrograph of [FeCoBN/Si3N4] 5 thin film reveals a labyrinth structure consisted by short filamentary chains with interconnected metallic nearly equiaxed particles and the dispersed insulator material (Si3N4), filling in the free spaces. This aspect is evidentiated of the broad electron diffraction rings as compared with electron
e711
diffraction rings of the FeCoBN sample. By analyzing the presented results in Figs. 1 and 2, it can be seen that the structure of [FeCoBN/Si3N4] 30 films rather consist of a mixture of nanocrystalline grains embedded in a residual amorphous matrix. In conclusion, by controlling the layer thicknesses and annealing conditions in multilayer [FeCoBN/Si3N4] n films, a nanogranular structure and good resistive and soft magnetic properties are obtained. The [FeCoBN/ Si3N4] 30 films annealed at 300 1C, exhibit high electrical resistivity of about 82 107 O m, and good magnetic properties of saturation magnetization ffi172 A m2/kg and coercivity ffi318 A/m.
References [1] I. Kim, J. Kim, K.H. Kim, M. Yamaguchi, Phys. Status Solidi (a) 201 (2004) 1777–1780. [2] H.J. Jeon, I. Kim, J. Kim, K.H. Kim, M. Yamaguchi, J. Magn. Magn. Mater. 272–276 (2004) 382–384. [3] K. Ikeda, K. Kobayashi, K. Ohta, R. Kondo, T. Suzuki, M. Fujimoto, IEEE Trans. Magn. 5 (39) (2003) 3057–3061.