- Email: [email protected]
Preparation and characterization of thick magnetostrictive films
Journal of Magnetism and Magnetic Materials 261 (2003) 118–121
Preparation and characterization of thick magnetostrictive films Wenxu Zhang*, Wanli Zhang, Hongchuan Jiang, Bin Peng, Shiqing Yang College of Microelectronics and Solid State Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China Received 28 August 2002
Abstract In this paper, magnetostrictive thick films are prepared by screen-printing and sintering. The morphology, magnetic character and magnetostriction prepared at different temperatures are studied. Characteristics of composite films thus prepared are compared with the original magnetostrictive blocks. r 2002 Elsevier Science B.V. All rights reserved. PACS: 75.80; 75.70; 81.20 Keywords: Magnetostrictive; Thick film; Screen-printing; Cantilever
1. Introduction As a very important kind of energy transducing materials, magnetostrictive materials find their use in actuation, supersonic generator and as sensing element in structures and so on. Since the emergence of the micro-electro mechanical systems (MEMS), magnetostrictive films have been invented to be used in micropumps [1], optical scanners [2], and delay lines [3], etc. In most of the applications as actuators, deformation can be expected. According to our previous studies [4], deformation can be greatly improved when the thickness of the film is larger. Thus thick film technology is a good choice to improve the *Corresponding author. Tel.: +86-28-3201475. E-mail address: [email protected] (W. Zhang).
deflection of magnetostriction-based cantilever. In this paper, the process of growing thick films is presented in the second part. In the third part, the morphology, the magnetic character of the film and the static deflection of the cantilevers are examined by reflecting the laser beam.
2. Experimental details During the preparation process, the blocks of commercially available Tefernol-D are mixed with some glass frit and glycerol which are ball-milled in a steel ball-mill machine. The glass is devitrifed at 7001C in air and immediately put into cold water before ball-millling in order to make crushing easier. The glycerol protects the Tefernol-D from being oxidized during ball-milling and
0304-8853/03/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 2 ) 0 1 4 5 9 - 2
W. Zhang et al. / Journal of Magnetism and Magnetic Materials 261 (2003) 118–121
as the vehicle during printing. After 10 h of milling the Tefernol-D powder is crushed into particles with diameters around 3 mm. The paste is printed onto the DI water cleaned, polished silicon chips with dimensions of 20 5 0.2 mm3 by a standard thick film printer with 250 mesh size. The thick films are fried for 10 h in an infrared dryer. After drying, the films are put into a silica pipe furnace. The air is pumped out and pure nitrogen (4 N) is supplied continuously through the pipe, so that uniform atmosphere pressure is maintained. The increase rate of the temperature cannot be too fast (about 201C/min) to prevent the films from cracking, and the same with the decrease of the temperature (not more than 101C/min).
(a) Prepared at 550 °C
(c) Prepared at 750 °C
119
3. Results and discussion The morphology of the films is observed by SEM as shown in Fig. 1. Temperature affects the growing of the crystal mostly, which can be seen from the images directly. It can be seen that at higher temperatures, the crystals are larger with less pores and more are dense. The glass acts as the bonding medium which combines the powders together. This will be helpful to make the film more robust because at this relatively low temperature, the powder cannot be well sintered. How the morphology affects the magnetic and magnetostrictive character of the films will be explained later.
(b) Prepared at 650 °C
(d) Prepared at 850 °C
Fig. 1. SEM of the surfaces of the films proceeded at different temperatures.
W. Zhang et al. / Journal of Magnetism and Magnetic Materials 261 (2003) 118–121
120
emu 0.075
//
emu //
Hc = 4500e
Hc = 1900e
0.1
0.05 ⊥ ⊥
0 −1
Hc = 4500e
Hc = 1900e
0.05
−0.5
0.5
0
0.025
1
−5
0
5
0
10
kOe
kOe
(a) Prepared at 550 °C (Ms=21.21kA/m)
(b) Prepared at 650 °C (Ms=11.19kA/m)
emu emu 0.075
//
//
0.3
Hc = 2400e
Hc = 600e
0.05
⊥
⊥
0.2
Hc = 2500e
Hc = 710e
0.025 0.1 0 −1000
−500
0
500
1000
Oe
(c) Prepared at 750 °C (Ms=27.78kA/m)
−10
−5
0
5
kOe
(d) Prepared at 850 °C (Ms=66.67kA/m)
Fig. 2. VSM measurement of the hysteresis loop of the films prepared at different temperatures with the saturation magnetization in brackets. H ∆z
16 ∆z (m)
The magnetic hysteresis loops were measured by VSM in directions vertical and parallel to the film plane as shown in Fig. 2. The curve shapes of the same sample measured in parallel and vertical directions vary little, which means the shape effect does not play a significant role in these thick films (about 30 mm). From the loops, the coercievity field decreases with the sintering temperature, which may be the effects of increased crystal size and reduced defects of crystal interface. The saturated magnetization increases with the temperature because of the increased density of the film. But at a lower processing temperature (5501C), the saturated magnetization is relatively large. The decrease at higher temperature may be caused by oxidization of TbDyFe during processing. The saturated deflection of the cantilever is amplified and measured by the displacement of the light point of the reflected laser beam from the free
12 8 4 0
550 650 750 850 t (°C)
Fig. 3. Cantilever deflections with the film prepared at different temperatures.
end. The deflections varying with the processing temperature are shown in Fig. 3. It can be seen from the curve, that increase of temperature will improve the deflection of the cantilever, as a result of the increase in the film
W. Zhang et al. / Journal of Magnetism and Magnetic Materials 261 (2003) 118–121
hf
δz
film
hs
substrate
θ
121
thank professor Yang Zheng (Research Institute of Magnetic Materials, Lan Zhou University) for the VSM measurement.
L
Appendix Fig. 4. Estimation of the magnetostriction by the deflection of the cantilever.
density. The Tefernol-D used in this experiment had a magnetostriction coefficient of about 1000 ppm. The average coefficient of the composites is about 6 ppm with the maximum of 16 ppm, which is far below that of the block (how the deflection is converted the relative extension of the film is shown in the appendix). A lot of efforts are still needed for further improvement of the films thus made.
The method to estimate the magnetostriction coefficient by the deflection of the cantilever is as following (Fig. 4): Assuming that the neutral plane of the system is 2=3hs below the interface of the film and the substrate [4], when y is very small, the extending of the film being dl; then from Fig. 4 y¼
dl ; hf þ 23hs
ðA1Þ
at the same time: 4. Conclusion In our experiments, the mangetostrictive thick films were made on silicon substrates to form cantilevers. The morphology of the films were examined by SEM. The crystals were bigger and films were more dense when the sintering temperature was increased. The saturated magnetization also increases with it in general and so also the deflection of the cantilevers. A lot of efforts are still needed to improve the deflection when comparing the magnetostriction of the film with that of the blocks.
Acknowledgements This research was supported by the Application Foundation of Sichuan Province. We would like to
y¼
dz ; L
ðA2Þ
so that l¼
dl ðhf þ 23hs Þdz ¼ L2 L
ðA3Þ
can be deduced.
References [1] E. Quandt, A. Ludwig, Magnetostrictive actuation in microsystems, Sensors Actuators 81 (2000) 275–280. [2] T. Bourouina et al. http://www2.gov.con/users/sst/jst/bourouina.htm. [3] E. Hristoforon, Sensors Actuators A59 (1997) 183. [4] W.X. Zhang, B. Peng, H.C. Jiang, S.Q. Yang, J. Magn. Magn. Mater. 247 (2002) 111.
Preparation and characterization of thick magnetostrictive films Wenxu Zhang*, Wanli Zhang, Hongchuan Jiang, Bin Peng, Shiqing Yang College of Microelectronics and Solid State Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China Received 28 August 2002
Abstract In this paper, magnetostrictive thick films are prepared by screen-printing and sintering. The morphology, magnetic character and magnetostriction prepared at different temperatures are studied. Characteristics of composite films thus prepared are compared with the original magnetostrictive blocks. r 2002 Elsevier Science B.V. All rights reserved. PACS: 75.80; 75.70; 81.20 Keywords: Magnetostrictive; Thick film; Screen-printing; Cantilever
1. Introduction As a very important kind of energy transducing materials, magnetostrictive materials find their use in actuation, supersonic generator and as sensing element in structures and so on. Since the emergence of the micro-electro mechanical systems (MEMS), magnetostrictive films have been invented to be used in micropumps [1], optical scanners [2], and delay lines [3], etc. In most of the applications as actuators, deformation can be expected. According to our previous studies [4], deformation can be greatly improved when the thickness of the film is larger. Thus thick film technology is a good choice to improve the *Corresponding author. Tel.: +86-28-3201475. E-mail address: [email protected] (W. Zhang).
deflection of magnetostriction-based cantilever. In this paper, the process of growing thick films is presented in the second part. In the third part, the morphology, the magnetic character of the film and the static deflection of the cantilevers are examined by reflecting the laser beam.
2. Experimental details During the preparation process, the blocks of commercially available Tefernol-D are mixed with some glass frit and glycerol which are ball-milled in a steel ball-mill machine. The glass is devitrifed at 7001C in air and immediately put into cold water before ball-millling in order to make crushing easier. The glycerol protects the Tefernol-D from being oxidized during ball-milling and
0304-8853/03/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 2 ) 0 1 4 5 9 - 2
W. Zhang et al. / Journal of Magnetism and Magnetic Materials 261 (2003) 118–121
as the vehicle during printing. After 10 h of milling the Tefernol-D powder is crushed into particles with diameters around 3 mm. The paste is printed onto the DI water cleaned, polished silicon chips with dimensions of 20 5 0.2 mm3 by a standard thick film printer with 250 mesh size. The thick films are fried for 10 h in an infrared dryer. After drying, the films are put into a silica pipe furnace. The air is pumped out and pure nitrogen (4 N) is supplied continuously through the pipe, so that uniform atmosphere pressure is maintained. The increase rate of the temperature cannot be too fast (about 201C/min) to prevent the films from cracking, and the same with the decrease of the temperature (not more than 101C/min).
(a) Prepared at 550 °C
(c) Prepared at 750 °C
119
3. Results and discussion The morphology of the films is observed by SEM as shown in Fig. 1. Temperature affects the growing of the crystal mostly, which can be seen from the images directly. It can be seen that at higher temperatures, the crystals are larger with less pores and more are dense. The glass acts as the bonding medium which combines the powders together. This will be helpful to make the film more robust because at this relatively low temperature, the powder cannot be well sintered. How the morphology affects the magnetic and magnetostrictive character of the films will be explained later.
(b) Prepared at 650 °C
(d) Prepared at 850 °C
Fig. 1. SEM of the surfaces of the films proceeded at different temperatures.
W. Zhang et al. / Journal of Magnetism and Magnetic Materials 261 (2003) 118–121
120
emu 0.075
//
emu //
Hc = 4500e
Hc = 1900e
0.1
0.05 ⊥ ⊥
0 −1
Hc = 4500e
Hc = 1900e
0.05
−0.5
0.5
0
0.025
1
−5
0
5
0
10
kOe
kOe
(a) Prepared at 550 °C (Ms=21.21kA/m)
(b) Prepared at 650 °C (Ms=11.19kA/m)
emu emu 0.075
//
//
0.3
Hc = 2400e
Hc = 600e
0.05
⊥
⊥
0.2
Hc = 2500e
Hc = 710e
0.025 0.1 0 −1000
−500
0
500
1000
Oe
(c) Prepared at 750 °C (Ms=27.78kA/m)
−10
−5
0
5
kOe
(d) Prepared at 850 °C (Ms=66.67kA/m)
Fig. 2. VSM measurement of the hysteresis loop of the films prepared at different temperatures with the saturation magnetization in brackets. H ∆z
16 ∆z (m)
The magnetic hysteresis loops were measured by VSM in directions vertical and parallel to the film plane as shown in Fig. 2. The curve shapes of the same sample measured in parallel and vertical directions vary little, which means the shape effect does not play a significant role in these thick films (about 30 mm). From the loops, the coercievity field decreases with the sintering temperature, which may be the effects of increased crystal size and reduced defects of crystal interface. The saturated magnetization increases with the temperature because of the increased density of the film. But at a lower processing temperature (5501C), the saturated magnetization is relatively large. The decrease at higher temperature may be caused by oxidization of TbDyFe during processing. The saturated deflection of the cantilever is amplified and measured by the displacement of the light point of the reflected laser beam from the free
12 8 4 0
550 650 750 850 t (°C)
Fig. 3. Cantilever deflections with the film prepared at different temperatures.
end. The deflections varying with the processing temperature are shown in Fig. 3. It can be seen from the curve, that increase of temperature will improve the deflection of the cantilever, as a result of the increase in the film
W. Zhang et al. / Journal of Magnetism and Magnetic Materials 261 (2003) 118–121
hf
δz
film
hs
substrate
θ
121
thank professor Yang Zheng (Research Institute of Magnetic Materials, Lan Zhou University) for the VSM measurement.
L
Appendix Fig. 4. Estimation of the magnetostriction by the deflection of the cantilever.
density. The Tefernol-D used in this experiment had a magnetostriction coefficient of about 1000 ppm. The average coefficient of the composites is about 6 ppm with the maximum of 16 ppm, which is far below that of the block (how the deflection is converted the relative extension of the film is shown in the appendix). A lot of efforts are still needed for further improvement of the films thus made.
The method to estimate the magnetostriction coefficient by the deflection of the cantilever is as following (Fig. 4): Assuming that the neutral plane of the system is 2=3hs below the interface of the film and the substrate [4], when y is very small, the extending of the film being dl; then from Fig. 4 y¼
dl ; hf þ 23hs
ðA1Þ
at the same time: 4. Conclusion In our experiments, the mangetostrictive thick films were made on silicon substrates to form cantilevers. The morphology of the films were examined by SEM. The crystals were bigger and films were more dense when the sintering temperature was increased. The saturated magnetization also increases with it in general and so also the deflection of the cantilevers. A lot of efforts are still needed to improve the deflection when comparing the magnetostriction of the film with that of the blocks.
Acknowledgements This research was supported by the Application Foundation of Sichuan Province. We would like to
y¼
dz ; L
ðA2Þ
so that l¼
dl ðhf þ 23hs Þdz ¼ L2 L
ðA3Þ
can be deduced.
References [1] E. Quandt, A. Ludwig, Magnetostrictive actuation in microsystems, Sensors Actuators 81 (2000) 275–280. [2] T. Bourouina et al. http://www2.gov.con/users/sst/jst/bourouina.htm. [3] E. Hristoforon, Sensors Actuators A59 (1997) 183. [4] W.X. Zhang, B. Peng, H.C. Jiang, S.Q. Yang, J. Magn. Magn. Mater. 247 (2002) 111.