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Electrical and resonant characteristics of modified PbTiO3 ceramics for SMD-type high frequency resonators using 3rd overtone thickness vibration mode
Sensors and Actuators A 105 (2003) 55–61
Electrical and resonant characteristics of modified PbTiO3 ceramics for SMD-type high frequency resonators using 3rd overtone thickness vibration mode Juhyun Yoo∗ , Dongon Oh Department of Electrical Engineering, Semyung University, Jechon, Chungbuk 390-711, South Korea Accepted 3 February 2003
Abstract The micro-structural, electrical and resonant properties of (Pb, La, Nd)(Ti, Mn, Sb)O3 ceramics were investigated as a function of CuO addition and internal electrode weight. The best properties for the resonator application were observed from the 0.25 wt.% CuO added specimen sintered at 1200 ◦ C. Curie temperature and density of the specimen were measured to be 325 ◦ C and 7.72 g/cm3 , respectively. Dynamic characteristics of energy-trapped 30 MHz surface mount device (SMD) type resonators using 3rd overtone thickness vibration mode were also investigated as a function of internal electrode weight and CuO addition. Ceramic wafers for resonator were fabricated by evaporating electrode weights of 0.66, 1.765, 2.32, and 3.87 × 10−4 g/cm2 with silver, respectively. And then, 30 MHz SMD-type ceramic resonators were fabricated with the size of 3.7 mm ×3.1 mm and electrode diameter of 0.77 mm. With increasing electrode weight, resonant resistance was gradually decreased. At the electrode weight of 2.32 × 10−4 g/cm2 , mechanical quality factor (Qmt3 ) and dynamic range (DR) for the 3rd overtone thickness vibration mode showed the maximum value of 2152 and 49 dB, respectively. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Curie temperature; Resonator; 30 MHz SMD-type; Energy-trapped; Dynamic range (DR)
1. Introduction Recently, as information technologies (IT) have been advanced in many countries, concerns for information communication components such as ceramic filters and resonators have also been increasing. The operating frequency of ceramic resonators, which can be utilized as clock oscillator for hard disk driver (HDD) and floppy disk driver (FDD), is required to be higher. The reason can be illustrated as the increasing of operating frequency leads to make the speed of the electronic instruments higher. However, in order to increase the operating frequency of the resonator, its 3rd overtone thickness vibration mode must be utilized [1], because the devices using fundamental mode thickness vibration for high frequency have the difficult problems such as lapping and polishing in diminishing its thickness. As far as the composition ceramics for the 3rd overtone thickness vibration mode resonators are concerned, the dynamic range (DR) must be high enough to induce stable thickness vibration. Based on such requirement, PbLa(Ti,
∗ Corresponding author. Tel.: +82-43-649-1301; fax: +82-43-648-0868. E-mail address: [email protected] (J. Yoo).
Mn)O3 ceramics, which had been reported as a composition ceramics with high mechanical quality factor (Qmt3 )and DR for the 3rd overtone thickness vibration mode, have been widely used for high frequency resonators. However, the Qmt3 and DR for the 3rd overtone thickness vibration mode between compositions with deficient and excess PbO may result in significant differences in electrical characteristics primarily because of PbO evaporation during the manufacturing process. In this experiments, normal sintering process with the liquid phase composed of CuO additive and remnant PbO was used to facilitate sintering process resulting in final microstructure of high density and strength. Energy trapping effects, which had been announced by Shockly et al. [2] in 1963, have the relation with the frequency constant, the thickness and the partial electrode weight of specimen. Accordingly, in this study, the effect of the partial electrode weight on the energy trapping was investigated. Another requirement for high frequency resonator is the ceramic composition capable of resisting any change in resonance frequency that may be caused by the thermal shock during the soldering of surface mount device (SMD) type resonators [3]. In this study, 30 MHz SMD-type resonators
0924-4247/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0924-4247(03)00063-3
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J. Yoo, D. Oh / Sensors and Actuators A 105 (2003) 55–61
using 3rd overtone thickness vibration modes were fabricated using CuO added PbTiO3 ceramic composition modified with La, Nd, Mn and Sb. Electrical, structural and resonant characteristics were investigated as a function of internal electrode weight and CuO addition for the application of 30 MHz SMD-type ceramic resonators.
2. Experimental procedure The specimens were manufactured using conventional mixed oxide process. The ceramic composition used in this experiment is as follows:
from the disc. The specimens were electroded and poled, and then coated with photo-resistor for dot sizes of 0.77 mm in diameter. The specifications of the specimens studied in this work are referred in Fig. 1. As seen in Fig. 1, the PbTiO3 system ceramic resonator part is the intermediate part sandwiched between the cap and base parts. The cap and base fabricated using MgTiO3 are the upper and lower parts, respectively. The base is surface-mounted using solders. DR is defined as the decibel ratio of the impedance at resonance and anti-resonance frequencies based on the equation below [4]: Zmax DR = 20 log (1) Z min
Pb0.88 (La0.6 Nd0.4 )0.08 (Mn1/3 Sb2/3 )0.02 Ti0.98 O3 +0.1 wt.% excess PbO + 0.1 wt.% MnO2 The raw materials were acetone-milled and calcined at 850 ◦ C for 2 h. After calcinations, CuO of 0.25, 0.5, 0.75, and 1.0 wt.% were added and milled again. An 8 wt.% poly-vinyl alcohol (PVA) was mixed with the materials. The powders were uniaxially consolidated into discs with diameter of 30 mm. The green compacts were sintered at temperatures of 1200 ◦ C for 2 h and the sintered discs were thinned into the thickness of 0.255 mm. The resonators with the size of 3.7 mm × 3.1 mm × 0.255 mm were fabricated
DR was calculated from the impedances at resonance (Zmin ) and anti-resonance frequencies (Zmax ) measured using Agilent 4294 impedance analyzer. The temperature coefficient of resonant frequency (TCFr ) from −20 to 80 ◦ C was calculated by measuring the resonant frequency of specimen using an impedance analyzer in thermostatic chamber. The equation [5] used is as follows: TCFr =
fr (max) − fr (min) 1 × (ppm/◦ C) ◦ fr (25 C) 100
(2)
where fr (25 ◦ C), fr (max) and fr (min) are the resonant frequency at 25 ◦ C, maximum and minimum resonant
Fig. 1. Dimension and structure of SMD-type ceramic resonator: (a) front view; (b) side view; (c) interior view.
J. Yoo, D. Oh / Sensors and Actuators A 105 (2003) 55–61
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frequency in the regions ranged from −20 to 80 ◦ C, respectively. 3. Results and discussion 3.1. CuO addition effects Fig. 2 shows the X-ray diffraction patterns for the specimens fabricated through the process described above. As can be seen from (0 0 2) and (2 0 0) peaks, the crystal structure is tetragonal and the tetragonality varies from 1.02869 to 1.03026, smaller than 1.064 of pure PbTiO3 . However, the amount of unidentified phase increases with CuO. It is likely that the CuO reacted with remnant PbO and then the second phase is formed. Further investigation on the phase is needed. The scanning electron micrographs of the specimens with different CuO composition are illustrated in Fig. 3. The grain size increases with the amount of CuO. This is due to the acceleration of grain growth by the liquid phase sintering of CuO and PbO [6]. Fig. 4 shows the variation in grain size as a function of CuO. Dielectric constant (εr ) and Curie temperature (Tc ) of the specimens with different CuO addition are listed in Table 1. The minimum dielectric constant was observed in the 0.5–0.75 wt.% CuO added specimens with grain size near 1.7 m, representing the boundary between mono-domain and multi-domain [7]. To maintain a stable oscillation of resonator, higher DR is required. Also higher DR can be obtained from the ceramic substrate with high density. In this study, for dense microstructure by the liquid phase sintering, CuO was added after calcinations. The liquid phase is due to the reaction between CuO additive and remnant PbO and facilitates sintering process resulting in final microstructure of high density and strength. The amount of additives for liquid phase sintering, however, must be controlled small enough because the additives residing mainly at grain boundaries deteriorate electrical properties of the final sintered material. As shown in Table 2, higher DR and
Fig. 3. Microstructures as a function of CuO addition.
Fig. 2. X-ray diffraction patterns as a function of CuO addition.
Qmt3 for the 3rd overtone vibration mode are available only from the high density. In other words, the resonators with high DR can be obtained through the controlled liquid phase sintering process. In general, final density of ceramics is closely related to the sintering parameters such as temperature, time and atmosphere. In this experiment, the maximum density of 7.72 g/cm3 , maximum DR of 49 dB and maximum Qmt3 of 2152 were obtained from the sample with 0.25 wt.% CuO, sintered at 1200 ◦ C. The high value of the Qmt3 means the low value of resonant impedance, providing the advantage that the ceramic resonators are resonating or oscillating under the condition of lower driving voltage [8].
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Table 1 Physical, dielectric and TCFr properties as a function of CuO addition CuO (wt.%)
Dielectric constant
Grain size (m)
Tc (◦ C)
Density (g/cm3 )
TCFr (ppm/◦ C)
0 0.25 0.5 0.75 1
220 211 184 185 204
0.67 1.18 1.60 1.62 1.87
329 325 323 318 325
7.56 7.72 7.66 7.57 7.53
12 17 26 27 31
Fig. 5. TCFr (%) as a function of CuO addition. Fig. 4. Variation of grain size as a function of CuO addition.
Fig. 6. Impedance and DR of SMD-type ceramic resonator as a function of electrode weight. Table 2 Piezoelectric and resonant characteristics of SMD-type ceramic resonator as a function of CuO addition CuO (wt.%)
Electrode diameter (mm)
fr (MHz)
fa (MHz)
Zr ()
Za (k)
DR (dB)
Qmt3
kt3
0 0.25 0.75
0.77 0.77 0.77
29.85 30.94 29.19
30.03 31.12 29.34
89.0 52.0 139.5
7.73 18.05 6.10
38.21 49.00 33.35
1184.48 2152.00 1155.37
0.12 0.12 0.11
J. Yoo, D. Oh / Sensors and Actuators A 105 (2003) 55–61
Fig. 7. kt3 and Qmt3 of SMD-type ceramic resonator as a function of electrode weight.
Fig. 8. Characteristic impedance curves of SMD-type ceramic resonator as a function of electrode weight.
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Table 3 Piezoelectric and resonant characteristics of SMD-type ceramic resonator as a function of electrode weight Electrode weight (×10−4 g/cm2 )
fr (MHz)
fa (MHz)
Zr ()
Za ()
DR (dB)
Qmt3
kt3
0.66 1.765 2.32 3.87
30.75 30.68 30.94 31.44
30.93 30.86 31.12 31.64
85 66 52 63
9585 12766 18050 14183
41 44 49 46
1444 1824 2152 1750
0.1194 0.1196 0.1191 0.1241
It can be illustrated that this is an extremely advantageous characteristic for a resonator or oscillator. Furthermore, if the mechanical quality factor, Qmt3 for the 3rd overtone vibration mode is higher, thereby the ratio of resonant and anti-resonant impedances becomes greater, thus making it possible to stabilize resonating or oscillating. Fig. 5 also shows the TCFr variations as a function of CuO addition at 3rd overtone thickness vibration mode. With the addition of CuO, the TCFr moved to positive side and further deteriorated. Such variation in TCFr probably seems to be related to the behavior of Cu2+ ions capable of occupying the B-site in the ABO3 perovskite lattice that may degrade TCFr by increasing the oxygen vacancies acting as the acceptor dopants [9]. 3.2. Electrode weight effects of ceramic resonator Fig. 6 shows impedance and DR of SMD-type ceramic resonator as a function of electrode weight. As the electrode weight of the resonator is increased, resonant resistance decreased and energy trapping effect apparently appeared. However, the over weight of electrode may suppress the mechanical vibration of the specimen and cause the increase of loss. Accordingly, the optimal condition for electrode weight may be obtained from the experiment. The highest DR of 49 dB was obtained from the specimen with the electrode weight of 2.32 × 10−4 g/cm2 . Fig. 7 shows kt3 and Qmt3 of SMD-type ceramic resonator with the size of 3.7 mm × 3.1 mm as a function of electrode weight. While the kt3 nearly showed constant value, the Qmt3 showed the maximum value of 2152 from the specimen with the electrode weight of 2.32 × 10−4 g/cm2 because of mass loading effect of electrode weight. After that electrode weight, it is considered that the Qmt3 is decreased by the suppression of thickness vibration because of over electrode weight. The characteristic impedance curves of SMD-type ceramic resonator are shown in Fig. 8. As can be seen, in the impedance characteristics of specimen with the electrode weight of 2.32 × 10−4 g/cm2 , the 3rd overtone vibration mode shows relatively sharp curve by the energy trapping and the proper mass loading effect [10]. Table 3 summarizes piezoelectric and resonant properties of the 30 MHz SMD-type resonators as a function of the electrode weight.
4. Conclusion The micro-structural, electrical and resonant properties of (Pb, La, Nd)(Ti, Mn, Sb)O3 ceramics were investigated as a function of internal electrode weight and CuO addition. Ceramic wafers for resonator were fabricated by evaporating electrode weights of 0.66, 1.765, 2.32, and 3.87 × 10−4 g/cm2 with silver, respectively. And then, 30 MHz SMD-type ceramic resonators were fabricated with the size of 3.7 mm × 3.1 mm and electrode diameter of 0.77 mm. Electrical and resonant characteristics of the resonators were investigated and the following conclusions were obtained: (1) The grain size increased with the CuO addition. (2) The 0.25 wt.% CuO added specimen showed the best characteristics for the resonator application. The density and Tc were obtained to be 7.72 g/cm3 and 325 ◦ C, respectively. (3) With increasing CuO, the TCFr moved to positive side and further deteriorated. (4) With increasing electrode weight, resonant resistance was gradually decreased. At the electrode weight of 2.32 × 10−4 g/cm2 , mechanical quality factor (Qmt3 ) and DR for the 3rd overtone thickness vibration mode showed the maximum value of 2152 and 49 dB, respectively. Acknowledgements This work was supported by Korea Research Foundation (Grant no. KRF-2000-042-E00023). References [1] Y. Yamashita, S. Sakano, I. Toba, Jpn. J. Appl. Phys. 36 (1997) 6096. [2] W. Shockly, D.R. Curran, D.J. Koneval, in: Proceedings of the 17th Annual Frequency Control Symposium 1963, p. 88. [3] K. Takahashi, M. Nishida, H. Hase, Jpn. J. Appl. Phys. 37 (1998) 5285. [4] S.K. Min, D.U. Oh, K.H. Yoon, J.H. Yoo, C.Y. Park, J.S. Kim, J. KIEEME 14 (9) (2001) 720. [5] C.-K. Liang, L. Wu, T.-S. Wu, Ferroelectrics 120 (1991) 185. [6] D.L. Corker, R.W. Whatmore, E. Ringgaard, W.W. Wolny, J. Eur. Ceram. Soc. 20 (2000) 2039. [7] K. Uchino, Piezoelectric Actuators and Ultrasonic Motor, Academic Press, London, 1997.
J. Yoo, D. Oh / Sensors and Actuators A 105 (2003) 55–61 [8] T. Ogawa, T. kittaka, US Patent 4 605 876 (1986). [9] K. Takahashi, M. Nishida, H. Hase, Jpn. J. Appl. Phys. 37 (1998) 5285. [10] J.H. Yoo, D.O. Oh, S.K. Min, S.H. Lee, C.Y. Park, J.S. Kim, E.T. Park, Sens. Actuators A 3297 (2002).
Biographies Juhyun Yoo received his PhD degree in Electrical Engineering from the Yonsei University, Korea in 1990. He is currently working in
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Semyung University as an associate professor of Electrical Engineering. His research interests are in the area of piezoelectric devices, including piezoelectric transformers, actuators, resonators and filters. Dongon Oh received his BS degree in Electrical Engineering from the Semyung University, Korea in 2002. He is currently involved in Graduate School of the same University. His current research interests are piezoelectric materials and their application, including resonators and filters.
Electrical and resonant characteristics of modified PbTiO3 ceramics for SMD-type high frequency resonators using 3rd overtone thickness vibration mode Juhyun Yoo∗ , Dongon Oh Department of Electrical Engineering, Semyung University, Jechon, Chungbuk 390-711, South Korea Accepted 3 February 2003
Abstract The micro-structural, electrical and resonant properties of (Pb, La, Nd)(Ti, Mn, Sb)O3 ceramics were investigated as a function of CuO addition and internal electrode weight. The best properties for the resonator application were observed from the 0.25 wt.% CuO added specimen sintered at 1200 ◦ C. Curie temperature and density of the specimen were measured to be 325 ◦ C and 7.72 g/cm3 , respectively. Dynamic characteristics of energy-trapped 30 MHz surface mount device (SMD) type resonators using 3rd overtone thickness vibration mode were also investigated as a function of internal electrode weight and CuO addition. Ceramic wafers for resonator were fabricated by evaporating electrode weights of 0.66, 1.765, 2.32, and 3.87 × 10−4 g/cm2 with silver, respectively. And then, 30 MHz SMD-type ceramic resonators were fabricated with the size of 3.7 mm ×3.1 mm and electrode diameter of 0.77 mm. With increasing electrode weight, resonant resistance was gradually decreased. At the electrode weight of 2.32 × 10−4 g/cm2 , mechanical quality factor (Qmt3 ) and dynamic range (DR) for the 3rd overtone thickness vibration mode showed the maximum value of 2152 and 49 dB, respectively. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Curie temperature; Resonator; 30 MHz SMD-type; Energy-trapped; Dynamic range (DR)
1. Introduction Recently, as information technologies (IT) have been advanced in many countries, concerns for information communication components such as ceramic filters and resonators have also been increasing. The operating frequency of ceramic resonators, which can be utilized as clock oscillator for hard disk driver (HDD) and floppy disk driver (FDD), is required to be higher. The reason can be illustrated as the increasing of operating frequency leads to make the speed of the electronic instruments higher. However, in order to increase the operating frequency of the resonator, its 3rd overtone thickness vibration mode must be utilized [1], because the devices using fundamental mode thickness vibration for high frequency have the difficult problems such as lapping and polishing in diminishing its thickness. As far as the composition ceramics for the 3rd overtone thickness vibration mode resonators are concerned, the dynamic range (DR) must be high enough to induce stable thickness vibration. Based on such requirement, PbLa(Ti,
∗ Corresponding author. Tel.: +82-43-649-1301; fax: +82-43-648-0868. E-mail address: [email protected] (J. Yoo).
Mn)O3 ceramics, which had been reported as a composition ceramics with high mechanical quality factor (Qmt3 )and DR for the 3rd overtone thickness vibration mode, have been widely used for high frequency resonators. However, the Qmt3 and DR for the 3rd overtone thickness vibration mode between compositions with deficient and excess PbO may result in significant differences in electrical characteristics primarily because of PbO evaporation during the manufacturing process. In this experiments, normal sintering process with the liquid phase composed of CuO additive and remnant PbO was used to facilitate sintering process resulting in final microstructure of high density and strength. Energy trapping effects, which had been announced by Shockly et al. [2] in 1963, have the relation with the frequency constant, the thickness and the partial electrode weight of specimen. Accordingly, in this study, the effect of the partial electrode weight on the energy trapping was investigated. Another requirement for high frequency resonator is the ceramic composition capable of resisting any change in resonance frequency that may be caused by the thermal shock during the soldering of surface mount device (SMD) type resonators [3]. In this study, 30 MHz SMD-type resonators
0924-4247/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0924-4247(03)00063-3
56
J. Yoo, D. Oh / Sensors and Actuators A 105 (2003) 55–61
using 3rd overtone thickness vibration modes were fabricated using CuO added PbTiO3 ceramic composition modified with La, Nd, Mn and Sb. Electrical, structural and resonant characteristics were investigated as a function of internal electrode weight and CuO addition for the application of 30 MHz SMD-type ceramic resonators.
2. Experimental procedure The specimens were manufactured using conventional mixed oxide process. The ceramic composition used in this experiment is as follows:
from the disc. The specimens were electroded and poled, and then coated with photo-resistor for dot sizes of 0.77 mm in diameter. The specifications of the specimens studied in this work are referred in Fig. 1. As seen in Fig. 1, the PbTiO3 system ceramic resonator part is the intermediate part sandwiched between the cap and base parts. The cap and base fabricated using MgTiO3 are the upper and lower parts, respectively. The base is surface-mounted using solders. DR is defined as the decibel ratio of the impedance at resonance and anti-resonance frequencies based on the equation below [4]: Zmax DR = 20 log (1) Z min
Pb0.88 (La0.6 Nd0.4 )0.08 (Mn1/3 Sb2/3 )0.02 Ti0.98 O3 +0.1 wt.% excess PbO + 0.1 wt.% MnO2 The raw materials were acetone-milled and calcined at 850 ◦ C for 2 h. After calcinations, CuO of 0.25, 0.5, 0.75, and 1.0 wt.% were added and milled again. An 8 wt.% poly-vinyl alcohol (PVA) was mixed with the materials. The powders were uniaxially consolidated into discs with diameter of 30 mm. The green compacts were sintered at temperatures of 1200 ◦ C for 2 h and the sintered discs were thinned into the thickness of 0.255 mm. The resonators with the size of 3.7 mm × 3.1 mm × 0.255 mm were fabricated
DR was calculated from the impedances at resonance (Zmin ) and anti-resonance frequencies (Zmax ) measured using Agilent 4294 impedance analyzer. The temperature coefficient of resonant frequency (TCFr ) from −20 to 80 ◦ C was calculated by measuring the resonant frequency of specimen using an impedance analyzer in thermostatic chamber. The equation [5] used is as follows: TCFr =
fr (max) − fr (min) 1 × (ppm/◦ C) ◦ fr (25 C) 100
(2)
where fr (25 ◦ C), fr (max) and fr (min) are the resonant frequency at 25 ◦ C, maximum and minimum resonant
Fig. 1. Dimension and structure of SMD-type ceramic resonator: (a) front view; (b) side view; (c) interior view.
J. Yoo, D. Oh / Sensors and Actuators A 105 (2003) 55–61
57
frequency in the regions ranged from −20 to 80 ◦ C, respectively. 3. Results and discussion 3.1. CuO addition effects Fig. 2 shows the X-ray diffraction patterns for the specimens fabricated through the process described above. As can be seen from (0 0 2) and (2 0 0) peaks, the crystal structure is tetragonal and the tetragonality varies from 1.02869 to 1.03026, smaller than 1.064 of pure PbTiO3 . However, the amount of unidentified phase increases with CuO. It is likely that the CuO reacted with remnant PbO and then the second phase is formed. Further investigation on the phase is needed. The scanning electron micrographs of the specimens with different CuO composition are illustrated in Fig. 3. The grain size increases with the amount of CuO. This is due to the acceleration of grain growth by the liquid phase sintering of CuO and PbO [6]. Fig. 4 shows the variation in grain size as a function of CuO. Dielectric constant (εr ) and Curie temperature (Tc ) of the specimens with different CuO addition are listed in Table 1. The minimum dielectric constant was observed in the 0.5–0.75 wt.% CuO added specimens with grain size near 1.7 m, representing the boundary between mono-domain and multi-domain [7]. To maintain a stable oscillation of resonator, higher DR is required. Also higher DR can be obtained from the ceramic substrate with high density. In this study, for dense microstructure by the liquid phase sintering, CuO was added after calcinations. The liquid phase is due to the reaction between CuO additive and remnant PbO and facilitates sintering process resulting in final microstructure of high density and strength. The amount of additives for liquid phase sintering, however, must be controlled small enough because the additives residing mainly at grain boundaries deteriorate electrical properties of the final sintered material. As shown in Table 2, higher DR and
Fig. 3. Microstructures as a function of CuO addition.
Fig. 2. X-ray diffraction patterns as a function of CuO addition.
Qmt3 for the 3rd overtone vibration mode are available only from the high density. In other words, the resonators with high DR can be obtained through the controlled liquid phase sintering process. In general, final density of ceramics is closely related to the sintering parameters such as temperature, time and atmosphere. In this experiment, the maximum density of 7.72 g/cm3 , maximum DR of 49 dB and maximum Qmt3 of 2152 were obtained from the sample with 0.25 wt.% CuO, sintered at 1200 ◦ C. The high value of the Qmt3 means the low value of resonant impedance, providing the advantage that the ceramic resonators are resonating or oscillating under the condition of lower driving voltage [8].
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Table 1 Physical, dielectric and TCFr properties as a function of CuO addition CuO (wt.%)
Dielectric constant
Grain size (m)
Tc (◦ C)
Density (g/cm3 )
TCFr (ppm/◦ C)
0 0.25 0.5 0.75 1
220 211 184 185 204
0.67 1.18 1.60 1.62 1.87
329 325 323 318 325
7.56 7.72 7.66 7.57 7.53
12 17 26 27 31
Fig. 5. TCFr (%) as a function of CuO addition. Fig. 4. Variation of grain size as a function of CuO addition.
Fig. 6. Impedance and DR of SMD-type ceramic resonator as a function of electrode weight. Table 2 Piezoelectric and resonant characteristics of SMD-type ceramic resonator as a function of CuO addition CuO (wt.%)
Electrode diameter (mm)
fr (MHz)
fa (MHz)
Zr ()
Za (k)
DR (dB)
Qmt3
kt3
0 0.25 0.75
0.77 0.77 0.77
29.85 30.94 29.19
30.03 31.12 29.34
89.0 52.0 139.5
7.73 18.05 6.10
38.21 49.00 33.35
1184.48 2152.00 1155.37
0.12 0.12 0.11
J. Yoo, D. Oh / Sensors and Actuators A 105 (2003) 55–61
Fig. 7. kt3 and Qmt3 of SMD-type ceramic resonator as a function of electrode weight.
Fig. 8. Characteristic impedance curves of SMD-type ceramic resonator as a function of electrode weight.
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Table 3 Piezoelectric and resonant characteristics of SMD-type ceramic resonator as a function of electrode weight Electrode weight (×10−4 g/cm2 )
fr (MHz)
fa (MHz)
Zr ()
Za ()
DR (dB)
Qmt3
kt3
0.66 1.765 2.32 3.87
30.75 30.68 30.94 31.44
30.93 30.86 31.12 31.64
85 66 52 63
9585 12766 18050 14183
41 44 49 46
1444 1824 2152 1750
0.1194 0.1196 0.1191 0.1241
It can be illustrated that this is an extremely advantageous characteristic for a resonator or oscillator. Furthermore, if the mechanical quality factor, Qmt3 for the 3rd overtone vibration mode is higher, thereby the ratio of resonant and anti-resonant impedances becomes greater, thus making it possible to stabilize resonating or oscillating. Fig. 5 also shows the TCFr variations as a function of CuO addition at 3rd overtone thickness vibration mode. With the addition of CuO, the TCFr moved to positive side and further deteriorated. Such variation in TCFr probably seems to be related to the behavior of Cu2+ ions capable of occupying the B-site in the ABO3 perovskite lattice that may degrade TCFr by increasing the oxygen vacancies acting as the acceptor dopants [9]. 3.2. Electrode weight effects of ceramic resonator Fig. 6 shows impedance and DR of SMD-type ceramic resonator as a function of electrode weight. As the electrode weight of the resonator is increased, resonant resistance decreased and energy trapping effect apparently appeared. However, the over weight of electrode may suppress the mechanical vibration of the specimen and cause the increase of loss. Accordingly, the optimal condition for electrode weight may be obtained from the experiment. The highest DR of 49 dB was obtained from the specimen with the electrode weight of 2.32 × 10−4 g/cm2 . Fig. 7 shows kt3 and Qmt3 of SMD-type ceramic resonator with the size of 3.7 mm × 3.1 mm as a function of electrode weight. While the kt3 nearly showed constant value, the Qmt3 showed the maximum value of 2152 from the specimen with the electrode weight of 2.32 × 10−4 g/cm2 because of mass loading effect of electrode weight. After that electrode weight, it is considered that the Qmt3 is decreased by the suppression of thickness vibration because of over electrode weight. The characteristic impedance curves of SMD-type ceramic resonator are shown in Fig. 8. As can be seen, in the impedance characteristics of specimen with the electrode weight of 2.32 × 10−4 g/cm2 , the 3rd overtone vibration mode shows relatively sharp curve by the energy trapping and the proper mass loading effect [10]. Table 3 summarizes piezoelectric and resonant properties of the 30 MHz SMD-type resonators as a function of the electrode weight.
4. Conclusion The micro-structural, electrical and resonant properties of (Pb, La, Nd)(Ti, Mn, Sb)O3 ceramics were investigated as a function of internal electrode weight and CuO addition. Ceramic wafers for resonator were fabricated by evaporating electrode weights of 0.66, 1.765, 2.32, and 3.87 × 10−4 g/cm2 with silver, respectively. And then, 30 MHz SMD-type ceramic resonators were fabricated with the size of 3.7 mm × 3.1 mm and electrode diameter of 0.77 mm. Electrical and resonant characteristics of the resonators were investigated and the following conclusions were obtained: (1) The grain size increased with the CuO addition. (2) The 0.25 wt.% CuO added specimen showed the best characteristics for the resonator application. The density and Tc were obtained to be 7.72 g/cm3 and 325 ◦ C, respectively. (3) With increasing CuO, the TCFr moved to positive side and further deteriorated. (4) With increasing electrode weight, resonant resistance was gradually decreased. At the electrode weight of 2.32 × 10−4 g/cm2 , mechanical quality factor (Qmt3 ) and DR for the 3rd overtone thickness vibration mode showed the maximum value of 2152 and 49 dB, respectively. Acknowledgements This work was supported by Korea Research Foundation (Grant no. KRF-2000-042-E00023). References [1] Y. Yamashita, S. Sakano, I. Toba, Jpn. J. Appl. Phys. 36 (1997) 6096. [2] W. Shockly, D.R. Curran, D.J. Koneval, in: Proceedings of the 17th Annual Frequency Control Symposium 1963, p. 88. [3] K. Takahashi, M. Nishida, H. Hase, Jpn. J. Appl. Phys. 37 (1998) 5285. [4] S.K. Min, D.U. Oh, K.H. Yoon, J.H. Yoo, C.Y. Park, J.S. Kim, J. KIEEME 14 (9) (2001) 720. [5] C.-K. Liang, L. Wu, T.-S. Wu, Ferroelectrics 120 (1991) 185. [6] D.L. Corker, R.W. Whatmore, E. Ringgaard, W.W. Wolny, J. Eur. Ceram. Soc. 20 (2000) 2039. [7] K. Uchino, Piezoelectric Actuators and Ultrasonic Motor, Academic Press, London, 1997.
J. Yoo, D. Oh / Sensors and Actuators A 105 (2003) 55–61 [8] T. Ogawa, T. kittaka, US Patent 4 605 876 (1986). [9] K. Takahashi, M. Nishida, H. Hase, Jpn. J. Appl. Phys. 37 (1998) 5285. [10] J.H. Yoo, D.O. Oh, S.K. Min, S.H. Lee, C.Y. Park, J.S. Kim, E.T. Park, Sens. Actuators A 3297 (2002).
Biographies Juhyun Yoo received his PhD degree in Electrical Engineering from the Yonsei University, Korea in 1990. He is currently working in
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Semyung University as an associate professor of Electrical Engineering. His research interests are in the area of piezoelectric devices, including piezoelectric transformers, actuators, resonators and filters. Dongon Oh received his BS degree in Electrical Engineering from the Semyung University, Korea in 2002. He is currently involved in Graduate School of the same University. His current research interests are piezoelectric materials and their application, including resonators and filters.