1038 ieee transactions on ultrasonics, ferroelectrics, and frequency control, vol. 55, no. 5, may 2008

Dielectric Properties of Ni-coatedBaTiO3-PMMA Composite

Jung Min Park, Hee Young Lee, Jeong-Joo Kim, Eun Tae Park, and Yul-Kyo Chung

Abstract—Dielectric properties of Ni-coated BaTiO3-PMMA (polymethyl methacrylate) composite were stud-ied from an embedded capacitor application viewpoint. Vol-ume loading of up to 50% was attempted, and the resultswere compared with uncoated BaTiO3-PMMA composite.Ni-coating on BaTiO3 powder was found to greatly im-prove the dielectric properties of the composite, especiallythe dielectric constant value. K values of about 100 withtemperature-stable X7E characteristics were realized.

I. Introduction

The integration of embedded passive components intoprinted circuit boards offers significant reduction in

package size, improved electrical performance and reliabil-ity, faster switching speed, and lower manufacturing cost.Among all of the embedded passive components, the em-bedded capacitor plays an important role as a decouplingor by-pass capacitor in the circuits and occupies more than40% of the passive components. Recently, significant ef-forts have focused on developing percolative compositesthat are suitable for dielectric material that can be usedas a capacitor in embedded passive devices [1], [2].

Two-phase composites of metal-polymer or ceramic-polymer have been investigated in an attempt to obtainhighly effective dielectric constant values. While the fer-roelectric ceramic-polymer composites generally show anincreasing effective dielectric constant with increasing ce-ramic volume fraction, which is in good agreement withthe mixing rule, metal-polymer composites show an abruptrise in the dielectric constant near the percolation thresh-old of metal. Therefore, the dielectric constant of themetal-polymer composite can become much larger thanthat of the polymer matrix [3]–[5]. However, the dielectricloss also increases very rapidly near the threshold, whichlimits the use of 2-phase composites in actual devices.

In order to further enhance the dielectric properties ofpolymer-based composites, 3-phase composites, consistingof ceramic, metal, and polymer phases, have attracted sig-nificant attention due to higher dielectric constant feasi-

Manuscript received May 28, 2007; accepted January 2, 2008. Thisresearch was supported by the Yeungnam University research grantsin 2006.

J. M. Park and H. Y. Lee are with the School of Materials Scienceand Engineering, Yeungnam University, Gyeongsan, 712-749, Korea(e-mail: hyulee@yu.ac.kr).

J.-J. Kim is with the Department of Inorganic Materials Engineer-ing, Kyungpook National University, Daegu, 702-701, Korea.

E. T. Park and Y.-K. Chung are with Samsung Electro-MechanicsCo. Ltd., Suwon, 443-803, Korea.

Digital Object Identifier 10.1109/TUFFC.2008.752

bility with low processing temperature. We have reportedthe role of high K BaTiO3 filler and Ni particle sizein Ni-BaTiO3-PMMA (polymethyl methacrylate) compos-ites, where both Ni and BaTiO3 particles are dispersed inthe polymer matrix [6], [7]. The alternative composite canalso be made from BaTiO3 particles coated with thin Nilayer, which is the topic of this paper.

II. Experimental Procedure

Nickel ion-containing solution was prepared and usedfor coating commercially available high purity capacitor-grade BaTiO3 nano-powder. The median particle size ofthe BaTiO3 powder was about 500 nm. The powder wasmixed with the solution, dried on the hot plate at 70◦C,and heat-treated in 5% forming gas at 900◦C. X-raydiffraction (XRD) and transmission electron microscopy(TEM) were then utilized for observation of the crystal-lization and morphology of the particles.

Ni-coated powder of up to 50 volume % was then mixedwith PMMA polymer beads and warm-pressed at 4500 psiand 180◦C for 8 min in a disk-shape mold. Copper foilswhich acted as electrodes were laminated on both top andbottom surfaces. Dielectric properties of composite capaci-tors were then measured using an HP 4194 impedance ana-lyzer (Agilent Technologies, Inc., Santa Clara, CA) and anenvironmental chamber. Typical dimensions of the capac-itor are 32 mm in diameter and 1.5∼2.7 mm in thickness.

III. Results and Discussion

A. Ni Coating

Fig. 1 shows x-ray diffraction patterns obtained for thepowders before and after the coating treatment. It is evi-dent that the solution coating process changed the phasespresent in the powder. It was found that the reflectionpeaks at approximately 44◦ and 52◦ belonged to metal-lic nickel, and their strength was strongly dependent onthe stirring and drying treatments before forming gas an-neal. To identify the state of the coated particle and themorphology of nickel, the annealed BaTiO3 powder wasexamined using TEM, which is illustrated in Fig. 2. Asseen in the figure, both completely coated and partiallycoated particles were identified, and the thickness of thecoating was approximately 5.7 nm. It is not yet clear whichexperimental factors affected the amount or completenessof the coating, and this is under continuing investigation.

0885–3010/$25.00 c© 2008 IEEE

park et al.: dielectric properties of ni-coated batio3-pmma composite 1039

Fig. 1. XRD patterns of BaTiO3 powders: (a) untreated, (b) wet-coated and dried, and (c) annealed in forming gas.

Fig. 2. Transmission electron micrographs of BaTiO3 powder:(a) completely coated (A: Ni, B: BaTiO3), and (b) partially coatedwith thin Ni layer.

B. Dielectric Properties

Fig. 3 shows the measured dielectric properties of Ni-coated BaTiO3-PMMA composite capacitors. It is clearlyseen that the effect of Ni coating greatly increased theeffective dielectric constant, K, value, reaching the maxi-mum of 98 at 40% loading. Dielectric loss, however, also in-creased with Ni coating, probably due to the segregation ofisolated uncoated Ni particles and partially coated BaTiO3particles, when compared with 2-phase BaTiO3-PMMAcomposites. It is also noted that the K value decreasedabove about 40% loading. This is attributable to the in-crease of pore volume resulting from uneven mixing of con-

Fig. 3. (a) Dielectric constant, and (b) loss values of composite ca-pacitors as a function of volume loading at 1 MHz.

stituents, which is evident from the SEM pictures of thefracture surfaces of the 3-phase composite capacitor sam-ples corresponding to 40% and 50% volume fractions of Ni-coated BaTiO3 particles (Fig. 4). The 40% sample whichshowed the maximum effective dielectric constant revealeda microstructure with rather uniformly coated particles,whereas the 50% sample showed the discontinuous networkof PMMA matrix and the pores randomly scattered withinthe composite. The optimum volume loading of about 40%agrees well with the results obtained for 2-phase and 3-phase composites reported earlier [5].

Frequency responses of the Ni-coated BaTiO3-PMMAcomposite capacitors are illustrated in Fig. 5. The result issimilar to the characteristics often found in a temperature-stable class I dielectric with no evidence of interfacial orspace charge polarization up to 1.2 MHz. This probably in-dicates that Ni-coated BaTiO3 particles are not connectedacross the Cu foil electrodes, and the composite maintainsthe particulate composite structure, or still remains in a 0–3 connectivity pattern. If connected, the composite dielec-tric loses its insulating characteristics, and consequently isnot desirable for capacitor application.

1040 ieee transactions on ultrasonics, ferroelectrics, and frequency control, vol. 55, no. 5, may 2008

Fig. 4. Scanning electron micrographs of the fractured samples with(a) 40% and (b) 50% of Ni-coated BaTiO3 particles.

Voltage dependence was also studied at room tempera-ture and 1 MHz by applying up to ± 35 V bias. There wasno change in capacitance with dc bias, which is typical oflinear dielectric, and the results are summarized in Table I.

Fig. 6 illustrates the variation of the capacitance withtemperature for the composite capacitors with 40% volumeloading with and without Ni coating treatment. It is ap-parent that both BaTiO3-PMMA and Ni-coated BaTiO3-PMMA composite capacitors satisfy temperature-stableX7P characteristics, which is desirable for reliable cir-cuit operation of electrical and electronic systems intendedfor outdoor use under extreme conditions. Between the2 types of composites, the latter showed more stable re-sults, with maximum variation equal to or smaller than± 4.7%, which corresponds to X7E characteristics. It isnoted that the rather high loss of about 2.5% for theNi-coated BaTiO3-PMMA composite capacitor, comparedwith about 1% for the uncoated 2-phase BaTiO3-PMMAcomposite, could be related to the thickness of the Ni layer,the degree of coverage, and the morphology of coated par-ticles. Further studies are currently underway to addressthis issue.

Fig. 5. Frequency response of Ni-coated BaTiO3-PMMA compositecapacitors.

TABLE ISummary of C-V Data Measured at Room Temperature and

1 MHz for Three Types of Dielectrics.∗

Ni-coatedBT(40%) BT(40%)

PMMA -PMMA -PMMA

Dielectric constant 3.4 21.5 98tan δ 0.02 0.015 0.025∆Cmax/C0 V (%) 0 0.13 0.37

∗Maximum electric field intensity was about ± 20 V/mm.

park et al.: dielectric properties of ni-coated batio3-pmma composite 1041

Fig. 6. Temperature dependence of capacitance for 2 types of com-posite capacitors.

IV. Summary and Conclusions

Ni-coated BaTiO3-PMMA composites were fabricatedby stirring and drying BaTiO3 powder in Ni-ion-containing solution, followed by forming gas anneal at900◦C. Powder morphology was examined by TEM, andboth complete and partially coated particles were identi-fied with the Ni layer thickness corresponding to 5.7 nm.

The effective dielectric constant value of Ni-coatedBaTiO3-PMMA composite capacitors showed a maximumaround 40% volume loading, which was higher than thatof 2-phase BaTiO3-PMMA composite capacitors. The de-crease in K value above 40% loading was attributed tothe increased pore volume resulting from uneven mix-ing of constituents. K values of approximately 100 withtemperature-stable X7E characteristics were realized fromthis study.

References

[1] S. Ogitani, S. A. Bidstrup-Allen, and P. A. Kohl, “Factors in-fluencing the permittivity of polymer/ceramic composites forembedded capacitors,” IEEE Trans. Adv. Packag., vol. 23, pp.313–322, 2000.

[2] S. K. Bhattacharya and R. R. Tummala, “Next generation in-tegral passives: Materials, processes, and integration of resistorsand capacitors on PWB substrates,” J. Mater. Sci. Mater. Elec-tron., vol. 11, pp. 253–268, 2000.

[3] D.-H. Kuo, C.-C. Lai, T.-Y. Su, W.-K. Wang, and B.-Y. Lin,“Dielectric behaviours of multi-doped BaTiO3/epoxy compos-ites,” J. Eur. Ceram. Soc., vol. 21, pp. 1171–1177, 2001.

[4] Y. Rao, S. Ogitani, P. Kohl, and C. P. Wong, “Novel polymer-ceramic nanocomposite based on high dielectric constant epoxyformula for embedded capacitor application,” J. Appl. Polym.Sci., vol. 83, pp. 1084–1090, 2002.

[5] E.-S. Lim, J.-C. Lee, J.-J. Kim, E.-T. Park, Y.-K. Chung, andH.-Y. Lee, “Dielectric characteristics of polymer-ceramic-metalcomposites for the application of embedded passive devices,” In-tegr. Ferroelectr., vol. 74, pp. 53–60, 2005.

[6] H.-W. Choi, Y.-W. Heo, J.-H. Lee, J.-J. Kim, H.-Y. Lee, E.-T.Park, and Y.-K. Chung, “Effects of BaTiO3 on dielectric behav-ior of BaTiO3-Ni-Polymethyl methacrylate composites,” Appl.Phys. Lett., vol. 89, art. no. 132910, 2006.

[7] H.-W. Choi, Y.-W. Heo, J.-H. Lee, J.-J. Kim, H.-Y. Lee, E.-T.Park, and Y.-K. Chung, “Effects of Ni particle size on dielec-tric properties of PMMA-Ni-BaTiO3 composites,” Integr. Fer-roelectr., vol. 87, pp. 85–93, 2007.

Jung Min Park graduated from YeungnamUniversity, Gyeongsan, Korea, in 2007 withan M.S. degree in materials science and en-gineering. He is currently a graduate studentin solid state electronics at Osaka University,Japan. His research interests include multifer-roic thin films and devices and thick-film em-bedded capacitors for LTCC mpplications.

Hee Young Lee is a professor of materi-als science and engineering at Yeungnam Uni-versity, Gyeongsan, Korea. Prior to his cur-rent position, he was an assistant professorof materials and metallurgical engineering atNew Mexico Tech, Socorro, NM. His cur-rent research interests include thin film pro-cessing and characterization of ferroelectricceramics and transparent conducting oxides(TCOs). He served as a guest associate edi-tor for the Journal of Electroceramics in 2006.At present, he is a member of the Korean Ce-

ramic Society and the Korean Institute of Electrical and ElectronicMaterial Engineers.

Jeong-Joo Kim is a professor of inorganicmaterials engineering at Kyungpook NationalUniversity, Daegu, Korea. He has also beenthe director of the KOSEF Information Cen-ter for Materials, Daegu, Korea. He earnedhis B.S., M.S., and Ph.D. degrees in ceram-ics from Seoul National University. His re-search interests include microstructure evolu-tion and ferroelectric properties of perovskiteand tungsten bronze structured ceramics, andtransparent conducting oxides (TCOs). Heserved on the technical committee of the Pow-

der Metallurgy World Congress and Exhibition 2006. He is a memberof the American Ceramic Society and Materials Research Society.

Eun Tae Park is currently a principal re-searcher in the LTCC (Low Temperature Co-fired Ceramics) group of the eMD (electro Ma-terials & Device) Center at Samsung Electro-Mechanics (SEMCO) since 2000. He receivedthe B.S. and M.S. degrees in materials sci-ence and engineering from Kyungpook Na-tional University, Daegu, Korea, in 1990 and1992, respectively; and the Ph.D. degree inmetallurgical and materials engineering fromthe Illinois Institute of Technology (IIT),Chicago, IL, in 1997. Before joining SEMCO,

he was a post-doctoral fellow in materials science and engineeringat the University of Cincinnati, Cincinnati, OH, (1999 to 2000) andArgonne National Laboratory, Argonne, IL, (1997 to 1998). At thetime, he focused on the processing and high temperature deformationof ceramics and ceramic matrix composites, and crack propagationin piezoelectric ceramics. His current research interests in SEMCO

1042 ieee transactions on ultrasonics, ferroelectrics, and frequency control, vol. 55, no. 5, may 2008

include development of LTCC glass and paste composition for sub-strate, especially high electric constant materials, and processing forembedded capacitors in LTCC module.

Yul-Kyo Chung has been a principal re-search engineer at Samsung Electro-Mechan-ics, Suwon, Korea, for 10 years in the field ofembedded PCB, LTCC, and MLCC. His re-cent research interests are embedding passivesinto PCB and system modules in a package.Prior to joining SEMCO, he was a researchengineer for Tongyang Cement Co., Seoul, Ko-rea. During his 10 years at Tongyang, he hadresearched electronic ceramic devices such aspiezoelectric sensors, filters, and resonators.He received B.S. and M.S. degrees in inorganic

materials engineering from Seoul National University. He also visitedShizuoka Rikoka University, Fukuroi City, Japan, for six months asa special research scientist.