Analysis the Reliability of Multilayer Ceramic Capacitor with inner Ni ...

Trans. EEM 10(1) 5 (2009): J.-R. Yoon et al. 7Table 2. Summary of MTTF and m(shape parameter) under various stressconditions.Voltage 34 V 44 VTempMTTF(min)m(ShapeParameter)MTTF(min)m(ShapeParameter)125 ℃ 1596.78 - 894.43 2.076150 ℃ 610.8 1.988 338.19 2.382175 ℃ 306.1 2.117 142.53 3.219ttVV(1 2 n= ( ) ⋅22 1T2−θT1)A voltage stress exponent, n, was 2.24 ~2.96 andtemperature stress Θwas 17.08 ~ 20.05. n value of 2.24 ~2.96 is similar to accepted in the industry of ceramiccapacitor. However, temperature exponential (Θ) is higherthan any other values reported earlier[7]. It is clear that Θis significantly affected by the thickness of active layer .Figure 3 shows the MTTF predictions for applied voltageand temperature. The relation between the logarithm of thelife time reciprocal of temperature showed linearity ascharacteristic of Arrhenius-type. Raising the test voltage hassignificantly decrease the predicted MTTF as Arrheniustypeformula, because the migration of ions and otherdefects upon a chemical defect reaction.1000000Table 3. Individual voltage exponential (n) and temperature exponential(Θ) for each stress condition.n(34 V ~ 44 V)2.24 (125 ℃)2.29 (150 ℃)2.96 (175 ℃)θ (34 V) θ (44 V)18.03(125 ~ 150 ℃)25.05(150 ~ 175 ℃)17.08(125 ~ 150 ℃)20.05(150 ~ 175 ℃)100000100001000100101000001000020406080 100Temp(℃)(a)120140160180Figure 4 shows degradation model of MLCC with thinactive layer. When a strong electric field applied to activelayer, a tunnel current flows (Fowler-Nordheim electrontunneling). For the insulation resistance degradationbehavior with thin active layer, it was found that thetunneling current through grain boundary was dominant atinitial stage of a leakage current and then oxygen vacanciesare present in significant amount in the core region, migratetowards the cathode[8]. The formation of electrical barriersis attributed to acceptor and doping of the n-type BaTiO 3dielectric and segregation of the dopants. In general, thelarge amount of oxygen vacancies in BaTiO 3 varies as afunction of the distance from the Ni electrode. Whenapplying dc field to the capacitor, oxygen vacancieselectromigrate from the anode to cathode. DC biasing leads to100010020406080100 120Temp(℃)140160180(b)Fig. 3. MTTF predictions for applied voltage and temperature.(a) Stress condition : 34 V, at 125, 150, 175 ℃(b) Stress condition : 44 V, at 125, 150, 175 ℃Table 3 indicated the importance of individual voltageexponential (n) and temperature exponential (Θ)for eachstress condition. The empirical MTTF equation for ceramiccapacitor by :Fig. 4. Tunneling schematic of the degradation model.

8 Trans. EEM 10(1) 5 (2009): J.-R. Yoon et al.chemical potential gradients and electromigration ofcharged defects. The concentration of oxygen vacanciesnear the cathode of Ni electrode is much higher than withinthe dielectric layers, leading to local high conductivity. Theintrinsic defect of oxygen vacancies in BaTiO 3 are related tomaterial imperfections and cause the capacitors to fail in athermal runaway mode.4. CONCLUSIONThe reliability of MLCC with active dielectric layer wasinvestigated by HALT test:(1) The relation between the logarithm of the life timereciprocal of temperature showed linearity ascharacteristic of Arrhenius-type.(2) A voltage stress exponent was n=2.24 ~2.96 andtemperature stress was Θ=17.08 ~ 20.05. The value ofn=2.24 ~ 2.96 is similar to accepted in the industry ofceramic capacitor.(3) The concentration of oxygen vacancies near the cathodeof Ni electrode is much higher than within the dielectriclayers, leading to local high conductivity.REFERENCES[1] H. Kishi, Y. Mizuno, and H. Chazono, Jpn.J.Appl.Phys. 42, 1 (2003).[2] A. Kirianov, T. Hagiwara, H. Kishi, and H. Ohsato, Jpn. J. Appl. Phys.41, 6934 (2002).[3] H. Kishi, N. Kohzu, Y. Mizuno, Y. Iguchi, J. Sugino, H. Ohsato, andT. Okuda, Jpn. J. Appl. Phys. 38, 5452 (1999).[4] T. I. Propokowice and A. R. Vaskas, ECOM Report No. 90705-F,(1969).[5] R. Municoti and P. Dhar, IEEE Trans. Comp., Hybrids, Manu. 11,346 (1988).[6] J. R. Yoon, B. C. Woo, H. Y. Lee, and S. W. Lee, J. of KIEEME(inKorean) 20, 118 (2007).[7] M. S. Randall, A. S. Gurav, D. J.Skamser, and J. J. Beeson, CARTS2003, p. 134.[8] G. Y. Yang, G. D. Lian, E. C. Dickey, C. A. Randall, D. E. Barber, P.Pinceloup, M. A. Henderson, R. A. Hill, J. J. Beeson, and D. J.Skamser, Jpn. J. Appl. Phys. 96, 7500 (2004).