MLCC replacements for tantalum capacitors - Yageo

MLCC replacements for tantalum capacitors - Yageo

MLCC replacements fortantalum

MLCC replacements for tantalum capacitorsThe past 5 to 10 years have seen increases of between10 and 100 fold in capacitance per unit volume for bothceramic multilayer capacitors and solid tantalumcapacitors (Refs 1 and 2). Figure 1 shows this increasefor ceramic capacitors.As a result, the application areasfor MLCCs have gradually extended into those formerlydominated by tantalum capacitors and these, in turn,have extended into even higher capacitance applicationareas formerly occupied by, for example, electrolytics.10priceindex1MLCC X7RMLCC Y5VMSD100Atantalum10 2cap/vol(mF/mm 3 )10 210 -21985 1990 1995 200010 2 MSD099Fig. 210 -1Cost reduction for 1 µF capacitors.2SUMMARYFor certain capacitance values, many circuitdesigners who traditionally use tantalumcapacitors might well find that their applicationis now better served by MLCCs. Moreover, theever higher production levels of MLCCs coupledwith new developments such as the introductionof base-metal electrodes have greatly reducedthe unit production cost of MLCCs.This meanson price too, they can now compete withtantalum capacitors in many applications.Fig. 110 -110 -210 -3Y5VX7R1980 1985 1990 1995 2000MLCC capacitance per unit volume increaseIn the area of overlap between 0.1 µF and 100 µF,therefore, the two technologies compete and manycircuit designers who traditionally use tantalumcapacitors might well find that their application is nowbetter served by MLCCs. The ever higher productionlevels of MLCCs (currently 600 billion annuallycompared with 25 billion for tantalum capacitors)coupled with new developments such as theintroduction of base-metal electrodes have also greatlyreduced the unit production cost of MLCCs, whichmeans on price too, they can now compete withtantalum capacitors in many applications.Figure 2 gives a schematic view of the price decreasebetween 1985 and 1995 for 1 µF capacitors in ceramicmultilayer and tantalum technology. In 1990,Y5V MLCCprices reached the tantalum level and since 1995 X7Rtypes too have reached the price levels of 1 µF tantalumcapacitors.In this graph the cheapest solutions in bothtechnologies are compared based on equal nominalcapacitance. In this publication, however, it will be shownthat instead of comparing costs of equal nominalcapacitance it is better to compare costs ofcapacitance/size combinations which give equalelectrical performance.Since in each application area the requirements ofelectrical performance differ, it’s necessary to make acomparison per functional application area. In thispublication, therefore, we shall compare two typicalapplication areas in which MLCCs and tantalumcapacitors compete: decoupling and smoothing.First, however, let’s look at the general differences inspecification and performance of tantalum capacitorsand MLCCs.General comparison of specificationsA general problem in comparing capacitors made bydifferent technologies is that in nearly all relevantspecification points there are small or larger differences(see Table 1).Table 1 Comparison of specifications:MLCCs versus tantalum capacitorsMLCC tantalumcapacitorcapacitance 1 kHz, 120 Hzmeasurement 1 V AC 0.5 V ACconditionssize: 0603 1.6 x 0.8 mm 1.6 x 0.85 mm0805 2.0 x 1.25 mm 2.0 x 1.35 mmlife-test conditions max. temperature max. temperature2 x U rated U ratedThese differences originate from the early days ofcapacitor development in which specifications were setmore by the performance inherent to the specificmanufacturing technology than by common customerneeds. Ceramic capacitor manufacturers, therefore, setup their specifications to provide comparisons withother capacitors of similar technology, as did3

4manufacturers of tantalum capacitors, electrolytics andcapacitors in other technologies.Bearing this in mind we start comparing basicperformance characteristics of MLCCs and tantalumcapacitors by looking at major categories such ascapacitance/volume per case size, rated voltages andtemperature characteristics.Capacitance per unit volumeBased on nominal specifications, tantalum capacitorsoffer the highest maximum capacitance at rated voltageof 2 to 4 V. For higher rated voltages, however, i.e.between 6 and 10 V, there is little difference in maximumcapacitance between 0603, 0805 and 1206 Y5V MLCCsand tantalum capacitors.In contrast, X7R MLCCs offering the same maximumcapacitance are at least one and sometimes two casesizes larger than their counterparts in Y5V or tantalum.Rated voltageFor tantalum capacitors, the rated voltage is close to thebreakdown voltage and is clearly to be interpreted asmore or less the maximum voltage at which thecapacitors can operate. In the interests of reliability,therefore, designers commonly derate tantalumcapacitors to operate at voltages between 20% and 50%below their rated voltage.In contrast to tantalums, the rated voltage of MLCCs isfar less than their breakdown voltage and is usuallydetermined by the performance in dry endurance tests.A point worth noting here is that in order to complywith EIA and EIAJ standards, MLCCs are required toundergo long-term reliability testing at twice their ratedvoltage.The obvious conclusion of this is that in circuits whereeither type may be used, to get the same circuit reliabilityit would be necessary to choose a tantalum with roughlytwice the rated voltage of the equivalent MLCC.Temperature characteristicsIn the temperature range 0 to 85 °C, tantalum capacitorsoffer a relatively flat temperature characteristic.MLCCs, on the other hand, come in differenttemperature classes defined by their dielectric, such asY5V, Z5U,Y5U, X7R, and X5R.As a general rule one cansay that for MLCCs, temperature characteristic canalways be improved at the expense of capacitance perunit volume.In general, X5R and X7R specifications are comparable tothose of tantalum in the temperature range 0 to 85 °C.This does not mean, however, that in comparingtantalum capacitors with MLCCs, one should consideronly X5R or X7R products. As we’ll show later, Y5VMLCCs despite their strong temperature dependencecan offer attractive alternatives to tantalum capacitorsin certain areas.Other general specification itemsThere are many other differences between the generalspecifications of MLCCs and tantalum capacitors. Table2 gives a survey of these differences many of which may,in particular cases, be decisive in deciding on whichtechnology to choose.Table 2 General comparison of MLCCsand tantalum capacitorscharacteristic Y5V X7R solidMLCC MLCC Tacapacitance range ++ + ++bipolarity ++ ++ -resistance to pulse voltage ++ ++ +lifetime at T > 85 °C +/- + -high-frequency performance + ++ -breakdown voltage ++ ++ -voltage dependency (DC) - +/- +product height ++ ++ +SMD compatibility ++ ++ +reliability ++ ++ +In many instances, the criteria in Table 2 may make thechoice between MLCC and tantalum clear. In otherinstances, however, to make a proper choice we need tolook further at the influence of frequency, temperatureand bias voltage on the more fundamental properties ofimpedance, ESR and ESL.Comparison of impedanceFigure 3 gives a comparison of room-temperatureimpedance as a function of frequency for 1 µFcapacitors in tantalum and Y5V MLCC technologies.10 2MSD101Aimpedance(Ω)10tantalum1MLCC10 -110 -2Fig. 3 Impedance as a funcion of frequency for a 1 µFtantalum capacitor (16 V) and a 1 µF Y5V MLCCSince decoupling performance, in particular, is oftendetermined by the capacitor’s impedance, the lowerimpedance of the MLCC for frequencies above 100 kHzin this case makes it the preferred choice.Influence of temperature on impedance.The influences of temperature on the decouplingperformance should also be taken in account. For the1 µF capacitors in the example above, Fig.4 shows thetemperature dependence of impedance between 0 and+85 °C.Fig. 410 3impedance(Ω)10 21010 -3 10 -2 10 -1 1 10 10 2110 -1MLCC 85 ˚CMLCC 20 ˚CTa 85 ˚Cf (MHz)MSD102ATa 20 ˚C10 -210 -3 10 -2 10 -1 1 10 10 2f (MHz)Impedance as a function of frequency andtemperature for a 1 µF 16 V tantalum capacitor anda 1 µF 16 V Y5V MLCCFrom this figure we see that at low frequencies theimpedance of a 1 µF Y5V MLCC roughly doubles itsvalue between room temperature and 85 °C. Chieflybecause of this, the frequency at which the impedanceof the Y5V capacitor becomes lower than that of thetantalum capacitor of the same values shifts fromapproximately 60 kHz to 200 kHz. Although thissuggests that the frequency range over which thetantalum capacitor competes with the MLCC isextended at these higher temperatures, most modernapplications in, for example, EDP and power suppliesoperate at frequencies well in excess of 100 kHz whichmeans that even with this relatively high dependence ofimpedance on temperature, the Y5V MLCC is usuallystill preferred.X7R/X5R MLCCsFor X7R and X5R MLCCs, the low frequencyimpedance up to 10 kHz is approximately the same asfor tantalum capacitors. Above this frequency, however,these MLCCs show rapidly decreasing impedancerelative to tantalum and this impedance remains lowerover the whole frequency range above 10 kHz.X7R and X5R capacitors show hardly any variation inimpedance with temperature so that with increasingtemperature, the difference in impedance between atantalum and X7R/X5R capacitor stays approximatelythe same.Influence of DC-bias on impedanceA well-known feature of tantalum capacitors is thattheir capacitance remains relatively unchanged whenDC-bias voltage is applied.In contrast, the capacitance of class 2 MLCCs falls withDC bias voltage.The magnitude of this fall depends bothon the dielectric material and on the applied fieldstrength. It therefore differs for X7R and Y5V and foreach rated voltage.For X7R MLCCs, this effect is limited.A typical 16 V typewill lose a maximum of 20% of its capacitance when a16 V bias is applied.For a 16 V Y5V MLCC, the effect is relatively large, acapacitor losing over 80% of its impedance when a 16 Vbias voltage is applied.Figure 5 shows the influence of this change on theimpedance of the capacitor. Again we see that, despitethe large dependence on bias voltage, for frequenciesabove 100 kHz the impedance levels of the MLCC aremuch lower than those of the tantalum capacitor. In the1 to 10 MHz region, the difference is a factor 10.5

10 3MSD103Aimpedance(Ω) MLCC at V dc = 10 V10 2MLCC at V dc = 5 V10Ta at V1dc

currents. Even so, design constraints such as maximumoperating temperature, capacitance required and highfrequencyswitching requirements of modern SMPSdesigns often make the choice of capacitor technologyclear. In those areas where the choice is not clear,however, it is sensible to make a cost-performanceanalysis.For this we use what’s known as a spice model (Ref.3) tocompare the smoothing performances of the productsin Table 3.The simulation circuit consists of a full-waverectifier bridge excited by a 10 V sine-wave voltagesource with an internal resistance of 1 Ω.The rectifierbridge is smoothed by either an MLCC or an tantalumcapacitor.The circuit is loaded with a 100 Ω resistor.Thecapacitor models are basically RLC-models with thevalues properly chosen as a function of frequency,temperature and bias voltage. This approach is validbecause the circuit is simulated for a single frequency.Based on the cost index as given in Table 3, thesmoothing performance is translated into costperformancediagrams. Figures 9, 10 and 11 areexamples of these diagrams.Fig. 94costindex321100 µFtantalum2.2 µF10 µFMLCC Y5V10 µF1 µFCost-performance diagram at 40 °C, 100 kHz, 5 Vbias for smoothingIn the cost-performance diagram, both cost andperformance are given relative to the tantalum 1 µF level.Good performance corresponds to low ripple index.1 µFMLCC X7R0.1 µFMSD107A010 -1 1ripple index10From Fig.9, the following conclusions can be drawn:• Within the MLCC range, a cheaper solution can befound for all performance levels• For low and medium performance levels, a Y5V MLCCis the most cost-effective solution• For high performance levels (including the best level)an X7R MLCC is always the best choice.In a next step we look at the effects of an increase ofoperating temperature. The results are summarized inFig.10 which gives the cost-performance at 60 °C,100 kHz and 5 V bias.Fig. 104costindex321100 µFtantalum2.2 µF10 µF1 µFMLCC Y5VCost-performance diagram at 60 °C, 100 kHz, 5 Vbias for smoothingBasically at 60 °C the conclusions differ little from thosedrawn from Fig.9. The main difference is that the Y5VMLCCs are less competitive as a result of their reducedeffective capacitance.Figure 11 illustrates the influence of both a furthertemperature and frequency increase. The Y5V MLCChas been omitted here because it is no longercompetitive at these high temperature.One further conclusion can be added:• At 1 MHz the competitive position of the X7R MLCCimproves due to the tantalum capacitors’ reducedeffective capacitance and high ESR.1 µFMLCC X7R0.1 µFMSD108A010 -1 1ripple index10Fig.11 Cost-performance diagram at 85 °C, 1 MHz, 5 Vbias for smoothingInfluence of the DC-bias levelsThese results have all been simulated with parametersbased on a DC-bias level of 5 V.When reducing the biaslevel to 3 or 1.5 V, the performance of tantalumcapacitors stays the same, but the performance ofMLCCs improves. In this respect it’s worth noting thatthe performance of the Y5V MLCCs improves moresince it is more sensitive to DC-bias. As a result, Y5VMLCCs become more cost effective at lower circuit voltages.DecouplingWhen looking at local decoupling one has to assess theamount of charge required by the IC to perform itsstate change without causing excess voltage ripple.Thevoltage ripple can seriously degrade IC performance.The capacitor, therefore, has to respond as a lowimpedancecharge source.To assess the capacitors’ behaviour in this respect, theperformance of 0.1 to 10 µF MLCCs and 1 to 100 µFtantalum capacitors from Table 3 were investigated inthe 100 kHz to 1 MHz frequency range. In the initialtests, the capacitors were subjected to a 100 kHzsquare wave and in the later tests they were subjectedto a 1 MHz sine wave.The influence of temperature andintermediate frequencies was simulated using a generaldecoupling model.Figures 12, 13 and 14 show typical cost-performancediagrams. As with smoothing, performance was seen toimprove with increasing capacitance.Fig.12 Cost-performance diagram at 40 °C, 100 kHz, 5 Vbias for decouplingFrom Fig.12 it’s evident that at 100 kHz and 40 °C, a1 µF MLCC offers a more cost effective solution than a1 µF 16 V tantalum but does not perform as well as the10 µF tantalum capacitor.The 33 µF in case size C and100 µF in case size D achieve even better performancelevels at, it should be noted, considerably greater cost.Additionally, since the size of these components is muchgreater, a designer may well consider using more thanone MLCC in preference to a larger tantalum capacitor.Fig.13 Cost-performance diagram at 40 °C, 1 MHz, 5 Vbias for decouplingThe lines in the figure connect the data for the typesFigure 13 shows the influence of increasing the decouplingfrom Table 3 manufactured in the same technology. Forfrequency to 1 MHz. Here the situation has changed.Weall 3 series the performance improves with increasingsee now that at this frequency the 1 µF X7R MLCC offerscapacitance.a more cost-effective solution than even the 10 µFtantalum capacitor. Moreover, the cost effectiveness of theY5V capacitor has also improved. Both effects come fromthe reduced need for effective capacitance at this8 frequency and the increased importance of low ESR.94costindex3212.2 µFMLCC X7R100 µFtantalum1 µF10 µF1 µF0.1 µFMSD109A010 -2 10 -1 1ripple index104costindex321100 µFtantalum2.2 µF10 µF10 µFMLCC Y5V1 µFMLCC X7RMSD110A0.1 µF010 -2 10 -1 1ripple index104costindex3212.2 µF10 µF100 µFMLCC Y5Vtantalum10 µF1 µF1 µFMLCC X7R0.1 µFMSD111A010 -2 10 -1 1ripple index10

We also notice that despite the high nominalcapacitance, the 33 µF and 100 µF tantalum capacitorsno longer offer the best performance. In this example,the 2.2 µF X7R MLCC is, in fact superior to thesecapacitors.4costindex3212.2 µF10 µF C100 µFMLCC Y5Vtantalum10 µF1 µF0.1 µFMSD112A010 -2 10 -1 1ripple index10Fig.14 Cost-performance diagram at 60 °C, 1 MHz, 5 Vbias for decouplingFigure 14 shows the influence of increasing theoperating temperature to 60 °C. Compared with thesituation of Fig.13, the major change here is theincreased cost effectiveness of the X7R MLCCs. In fact,under these conditions X7R MLCCs are unique in theirability to achieve the best performance.From the simulation results it can be concluded thatMLCCs with nominal capacitance both in X7R and Y5Vdielectric offer cost-effective alternatives to equivalenttantalum capacitors over a large frequency andtemperature range.For frequencies up to 500 kHz, it is possible to improvethe decoupling performance in tantalum technology bychoosing a larger capacitance. Since the ESR of thislarger capacitance is lower, the impedance will also belower over a large proportion of the frequency range.Usually, however, a larger value tantalum capacitor hasthe disadvantages of a lower rated voltage or a largercase size and a poorer performance at higherfrequencies. This can give additional problems if EMCregulations have to be taken into account.1 µFMLCC X7RFuture developmentsIn both technologies, developments continue towardsfurther increase of capacitance per unit volume andsmaller sizes (Refs 2, 3 and 4). In addition, bothtechnologies are introducing products with lower ESRlevels. In tantalum technology, new series like theNeocapacitor (Ref.5) and the dedicated Low ESR seriesare finding their application segments. Likewise, inMLCC technology increased numbers of layers andgreater effective capacitances are leading to reducedESR levels (Ref.6).First indications based on extrapolations of Figs 1 and 2lead to the expectation that MLCCs will furtherpenetrate the tantalum area and that tantalumcapacitors will strengthen their position in the highcapacitance area (currently dominated by electrolytics).Conclusions• MLCCs and tantalum capacitors have been comparedon general and functional specifications• A detailed understanding of the behaviour is neededto predict the performance in relation to circuitdemands• Cost-performance diagrams can help in selecting theoptimal capacitor.• Both in smoothing and in decoupling, MLCCs havebeen shown in most cases to be more cost effectivethan tantalum capacitors• The cost effectiveness of MLCCs improves withfrequency• Y5V MLCCs are most cost effective at low biasvoltage, medium performance levels and temperatureup to 40 to 60 °C• X7R MLCCs are most cost effective at highperformance levels and higher temperatures• The battle between MLCC and tantalum capacitortechnologies will continue.More informationFor more information and data, contact your local Yageosales representative or visit our web site on Development of large Capacitance Multilayerceramic Capacitors with thin dielectric layersH. Kanai, K. Harada,Y.Yamashita, K. Handa,Carts USA 1995 page 9-142. Dielectric Characteristics of Complex perovskiteMultilayer Ceramic Capacitors with Thin DielectricLayersS.Takakura, K. Katoh, M.Yamada,Y.Yoneda.Murata Manufacturing Co.,Ltd.Jpn. Journal of applied Phys.Vol. 34 (1995) .3. Spice modeling of capacitors,John D. Prymak. Kemet Electronics.Carts USA 1995 page 39-46.4. New design of tantalum capacitor.Ian SalisburyAVX CorporationCarts Europe 1996 page 25-30.5. The history and future development of tantalumcapacitorsA. Kobayashi, T. Nishiyama, K. Watamabe,T. Nakata, K. Morimoto.NEC Corporation.Carts Europe 1996 page 49-58.6. Relation between microstructure and characteristicsof MLCCs having "core-shell" structure.Y.Yoneda,T. Hosokawa, N. Omori, S.Takeuchi.Murata Manufacturing Co. LtdCarts Europe 1996.Moreover, it is often possible to use a much smallercapacitance in MLCC technology to achieve the samedecoupling performance. This is because in tantalumtechnology it is always necessary to choose a largercapacitance to reduce ESR and compensate for loss ofcapacitance at higher frequencies.10 11

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