capacitance measurement[1]

Capacitance Measurement

Apr. 2012LCR Division

All Rights Reserved, Copyright Samsung Electro-Mechanics Co., Ltd.

LCR Division

CONTENTS Confidential

1. Introduction

2. LCR meters and Measurement Principle2-1. LCR meters

2-2. Measurement Theory

2-3. ALC Function for High CV2 3. ALC Function for High CV

3. Characteristics of MLCC3 1 T t Ch t i ti3-1. Temperature Characteristics

3-2. DC Bias Characteristics

3-3. AC Voltage Characteristics

3-4. Aging Characteristics


3-5. DC Bias Aging Characteristics

1. Introduction Confidential

A capacitor is an electrical device that can store energy in the electric field between a pair of closely spaced conducting plates. Capacitance value means the measure of how much charge a capacitor can store at a certain

lt C it f MLCC h ld b d d i t i diti h t tvoltage. Capacitance of MLCC should be measured under appropriate measuring conditions such as temperature, voltage (AC/DC), and frequency. Especially, when you measure a high dielectric MLCC (Class II: X7R, X6S, X5R, Y5V) by LCR meter, you may be careful to obtain a reasonable capacitance using specified measurement conditions. Before measurement, the equipment should be used with correct meter setting and have the capability required for

t it t Th t l t diti f it f Cl I d II MLCCaccurate capacitance measurement. The actual measurement conditions of capacitance of Class I and II MLCCs are shown in tables below. The temperature used for these conditions is 25 degree.

CLASS I

Nominal Capacitance Frequency Voltage(AC) Voltage(DC)

≤ 1,000pF 1MHz ± 10% 0.5~5Vrms(Generally 1Vrms)

No Bias

CLASS I

(Generally, 1Vrms)> 1,000pF 1KHz ± 10%

CLASS II

Nominal Capacitance Frequency Voltage(AC) Voltage(DC)

≤ 10uF 1KHz ± 10% 1.0 ± 0.2Vrms No Bias

* ≤ 10uF 1KHz ± 10% 0.5 ± 0.1Vrms


> 10uF 120Hz ± 20% 0.5 ± 0.1Vrms

* Exceptions: Please check the specification on the web site

2-1. LCR meters Confidential

LCR M O i A li i

LCR meters are used for measurement of the capacitance and dissipation factor of MLCCs. Typical LCR meters are shown in Table including 4288A, 4268A, 4284A, and E4980A by Agilent Technologies Corp.

LCR Meter Overview Application

4288A 1kHz/1MHzCapacitance

High-speed sorting tests of ceramic capacitors.

Class IClass II(≤ 10 F)Capacitance

Meter (≤ 10uF)

4268A 120Hz/1kHz

Constant test level for high value ceramic capacitor tests.

Class II

Capacitance Meter *Auto level control (ALC)

4284A Precision

Wide frequency Range Class IPrecision LCR Meter

4284A : 20Hz to 1 MHzE4980A : 20Hz to 2 MHz Auto level control (ALC)

Class II

Option 001. power and DC bias enhancement (+/- 40V)

E4980A Precision LCR Meter


• ALC: The automatic level control (ALC) feature adjusts the voltage across the DUT to the same level as the signal voltage levelsetting. By this feature, you can maintain a constant level of voltage of measurement signals applied to the DUT. • Technical overview is available at www.agilent.com

2-2. Measurement Theory Confidential

When the AC voltage (V) is applied to the DUT and the AC current (I) is flowing through the DUT, the impedance

(|Z|) can be calculated according to the Ohm’s raw (|Z|=V/I). The measurement circuit depends on the frequency.

So, there are two methods (Auto Balance Bridge and RF I-V). It also depends on the type of fixture.

DUT

IV

R: ResistanceAV

SourceV lt

VoltageMeter

CurrentMeter X: Reactance

IZI: Absolute value of impedance

Θ: Phase of impedance

Voltage Meter Meter

IVZ

Fig. Circuit model


2-2. Measurement Theory Confidential

Energy loss is zero in the ideal capacitor. But, real capacitor has dielectric loss and electrode loss by the parasitic

resistance. Loss of capacitor is shown by the delaying of phase angle between AC voltage and current.p y y g p g g

DF (Dissipation Factor) is described as tan. Here, means delayed phase angle.

Imaginary (X)

jXESRZ

jImaginary (X)

Inductive(High freq.)

CLX

jXESRZ

c

cc

1

X

|Z|

ESRDF

ZXZESR

1tan

sin,cos

| |

Capacitive (Low freq )

XQDF

tanESR

-j

Real (R)(Low freq.)


jFig . Impedance characteristics of general Capacitor

2-3. ALC (Automatic Level Control) Function Confidential

The automatic level control (ALC) feature adjusts the voltage across the DUT to the same level as the signal

voltage level setting. By this feature, you can maintain a constant level of voltage of measurement signals applied

to the DUT. The ALC feature uses a monitorable feedback circuit to iterate a feedback loop as shown in figure.

The feedback loop consists of level measurement and level change. The time is required for level adjustment

and dependent on how many times the feedback loop is iteratedand dependent on how many times the feedback loop is iterated.

Feedback loop

DUT

V

p

DUT

SourceV lt

RHIGH LOW

Voltage


Fig. Circuit model from User’s Guide provided by Agilent Technologies

2-3. ALC Function Confidential

The automatic level control (ALC) feature adjusts the voltage across the DUT to the same level as the signal voltage level setting. When ALC function is off, the capacitance was measured as ~43 μF and when ALC function if on the capacitance was measured as ~49 μF at AC voltage of 0 5V The difference between ALC function onif on, the capacitance was measured as ~49 μF at AC voltage of 0.5V. The difference between ALC function on and off was ~6 μF. However, we can’t see the difference at AC voltage of 0.5V when looking at the figure of capacitance change. Therefore, the correct capacitance value can be obtained by using ALC function.

40 ALC (on)

ALC (off)50.0

55.0

0

20

C(%

)

( )

35.0

40.0

45.0

ap (u

F)

-40

-20

0 0 0 5 1 0

ΔC

20.0

25.0

30.0

0 0 0 5 1 0

Ca

ALC (on)

ALC (off)

Fig. Capacitance of 0603 X5R 47μF with AC voltage Fig. Capacitance change of 0603 X5R 47μF with AC voltage

0.0 0.5 1.0 AC voltage(V)

0.0 0.5 1.0 AC voltage(V)


for ALC on and off (Agilent 4284A, 120Hz) for ALC on and off (Agilent 4284A, 120Hz)

3-1. Temperature Characteristics Temp vs. ΔCConfidential

Temperature coefficient of capacitance (TCC) can be described as the change of capacitance dependent on temperature in MLCCs. There are several TCC categories found in Class I and II. TCC of Class I and II MLCCs are shown in figure. Class I MLCCs are composed of paraelectric material and show simple TCC behaviors. It has a li i ti i it ith t t Th h i it ith t t i d li llinear variation in capacitance with temperature. The change in capacitance with temperature is expressed linearly as parts per million per degree centigrade (PPM/℃).Class II MLCCs such as X5R and X7R show irregular and high change in capacitance with temperature. This is due to the ferroelectric nature of the dielectric material of barium titanate (BaTiO3). The change in capacitance with t t i d t h ifi d t t F l X7R th ttemperature is expressed as a percent change over a specified temperature range. For example, X7R means that the capacitance can change by +/-15% across a temperature range of -55℃ to 125℃.

40% C

Table. Temperature characteristics of Class I and II MLCCs

ClassTemperature Coefficient

Dielectric Constant

Operating Temperature

Capacitance Change

20+15%

+85 oC

+125oC

+22%+105oC

p g

Class I C0G 6 ~ 400 -55 ~ +125℃ 0 ±30ppm/℃

X5R -55 ~ +85℃ ±15%

6S ℃ %-20-40-60 25 40 60 80 100 120

+15%

C0G

Class II 1,000 ~20,000

X6S -55 ~ +105℃ ±22%

X7R -55 ~ +125℃ ±15%

Y5V -30 ~ +85℃ -82 ~ +22%-20

204060 25 40 60 80 100 120X7RX5R

-15%

-22%X6S

All Rights Reserved, Copyright Samsung Electro-Mechanics Co., Ltd.-40

X6S

Fig. Capacitance change of X5R, X7R, Y5V, C0G with temperature

3-2. DC Bias characteristics DC bias vs. ΔCConfidential

DC bias is an important electrical parameter affecting the capacitance of MLCCs. DC bias characteristics can be described as the phenomena of capacitance loss in Class II with increasing DC voltage. This behavior is dependent on the dielectric formulation, microstructure, and internal construction of MLCC as well as DC voltage load.Cl II MLCC b d B TiO ith f l t i di l d DC bi li it th di l t lti iClass II MLCCs are based on BaTiO3 with ferroelectric dipoles and DC bias limits the dipole movements resulting in reduction of the dielectric constant and capacitance. The DC bias characteristics of C0G, X5R, X7R, and Y5V MLCCs are shown in figure. Class I MLCC, C0G shows the stable capacitance value because of its paraelectric structure without dipoles although its relative dielectric constant i d f it d l th Cl II h X5R X7R d Y5V I f Y5V it h th t

.]

is orders of magnitude lower than Class II such as X5R, X7R, and Y5V. In case of Y5V, it shows the most severe degradation despite of the highest dielectric constant. X5R/X7R have high dielectric constants which are preferred for high capacitance applications.

X5R / X7R

C0G

hang

e [a

rb

Y5Vacita

nce

ch

10 20 30 40 50

Y5V

DC voltage [V]

Cap

a


Fig. Capacitance change of X5R, X7R, Y5V, C0G with DC voltage

(HP 4284A, 25oC, 1.0Vrms, 1kHz (X7R, Y5V) / 1MHz (C0G))

AC voltage vs. ΔC3-3. AC voltage characteristics Confidential

AC voltage characteristics can be described as the phenomena of capacitance change in Class II with increasing AC voltage. Class I MLCCs composed of paraelectric material do not show this phenomenon. The AC voltage h t i ti f Cl II MLCC h i fi I Cl II MLCC Y5V h th h ithcharacteristics of Class II MLCCs are shown in figure. In Class II MLCCs, Y5V shows the more severe change with

AC voltage than X5R/X7R. This is due to the non-linear characteristics in voltage-polarization curve of ferroelectric materials. Thus, the slope in the curve increases and the capacitance increases as AC voltage increases.

20

40

20

40

0

20

C(%

) 0

20

C(%

)

-40

-20

ΔC

-40

-20

ΔC

Fig Capacitance change of 0402 X5R 10 μF 6 3V

40 0.0 0.5 1.0

AC voltage(V)

40 0.0 0.5 1.0

AC voltage(V)

Fig Capacitance change of 0603 X5R 47μF 4 0V


Fig. Capacitance change of 0402 X5R 10 μF, 6.3V

with AC voltage (Agilent 4284A, 1kHz)

Fig. Capacitance change of 0603 X5R 47μF, 4.0V

with AC voltage (Agilent 4284A, 120Hz)

3-4. Aging Characteristics Time vs. ΔCConfidential

Aging is a time dependent phenomenon encountered in Class II MLCCs. Class I MLCCs do not show aging due to the paraelectric nature of the composed material. However, Class II MLCCs such as X5R, X7R, and Y5V have ferroelectric dielectrics based on BaTiO3 and the capacitance is decreased logarithmically over time. Figure shows the aging behavior of Class I and II MLCCs with different temperature characteristics. Aging rate g g g p g gincreases with dielectric constant of the material. C0G shows a constant capacitance value independent of time due to its paraelectric characteristics while Y5V the highest capacitance value and X5R/X7R have an intermediate aging rate. Aging is intrinsically reversible. The capacitance can be recovered after heat treatment. MLCCs can be returned to ferroelectric structure by heating above the Curie point (at least 1 hr at

Ct = C0 (1 - k log10 t)Ct = Capacitance value, t hours after the start of agingC0= Initial capacitance value, k = Aging constant, t = Aging time

y g p (150℃) and cooling to room temperature.

0C0G

X7R/X5Rg ra

te [%

] C0G

X7R/X5R-10

0

Slope (k) 2~5%

Y5V

ypic

al a

gin

Y5V

-20

-30

Slope (k) 5%~

1 2 3Time [log10t hr]

4 50 1 2 3Time [log10t hr]

Ty

4 5-40


Fig. Typical aging rate of X7R/X5R, Y5V, C0G with aging timeDe-aging : Decreased capacitance is recovered after heat treatment ( above 150℃)

3-5. DC Bias Aging Characteristics DC bias, Time vs. ΔCConfidential

In order to increase the capacitance density of MLCCs, the dielectric layer thickness should be reduced and this means the increase in the electric field applied to dielectric layers. The aging characteristics under DC bias becomes more important in the high-end products with ultra thin dielectric layers. DC bias aging characteristics can be explained as the capacitance change with time under DC bias applied because the aging can becan be explained as the capacitance change with time under DC bias applied because the aging can be observed in the working condition. The effective capacitance can be described as the capacitance observed in working condition. The effective capacitance is more important than the nominal capacitance because the nominal capacitance is dependent on DC-bias, temperature and time. Better effective capacitance can be obtained by the improvement of DC-bias and aging characteristics.

34

34

28

30

32

nce

(uF)

ce (μ

F)

32

30

28

22

24

26

28

Cap

acita

nC

apac

itanc 28

26

24

22

1 10 100 1000 1000020

22

Time (hr)

22

201 10 100 1000 10000

Time (hr)


Fig. Capacitance of 0805 X5R47uF, 6.3V with time in the measurement condition of 85℃, 1.2V(DC) (E4980A, 1kHz)

capacitance measurement[1]

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