RF stands for radio frequency and refers to frequencies between low MHz to 300GHz used in telecommunications, medical, IoT, and other applications. RF capacitors are designed specifically for high frequency use, with characteristics like low ESR, high Q, and high SRF optimized through the dielectric material, electrode design, and physical construction. KEMET's CBR series of RF capacitors use a C0G dielectric and copper electrodes to provide low ESR and high Q for operating frequencies up to 50GHz.

1. Taking the Mystery Out of RF Ceramics Capacitors

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Outline
What is RF?
Capacitor Basics
RF Capacitors
Properties and Characterization
KEMET CBR Series

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RF Overview
• Low MHz to 300GHz.
• Higher frequency ranges allow for:
• More use of the frequency spectrum
• Efficiency in propagating signals from one point to another
• Reduction in size of components such as antennas.
• Markets
• Telecom
• Medical
• IoT
• Autonomous Driving
• Military, Space and Aeronautics, etc

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What is RF?
Capacitor Applications
Bypass
DC BLOCKING MATCHING BYPASS

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Capacitor Basics
A Refresher

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Capacitor Basics
C = Design Capacitance
K = Dielectric Constant
A = Overlap Area
d = Ceramic Thickness
n = Number of Electrodes
C = e0KA(n-1)
d
Detailed Cross Section
Inner Electrode
End Termination
Barrier Layer
Termination Finish
Dielectric Material

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Capacitor Basics
The Ideal Capacitor
Ideal Capacitor
• Pure Capacitance
• No resistance (ESR)
• No Inductance (ESL)
Z=Capacitive Impedance or Reactance
Ideal Model
10pF example

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Capacitor Basics
Real Capacitor
Real Capacitor
• C - Nominal capacitance
• ESR - Series resistance (terminations,
dielectric, and electrodes)
• ESL - Series inductance
Simplified Real Model
10pF example
SRF
C ESR ESL

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Capacitor Basics
Closer Look at ESR
RF Frequencies

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RF Capacitors
What’s the Difference?
“Regular” Capacitor RF Capacitor

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RF Capacitor Basics
Some Key Parameters
C0G → ppm/ oC level
X7R → % level
Effective Series ResistanceESR
The resistance of the capacitor which includes resistance due to the dielectric as well as electrodes.
Quality FactorQ
Quantifies the amount of energy stored versus how much is dissipated as heat. It represents the efficiency of the
capacitors. Higher Q’s are needed for RF capacitors to limit power dissipation.
Series Resonant FrequencySRF
Shows where the total impedance is no longer capacitive and begins an upward trend (becomes inductive). Higher
SRF = better RF capacitor, since some applications require the designer to stay well below the SRF.
Temperature Coefficient of CapacitanceTCC
Determines how much the capacitance values will shift at different temperatures. RF capacitors need to be very
stable over a broad temperature range.
𝑸 =
𝑿𝒄
𝑬𝑺𝑹
=
𝟏
𝑫𝑭
𝑺𝑹𝑭 =
𝟏
𝟐 ∗ 𝝅 ∗ 𝑪 ∗ 𝑳

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So, What is an RF Capacitors
An RF capacitor is a capacitor whose “characteristics” are favorable at RF frequencies
So, for RF capacitors, materials are chosen and the design is optimized so that the capacitors’
characteristics are well suited at the higher frequencies.
Characteristic RF Capacitor Requirements
ESR (Effective Series Resistance) RF Capacitors are designed to have the lowest possible ESR. This allows for
minimal power loss at RF frequencies.
Q (Quality Factor) RF Capacitors are designed to have a high Q.
SRF (Series Resonant Frequencies) RF Capacitors are designed to have high SRF allowing for a higher operating
frequency range.
TCC (Temperature Coefficient of Capacitance) Dielectric chosen to have minimal capacitance shift across entire operating
temperature range.

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Optimizing for RF
Design Design Goal How?
Dielectric • Low Loss
• Temperature and Voltage Stability
High Q class 1 dielectrics such as C0G or NPO
Electrodes • Low Loss
• Low Inductance
Non-ferrous electrode materials
Construction / Physical
Geometry
• Low Loss
• Low Inductance
Consider square case size
Long/Narrow vs Short/Wide
0
5
10
15
20
25
30
0.1 1 10 100 1000 10000
RESISTANCE(OHMS)
FREQUENCY(MHZ)
Resistance of 100mm Wire
Diameter = 1.5mm
Resistance
Copper (Ohms)
Resistance
Nickel (Ohms)

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RF Capacitors
Why Copper BME
0
5
10
15
20
25
30
35
40
150 300 600 1200
PowerDissipationmW
Frequency
Power Dissipation vs. Frequency
Ni BME Cu BME
Copper BME = Lower ESR = Better power dissipation = Ideal for High Frequency applications
Ag-PME
Pd-PME
Ni-BME
Cu-BME
0
3
6
9
12
15
ElectricalResistanceΩ-cm
Electrode Material
Electrical Resistance

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RF Capacitor Properties and Characterization

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ESR and Q

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Low Frequency Design vs RF Design
Impedance / ESR Approach S-Parameter Network Approach
S11
S21 S22
S12
Z
a1
b1
a2
b2

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S-Parameters
Incident Wave a1
Transmission b2
Lens
S11= b1/ a1 S21= b2/ a1

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S-Parameters
Looks like an
impedance
curve
S11 S21
Reflected Transmitted

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S-Parameters
How Designers Use Them?
• RF designers use simulation tools to run analysis on circuits similar to P-Spice.
• Keysight’s Advanced Design Systems (ADS)
• Keysight’s Eagleware Genesys
• AWR’s Microwave Office
Schematic of circuit to simulate S-
Parameter file in Eagleware Genesys

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What about the substrate?
High Frequency (RF Capacitors)
• Parasitic capacitances and ESL dependent on
• Substrate properties
• Height
• Er
• Loss Tangent
• Metal Thickness
• Pad Dimensions
• Length
• Width
• Spacing

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What about the substrate?
SUBST=5mil FR4
PADG=0.6 mm
PADL=1 mm
PADW=1.45 mm
Tolerance=1
Sim_mode=0 - Full Parasitic Model
C=47 pF
Part=KEMET CBR08
CAP_KMT_0805_107_4
Measurement Based
Part Value Scalable
Substrate Scalable
Pad Scalable
Modelithics Global ModelTM

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What about the substrate?
Poor Fit
Excellent Fit

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KEMET CBR Series

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Ultra High Q-CBR Squared Series Offering
Case Size
Typical ESR (10pF
@ 1 GHz)
Dielectric
Operating Frequency
Range
Operating
Temperature Range
Temp Coef.
(TCC)
Capacitance Range Max Voltage
0505 (NEW!) < 0.068 C0G 1MHz - 50GHz –55ºC to +125ºC 0 ±30 ppm/ºC 0.4pF - 100pF 250
High Q-CBR Series Offering (EIA Case Sizes)
Case Size
Typical ESR Ohms
(10pF @ 1 GHz)
Dielectric
Operating Frequency
Range
Operating
Temperature Range
Temp Coef.
(TCC)
Capacitance Range Max Voltage
0201 -
C0G 1MHz - 50GHz –55ºC to +125ºC
0 ±30 ppm/ºC
(0 ±60 ppm/ºC for 0201
case size
≥ 22 pF)
0.1pF - 33pF 50
0402 < 0.095 0.1pF - 100pF 200
0603 < 0.100 0.3pF - 100pF 250
0805 < 0.085 0.3pF - 100pF 500
KEMET CBR Series
Copper Electrodes

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Summary
• RF adoptions continues to grow
• RF capacitors are designed and optimized to
operate at higher frequencies
• High frequencies bring unique design challenges
• Design tools are readily available

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Thank You!!!
Mark R. Laps
Technical Product Manager
Ceramic Business Unit
KEMET Electronics
Cell Phone: +1-864-399-4879
Office Phone: +1-864-963-6383
www.kemet.com | marklaps@kemet.com