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AA 2012/2012 Lezioni di Tecnologie e Materiali per l’Elettronica
Passive Components
Danilo [email protected]
microlab.unipv.it/microlab.unipv.it/
Università degli Studi di Pavia
AA 2011/2012 Prof. D. Manstretta
Capacitors
Applications:
• Supply filteringSupply filtering
• Interference suppression
• AC coupling
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 2
• AC coupling
AA 2011/2012 Prof. D. Manstretta
Capacitors
A capacitor is usually made of one dielectric layer and two conducting layerslayer and two conducting layers
CapacitancedQC Capacitance
Parallel plate capacitor
dVC
SC Parallel plate capacitor
Dielectric properties change with temperature:
dC
Dielectric properties change with temperature:
Temperature coefficientTC
C
1
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 3
TC
AA 2011/2012 Prof. D. Manstretta
Capacitors A capacitor is essentially an energy storage element:
Energy stored21
2SE CV
Only a limited amount of energy can be stored in a capacitor d e the ma im m oltage (ma electric field E )capacitor due the maximum voltage (max electric field ER) that the oxide can withstand before breakdown
Maximum energy density 21SEE E
Maximum electric field
Maximum energy density 2v RE EVol
Electric permettivity
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 4
permettivity
AA 2011/2012 Prof. D. Manstretta
Dielectric Electrical PropertiesElectric Permeability vs Frequency Loss tangent
ED tjeEE 0
tjDD ''' jr
tjeDD 0 '''0 j
'''''tan
tg
MHz GHz 100GHz 10THz f
interface
dipole
atomic Microscopic resonance ff t
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 5
dipole effects
AA 2011/2012 Prof. D. Manstretta
Capacitors: Distributed EffectsThe capacitor can be divided into several sections in series:Each section is modeled with an RLC equivalent circuitEach section is modeled with an RLC equivalent circuit Very accurate but very complicated Can account for frequency-dependent effects
Equivalent Circuit
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 6
AA 2011/2012 Prof. D. Manstretta
Simplified Equivalent CircuitDielectric and conductor losses
Dielectric resistivity (DC)
conductor losses
GCjY 'dSC r 0
SdRP
d S
21 GV
Retan
Imdiss
r
Y PY P
● Loss tangent2
GV
21 'C V
● Relaxation time constant rPCR 0
21 '2
C V
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 7
AA 2011/2012 Prof. D. Manstretta
Dielectric LossesIf we ignore all other sources of loss (connectors,metal plates resistive losses, etc.), the capacitor lossmetal plates resistive losses, etc.), the capacitor losstangent is given by the dielectric loss tangent (tan )
S
'''tan
0 ' '' SY j C j jd
GCjY ' 0' ' SC
d 0 '' SG
d
2,
1 ''2
dissdiss vol
PP ESd
212dissP GV
''P2Sd2
21 'rP C V 20
1 'rr vol
PP E
''tan'
diss
r
PP
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 8
2r , 02r vol Sd
AA 2011/2012 Prof. D. Manstretta
Capacitor Impedance vs Frequency
Resonance frequency fRESq y RES
The impedance magnitude |Z()| decreases as ~1/ up to theresonant frequency fRES .
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 9
q y RESAbove fRES the parasitic inductance dominates..
AA 2011/2012 Prof. D. Manstretta
Resonance Freq. vs Cap. Value
For a given capacitor type and package size, fRES decreases for
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 10
increasing capacitance
AA 2011/2012 Prof. D. Manstretta
Applications• Supply filtering
• Interference suppression
• AC coupling SUPPLY NOISE DC
Several capacitors inparallel provide a smallimpedance across alarge frequency rangePOSITIVE
SUPPLYPOWER SUPPLY
NOISE
HF NOISE
DC large frequency range
DC+- LARGE INTERM
.SMALL
NEGATIVE ACSUPPLY
SIGNAL GENERATOR
AC COUPLING
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 11
RF
AA 2011/2012 Prof. D. Manstretta
Film Capacitors Made from high quality polymer (polycarbonate, polystyrene,
polypropylene, polyester) or paper film, and a thin (~50m) Al foilD t 10 di l t i thi k Down to 10m dielectric thickness
Air and humidity removed to increase max voltage Conductive resin terminals Metallization of polymer sheet
increases energy per unit volume Improved reliabilityp y
Capacitance values: up to ~50F Frequency range: up to a few MHz
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 12
AA 2011/2012 Prof. D. Manstretta
Mica Capacitors Muscovite mica is a natural crystal
Easy to obtain layers (~50 m thickness) r ~5-7
L l t t (10 4 @1MH ) Low loss tangent (10-4 @1MHz) Low temperature coefficient ~100 ppm/°C High voltage applications High voltage applications 1% accuracy: trimming done removing top-plate metallization Moderate range of capacitance values: up to ~100nF
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 13
AA 2011/2012 Prof. D. Manstretta
Ceramic Capacitors A ceramic capacitor is based on a ceramic dielectric with
metal electrodesmetal electrodes Parameters depend on the dielectric materials:
Stetatites =6 tan=5·10-4 Stetatites r=6 tan=5·10 4
(TiO2)x(BaO)1-x r=37 tan=3·10-4
TiBaO3 r~1000 tan~10-23 r
Piezoelectric material
Production steps: Ceramic dielectric firing
El t d d iti d fi i
15·104 pF
Electrodes deposition and firing Multi-layer ceramic capacitors: several layers are pressed and
fired again together
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 14
g g
AA 2011/2012 Prof. D. Manstretta
Multi-layer Ceramic Capacitors
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 15
AA 2011/2012 Prof. D. Manstretta
Al - Electrolytic Capacitor The foil insulated by the oxide layer is the anode (+) The liquid electrolyte and the second foil act as cathode. (-) The layer of insulating aluminum oxide acts as the dielectric
thin Al2O3 dielectric → high capacitance (~mF) in a small volumeE 109 V/m high energy density Er ~109 V/m → high energy density
High series inductance → low frequency applications Applied voltage must have positive (Va-Vc) polarity
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 16
AA 2011/2012 Prof. D. Manstretta
Electrolytic Capacitor
Boric acid
O id thi kOxide thickness:
/1 tcell eVs Hydrogen gas
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 17
REHydrogen gas
release
AA 2011/2012 Prof. D. Manstretta
Ta Electrolytic Capacitor Porous sintered Tantalum (Ta) is used as first electrode (cathode)
Oxide Ta2O5 is formed during firing with Mn(NO3 )2
MnO2 acts as electrolyte
Second electrode (anode) is composed of graphite
Reduced size and values (up to several 100F) compared with Al l t l ti itelectrolytic capacitors
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 18
AA 2011/2012 Prof. D. Manstretta
Capacitor TypesPolymer
sheetMica Ceramic Electrolytic
(Al)sheet (Al)MAX Cap. 50F 50nF 10nF ~mF
% % % %Accuracy 10% 2% 5% 20%
fMAX ~MHz ~ 10MHz ~ 100MHz ~ 100kHz
Tan 5·10-4
(10kHz)10-4 (1MHz) 10-3 (1kHz) 10-2
(100Hz)[ /°C] ±100 100 ±20 ±1000 [ppm/°C] ±100 100 ±20 ±1000
EV [J/cm3] 100m 1m 1m 1
[ M·F ] 10.000 1000 1000 50
Università degli Studi di Pavia Lezioni di Tecnologie e Materiali per l'Elettronica 19