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Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 1, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear ResistorsResistance effect in polycrystalline metallic oxide (ceramics)
[Schau 90 / 129]
Type
Temperature-dependentresistance (Thermistor)*• Negative Temperature Coefficient (NTC)• Positive Temperature Coefficient (PTC)Voltage-dependentresistance (Varistor)*
Bond type: predominantly or partially heteropolar (ionic) bond(metal: cation, oxygen: anion)
Semiconducting properties can result from valence exchange of the cations in the oxide.charge transport through hopping-mechanism (valence „transfer “)
Lattice structure: A2+ B3+2 O2-
4 (spinel)
typical NTC: Ni2+ Mn3+2 O2-
4
element: Ti V Cr Mn Fe Co Ni Cu Znvalence: +2 +2 +2 +2 +2 +2 +2 +2
+3 +3 +3 +3 +3 +3 +3+4 +4 +4 +4 +4
+5 valence exchangehopping conduction
Mn2+ Mn3+ Mn2+ Mn3+- -
thermal activated
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 5, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / PTCApplications of Positive Temperature Coefficient Resistors
S+M
1. Thermal valve heating2. Carburetor heating3. Mirror heating4. Spray nozzle heating5. Headlight washing system6. Preheating of intake air (carburetors)7. Mixture preheating (injector)8. Door lock heating
1. Lamp protection2. TV-demagnetizing3. Switching power supply overload protection4. Video overload protection5. Loudspeaker protection6. Switching power supply startup7. Telephone over-current protection8. Sticking pistol9. Styrofoam cutter10. Voltage tester
1
2 34
52
34
566 7
8 9
10
1112 13
14
15
16
17
89
10
11
1213
1415
16
7
9. Überlastschutz (elec. small motor)10. Back window ventilation11. Windshield wiper system check12. Brake fluid check13. Oil level check14. Cooling water check15. Gasoline display
11. Overload protection for small motors12. Curls rolling rod13. Insect annihilator14. Engine start compressor15. Warm retaining plate16. Tank overfilling protection17. Oil preheating18. Washing machine door locking 19. Hand dryer20. heater
18
1920
1
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 6, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / PTCResistance - temperature Characteristic Curve of PTC
[Hey 84 / 166]
Material:semiconducting BaTiO3(n- i.e. donor doped)
Rmin, Rmax:extreme values of the PTC
branch with sign change in temperature coefficients
of the component at RB = 2 RminTB-values from -30...+250 °C
RB
Rmin
Rmax
TBTemperature [°C] →→→→
Res
ista
nce
[ Ω]
Ω]
Ω]
Ω]
→→ →→
RB = 2 RminRB = 2 Rmin
TKR: Temperature coefficient of the resistance , TKR-values from 0,1...0,3 K-1dTdR
R1TKR ⋅⋅⋅⋅====
0 100 200 300100
102
104
106
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 7, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / PTCApplications
[Schau 94 / 203]
SensorSensor ControllerController HeaterHeater
heat from the environment self-heating heat emission
• electrical thermometer• temperature rise protection
• current stabilization• switch time delay• level monitoring • current measurement
• heating components self-regulating
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 8, 12.02.02source: M&D-Nonlinear Resistors.PPT,
-
Nonlinear Resistors / PTCVacancy and Doping Profile
IWE
x
Don
or c
once
ntra
tion
Acc
epto
r con
cent
ratio
n
grain
insulating grain boundary layer
[LaBa••••]
2[VBa´´]
Oxygen ion O2-
Barium ion Ba2+
VBa´´VO
••••••••-
-
--
VBa´´: Ba-vacancy (acceptor)VO
•••••••• : O-vacancy (donor)LaBa
••••: La3+ (doping) at Ba2+-place, (donor) e´, (n): electron (-concentration)-
LaBa••••
x
n
Oxygen vacancy
Barium vacancy
Lanthanum doping at Ba-place
slow cooling Barium vacancy concentration and profile are determined by the cooling rate
Barium vacancy concentration and profile are determined by the cooling rate
fast cooling→→→→ thinner insulating grain surrouding layer
charge carrierconcentration
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 9, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / PTCMaterial Engineering with Ceramic PTC Resistors
Siemens
Form
Stoichiometry
Heating rate
Doping
Cooling rate
Isovalentsubstitution
SurfaceThickness
Structure(grain size)Structure
(grain size)
Intrinsicdefects
Intrinsicdefects
Thermal resistanceMaximal voltage
I = f (U)I = f (U)
Resistivity
ρρρρ = f (T)ρρρρ = f (T)
Resistance rise slopeCurie temperature
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 10, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / PTCTemperture-dependent Potential Barrier at Grain boundary in BaTiO3
[Hey 76 / 100, Schau 94]
T < TC : ferroelectricity →→→→ spontaneous polarization
T > TC : disappearance of the spontaneous polarization
0
5
10
εε εε r [
103]
→→ →→
T [°C] →→→→0
ρρ ρρ sp
[ ΩΩ ΩΩcm
] →→ →→
107
106
105
104
103
102
ρρρρsp
εεεεr
X
W
PSPS
W0
X
W
W0
polarization charges compensate negative
grain boundary charges →→→→ W0 small
W0 ~ εεεεr-1 ~ T-TC
space charges compensate negative
grain boundary charges →→→→ W0 largekT
W
sp
0
e~ρρρρ
WL100 200
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 11, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / PTCBand Model, E-field Strength and Space Charge at the Grain Boundary
[Schau 92 / 102]
-
++
E
x
x
WV
WF
WL
WVak0W
positive permanentsurface charge
positive permanentsurface charge
negativeboundary surface charge
negativeboundary surface charge
QR
x
T < TC →→→→ ferroelectricity: permanent dipole T < TC →→→→ ferroelectricity: permanent dipole
x
WV
WF
WL
WVak0W
E
x
+ +
QR
-
positive chargeof ionized donors
positive chargeof ionized donors
negativeboundary surface charge
negativeboundary surface charge
x
T > TC →→→→ space charge of ionized donors T > TC →→→→ space charge of ionized donors
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 12, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / PTCTemperature dependence of resistivity ρsp of PTC ceramics
[Schau 94 / 200]
Ferroelectric, semiconducting BaTiO3 shows an anomaly of resistance at T>TC (PTC-effect)Ferroelectric, semiconducting BaTiO3 shows an anomaly of resistance at T>TC (PTC-effect)
compositions: donor-doped BaTiO3
donor-doped (Ba, Pb)TiO3
donor-doped (Ba, Sr)TiO3
TC: Curie Temperature of the solid solution
Temperature [K] →→→→
Res
istiv
ity ρρ ρρ
sp [ Ω
]Ω
]Ω
]Ω
] →→ →→
10-1
100
101
102
103
104
105
106
200 400 600
+60%Sr
+50%Sr
+40%Sr+3
0%Sr
+20%
Sr
+5%Pb+10%Pb
+15%Pb+20%Pb
+30%
Pb+4
0%Pb
+50%
Pb
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 13, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / PTCMiddle Grain Size and ρsp as a Funktion of the Dopant Concentration
[Schau 94 / 200]
variation of ρρρρsp und d50 : independent of the type of donor strongly dependent on the donor concentration
variation of ρρρρsp und d50 : independent of the type of donor strongly dependent on the donor concentration
• donor doping in perovskite BaTiO3 (A2+B4+O2-
3)
→→→→ A3+ in stead of Ba2+: La3+, Y3+, Gd3+
→→→→ B5+ in stead of Ti4+: Sb5+, Nb5+, Ta5+
→→→→ decrease of the resistivity ρρρρsp (electron conduction) only with donor concentration ≤≤≤≤ 0,3 at%→→→→ decrease of the middle grain size d50 with increasing donor concentration
• doping effects
Gd [at%] →→→→
Res
istiv
ity ρρ ρρ
sp [ Ω
]Ω
]Ω
]Ω
] →→ →→
d 50
[µµ µµm
] →→ →→
d50
ρρρρsp
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 14, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / PTCDevice Description
[Schau 94 / 203]
General purpose PTC resistors Overload protection
PTC resistors
Demagnetising PTC resistors
Temperature sensors
Heating components
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 15, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / VaristorsApplications of Varistors
S+M
1. Lightning protection for television, video, PC, ...2. Washing machine3. Deep-freezer4. Telephone5. Total protection
1. Central electrical system protection 2. Overvoltage-protected electronic ignition3. Airbag4. ABS5. Board computer6. Combination protection
1
2 3
45 123
45
6
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 16, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / VaristorsExamples
[Hey 84 / 233, 234]
• Designs of ZnO Varistors • Varistors as high voltage deflector
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 17, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Varistor Variable Resistor voltage-dependent resistance with symmetric I(U)-characteristic curve
αααα⋅⋅⋅⋅±±±±==== UKI
nonlinearcoefficient ααααgeometry-
dependentconstant K
typical α α α α-values: 5...70Materials: SiC, ZnO
application of varistors as protection from overvoltagesapplication of varistors as protection from overvoltages
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 18, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / Varistors Current-Voltage-Curve of SiC and ZnO Varistors
[Hey 84 / 209]
• ohmic resistance αααα = 1
• silicon carbide SiC varistor p-type (Al-doped) SiC grain size approx. 100 µµµµm α α α α ≈≈≈≈ 5...7
• zinc oxide ZnO varistor n-type doped ZnO with insulating grain boundaries grain size variable: < 1 µµµµm to 100 µµµµm α α α α-values from 30...70 very low leakage current
Electrical field strength E [V/cm] →→→→
Cur
rent
des
ity j[
A/c
m²]
→→ →→
αααα = 5αααα = 40
αααα = 1
ZnO-Varistor
SiC-Varistor
104
100
10-4
10-8
10-12
102 103 104
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 19, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / VaristorsComparison of SiC and ZnO Varistors as Overvoltage Protection
[Hey 84 / 212]
Double-logarithmic curve U(I)• during normal operating voltage• during overvoltage US = 9,8 kV
UB = 200 V
Ri = 10 ΩΩΩΩ
varistor
I
US = 9,8 KV
The voltage U is temporary increasedby an interference voltage US(t).
U(t) = US(t) + UB - Ri · I(t)
load
U
without varistor
with SiC varistor
with ZnO varistor
operating voltage
Current I / A →→→→
Volta
ge U
/ V
→→ →→
3 %
25 %
100 %
104
103
102
10-1 101 103
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 20, 12.02.02source: M&D-Nonlinear Resistors.PPT,
Nonlinear Resistors / VaristorsPolycrystalline ZnO - Structure with Secondary Phases
Siemens
Polycrystalline ceramic: network from parallelly and serially connected micro-varistorsVaristor operating voltage: depending on the grain size and geometry of the component
Polycrystalline ceramic: network from parallelly and serially connected micro-varistorsVaristor operating voltage: depending on the grain size and geometry of the component
Micrograph of a ZnO varistor ceramic Scheme of the structure of a ZnO varistor ceramicZnO grain size variableby doping/sinteringprocess
A pair of grains“micro- varistor”
Gusset, from dopants with the sinteringprocess, the “secondary phases” are formed.
20 µµµµm
Institut fürWerkstoffe der Elektrotechnik IWEWerkstoffkunde
der Elektrotechnikslide: 21, 12.02.02source: M&D-Nonlinear Resistors.PPT,