Amorphous-Si TFT Model (ATFT)
Equivalent Circuit
Model Features
Features of the ATFT model include:
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The unified DC model covers all regimes of operation
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The model parameters are automatically scaled to accurately model a wide range of device geometries
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The modified charge control model includes induced charge trapped in localized states
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Above threshold includes:
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Field effect mobility becoming a function of gate bias
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Band mobility dominated by lattice scattering
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Below threshold includes:
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Fermi level located in deep localized states
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Realting position of fermi level, incluing deep DOS, back to the gate bias
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Emperical expression for current at large negative gate biases for hole-induced leakage current
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Temperature effects include:
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Linear dependence of threshold voltage
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Temperature activated field-effect mobility
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Temperature activated leakage current
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Dependence of subthreshold slope includinga possible back channel effect.
Drain Current
(-107)
(-108)
where
(-109)
(-110)
(-111)
(-112)
(-113)
(-114)
(-115)
(-116)
(-117)
(-118)
(-119)
(-120)
(-121)
(-122)
(-123)
(-124)
(-125)
(-126)
Drain and Source Parasitic Resistance
If ACM is not given,
(-127)
(-128)
ACM=0:
(-129)
(-130)
If ACM=1,
(-131)
(-132)
If ACM=2, 3,
(-133)
(-134)
Temperature Dependence
(-135)
(-136)
(-137)
(-138)
(-139)
Capacitance
(-140)
(-141)
(-142)
(-143)
(-144)
(-145)
(-146)
Component Statements
This device is supported within altergroups.
Sample Instance Statement:
m4 (0 2 1 1) nch w=2u l=0.8u
Sample Model Statement
model nch atft type=n
Instance Syntax
Name d g s [b] ModelName parameter=value ...
Instance Parameters
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w (m)
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Channel width.
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l (m)
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Channel length.
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m=1
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Multiplicity factor (number of MOSFETs in parallel).
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trise=0
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Temperature rise from ambient.
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region=triode
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Estimated operating region. Possible values are off, triode, sat, or subth.
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nrd (m/m)
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Drain squares.
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nrs (m/m)
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Source squares.
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isnoisy=yes
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Should device generate noise.
Possible values are yes and no.
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Model Syntax
model modelName atft parameter=value ...
Model Parameters
Device type parameters
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type=n
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Transistor type. Possible values are n or p.
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Drain current model parameters
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compatible=spectre
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Spice compatible flag. Possible values are spectre, spice2, spice3, cdsspice, spiceplus, eldo, or sspice.
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cdnver=1
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Cadence version selector.
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vto=0 V
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Zero-bias threshold voltage.
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lambda=0.0008 1/V
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Channel length modulation parameter.
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tox=1e-7 m
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Thin-oxide thickness.
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def0=0.6 eV
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Dark Fermi level position.
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alphasat=0.6
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Saturation modulation parameter.
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delta=5
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Transition width parameter.
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el=0.35 eV
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Activation energy of the hole leakage current.
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emu=0.06 eV
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Field effect mobility activation energy.
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eps=11
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Relative dielectric constant of substrate.
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epsi=7.4
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Relative dielectric constant of gate insulator.
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vfb=-3 V
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Flat band voltage.
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gamma=0.4
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Power law mobility parameter.
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gmin=1.0e23 1/m3 eV
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Minimum density of deep states.
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iol=3.0e-14 A
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Zero bias leakage current parameter.
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kasat=0.006 1/C
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Temperature coefficient of ALPHASAT.
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kvt=-0.036 V/C
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Threshold voltage temperature coefficient.
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m=2.5
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Knee shape parameter.
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muband=0.001 m2/V s
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Conduction band mobility.
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rs=0 Ω
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Source resistance.
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rd=0 Ω
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Drain resistance.
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sigma0=1.0e-14 A
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Minimum leakage current parameter.
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v0=0.12 V
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Characteristic voltage for deep states.
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vaa=7.5e3 V
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Characteristic voltage for field effect mobility.
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vdsl=7 V
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Hole leakage current drain voltage parameter.
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vgsl=7 V
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Hole leakage current drain voltage parameter.
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vmin=0.3 V
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Convergence parameter.
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cgdo=0 F/m
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Gate-drain overlap capacitance.
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cgso=0 F/m
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Gate-source overlap capacitance.
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ACM parameters
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acm=0
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Area calculation method.
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xw=0.0 m
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Accounts for masking and etching effects.
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xl=0.0 m
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Accounts for masking and etching effects.
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ld (m)
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Lateral diffusion into channel from source and drain diffusion.
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wd=0.0 m
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Lateral diffusion into channel from bulk along width.
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lmlt=1.0
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Length diffusion layer shrink reduction factor.
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wmlt=1.0
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Width diffusion layer shrink reduction factor.
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rsh=0 Ω/sqr
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Source/drain diffusion sheet resistance.
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rdc=0.0 Ω
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Additional drain resistance due to contact resistance.
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rsc=0.0 Ω
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Additional source resistance due to contact resistance.
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ldif=0.0 m
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Length of heavily doped diffusion adjacent to gate.
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hdif=0.0 m
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Length of heavily doped diffusion from contact to lightly doped region.
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meto=0.0 m
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Fringing field factor for gate to source and gate to drain overlap capacitance.
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xj=0.0 m
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Metallurgical junction depth.
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Temperature effects parameters
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tnom (C)
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Parameter measurement temperature.
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trise=0 C
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Temperature rise from ambient.
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Operating region warning control parameters
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alarm=none
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Forbidden operating region. Possible values are none, off, triode, sat, subth, or rev.
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Auto Model Selector parameters
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wmax=1 m
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Maximum channel width for which the model is valid.
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wmin=0 m
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Minimum channel width for which the model is valid.
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lmax=1 m
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Maximum channel length for which the model is valid.
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lmin=0 m
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Minimum channel length for which the model is valid.
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Noise model parameters
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noisemod=1
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Noise model selector.
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kf=0
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Flicker (1/f) noise coefficient.
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af=1
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Flicker (1/f) noise exponent.
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ef=1
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Flicker (1/f) noise frequency exponent.
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wnoi=1e-5 m
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Channel width at which noise parameters were extracted.
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Operating-Point Parameters
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type=n
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Transistor type. Possible values are n or p.
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region=triode
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Estimated operating region. Possible values are off, triode, sat, or subth.
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reversed
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Reverse mode indicator. Possible values are no or yes.
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ids (A)
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Resistive drain-to-source current.
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vgs (V)
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Gate-source voltage.
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vds (V)
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Drain-source voltage.
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vth (V)
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Threshold voltage.
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vdsat (V)
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Drain-source saturation voltage.
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gm (S)
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Common-source transconductance.
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gds (S)
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Common-source output conductance.
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cgd (F)
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Gate-drain capacitance.
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cgs (F)
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Gate-source capacitance.
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ron (Ω)
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On-resistance.
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id (A)
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Resistive drain current.
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pwr (W)
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Power at op point.
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i1 (A)
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Resistive drain current.
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