(PN-Junction Diode Model

Nonlinear Devices >Chapter 1: Devices and Models, Diode 
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Diode_Model (PN-Junction Diode Model)

Symbol

Available in    ADS and RFDE

Supported via model include file in RFDE

Parameters

Model parameters must be specified in SI units.

Name 

Description 

Units 

Default 

Level
model level selector (1=standard, 3=Hspicegeometry, 11=Spectre)
 
1
Is (Js)^, 
saturation current (with N, determines diode DC characteristics)
A
10^-14
Rs
ohmic resistance
ohm
0.0
Gleak
bottom junction leakage conductance
S
0
N
emission coefficient (with Is, determines diode DC characteristics)
 
1.0
Tt
transit time
sec
0.0
Cd
linear capacitance
F
0
Cjo^, 
zero-bias junction capacitance
F
0.0
Vj (Pb) 
junction potential
V
1.0 V
M
grading coefficient
 
0.5
Fc
forward-bias depletion capacitance coefficient
 
0.5
Imax
explosion current beyond which diode junction current is linearized
A
1.0
Imelt
(similar to Imax; refer to Note 4)
A
1.0
Isr^, 
recombination current parameter
A
0.0
Nr
emission coefficient for Isr
 
2.0
Ikf (Ik)
high-injection knee current
A
infinity
Ikr
Reverse high injection knee current
A
0
IkModel
Model to use for Ikf/Ikr: 1=ADS/Libra/Pspice, 2=Hspice, Spectre
 
1
Bv
reverse breakdown voltage
V
infinity
Ibv
current at reverse breakdown voltage
A
0.001
Nbv (Nz)
reverse breakdown ideality factor
 
1.0
Ibvl
low-level reverse breakdown knee current
A
0.0
Nbvl
low-level reverse breakdown ideality factor
 
1.0
Kf
flicker noise coefficient
 
0.0
Af
flicker noise exponent
 
1.0
Ffe
flicker noise frequency exponent
 
1.0
Jsw (Isw)^, 
sidewall saturation current
A 
0.0
Rsw
sidewall series resistance
ohm
0
Gleaksw
sidewall junction leakage conductance
S
0
Ns
sidewall emission coefficient


I (when Level=11)
N (when Level11
Ikp
high-injection knee current for sidewall
A
Ikf
Cjsw^, 
sidewall zero-bias capacitance
F
0.9
Msw (Mjsw)
sidewall grating coefficient
 
0.33
Vjsw (Pbsw)
sidewall junction potential
V
Vj
1 (when Level=11)
Fcsw
sidewall forward-bias depletion capacitance coefficient
 
0.5
Fc (when Level = 11)
Area
default area for diode
 
1
Periph (Perim)
default periphery for diode
m
0
Width
default width for diode
m
0
Length
default length for diode
m
0
Etch
narrowing due to etching per side
m
0
Etchl
length reduction due to etching per side
m
Etch
Dwl
geometry width and length addition
m
0
Shrink
geometry shrink factor
 
1.0
AllowScaling
allow instance Scale parameter to affect diode instance geometry parameters: yes or no


no
Tnom
temperature at which parameters were extracted 
^oC
25
Trise
temperature rise above ambient
°C
0
Tlev
temperature equation selector (0/1/2)
 
0
Tlevc
temperature equation selector for capacitance (0/1/2/3)
 
0
Xti
saturation-current temperature exponent (with Eg, helps define the dependence of Is on temperature)
 
3.0 PN junction diode
2.0 Schottky barrier diode
Eg
energy gap (with Xti, helps define the dependence of Is on temperature)
eV
1.11
0.69 Schottky barrier diode
0.67 Ge
1.43 GaAs
EgAlpha (Gap1)
energy gap temperature coefficient alpha
eV/^oK
7.02e-4
EgBeta (Gap2)
energy gap temperature coefficient beta
K
1108
Tcjo (Cta)
Cjo linear temperature coefficient
1/^oC
0
Tcjsw (Ctp)
Cjsw linear temperature coefficient
1^oC
0
Ttt1
Tt linear temperature coefficient
1/^oC
0
Ttt2
Tt quadratic temperature coefficient
1/(^oC)²
0
Tm1
Mj linear temperature coefficient
1/^oC
0
Tm2
Mj quadratic temperature coefficient
1/(^oC)²
0
Tvj (Pta)
Vj linear temperature coefficient
1/^oC
0
Tvjsw (Ptp)
Vjsw linear temperature coefficient
1/^oC
0
Trs
Rs linear temperature coefficient
1/^oC
0
Trs2
Rs quadratic temperature coefficient
1/(^oC)²
0
Tgs
Gleak, Gleaksw linear temperature coefficient
1/^oC
0
Tgs2
Gleak, Gleaksw quadratic temperature coefficient
1/(^oC)²
0
Tbv (Tbv1)
Bv linear temperature coefficient
1/^oC
0
Tbv2
Bv quadratic temperature coefficient
1/(^oC)²
0
wBv (Bvj)
reverse breakdown voltage (warning)
W
infinity
wPmax
maximum power dissipation (warning)
W
infinity
AllParams
name of DataAccessComponent for file-based parameter values
 
 
 Parameter value is scaled with Area specified with the Diode device.
 Value varies with temperature based on model Tnom and device Temp.
 Parameter value is scaled with 1/Area.
 Value 0.0 is interpreted as infinity. 
 Parameter value is scaled with the Periph specified with the Diode device. 
 Parameter value is scaled with 1/Periph.

Netlist Format

Model statements for the ADS circuit simulator may be stored in an external file. This is typically done with foundry model kits. For more information on how to set up and use foundry model kits, refer to the Design Kit Development manual.

model modelname Diode [parm=value]*

The model statement starts with the required keyword diode. It is followed by the modelname that will be used by diode components to refer to the model. The third parameter indicates the type of model; for this model it is Diode. The rest of the model contains pairs of model parameters and values, separated by an equal sign. The name of the model parameter must appear exactly as shown in the parameters table-these names are case sensitive. Some model parameters have aliases, which are listed in parentheses after the main parameter name; these are parameter names that can be used instead of the primary parameter name. Model parameters may appear in any order in the model statement. Model parameters that are not specified take the default value indicated in the parameters table. For more information about the ADS circuit simulator netlist format, including scale factors, subcircuits, variables and equations, refer to "ADS Simulator Input Syntax" in the Using Circuit Simulators manual.

Example:

model SimpleDiode Diode \ 
    Is=1e-9 Rs=4 Cjo=1.5e-12

Notes/Equations

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For RFDE Users    Information about this model must be provided in a model file; refer to Netlist Format.

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1.  This model supplies values for a Diode device.

2.  Use AllParams with a DataAccessComponent to specify file-based parameters (refer to DataAccessComponent). Note that model parameters that are explicitly specified take precedence over those specified via AllParams.

3.  Area and Periph

When Level is set to 1 (standard):

Device Area will be used if specified and > 0; 
otherwise the model Area will be used.

Device Periph will be used if specified; 
otherwise the model Periph will be used.

When Level is set to 3 (Hspice geometry):

Device Width and Length will be used if specified;
otherwise the model Width and Length will be used.

If Width > 0 and Length > 0

    Area = wl
    Periph = 2(w + l)
    where w = WidthShrink + Dwl
                   = LengthShrink + Dwl
    otherwise the Area and Periph specified in the device or model 
    (follow the same logic described when Level=1)
    will be used to calculate the new area and periph.

Area = area (from device/model)Shrink²
Periph = periph (from device/model)Shrink

When Level is set to 11 (Spectre):

Device Area will be used if it is specified and > 0;

Otherwise

    if Length and Width in device or model (in this order) are specified and > 0,

        Area = Weff  Leff
        where
            Weff = Width - Etch
            Leff = Length - Etch1

    otherwise use model Area if it is specified and > 0

    otherwise, Area = 1 (default)

Device Periph will be used if it is specified and > 0

Otherwise,

    if Length and Width in device or model (in this order) are specified and > 0,

        Periph = 2  (Weff + Leff)
        where
            Weff = device Width - Etch
            Leff = device Length - Etch1

    otherwise use model Periph if it is specified and > 0
    otherwise, Periph = 0 (default)

If model parameter Allowscaling is set to yes, the diode geometry parameters Periph, Width, and Length are multiplied by Scale, while Area is multiplied by Scale  Scale (for Level = 11 only).

4.  Imax and Imelt Parameters

Imax and Imelt specify the P-N junction explosion current ExplI which is used in the following equations. Imax and Imelt can be specified in the device model or in the Options component; the device model value takes precedence over the Options value. If the Imelt value is less than the Imax value, the Imelt value is increased to the Imax value.

If Imelt is specified (in the model or in Options) ExplI = Imelt; otherwise, if Imax is specified (in the model or in Options) ExplI = Imax; otherwise, ExplI = model Imelt default value (which is the same as the model Imax default value).

5.  Currents and Conductances

Is and Isr in the following equations have been multiplied by the effective area factor aeff.

If vd > vmax

idexp = [Imax + (vd - vmax)  gmax]
gdexp = gmax

where

 
vt is thermal voltage

If vmax  vd  - 10  N  vt

 

If vd < -10  N  vt

 

Breakdown current contribution is considered if Bv is specified and Ibv is not equal to zero.

If -(vd + Bv) > vbmax

ib= -{ExplI + [-(vd + Bv) - vbmax]  gbmax - ibo}
gb = gbmax

where

If vbmax  -(vd + Bv) > -MAXEXP  Nbv  vt

 

Otherwise

ib = 0
gb = 0

For ibo

If (vd+ Bv) < MAXEXP  Nbv  vt

Otherwise

ibo = 0

MAXEXP is the maximum exponent supported by the machine; value range is 88 to 709.

Low level reverse breakdown current is considered if Ibvl is specified and not equal to zero.

If -(vd + Bv) > vlbmax

ilb = -{ExplI + [-(vd + Bv) - vlbmax]  glbmax - ilbo}
glb = glbmax

where

If vlbmax  -(vd + Bv) > - MAXEXP  bvl  vt

Otherwise

ilb = 0
glb = 0

For ilbo

If (vd + Bv) < MAXEXP  Nbvl  vt

Otherwise

ilbo = 0

Recombination current is considered if Isr is specified and not equal to zero.

If vd > vrmax

ir = ExplI + (vd - vrmax)  grmax
|gr = grmax

where

 

If vrmax  vd  - 10  Nr  vt

 

If vd < - 10  Nr  vt

 

iexp = idexp + ib + ilb

gexp = gdexp + gb + glb

There are two ways to model high-injection effect.

When IkModel is set to ADS/Libra/Pspice and when Ikf0 and iexp > 0.

 

When IkModel is set to Hspice:

If Ikf is not equal to zero and iexp > 0

     
    

Otherwise if Ikr is not equal to zero and iexp < 0

     
    

The total diode DC current and conductance

id = idh + ir
Id = id + Gleak  vd + Gmin  vd
gd = gdh + gr
Gd = gd + Gleak + Gmin

where Gmin is minimum junction conductance.

Sidewall diode:

Sidewall diode equations have been multiplied by Periph, Isw, Ibv, Ikp, Gleaksw.

If vdsw > vmaxsw

idexpsw = [ExplI + (vdsw - vmaxsw)  gmaxsw]
gdexpsw = gmaxsw

where

vdsw is sidewall diode voltage
 
 
vt is thermal voltage

If vmaxsw  vdsw  - 10  Ns  vt

 

If vdsw < -10  Ns  vt

 

Breakdown current contribution is considered if Bv is specified and Ibv0 and Level 11.

If -(vdsw + Bv) > vbmaxsw

ibsw = -{ExplI + [-(vdsw + Bv) - vbmaxsw]  gbmaxsw - ibosw}
gbsw = gbmaxsw

where

 

If vbmaxsw  -(vd + Bv) > -MAXEXP  Nbv  vt

 

Otherwise

ibsw = 0
gbsw = 0

For ibosw

If (vd + Bv) < MAXEXP  Nbv  vt

Otherwise

ibosw = 0

MAXEXP is the maximum exponent supported by the machine; value range is 88 to 709.

iexpsw = idexpsw + ibsw
gexp = gdexp + gb

There are two ways to model sidewall diode high-injection effect.

When IkModel is set to ADS/Libra/Pspice and when Ikp  0 and iexp > 0.

When IkModel is set to Hspice:

If Ikp  0 and iexp > 0

 

The total diode DC current and conductance

Idsw = idsw + Gleaksw  vdsw + Gmin  vdsw
Gdsw = gdsw + Gleaksw + Gmin

6.  Diode Capacitances

For main diode capacitance

Diffusion capacitance

Cdiff = Tt  gdexp

Junction capacitance

If vd  Fc  Vj

If Vd > Fc  Vj

Total main capacitance

Cdj = Cdiff + Cj + Cd  Area

For sidewall capacitance

If vdsw  Fcsw  Vjsw

If vdsw > Fcsw  Vjsw

7.  Temperature Scaling

Parameters Is, Jsw, Isr, Cjo, Cjsw, Vj, Vjsw, Bv, Tt, and Rs are temperature dependent.

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Note    Expressions for the temperature dependence of the energy bandgap and the intrinsic carrier concentration are for silicon only. Depletion capacitance for non-silicon diodes may not scale properly with temperature, even if values of Eg and Xti are altered from the default values given in the parameters list.

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The model specifies Tnom, the nominal temperature at which the model parameters were calculated or extracted. To simulate the device at temperatures other than Tnom, several model parameters must be scaled with temperature. The temperature at which the device is simulated is specified by the device item Temp parameter. (Temperatures in the following equations are in Kelvin.)

The energy bandgap E_G varies as:

 if Tlev = 0, 1
 if Tlev = 2

The intrinsic carrier concentration n_i for silicon varies as:

The saturation currents Is, Isr, and Jsw scale as:

if Tlev = 0 or Tlev = 1

 
 

else if Tlev = 2

 
 

The breakdown voltage Bv scales as:

if Tlev = 0

if Tlev = 1 or Tlev = 2

The breakdown current Ibv does not scale with temperature.

The transit time Tt scales as:

The series resistance Rs scales as:

The depletion capacitances Cjo and Cjsw and the junction potentials Vj and Vjsw vary as:

if Tlevc = 0

 
 
 

if Tlevc = 1

 
 
 

if Tlevc = 2

 
 
 

if Tlevc = 3

    if Tlev = 2

 

if Tlev = 0 or Tlev = 1

 
 
 
 
 

The junction grading coefficient M scales as:

The sidewall grading coefficient Msw does not scale.

8.  Noise Model

Thermal noise generated by resistor Rs is characterized by the following spectral density:

Shot noise and flicker noise (Kf, Af, Ffe) generated by the DC current flow through the diode is characterized by the following spectral density:

In the preceding expressions, k is Boltzmann's constant, T is the operating temperature in Kelvin, q is the electron charge, Kf, Af, and Ffe are model parameters, f is the simulation frequency, and f is the noise bandwidth.

9.  The sidewall model parameters model a second ideal diode that scales with the instance parameter Periph, in parallel with the main diode that scales with the instance parameter Area. The series resistance Rs scales only with Area, not with Periph.

10.  To model a Zener diode, the model parameters Bv and Ibv can be used. Bv should be set to the Zener reverse breakdown voltage as a positive number. Ibv is set to the breakdown current that flows at that voltage as a positive number; typically this is in the range of 1 to 10 mA. The series resistance Rs should also be set; a typical value is 1 Ohm.

References

[1] Antognetti and G. Massobrio. Semiconductor device modeling with SPICE, New York: McGraw-Hill, Second Edition 1993.

Equivalent Circuit

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