3.15.1 Parasitic Resistance Model

The total parasitic resistance at the source/drain terminal consists of two parts: (a) bias-independent and (b) bias-dependent. BSIM-CMG offers three different options to model parasitic resistance with variations on the way the bias dependent and bias independent parts of the parasitic resistance are handled. These options can be exercised by the switch $RDSMOD$ as described below:

For $RDSMOD = 0$,

Bias-dependent part of parasitic resistance is internal to the model, while bias-independent part is external to the model. Additional nodes are created. This is same as BSIM3 model.

$R_{source} = R_{s,geo} \qquad (3.444)$

$R_{drain} = R_{d,geo} \qquad (3.445)$

$R_{ds} = \dfrac{1}{NFIN_{total} \times {W_{eff0}}^{WR_i}} \cdot \Bigg( RDSWMIN(T) + \dfrac{RDSW(T)}{1 + PRWGS_i \cdot q_{ia}} \Bigg) \qquad (3.446)$

$D_r = 1 + NFIN_{total} \cdot \mu_0(T) \cdot C_{ox} \cdot \dfrac{W_{eff}}{L_{eff}} \cdot \dfrac{i_{ds0}}{\Delta q_i} \cdot \dfrac{R_{ds}}{D_{vsat} \cdot D_{mob}}$

$D_r$ goes into the denominator of the final $I_{ds}$ expression.

For $RDSMOD = 1$,

Both bias-dependent and bias-independent parts of parasitic resistances are external to the model. The bias-dependent extension resistance model is adopted from BSIM4 [10]. Similar to BSIM4, this option in BSIM-CMG allow the source extension resistance $R_s(V)$ and the drain extension resistance $R_d(V)$ to be external and asymmetric (i.e. $R_s(V)$ and $R_d(V)$ can be connected between the external and internal source and drain nodes, respectively; furthermore, $R_s(V)$ does not have to be equal to $R_d(V)$). This feature makes accurate RF CMOS simulation possible.

$V_{gs,eff} = \dfrac{1}{2} \Bigg[ V_{gs} - V_{fbsd} + \sqrt{(V_{gs} - V_{fbsd})^2 + 0.1} \Bigg] \qquad (3.447)$

$V_{gd,eff} = \dfrac{1}{2} \Bigg[ V_{gd} - V_{fbsd} + \sqrt{(V_{gd} - V_{fbsd})^2 + 0.1} \Bigg] \qquad (3.448)$

$V_{si,s,eff} = \sqrt{V(si,s)^2 + 1.0e^{-6}} \qquad (3.449)$

$R_{sw} = \dfrac{RSW(T) \cdot (1 + RSDR_a \cdot {V_{si,s,eff}}^{PRSDR})}{1 + PRWGS_i \cdot V_{gs,eff}} \qquad (3.450)$

$R_{source} = \dfrac{1}{ { W_{eff0} }^{WR_i} \cdot NFIN_{total}} \cdot (RSWMIN(T) + R_{sw}) + R_{s,geo} \qquad (3.451)$

$V_{di,d,eff} = \sqrt{V(di,d)^2 + 1.0e^{-6}} \qquad (3.452)$

$R_{dw} = \dfrac{RDW(T) \cdot (1 + RDDR_a \cdot {V_{di,d,eff}}^{PRDDR})}{1 + PRWGD_i \cdot V_{gd,eff}} \qquad (3.453)$

$R_{drain} = \dfrac{1}{ { W_{eff0} }^{WR_i} \cdot NFIN_{total}} \cdot (RDWMIN(T) + R_{dw}) + R_{d,geo} \qquad (3.454)$

$D_r = 1.0 \qquad (3.455)$

For $RDSMOD = 2$,

Both bias-dependent and bias-independent parts of parasitic resistances are internal to the model. This option assumes symmetric source/drain resistances. No additional nodes are created in this option.

$R_{source} = 0.0 \qquad (3.456)$

$R_{drain} = 0.0 \qquad (3.457)$

$R_{ds} = \dfrac{1}{NFIN_{total} \times {W_{eff0}}^{WR_i}} \cdot \Bigg( R_{s,geo} + R_{d,geo} + RDSWMIN(T) + \dfrac{RDSW(T)}{1 + PRWGS_i \cdot q_{ia}} \Bigg)$

$(3.458)$

$D_r = 1 + NFIN_{total} \cdot \mu_0(T) \cdot C_{ox} \cdot \dfrac{W_{eff}}{L_{eff}} \cdot \dfrac{i_{ds0}}{\Delta q_i} \cdot \dfrac{R_{ds}}{D_{vsat} \cdot D_{mob}}$

$R_{s,geo}$ and $R_{d,geo}$ are the source and drain diffusion resistances, which we will describe as follows.

References

[10] BSIM4 model. Department of Electrical Engineering and Computer Science, UC Berkeley.