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8.2.6 Semiconductor Capacitor Model (C)

The capacitor model contains process information that may be used to compute the capacitance from strictly geometric information.

name parameter units default example
CAP model capacitance F 0.0 1e-6
CJ junction bottom capacitance F/meters^2 - 5e-5
CJSW junction sidewall capacitance F/meters - 2e-11
DEFW default device width meters 1e-6 2e-6
DEFL default device length meters 0.0 1e-6
NARROW narrowing due to side etching meters 0.0 1e-7
SHORT shorting due to side etching meters 0.0 1e-7
TC1 first order temperature coeff. F/^oC 0.0 0.001
TC2 second order temperature coeff. F/^oC^2 0.0 0.0001
TNOM parameter measurement temperature ^oC 27 50
DI relative dielectric constant F/m 0.0 1
THICK insulator thickness meters 0.0 1e-9

The capacitor has a capacitance computed as:

If value is specified on the instance line then

                        Cnom = value * scale * m

If model capacitance is specified then

                        Cnom = CAP * scale * m

If neither value nor CAP are specified, then geometrical and physical parameters are take into account:

                 C0 = CJ (l - NARROW) (w - NARROW) +
                        2 CJSW (l - SHORT + w -  NARROW)

CJ can be explicitly given on the .model line or calculated by physical parameters. When CJ is not given, is calculated as:

If THICK is not zero:

                             DI * eps
     			        0
                        CJ = ---------   if DI is specified
     		         THICK
     
                              eps
     			    SiO
     			       2
                        CJ = ---------   if DI is not specified
     		         THICK
     
     with:
     
     eps =    8.854214871e-12 F/m
        0
     
     eps    = 3.4531479969e-11 F/m
        SiO
           2
     
                        Cnom = C0 * scale * m

After the nominal capacitance is calculated, it is adjusted for temperature by the formula:

                                                          2
       C(T) = C(TNOM) [1 + TC  (T - TNOM) + TC  (T - TNOM) ]
                             1                2
       where C(TNOM) = Cnom

In the above formula, `T' represents the instance temperature, which can be explicitly using the temp keyword or os calculated using the circuit temperature and dtemp, if present.