Accurate Junction Capacitance Modeling for Substrate Crosstalk ...

with r 1 denoting the inner and r 2 the outer radius and l the length of the
cylindrical capacitor;
2π
lε
0ε
r
Ccyl
= .
⎛ r2
⎞
ln
⎜
⎟
⎝ r1
⎠
4πε
0ε
r r1
r2
Csph
=
r2
− r1
with r 1 being the inner and r 2 the outer radius of the spherical capacitor. It can be
seen from Fig. 1 and Fig. 3 that three different regions exist:
1. a planar region for the bottom
2. a cylindric region for the sidewalls
3. a spheric region for the corners
(5)
(6)
4. Sidewall calculation
Fig. 3: Different regions
Cylindric region
Planar region
Spheric region
Due to the lateral diffusion length o, with o≠d the shape of the sidewalls is
elliptical instead of cylindrical.
o
Mask
d
Substrate
Fig. 4: Diffused region
Fig. 5 shows a cut through a sidewall. F1 through F5 are five surfaces that result
in five junction capacitors, that may be combined later on. First the height h and
the width w are determined for each surface. To do so, the range of the quarterellipse
is divided into equal parts depending on the maximal structure size. The