Page 316 - Semiconductor For Micro- and Nanotechnology An Introduction For Engineers

Inhomogeneities
-
+
ε
1
a
d
C = dQ ----------------------------------------------------------------------  N N q (7.179)
------- =
--- -------------------------
dV 2k T 2  ( N + N )
-
+
B
( V ) − V Applied – ------------- a d
+
bi Abrupt
q
for the abrupt junction.
7.6.5 Metal-Semiconductor Contacts
In order to electrically interface the semiconductor devices to circuitry in
the outside world, we have to connect metallic wires to its surface. Typi-
cally, metal pads are deposited onto the semiconductor surface at posi-
tions where the doping has been increased to ensure that good electrical
contact is made. Bonding wires are then attached to the metal pads to
connect them to the metal pins of the chip package. The whole geometri-
cal arrangement is illustrated in Figure 7.22. As we will soon see, the
Metal bonding
wire
Aluminium
© ESEC AG Dielectric
pad

Impurity
Doping
Silicon
chip

Figure 7.22. Schematic and scanning electron micrograph (SEM) of the geometry at a
semiconductor-metal contact pad. SEM © ESEC AG, Cham [7.21].

metal pads can be operated both as good ohmic contacts to the semicon-
ductor surface, as well as to create a high-speed diode. In a third applica-
tion, metal contacts can be used to characterize the underlying

Semiconductors for Micro and Nanosystem Technology 313