Model 4200A-SCS Parameter Analyzer Reference Manual
Section 4: Multi-frequency capacitance-voltage unit
4200A-901-01 Rev. C / February 2017
4-63
Q
EFF
is distinguished from interface-trapped charge (
Q
IT
), in that
Q
IT
varies with gate bias and
Q
EFF
does not (Nicollian and Brews pp. 424-429, Sze pp. 390-395; see
(on page 4-63)).
Simple measurements of oxide charge using C-V measurements do not distinguish the three
components of
Q
EFF
. These three components can be distinguished from one another by temperature
cycling, as discussed in Nicollian and Brews, p. 429, Fig. 10.2. Also, since the charge profile in the
oxide is not known, the quantity,
Q
EFF
, should be used as a relative, not absolute, measure of charge.
It assumes that the charge is located in a sheet at the silicon-silicon dioxide interface.
From Nicollian and Brews, Eq. 10.10, we have:
Where:
•
V
FB
= flatband potential (V)
•
W
MS
= metal-semiconductor work function (V)
•
Q
EFF
= effective oxide charge (C)
•
C
OX
= oxide capacitance (F)
Note that C
OX
here is per unit of area. So that:
Where:
•
Q
EFF
= effective oxide charge (C)
•
C
OX
= oxide capacitance (F)
•
W
MS
= metal-semiconductor work function (V)
•
V
FB
= flatband potential (V)
•
A = gate area (cm
-2
)
For example, assume a 0.01 cm
2
, 50 pF, p-type MOS capacitor with a flatband voltage of
−
5.95 V; its
N
BULK
of 10
16
cm
-3
corresponds to a
W
MS
of
−
0.95 V. For this example,
Q
EFF
calculates to be
2.5 x 10
-8
C/cm
2
, which then causes the threshold voltage to shift ~5 V in the negative direction. Note
that in most cases where the bulk charges are positive, there is a shift toward negative gate voltages.
The effective oxide charge concentration (
N
EFF
) is computed from effective oxide charge (
Q
EFF
) and
the electron charge as follows:
Where:
•
N
EFF
= effective oxide charge density (cm
2
)
•
Q
EFF
= effective oxide charge (C)
•
q = electron charge (1.60219 x 10
-19
C)
References
Nicollian, E.H. and Brews, J.R., MOS Physics and Technology, Wiley, New York (1982).
Sze, S.M., Physics of Semiconductor Devices, 2nd edition. Wiley, New York (1985).
