Keithley 4200A-SCS Reference Manual page 1191

Appendix D: Using a Model 82 C-V System
Gain and offset
Gain and offset can be applied to C
measurement errors. A gain factor is a multiplier that is applied to all elements of C
before plotting or graphics array calculation. Offset is a constant value added to or subtracted from all
C and C data before plotting or array calculation.
Q H
For example, assume that you compare the C
2.3 pF less than Cn. If you then add an offset of +2.3 pF to C
will then be the same, and the C
Gain and offset values do not affect raw C
offset values are stored in the data file so compensated curves can be easily regenerated at a later
date.
Flatband capacitance and flatband voltage
The Model 82 uses the flatband capacitance method of finding flatband voltage, V
length is used to calculate the ideal value of flatband capacitance, C
known, the value of V
The method used is invalid when interface trap density becomes very large (1012-1013 and greater).
However, this algorithm should give satisfactory results for most users. Those who are dealing with
high values of D
Based on doping, the calculation of C
type, acceptors) or N
C is calculated as follows:
FB
Where:
•
C = flatband capacitance (pF)
FB
•
C = oxide capacitance (pF)
OX
•
ε
= permittivity of substrate material (F/cm)
S
•
A = gate area (cm
•
1 × 10 -4 = units conversion for λ
•
1 × 10
-12
And λ = extrinsic Debye length =
Where:
•
kT = thermal energy at room temperature (4,046 × 10
•
q = electron charge (1.60219 × 10
•
N = N at 90% W
x
•
N at 90% W
D-50
and C
Q
and C
Q
is interpolated from the closest V
FB
should consult the appropriate literature for a more appropriate method.
IT
FB
(bulk doping for n-type, donors).
D
2
)
= units conversion for C
OX
, or N , or N
MAX A D
is chosen to represent bulk doping
MAX
Model 4200A-SCS Parameter Analyzer Reference Manual
data to allow for curve alignment or to compensate for
H
and Cn values at reading #3, and you find that C
Q
, the C
Q
curves will be aligned at that point.
H
and C values stored in the data file, but the gain and
Q H
values (Nicollian and Brews 487-488).
G
uses N at 90% W , or user-supplied N
MAX
-21
J)
-19
coulombs)
when input by the user
or C array data
Q H
and C values at reading #3
Q H
. The Debye
FB
. Once the value of C
FB FB
(bulk doping for p-
A
4200A-901-01 Rev. C / February 2017
is
Q
is