Keithley 4200A-SCS

Appendix
D: Using a Model 82 C-V System Model 4200A-SCS Parameter Analyzer
Reference Manual
D-48 4200A-901-01 Rev. C / February 2017
Basic device parameters
The following topics provide additional detail on device parameters and how they are calculated.
Determining device type
The semiconductor conductivity type (p or n dopant ions) can be determined from the relative shape
of the C-V curves (see Analysis methods (on page D-47
)). The high-frequency curve gives a better
indication than the quasistatic curve because of its highly asymmetrical nature. Note that the C-V
curve moves from the accumulation to the inversion region as gate voltage, V
GS
, becomes more
positive for p-type materials, but the curve moves from accumulation to inversion as V
GS
becomes
more negative with n-type materials (Nicollian and Brews 372-374).
• If C
H
is greater when V
GS
is negative than V
GS
when poitive, the substrate material is p-type.
• If C
H
is greater with positive V
GS
than negative V
GS
, the substrate is n-type.
• The end of the curve where C
H
is greater is the accumulation region, while the opposite end of
the curve is the inversion.
Oxide capacitance, thickness and gate area
The oxide capacitance, C
OX
, is the high-frequency capacitance with the device biased in strong
accumulation. Oxide thickness is calculated from C
OX
and gate area as follows:
Where:
• t
ox
= oxide thickness (nm)
• A = gate area (cm
2
)
• ε
ox
= permittivity of oxide material (F/cm)
• C
ox
= oxide capacitance (pF)
You can rearrange the above equation to calculate gate area if the oxide thickness is known. Note
that ε
OX
and other constants are initialized for use with silicon substrate, silicondioxide insulator, and
aluminum gate material, but may be changed for other materials.