Keithley 4200A-SCS Reference Manual page 1193

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Appendix D: Using a Model 82 C-V System

In tests, the values for W

values depending on the type of materials.

For silicon, silicon dioxide, and aluminum:

k = Boltzmann's constant (1.3807 x 10

T = Test temperature (K)

q = Electron charge (1.60219 x 10

= Bulk doping (cm

DopeType = is +1 for p-type materials and -1 for n-type materials; the value for DopeType is

changed in the Constants area of the Formulator

For example, for a MOS capacitor with an aluminum gate and p-type silicon

For the same gate and n-type silicon

Because the supply voltage of modern CMOS devices is decreasing and since aluminum reacts with

silicon dioxide, heavily doped polysilicon is often used as the gate material. The goal is to achieve a

minimal work-function difference between the gate and the semiconductor, while maintaining the

conductive properties of the gate.

Effective oxide charge

The effective oxide charge, Q

and oxide trapped charge, Q

varies with gate bias and Q

395). Simple measurements of oxide charge using C-V measurements do not distinguish the three

components of Q

These three components can be distinguished from one another by temperature cycling, as

discussed in Nicollian and Brews, 429, Fig. 10.2. Also, since the charge profile in the oxide is not

known, the quantity Q

that the charge is in a sheet at the silicon-silicon dioxide interface. From Nicollian and Brews, Eq. 10.

10, we have:

, represents the sum of oxide fixed charge, Q

should be used as a relative, not absolute, measure of charge. It assumes

Model 4200A-SCS Parameter Analyzer Reference Manual

are listed in the Formulator as constants. You can change the

is distinguished from interface trapped charge, Q

does not (Nicollian and Brews 424-429, Sze 390-

, mobile ionic charge,

4200A-901-01 Rev. C / February 2017