Determining The Optimal Delay Time - Keithley 4200A-SCS Reference Manual

Appendix D: Using a Model 82 C-V System Model 4200A-SCS Parameter Analyzer Reference Manual

Determining the optimal delay time

For accurate interface trap density measurement, delay time must be carefully chosen to ensure that
the device remains in equilibrium in the inversion region during a sweep. An equilibrium test is
provided to determine the optimum delay time.
The equilibrium test uses the Model 595 to perform a series of quasistatic capacitance and Q/t
current measurements using different delay times. The figure below shows the typical capacitance
and Q/t curves generated for this test. As shown, the optimal delay is the second TDelay point after
both curves have flattened out.
For long delay times, the measurement process can become very long with some devices. You may
be tempted to speed up the test by using a shorter delay time. However, doing so is not
recommended because it is difficult to quantify the amount of accuracy degradation in any given
situation.
See QTsweep (equilibrium test) (on page D-12) for details on the equilibrium test.
Figure 602: Choosing optimal delay time
D-26 4200A-901-01 Rev. C / February 2017