MOS Capacitor

Vt only has meaning for a MOS*FET* but not a MOS*CAP*. It's a bit frightening if you don't already know that.

You can measure Vfb using quasi-static (LF) CV and high-frequency CV plots. Strictly there are more variables than unknowns even then (flat band is a bit of a idealized theoretical concept rather than a real measureable phenomena) but you can get a usable value for engineering purposes. Again this is basic MOS theory 101 - first week of class, no less.

Agilent, nee Hewlett-Packard, (e.g. 4140B/42XX) and Keithley make the appropriate instruments for this.

MM

: Vt only has meaning for a MOS*FET* but not a MOS*CAP*. It's a bit : frightening if you don't already know that.

Absolutely not true.

The capaciatance of a MOS CAP (MOSFET with its source and drain tied together) when the voltage across is less than Vt (i.e. no inversion channel) is very small (= Cgdo + Cgso where Cgdo and Ggso are small overlap capacitances.)

When the voltage across the MOS CAP is larger than Vt, the channel is inverted, the device is in the linear region, and the Capacitance is approximately Cox * The Area of the Device (i.e. Much larger than Cgdo + Cgso.) If you understand this, you should be able to answer your own question now.

Someone else can help you with your question about Vfb.

Joe