In the ideal case the oxide in an MOS capacitor is of infinite resistance. Hence charge carriers cannot flow from metal to semiconductor.Can someone help? Regards and thanks.
I am not sure if the MOS capacitor will be in thermal equilibrium once fabricated ( assuming it is not shorted by any other circuitry on the IC), it probably may end up with quite some embedded charge.
in typical Silicon MOS capacitors an embedded charge... fixed or trapped more or lesso close to interfaces, is present just for "natural" chemical/structural defects in the dielectric layer... So a localized charging in the oxide may be expected, with a surface density in the range e10 - e12 electrically active defects per square centimeter.
A Current-Voltage curve (at high frequency, say 1 MHz) is enaugh to identify and quantify the embedded charge in terms of internal voltage (or flat-band voltage), that may be in the 0.2-0.6 V range for usual capacitors just after fabrication.
Equilibrium is reached intrinsecally by natural band bending, that is localization of counteracting and "free" charges close to the interface with the dielectric layer just to oppose a shield to the above said fixed oxide charge.
Hope it is of some help
Dear friends,
My question is about an ideal MOS structure where there are no fixed/trapped mobile/interface charges. The band bending in such case can only be due to the difference of work functions of metal and semiconductor. In the case of Schottky barriers under such case Fermi levels of M and S get aligned by transfer of charges from one side to the other and due to this process the bands bend. But in the case of IDEAL MOS, charges cannot be transferred as the oxide layer is of infinite resistance.But we know that in this case , Fermi levels of M and S, which are on either side of the perfectly insulating (IDEAL) oxide get aligned. How this happens without a charge transfer?
Regards.
There's not such band bending in MOS capacitor by itself. But an MOS capacitor itself is useless right, you need to connect the metal and S/C to a circuit to use it.
When you wire probes into metal and S/C contacts to an electrical circuit, they're connected somehow outside the M-O-S junction.
Thank you everybody. Hope you can clear another doubt of mine regarding MOS: What is the physical significance of the x-intercept of (not slope) 1/C^2 vs Vg curve?
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