[SOLVED] [Moved]: Reverse (Inverse) narrow width effect

[CHL]

Hello

I tried to understand the reverse narrow width effect, but I couldn't.


- The STI corner has high electric field, so the threshold voltage of the FET decreases


I don't understand why the corner shows high electric field.

 

[erikl]

I don't understand why the corner shows high electric field.

That's valid for all corners. Here's a nice . And here are simulation plots for rounded structure tips:

Inside corner: highest field blue:
Outside corner: highest field red:

 

[timof]

Its all about 2D electrostatics and geometry (determined by process).

Attached image - a vertical cross-section of MOSFET's channel, showing the gate, gate oxide, STI (shallow trench isolation, and active Si - gives an idea of why electric field between the gate and active Si is higher at the corner.

This image is copied (and annotated) from **broken link removed** article.


That's why corner rounding is so important in STI-isolated MOSFETs - properly rounded corner minimizes electric field.

It's called "inverse narrow channel effect" (decrease of Vt with narrowing channel width) because a "classical" narrow channel effect, observed in older, LOCOS-isolated MOSFETs, showed an increase in Vt for narrow channel devices.