Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!ucsd!sdcsvax!ucsdhub!hp-sdd!hplabs!hpfcdc!hpfclm!hpfcdj!myers
From: myers@hpfcdj.HP.COM (Bob Myers)
Newsgroups: sci.electronics
Subject: Re: How do FETs REALLY work?
Message-ID: <16750015@hpfcdj.HP.COM>
Date: 30 Jan 89 19:26:27 GMT
References: <609@uvicctr.UUCP>
Organization: Hewlett Packard -- Fort Collins, CO
Lines: 28

>OK, net, here's a question for you:

>I know what a real MOSFET looks like and I have a vague notion of how it
>works but how about this:  Say we get a piece of, say, N type silicon and
>we oxidize it and stick on a gate.  Now we etch the Si so that it is very
>thin under the gate.  Is this thing now a MOSFET even though there is no
>junction nearby?  Does the MOSFET actually need the junction between the
>substrate and the channel?

Yes, it is a FET; no, it does not need a "junction", since there isn't a
junction there in the first place.  The SiO2 is simply an insulator -
the generic name for this device is actually MISFET, for Metal-Insulator-
Semiconductor FET.

>Next step: replace the semiconductor with a metal (Making a MOMFET!) -
>increasing the gate voltage to a sufficiently high level should eventually
>drive away all the free electrons rendering the channel an insulator.
>What field strength would this require?

Lots and lots and lots.  I haven't done the calculations, but remember what
makes a conductor a conductor, and what makes a semiconductor a semiconductor.
Now, your next problem is to find an insulator that will stand up to the
field required (see "Dielectric Breakdown") :-).


Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
{the known universe}!hplabs!hpfcla!myers |  sentient life-form on this planet.