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From: straka@ihlpf.UUCP
Newsgroups: sci.electronics
Subject: Re: MOSFET handling
Message-ID: <1410@ihlpf.ATT.COM>
Date: Tue, 14-Apr-87 14:31:04 EST
Article-I.D.: ihlpf.1410
Posted: Tue Apr 14 14:31:04 1987
Date-Received: Thu, 16-Apr-87 01:07:51 EST
References: <6599@allegra.UUCP>
Distribution: na
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 46
Summary: Whooooooah! .

In article <6599@allegra.UUCP>, mc@allegra.UUCP (Mark Cravatts) writes:
> I've been handling mosfets for a long time now, and this is what I suggest
> you do->    NOTHING!!!
> 
> As long as the humidity level in the room is high, meaning, if you can 
> walk across a carpeted room dragging your feet behind you and finally
> touch ground without an observable static discharge, your safe. The 

> I have handled cmos digital chips, ccd chips, along with a variety of
> small signal(especially sensitive) and power MOSFETS, and I've never blown
> one out!  Maybe I've been lucky or maybe the precautions I take are valid,
> but nevertheless what I'm trying to say is that people usually over react
> to these devices.

Whooooah!

I have personally designed, manufactured and tested semiconductor
integrated circuits.  Yes, people often over-react to static with MANY
semiconductor devices.  This is because the manufacturers have done
their jobs and designed in protection in the input pads of the chips.
This is particularly common in integrated circuits, even MOS memory chips
and the like.

However:

Some devices (discrete MOSFET RF front-end xistors) are designed for
essentially infinite input impedance.  These devices have NO input
protection whatsoever, as if they did, their impedance would be
degraded.  Voltages of as low as 50-100v can and do blow the gate oxides
of devices of this type.  These voltages are EASY to come by with no
protection circuitry to discharge those extra electrons.  A perfect SiO2
gate will take up to about 120v/1000 Angstroms of thickness.  Most gates
are ~~1000 angstroms thick.

Moral: Either know very well what you are doing, or be conservative.
       If the data sheet says >20Megohms input impedance, be *real* careful.

BTW, CMOS, and CCDs all have protection on their input pads (it's just a
reverse-biased junction to the substrate, and conducts at <30v,
providing reasonable static protection), and I believe that power
MOSFETs also have them (They don't need ridiculous impedances, like the
RF MOSFETs go after).
-- 
Rich Straka     ihnp4!ihlpf!straka

New word for the day: arithmoquinification.  Use it *every* day.