[SI-LIST] Re: si-list Digest V5 #210
- From: <Christopher.Jakubiec@xxxxxxxxxxxx>
- To: <sch@xxxxxxxxxxxxxx>, <weirsi@xxxxxxxxxx>
- Date: Mon, 23 May 2005 13:11:26 -0700
I agree with Steve's statement for MOSFETs. My experience has been when
measuring CMOS ring oscillators, the increased leakage current due to
temperature significantly lowers the threshold voltage and thus speeds
up the circuit.
-Chris
Infineon Technologies
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Steve Horne
Sent: Monday, May 23, 2005 3:55 PM
To: weirsi@xxxxxxxxxx
Cc: venkat@xxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: si-list Digest V5 #210
That's true for wires, but it's not that simple for circuits including
MOSFETs. If you operate the circuit at a sufficiently low voltage, the
effect of the increasing threshold voltages at low temp can more than
compensate for the other effects. This can lead to the digital circuit
operating slower at, say, 0C than at 85C. In a microprocessor in a 130nm
process, I've observed this speed/temperature slope transition occur at
an operating voltage of roughly .75V. Your mileage will vary based on
the Vts in the process and the amount of wire (RC) delay in your
critical paths.
Steve
steve weir writes:
> Venkat, it's a simple RC relation. MOSFET's have a positive tempco
of=20
> resistivity.
>=20
> Steve.
> At 12:25 PM 5/23/2005 -0500, Satagopan, Venkat Raghavan
\(UMR-Student\) wrote: > >I guess I am missing something about this
thread. > >My understanding from few of the threads is that=3D20 >
>Increase temperature leads to more number of electrons in conduction =
=3D
> >band > >Increased temperature leads to reduction in threshold
voltage Vt of say =3D > >MOSFET. > >Reduction of Vt would increase the
switching speed of the device making =3D > >it faster. > >=3D20 > >So =
how
would reducing the temperature to liquid nitrogen levels make the =3D >
>device work two to three times faster. > >Kindly help me clear my
confusion. > >Thanks > >Venkat > >=3D20 > > >
>________________________________ > > > >From:
si-list-bounce@xxxxxxxxxxxxx on behalf of Tom Dagostino > >Sent: Mon
5/16/2005 6:51 PM > >To: arpad.muranyi@xxxxxxxxx; si-list@xxxxxxxxxxxxx
> >Subject: [SI-LIST] Re: si-list Digest V5 #210 > > > > > > > >
From the Handbook of Physics > > > >Semiconductors..."At absolute zero
the ideal structure is an insulator. =3D > >At > >elevated
temperatures, electrons can be thermally excited from the =3D > =
>valence
> >band to the conduction band, giving intrinsic conductivity from equal
=3D > >number > >of conduction electrons and holes....." > > > >Tom
Dagostino > >Teraspeed Labs > >13610 SW Harness Lane > >Beaverton, OR
97008 > >503-430-1065 > >http://www.teraspeed.com >
>tom@xxxxxxxxxxxxx > > > >Teraspeed Consulting Group LLC > >121 North
River Drive > >Narragansett, RI 02882 > >401-284-1827 > > >
>Teraspeed is the registered service mark of > >Teraspeed Consulting
Group LLC > > > >-----Original Message----- > >From:
si-list-bounce@xxxxxxxxxxxxx > >[mailto:si-list-bounce@xxxxxxxxxxxxx]On
Behalf Of Muranyi, Arpad > >Sent: Monday, May 16, 2005 4:02 PM > >To:
si-list@xxxxxxxxxxxxx > >Subject: [SI-LIST] Re: si-list Digest V5 #210
> > > > > >Thanks for the two responses to my question from Lynne, and
Chris. > > > >Let me recap the thread, and restate my question,
because I don't > >feel that it was completely answered yet. > > >
>The thread started with the question on what happens with silicon >
>semiconductor devices below -55 C. A response came back to say >
>that at 77 K silicon will act as an insulator. Someone else >
>responded that this was not the case. Then the previous writer >
>corrected themselves saying that they were referring to pure >
>silicon being an insulator at such low temperatures. > > > >This is
when I asked my question. I may have read too much into > >the thread,
but it seemed to imply that PURE silicon is an insulator > >at those
low temperatures, but less of an insulator at higher > >temperatures,
such as room temperature. This surprised me. > > > >I am certainly
not an expert in this area, but I thought that PURE > >silicon was an
insulator because the way its crystal structure is > >built. There are
no free electrons in it. I don't see how temperature > >can effect its
conductance, unless something drastic starts happening > >in the
crystal structure. Chris' response to my question pretty > >much
confirmed this, although I would be curious to hear more about > >what
those mechanisms are which can do that. > > > >Lynne's response seems
to apply to doped silicon. I agree the mobility > >of those carriers
can be influenced by temperature a great deal, but > >again, I was
curious about PURE silicon, since that's what my first > >response
(question) was triggered by. > > > >So is my recollection correct that
at normal room temperatures and > >thereabout, PURE silicon would still
be a perfect insulator, or does > >it have to be cooled way down (say
to 77 K) to become an insulator? > > > >Thanks, > > > >Arpad >
>-----------------------------------------------------------------------
> >-----Original Message-----
> >From: lgreen [mailto:lgreen22@xxxxxxxxxxxxxx]=3D3D20
> >Sent: Monday, May 16, 2005 3:28 PM
> >To: Christopher.Jakubiec@xxxxxxxxxxxx; Muranyi, Arpad; =3D3D >
>si-list@xxxxxxxxxxxxx > >Subject: RE: [SI-LIST] Re: si-list Digest V5
#210 > > > >Hi, Arpad, > > > >Silicon bulk resistivity (and
conductivity) is strongly temperature > >dependent. At room
temperature, the resistivity is higher than metals, =3D > >=3D3D > =
>but >
>too high to use it as a good insulator (hence the name semi-conductor).
> >Resistivity is also very sensitive to impurities, with the usual =
=3D3D
> >impurities > >leading to a slightly n-type material in silicon. > >
> >At "low" doping (about 10-100x the impurity level), the resistivity
=3D3D > >becomes > >both lower and less sensitive to temperature. It
also becomes possible =3D > >=3D3D > >to > >predictably control the
built-in junction potential. > > > >At very high temperatures, of
course, the thermally generated carriers =3D > >=3D3D > >can > =
>dominate
over the doping. But that is normally outside the operating =3D > =
>=3D3D
> >range, > >unless you get a local high current density. > > > >-
Lynne > > > > > >-----Original Message----- > >From:
si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =3D =
>
>=3D3D > >On > >Behalf Of Christopher.Jakubiec@xxxxxxxxxxxx > >Sent:
Monday, May 16, 2005 2:17 PM > >To: arpad.muranyi@xxxxxxxxx;
si-list@xxxxxxxxxxxxx > >Subject: [SI-LIST] Re: si-list Digest V5 #210
> > > >Arpad, > > > >I agree with your statement to an extent.
Current flow in silicon is > >related to the amount of free carriers
(either holes or electrons) that =3D > >=3D3D > >are > >available to
participate. Free carriers can be induced both by means of > >impurity
doping in the silicon, and electron/hole pairs can be thermally >
>generated even in pure silicon (although not normally for a practical
> >purpose). > > > >Regards, > > > >Chris > >Infineon Technologies
> >=3D3D3D20 > > > >-----Original Message----- > >From:
si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >On Behalf Of Muranyi, Arpad
> >Sent: Monday, May 16, 2005 2:15 PM
> >To: si-list@xxxxxxxxxxxxx
> >Subject: [SI-LIST] Re: si-list Digest V5 #210
> >
> >
> >Jut to clarify things I would like to ask a question:
> >
> >My understanding was that pure silicon is not conductive, not even
at =3D > >=3D3D > >room > >temperature(?). The doping is what =
freezes up
some electrons to make it > >conductive. How does this relate to
temperature? > > > >Thanks, > > > >Arpad >
>-----------------------------------------------------------------------
--=3D
> >=3D3D
> >--
> >-----Original Message-----
> >From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> >=3D3D3D3D On Behalf Of Daniel Chow
> >Sent: Monday, May 16, 2005 10:44 AM
> >To: John Zasio
> >Cc: si-list@xxxxxxxxxxxxx
> >Subject: [SI-LIST] Re: si-list Digest V5 #210
> >
> >My bad.
> >
> >My statement was true for pure silicon.
> >
> >Heavy doping significantly changes the properties of silicon. > >
> > > > > >-----Original Message----- > >From: John Zasio
[mailto:zasio@xxxxxxxxxxxxxxxxxxx]=3D3D3D3D3D20
> >Sent: Monday, May 16, 2005 10:25 AM
> >To: Daniel Chow
> >Cc: si-list@xxxxxxxxxxxxx
> >Subject: Re: [SI-LIST] Re: si-list Digest V5 #210
> >
> >Daniel,
> >
> >Silicon devices do work and work well at liquid nitrogen =3D3D3D3D =
>
>temperatures.=3D3D3D3D3D20 CMOS devices will run at two to three times
=3D3D > >faster than > >at room temperature. > > > >In the mid 80s =
ETA
Systems shipped a CMOS Supercomputer cooled by liquid > > > >nitrogen.
Although the product was not a commercial success, =3D3D >
>the=3D3D3D3D3D20 > >technology worked very well. > > > >John Zasio =
>
> > >Daniel Chow wrote: > > > > >Jon, > > > > > >No silicon part
will work at liquid nitrogen temperatures (77 Kelvin). > > > > >
>Silicon is an insulator at that temperature. The charge carriers are
> > >"frozen out" at low temperatures. > > > > > >Please refer to
Chapter 8 of "Solid State Physics" by Charles Kittel > >for more
details. > > > > > >Thanks! > > > > >Daniel Chow, Ph.D. > > >Sr.
Product Engineer > > >ALTERA > > >Office: (408) 544-8100 > > >Fax:
(408) 544-7602 > > >Email: dchow@xxxxxxxxxx=3D3D3D20 >
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