I guess I am missing something about this thread. My understanding from few of the threads is that=20 Increase temperature leads to more number of electrons in conduction = band Increased temperature leads to reduction in threshold voltage Vt of say = MOSFET. Reduction of Vt would increase the switching speed of the device making = it faster. =20 So how would reducing the temperature to liquid nitrogen levels make the = device work two to three times faster. Kindly help me clear my confusion. Thanks Venkat =20 ________________________________ 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. = At elevated temperatures, electrons can be thermally excited from the = valence band to the conduction band, giving intrinsic conductivity from equal = 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]=3D20 Sent: Monday, May 16, 2005 3:28 PM To: Christopher.Jakubiec@xxxxxxxxxxxx; Muranyi, Arpad; =3D 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 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 =3D impurities leading to a slightly n-type material in silicon. At "low" doping (about 10-100x the impurity level), the resistivity =3D becomes both lower and less sensitive to temperature. It also becomes possible = =3D to predictably control the built-in junction potential. At very high temperatures, of course, the thermally generated carriers = =3D can dominate over the doping. But that is normally outside the operating = =3D range, unless you get a local high current density. - Lynne -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] = =3D 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 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 =3D3D20 -----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 room temperature(?). The doping is what freezes up some electrons to make it conductive. How does this relate to temperature? Thanks, Arpad -------------------------------------------------------------------------= =3D -- -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =3D3D3D 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]=3D3D3D3D20 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 =3D3D3D temperatures.=3D3D3D3D20 CMOS devices will run at two to three times =3D 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, =3D the=3D3D3D3D20 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=3D3D20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu