update on cryostation

Jim McVittie mcvittie at cis.Stanford.EDU
Fri Jun 6 17:55:59 PDT 2008


Arash,

I agree with Yasuhiro that the vacuum system is a poor design in terms of
oil backstreaming. I suspect that the vendor subsituted a cheaper pump to
get the cost when he was selling us the system.

	Jim  

On Fri, 6 Jun 2008, Duygu Kuzum wrote:

> I also observed that last year too.Probing at low temperature was very  
> difficult.Sometimes I got bad contact causing a lot of noise.Sometimes  
> I couldnt get contact.
> 
> Thanks Yasuhiro,
> 
> Duygu
> 
> Quoting Yasuhiro Oshima <yoshima at stanford.edu>:
> 
> > Hi Arash,
> >   I checked all the tips' continuity before cool it down and found 3& 4 were
> > strange. So it happened without oil condensation.
> >
> >   As for oil back diffusion... The design of this vacuum system, including
> > automatic pump down/vent sequence is not good. There are no isolation valves
> > and this sequence supply the vent nitrogen from downstream of TMP into the
> > chamber right after stopping pump. Once these back diffused oil accumulate
> > in the chamber, it is very difficult to remove, just increase gradually. My
> > another suggestion is that to put valves between chamber/TMP and TMP/rotary
> > pump, and nitrogen line directly into the chamber, though it may make the
> > procedure complicated.
> >   Actually, we have seen hazy surface on our sample every time. But I did
> > not realized that this may behave as insulator.
> >
> > Thanks,
> >   Yasuhiro
> > 2008/6/6 Arash Hazeghi <ahazeghi at stanford.edu>:
> >
> >>  Yasuhiro,
> >>
> >> Thanks for reporting the issues.
> >>
> >>  Regarding the back diffusion I will look at the pump and contact Varian,
> >> this shouldn't be a problem if the pump is operating correctly since we
> >> never had this issue before. There should not be back diffusion to the
> >> extent that you can detect oil in the chamber, if this is the case the pump
> >> has aged and gone bad, not that we need a dry pump.
> >>
> >> I checked the continuity between all probes at room T and they were OK, it
> >> is very strange that you are not getting good contact my guess is you are
> >> not touching the pads or as you mention there is a thin layer of something
> >> on your sample and at low voltages this may be an issue since the tips are
> >> really soft. Per your request, I will check this again.
> >>
> >> Now regarding the probe tips,* All four probe tips* were brand new and in
> >> *perfect* shape when I replaced them just last week. I will look in the
> >> logbook to see who used them. This is becoming a major issue, I cannot
> >> replace the probe tips every week and our group will not pay for it.  Per
> >> prof. Wong's suggestion from now on, whoever breaks the tips and don't
> >> report it will not only have to buy new tips but will also be suspended from
> >> the system for two weeks. No exceptions.
> >>
> >> Please be considerate when lowering and raising the tips. Never keep the
> >> tips contacted to the sample or in close proximity before pumping down or
> >> cooling. As the chamber goes to high vacuum the bellows  are stressed and
> >> bow a little bit, as a result tips that are close to surface will crush or
> >> may even run into each other. Position and lower the tips only when pressure
> >> and temperature have been stabilized. Never lean on the table, yank the
> >> cables or subject the system to mechanical shock when tips are in contact.
> >> If users operate the probes according to the training these tips should last
> >> for months.
> >>
> >>
> >>
> >> Thank you all for your cooperation ,
> >>
> >> Arash
> >>
> >>
> >>
> >>
> >>
> >>
> >> ----------------------------------------------------------------------------------
> >>
> >> Arash Hazeghi
> >>
> >>
> >>
> >> PhD Candidate
> >>
> >> Stanford Center for Integrated Systems
> >>
> >> CIS-X 300, 420 Via Palou Mall,
> >>
> >> Stanford, CA 94305
> >>
> >>
> >>
> >> phone: +1-650-725-0418
> >>
> >> web: http://www.stanford.edu/~ahazeghi
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> *From:* yoshima73 at gmail.com [mailto:yoshima73 at gmail.com] *On Behalf  
> >>  Of *Yasuhiro
> >> Oshima
> >> *Sent:* Friday, June 06, 2008 3:13 PM
> >> *To:* Arash Hazeghi; Duygu Kuzum; shanbin at stanford.edu
> >> *Subject:* update on cryostation
> >>
> >>
> >>
> >> Hi all,
> >>
> >>   Now the cyostation working at 77K very well. As Shanbin pointed out, it
> >> seems that we had a contact issue between needle and metal pad due to very
> >> hard condensed liquid (maybe vacuum oil back diffused into chamber). I just
> >> replaced old vacuum oil of rotary pump. It turn into yellowish color
> >> gradually. It seems to be important to replace it like once in 3 months.
> >> Thanks for good suggestion, Arash! Another information are bellow.
> >>
> >>
> >>
> >> - new oil and container for old oil are near the cryostation. (Arash, could
> >> you move to good position?)
> >>
> >> - I still see some liquid (solid. maybe oil) on my samples. They look hazy.
> >>
> >> - if you'd like to solve this problem permanently, I would recommend to
> >> replace oil pump with diaphragm pump (this is dry).
> >>
> >> - probe tips 3 & 4 are not working (it seems completely isolated). Arash,
> >> please take a look at it!
> >>
> >> - probe tips 1 & 2 are bent and not comfortable.(It is not me...)
> >>
> >>
> >>
> >> Best,
> >>
> >>   Yasuhiro
> >>
> >>
> >> --
> >> Yasuhiro Oshima
> >> 408-398-4753 (cell)
> >>
> >
> >
> >
> > --
> > Yasuhiro Oshima
> > Visiting Scholar
> > Prof. McIntyre Gr.
> > Materials Science and Engineering
> > Stanford University
> > 650-725-3458
> > 408-398-4753 (cell)
> >
> 
> 
> 

-- 
--------------------------------------------------------------
Jim McVittie, Ph.D.    			Senior Research Scientist 
Allen Center for Integrated Systems     Electrical Engineering
Stanford University             	jmcvittie at stanford.edu
Rm. 336, 330 Serra Mall			Fax: (650) 723-4659
Stanford, CA 94305-4075			Tel: (650) 725-3640





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