update on cryostation

Yasuhiro Oshima yoshima at stanford.edu
Sun Jun 8 00:32:06 PDT 2008


Hi Jim,
  Thank you for your comment.

Hi Arash,
  By the way, tips 1&2 are bent but still usable. Tips 3&4 have good shape
but I couldn't use for their discontinuity.

Yasuhiro

2008/6/6 Jim McVittie <mcvittie at cis.stanford.edu>:

> 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
>
>
>


-- 
Yasuhiro Oshima
Visiting Scholar
Prof. McIntyre Gr.
Materials Science and Engineering
Stanford University
650-725-3458
408-398-4753 (cell)
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