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Re: Cathode Films from Sheldahl



On Tue, 25 Mar 2008, Gerard Visser wrote:

Dear Gerard,

funny our mails must have crossed in cyber space, but I agree with you
1000% this needs a bit more time and thoughts before we can jump on some
new option.

cheers elke


> Date: Tue, 25 Mar 2008 12:04:02 -0400
> From: Gerard Visser <gvisser@indiana.edu>
> To: Simon Taylor <staylor@jlab.org>
> Cc: Fernando J. Barbosa <barbosa@jlab.org>,
>      Daniel S. Carman <carman@jlab.org>, Roger Flood <flood@jlab.org>,
>      Elke-Caroline Aschenauer <elke@jlab.org>,
>      "halld-tracking-hw@jlab.org" <halld-tracking-hw@jlab.org>
> Subject: Re: Cathode Films from Sheldahl
>
> Hi Simon,
> 	I think you may be overlooking something... -->
>
> resistivity of gold
>   2.2E-8 Ohm*m
>
> surface resistivity @ 900 Angstroms
>   2.2E-8 Ohm*m / 9E-8 m = 0.244 Ohm (per square)
>
> length of longest strip
>   about 242 squares
>
> characteristic impedance
>   who knows - not simulated - but surely on the order of 100 Ohms at the
> most
>
> signal loss (at the most optimistic) 1-exp(-242*0.244/100)=45%
>
> not so good, I think.
> and this simple analysis did not mention the noise contribution of this
> resistance. probably nonzero.
>
> I think this all needs to be considered more carefully. A real
> calculation of the cathode line impedance and attenuation and the noise
> contributed by it, should be done.
>
> 	- Gerard
>
> p.s. Yes I do agree with the concern about handling (and connecting to)
> any super-thin layers whether copper or gold.
>
>
> Simon Taylor wrote:
> > Hi, Fernando,
> >
> > As far as thickness goes, 900 Angstroms of Gold should be okay:
> > For each gold layer I get  900 x 10^-10 m x 19.3 g/cm^3 / (6.4 g/cm^2) =
> > 2.7 x 10^-5 X0,
> > compared to 1.3 x 10^-4 X0 for 2 microns of Copper.  My concern for such
> > a thin layer of conductor is handling:  I can well imagine it could be
> > quite easy to cause breaks in the strips due to scratches...  Also, we
> > would probably have to do some selective plating near where the strips
> > need to be connected to the outside world.
> >
> > Simon
> >
> >
> > Fernando J. Barbosa wrote:
> >> Sheldahl has a series of gold deposited materials that can be used for
> >> the cathodes. These materials are normally specified as thermal
> >> barriers in satellites but can be used for the FDC cathodes. Part #
> >> 146437 (see below) is a standard product with 900 angstroms of Au on
> >> 25 micrometer Polyimide and can be delivered in 48 inches wide rolls.
> >> The left column below is for standard products (available) and they
> >> range from 8 to 127 micrometer Polyimide.
> >
>

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