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Silicon samples

Discussion in 'Electronic Design' started by George Herold, Jan 9, 2014.

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  1. Hi All, I’m looking for a source of silicon wafers. Well those are easyto find on the web. What I’d really like are Si samples that have been sliced with ohmic contacts added. This will be for a student lab where they will look at conductivity and the Hall effect as a function of temperature (and doping). It’d be great if I could have a Hall bar patterned onto the device. (But perhaps that is asking too much?) Back in grad school we use to get samples (GaAs/AlAs QW) from the Cornell nanofabrication facility, and they always came with a hall bar and some C(V) pads so these are perhaps standard? Searching the web I didn’t have much luck. And I thought of asking here. Besides names of companies etc. even just a good search term would help. Should I look for people who do wire bonding for example?Will I need an epilayer put on the samples to protect them? (See, I’m not even sure exactly what I want.) Any ideas, thoughts would be much appreciated!

    George H.
  2. For a product. I could imagine ordering 100 of them.
    (well after checking out that they do work.)
    Yeah there are some schools that could do this, but it gets complicated if it's for a commercial product. And then of course the one guy at the school who knows how to run the wire bonder leaves... and we're left hanging.
    OK I should search for fab companies then?
    Part of my problem is I don't know what I should be searching for. Maybe it's just a guy who has some lithography and deposition equipment in his garage.
    (I've got some old pieces of Si kicking around at home.. maybe I'll start there.)

    Thanks Tim,
  3. Phil Hobbs

    Phil Hobbs Guest

    How about a piezoresistive pressure sensor? Those use diffused
    resistors, and come in nice packages if you like.


    Phil Hobbs

    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
  4. Chris Jones

    Chris Jones Guest

    Maybe this is what you want:

    I think you need aluminium deposited before you can wire-bond to the
    sample, so I doubt those places could help directly.

    You will get a greater Hall voltage with a thinner sample, or putting
    the current through a very thin diffusion on the surface of a thick sample.

    I wonder if you can use a piece of solar cell. Those usually have a thin
    diffusion on the front with contact fingers that make ohmic contact to
    it. Perhaps you can cut or break a cell in such a way that the fingers
    break into separate contacts in a useful configuration, though I can't
    think of a way to make a hall effect device from lots of parallel
    contact fingers.

    Otherwise you might be able to make your own! :

  5. Hmm Something like this?
    I think I might even have some of these....
    So are you suggesting that I could just use the diffused p region as a sample?
    Or can I somehow access the n-epi region too?

    George H.
  6. I found that also. Making my own just sounds too expensive... time-wise.

    There use to be a clean room at UB (where I went to grad school) that I hadaccess to. I think I could still get in, but then it's a whole project.
    Sure I didn't mean the wire bonding as a serious suggestion... but just that maybe I should be searching for something other than Si wafers.
    Yeah, I guess I'm not so much interested in big signals as much as showing the effect. Letting students measure thickness with some calipers would beOK.
    Yeah a commercial device that I could bend to my needs would be ideal cost-wise.
    Hmm I saw that before... HF scares me, but it's interesting that she just uses supermarket cleaner.... That might work. Maybe give up on hall bars and just do a van der Pauw type measurement.


    George H.
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