Silicon samples

[George Herold]

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!
Thanks,

George H.

 

[George Herold]

For a product, or just for your own use?

For a product. I could imagine ordering 100 of them.
(well after checking out that they do work.)

Worcester Polytechnic University used to have a research fab -- perhaps
there are universities that would do runs of these for you? If it's for
a commercial product it'll be an unreliable source, but it's a thought.

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.

At one point there were wafer aggregation companies out there: you made
your custom design, and sent it to the wafer aggregation company, and
then when they had a wafer full of design they'd run it through fab. I
know that it was less expensive than doing a full wafer, but I have
absolutely no clue how affordable of a "less expensive" that is, nor how
you'd find one.

There are fabs out there that specialize in making obsolete components on
obsolete processes -- if you're doing enough, maybe a 4" wafer full of
Hall bars the size of 2N2222's wouldn't be too expensive?

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,

 

[Phil Hobbs]

Hi All, I’m looking for a source of silicon wafers. Well those are easy to 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!
Thanks,

George H.

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

Cheers

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
http://electrooptical.net

 

[Chris Jones]

Hi All, I’m looking for a source of silicon wafers. Well those are
easy to 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! Thanks,

George H.

Maybe this is what you want:
http://www.bridgetec.com/sample_prep-insn.pdf

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! :

Chris

 

[George Herold]

How about a piezoresistive pressure sensor? Those use diffused

resistors, and come in nice packages if you like.

Hmm Something like this?
http://www.microsystems.metu.edu.tr/piezops/piezops.html
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?

Thanks,
George H.

 

[George Herold]

Maybe this is what you want:
http://www.bridgetec.com/sample_prep-insn.pdf

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.

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

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.

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.

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.

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.

Yeah a commercial device that I could bend to my needs would be ideal cost-wise.

Otherwise you might be able to make your own! :

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.

Thanks,

George H.