high value resistors on thin film ceramic

Question

high value resistors on thin film ceramic

zappedagain (Electrical)

(OP)

1 Mar 10 12:32

Is it possible to fabricate a > 1 gigohm resistor on a thin-film ceramic layer? I'm not talking thin-film resistors, but a resistor layer on a thin-film carrier (PCB). Or would I want to do it on a different type of layer, as the resistive layers typically are fairly low resistivity (100 ohm/sq). I thought I'd post a general question here before getting into specifics with the various ceramic vendors.

Thanks,

John D

biff44 (Electrical) · Answer 1 · 2010-03-03 13:43:34

I think the problem you will run into is that the resistance between the two electrical pads will change dramatically depending on if it is humid or dry, if there were any sort of contaminants on the surface (flux), etc. I have had trouble keeping 2.2 Mohm chip resistors reading 2.2 Mohm!

I would concentrate on that aspect...break it up into many discrete resistors in series, maybe 50 Mohm each, and machine away board material in between the resistors. Good luck.

www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

zappedagain (Electrical) · Answer 2 · 2010-03-03 14:02:21

Good point. I'm trying to reduce the parasitic parameters; I need to watch out I don't get a lot more variability in the ones that remain. If this may be in a hermetic package I still have a chance.

VEBill (Military) · Answer 3 · 2010-03-03 17:11:25

Ultra high value resistors are (often? sometimes?) used in smoke detectors. They're used to balance the bridge circuit with the radioactive air gap.

Beware of spiral cut or similar resistors if the application is RF (this being the Microwave etc. forum...).

Skogsgurra (Electrical) · Answer 4 · 2010-03-03 17:50:31

Sorry, this is not at all my field of expertise, but a design that requires a 1 Gohm resistor seems to be a solution that looks for another solution.

If this isn't a pH meter application or someting similar, I can not think of any application where this level of resistance is needed. And I know that such resistors are not used even in pH circuits. Or, at least, that such circuits can be built without such extreme resistors. Nanoamperes require teflon insulators - how can you get even close to that on a ceramic substrate?

I think that you need to rethink that spec.

Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

zappedagain (Electrical) · Answer 5 · 2010-03-04 13:41:42

Good point, Skogs; something for me to look into. I'm working on improving a transimpedance amplifier that presently has a gain (chip resistor) of 820K. My thought is that I may be able to reduce the parasitic capacitance and improve the gain while keeping the same bandwidth. This is in early feasibility stages so I'm checking out various ideas.

John D

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high value resistors on thin film ceramic