Searching for ultra low Cjo diodes

The diodes will be used for ultra low power, so it doesn't matter to me how small the junction area is.

Paul

Are there are *any* discrete components with capacitance that small? The capacitance between its mounting pads would likely be more than that.

I would like small caps. Makes for a nice stressful day under the microscope. :-)

Paul

The Skyworks Inc. DMK2790-000 GaAs Schottky diode has a device capacitance of 0.055pF. It says Cj0 is 0.05pF and average Ct is ~

Although I don't see any buy button for this diode. I think it's expensive.

Paul

The smallest commercial chip diode I've seen is 0.02 or maybe 0.03 pF. The smallest packaged one I know of is around 0.2 pF.

John

So he just has to put 20 in series? :)

I did a quick hack estimate of capacitance between a couple of 20mil square pads 40 mils apart on 1/16 inch FR-4, in this way: the capacitance per inch of a differential microstrip with 20 mil traces separated by 40 mils is 2.4pF/inch (more or less). So .02 inches of that would be about .05pF. I would expect fringing fields to add a bit to that. Putting a package on top of those pads makes things worse, as does having wires that come from the pads and end up very close together at their ends. Guess you could shrink the pads further, though you still end up with wires that come pretty close.

I wonder why the need for such low capacitance...

Cheers, Tom

May I ask what diode chip part number is and manufacture? I may be interested in purchasing a few hundred bucks worth initially if they are reasonably priced per diode.

Thanks, Paul

Some of the Metelics GaAs diodes get down there. Their silicon parts get below 0.1 pF.

M-pulse gets down to about 0.06 pF, chip or beam lead.

HP/Agilent used to sell some 0.03 pF parts, but I'm not sure if they still make them.

Yup, this one is obsolete:

Macom has some beam-lead 0.05 pF parts, probably expensive.

What are you working on?

John

Check out the MDT Corporation MP61000 series of PIN diodes: