Microwave PIN diodes available (shunt optimised, 2GHz)

Dr. Slack, Mon Jun 05 2017, 06:38AM

I have some diodes that were bought as BAR81W, typical ratings 700mohm 150pH at 5mA, 600fF at -1v, -0.7dB/-30dB at -3V/10mA when used in shunt at 1.89GHz. They are in a SOT343-like package.

Now for the interesting bit, and why I'm not putting them on fleaBay, or even surplus component handlers. They are in the wrong package, an experimental one that didn't make it through JEDEC. The silicon is as for the BAR81W The package is SOT343 sized, but the die is rotated through 90 degrees compared to that data sheet. They were supplied to us by Infineon at pre-production, and after the package was changed for full production, have lain unused since.

For those that don't know the subtleties of a shunt optimised package, the bonding is asymmetric. The cathodes go to ground via a massive leadframe and two connections for minimum inductance, that's the 150fF quoted in the data sheet. The anodes are bonded with normal bond wires, and the signal is intended to 'hop on' through one connection and 'hop off' through the other. This means that not only does the bond wire inductance not appear in the common shunt path when the diode is on, but also the sniff of inductance tends to turn the residual C of the off diode into a filter. Win - win.

Of course the diode can still be used as a series diode, albeit with slightly higher parasitics than a dedicated 2 terminal diode would be.

So these guys are not for professional use. They won't autoplace on an existing BAR81W footprint, and you won't be able to get any more, so you shouldn't prototype a board with them. However, they work just fine, and can be hand soldered onto tracks and into lashups for hobby use, even forced onto an existing BAR81W footprint with care.

Are there any hams that would like a strip of 100 diodes good for 2GHz? There's plenty to go round, I have a reel. Can any hams recommend a more ham-dedicated forum, that would be a better fit for them?