We got some samples of an NEC hj fet and were wondering what its time-domain response might be like. The part is only 2x2 mm and the leads are 1.2 mm pitch, and I hadn't previously had a lot of luck breadboarding stuff like this.
We found two tricks:
Get a piece of copperclad, epoxy-glass or preferably teflon; the teflon is easier to cut. Cut out "pads" with a very sharp xacto knife, under a Mantis magnifier. This will make horrible burrs and shorts, so the first trick is to scrub it really hard with a Scotchbrite pad between cuts. This cleans it up beautifully.
The second trick is to use small patches of kapton tape as insulators. like where parts join or whatever. Soldering doesn't bother it at all.
ftp://66.117.156.8/FetTest.zip
Here, the fet is in a first-pass test circuit, just to see how fast we can turn it on and off. The TDR pulse from the sampling head is the gate drive, 0 (Idss) to -0.5 (pretty much off) at 50 ohms source z.
The drain is pulled up through a 47 ohm resistor, and the 150 ohm resistor off to the side is an "attenuator" into the other scope channel. The turnon fall is very clean, no nasty ringing or whatever, with a 190 ps fall time. Turnoff is similar; these things don't store charge! The TDR of the gate (lower trace) indicates that the gate capacitance is loading the drive, so we need a bigger gate swing, from a lower source impedance, to make this thing switch really fast. That will be next.
John