MACOM GaN Wideband Transistor - Page 1
Forum section: electronics / beginners

author: tec5c
author_rank: Frequent Contributor
timestamp: January 12, 2018, 08:09:40 am
content: Hi all,I have a MACOM GaN wideband transistor which I am wanting to do some device characterisation with. However all attempts at doing simple DCIV measurements have been unsuccessful, i.e., for bias conditions of VDS = 10V, VGS = -5V (note: depletion mode FET), results in a gate current of ~ -1.6E-06 which is obviously incorrect. Drain current under these same conditions is ~ 1.6E-06.The datasheet for the device is here:https://cdn.macom.com/datasheets/NPTB00004A.pdfThe pinout for this device is a bit strange with there being 8 pins and a pad on the underside of the device which is source/ground. I have soldered wires to the drain, gate and source pins for biasing purposes. As shown here. Note, the datasheet specifies that the two gate pins are hard wired together internally, the same goes for the two drain pins.I do not understand what I am doing wrong with this device so if someone is able to share some insight it would be most appreciated.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 12, 2018, 08:53:25 am
content: Random wires? Noooo, that thing's going to oscillate a thousand ways from Sunday.Tim

author: tec5c
author_rank: Frequent Contributor
timestamp: January 12, 2018, 11:12:30 am
content: Tim, this was my first guess so I built a small breakout style board to avoid such problems however the same thing is happening.Even if the gate leakage current is "normal", I am still unable to produce any DC family curves. I haven't spent any considerable amount of time on this yet, so perhaps there is something that I am missing. I will report in once more rigorous testing has been done.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 12, 2018, 03:41:29 pm
content: Might it be ESD damaged? (Unlikely that Ids would be nonzero in that case, but who knows.)Tim

author: rfeecs
author_rank: Frequent Contributor
timestamp: January 12, 2018, 05:45:54 pm
content: Tim is right about oscillation. Measuring IV curves could be tough. I remember old datasheets for GaAs FETs that said "DO NOT attempt to measure DC parameters".Anyway, I've done this many times in fixtures as well as probe stations.Treat the thing like an RF amplifier that has gain well above 6GHz. Ideally, put it in an RF fixture like the PC board layout in the datasheet. Bias it through a bias tee and RF terminate the input and output. Put some resistance like 50 ohms in series with the gate to give you nice impedance down to DC. Bypass the drain side to kill RF gain. Ferrite beads are very helpful to help keep RF off the hookup wires.This is a chip I measured, wire bonded in a fancy RF fixture using Agilent bias Tees that go up to 26GHz:

author: tec5c
author_rank: Frequent Contributor
timestamp: January 12, 2018, 08:25:15 pm
content: Quote from: T3sl4co1l on January 12, 2018, 03:41:29 pmI actually have several of these devices so I have tried using at least four different devices now, each to no avail. I think there are some underlying issues which are giving me grief. Perhaps I'll contact MACOM and see what they have to say.Thanks to all for the replies.