enhancement to depletion

Yes it does!

First heating did change threshold voltage noticeably. Further annealing didn't do much at all.

From positive voltage torture kinetic, I though that positive voltage might be doing two things at the same time: change gate threshold voltage, and undo the changes. Because the timelapse looks like this: first, threshold voltage goes down, then it turns around and goes up and essentially returns to where it had started.

So I decided to use it to restore the lowered threshold by applying large positive voltage, that is large, but just a little smaller than what is needed to make the gate leak, and the threshold start to o down.

It works!

On this timelapse:

First, I reduced the threshold voltage of a mosfet by applying large negative voltage (23-36V, I actually was pulling a current). Then, I applied positive voltage. This caused threshold to rise.

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I also seems to have successfully restored a mosfet tortured to the end with positive current, here. That mosfet was behaving bad. When I inserted it into gate threshold measuring circuit, it drifted like crazy. After feeding +35V to gate for a few hours, its threshold didn't change much. But it doesn't do that awful drifting anymore!

I started reproducing the negative voltage torture with a new mosfet, and it is the same! Well, I didn't measure the actual torture curve. I just found out that it is the same 20-ish volts it takes to observe gate leakage. Either this mosfet is leaky too, or it is just the way it is. Strange.

So I stopped the attempt to reproduce, and will save this LAST mosfet for something more interesting.

Apparently, the mosfet has a leaky gate. Current of 0.1 uA takes less than usual voltage (-26 V), and only at 10 uA (50% duty) gate threshold began to change.

The process that followed is quite interesting. It ended with an almost killed mosfet. Gate-to-source now measures about 140 KOhm.

Interesting is that it started very slowly, then accelerated, and then slowed down and stopped.

This seems to be a slightly dodgy mosfet, so I won't do any further analysis of it. UPDATE: no, it is an all-right MOSFET.

UPDATE: attempt to recover it with +35V finished it off. This MOSFET is now a dead short across all 3 pins.

Overall torture kinetic

Slopes

Rate of threshold voltage change is not exactly proportional to gate current, but close to being so.

Post-torture drift

Surprisingly little drift. But the mosfet is likely very much damaged, so it doesn't make much sense.

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I have only one more fresh mosfet remaining for experimenting (same model, IPD10N03LA). I plan doing a negative voltage torturing for comparison with positive. After that, I either order more of them (if I can), or move to experimenting with other mosfet models.

UPDATE: found one more!

In progress now. So far, it is going rather similarly to a previous one, even though that previous one was done on defunct circuit.

The threshold voltage is now rising again.

.....

UPDATE: finished.

Unprocessed data available in files: TORTURE2.TXT. Note: torture currents are chopped with 50% duty cycle, so the average currents into gate are half the indicated values.

Kinda similar to what I got with broken circuit. Except, this time:

* fresh transistor

* final current was 1 uA, not 0.3 uA

* I almost reached the end of the process =)

Today I wanted to do another experiment with next mosfet. Only to find out that my experimentorture circuit is measuring some nonsense. DOH!

It turns out that I've blown the TL431 ic when setting up the datalogger, and it is a dead short in all directions. This means my previous experiment is completely and totally broken, and I will put a note there right now.

Arrrgh!

That mosfet apparently was tortured to near death, with gate threshold voltage (1 mA) measuring 0.708 V, and with substantial conductivity at zero gate voltage.

As I found out earlier, the rate of MOSFET modification was very sensitive to torture voltage. Like, at 38 V it was barely progressing, but at 42 V it was pretty fast.

I thought that if I control current, the rate of change would be more predictable. And indeed, if I take the initial rates of change, they seem pretty proportional to current:

Except that for the first point, at torture current of 0.01 uA, I essentially didn't detect any effect at all. It might be because the current was not actually delivered to the mosfet gate (it may have leaked through the switch for example (see circuit), although I checked switch leakage beforehand). Or it was because the mosfet wasn't completely fresh... Anyway, there's not enough points to draw major conclusions yet...

And as you already know, this initial rate thing doesn't tell the whole story, as the threshold voltage ceases decreasing and starts to increase at later time.

Curious to see, what will happen for negative torture. Also curious to see if transfer characteristic is any different to what I got before.

This is the new circuit for torturing mosfets. The switches are actuated out of phase. As I explained earlier, the switches are now solid state (pairs of MOSFETs driven through photovoltaic optoisolator).

I have made my experimentorture circuit, and right now I'm torturing a MOSFET with a positive voltage, feeding 0.3 uA of current into gate at 50% duty cycle (2.5 s of current, then 2.5 s of gate threshold measurement).

Gate threshold voltage (for Ids = 1 mA) was going down. Then it kinda stopped at around -0.5V. But I decided to no stop the process, and it started to go UP!!! Isn't it fascinating!

I have datalogging now, so I will post a plot when I finish it.

measurement in a mess...

UPDATE. The mosfet has changed back into enhancement mode... probably... , with gate voltage for 1 mA at about +0.25 V. It's too late now, so I have to stop the torture. I leave threshold to datalog overnight. With 13 SPS recording rate, it's going to be a big file.

UPDATE: the plot!

I started with 0.01 uA of torture current. No effect. Increased to 0.1 uA. Saw something. Increased to 0.3 uA. Now we are talking! Somewhere close to minimum, I was thinking to increase the current further, but changed my mind. Glad I did!

The wiggles on rising part are caused by me tweaking the torture current, which was reducing a little bit (the tweaks were like 0.28 -> 0.3 uA). The very fact it was reducing is interesting by itself, as it must be gate voltage going up.

I failed to stop the torture cleanly, oops! Nothing serious, though.