Unusual Schottky leakage current measurement at low voltage

Thread Starter

Veracohr

Joined Jan 3, 2011
715
I was trying to measure the leakage current of a small signal Schottky diode at 0.1V reverse bias and what I'm seeing doesn't make sense. I'm assuming it's a measurement anomaly and not reality, but I'm hoping someone can confirm that.

I measure around 11-13uA in the forward direction (ie. opposite of the applied voltage) when applying 0.1V. This current (shown as negative on the meter) goes down as I increase the voltage to around 3-3.5V, above which the current becomes positive and falls within the diode's specified leakage current as stated in the datasheet (max 2uA at 25V). I did the same test on another small signal Schottky model, a small signal standard diode and a larger current (5A) standard diode. All 3 of the small signal diodes showed the same behavior, only changing in the voltage threshold where the negative current becomes positive. The higher current diode showed the same positive leakage current at 0.1V that it did at 20V.

The current was tested with a Keithley 2000 meter which shows about 0.18uA noise measurement when not probing anything. I also tried testing the current by measuring the voltage across a resistor, using a 33.2k and then a 220 ohm, and all 3 methods show the same negative current at low applied voltage. I verified the applied voltage by connecting another meter to the probes. It reduced the negative current measurement, but verified that the applied voltage was correct.

So this negative leakage current (opposite of the applied voltage) must be just a measurement anomaly, right?
 

AlbertHall

Joined Jun 4, 2014
9,875
Meaurement anomaly unless incident light causes the diodes to generate some voltage. Just to be sure, shield them from light and try again.
 

DarthVolta

Joined Jan 27, 2015
447
I have a 1N5711, and @29V backwards, I 1st noticed I went from seeing 0.01uA, to sometimes 0.02uA, with cheap alligator leads. Up to 60VDC, I still just see 10n-20nA, I wish I had a ucurrent reference, IDK. In FACT, I get the same reading without anything entering my DMM. I'll try my benchmeter, but I think it's a little broken in some-way.

I have transformers here to someday make switchable LV/HV curve tracer, if the circuirty fits in a little box, otherwise who cares, more junk.
 

Thread Starter

Veracohr

Joined Jan 3, 2011
715
Meaurement anomaly unless incident light causes the diodes to generate some voltage. Just to be sure, shield them from light and try again.
Shielding it from light didn't change the measurement, which isn't surprising since the junction isn't exposed.

I was trying to prove that the leakage current was to blame for a low resistance measurement on a 143k resistor that is in parallel with the diode. The tester uses 0.1V to measure resistance but the diode leakage current is only specified at higher voltage. I guess I'll assume that the diode is the reason and that the leakage current is OK since it measures in spec at a normal working voltage. It would only have to be a few tens of nA to cause the slightly low resistance measurements.
 
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