What causes oscillations on PicoAmmeter when measuring capacitor leakage current?

Hi Everyone,

I'm trying to measure leakage current in two types of capacitors, one is a surface mount ceramic capacitor (Cap A) about 10 nF tested with an LCR meter to have Rp of about 1 MegaOhm, and the other is a thin film capacitor (Cap B) 2 pF tested with an LCR meter to have a very high Rp (Hundreds of GigaOhms).  I'm using the schematic as shown in the attached picture, except i don't have a series resistor.

When I measure Cap A, I observe an oscillation on my PicoAmmeter, about +/-50 picoamps.  When I measure Cap B, I observe an oscillation on my PicoAmmeter of about +/- 1 picoamp.  It's very clearly an oscillation and not noise. 

My question is, what phenomenon could be causing this oscillation?

Hi Johnny,

Good day! How are you?

Sorry, may I know what instrument(s) you're using? Measurements in the pA range are very sensitive, so any setup variables could be significant sources of interference.

Also, I'm not sure but there seems to be something wrong with the schematic setup you posted. Is it the exact setup you use in measuring leakage currents of capacitors?

In my opinion, an oscillation of 1 pA shouldn't be taken seriously [might be just ADC noise or so...] unless you're using a state-of-the-art ammeter.

Thats all.

Best regards,
Justin