For electrical properties of MOS capacitors, the C-V curves were obtained by LCR meter (HP4284A), and picoampere meter (HP4140B) was used to measure the J-V curves.
The leakage of the 1N3595 diode is generally less than one picoampere even with 1mV of forward bias, so the circuit won't interfere with measurements of 10pA or more.