capacitorleakage-current
I am looking for capacitor type which has very low leakage such as 0.5nA since I am working with a sensor which generates between 0.9nA to 0.55uA.
Based on my research Film or foil Capacitor has the lowest leakage but not even close what I looking for, they all close to micro and not nano.
Note: the cable lenght is 20ft not 200 sorry
There's no guarantee with your device.. it's 300nA at 25C and 3.3uA at high temperature typical. In fact, if the distribution of leakage is Gaussian (a rather big "if"), you'd expect 1uA would be a reasonable guess for the maximum (\$3 \sigma\$).
If you want low typical leakage, you should pick a device that's no bigger (in terms of drain current rating) than you need, and one with a relatively high \$V_{TH}\$ rather than a ginormous MOSFET rated for 1.8V drive. Some small signal MOSFETs are typically 1pA at 25°C, which is 300,000 times better than the SM74611.
Most people don't care about leakage that much, so the maximum figures tend to be conservative. I don't know any alternative to looking at data sheets to see what is guaranteed or specified as typical. You can always measure it yourself, but the next batch could (in theory anyway) be wildly different. The same part number from a different manufacturer probably will be different.
Current is defined as voltage divided by resistance.
Therefore, you need to find a way to relate charge to voltage, and resistivity to resistance.
Voltage on a capacitor is charge divided by capacitance. Capacitance is related to plate area, spacing and dielectric constant.
Resistance is resistivity multiplied by thickness and divided by area.
Are these hints enough to get you started?
Best Answer
In my experience any standard ceramic capacitor will be good enough. For example, I have measured a 100pF NP0 capacitor having <10fA of leakage with a 2V bias.
You probably won't get a good result with electrolytics though.