This technical note from Analog Devices indicates that low dielectric absorption is a prime requirement for choosing a capacitor for a sample-and-hold circuit (see page 11). It also suggests to look for capacitors advertised as low dielectric absorption.
How do I go about searching for capacitors designed for low dielectric absorption? On Digikey and Mouser, it's not one of the listed parameters.
I also tried searching based on dielectric type, based on information from Kemet and Wikipedia linking dielectric absorption to material. In this case, it seems like film capacitors are the best candidates (still can't find any datasheets that actually report absorption), but they have very low capacitance. Ideally I want 1uF or more capacitance, to limit the effects of charge injection from the analog switching logic.
What terms and parameters should I use to guide my search?
Answer
The dielectrics with lowest absorbtion are vacuum and air (which is jinxed in normal conditions by porcellain, glass or saphire). Out of normal dielectrics, teflon was the best in last century. There possibly some improvements done for polypropylene and plyester caps. There is an article by Bob Pease about the phenomena http://electronicdesign.com/article/analog-and-mixed-signal/what-s-all-this-soakage-stuff-anyhow-6096
So you solution may involve teflon or normal plastics. But if you are designing new 9 digit voltmeter, then the capacitor design becomes very interesting, as interesting as real analog trade secret can be.
BTW the percentages for DA cited on Analog Devices pages are in range of 0.001%..
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