Parallel Plate Capacitor Design

[decaf14]

TL;DR Summary

How to design a parallel plate capacitor.

Hello,

A question came up in my head that I couldn't think of a way to math out.

Say I want to design a parallel plate capacitor. The equation for capacitance is quite simple:

Everything in this equation makes sense, besides for the distance. This is saying that an infinitely small length of material would have infinite capacitance. This doesn't seem right, as a material can only hold so much charge/electric field. How would I go about factoring in the amount of charge a material can hold when designing a parallel plate capacitor?

I'm going through an exercise of designing a silicon dioxide capacitor (dielectric constant = ~4).

 

[gleem]

The solution to the problem lies in the relation between charge, voltage and capacitance. Q = CV and the dielectric strength of the insulator.

 

[decaf14]

The solution to the problem lies in the relation between charge, voltage and capacitance. Q = CV and the dielectric strength of the insulator.

Thanks, that makes sense. This probably gives rise to those "maximum voltage" specifications we see in capacitor datasheets?

 

[Baluncore]

The critical thing that determines capacitor physical volume is the thickness of the dielectric needed to separate and reliably insulate the plates. That thickness will be determined by the breakdown voltage, a function of dielectric strength in volts / metre.