This question is a bit premature as I don't have any intention to create any silicon chips right away. But I have an idea of an integrated circuit which depends on what I will be able to squeeze into one.
And the main thing I have doubts about is a HV capacitor. My simulation shows that I will need to have 350 (or 400 even better - 230 VAC + 10-15%) Volts with 100 pF capacitance.
Unfortunately I don't know which limitations are applied to capacitors integrated into silicon chips. Does anybody knows?