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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?

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On chip capacitors take a lot of chip area making them expensive. I'm currently working on a process where they can make metal capacitors of 2 femto Farad per square micrometer. So a 100 pF capacitor would have take up an area of 50000 sq um so 500 x 100 um.

But these capacitors can handle only up to 10 Volts or so, nowhere near your 350-400 V requirement.

Maybe there are specialist high-voltage processes in which high voltage capacitors can be made but I doubt that. Edit: Doubt taken away, there are, see comments.

For 350-400 V you need a strong and/or large dielectric which can withstand the fieldstrength. This is not easy to fit in a small size (like an IC).

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  • \$\begingroup\$ Not to mention no lithography processes are available for those dielectrics that are compatible with chip-scale wafer processing. \$\endgroup\$ – Asmyldof Mar 22 '16 at 11:01
  • \$\begingroup\$ TI's ISO721 has 4kV capacitors made with 8um of SiO2, so probably okay for mains voltage, but 100pF would be huge (easy to work out the area from the permittivity of SiO2). An external capacitor would be cheaper. \$\endgroup\$ – Spehro Pefhany Mar 22 '16 at 11:37
  • \$\begingroup\$ @SpehroPefhany this is a good point! Mainly I should consider not the possibility but the cost efficiency. \$\endgroup\$ – Roman Matveev Mar 22 '16 at 11:39
  • \$\begingroup\$ @SpehroPefhany BTW, what is the capacitance of this 4kV capacitor? Didn't find this info in the datasheet \$\endgroup\$ – Roman Matveev Mar 22 '16 at 11:45
  • \$\begingroup\$ @RomanMatveev Don't know offhand- BUT very low. Maybe << 1pF. \$\endgroup\$ – Spehro Pefhany Mar 22 '16 at 11:51
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If you want to connect 230 VAC to an IC, you generally need capacitors rated at 1 kV DC and 6 kV transiently for safety reasons (think lightning strikes). These are possible on ICs, but practically limited to 1 pF.

For 'only' 400 V, you can build a denser capacitor using the capacitance between adjacent fingers of metal (like two combs intertwined). These are called fringing capacitors, but still are generally limited to a few pF for cost (area) reasons.

In addition, to use these you need components (transistors, diodes etc.) able to handle these voltages. Most IC processes cannot.

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