# Why do you need a conductive layer with conductivity of $~10^4$ S/cm in a capacitance touchscreen?

ITO has has conductivity of $~10^4$ S/cm. A capacitive touchscreen measures the change in capacitance or electric field.

1) Why do you need a conductive layer in a capacitance touchscreen in the first place, if you just measure the capacitance or electric field?

2a) Does it really need to be as low as $10^4$ S/cm or can it also be something like $10^3$ S/cm or $10^2$ S/cm?

2b) What happens when the conductivity gets lower?

• @Andy_aka: A higher resistance would increase the RC time constant, but since you only have a few pF ($10^{−12}$ F ) as capacitance, this RC time constant would still be small for resistance as high as 100KΩ Since you are measuring a change in capacitance, why would you care about resistance, if the time delay would be negligible? Numerous different methods exist to measure capacitance: shift of resonance frequency, frequency modulation, amplitude modulation, charge time measurement, time delay measurement, duty cycle, etc. – Per Jan 21 '17 at 0:57