Sub-threshold Slope Factor

Sub-threshold slope factor is given by : [1+ Cd/Cox]

Cd = depletion capacitance
Cox= oxide capacitance

How to calculate the Sub-threshold slope factor for different technology nodes? I m able to substitute for Cox but i don't know how to calculate Cd...i m using the basic inverter circuit

not sure if they got the answer → https://www.google.com/search?q=vlsi+subthreshold+current → https://en.wikipedia.org/wiki/Subthreshold_conduction → https://en.wikipedia.org/wiki/MOSFET#Modes_of_operation