A mosfet can be considered as a transconductance amplifier with unity gain frequency gm/(Cgs + Cgd).
The unity gain frequency is defined as the frequency where the current gain is one. What I am confused is why should we care about this frequency? What is so special about it?
Also because mosfet is a transconductance device meaning that it receives an input voltage and gives out a current.
So why do we focus on current gain Iout/Iin instead of Iout/Vin?