to a given process such as 0.18u cmos,if L is a definite value,i think ft is constant,but some book say ft depend on bais condition,am i wrong?

thanks for replying

Hello,


ft ~ tech_const × (Vgs-Vt)/L²

So, ft only depends on the overdrive voltage of your device (bias) and its length. High frequency performance thus requires minimal length and large Vgs-Vt.

Kind Regards,

Peter

Hi Frank,


the statement in Lee's book is correct, but it describes ft when the transistor is operating in velocity saturation,
so the dependency on Vgs-Vt disappears. This effect becomes important for deep-submicron technologies and is less apparent for older technologies (in which the formula I posted previously is valid).


Kind Regards

Peter