7. What happens with drain current, ip in MOSFET saturation? Why a MOSFET saturates at a...

As the drain voltage increases, the voltage drop across the oxide near the drain terminal decreases which means that the induced charge density near the drain also decreases. As the result I_D vr V_DS curve will decreases V_DS > V_DS sat at the saturation when a larger V_DS > V_DS sat the is under saturation region and the channel get highly tapered and will be broken. The drain current is a draft current. When the channel is broken, the channel length reduces. The inversion charge density Q�_n can be written as -E_ox E_ox = -E_ox/tox [(v_qs - v_t) - (phi_ms + 2 phi_fp)] V_T rightarrow Threshold voltage phi_ms rightarrow metal semiconductor work function Now integrate over the length of the channel integral^L_0 t_x dx = -w c_ox integral [(v_qs - v_t) - v_x] dV_x I_D = w mu n c_ox/2L [2 (v_95 - v_t) v_DS - V^2_DS] I_D (sat) = w mu n c_ox/2L (v_95 - v_t)^2