张灿鹏 274-275-C35.doc

274 CHAPTER 6 Fundamentals of the Metal-Oxide-Semiconductor Helmet Transistor figure qualitatively indicates the relative charge density, which is essentially constant along the entire channel length for this case. The corresponding DI versus DSV re is shown in the figure. Figure shows the situation when the DSV value increases. As the drain voltage increases, the voltage drop across the oxide near the drain terminal decreases, which means that the induced inversion charge density near the draw also decreases. The increments conductance of the channel at the drain decreases, which then means that the slope of the DI versus DSV curve will decrease. This effect is shown in she. DI fetus DSV curve in the figure. When DSV Creases to the point where the potential drop across the oxide at the drain terminal is equal to VT, the induced inversion charge density is zero at the darn terminal. This effect is schematically shown in Figure . At this point. the incremental conductance at the drain is zero, which means that the slope of the Id Vies DSV curve is zero. We can write ( ) or( ) Drain-to-source where DSV (Sat) is the drain-to-source voltage producing zero inversion charge density at the drain saturation voltage ter m inal. When DSV es larger than the DSV (sat) value, the point in the channel at which the inversion charge is just zero moves toward the source t