mosfet-2 - THE P-CHANNEL MOSFET A p-channel...

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THE P-CHANNEL MOSFET A p-channel enhancement-type MOSFET (PMOS transistor), fabricated on an n-type substrate with p+ regions for the drain and source. The device operates in the same manner as the n- channel enhancement MOSFET except that v GS and v DS are negative and the threshold voltage V t is negative. Also, the current i D enters the source terminal and leaves through the drain terminal. PMOS technology originally dominated MOS manufacturing. However, because NMOS devices can be made smaller and thus operate faster, and because NMOS historically required lower supply voltages than PMOS, NMOS technology has virtually replaced PMOS. COMPLEMENTARY MOS OR CMOS Figure 1.7 Cross-Section of a CMOS IC. As the name implies, complementary MOS technology employs MOS transistors of both polarities. Indeed, at the present time CMOS is the most widely used of all the IC technologies. Figure 1.7 shows a cross-section of a CMOS chip illustrating how the PMOS and NMOS transistors are fabricated. Observe that while the NMOS transistor is implemented directly in the p-type substrate. The PMOS transistor is fabricated in a specially created n region, known as an n well. The two devices are
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