![]() This led to MOS semiconductor memory replacing earlier bipolar and ferrite-core memory technologies in the 1970s. The first IBM NMOS product was a memory chip with 1 kb data and 50–100 ns access time, which entered large-scale manufacturing in the early 1970s. Dennard at IBM also fabricated NMOS devices in the 1960s. Grove at Fairchild Semiconductor fabricated several NMOS devices with channel lengths between 8 µm and 65 µm. In 1965, Chih-Tang Sah, Otto Leistiko and A.S. However, the NMOS devices were impractical, and only the PMOS type were practical working devices. They fabricated both PMOS and NMOS devices with a 20 µm process. History and background įollowing the invention of the MOSFET by Mohamed Atalla and Dawon Kahng at Bell Labs in 1959, they demonstrated MOSFET technology in 1960. One example of this is the Z84015 and Z84C15. ![]() This is normally performed using ion implantation.Īlthough the CMOS process replaced most NMOS designs during the 1980s, some depletion-load NMOS designs are still produced, typically in parallel with newer CMOS counterparts. The inclusion of depletion-mode NMOS transistors in the manufacturing process demanded additional manufacturing steps compared to the simpler enhancement-load circuits this is because depletion-load devices are formed by increasing the amount of dopant in the load transistors channel region, in order to adjust their threshold voltage. This is partly because the depletion-mode MOSFETs can be a better current source approximation than the simpler enhancement-mode transistor can, especially when no extra voltage is available (one of the reasons early PMOS and NMOS chips demanded several voltages). Although manufacturing these integrated circuits required additional processing steps, improved switching speed and the elimination of the extra power supply made this logic family the preferred choice for many microprocessors and other logic elements.ĭepletion-mode n-type MOSFETs as load transistors allow single voltage operation and achieve greater speed than possible with pure enhancement-load devices. In integrated circuits, depletion-load NMOS is a form of digital logic family that uses only a single power supply voltage, unlike earlier NMOS (n-type metal-oxide semiconductor) logic families that needed more than one different power supply voltage.
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