PMOS

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PMOS or pMOS logic, from p-channel metal–oxide–semiconductor, is a family of digital circuits based on p-channel, enhancement mode metal–oxide–semiconductor field-effect transistors (MOSFETs). In the late 1960s and early 1970s, PMOS logic was the dominant semiconductor technology for large-scale integrated circuits before being superseded by NMOS and CMOS devices. Mohamed Atalla and Dawon Kahng manufactured the first working MOSFET at Bell Labs in 1959. They fabricated both PMOS and NMOS devices but only the PMOS devices were working. It would be more than a decade before contaminants in the manufacturing process (particularly sodium) could be managed well enough to manufacture practical NMOS devices. Compared to the bipolar junction transistor, the only other device available at the time for use in an integrated circuit, the MOSFET offers a number of advantages: Disadvantages relative to bipolar integrated circuits were: General Microelectronics introduced the first commercial PMOS circuit in 1964, a 20-bit shift register with 120 MOSFETs – at the time an incredible level of integration. The attempt by General Microelectronics in 1965 to develop a set of 23 custom integrated circuits for the Victor 3900 electronic calculator for Victor Comptometer proved to be too ambitious given the reliability of PMOS circuits at the time and ultimately led to the demise of General Microelectronics. Other companies continued to manufacture PMOS circuits such as large shift registers (General Instrument) or the analogue multiplexer 3705 (Fairchild Semiconductor) which were not feasible in bipolar technologies of the day. A major improvement came with the introduction of polysilicon self-aligned gate technology in 1968. Tom Klein and Federico Faggin at Fairchild Semiconductor improved the self-aligned gate process to make it commercially viable, resulting in the release of the analogue multiplexer 3708 as the first silicon-gate integrated circuit.