MOSFET

The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), also known as the metal–oxide–silicon transistor (MOS), is a type of field-effect transistor (FET) that is fabricated by the controlled oxidation of silicon. It has an insulated gate, whose voltage determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. The MOSFET was invented by Mohamed Atalla and Dawon Kahng at Bell Labs in November 1959, and is the most widely used semiconductor device in the world. The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), also known as the metal–oxide–silicon transistor (MOS), is a type of field-effect transistor (FET) that is fabricated by the controlled oxidation of silicon. It has an insulated gate, whose voltage determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. The MOSFET was invented by Mohamed Atalla and Dawon Kahng at Bell Labs in November 1959, and is the most widely used semiconductor device in the world. The main advantage of a MOSFET is that it requires almost no input current to control the load current, when compared with bipolar transistors (bipolar junction transistors, or BJTs). In an enhancement mode MOSFET, voltage applied to the gate terminal increases the conductivity of the device. In depletion mode transistors, voltage applied at the gate reduces the conductivity. MOSFETs are capable of high scalability (Moore's law and Dennard scaling), with increasing miniaturisation, and can be easily scaled down to smaller dimensions. They also consume much less power, and allow higher density, than bipolar transistors. The MOSFET is also cheaper and has relatively simple processing steps, resulting in a high manufacturing yield. Since MOSFETs can be made with either p-type or n-type semiconductors (PMOS or NMOS logic, respectively), complementary pairs of MOS transistors can be used to make switching circuits with very low power consumption, in the form of CMOS logic. The name 'metal-oxide-silicon' (MOS) typically refers to a metal gate, oxide insulation, and silicon semiconductor. However, the 'metal' in the name MOSFET is sometimes a misnomer, because the gate material can also be a layer of polysilicon (polycrystalline silicon). Similarly, 'oxide' in the name can also be a misnomer, as different dielectric materials can be used with the aim of obtaining strong channels with smaller applied voltages. The MOSFET is the most widely manufactured device in history, with an estimated total of 13 sextillion MOS transistors manufactured as of 2018. It is by far the most common transistor used in digital circuits and power electronics, and is fundamental to building high-density integrated circuits (ICs) and VLSI (very large-scale integration) devices. It revolutionized the electronics industry, has been central to the microelectronic and digital revolutions, and is the fundamental building block of digital electronics in the information age. Billions of MOS transistors are often found within a single integrated circuit, such as a memory chip or microprocessor. The US Patent and Trademark Office calls the MOSFET a 'groundbreaking invention that transformed life and culture around the world'. The basic principle of the field-effect transistor (FET) was first patented by Julius Edgar Lilienfeld in 1925. However, this early FET design was not practical. The FET concept was later also theorized by Oskar Heil in the 1930s and William Shockley in the 1940s, but there was no working practical FET built at the time. Shockley's research team initially attempted to build a working FET, by trying to modulate the conductivity of a semiconductor, but they were unsuccessful, mainly due to problems with the surface states, the dangling bond, and the germanium and copper compound materials. In the course of trying to understand the mysterious reasons behind their failure to build a working FET, this led them to instead invent the bipolar point-contact and junction transistors. None of these early FET proposals involved thermally oxidized silicon, which later made the MOS transistor possible. A breakthrough in FET research came with the work of Mohamed Atalla in the late 1950s. He investigated the surface properties of silicon semiconductors at Bell Labs, where he adopted a new method of semiconductor device fabrication, coating a silicon wafer with an insulating layer of silicon oxide, so that electricity could reliably penetrate to the conducting silicon below, overcoming the surface states that prevented electricity from reaching the semiconducting layer. This is known as surface passivation, a method that later became critical to the semiconductor industry as it made possible the mass-production of silicon integrated circuits (ICs). The surface passivation method, which substantially reduced the influence of the dangling bond that had prevented Shockley's research team from building a working FET, was presented by Atalla in 1957. Building on the surface passivation method, Atalla developed the metal–oxide–semiconductor (MOS) process, with the use of thermally oxidized silicon. He proposed that the MOS process could be used to build the first working silicon FET, which he began working on building with the help of his colleague Dawon Kahng. The MOSFET was invented by Mohamed Atalla and Dawon Kahng in 1959. They fabricated the device in November 1959, and presented it as the 'silicon-silicon dioxide field induced surface device' in 1960. Operationally and structurally different from the bipolar junction transistor, the MOSFET was made by putting an insulating layer on the surface of the semiconductor and then placing a metallic gate electrode on that. It used crystalline silicon for the semiconductor and a thermally oxidized layer of silicon dioxide for the insulator. The silicon MOSFET did not generate localized electron traps at the interface between the silicon and its native oxide layer, and thus was inherently free from the trapping and scattering of carriers that had impeded the performance of earlier attempts at building a field-effect transistor. Despite the breakthrough, the MOSFET was initially overlooked and ignored by Bell Labs in favour of bipolar transistors, which led to Atalla resigning from Bell Labs and joining Hewlett Packard in 1961. However, the MOSFET generated significant interest at RCA and Fairchild Semiconductor. Inspired by the first MOSFET demonstration by Atalla and Kahng in early 1960, researchers at RCA and Fairchild fabricated MOSFETs later that year, with Karl Zaininger and Charles Meuller fabricating a MOSFET at RCA, and Chih-Tang Sah building an MOS-controlled tetrode at Fairchild. MOS devices were later commercialized by General Microelectronics and Fairchild in 1964, with p-channel devices for logic and switching applications. The development of MOS technology, which was capable of increasing miniaturisation, eventually became the focus of RCA, Fairchild, Intel and other semiconductor companies in the 1960s, fuelling the technological and economic growth of the early semiconductor industry in California (centred around what later became known as Silicon Valley) and Japan. The MOSFET revolutionized the electronics industry, including power electronics, consumer electronics, control systems, and computers. It is the most widely used semiconductor device in the world, and is the most common transistor in computers, electronics, and communications technology (such as smartphones). The MOSFET has been central to the microelectronics revolution since the late 20th century.