A transistor gate is the part of a transistor that switches it on and off, by controlling the flow of electrons between two other parts called the source and the drain. In chips of the generation known as "5 nanometer", each gate is 18–20 nanometers long, measured along the path from source to drain. A nanometer is a billionth of a meter. That name is not a measurement of the gate.

Size

A gate's length is the gap between a transistor's source and drain, which the gate sits over. Historically, a shorter gate meant a faster-switching transistor. Chipmakers do not agree on how to name their generations. The International Roadmap for Devices and Systems (IRDS), published by the engineering organization IEEE, forecasts typical dimensions for the whole industry.

The IRDS lists the "5 nanometer" generation, in production from 2020, with gates 18 nanometers long in its fastest circuits and 20 nanometers in its most tightly packed ones. Neighboring gates sit 48 nanometers apart. The transistors are built on thin fins of silicon 7 nanometers wide and 50 nanometers tall. None of these dimensions is as small as 5 nanometers.

Later generations have shorter gates. The IRDS gives 16–18 nanometers for the "3 nanometer" generation of 2022 and 14 nanometers for the "2 nanometer" generation of 2025. It expects gate lengths to stop shrinking at about 12 nanometers.

Size comparisons

• An 18-nanometer gate is about as long as a porcine circovirus, one of the smallest viruses known as of 2026, is wide.
• Neighboring gates are 48 nanometers apart, a little more than the width of a hepatitis B virus.
• One nanometer is barely the width of five silicon atoms, so an 18-nanometer gate spans roughly 90 of them.
• Between about 4,000 and 5,600 gates placed end to end would span the width of a human hair, which is 80,000–100,000 nanometers wide.
• Enlarged ten million times, each gate would be 18–20 centimeters (7–8 inches) long, and a human hair would be 800–1,000 meters (about half a mile) wide.

Why chip names stopped matching

Until the mid-1990s, a chip generation's name was its gate length. The spacing of the chip's metal wiring, measured as half the distance from one wire to the next, was about the same number. Then chipmakers began shrinking gates faster than everything else, while keeping the old naming pattern.

Transistors in the "130 nanometer" generation had gates 70 nanometers long. When Intel moved to fin-shaped transistors for its "22 nanometer" generation in 2011, the gates were 26 nanometers long.

The generation number "had by then absolutely no meaning", Paolo Gargini told IEEE Spectrum in 2020. Gargini led the International Technology Roadmap for Semiconductors, the forecast that came before the IRDS. The IRDS now prints generation names in quotation marks. It proposes naming each one by its gate spacing and wire spacing instead: the "5 nanometer" generation would be G48M36.

Gates in the laboratory

Research transistors have been built with far shorter gates. In 2016, a team made a transistor from molybdenum disulfide with a gate 1 nanometer long, using a single carbon nanotube as the gate. In 2017, another team built carbon nanotube transistors with 5-nanometer gates that performed better than silicon transistors of the same size. Researchers predict that shrinking silicon transistors will stop working properly below gate lengths of 5 nanometers.

Sources

• International Roadmap for Devices and Systems 2020 Edition: More Moore. IEEE, 2020.
• International Roadmap for Devices and Systems 2022 Edition: More Moore. IEEE, 2022.
• A Better Way to Measure Progress in Semiconductors. Samuel K. Moore, IEEE Spectrum, 2020.
• MoS2 Transistors with 1-Nanometer Gate Lengths. Desai et al., Science, 2016.
• Scaling Carbon Nanotube Complementary Transistors to 5-nm Gate Lengths. Qiu et al., Science, 2017.
• Conformational Changes and Nuclear Entry of Porcine Circovirus without Disassembly. Wang et al., Journal of Virology, 2019.
• Hepatitis B Virus Biology. Seeger and Mason, Microbiology and Molecular Biology Reviews, 2000.
• Just How Small Is "Nano"?. National Nanotechnology Initiative.