The news says "angstrom era". What is it, and how small is an angstrom?

An angstrom is a unit of length: 1 angstrom is 0.1 nanometer, or a ten-billionth of a meter. Turned around, 1 nanometer is 10 angstroms. Its symbol is Å. When the news talks about the "angstrom era", it means that chip generations, named by counting down in nanometers, have reached names below 2 nm and are now named in angstroms instead. Just like "2 nm", it is the name of a generation, not something on the chip that measures exactly so many angstroms.

What is an angstrom, and where does the name come from?

A nanometer is a billionth of a meter. An angstrom is ten times smaller.

The name comes from a 19th-century physicist who studied light. He spread sunlight out into a spectrum and measured the wavelengths of the many thin lines in it, using a ten-billionth of a meter as his unit. Later, people named that unit after him.

It is not an official unit of the International System of Units (SI, the meter, kilogram and second system), but science has used it for more than a hundred years.

How small is 1 angstrom?

About the size of an atom. Most atoms are only one to a few angstroms across. In a silicon crystal, the centers of two neighboring silicon atoms are about 2.35 angstroms apart, so only a few silicon atoms fit in 1 nanometer (10 angstroms).

Compared with everyday things (these are only rough scales):

Thing	Roughly how big
The thickness of a hair	hundreds of thousands of angstroms
A bacterium	around 10,000 angstroms
A virus	around 1,000 angstroms
1 nanometer	10 angstroms
The distance between two neighboring silicon atoms	a little over 2 angstroms

If that's still hard to picture, blow 1 angstrom up to the smallest mark on a ruler, 1 millimeter. Then two silicon atoms sit a little over 2 millimeters apart; a virus is about 1 meter, as tall as a small child; a bacterium is about 10 meters, like a three-story building; and a hair becomes several hundred meters to a kilometer thick, wider than a small hill.

What was the angstrom used for before?

Long before the news started saying "angstrom era", science and chip fabs were using angstroms every day.

• Atoms and crystals: how big an atom is, how far apart two atoms are. In angstroms, these come out as one- or two-digit numbers. Silicon atoms line up neatly, and the small box that repeats over and over is about 5.4 angstroms on a side.
• Wavelengths of light: people who studied spectra often wrote wavelengths in angstroms. The light our eyes can see is about 4,000 to 7,000 angstroms.
• Thin films in a fab: a chip is built up layer by layer, and the thinnest layers are only a few nanometers thick (see "What is thin film deposition?"). Fabs often measure these thicknesses in angstroms because the numbers are easier to write: "35 angstroms" needs no decimal point, while "3.5 nanometers" does. In one common way of atomic layer deposition, which grows a film a little at a time, each round adds only about 1 angstrom.
• The insulating layer under the gate: the part of a transistor that turns the switch on and off is called the gate, and under it sits a very thin insulating layer, once made of silicon dioxide. It went from several hundred angstroms in the early days down to only ten-something angstroms, one generation at a time. At that thickness, electrons pass straight through it, so leakage grows; later the material was changed.

Why did the news start saying "angstrom era"?

Think back to "The news says "2 nm". What exactly is 2 nm?": each generation's name was roughly the last one times 0.7, counting down from 90, 65 and 45 all the way to 5, 3 and 2 nm.

Keep going the same way and you get 1-point-something, 1, then 0-point-something nanometers, which is awkward to say. In angstroms, 1-point-something nanometers becomes ten-something angstroms, and 0-point-something nanometers becomes a single-digit number of angstroms: whole numbers again. It's like saying 50 centimeters instead of 0.5 meters.

So the industry and the news started naming the generations after 2 nm in angstroms, and the "angstrom era" roughly means those generations. People don't fully agree on where it starts: some count from the first generation named below 2 nm, while some research papers call only the generations below 1 nm angstrom nodes. Public technology roadmaps already give future generations names around 1 nm, and even 0-point-something nm.

Are transistors in the "angstrom era" really only a few angstroms?

No. This is the most important point: just like "2 nm", the generation's name only means "which generation this is"; it is not a size measured on the chip.

A public technology roadmap drawn up jointly by the industry estimates that in the "1 nm" generation, the spacing between transistors in a row is still several tens of nanometers, and the tightest metal wiring is still spaced in the teens of nanometers. In angstroms, that is hundreds of angstroms and over 100 angstroms, much bigger than the number in the name.

Use the same ruler where 1 angstrom becomes 1 millimeter: in this generation the transistors are spaced tens of centimeters apart and the tightest wires ten-something centimeters apart, while the "1 nm" in the name is just 1 centimeter.

The things on a chip that really are a few or a few tens of angstroms are the thinnest films, such as the insulating layer under the gate and the thin sheets the gate wraps around on all four sides. But the name isn't measuring them either.

So what really changes from one generation to the next?

Behind the names counting down are new ways of making chips, generation after generation. Other articles cover these, so here is just the list:

• The shape of the transistor: from flat, to a fin standing upright, to thin sheets surrounded on all four sides ("What are FinFET and GAA?").
• Power lines moved to the back: the wires that deliver power move from the front of the wafer to the back, leaving the front for the wires that carry signals ("What is backside power delivery?").
• Finer light: the finest patterns are printed with extreme ultraviolet light, which has a much shorter wavelength ("What is extreme ultraviolet (EUV) light").

Overall it is still "more in the same space and less power each generation", only at a slower pace and at a higher cost ("What is Moore's law").

Alongside the process, another path is being taken at the same time: splitting up and putting back together. Instead of building everything on one big chip, it's split into several pieces that are placed side by side or stacked and packaged together ("The news says "advanced packaging". What is it", "What is a chiplet?"). This is packaging, not part of any process generation.

Next time you see it in the news

• "Entering the angstrom era": generation names have gotten small enough to be said in angstroms, roughly the generations after 2 nm. It does not mean transistors are down to a few angstroms.
• "Below 1 nm" or "sub-nanometer": again the name of a generation, not something on the chip that measures less than 1 nm.
• "Angstrom-level precision": when measuring or control is said to work "at the angstrom level", that is a real length: off by no more than an atom or two. It's a different thing from a generation's name.

In fab24hr

The game never uses the angstrom, and the fictional fab never says how many nanometers it is. The closest you get is very thin films.

In A day in the fab, as the furnace R&D process engineer on the R&D line, the morning shift asks how thin to grow the oxide layer under the gate for Glowmere (a fictional hearing-aid chip). Three runs differ only in oxidation time, and you look at the monitor wafers grown alongside them to see which run landed on target. Thinner, and the switch is faster; too thin, and it leaks. The game only says "the target is very thin" and never gives a number of angstroms. Tap "Clock in", choose "A day in the fab", then on the "Your role today" card tap "R&D line", swipe to the R&D process engineer and tap "Furnace".

In the main story, The life of a chip, chapter 2, "Station by Station", also has you measure yesterday's furnace run at the R&D line's metrology tool: shine light on the film, look at the light that comes back, and work out how thick the film is.

The companies, chips, people and numbers in the game are fictional; the parts about the angstrom and generation names come from public, general sources, and where there's no agreed number, only the scale is given. For other jargon, see "Chip fab jargon in plain English".