What is a chip, and how is it different from a wafer, an IC or a semiconductor?

A chip is a small piece of silicon with many transistors and the wires that connect them built right on it, joined into one whole circuit. Its formal name is integrated circuit, or IC for short, and it's also called a microchip or a computer chip. A wafer is the big round slice of silicon that chips are made on: anywhere from dozens to more than ten thousand chips are made on one wafer at the same time, and only after it's cut apart do you get separate chips. A semiconductor is the material chips are made of, and also the name of the whole industry.

Think of a full sheet of postage stamps. The printed sheet is the wafer. It's covered in rows of the same picture, and each square is one chip. Tear along the perforations and you get single stamps. Stamps are printed on paper; chips are built on a semiconductor, usually silicon.

What's actually inside a chip?

More transistors than anything else. A transistor is a tiny switch controlled by electricity: on is 1, off is 0 (how it switches is in "What is a transistor?"). One switch can't do much on its own. It takes a great many of them, connected according to a design, to calculate anything or remember data.

That's why the other key part of a chip is wiring. The transistors sit at the very bottom, and above them, layer after layer of very fine metal wires connect the switches. Think of a tall building: the ground floor is packed with switches, and the floors above are all hallways and stairs. In the most advanced chips, the wiring is stacked more than ten layers high. Some tiny resistors and capacitors are built into the same piece, too.

All of this is squeezed onto a small piece of silicon. Chips range from smaller than a grain of rice to about the size of a fingernail, or even bigger. The processor chip in a phone today holds more than ten billion transistors, and its finest wires are more than a thousand times thinner than a human hair.

Why is it called an "integrated" circuit?

Integrated means combined into one piece.

Before integrated circuits, circuits were built from separate parts: one transistor, one resistor, one capacitor, each wired and soldered onto a board by hand. More parts meant more solder joints, and a single bad joint could stop the whole machine.

In the late 1950s, engineers came up with a way around this: build all the parts, and the wires between them, together on one piece of semiconductor. No more soldering parts one by one; the whole circuit is made in one go. That's an integrated circuit. Since then the parts have kept getting smaller, from just a few on one piece to more than ten billion today.

What's the difference between a chip and a wafer?

A wafer is a thin, round slice of silicon. The most common size today is 300 mm (12 inches) across. Why it's round is in "Why are wafers round?".

Chips aren't made one at a time. A fab lays out copies of the same chip design across the whole wafer like a chessboard, and all of them are made together and finished together. How many fit depends on how big the chip is: about a fingernail's size, and one wafer holds a few hundred; tiny chips just a millimeter or two across, and one wafer can hold more than ten thousand; a very large chip, and only a few dozen fit.

Between the chips run narrow lanes, left there on purpose. When the wafer is done, every chip is tested while still on the wafer, then the wafer is diced along those lanes into separate chips. A piece that has been cut out but not yet packaged is called a die (plural dies). Finally it goes into a protective case, and that's packaging ("What is chip packaging?").

In one line: the wafer is the whole sheet; a chip is one square on it.

Chip, microchip, IC, die: are they the same thing?

More or less, just used in different places:

• Chip, microchip, computer chip: everyday words. A chip originally meant a small piece broken off something, like a chip of wood. That's what this is: a small piece of silicon.
• Integrated circuit, IC: the formal name. It says more about how the thing is made: all the parts and wires built together on one piece. Engineers and news reports use it a lot, as in "IC design".
• Die: the small piece cut from the wafer, before it's packaged.

One more common mix-up: in everyday speech, "chip" can mean that small piece of silicon, or the small black square on a circuit board. Strictly speaking, the black square is the package, and the real chip is inside it.

Is a chip the same as a semiconductor?

No. A semiconductor is a material: it conducts electricity better than an insulator but worse than a conductor, and whether it conducts can be controlled. The most common one is silicon (why it's "semi" is in "What is a semiconductor?"). A chip is a thing made from that material. When the news talks about "semiconductors", it often means the whole industry that makes chips.

What kinds of chips are there?

Many. Roughly: processors that calculate (also called logic chips); memory that stores data; power management chips that split a battery's power into the voltages each part needs; sensors that turn light and sound into electrical signals; and communication chips that send and receive wireless signals. A phone has all of these. How processors and memory differ is a topic for another article.

How is a chip made?

In four broad steps:

1. Design: engineers design the circuit on computers, deciding which switches go where and how they connect, and simulate and check it many times. When it's final, the design goes out to be made into photomasks (the stencils the circuit is printed from, one for each patterned layer). This is called tape-out. Changing the design after tape-out means making new masks.
2. Manufacturing in a fab: after wafer start, the wafers go through hundreds of steps: printing patterns, etching them in, adding films, polishing flat. Layer by layer, they build the transistors and the wiring. This takes weeks to months ("What do the seven process areas of a chip fab do?").
3. Assembly & test: every chip is first tested on the wafer (wafer sort), then cut apart and packaged, then tested once more (final test). Only the good ones ship.
4. Into a product: the chip is soldered onto a circuit board and goes into a phone, a computer, a car or an appliance.

These four steps are often done by different companies. Some companies only design chips and have no fab of their own; some fabs make chips for other companies; and there are factories that do only assembly and test.

In fab24hr

fab24hr's main story, The life of a chip, follows a made-up hearing-aid chip, "Glowmere", along this whole road. It was designed by a small hearing-aid company. The first time you play the main story, you see the prologue, "Tape-out": the design goes to the fab and becomes a set of masks. Act one is the pilot run on the R&D line. In act two, at the production fab, the wafers in the hot lot H-2417 carry this chip. In act three, at the test-and-assembly house, it's tested, cut apart, packaged and tested again. In the finale, it goes into a hearing aid and into Mr. Shen's hands. The life of a chip page in the codex has its chip passport, showing where it is now.

The wafers in the game are 30 cm across, 25 to a box. The companies, the chip, the people and the numbers are fictional; what a chip is and how it's made come from public, general sources. For other jargon, see Chip fab jargon in plain English.