What is a semiconductor? An electrical engineer explains how these critical electronic components work and how they are made

Semiconductors are a critical part of almost every modern electronic device, and the vast majority of semiconductors are made in Tawain. Increasing concerns over the reliance on Taiwain for semiconductors – especially given the tenuous relationship between Taiwan and China – led the U.S. Congress to pass the CHIPS and Science act in late July 2022. The act provides more than US$50 billion in subsidies to boost U.S. semiconductor production and has been widely covered in the news. Trevor Thornton, an electrical engineer who studies semiconductors, explains what these devices are and how they are made.

Two shiny black discs.

Thin, round slices of silicon crystals, called wafers, are the starting point for most semiconductor chips.
Hebbe/Wikimedia Commons

1. What is a semiconductor?

Generally speaking, the term semiconductor refers to a material – like silicon – that can conduct electricity much better than an insulator such as glass, but not as well as metals like copper or aluminum. But when people are talking about semiconductors today, they are usually referring to semiconductor chips.

These chips are typically made from thin slices of silicon with complex components laid out on them in specific patterns. These patterns control the flow of current using electrical switches – called transistors – in much the same way you control the electrical current in your home by flipping a switch to turn on a light.

The difference between your house and a semiconductor chip is that semiconductor switches are entirely electrical – no mechanical components to flip – and the chips contain tens of billions of switches in an area not much larger than the size of a fingernail.

2. What do semiconductors do?

Semiconductors are how electronic devices process, store and receive information. For instance, memory chips store data and software as binary code, digital chips manipulate the data based on the software instructions, and wireless chips receive data from high-frequency radio transmitters and convert them into electrical signals. These different chips work together under the control of software. Different software applications perform very different tasks, but they all work by switching the transistors that control the current.

A diagram showing more than a dozen layers of material.

This schematic of a semiconductor chip shows many different materials in different colors and the complicated layering involved in producing a modern chip.
Cepheiden/Wikimedia Commons, CC BY

3. How do you build a semiconductor chip?

The starting point for the vast majority of semiconductors is a thin slice of silicon called a wafer. Today’s wafers are the size of dinner plates and are cut from single silicon crystals. Manufacturers add elements like phosphorus and boron in a thin layer at the surface of the silicon to increase the chip’s conductivity. It is in this surface layer where the transistor switches are made.

The transistors are built…

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