By Jonny Lupsha, Wondrium Staff Writer
More semiconductor chip plants may soon be built in the United States. The Senate has passed a bill to encourage companies that make the chips to do so on domestic soil. Semiconductors use a unique kind of intrinsic conductivity.
A bill meant to entice semiconductor companies to build chip factories in the United States passed in the Senate with bipartisan support, with a vote of 64-33. The bill was created to help the United States with its competition with foreign countries that spend big money—such as offering chipmakers $52 billion in grants, as well as a 25% tax credit—to lure semiconductor companies to their markets.
A semiconductor shortage that sprang from the coronavirus pandemic has hindered production of everything from cars to video game consoles. How do semiconductors work? In his video series Understanding Modern Electronics, Dr. Richard Wolfson, the Benjamin F. Wissler Professor of Physics at Middlebury College, explains the silicon-based microchips.
Silicon and Holes
“[Silicon is] the second most abundant element in Earth’s crust after oxygen, and it’s the element at the heart of semiconductor electronics,” Dr. Wolfson said. “Every silicon atom is bonded to its nearest neighbors by sharing two electrons. They conduct by a unique mechanism, and we need to understand that mechanism to see how semiconductor electronic devices work.”
Semiconductors get their name from being acceptable, but not great, conductors of electricity. Metals are better, while insulators are worse. Random thermal motions can knock an electron in a silicon crystal out of its bond and make it “free.” When an electric field is applied, the free electron could then carry a current the way electrons do in metals.
Sometimes, something far more interesting happens.
“Notice that the bond that’s been broken by the loss of that electron is an empty spot,” Dr. Wolfson said. “An electron could go there—an electron would like to go there. We call that blank spot a hole, and that hole basically acts like something with a positive charge. Again, in the presence of that electric field, another nearby electron might jump into that hole, and in that process, the hole has moved.”
Silicon is an intrinsic semiconductor and has an equal number of electrons and holes that carry currents.
Bringing It Back to Computer Chips
Pure silicon conduct electricity weakly and don’t have much use. Instead, scientists make pure silicon and then “dope” it with phosphorus or boron to determine what the dominant charge carrier is. The majority of charge carriers in a semiconductor can either be electrons, which are negative, or holes, which are positive. A semiconductor with a majority of electrons as charge carriers is called an n-type semiconductor while its counterpart, with more holes as carriers, is a p-type.
“P doesn’t mean it’s positively charged; it means the majority charge carriers are holes, positive,” Dr. Wolfson said. “N doesn’t mean it’s negatively charged; it means the majority charge carriers are negative, electrons. The whole business of semiconductor electronics consists in getting the doping right and then putting p- and n-type semiconductors in proximity.”
Semiconductors—what Dr. Wolfson called “miracle materials”—are at the heart of most modern electronic devices. They replaced vacuum tubes from the first half of the 20th century, are solid-state, consume a very small amount of power, and can fit billions onto one chip.
Understanding Modern Electronics is now available to stream on Wondrium.