Being in business school, or at least being someone who reads a business school newspaper, you know how important semiconductors are in the modern economy. You know that they are a critical component for everything that uses electronic chips to operate (which is everything) and that the largest nations like the U.S. and China see the semiconductor supply chain as critical to operating their economies and to maintaining national security. It recently occurred to me though that I didn’t know what a semiconductor actually is. Call me a stickler for details, but I think it is important to know what a thing is when that thing affects hundreds of billions of dollars every year and receives a high level of scrutiny from every major government. So, what is a semiconductor? Something that semi-conducts? Yes, essentially. But what does it conduct? And why?
The short answer is, it conducts electric current. You may have heard of some materials labeled as conductors (like copper wire) and some materials as resistors (like rubber). Like everything complicated in life, the real definition of conductivity lies on a spectrum. Conductivity is typically measured by its inverse, resistivity. Highly resistive materials like rubber have resistivities of around 1013 ohm-meters (Ωm), the measure of resistivity. Highly conductive materials like copper have low resistivities around 10-8 Ωm. Semiconducting materials have resistivities in the middle of the spectrum (duh), like silicon which has a resistivity of 103 Ωm.
It is useful to manipulate resistivity to make an electrical circuit that either allows or prevents the flow of electric current. This behavior can be used like a light switch to turn parts of a circuit on or off. It can also be used to amplify or reduce the power that another component receives, among other uses. To do this, engineers use semiconducting materials like silicon with a middle-level resistivity and scale that resistivity up or down to be more resistive or conductive depending on what a circuit or component needs to do at a certain time.
A semiconducting material is calibrated through a process called doping, in which a small amount of impurity is added to the material. This doped semiconducting material is what is really being referred to by the term “semiconductor”. The small but precise impurity calibrates the semiconductor to conduct or resist based on the signal that it receives. For example, if the semiconductor is acting as a switch, then the semiconductor will be signaled to be more conductive to turn the circuit on and more resistive to turn the circuit off.
A semiconductor does not just hang out on a wire by itself. It is housed in a transistor. Every transistor contains a semiconductor and is calibrated to perform a specific task when it receives a specific signal. The most common transistor is the metal-oxide-semiconductor field-effect transistor (MOSFET). The MOSFET is where the money is. The competition has for decades been about who can make the smallest MOSFET. MOSFET size is what is being referred to when you hear about the latest “5 nanometer chip” (though their exact size is not 5nm, that is just a naming convention at this point). The more MOSFETs you can cram onto your chip, the more control you have and the more you can do.
I know that may have been a lot of gibberish, so let me put it in perspective. Apple’s A15 chip, which runs the iPhone 13 Pro, contains around 15 billion MOSFETs. In fact, the MOSFET is believed to be the most produced device in the history of humanity, with 13 sextillion having been produced through 2018, which is 1.3*1022.
Talk about demand! This is why companies like Taiwan Semiconductor Manufacturing Company (TSMC), Intel, and Samsung are racing to invest in semiconductor manufacturing technology. In April, TSMC said it would spend $100 billion over the next three years in semiconductor manufacturing, and in August, Samsung said it would spend $205 billion between semiconductors and biotech over the same time period. Nowadays, every device that requires some computing power to operate and control – whether it be a smartphone, car, or Peloton Bike+ – will need billions of MOSFETs. Because the semiconductors in these MOSFETs are so small, and the doping impurities in each semiconductor have to be precise for them to work properly, smaller MOSFETs are increasingly difficult and expensive to manufacture. The bottom line is that semiconductors are here to stay and it is worthwhile to learn about something that permeates our everyday lives.
Photo Credit: Apple