Pushing computers to the limit

This exercise is a part of Educator Guide: Computer Chip Milestone Reached / View Guide

Directions for teachers: After your students read “Computer chip milestone reached,” ask them to answer the following questions.

1.  A milestone is a significant point in the progress or development of something. What milestone does the headline refer to and why is that milestone important?

Scientists built the first computer chip that uses thousands of carbon nanotube transistors to run programs. Carbon nanotube computer chips could lead to faster, more energy-efficient electronics.

2.What is a transistor and what does it do inside a computer?

A transistor is a tiny electronic switch. Transistors’ “on” and “off” states are determined by whether electric current is flowing or not. Those states encode the 1s and 0s of computer data. Groups of transistors together perform computations.

3. Computer chips have traditionally been made with silicon transistors. Why are scientists now looking for alternatives to silicon?

Silicon transistors can’t get much smaller and more efficient than they already are, which means the performance of computers that rely on these transistors can’t improve much more either.

4. What does a carbon nanotube look like? What advantages could carbon nanotube transistor technology have over silicon in the future?

The nanotubes are cylindrical tubes made of atomically thin sheets of carbon, which means researchers can pack a lot of the nanotubes onto a single chip. The nanotubes also conduct electricity better than silicon. Taken together, that means carbon nanotube–based computer chips could run faster while consuming less energy than traditional computer chips. Carbon nanotubes could help overcome the barrier to performance gains.

5. Identify and explain two problems that the scientists ran into when designing a computer chip with carbon nanotube transistors.

The researchers found that carbon nanotubes tended to clump together when the tubes were put on a computer chip wafer, which prevented the transistors from working. The researchers also found that some of the nanotubes were metallic. Metallic nanotubes cannot properly switch between being conductive and insulating, which can affect how transistors process information.

6.  How did the scientists solve the problems?

To address the clumping, the researchers gently vibrated the wafer after spreading the nanotubes onto the chip. The researchers also designed the computer chip’s circuits to avoid transistor layouts that were most affected by metallic nanotubes.

7. Identify and explain an analogy that Science News reporter Maria Temming uses in the article. How does the analogy help you understand the scientific concept being discussed? Write your own analogy that incorporates information from the article.

Temming likened metallic nanotubes to missing letters in a word. Some words are readable when letters are missing while others are completely garbled. In the same way, some transistor layouts are less affected than others by the metallic nanotubes. Student reasons and analogies will vary.  

8.  How does the performance of carbon nanotube transistors in this chip prototype compare with silicon transistors used in modern electronics? How do the transistors’ sizes compare? What is the order of magnitude difference in each case?

The carbon nanotube transistors can switch on and off about a million times each second, compared with silicon nanotubes, which can switch billions of times per second. That’s three orders of magnitude. The carbon nanotube transistors are about a micrometer in diameter each. Current silicon transistors are two orders of magnitude smaller, measuring just tens of nanometers across.

9.  What can researchers do to improve carbon nanotube transistors?

Making the nanotube transistors smaller could help them switch on and off more quickly. And placing the transistors parallel within a circuit could boost processing speed.