Directions for teachers:

As a class, watch the video “How transistors work” by TED-Ed and discuss the general history, structure and function of a transistor. Then divide students into small groups and have them analyze the graph “Transistor count on largest microprocessors 1975–2010” and the mathematical expression of Moore’s Law in the Computer History Museum article “Moore’s Law@50: ‘The most important graph in human history.’” Students should skim the article to learn the basics of Moore’s Law but focus mostly on the graph. Next, ask groups to read the Science News article “Computer chip milestone reached” and answer the questions in that section. Finally, come together as a class to discuss students’ predictions for what the future trend of computer processing might look like. (Note: If you would like to dig deeper into how computers work, check out this series of videos from Khan Academy.)

Directions for students:

As a class, watch the video “How transistors work” by TED-Ed and discuss the history, structure and function of a transistor. Then divide up into small groups and answer questions based on the Computer History Museum article “Moore’s Law@50: ‘The most important graph in human history’” and the Science News article “Computer chip milestone reached.” Finally, as a class, discuss what the future trend of computer processing might look like.

Transistors in focus

After watching the TED-Ed video “How transistors work,” discuss these questions as a class. Consult other resources if necessary.

Before transistors existed, what technology was used in early computing devices? How did this early technology work?

Before transistors, diode or triode vacuum tubes were used as “switches” to control the flow of electric current in a computing device. Heating up a triode’s negatively charged cathode by applying a voltage freed electrons. The electrons flowed across an electrode called a grid to the positively charged anode. Adjusting the voltage applied to the grid controlled the flow of electrons between the cathode and the anode, making fast current switching possible.

What is the function of a transistor in a computer? How does a transistor work?
Transistors act as switches to control the flow of electric current through microprocessors, or computer chips. Transistors have two states, “on” and “off.” Varying the input voltage can switch the transistor’s states. When a high electric voltage is applied to a transistor, it is “on.” When the voltage is low or zero, the transistor is “off.” In a computer program, these states are represented by the numbers 1 and 0.

What are common transistors made of? List a few properties of this substance and explain how it reacts with neighboring atoms.

Commonly used transistors are made out of silicon. Silicon is a semiconductor with four valence electrons that covalently bonds with four other silicon atoms in its crystalline solid structure. Silicon atoms can bond with atoms of other elements, which can enhance the ability to conduct electricity.

How are triodes and transistors different, and how are they similar?

Instead of the electrodes used by triodes, transistors use semiconductors — typically silicon. Combining silicon with other elements creates N type and P type components. N type components emit electrons, akin to the negatively charged cathode in a triode. P type components absorb electrons, akin to the triode’s positively charged anode. Some transistors are layered in an NPN configuration. The point where the N and P layers meet, called a P-N junction, acts sort of like a triode’s grid. It conducts electricity (turning the transistor “on”) only when a certain voltage is met or exceeded.

Why are transistors considered revolutionary?

Transistors are much smaller, more durable and don’t require as much energy as triodes. Because of this, transistors have made computing devices smaller while boosting the devices’ efficiency and computing power.

Level up

In small groups, use the Computer History Museum article “Moore’s Law@50: ‘The most important graph in human history’” and other online resources to answer the following questions.   

Who is Gordon E. Moore, and what does his “law” state? Is Moore’s Law considered a scientific law?Based on his observations of technology trends, engineer Gordon E. Moore predicted that computing would increase in power, and decrease in relative cost, at an exponential rate. Moore’s Law says that the number of transistors on a computer chip should double every two years. Moore’s Law is not a scientific law, rather it’s an observation of technological computing advances. The law has served as a guiding principle for computer technology for more than 50 years.

According to Moore’s Law, if 1 million transistors were on an integrated circuit one year, how many would be on it two years later? What about after four, eight and 10 years?

There would be twice as many, or 2 million transistors on the integrated circuit after two years, 4 million after four years, 16 million after eight years and 32 million after 10 years.

Does Moore’s Law describe linear or exponential growth? Write an expression that explains the growth, based on the dataset that you just created. Hint: Write the expression in terms of n, where n equals the number of years that have passed divided by 2.

Moore’s Law is a function that shows exponential growth, as it states the number of transistors will double every two years. A general expression for Moore’s Law could be written as T_final = T_initial * 2ⁿ.

Look at the graph “Transistor count on largest microprocessors 1975–2010,” in the article. Do your answers in the previous question align with the trend line shown? Explain why the trend line in the graph is straight.

Yes, my answers generally align with the trend line given. In 1990, approximately 1 million transistors were on an integrated circuit. Ten years later, in 2000, it appears that computer chips contained roughly 30 million transistors. The trend line is straight because the y-axis values are given on an exponential scale. If the y-axis were on a linear scale, the result would be a curved graph, increasing exponentially.

Elemental search

In your same groups, refer to the Science News article “Computer chip milestone reached” and other resources to answer the following questions.

According to the Science News article, scientists are engineering transistors made of carbon nanotubes that might one day replace silicon transistors. On an atomic level, how does carbon compare with silicon?

Carbon atoms and silicon atoms are different elements with their own unique number of protons. However, because carbon and silicon atoms have the same number of valence electrons, the atoms will react similarly with neighboring atoms of other elements within a crystalline structure.    

Why are scientists engineering new types of transistors? What problem are scientists trying to solve?

Performance gains of silicon transistors are beginning to level off, because the transistors are nearly as fast and efficient as they can get. To continue to uphold Moore’s Law, new materials and technologies may be needed.

Pushing limits

Discuss the following questions as a class.
 
Is it important to explore alternative transistor materials, and find new ways to continue the current rate of performance improvement? Why or why not?

Student answers will vary. They may express that it is important to continue developing computing technology at an exponential rate, but might not know how it could be possible. Or, students may think that carbon nanotube technology is a viable solution that should receive more resources. 

In addition to transistor materials, what factors might affect the rate of computing technology progress?

Student answers will vary, but may include the amount of scientific funding this research receives, consumer demand based on social and cultural trends, discovery of new materials, mining technologies and geopolitical relations since materials come from around the world.

Why has Moore’s Law been important over the last 50 years? Will Moore’s Law hold true in the future? If so, for how long? You may want to think back to the graph “Transistor count on largest microprocessors 1975–2010,” in the article “Moore’s Law@50: ‘The most important graph in human history.’”

Student answers will vary. They may discuss how engineers and scientists in the tech industry try to keep up with Moore’s Law. Students should think about how factors including the maximum speed at which information can travel and the physical limitations of silicon and potential replacement materials might affect the exponential rate of computing power improvement dictated by Moore’s Law. Students may make an educated guess at when the graph will become asymptotic because of the limitations of silicon transistor technology, because of the absence of replacements to silicon transistors that are as efficient, or a combination of factors.

Why is increasing computing power important?

Student answers will vary. They might mention that increasing computing power is important for running climate simulations or other complex computing tasks. Ask students to reflect on how increasing computing power may be important for their everyday lives.