Figure 21 A mobile phone uses many solid-state components. Drawing Conclusions Would it be possible to make a mobile phone using vacuum tubes rather than solid-state components?
Integrated Circuits
An integrated circuit is a thin slice of silicon that contains many solid-state components. The components are carefully built layer by layer on the silicon base. Integrated circuits are sometimes called chips or microchips. They perform as well as a network of vacuum tubes, but they need only a tiny fraction of the space. Mobile phones, pagers, and computers all use microchips.
Electronic devices today are so small because hundreds of millions of components fit on a microchip smaller than your fingertip. Integrated circuits are also blindingly fast compared to vacuum tubes. One reason is that current does not have to travel far to get from point to point in the circuit. So it shouldn't be surprising that as technology improves, and chips get smaller, the chips operate at higher speeds.
Communications Technology
A computer is a programmable device that can store and process information. Today you find microchips in all sorts of devices that you wouldn't call computers. 
Communication devices use microchips to make them more portable, reliable, and affordable.
Figure 21 shows the inside a mobile phone, which contains many solid-state components. Transistors amplify the phone's incoming signal. Electronic devices called capacitors store electric charge. They allow a mobile phone to store data such as phone numbers, even if the battery is removed for a short time. Diodes maintain proper voltage levels in the circuits. Without solid-state components, none of this would be possible.
Section 20.4 Assessment
Reviewing Concepts
How are electronic devices used to process information?- Describe how electron flow is controlled in vacuum tubes.
- What are two types of semiconductors?
- How are solid-state components used?
- How are microchips beneficial for communication devices?
Critical Thinking
Comparing and Contrasting How are solid-state components like vacuum tubes? How are they different?
Applying Concepts Explain how a diode can be used to change alternating current into direct current.
Using Analogies Explain how a diode is like a one-way street.
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