Amplification and switching
A transistor uses a control signal to regulate current or voltage in a circuit, allowing amplification or switching. In an amplifier, the additional output energy comes from the power supply; the device does not create energy from nothing.
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The point-contact device of 1947
Bardeen and Brattain achieved transistor action in a germanium point-contact device at Bell Labs. Shockley directed the group and developed further theory and structures. Experimental success, public disclosure and reliable production were separate stages with distinct contributions.
Junction and field-effect designs
Later junction transistors used differently doped regions, while field-effect transistors controlled a conducting channel through an electric field. Devices sharing the transistor name do not have identical internal structures. Dense integrated circuits rely on designs compatible with repeated fabrication.
From individual components to circuits
Transistors enabled smaller, lower-power equipment in many applications, but a system still required supplies, interconnections, other components and design. Integrating many transistors onto a chip represented additional achievements in fabrication and circuit engineering beyond the original device.