The active area comprises all the transistor and interconnecting layers in a chip. In a CPU, it is where all the transistor switching takes place to execute instructions extracted from memory. Depending on transistor type, the active area is from five to 90 nanometers (nm) thick. In the future, 3D stacking of transistors will create thicker active areas because a chip will have multiple transistor layers (see
CFET). See
chip,
half-adder and
Boolean logic.
Entirely Magical
No man-made object is more incredible than the chip. Today's state-of-the-art CPUs and SoCs contain billions of transistors, many of which are simultaneously switching their state from on to off and off to on every second. In fact, so many transistors are changing at the same time that there can be billions, trillions and even quadrillions of transistor state changes ("transistor toggles") taking place every second. See
head of a pin,
transistor toggle and
SoC.
A Digital Miracle
When people look at a chip package like this, they see an object about the size of a cracker. However, inside the package, the chip may be larger or smaller than a postage stamp, but the active area on the chip is significantly thinner. The transistor layer, the metal interconnection layers and the top (or bottom) power layer all combined are approximately 10,000 nanometers (nm) deep. A postage stamp is about 150,000 nm. See
microcontroller and
chip package.
There Are Many Layers on a Chip
Because all the transistors cannot connect to each other on a single plane, multiple "metal layers" are created to provide all the interconnections. In fact, in state-of-the-art chips, there can be as many as 50 layers. Compare the 10,000 to 30,000-nanometer thickness of chip layers with a single human hair, which can be from 50,000 to 120,000 nanometers in diameter. See
chip feature size.