Tag: Tiny

Perhaps the second most famous law in electronics after Ohm’s law is Moore’s law: the number of transistors that can be made on an integrated circuit doubles every two years or so. Since the physical size of chips remains roughly the same, this implies that the individual transistors become smaller over time. We’ve come to expect new generations of chips with a smaller feature size to come along at a regular pace, but what exactly is the point of making things smaller? And does smaller always mean better?

Smaller Size Means Better Performance

Over the past century, electronic engineering has improved massively. In the 1920s, a state-of-the-art AM radio contained several vacuum tubes, a few enormous inductors, capacitors and resistors, several dozen meters of wire to act as an antenna, and a big bank of batteries to power the whole thing. Today, you can listen to a dozen music streaming services on a device that fits in your pocket and can do a gazillion more things. But miniaturization is not just done for ease of carrying: it is absolutely necessary to achieve the performance we’ve come to expect of our devices today.

One obvious benefit of smaller components is that they allow you to pack more functionality in the same volume. This is especially important for digital circuits: more components means you can do more processing in the same amount of time. For instance, a 64-bit processor can, in theory, process eight times as much information as an 8-bit CPU running at the same clock frequency. But it also needs eight times as many components: registers, adders, buses and so on all become eight times larger. So you’d need either a chip that’s eight times larger, or transistors that are eight times smaller.

The same thing holds for memory chips: make smaller transistors, and you have more storage space in the same volume. The pixels in most of today’s displays are made of thin-film transistors, so here it also makes sense to scale them down and achieve a higher resolution. However, there’s another, crucial reason why smaller transistors are better: their performance increases massively. But why exactly is that?

It’s All About the Parasitics

Whenever you make a transistor, it comes with a few additional components for free. There’s resistance in series with each of the terminals. Anything that carries a current also has self-inductance. And finally, there’s capacitance between any two conductors that face each other. All of these effects eat power and slow the transistor down. The parasitic capacitances are especially troublesome: they need to be charged and discharged every time the transistor switches on or off, which takes time and current from the supply.

The capacitance between two conductors is a function of their physical size: smaller dimensions mean smaller