主题：【原创】闲话88：美国战略转变（三） -- 井底望天

IEEE Spectrum: We’ve been shrinking two-dimensional, or planar, transistors just fine for 50 years. Why are we seeing a switch to three-dimensional FinFETs?

Chenming Hu: I’ll distill the problem with planar transistors to a single point. It all stems from the fact that it is very difficult to turn off a transistor when it’s very small. In other words, you can’t stop the current flowing through the transistor when you don’t want the current to flow.

I’ll use an analogy to explain this. There is a garden hose lying on a soggy lawn, and you want to stop the water from flowing into this lawn. If there’s a long hose, you can call your friends to come in and put 10 pairs of hands down, and you can stop the water. Now imagine you shorten the hose so you cannot even put one palm on it to stop it. Now you shorten it even more, so you can only put one finger on it. It’s impossible to stop.

In the past 10 years, people have dealt with this garden hose problem in various ways, and one way has been to sacrifice power. For 250-nm transistors, the power-supply voltage was 2.5 volts; for 180 nm, it was 1.8 V; for 130 nm, it was 1.3 V. The pattern was very regular until 90 nm, but it reached a limit. Instead of 0.9 V, you know what the industry used? 1.2 V. Even at 45 nm, the industry still used 0.9 V instead of 0.45 V.