3 ms·

What's the story for an insulator? Silicon's pretty awesome, but in many ways silicon dioxide (grown in place) is the real magic.

• adrian_b 1y ago
  Unfortunately, even if the thermally-grown silicon dioxide is what has enabled the appearance of the monolithic integrated circuits and of the MOSFET transistors, eventually it had to be replaced. There are already around two decades since silicon dioxide is no longer used as the gate insulator in high-performance transistors. The reason is that its dielectric constant is too low, so for very small transistors the gate would have to be too thin, so thin that it is impossible for it to not have holes and also impossible to prevent electrons from tunneling through it. Therefore silicon dioxide has been replaced by hafnium dioxide (a part of the hafnium may be substituted with zirconium or rare-earth elements), which has a much higher dielectric constant, and which is also chemically resistant enough to survive the following wafer processing steps. Because HfO2 cannot be grown in place, but it must be deposited in its entirety, it is much more difficult to ensure that the insulator-semiconductor interface is perfect, but the industry had to solve this problem decades ago, otherwise it would have been impossible to make the transistors smaller. For other semiconductors than silicon, the gate insulator always had to be deposited. Because this is hard, metal-insulator-semiconductor FETs not made of silicon or of silicon carbide had only very rarely been used in the past. The transistors that are not made of Si or SiC typically are either Shottky-gate FETs or heterojunction bipolar transistors.