For microwave transistors, whether discrete or in integrated circuits, the gate length measured in the direction source-drain is critical, in the submicronic field. Optical masking equipment is the most common, and is suitable for mass production, but it cannot mask gates of smaller length than about 1 micron. To construct so-called submicronic transistors, electronic means of masking must be used, which are much more expensive and above all much slower, but enable gates 0.2 micron in length to be constructed.
USPTO Backgrounds
USPTO Backgrounds