The active part of a FET is the area that is under the gate or surrounded by the gate.
It makes no sense to speak about a transistor that would be smaller than the gate, there is no such thing.
Besides the active part, whose conductance is controlled and variable, the transistor includes parts that are either electrical conductors, like the source , the drain and the gate electrode, or electrical insulators.
While those parts may be less important than the active part, they also have a major influence on the transistor characteristics, by introducing various resistances and capacitances in the equivalent schematic.
What matters is always the complete transistor. The only dimensions in a current transistor that are around 1 nm are vertical dimensions, in the direction perpendicular on the semiconductor, e.g. the thickness of the gate insulator.
The 2D semiconductors that are proposed for the TSMC "1 nm" process are substances that have a structure made of 2D sheets of atoms, like graphite, but which are semiconductors, unlike graphite, which is a 2D electrical conductor.
In this case the thickness of the semiconductor can be reduced to single layer of atoms, which is not possible with semiconductors that are 3D crystals, like silicon, because when they no longer form a complete crystal their electrical properties change a lot and they can become conductors or insulators, instead of remaining semiconductors.
There is little doubt that for reducing the transistor dimensions more than it is possible with a 3D semiconductor like silicon, at some point a transition to 2D semiconductors will be necessary. It remains to be seen when that will be possible at an acceptable cost and whether such smaller transistors can improve the overall performance of a device, because making smaller transistors makes sense only when that allows a smaller price, smaller volume or higher performance of a complete product.
It makes no sense to speak about a transistor that would be smaller than the gate, there is no such thing.
Besides the active part, whose conductance is controlled and variable, the transistor includes parts that are either electrical conductors, like the source , the drain and the gate electrode, or electrical insulators.
While those parts may be less important than the active part, they also have a major influence on the transistor characteristics, by introducing various resistances and capacitances in the equivalent schematic.
What matters is always the complete transistor. The only dimensions in a current transistor that are around 1 nm are vertical dimensions, in the direction perpendicular on the semiconductor, e.g. the thickness of the gate insulator.
The 2D semiconductors that are proposed for the TSMC "1 nm" process are substances that have a structure made of 2D sheets of atoms, like graphite, but which are semiconductors, unlike graphite, which is a 2D electrical conductor.
In this case the thickness of the semiconductor can be reduced to single layer of atoms, which is not possible with semiconductors that are 3D crystals, like silicon, because when they no longer form a complete crystal their electrical properties change a lot and they can become conductors or insulators, instead of remaining semiconductors.
There is little doubt that for reducing the transistor dimensions more than it is possible with a 3D semiconductor like silicon, at some point a transition to 2D semiconductors will be necessary. It remains to be seen when that will be possible at an acceptable cost and whether such smaller transistors can improve the overall performance of a device, because making smaller transistors makes sense only when that allows a smaller price, smaller volume or higher performance of a complete product.