For decades, microchip transistors have become smaller, faster, and cheaper; however, miniaturization has reached a natural limit, as completely new problems arise when a length scale of only a few nanometers is approached.
With the help of a novel insulator made of calcium fluoride, an ultra-thin transistor was developed that has excellent electrical properties and, in contrast to previous technologies, can be miniaturized to an extremely small size using two-dimensional (2D) materials that may consist of only a single atomic layer.
In addition to the ultra-thin semiconductor, an ultra-thin insulator also is required. This is due to the fundamental design structure of a transistor: current can flow from one side of the transistor to the other but only if a voltage is applied in the middle, creating an electric field. The electrode providing this field must be electrically insulated from the semiconductor itself. There have been transistor experiments with ultra-thin semiconductors but until now, they were coupled with ordinary insulators. At very small length scales, the insulator surface turned out to disturb the electronic properties of the semiconductor.
The new transistors use ultra-thin 2D materials not only for the semiconductor part of the transistor but also for the insulating part. By selecting ultra-thin insulating materials such as ionic crystals, a transistor with a size of only a few nanometers can be built. The electronic properties are improved because ionic crystals can have a perfectly regular surface, without a single atom protruding from the surface to disturb the electric field. To produce the new ultra-thin transistor, calcium fluoride was selected as the insulating material.