Picturing How Vertical Transistors Work
Modern electronics are mostly flat, with millions of planar silicon transistors lying on a chip’s surface. In search of better-performing devices, researchers are now exploring 3D structures, such as vertical transistors, whose advantages include low power consumption, smaller current leaks toward the substrate, and better suitability for flexible electronics. The deployment of vertical transistors, however, is hampered by the lack of a simple model that describes how these transistors work in a circuit. Now, Chuan Liu and co-workers at Sun Yat-sen University in Guangzhou, China, have developed a new theory for vertical transistors that can be turned into formulas and schematic representations of these devices.
When designing a circuit based on conventional transistors, engineers rely on simple schemes that can predict a device’s behavior without accounting for the microscopic mechanisms underpinning its operation. Such tools were previously unavailable for vertical transistors, in which currents flow through vertical channels made of nanotubes or nanowires. Instead, each specific transistor had to be modeled with complex 3D simulations.
Liu and co-workers have now filled this gap, developing a theory that computes the distribution of the electrostatic potential in a device. Their theory shows that the lines that trace the strength of the electric potential behave like fixed strings that get “plucked” when a voltage is applied to the electrode that controls the current flow in the device. Using the theory, the team derived formulas that relate the currents to the voltages at the transistor’s electrodes. They then used those relationships to create schemes that describe the operation of different types of vertical transistors.
This research is published in Physical Review Applied.
Matteo Rini is the Deputy Editor of Physics.