Ternary Logic Transistors Using Multi-Stacked 2D Electron Gas Channels in Ultrathin Oxide Heterostructures.

2D electron gas field-effect transistors (2DEG-FETs), employing 2DEG formed at an interface of ultrathin (≈6 nm) AlO/ZnO heterostructure as the active channel, exhibit outstanding drive current (≈215 µA), subthreshold swing (≈132 mV dec), and field effect mobility (≈49.6 cm V s) with a high on/off current ratio of ≈10. It is demonstrated that the AlO upper layer in AlO/ZnO heterostructure acts as the source/drain resistance component during transistor operations, and the applied potential to the 2DEG channel is successfully modulated by AlO thickness variations so that the threshold voltage (V) is effectively tuned. Remarkably, double-stacked 2DEG-FETs consisting of two AlO/ZnO heterostructured 2DEG channels with a single gate exhibit multiple V, enabling a ternary logic state in a single device. By inducing a voltage difference between the stacked channels, a sequential operation of the upper and lower FETs is achieved, successfully realizing a stable ternary logic operation.