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) Al₂O₃/ZnO heterostructure as the active channel, exhibit outstanding drive current (≈215 µA), subthreshold swing (≈132 mV dec^-1), and field effect mobility (≈49.6 cm² V^-1 s^-1) with a high on/off current ratio of ≈10⁷. It is demonstrated that the Al₂O₃ upper layer in Al₂O₃/ZnO heterostructure acts as the source/drain resistance component during transistor operations, and the applied potential to the 2DEG channel is successfully modulated by Al₂O₃ thickness variations so that the threshold voltage (V_th) is effectively tuned. Remarkably, double-stacked 2DEG-FETs consisting of two Al₂O₃/ZnO heterostructured 2DEG channels with a single gate exhibit multiple V_th, 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.