Oxygen-Tunnel Indium Tin Oxide Vertical Channel Transistors with Enhanced Current Density and Reliability for Monolithic 3D Compute-In-Memory Systems

Monolithic three-dimensional integration demands embedded memory technologies that achieve extreme density scaling under limited back-end-of-line thermal budget. Atomic layer deposition-grown amorphous oxide semiconductors (AOS) are attractive for this purpose because of their excellent conformality and intrinsically low off-state current I_OFF, enabling vertical channel transistors (VCTs) for capacitor-less gain-cell memory operation. However, in VCT, oxygen-deficient AOS channels required for low leakage and high conductivity coexist with oxygen-rich dielectric sidewalls, introducing a fundamental materials-stack challenge associated with oxygen-vacancy-induced instability and parasitic oxidation at electrode interfaces. Indium tin oxide (ITO) offers a balance between low leakage and high carrier mobility, yet is particularly vulnerable to oxygen-migration-induced degradation in vertical geometries. Here, we introduce an oxygen-tunnel stack based on SiN/SiO₂/SiN layers that spatially regulates oxygen transport. This architecture stabilizes oxygen vacancies in the ITO channel while suppressing electrode oxidation, enabling a record-high current density of 436 µA/µm and a negligible threshold voltage shift of less than 50 mV after 10⁷ bias-stress cycles. A gain-cell memory demonstrated retention exceeding 648 s and endurance beyond 1200 cycles enabled by the exceptionally low I_OFF of 2.6 × 10⁻¹⁹ A/µm. A Si-ITO hybrid gain-cell integration framework was developed and evaluated, demonstrating the feasibility and system-level benefits of incorporating oxygen-regulated ITO VCTs into Si-based embedded memory and compute-in-memory architectures.