Multi-layer tunnel barrier (Ta2O5/TaOx/TiO2) engineering for bipolar RRAM selector applications

Ultrathin stoichiometric Ta₂O₅ layer, which was formed by thermal oxidation of Ta layer on ALD TiO₂, exhibits excellent selector characteristics. To maximize the selector performance, we adopted various interface engineering techniques such as Ta₂O₅ thickness, control of oxygen profile in TaO_x layer, top electrode materials, and band gap of bottom insulating oxide layer. By optimizing process conditions, we obtained outstanding selector performances such as high current density (>10⁷A/cm²), high selectivity (~10⁴), better off-current (<;100nA) and excellent reliabilities. Furthermore, the selector was fabricated in 1K cross-point array and vertically-integrated with Conductive-Bridge RAM (CBRAM).