Improving the memory window of a ferroelectric thin film transistor using an atomic layer deposited HfNx interfacial layer

Abstract

This work examines the impact of atomic-layer-deposited 1-nm-thick HfN_x interfacial layer (IL) deposition and NH₃ annealing conditions on the ferroelectric properties of Hf_0.5Zr_0.5O₂ (HZO) thin film capacitors and ferroelectric thin-film transistors (FeTFTs) with an amorphous InGaZnO channel. Adjusting these processing parameters enabled significant improvements in key device performance metrics, including the memory window (MW) and data retention stability of the FeTFTs. The optimized NH₃ annealing process at 450 °C facilitated nitrogen diffusion into the HZO matrix, decreasing charge trap density and oxygen vacancies. This annealing condition decreased the remanent polarization and slightly increased the coercive field, yielding a maximum MW of ∼1.9 V. A MW of ∼1.0 V could be retained for up to 10 years. In contrast, the device without the optimized IL showed a MW of only ∼0.6 V with a retention time shorter than ∼1 year. These findings demonstrate the effectiveness of HfN_x IL deposition and NH₃ annealing for enhancing the performance and reliability of amorphous InGaZnO channel FeTFTs, making them promising candidates for nonvolatile memory applications. It also provides a viable method to independently control the remanent polarization and coercive field, which are conventionally deemed material-specific properties.