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Compared to Si, IGZO is a competitive choice for FeFET channel material, because of the interlayer-free structure, which can lead to a higher endurance. However, the ferroelectric switching mechanism of erasure remains unclear due to the lack of holes in IGZO. In this work, we present a quasi-static charge sheet model of Metal/Ferroelectric/IGZO stack, considering the charges supplied by IGZO Density of States and interface states. The modeling results suggest that shallow donors, by emitting electrons into the conduction band and thereby partially ionized, can become positively charged and thus support the erase operation. Cryogenic Negative Bias Illumination Stress measurement indicates the presence of shallow donors.

Capacitive memory window-based non-destructive read-out (NDRO) is a promising operating mode in improving the read endurance of ferroelectric random-access memories (FeRAMs). This work presents the first successful attempt toward a unified, capacitance-enabled compact model for ferroelectric capacitors (FeCAPs) and explores the attainable sensing margin (SM) in the NDRO operation of 1T1C FeRAM. Using a Preisach multidomain, quasi-static Landau free energy-based approach, the model captures measured P–V and C–V characteristics on hafnium zirconate FeCAPs with one unified polarization, including both non-switching oscillatory behaviors in small-signal (SS) C–V and switching behaviors in large-signal (LS) P–V. Based on it, we predict that the key figure of merit permittivity window ( $\Delta \epsilon _{\text {r}}\text {)}$ can be enhanced by increasing the remnant polarization of the FE layer. Device exploration based on the model however suggests that the theoretical maximum charge window depends additionally on the coercive field of the FE layer, which requires tradeoff with $\Delta \epsilon _{\text {r}}$ . At the bitcell level, we identify that the bitline (BL) SM of a 1T1C FeRAM is constrained by the: 1) voltage-dividing and 2) charge-sharing effects between the FeCAP and the BL capacitance, which as a result limits itself to <100 mV with a sub-unity BL-to-FeCAP loading ratio. The article thus highlights the quest for novel FeCAP materials/device structures and/or disruptive sensing schemes in order to best exploit the signal-limited capacitive NDRO-FeRAM.

Contact resistance ( ${R} _{\text {c}}$ ) is a major limitation to the scaling of amorphous indium-gallium-zinc-oxide (a-IGZO) transistors, and it has not been thoroughly investigated on devices with sub-100-nm dimensions. In this work, we characterize back-gated a-IGZO transistors with scaled channel length down to 45 nm, showing that the ON-current is strongly limited by ${R} _{\text {c}}$ in short-channel devices. As a case study to investigate the origins of ${R} _{\text {c}}$ , we compare physical vapor deposited (PVD) TiN and atomic layer deposited (ALD) TiN as the contact metal, revealing that ${R} _{\text {c}}$ in ALD-TiN/a-IGZO devices is three times higher than in PVD-TiN/a-IGZO devices. By investigating multiple components of the contact resistance, we demonstrate that while both contacts have similar Schottky barrier heights (SBHs), a thicker oxide interfacial layer between ALD-TiN and IGZO may be one cause for the higher ${R} _{\text {c}}$ . We also investigate that reduced hydrogen-induced doping can lead to an increase in contact resistance.

In this work, the impact of a tungsten oxide (WO3) seed and capping layer for ferroelectric La-doped (Hf, Zr)O2(La:HZO) based capacitors, designed with back-end-of-line (BEOL) compatibility, is systematically investigated. The WO3capping layer supplies oxygen to the La:HZO layer throughout the fabrication process and during device cycling. This facilitates the annihilation of oxygen vacancies (Vo) within the La:HZO layer, thereby stabilizing its ferroelectric orthorhombic phase and resulting in an increase of the remanent polarization (Pr) value in the capacitor. Moreover, the effectiveness of the WO3capping layer depends on the seed layer of the HZO film, suggesting that proper combination of the seed and capping layers should be employed to maximize the ferroelectric response. Finally, a TiN/TiO2seed layer/La:HZO/WO3capping layer/TiN capacitor is successfully fabricated and optimized by a complete set of atomic layer deposition (ALD) processes, achieving a superior 2Prvalue and endurance value of more than 109cycles at an electric field of 2.5 MV/cm. The WO3capping layer is anticipated to offer a viable solution for doped HZO capacitors with reduced thickness, addressing the challenge of elevated Volevels that favor the tetragonal phase and result in low 2Prvalues.