Hsien-Yang Liu

This work investigates the impact of annealing temperature on the performance and reliability of morphotropic phase boundary (MPB) Hf ${}_ {{0}.{25}}$ Zr ${}_ {{0}.{75}}$ O₂ capacitors for DRAM applications. The films were deposited by atomic layer deposition (ALD) and capacitance-voltage ( $C$ – ${V}\text {)}$ measurements exhibited distinct asymmetric double peaks with a high dielectric constant (57) at $500~^{\circ }$ C annealing temperature. Grazing incidence x-ray diffraction (GIXRD) analysis confirmed that the high dielectric constant originates from a large T-phase fraction (64%) at this annealing temperature. Leakage current and time-dependent dielectric breakdown (TDDB) measurements reveal that the $500~^{\circ }$ C annealed sample achieves the best reliability, yielding a ten-year ${E}_{\text {TDDB}}~\approx ~2.68$ MV/cm at EOT = 6.1 Å while maintaining a very low leakage current density of $6.16\times 10^{-{9}}$ A/cm² at 1 V. These results indicate that the increased T-phase ratio enhances both dielectric performance and TDDB reliability, which can be attributed to the larger oxygen vacancy diffusion barrier of the T-phase. The proposed MPB HZO structure, therefore, satisfies the voltage and leakage specifications for DRAM storage node capacitors under back end of line (BEOL)-compatible thermal budgets.

This work demonstrates a novel nondestructive methodology combining a polarization-voltage (PV) measurement and grazing incidence X-ray diffraction (GIXRD) to comprehensively characterize the orthorhombic (O), tetragonal (T), and monoclinic (M) phases in ferroelectric (FE) HfZrO₂ (HZO) films. The O/T phases are analyzed based on nucleation-limited switching (NLS) model with Weibull distribution to model antiferroelectric (AFE) polarization, while the M phase analysis employs a conventional GIXRD method. Results align with Monte Carlo simulations and Raman analysis, demonstrating consistency in phase percentages and PV characteristics. This approach offers an efficient and nondestructive methodology to analyze O/T/M phase percentages in FE materials and is very promising for FE technology.

2D field-effect transistors (FETs) fabricated with transition metal dichalcogenide (TMD) materials are a potential replacement for the silicon-based CMOS. However, the lack of advancement in p-type contact is also a key factor hindering TMD-based CMOS applications. The less investigated path towards improving electrical characteristics based on contact geometries with low contact resistance (R_C) has also been established. Moreover, finding contact metals to reduce the R_C is indeed one of the significant challenges in achieving the above goal. Our research provides the first comparative analysis of the three contact configurations for a WSe₂ monolayer with different noble metals (Rh, Ru, and Pd) by employing ab initio density functional theory (DFT) and non-equilibrium Green’s function (NEGF) methods. From the perspective of the contact topologies, the R_C and minimum subthreshold slope (SS_MIN) of all the conventional edge contacts are outperformed by the novel non-van der Waals (vdW) sandwich contacts. These non-vdW sandwich contacts reveal that their R_C values are below 50 Ω∙μm, attributed to the narrow Schottky barrier widths (SBWs) and low Schottky barrier heights (SBHs). Not only are the R_C values dramatically reduced by such novel contacts, but the SS_MIN values are lower than 68 mV/dec. The new proposal offers the lowest R_C and SS_MIN, irrespective of the contact metals. Further considering the metal leads, the WSe₂/Rh FETs based on the non-vdW sandwich contacts show a meager R_C value of 33 Ω∙μm and an exceptional SS_MIN of 63 mV/dec. The two calculated results present the smallest-ever values reported in our study, indicating that the non-vdW sandwich contacts with Rh leads can attain the best-case scenario. In contrast, the symmetric convex edge contacts with Pd leads cause the worst-case degradation, yielding an R_C value of 213 Ω∙μm and an SS_MIN value of 95 mV/dec. While all the WSe₂/Ru FETs exhibit medium performances, the minimal shift in the transfer curves is interestingly advantageous to the circuit operation. Conclusively, the low-R_C performances and the desirable SS_MIN values are a combination of the contact geometries and metal leads. This innovation, achieved through noble metal leads in conjunction with the novel contact configurations, paves the way for a TMD-based CMOS with ultra-low R_C and rapid switching speeds.

In this study, we comprehensively investigate the constant voltage stress (CVS) time-dependent breakdown and cycle-to-breakdown while considering metal-ferroelectric-metal (MFM) memory, which has distinct domain sizes induced by different doping species, i.e., Yttrium (Y) (Sample A) and Silicon (Si) (Sample B). Firstly, Y-doped and Si-doped HfO₂ MFM devices exhibit domain sizes of 5.64 nm and 12.47 nm, respectively. Secondly, Si-doped HfO₂ MFM devices (Sample B) have better CVS time-dependent breakdown and cycle-to-breakdown stability than Y-doped HfO₂ MFM devices (Sample A). Therefore, a larger domain size showing higher extrapolated voltage under CVS time-dependent breakdown and cycle-to-breakdown evaluations was observed, indicating that the domain size crucially impacts the stability of MFM memory.