The Y2O3 films grown with a new and heteroleptic liquid Y precursor, (iPrCp)2Y(iPr-amd), have been investigated with chemical properties of precursor, atomic layer deposition process, and material characterization of the deposited film and its non-volatile resistive switching behaviour.

Since the first report on the unexpected ferroelectricity of fluorite-structure oxides in 2011, this topic has provided a pathway for new research directions and opportunities. Based on theoretical calculations and experimental demonstrations, it is now well known that fluorite-structure ferroelectrics are compatible with complementary metal-oxide-semiconductor technology and exhibit ferroelectric properties at extremely thin (<10 nm) thicknesses. It should be noted that the noncentrosymmetric orthorhombic phase, which is responsible for ferroelectric behavior, is formed even at low temperatures (400 C or less). Herein, the various factors such as doping effects, deposition method, annealing method and conditions, and substrate material are reviewed, focusing on thermal budget, especially the low-temperature annealing process for formation of the ferroelectric phase. These low-thermal-budget processes facilitate not only the integration of ferroelectric circuits in the back-end-of-line to increase the effective memory area and add more functionalities but also applications for flexible and wearable electronics.

Low-temperature annealing of Zinc oxide (ZnO) films as electron transport layers for inverted polymer solar cells was investigated. A wrinkled morphology of the ZnO film has previously been mostly observed after dynamic annealing (DA). In this study, we investigated the effect of static annealing (SA) of ZnO layers deposited by the sol−gel method at 25 °C, 150 °C, and 200 °C for 10 min in air. We observed the formation of the wrinkle structures on the surface of the ZnO sample annealed at 150 °C, while flat structures were formed at 200 °C. Here, a variable ramping/heating rate provided by a static annealing process resulted in a variable solvent evaporation rate and transformation of the precursor. The tensile stresses induced by slower heating (∼40 °C/min in a 0.75 M ZnO solution) and residual solvent resulted in an amorphous layer with a wrinkled structure at a low temperature of 150 °C. A flat structure was obtained with slightly different dynamics at a faster heating rate (∼56 °C/min) at 200 °C. Consequently, the SA process enabled us to fabricate the desired wrinkled morphology at lower annealing temperatures (e.g., 150 °C) than ever reported for DA processes; the ramp rate in the 200 °C SA process was too high to form the wrinkled structure. The short circuit current of the device using a wrinkle structure was better than that of the device with flat structure due to optical effects of internal reflection, scattering and light-trapping by wrinkles, while the transmittance and fill factor of the device using a flat ZnO layer annealed at 200 °C was better than those of the device with a ZnO layer annealed at 150 °C. This was due to better film quality from the higher processing temperature, a low surface roughness, and less defects. However, the power conversion efficiency of devices with both films was similar, meaning that the low temperature annealing process producing the wrinkle structure can be used for fabricating devices with polymer substrates and gas barriers for flexible electronics. In the case of the wrinkled structure, we observed that the wrinkle height was highly dependent on the ramping rate, ZnO solution concentration, and annealing temperature, compared with previous works.

The discovery of ferroelectricity in HfO2-based materials in 2011 provided new research directions and opportunities. In particular, for atomic layer deposited Hf0.5Zr0.5O2 (HZO) films, it is possible to obtain homogenous thin films with satisfactory ferroelectric properties at a low thermal budget process. Based on experiment demonstrations over the past 10 years, it is well known that HZO films show excellent ferroelectricity when sandwiched between TiN top and bottom electrodes. This work reports a comprehensive study on the effect of TiN top and bottom electrodes on the ferroelectric properties of HZO thin films (10 nm). Investigations showed that during HZO crystallization, the TiN bottom electrode promoted ferroelectric phase formation (by oxygen scavenging) and the TiN top electrode inhibited non-ferroelectric phase formation (by stress-induced crystallization). In addition, it was confirmed that the TiN top and bottom electrodes acted as a barrier layer to hydrogen diffusion into the HZO thin film during annealing in a hydrogen-containing atmosphere. These features make the TiN electrodes a useful strategy for improving and preserving the ferroelectric properties of HZO thin films for next-generation memory applications.

The change in the interplanar spacing (d-spacing) including the ferroelectric orthorhombic (O) phase in the low-temperature fabricated HfxZr1−xO2 (HZO) films was studied using synchrotron grazing-incidence wide-angle x-ray scattering analysis. The 10-nm-thick HZO films were fabricated by thermal and plasma-enhanced atomic layer deposition (TH- and PE-ALD) methods using H2O gas and O2 plasma as oxidants, respectively, and a post-metallization annealing (PMA) was performed at 300–400 °C. The d-spacing of the mixture of (111)-, (101)-, and (111)-planes of O, tetragonal (T), and cubic (C) phases, respectively, for the TH- and PE-ALD HZO films increased up to 2.99 Å with an increase in PMA temperature, while the d-spacing estimated by conventional x-ray diffraction was 2.92 Å regardless of the PMA temperature. The remanent polarization (2Pr = Pr+ − Pr−) of the HZO films increased as the PMA temperature increased. It is clear that the 2Pr value satisfied a linear relationship as a function of the d-spacing of O(111)/T(101)/C(111) phases. Furthermore, the wake-up effect was found to depend on the ferroelectric O phase formation. The wake-up effect was significantly reduced in both the TH- and PE-ALD HZO films after the PMA at 400 °C due to the increase in the ferroelectric O phase formation. The leakage current density (J)–electric field properties of the PE-ALD HZO film with the lowest d-spacing were divided into three steps, such as low, middle, and large J values, in the wake-up (103 cycles), pristine (100 cycle), and fatigue (107 cycles) states, respectively. Therefore, an analysis of the ferroelectric O phase is very important for understanding the ferroelectricity including endurance.