Pulsed Laser Deposition of Rocksalt Magnetic Binary Oxides

Here we systematically explore the use of pulsed laser deposition technique (PLD) to grow three basic oxides that have rocksalt structure but different chemical stability in the ambient atmosphere: NiO (stable), MnO (metastable) and EuO (unstable). By tuning laser fluence, an epitaxial single-phase nickel oxide thin-film growth can be achieved in a wide range of temperatures from 10 to 750 {\deg}C. At the lowest growth temperature, the out-of-plane strain raises to 1.5%, which is five times bigger than that in a NiO film grown at 750 {\deg}C. MnO thin films that had long-range ordered were successfully deposited on the MgO substrates after appropriate tuning of deposition parameters. The growth of MnO phase was strongly influenced by substrate temperature and laser fluence. EuO films with satisfactory quality were deposited by PLD after oxygen availability had been minimized. Synthesis of EuO thin films at rather low growth temperature prevented thermally-driven lattice relaxation and allowed growth of strained films. Overall, PLD was a quick and reliable method to grow binary oxides with rocksalt structure in high quality that can satisfy requirements for applications and for basic research

Defect Engineering to Achieve Wake-up Free HfO2-Based Ferroelectrics

Wake-up effect is still an obstacle in the commercialization of hafnia-based ferroelectric thin films. Herein, the effect of defects, controlled by ozone dosage, on the field cycling behavior of the atomic layer deposited Hf0.5Zr0.5O2(HZO) films is investigated. A nearly wake-up free device is achieved after reduction of carbon contamination and oxygen defects by increasing the ozone dosage. The sample which is grown at 30 s ozone pulse duration shows about 97% of the woken-upP(r)at the pristine state whereas that grown below 5 s ozone pulse time shows a pinched hysteresis loop, that underwent a large wake-up effect. This behavior is attributed to the increase in oxygen vacancy and carbon concentration in the films deposited at insufficient O(3)dosage, which is confirmed by X-ray photoelectron spectroscopy (XPS). The X-ray diffraction (XRD) scan shows that the increase in ozone pulse time yields the reduction of tetragonal phase; therefore, the dielectric constant reduces. TheI-Vmeasurements reveal the increase in current density as the ozone dosage decreases, which might be due to the generation of oxygen vacancies in the deposited film. Finally, the dynamics of wake-up effect is investigated, and it appears to be explained well by the Johnson-Mehl-Avrami-Kolmogoroff model, which is based on structural phase transformation.11Nsciescopu

Effect of dead layers on the ferroelectric property of ultrathin HfZrOx film

In this study, we investigate the effects of various electrodes on the ferroelectric properties of ultrathin HfZrOx (HZO) films. The ferroelectric polarization is totally suppressed in the HZO films with TiN and W bottom electrodes when the film thickness is below 5nm. These results can be attributed to the formation of a dead layer at the bottom electrode/HZO interface during the atomic layer deposition (ALD) and annealing processes. On the other hand, the HZO film with a Pt bottom electrode shows an excellent P-E loop with a very high switchable polarization (2P(r)) of 42.5 mu C/cm(2) even at a film thickness of 2.5nm. Through the short pulse switching technique, we confirm the formation of a thick dead layer in the HZO films with TiN and W electrodes, which inhibits the formation of the orthorhombic phase in these ultrathin HZO films. This implies that the ferroelectric property of ultrathin HZO films can be improved by choosing an appropriate electrode material capable of suppress ing the formation of a dead layer.11Nsciescopu

Defect Engineering을 통한 TiN/H0.5Z0.5O2/TiN 커패시터의 Wake-up Effect와 강유전성 개선

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Large Remnant Polarization in a Wake-Up Free Hf0.5Zr0.5O2 Ferroelectric Film through Bulk and Interface Engineering

A wake-up free Hf0.5Zr0.5O2 (HZO) ferroelectric film with the highest remnant polarization (P-r) value to date was achieved through tuning of the ozone pulse duration, the annealing process, and the metal/insulator interface. The ozone dosage during the atomic layer deposition of HZO films appears to be a crucial parameter in suppressing the mechanisms driving the wake-up effect. A tungsten capping electrode with a relatively low thermal expansion coefficient enables the induction of an in-plane tensile strain, which increases the formation of the orthorhombic phase while decreasing the formation of the monoclinic phase during the cooling step of the annealing process. Therefore, increasing the annealing temperature T-A followed by rapid cooling to room temperature resulted in a substantial increase in the 2P(r) value (similar to 64 mu C/cm(2)). However, the leakage current increased considerably, which can affect the performance of metal-insulator-metal devices. To reduce the leakage current while maintaining the mechanical stress during thermal annealing, a 10 nm Pt layer was inserted between the W/HZO bottom interface. This resulted in an similar to 20-fold decrease in the leakage current while the 2P(r) value remained almost constant (similar to 60 It mu C/cm(2)). The increase in barrier height at the Pt/HZO interface compared to that of the W/HZO interface coupled with the suppression of the formation of interfacial oxides (WOx) by the introduction of a Pt/HZO interface serves to decrease the leakage current.11Nsciescopu

Effects of high pressure oxygen annealing on Hf0.5Zr0.5O2 ferroelectric device

We report a high-pressure oxygen annealing (HPOA) process to improve the performance of TiN/Hf0.5Zr0.5O2 (HZO)/TiN devices by controlling the number of oxygen vacancies and carbon contaminants. The ferroelectric properties of HZO film after HPOA at 250 degrees C for 30 min under different oxygen pressures from 0 to 80 bar were evaluated by electrical and structural characterizations. We found that a sample treated with an oxygen pressure at 40 bar exhibited large switchable polarization (2P(r)) of approximately 38 and 47 mu C cm(-2) in its pristine and wake-up states, respectively. Compared to a control sample, an approximately 40% reduction in the wake-up effect was achieved after HPOA at 40 bar. Improved ferroelectric properties of HZO film can be explained by the appropriate amount of oxygen vacancies and reduced carbon contaminants after HPOA.11Nsciescopu