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In this study, the piezoelectric properties of scandium-alloyed gallium nitride (ScGaN), which is expected to be applied to microelectromechanical systems devices, are evaluated by first-principles calculations. The piezoelectric constant (d33) of GaN is found to increase by up to approximately 30 times upon the addition of 62.5 mol. % of Sc. The piezoelectric stress constant (e33) increases and the elastic constant (C33) decreases with increasing Sc content of ScGaN, driving the rise of d33. The improved piezoelectric properties of ScGaN compared with those of GaN are largely attributed to elastic softening, which is thought to be related to the transition from a wurtzite to hexagonal boron nitride (h-BN) structure driven by the change in bonding states between atoms caused by the addition of Sc to GaN. The crystal orbital Hamilton population analysis suggests that addition of Sc to GaN results in the combination of weaker Sc–N and Ga–N bonding, which makes the crystal structure unstable. This weakened bonding is thought to be the main cause of the destabilization of the wurtzite structure and transition to the h-BN structure of ScGaN. The elastic softening associated with this structural transition leads to the dramatic improvement in piezoelectric properties. [ABSTRACT FROM AUTHOR]

In this study, the switching kinetics in a (001)-out-of-plane-oriented (Al0.8Sc0.2)N thin film were systematically investigated as a function of temperature and frequency. The switching behavior followed the Kolmogorov–Avrami–Ishibashi model within the temperature and write-pulse width ranges of 300–473 K and 10 Hz–600 kHz, respectively. The switching speed increased linearly with the electric field, even at high electric fields. The frequency dependence of the coercive field (Ec) evaluated at room temperature revealed that the scaling regime of the domain-wall propagation did not transition to the flow regime, and the switching velocity of the domain increased linearly with the electric field even at high frequencies up to 600 kHz. The invariant domain-wall motion regime implies the potential of using (Al,Sc)N films for high-frequency applications. In addition, a formula for estimating the coercive field of an (Al,Sc)N film was derived by fitting the parameters obtained from the study of switching behavior. The formula indicated that the switching electric field tends to become insensitive to frequency as temperature increases. Moreover, the frequency dependency of the field was minimal even at room temperature. This is a useful index for estimating the drive voltage at the operating frequency and temperature. [ABSTRACT FROM AUTHOR]

The aim of this study is to obtain a systematic insight into the scandium (Sc) concentration dependence of the spontaneous polarization (Psp) in ScxAl1−xN by using first-principles calculations. From the calculated results, we observe that a structural change from a c-axis polarized wurtzite structure to a nonpolarized layered hexagonal structure takes place at x = 0.67, and the spontaneous polarization decreases nonlinearly with a change in the Sc concentration. Furthermore, we calculate the spontaneous polarizations from each cation individually and find that the spontaneous polarization from aluminum–nitrogen (Al–N) (P sp AlN ) is higher than that from scandium–nitrogen (Sc–N) (P sp ScN ). This difference in spontaneous polarization arising from the cationic origin is attributed to the difference in the internal parameter along the c axis (Δ u 3 k) based on the layered hexagonal structure. [ABSTRACT FROM AUTHOR]

The ferroelectricity of (Al1−xScx)N (x = 0–0.34) thin films with various thicknesses was investigated. (Al1−xScx)N films were prepared at 400 °C on (111)Pt/TiOx/SiO2/(001)Si substrates by the radio frequency dual-source reactive magnetron sputtering method using Al and Sc targets under pure N2 gas or a mixture of N2 and Ar gases. The film deposited under N2 gas showed larger remanent polarization than those under N2 + Ar mixture. Ferroelectricity was observed for films with x = 0.10–0.34 for about 140-nm-thick films deposited under N2 gas. The x = 0.22 films showed ferroelectricity down to 48 nm in thickness from the polarization–electric field curves and the positive-up-negative-down measurement. The ferroelectricity of the 9 nm-thick film also was ascertained from scanning nonlinear dielectric microscopy measurement. These results reveal that ferroelectric polarization can switch for films with much broader compositions and thicknesses than those in the previous study. [ABSTRACT FROM AUTHOR]

A study was conducted to examine the electrical power generation features of Mn-doped lead zirconate titanate ceramics supporting slow mechanical stress. Released charge and energy responding to increases and decreases in stress were compared against each other. Response curves of the piezoelectric voltage was represented against the impact stress. Results indicated that the energy conversion efficiency of piezoelectric ceramics correlated with the method of stress application.

The deposition temperature dependence of the crystal structure and ferroelectricity for Sc‐doped AlN [(Al0.78Sc0.22)N] films is investigated. (Al0.78Sc0.22)N films 120–190 nm thick are deposited at various deposition temperatures between 500 °C and ambient temperature without heating on (111)Pt/TiOx/SiO2/(100)Si substrates. Crystalline films are obtained for all films, but its (001) orientation decreases with decreasing deposition temperature below 300 °C. Crystal anisotropy increases with decreasing deposition temperature due to the decrease in the thermal strain that originates from the larger thermal expansion coefficient of (Al0.78Sc0.22)N than Si. Ferroelectricity is observed by both of the polarization–electric field (P–E) curves and the positive‐up–negative‐down (PUND) measurement for all films. The ferroelectric polarization switching of the films deposited without heating is ascertained not only by P–E curves but also by the phase change of the piezoresponse. Slight increase in the coercive field with decreasing deposition temperature can be explained by the increase in crystal anisotropy. [ABSTRACT FROM AUTHOR]

Aluminum nitride microtubes formed from aluminum nitride thin film were studied.

We report a correlation between polarity distribution and piezoelectric response of Li-doped zinc oxide (Zn1-xLixO) films prepared by a facile chemical solution deposition (CSD) method. The correlation supports the importance of controlling the polarity distribution for obtaining high piezoelectric response of ZnO films. Although the Zn1-xLixO films were easily prepared on Inconel substrates by heating randomly-stacked nanoparticle films, Zn0.97Li0.03O and Zn0.94Li0.06O films showed high piezoelectric response of 5.6-5.8 pC/N and high O-polarity distribution ratio of 76-74%. This study presents the CSD method is promising as a low-cost and large-area fabrication method of piezoelectric ZnO films. [ABSTRACT FROM AUTHOR]

We have investigated the high sensitive piezoelectric response of c-axis oriented aluminum nitride (AlN) thin films prepared on polyethylene terephthalate (PET) films. The AlN films were deposited using a radio frequency magnetron sputtering method at temperatures close to room temperature. The c axes of the AlN films were perpendicularly oriented to the PET film surfaces. The sensor consisting of the AlN and PET films is flexible like PET films and the electrical charge is linearly proportional to the stress within a wide range from 0 to 8.5 MPa. The sensor can respond to the frequencies from 0.3 to over 100 Hz and measures a clear human pulse wave form by holding the sensor between thumb and middle finger. The resolution of the pulse wave form is comparable to a sphygmomanometer at stress levels of 10 kPa. We think that the origin of the high performance of the sensor is the deflection effect, the thin thickness and high elastic modulus of the AlN layer, and the thin thickness and low elastic modulus of the PET film. [ABSTRACT FROM AUTHOR]