Effective Transverse Piezoelectric E31 Research Articles

A film-texture driven piezoelectricity of AlN thin films grown at low temperatures by plasma-enhanced atomic layer deposition

Simultaneously inducing preferred crystalline orientation with a strong piezoelectric response in polycrystalline aluminum nitride (AlN) thin films by atomic layer deposition is a technical challenge due to the upscaling of the integration of piezoelectric functionalities, such as sensing and actuation, in micro-devices without any poling process. Utilizing low-temperature plasma-enhanced atomic layer deposition (PE-ALD), highly c-axis-oriented AlN films have been prepared with precise control over the relative composition, purity levels, and chemical states of constituent elements. Tailoring thermodynamic parameters, such as the growth temperature and purging time after the trimethylaluminum precursor pulsing before the N2:H2:Ar plasma reaction, provide the possibility of modulating the texture coefficient and the relative piezoelectric response. The effective transverse piezoelectric e31,f coefficient of 0.37 C/m2 was achieved on the AlN film grown at 250 °C and 30 s with the highest texture coefficient TC(002) of 2.75 along the c-axis orientation. The process proposed, at a low temperature with the highly conformal growth of aluminum nitride thin films by PE-ALD, opens up pathways to design novel piezoelectric functional materials for micro-electro-mechanic system devices with complementary metal oxide semiconductor process temperature compatibility.

Structure and piezoelectric properties of sol–gel-derived (001)-oriented Pb[Yb1/2Nb1/2]O3–PbTiO3 thin films

(1−x) Pb[Yb 1/2 Nb 1/2 ] O 3 –x PbTiO 3 (PYbN–PT, x=0.5) (001)-oriented thin films were deposited onto (111)Pt/Ti/SiO2/Si substrates by sol–gel processing. The crystallographic texture of the films was affected by heating rate, annealing temperature, and film thickness. The dielectric permittivity and loss factor varied only slightly with frequency in the range of 100 Hz–100 kHz. At 1 kHz, the dielectric permittivity of (001)-oriented films was 1030 and the dielectric loss was 0.03. Compared with (111)-oriented PYbN–PT films, (001)-oriented PYbN–PT films exhibited better piezoelectric properties. The effective transverse piezoelectric e31,f coefficient of the films were −8.2 C/m2 when films were poled at room temperature. Enhanced piezoelectric properties were observed by poling the films at higher temperatures. The transition temperature of the (001)-oriented PYbN–PT (50/50) films was around 360 °C.

Dielectric and transverse piezoelectric properties of sol-gel-derived (001) Pb[Yb1/2Nb1/2]O3–PbTiO3 epitaxial thin films

(1−x) Pb [ Yb 1/2 Nb 1/2 ] O 3 –x PbTiO 3 (PYbN–PT, x=0.5) epitaxial thin films were deposited on (001) SrRuO3/(001) MgO substrates by sol-gel processing. X-ray diffraction analysis revealed that the films were pyrochlore-free (001) epitaxial films when crystallized at 750 °C for 1 min. The dielectric permittivity and loss factor varied only slightly with frequency in the range of 100 to 10 000 Hz. At 1 kHz, the dielectric permittivity was 870 and the dielectric loss was 0.03 at room temperature. Compared with (111) PYbN–PT films, (001) PYbN–PT films exhibited better ferroelectric and piezoelectric properties. The remanent polarization (Pr) was 37 μC/cm2. The effective transverse piezoelectric e31,f coefficient of the films were −10.2 C/m2 when films were poled at room temperature. Enhanced piezoelectric properties were obtained using unique two-step method poling the PYbN–PT films at higher temperatures.

Structure and piezoelectric properties of sol–gel-derived 0.5 Pb[Yb1/2Nb1/2]O3–0.5 PbTiO3 thin films

0.5 Pb[Yb1/2Nb1/2]O3–0.5 PbTiO3 thin films were deposited on (111) Pt/Ti/SiO2/Si substrates by sol–gel processing using a thin Pb(Zr0.52Ti0.48)O3 seed layer. X-ray diffraction analysis and scanning electron microscopy revealed that the films were strongly (111) oriented, mimicking the orientation of the (111) Pt/Ti/SiO2/Si substrate. No pyrochlore phase was observed by x-ray diffraction and the films had a uniform grain size of about 50–60 nm. The dielectric permittivity and loss factor varied only slightly with frequency in the range of 100–10 000 Hz. At 1 kHz, the dielectric permittivity was 1025 and dielectric loss was 0.028. The films exhibited good ferroelectric and piezoelectric properties. The remanent polarization (Pr) was 30 μC/cm2. The effective transverse piezoelectric e31,f coefficient (−4.8 C/m2) of the films was measured using a modified wafer flexure method.