Phoi Chin Goh

Lead-free piezoelectric (K0.5Na0.5)NbO3 thin films derived from chemical solution modified with stabilizing agents

(K0.5Na0.5)NbO3 (KNN)-based ferroelectric thin films were prepared by a chemical solution approach modified with both diethanolamine (DEA) and ethylenediaminetetraacetic acid (EDTA) as the stabilizing agents. The obtained KNN thin films exhibited a remarkably low leakage current and well-saturated polarization hysteresis loop. The effective piezoelectric strain coefficient d33 and voltage coefficient g33 under the clamping of the substrate were improved to 74.0 pm/V and 28.3 mm V/N, respectively. The reason for the superior properties was found that the addition of EDTA and DEA was effective in suppressing the volatilization of K and Na at moderate temperature before the crystallization.

An Ultraviolet (UV) Detector Using a Ferroelectric Thin Film With In-Plane Polarization

Different from the semiconductor photovoltaic device on the basis of an interfacial effect, UV detection was realized in this letter by using bulk photovoltaic mechanism involving the depolarization field in a W-doped Pb0.97La0.03(Zr0.52Ti0.48)O3 (PLWZT) ferroelectric thin film. A prototype of UV detector was demonstrated in the laboratory as well as under sunlight, in which the ferroelectric PLWZT thin film was polarized in the plane of the film surface. Characteristics of the photovoltaic response of the ferroelectric thin films and their application values for UV detection were analyzed.

Lithium diffusion in (Li, K, Na)NbO3 piezoeletric thin films and the resulting approach for enhanced performance properties

Dramatic out-diffusion of lithium from (Li, K, Na)NbO3 (KNN-LN) thin films into substrate was identified as the cause of seriously degraded electrical properties. Utilizing the strong diffusion ability of lithium, lithium composition could be effectively introduced to the KNN film through the diffusion from the surface to the film. The distributions of the lithium diffused across the KNN films were found complementary to that of potassium, as lithium tended to be retained where A-site vacancies existed. With more lithium retained and reduced A-site vacancies, outstandingly large piezoelectric strain coefficient and voltage coefficient were demonstrated in the resulting Li-KNN film.

A Ferroelectric Ultraviolet Detector With Constructive Photovoltaic Outputs

Photovoltaic outputs in semiconductor photodetectors are typically generated at an interfacial space charge region. Here, the output of our ultraviolet detector was enhanced by incorporating a photovoltaic output over the bulk of a ferroelectric thin film for providing a constructive photovoltaic effect in addition to the response from the interfacial mechanism. The working principle was demonstrated with a ferroelectric (Pb_0.97La_0.03)(Zr_0.52Ti_0.48)O₃ (PLZT) thin film sandwiched between a (La_0.7Sr_0.3)MnO₃ top electrode and a Pt bottom electrode, in which the depolarization electric field in the PLZT film was in the same direction with that at the Schottky barrier at the PLZT/Pt interface to realize the constructive photovoltaic effect.

THICKNESS-DEPENDENCE OF RESIDUAL STRESS IN LEAD-FREE FERROELECTRIC K0.5Na0.5NbO3 FILMS

Lead-free ferroelectric K0.5Na0.5NbO3 (KNN) films with different thicknesses were prepared by polyvinlypyrrolidone (PVP)-modified chemical solution deposition (CSD) method. Their residual stresses were studied with two methods of X-ray diffraction (XRD) and nanoindentation fracture. It was found that the tensile stress occurs in KNN films with small thickness of 1.3 μm after all kinds of stresses were neutralized, which is mainly originated from the interaction across grain boundaries. With increasing the thickness to 2.5 μm and above it, the residual stress changed from tensile stresses to compressive stresses, and the compressive stress decreased with the thickness increased. These results could explain why a thicker KNN film can show improved electrical properties and the larger the thickness, the better the ferroelectric and piezoelectric properties.

Ferroelectric thin films with complex composition of PNN–PZN–PMN–PZ–PT and excess NiO

Ferroelectric thin films of the 0.1Pb(Ni 1/3 Nb 2/3 )O 3 –0.35Pb(Zn 1/3 Nb 2/3 )O 3 –0.15Pb (Mg 1/3 Nb 2/3 )O 3 –0.1PbZrO 3 –0.3PbTiO 3 (PNN–PZN–PMN–PZ–PT) complex oxide system were prepared on Pt/Ti/SiO 2 /Si substrates using a polymer-modified sol-gel method followed by a rapid thermal annealing (RTA) process. It was found that the addition of excess NiO is effective in stabilizing the perovskite phase while suppressing the pyrochlore phase. The crystalline structure and morphology of the films with different amounts of access NiO were studied with x-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM), respectively. The electrical properties, including dielectric, ferroelectric, and piezoelectric, showed a significant improvement with excess NiO. The film sample with 3 mol% of excess NiO exhibited optimized electrical properties. Different parameters, including tolerance factors on the basis of ionic radii, electronegativity differences between cations and anions, and oxygen bond valences, were applied to analyze the stability of the perovskite phase with different amount of excess NiO. Analysis results indicated that only the bond-valence theory could explain the effect of excess NiO on the stability of the perovskite phase under the assumption that the excess Ni 2+ entered the A sites of the perovskite structure.