Piezoelectricity of ZnO Films Prepared by Sol-Gel Method

Abstract

ZnO piezoelectric thin films were prepared on crystal substrate Si(111) by sol-gel technology, then characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy (AFM). The ZnO films characterized by X-ray diffraction are highly oriented in (002) direction with the growing of the film thickness. The morphologies, roughness and grain size of ZnO film investigated by AFM show that roughness and grain size of ZnO piezoelectric films decrease with the increase of the film thickness. The roughness dimension is 2.188-0.914 nm. The piezoelectric coefficient d 33 was investigated with a piezo-response force microscope (PFM). The results show that the piezoelectric coefficient increases with the increase of thickness and (002) orientation. When the force reference is close to surface roughness of the films, the piezoelectric coefficient measured is inaccurate and fluctuates in a large range, but when the force reference is big, the piezoelectric coefficient d 33 changes little and ultimately keeps constant at a low frequency.

Piezoelectric Templates – New Views on Biomineralization and Biomimetics

“…ZnO has been brought into the focus of research due to the high electromechanical coupling factor and more specifically its piezoelectric coefficient, since piezoelectricity provides a direct conversion between mechanical and electrical energy and thus opens up the possibility of using these materials for sensing, actuation or energy harvesting applications. Several investigations have been performed on both, nanostructures such as nanowires 18 19 20 , and thin films 21 22 23 . As, a result, ZnO nanowires and nanobelts have also been suggested for applications in piezoelectric nanogenerators 24 .…”

Template-controlled piezoactivity of ZnO thin films grown via a bioinspired approach

“…This also reflects in the value obtained for d eff of 3.2 pm V −1 ( d 33 = 6.4 pm V −1 ). This value is in the range or higher than the one of other oriented, ZnO thin films prepared by RF magnetron sputtering (2–13 pm V −1 ) [ 14 ] or sol–gel process (5 pm V −1 ) [ 15 ]. Since XRD data show that the crystal orientation is not perfect, the obtained d 33 is slightly lower compared to the values obtained on single crystalline ZnO of 9.9 pm V −1 [ 48 – 49 ].…”

“…Growth of such oriented films was achieved via technically sophisticated methods under harsh reaction conditions [ 14 – 17 ]. For example radio-frequency magnetron sputtering [ 14 , 17 ], pulsed laser deposition [ 16 ] or sol–gel methods followed by annealing [ 15 ] were applied. Another approach is bioinspired mineralization.…”

Textured dense zinc oxide layers for active noise canceling windows

“…Sputtering of ZnO can provide layers with similar morphology, also. With a sol‐gel approach piezoactive ZnO layers with a thickness of 88 nm and uniform c ‐axis orientation were obtained by repeatedly dipping . The same method used here is normally used for the synthesis of nanorods or nanowires which are no dense layers and are therefore not suitable for an active layer in a noise canceling window.…”

“…On the other hand, little research is devoted to the generation of dense and thick (>10 μm) ZnO films. There are reports from sputtered dense ZnO films and other methods such as sol‐gel, PLD, chemical vapor deposition (CVD), but generally these methods have disadvantages intrinsic to the particular coating process, for example, limitations in substrate size, crystal orientation, use of hazardous and harmful precursors, maximum achievable film thickness or they simply require too costly equipment. With the sol‐gel approach a time‐consuming repetition of the dip‐coating process is necessary to build up layers of a thickness of 1 μm.…”