Effect of post-deposition annealing on transverse piezoelectric coefficient and vibration sensing performance of ZnO thin films (original) (raw)
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We report on the systematic comparative study of highly c-axis oriented and crystalline piezoelectric ZnO thin films deposited on four different flexible substrates for vibration sensing application. The flexible substrates employed for present experimental study were namely a metal alloy (Phynox), metal (aluminum), polyimide (Kapton), and polyester (Mylar). ZnO thin films were deposited by an RF reactive magnetron sputtering technique. ZnO thin films of similar thicknesses of 700 ± 30 nm were deposited on four different flexible substrates to have proper comparative studies. The crystallinity, surface morphology, chemical composition, and roughness of ZnO thin films were evaluated by respective material characterization techniques. The transverse piezoelectric coefficient (d 31) value for assessing the piezoelectric property of ZnO thin films on different flexible substrates was measured by a four-point bending method. ZnO thin films deposited on Phynox alloy substrate showed relatively better material characterization results and a higher piezoelectric d 31 coefficient value as compared to ZnO films on metal and polymer substrates. In order to experimentally verify the above observations, vibration sensing studies were performed. As expected, the ZnO thin film deposited on Phynox alloy substrate showed better vibration sensing performance. It has generated the highest peak to peak output voltage amplitude of 256 mV as compared to that of aluminum (224 mV), Kapton (144 mV), and Mylar (46 mV). Therefore, metal alloy flexible substrate proves to be a more suitable, advantageous, and versatile choice for integrating ZnO thin films as compared to metal and polymer flexible substrates for vibration sensing applications. The present experimental study is extremely important and helpful for the selection of a suitable flexible substrate for various applications in the field of sensor and actuator technology.
Development and characterization of ZnO thin film for piezoelectric applications
Materials Today: Proceedings, 2020
This paper reports a structural study of the ZnO thin film deposited on p-type silicon substrate using radio frequency (RF) sputtering technique. The structural study of the deposited ZnO thin film is done. The Xray diffraction (XRD) spectra shows a strong peak of (0 0 2) orientation which ensures high quality of piezoelectric film. The roughness of the ZnO film is measured and found to be 1.85 nm which attributed to lower acoustic loss during wave propagation. These sputtering parameters can be used to deposit good quality ZnO thin film which can be utilized as piezoelectric layer in acoustic sensors, pressure sensors and many other optoelectronics devices.
Local piezoresponse and piezoelectric output voltage were evaluated on ZnO thin films deposited by radio-frequency magnetron sputtering on hard Si/Ti/Au and flexible Cu-coated polyimide substrates. Three different thicknesses of ZnO films were studied (285 nm, 710 nm, and 1380 nm), focusing on characteristics like crystallinity, grain size, surface roughness, and morphology. Independent of the nature of the metal layer and the substrate, our results show that thicker films presented a higher level of crystallinity and a preferential orientation along the c-axis direction, as well as a lower density of grain boundaries and larger crystal sizes. The improvement of the crystalline structure of the material directly enhances its piezoelectric properties, as confirmed by the local characterizations performed by piezoresponse force microscopy and by the evaluation of the output voltage generation under the application of a periodical mechanical deformation on the whole film. In particular, the highest value of the d 33 coefficient obtained (8 pm V −1) and the highest generated output voltage (0.746 V) belong to the thickest films on hard and flexible substrates, respectively. These results envision the use of ZnO thin films—particularly on flexible substrates—as conformable, reliable, and efficient active materials for use in nanosensing, actuation, and piezoelectric nanogenerators.
Deposition, characterization and optimization of zinc oxide thin film for piezoelectric cantilevers
Applied Surface Science, 2012
In this work, piezoelectric zinc oxide (ZnO) thin films are deposited under different deposition conditions using RF magnetron sputtering method. The influence of RF power, O 2 /(Ar + O 2) gas ratio and sputtering pressure on the deposition rate, crystalline structures, surface roughness and composition purity of ZnO film are investigated by X-ray Diffractometer (XRD), scanning electron microscopy (SEM), atom force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDS). All the fabricated ZnO films have a preferred ZnO(0 0 2) orientation. When the gas ratio of O 2 /(Ar + O 2) is 25% and the working pressure is 0.8 Pa, the grain size in the ZnO thin film is of the largest and the ZnO film has a very smooth and dense surface. The SEM cross-sectional image of the ZnO film confirms that the ZnO thin film has a columnar structure and the c-axis is perpendicular to the substrate surface. The EDS analysis shows the ZnO film has only Zn and O elements. Different ZnO film based piezoelectric micro cantilevers are fabricated using micromachining techniques and the dynamic response of these piezoelectric cantilevers are measured by laser Doppler vibrometer (LDV). The tested results from LDV show that the deflection of the piezoelectric cantilever is linear with the driving voltage. The transverse piezoelectric constant d 31 of the ZnO thin film deposited under best conditions is calculated as −3.21 pC/N by the LDV data. This value is higher than other published works. In future, these ZnO thin films will be used in our ongoing project for the design, simulation and fabrication of smart slider with a built-in ZnO sensor/actuator in the hard disk drives.
Evaluation of Piezoresistivity Properties of Sputtered ZnO Thin Films
Zinc oxide (ZnO) thin films were deposited by RF reactive magnetron sputtering on silicon (100) substrates under different experimental conditions. ZnO films were studied before and after annealing treatment at 600 °C. The crystallinity, electrical resistivity, stoichiometry, thickness, and elastic modulus of the films were investigated. ZnO piezoresistors were produced using microelectronics processes, such as photolithography, lift-off, and reactive ion etching (RIE). Cantilever method was used to determine the gauge factor, and measurements of Temperature Coefficient of Resistance (TCR) were performed on a hotplate. The optimization of the deposition conditions produced ZnO thin films with controlled stoichiometry (ZnO), crystalline microstructure (phase wurzite, 002), high elastic modulus (156 GPa), and low electrical resistivity (0.072 ohm.cm), which are good properties for application as piezoresistive pressure microsensor. In addition, the ZnO piezoresistors had a GF of 2.6 on the deformation in the plane (100) and TCR of –1610 ppm/K up to 250 °C.
ZnO Piezoelectric Films for Acoustoelectronic and Microenergetic Applications
Coatings
Zinc oxide is one of the most popular materials for acoustoelectronic sensors and vibro-piezo-transducers used in nano-piezo-generators. In the present paper, thick piezoelectric ZnO films are fabricated on both sides of various substrates using magnetron sputtering technique. It is shown that the main problem for double film deposition is the difference in thermal expansion coefficients of the ZnO films and the substrate materials. The problem is solved by decreasing the plate temperature up to 140 °C, reducing the growing rate up to 0.8 ± 0.05 μm/h, and diminishing the oxygen content in Ar mixture up to 40%. Using the modified sputtering conditions, the ZnO films with thickness up to 15 μm, grain size 0.3 μm, and piezoelectric module as large as 7.5 × 10−12 C/N are fabricated on both faces of quartz and lithium niobate plates as well as on flexible polyimide flexible film known as Kapton. The films are characterized by chemical composition, crystallographic orientation, piezoelect...
Journal of Physics: Conference Series
We present the results of studies on the structural, optical and piezoelectric properties of ZnO thin films deposited by ALD on flexible polyethylene naphthalate (PEN) substrates. Changes were observed in the optical transmission and crystal structures as the deposition temperature was varied. The electromechanical behavior, dielectric losses and voltage generated from ZnO flexible devices were investigated and discussed, in order to estimate their suitability for potential application as microgenerators activated by human motion.
ZnO Thin Films Growth Optimization for Piezoelectric Application
Sensors, 2021
The piezoelectric response of ZnO thin films in heterostructure-based devices is strictly related to their structure and morphology. We optimize the fabrication of piezoelectric ZnO to reduce its surface roughness, improving the crystalline quality, taking into consideration the role of the metal electrode underneath. The role of thermal treatments, as well as sputtering gas composition, is investigated by means of atomic force microscopy and x-ray diffraction. The results show an optimal reduction in surface roughness and at the same time a good crystalline quality when 75% O2 is introduced in the sputtering gas and deposition is performed between room temperature and 573 K. Subsequent annealing at 773 K further improves the film quality. The introduction of Ti or Pt as bottom electrode maintains a good surface and crystalline quality. By means of piezoelectric force microscope, we prove a piezoelectric response of the film in accordance with the literature, in spite of the low ZnO...
Characterization of ZnO Thin Film as Piezoelectric for Biosensor Applications
Proceedings of International Electronic Conference on Sensors and Applications, 2014
Biosensor is an analytical device that consists of immobilized biological sensitive materials. When these materials are in contact with certain transducers, the sensor is able to convert biological signal into an electrical signal, hence allowing for certain measurement to be conducted. These sensors have the capability to detect certain human traits such as DNA, tissues, enzyme, antibody and antigen. To increase the biosensor performance, especially the interaction between the sensor and biological elements, high uniformity and good optical transmittance sensors are strongly important. Therefore, this paper will presents early characterization of biosensors using Zinc Oxide (ZnO) piezoelectric thin film deposited as sensing layer on Silicon substrate. We investigated the thin film surface morphology and optical characterization using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and UV-Visible Spectrophotometer. We found that the surface roughness of the thin film varied from 1.1 NM to 4 NM and the grain size increased with the increase of annealing temperature, thus provide high surface uniformity that will enhance the sensitivity and specificity of the sensor.