Alkali ratio control for lead-free piezoelectric thin films utilizing elemental diffusivities in RF plasma

The reliability of piezoelectric thin films is crucial for piezoelectric micro-electromechanical system applications. The understanding of resistance degradation in piezoelectric thin films requires knowledge about point defects. Here, we show the resistance degradation mechanism in the lead-free alternative sodium potassium niobate (KNN) thin films and the relationship to point defects in both field-up and field-down polarities. The conduction mechanism of KNN thin films is found to be Schottky-limited. Furthermore, a reduction in Schottky barrier height accompanies the resistance degradation resulting from interfacial accumulation of additional charged defects. We use thermally stimulated depolarization current measurements and charge-based deep level transient spectroscopy to characterize the defects in KNN thin films. Our results show that oxygen vacancies accumulate at the interface in field-up polarity, and multiple defects accumulate in field-down polarity, potentially oxygen vacancies and holes trapped by potassium vacancies. We use wafer deposition variation to create samples with different film properties. Measurement results from these samples correlate resistance degradation with the defect concentration. We find the natural logarithm of leakage current to be linearly proportional to the defect concentration to the power of 0.25. The demonstrated analysis provides a precise and meaningful process assessment for optimizing KNN thin films.

The aim of this study is to create and examine thin layers of Mn-doped potassium sodium niobate (KNN) using the sol-gel method. The objective is to examine and resolve the problem of elevated leakage current density that arises at high electric fields in KNN films. The objective is to enhance the dielectric and ferroelectric characteristics by including manganese (Mn) dopants at various concentrations ranging from pure KNN to 0.9%, while maintaining acceptable insulation resistance. X-ray diffraction (XRD) was employed to investigate the crystalline structure of Mn-doped KNN thin films. Based on the XRD analysis, the Mn-doped KNN thin films exhibit an orthorhombic crystal structure during manufacture. The presence of KNN thin films is confirmed by the XRD peaks, indicating a successful synthesis. The microstructure and surface morphology of the thin films were examined using field-emission scanning electron microscopy (FESEM). The most significant outcomes in terms of dense grain growth and uniform grain size were observed in thin films of KNN doped with 0.3% Mn. Based on the findings from the FESEM and AFM, the cracks were covered with thin films of uniform thickness, and the surface data of the KNN thin films did not provide any support for them. Atomic Force Microscopy (AFM) and Piezoresponse Force Microscopy (PFM) analysis indicate a notable enhancement in the surface morphology and the value of the piezoelectric coefficient in Mn-doped KNN thin films, with an increase of 0.3%.

Piezoelectric thin films offer a number of advantages in various applications, such as high energy density harvesters, a wide dynamic range, and high sensitivity sensors, as well as large displacement and low power consumption actuators. This review covers the available material forms and applications of piezoelectric thin films: lead zirconate titanate (PZT)-based thin films, lead-free piezoelectric thin films, piezopolymer films, cellulose-based electroactive paper (EAPap), and many other thin films used for electromechanical transduction. The electromechanical properties and performances of piezoelectric films are compared and their suitability for particular applications are reported. The key ideas of piezoelectric thin films are reviewed and discussed for sensory and actuation systems, energy harvesting, and medical and acoustic transducers. In the last section, an insight into the future outlook and possibilities for thin film-based devices and their integration into real-world applications is presented.

Thin films of AlN, CrN and Al1-xCrxN were grown epitaxially on c-cut sapphire by radio frequency (RF) plasma assisted pulsed laser deposition (PLD). The PLD growth mode employed for these Al1-xCrxN films was by delta doping layers of CrN 0.05-0.10 nm thick between layers of AlN of approximately 3.6 nm thick giving an estimated 1.3% and 2.5% Cr doping. The substrate temperature, nitrogen pressure and power parameters of the RF plasma were varied to optimize crystalline growth. X-ray diffraction (XRD) confirmed hexagonal wurtzite thin film growth of highly crystalline AlN and highly crystalline cubic CrN. The electronic structure of these thin films was examined by x-ray absorption (XAS) and soft x-ray emission spectroscopy (XES) at the N K edge. These measurements are compared with the results of density functional calculations for wurtzite-AlN, cubic-CrN and wurtzite-Al1-xCrxN. [DOI: 10.1380/ejssnt.2009.497]

Nitrogen-substituted TiO2 (N-TiO2) thin film photocatalysts have been prepared by a radio frequency magnetron sputtering (RF-MS) deposition method using a N2/Ar mixture sputtering gas. The effect of the concentration of substituted nitrogen on the characteristics of the N-TiO2 thin films was investigated by UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses. The absorption band of the N-TiO2 thin film was found to shift smoothly to visible light regions up to 550 nm, its extent depending on the concentration of nitrogen substituted within the TiO2 lattice in a range of 2.0-16.5%. The N-TiO2 thin film photocatalyst with a nitrogen concentration of 6.0% exhibited the highest reactivity for the photocatalytic oxidation of 2-propanol diluted in water even under visible (lambda > or = 450 nm) or solar light irradiation. Moreover, N-TiO2 thin film photocatalysts prepared on conducting glass electrodes showed anodic photocurrents attributed to the photooxidation of water under visible light, its extent depending on wavelengths up to 550 nm. The absorbed photon to current conversion efficiencies reached 25.2% and 22.4% under UV (lambda = 360 nm) and visible light (lambda = 420 nm), respectively. UV-vis and photoelectrochemical investigations also confirmed that these thin films remain thermodynamically and mechanically stable even under heat treatment at 673 K. In addition, XPS and XRD studies revealed that a significantly high substitution of the lattice O atoms of the TiO2 with the N atoms plays a crucial role in the band gap narrowing of the TiO2 thin films, enabling them to absorb and operate under visible light irradiation as a highly reactive, effective photocatalyst.

Radio frequency (RF) plasma in water was used for the degradation of methylene blue. The fraction of decomposition of methylene blue and the intensity of the spectral line from OH radical increased with RF power. RF plasma in water also produced hydrogen peroxide. The density of hydrogen peroxide increased with RF power and exposure time. When pure water (300 mL) is exposed to plasma at 310 W for 15 min, density of hydrogen peroxide reaches to 120 mg/L. Methylene blue after exposed to plasma degraded gradually for three weeks. This degradation may be due to chemical processes via hydrogen peroxide and tungsten. The comparison between the experimental and calculated spectral lines of OH radical (A–X) shows that the temperature of the radical is around 3,500 K. Electron density is evaluated to be ≃3.5 × 1020 m−3 from the stark broadening of the Hβ line.

RF compensation of single Langmuir probe in low density helicon plasma

We report here, the study carried out on piezoelectric thin film for MEMS/Microsensor applications. The study includes characterization of sputtered thin film using indirect methods and comparison of behavior using cantilever technique for the confirmation of piezoelectric property. A suitable experimental setup was designed and fabricated for subjecting the cantilever to vibrate. The data was recorded for piezoelectric thin films deposited with different compositions. It is clearly evident that the direct method is inexpensive and easier for determining the quality of the deposited piezoelectric thin film.

Applying the principle of water decomposition over photoelectrochemical cells to heterogeneous photocatalytic systems using powdered semiconductors is now a field of great interest, encouraging new fundamental investigations into chemical reactions which take place at the electrode surfaces in the electrochemical cells. In the present review, we have focused on systems, which can convert solar energy into chemical energy by using TiO2 photocatalysts. The photocatalytic decomposition of water under UV light irradiation has been achieved with systems using various nanoparticle photocatalysts such as TiO2. However, recently, visible light-responsive TiO2 thin films photocatalysts have been successfully prepared by a radio frequency magnetron sputtering (RF-MS) deposition method. These thin film photocatalysts were found to have enough potential for the separate evolution of H2 and O2 from water under solar light. The TiO2 thin films were prepared on metal substrates by RF-MS deposition and mounted on H-type containers filled with water. This unique system enabled the separate evolution of H2 and O2 from water under sunlight irradiation, opening new opportunities for the practical on-site production of pure and clean H2 from water using abundant and clean sunlight in a safe, environmentally harmonious way.

Biomass conversion by plasma has the advantage of mainly producing gaseous products, H2, CO and CO2. Though the thermal plasma has been used for this conversion, the plasma temperature is too high to be unfit for the conversion biomass. The temperature of cold plasma, however, is lower under 3000 K. It expects to be adequate for biomass conversion. Cold plasma can be obtained with irradiation microwave (2.45 GHz) or radio frequency (13.5 MHz) under reduce gas pressure. Therefore, in present study, the effective decomposition of cellulose by microwave plasma (MWP) and radio frequency plasma (RFP) is examined. The conversion of cellulose by MWP (XMWP) is higher than that by RFP (XRFP), irrespective of the reaction time. XMWP and XRFP reach 92.8 wt% at 10 min and 68.1 wt% at 30 min. The maximum yield of gaseous products (Ygas) by MWP is 85.1 wt% at 10 min, higher by 23.2 wt% than Ygas by RFP at 30 min. The amount of H2 and CO obtained by MWP is 18.0 mmol/g and 23.5 mmol/g, it is larger than that obtained by RFP. Comparing the relationship between conversion and yield, Ygas of MWP is slightly higher than that of RFP under X of 60 wt%, and both Ygas is almost same over 60 wt%. The amount of H2 and CO obtained by MWP is larger by 9.3 mmol/g and 9.6 mmol/g than that obtained by RFP. C, H and O element in cellulose is mainly distributed to H2 and CO by MWP. RFP mainly distributes H and O element to the other gases without H2 and CO. In addition, a large amount of C element is remains in the residue. Those results is found that MWP was more suitable for cellulose gasification than RFP, since MWP can highly convert C, H and O element to H2 and CO by higher energy of microwave frequency in comparison with radio frequency.

In this paper, the piezoelectric properties of Mg and Zr co-doped AlN (MgZr doped AlN) thin films are reported. MgZr doped AlN thin films were prepared on Si (100) substrates with a radio frequency magnetron reactive cosputtering system. The crystal structures and piezoelectric constants d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33</sub> of the films were investigated as a function of their concentrations, which was measured by X-ray diffraction and with a piezometer. The d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33</sub> of the MgZr doped AlN at total Mg and Zr concentrations of 35 atomic % was about three times larger than that of pure AlN. The experimental results of the crystal structure and d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33</sub> as a function of total Mg and Zr concentrations were in very close agreement with first-principle calculations. Finally, thin film bulk acoustic wave resonators (FBARs) that used MgZr doped AlN as a piezoelectric thin film were fabricated and compared with the AlN based FBAR. As a result, the electromechanical coupling coefficient improved from 7.1 to 8.5% with the Mg and Zr concentration at 13atomic % doped into AlN. The results from this study suggest that the MgZr doped AlN films have potential as a piezoelectric thin film for wide band and high frequency RF applications.

The properties of piezoelectric thin film layered structures are in the focus of many investigations. Significant decreasing piezoelectric properties have been observed with decreasing top-electrode size. These results are obtained by measurements of the effective piezoelectric small-signal coefficient d/sub 33,eff/ and the piezoelectric large signal-strain S using a double-beam laser interferometer. Samples are investigated with squared top-electrodes with dimensions of 0.1 mm to 1 mm edge length. The loss of d/sub 33,eff/ is as high as 50 %, whereas the influence on the relative permittivity is only small. This work investigates this behaviour by calculating the influence of varying elastic and geometrical properties of substrate, electrodes, and piezoelectric thin film on the effective piezoelectric small-signal coefficient d/sub 33,eff/ by means of finite element simulations. Beside the clamping effect of the substrate under electrical operating conditions also the influence of thermally induced mechanical stresses after cooling from 4000/spl deg/C to room temperature is calculated. From measurements and simulations it can be concluded that the source of the pad size effect on the measured piezoelectric properties can he attributed to the mechanics of the layered structure.

We performed an investigation by atomic force microscopy (AFM) of the hydrophilicity of TiO2 thin films obtained by radio frequency magnetron sputtering deposition (RFMSD) and plasma enhanced chemical vapor deposition (PECVD). On the basis of a theoretical model of the capillary and superficial tension force of the capillary water bridge formed at tip−sample contact, it is proved that AFM measurements in the atmospheric air of the tip−sample adhesion force provide information about the sample surface hydrophilicity at the microscopic level with a resolution of a few nanometers. Macroscopically, the film hydrophilicity was characterized by a water drop contact angle that, as a result of UV irradiation in atmospheric air, decreased from 60° to 20° for RFMSD films and from 60° to 4° for PECVD films. The AFM measurements revealed that the UV-induced macroscopic changes in the film hydrophilicity corresponded to an increase of the tip−sample adhesive force on the film surfaces. Very inhomogeneous adhesive force distributions were observed for RFMSD films, while even distributions were observed for PECVD films. Fluctuations in sample surface curvature due to grain occurrence on the film surface could not account for the wide spread of the adhesive force values noticed for RFMSD films, and such force distributions were ascribed to an uneven arrangement of oxygen bridging sites on the film surface. The relatively homogeneous distributions of the adhesive force values on the PECVD film surface were characterized by Gaussian probabilities of occurrence.

We discuss recent research and development efforts towards low cost, size, weight, and power gyroscopes based on piezoelectric MEMS technology. The potential advantages of piezoelectric and ferroelectric material integration into high performance inertial sensors include the following: significantly increased drive amplitudes for Coriolis Vibratory Gyroscopes relative to electrostatic actuators, dynamically equalized and stabilized Quality Factor mismatch (>>10×) in mode-match gyroscopes, and greatly improved drive amplitude (through 3D, sidewall piezoelectric integration) of mode-split gyroscopes. Piezoelectric thin films with large electromechanical coupling coefficients such as lead zirconate titanate (PbZr <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Th <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , PZT) can help to enable these performance benefits. Specifically, we will discuss efforts to optimize PZT thin film deposition using sputtering and new efforts to deposit 3D, conformal PZT using Atomic Layer Deposition (ALD). ALD is a well-established thin film growth technique that may enable conformal deposition of thin films on high aspect-ratio features. ALD of piezoelectric films on high aspect-ratio features, such as arrayed actuator elements, may improve the areal piezoelectric energy density (the total maximum piezoelectric energy projected onto the area of a planar substrate) by up to 200x or more, yielding proportionally larger drive amplitudes for CVGs compared to planar piezoelectric drive elements. However, ALD processes for piezoelectric films such as PZT or AlN are not widely reported. Recent laboratory demonstrations of ALD processes for PZT and a structural isomorph lead hafnate titanate (PbHf <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Th <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</inf> <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , PHT) have been successful, yielding piezoelectric perovskite films following a post-deposition anneal. Here, we present a modified process for ALD PHT which has yielded ferroelectric remanent polarizations (2P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> ) of 68 μC/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , apply the new process to ‘ALL ALD’ PHT film stacks on 3D-MEMS comb structures, and present initial results on the integration of ALD PHT into ‘planar’ MEMS QMG. We will also discuss recent efforts to grow AlN by ALD, which have yielded c-axis oriented polycrystalline films with high dielectric breakdown voltage > 10 MV/cm and e <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31,f</inf> of −0.53 C/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> on platinized substrates. This paper will also present results of applying piezo- and ferroelectric materials to gyroscopes to improve performance including 50% Q-tuning resulting in a>>10x improved quality factor mismatch.

A computational study of the piezoelectric response due to the material effect in periodic, single island thin films and the geometric effect in periodic, bi-island thin films