Titanium dioxide (TiO2) is a high-performance material for emerging device applications, such as in resistive switching memories, in high-k capacitors, or, due to its flexoelectricity, in micro/nano-electro-mechanical systems. Enhanced electrical properties of TiO2 are ensured, especially by a careful selection of the bottom electrode material. Iridium dioxide (IrO2) is an excellent choice, as it favors the high-k rutile phase growth of TiO2. In this study, we introduce the fabrication of IrO2/TiO2/IrO2 capacitors and thoroughly characterize their electrical behavior. These capacitors show a dielectric constant for low temperature sputtered TiO2 of ∼70. From leakage current measurements, a coupled capacitive–memristive behavior is determined, which is assumed due to the presence of a reduced TiO2−x layer at the IrO2/TiO2 interface observed from transmission electron microscopy analyses. The memristive effect most probably originates from trapping and detrapping of electric charges in oxygen vacancy defects, which themselves can be generated and annihilated through an applied electric field, subsequently changing the resistance of the capacitor. The electric degradation type is identified as a filament-forming mechanism. Additionally, the temperature dependence of the leakage current is measured, demonstrating that the temperature behavior is strongly influenced by the ambient atmosphere. The latter dependency leads to the hypothesis that the oxygen evolution reaction of water incorporated in the IrO2/TiO2 interface passivates vacancies, thus significantly impacting the vacancy density in TiO2 and, as a further consequence, the electrical performance.

The electroactive polymer polyvinylidene fluoride (PVDF) has gained much interest in smart materials research with a wide application range for industry and consumer applications due to the low cost, flexibility, chemical resistance, non-toxicity, and light weight. In this work, we present an α-phase PVDF cantilever that exploits electrostriction as the main transducer mechanism for excitation. We realize thin PVDF films with a thickness of ∼190 nm and a low roughness (∼19 nm RMS). Electrostrictive cantilevers need high electric fields to achieve amplitudes comparable to piezoelectric counterparts. At thinner films, lower voltage levels are requested for comparable electric fields, thus making electrostrictive PVDF cantilevers a viable route and subsequently allowing broader use of PVDF in MEMS devices. We use an asymmetric electrode design that has the advantage of shifting the neutral axis out of the PVDF without enhancing cantilever thickness with a supporting device layer. In addition, these devices can be produced by CMOS compatible micromachining techniques. We measured the electrostrictive and piezoelectric actuation signal with laser-Doppler vibrometry and showed the frequency spectrum and curvature of such α-phase PVDF cantilevers. The cantilevers have a curvate of up to 120 m−1 at 1500 kV/cm. We demonstrate that the electrostrictive actuation has a low temperature dependency in the range from 25 up to 130 °C. A typical cantilever exhibits a geometry dependent low spring constant (k ∼ 0.3 N m−1) and a low quality factor (Q ∼ 75) in air.

The flexoelectric effect describes the electromechanical coupling of a strain gradient to a polarization and vice versa. This effect scales linearly with permittivity and strain gradients can get very high for dimensions on the micro and nanoscale. Even though the flexoelectric effect can be best exploited within micro or nanoelectromechanical systems (M/NEMS) applications, it has not been established in today`s M/NEMS device architectures as other transducer principles, like piezoelectricity. In this work, values of the converse flexoelectric coefficient for one of the most promising flexoelectric materials, titanium dioxide (TiO2) are provided. The experimental results are based on a carefull characterization of IrO2/TiO2/IrO2 cantilevers. Besides CMOS compatiblity TiO2 is selected as functional thin film material as it offers a very high permittivity and shows no hysteresis or saturation effects as it is neither ferro- nor paraelectric. Additionally, it guarantees a low cost, lead-free realization and can be directly integrated in a standard silicon MEMS fabrication process by sputter deposition. In order to correctly determine the flexoelectric coefficient, other electromechanical coupling effects are considered and assessed. The flexoelectric coefficient is shown to be μ eff= 1.78 ± 0.16 nC m-1 at 10 kHz. The flexoelectric coupling constant with a value of 2.75 V is in good agreement with that theoretically predicted by Kogan`s estimate of 3.14 V.

In this study the influence of film thickness, adhesion promoters such as chromium (Cr) and rutile titanium dioxide (TiO2), sputtering power and substrate temperature on the electro-mechanical properties of platinum (Pt) thin films is investigated. The bilayered samples consisting of an adhesion promoter and a Pt thin film are deposited using direct current magnetron sputtering on sapphire substrates and characterized by Van-der-Pauw as well as gauge factor measurements up to 500 degrees C in air. Additionally, transmission electron microscopy and energy dispersive X-ray spectroscopy analysis are performed to investigate the microstructure and the chemical composition of the thin films before and after temperature loading. No substantial impact of the Pt film thickness on the electro-mechanical properties is determined. The diffusion of Cr into the Pt thin film at elevated temperatures leads to a lower gauge factor with a higher scatter range. Furthermore, higher sputtering power and substrate heating during deposition lead to a higher crystallinity of the Pt thin film and thus promote higher gauge factors. (C) 2018 Elsevier B.V. All rights reserved.