This paper reports on the deposition of AlN and AlXSc1-XN films by pulse magnetron sputtering. The influence of process parameters on the film properties and the evaluation of the films for micro energy harvesting are presented. For AlN it is shown, that film stress can be varied in a considerable range between compressive and tensile stress while maintaining good piezoelectric properties. Additionally, the effect of doping AlN with Sc regarding piezoelectric and mechanical properties is presented. The films show the expected increase of piezoelectric properties as well as the softening of the material with higher Sc concentrations. Above a threshold concentration of around 40% Sc in the AlXSc1-XN films, there exists a separation into two phases, an Al-rich and a Sc-rich wurtzite phase, which is shown by XRD. At Sc concentrations higher than 50%, the films are not piezoelectric, as the films are composed primarily of the cubic ScN phase. Sc doping allows to significantly increase the energy generated in test setup. Up to 350 μW power have been generated under optimum conditions.
The application of thermal wave measurement techniques was demonstrated for Strontium Barium Niobate (SBN) and
Lithium Tantalate (LT) crystals, Lead Zirconate Titanate (PZT) ceramics, and PZT thin films. We have investigated the
influence of poling conditions and of chromium and cerium doping on the polarization distribution and domain wall
pinning in SBN crystals, the impact of ion beam etching on the polarization distribution in high-detectivity LT infrared
sensors, the influence of poling procedure on the polarization distribution of PZT piezoceramics, and the polarization
distribution in self-polarized PZT thin films.
Temperature responsive hydrogels show a strong ability to change their swelling degree in dependence on organic solvent or salt concentration in aqueous solutions. This behavior can be used for appropriate sensors if a suitable transducer transforms the volume change into an electrical output signal. In the present work, piezoresistive sensors were used where the hydrogel led to a deflection of a silicon membrane within the sensor chip. This principle allows for a strict separation of the fluid from the piezoresistors as well as from other electronic components at the front side of the sensor chip. Poly(N-isopropylacrylamide) (PNIPAAm) as well as photo cross-linkable poly(N-isopropylacrylamide-co-dimethyl-acrylamide-co-2-(dimethyl maleimido)-N-ethyl-acrylamide) (PNIPAAm-DMAAm-DMIAAm) terpolymer have been applied and investigated for organic solvent concentration sensors and salt concentration sensors.
The sensor's output voltage was measured during the swelling of the hydrogel under influence of water solutions with different organic and inorganic solute concentrations at different temperatures. A complex "reentrant" swelling behavior of the hydrogel in mixed co-solvents as well as "salting in" and "salting out" effects of different salts were studied. It was found that the change in the gel volume phase transition temperature depends on the solution viscosity and the concentration of the additive affecting the stiffness of the polymer chain in the surrounding solution. The influence of an initial gel conditioning procedure on the signal value and the sensitivity of the proposed chemical sensors was investigated and the measurement conditions necessary for high signal reproducibility and long-term stability were determined.
The purpose of chemical sensors consists in converting chemical input data into output signals suitable for electronic measuring processes. The sensors are characterized by a material-recognizing element and a transducer. The transducer converts the non-electric measuring value into an electrical signal. Hydrogels are cross-linked polymers which swell in solvents to appreciable extent. The amount of solvent uptake depends on the polymer structure and can be made responsive to environmental factors, such as solvent composition, pH value, temperature, electrical voltage etc. Hydrogels are capable to convert reversibly chemical energy into mechanical energy making them interesting as sensitive material for appropriate sensors. In the present work, in order to realize pH sensors, poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) blend hydrogels with a pH value dependent swelling behavior were used as chemo-mechanical transducers. The influence of the kinetics of the induced charge (in the swollen polyelectrolyte gel) on the response time, the signal value and the sensitivity of the proposed pH sensors were investigated and the measurement conditions necessary for high signal reproducibility were determined.
In this work, the laser intensity modulation method (LIMM) is applied to the investigation of the polarization distribution profile inside ferroelectric thin films. Here, a sinusoidal thermal wave is generated by a laser, thus causing a pyroelectric current. This current is influenced by the frequency and, hence, the penetration depth of the thermal wave inside the thin film as well as by the polarization state of this layer. The spatial polarization profile is then determined from the pyroelectric current spectrum by inverse solution of the appropriate FREDHOLM integral equation. Mathematically considered, this represents an ill-posed problem, which usually leads to numerically unstable solutions with an often severely disturbed waveform. Taking both profiles with larger gradients and superimposed noise at the pyroelectric current spectra into account, a TIKHONOV regularization method has to be employed to accomplish numerically stable and reliable results for the reconstructed polarization profiles. Based on the consideration of different typical polarization profiles, the influence of various regularization approaches was investigated, which determine the uncertainty of the reconstruction result. This work explains the effects of uncertainties of measurement due to data noise, non-optimal regularization parameters, material parameter variations and deviations of the thermal model and the influence of uncertainties due to non-optimal model assumptions. It will be shown that the lacking knowledge of precise thin film material parameters and noise inside the measuring setup represent the most decisive uncertainty sources for the LIMM method to determine polarization thickness profiles inside ferroelectric thin films.
In this work, determination of the refractive index profile and the optical gap E02 of PbZr1-XTiO3 thin films is described. Measurements were performed with the J. A Woollam spectral ellipsometer working on rotate analyzer mode. The temperature dependence of optical constants was obtained with a specially designed heating device.