Capacitive sensors are widely used in industrial applications, such as CNC machine tools, where reliable positioning in the micrometer range with nanometer accuracy is required. Hence, these sensors are operated in harsh industrial environments. The accuracy of these sensors is mainly limited by slope errors and nonlinearities. In practice, the required accuracy of these sensors is achieved by a calibration against a metrological high-quality reference such as interferometric displacement measurement systems. This usually involves the use of high-order polynomials as calibration functions based on empirical data. In metrology, this is only the second-best approach and has disadvantages in terms of stability over the measurement range of the instrument. In addition, the validity of these empirical calibrations over time is questionable, and the associated uncertainty can only be roughly estimated. This makes regular recalibration of such sensors at short intervals mandatory to ensure the reliability of the displacement measurement. In this paper, we report on our investigations of the different parameters that affect the accuracy of capacitive sensors. Since the capacitance of these sensors results from the electric fields that build up between the electrodes, these field lines are calculated using FEM simulation models for typical commercial sensors. In the following the influence of various geometric parameters such as edge radius, guard ring size and shape, or thickness of the electrodes are individually analyzed according to their impact on the accuracy of these sensors. Based on these simulations, the deviations of the capacitance as they arise for real detector geometries can then be compared with idealized, de facto unrealizable parallel plate capacitors. This methodology allows overall uncertainty of capacitive sensors to be decomposed into their individual components and sorted in terms of their contribution to the uncertainty budget. The individual FEM-based analysis then enables a systematic analysis of the sources of uncertainty and, thus, reveals possibilities to improve manufacturing processes for capacitive sensors, to put these sensors on a solid metrological basis, and to improve the performance of these displacement measurement systems in the long run, i.e., to provide better sensors for the application.

Transferable substrate-less InGaN/GaN light-emitting diode (LED) chips have successfully been fabricated in a laser lift-off (LLO) process employing high power ultrashort laser pulses with a wavelength of 520 nm. The irradiation of the sample was conducted in two sequential steps involving high and low pulse energies from the backside of the sapphire substrate, which led to self-detachment of the GaN stack layer without any additional tape release procedure. To guarantee their optoelectrical function and surface quality, the lifted LED chips were assessed in scanning electron microscopy (SEM) and electroluminescence (EL) measurements. Moreover, surface characterizations were done using atomic force microscopy (AFM) and Auger Electron Spectroscopy (AES).

Chirped surface acoustic wave (SAW) resonators based on aluminum nitride (AlN) thin films have been designed and fabricated to comprehend the wave propagation characteristics induced by interdigitated transducers (IDTs) deposited on their surfaces. From the simulation results, design and geometry of the metal fingers including their width and pitch play critical roles on the wavelength of the acoustic wave and the mechanical displacement, which subsequently set the device resonant frequency. A single-step metal lift-off process involving photolithography and electron beam metal evaporation has been used to pattern and deposit Cr/Au IDT on AlN-on-Si wafers.

In this paper we present an investigation of the influence of different roughness of etched silicon surfaces on the measured nanomechanical properties. For the etching, inductively coupled plasma (ICP) reactive ion etching (RIE) was performed on the surface of silicon samples with different crystal orientations (i.e., Si <100>, Si <110>, and Si <111>). Different roughness levels were obtained on each sample by changing the bias voltage through the high-frequency (HF) power. The surface roughness was measured using atomic force microscopy (AFM). The obtained surface roughness for the same etching conditions was different for different crystal orientations. The nanomechanical properties were measured using nanoindentation.

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