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In this paper, we will provide information on the growth mechanism of 3C-SiC using alternating supply deposition (ASD). SiH 4 and C 3 H 8 were introduced successively in a low-pressure chemical vapor deposition (LPCVD) system at 1000 °C, forming a stoichiometric polycrystalline 3C-SiC thin film on Si substrates. We demonstrate the influence of different gas flow rates on thin film properties. In detail, altering the flow rates of the precursors and the carrier gas resulted in changes of the growth rate, the surface roughness, the crystal growth mechanisms as well as the crystal quality. Hydrogen inhibition and passivation are proposed to be the main effects influencing the growth behavior of ASD thin films. Applying ASD to grow 3C-SiC thin films with precursors from low to high flow rates resulted in a transition of different growth mechanisms influencing the surface roughness and grain size. Furthermore, we could prove that ASD is a cyclic step-by-step carbon-assisted redistribution of a prior deposited silicon film. This is shown by contact angle measurements of three differently terminated surfaces during the specific phases of one ASD cycle. High resolution transmission electron microscopy (HRTEM) analysis showed a continuous and homogenous thin film and confirmed the absence of silicon- or carbon-rich layers. ASD enables 3C-SiC thin films with customized properties for tailored micro electromechanical system (MEMS) applications. [Display omitted] • Tailored 3C-SiC thin film properties for MEMS applications using alternating supply deposition (ASD). • Discussion of control parameters affecting 3C-SiC properties during deposition. • Changes of the gas flow shows high impact on the roughness and crystallinity. • Characterization of the carbonization layer at the 3C-SiC/Si interface. • Insights into alternating supply deposition (ASD) growth mechanism. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate biocompatible micromachined buckled membranes for the operation in liquids. The membranes feature diameters between 600 and 800 $\mu \text{m}$ as well as integrated piezoelectric thin film actuators, thus enabling switching between the bistable states. The membrane material is known to be not biocompatible, hence a hydrogenated amorphous silicon carbide (a-SiC:H) layer is deposited on the surface. For demonstration purposes, a 70 nm ±3 nm thin a-SiC:H coating with a specific silicon to carbon ratio was chosen, with a negligible impact on the overall switching performance of the bistable membranes. Furthermore, a relation between the membrane center velocity at the first characteristic resonance frequency and the switching ability of a membrane in different viscous fluids is shown. Based on a small signal analysis the switching behavior can be predicted. The membranes were successfully switched in liquids with a dynamic viscosity up to 286 mPa $\cdot \text{s}$. The biocompatibility of the membranes was examined by growing Caco-2 cells, a human carcinoma cell line, on a-SiC:H thin films, featuring different carbon contents and organic surface treatments. The proliferation and adhesion of the cells on the substrates are examined in an empirical cell growth and removal study. Only a-SiC:H surfaces pre-treated with an O2-plasma and coated with Collagen Type I indicated to provide an environment of improved cell adhesiveness compared to other surface treatments. The biological investigations resulted in good cell proliferation, that also depends on the altered hydrophilicity of the surface, as well as on the carbon content of the a-SiC:H thin films. This study reveals that a broad range of biocompatible a-SiC:H surfaces can be prepared, whereby the cell growth can be tailored in terms of proliferation and adhesion for different biomedical application scenarios. Finally, this paper reports on the mechanical features of bistable, buckled membranes and their suitability as a growth substrate for human cell cultures, due to the good biocompatibility of a-SiC:H thin films. We therefore suggest that it will be feasible to grow cells on bistable MEMS membranes, enabling cell experiments in liquid medical environments, with both mechanically excitable and biocompatible surfaces. [2022-0006] [ABSTRACT FROM AUTHOR]

This work presents a new type of piezoelectric micromachined ultrasonic transducer (PMUT) based on a bi-stable MEMS membrane structure with integrated aluminum nitride (AlN) actuators. By switching the membrane between both stable ground states, large, design-dependent membrane center displacements in the range of $10~\mu \text{m}$ can be achieved, which result in sound pressure levels of up to 96.8 dB in the ultrasonic range at frequencies between 30 and 60 kHz at a distance of 10.5 mm. This bi-stable operation mode can be triggered by moderate voltage levels of up to 40 V, which is not uncommon for PMUT devices. The usage of AlN compared to the more commonly utilized lead zirconate titanates (PZT) significantly simplifies the device integration process and ensures CMOS compatibility. A comprehensive comparison with similar devices in literature shows that despite the lower piezoelectric coefficients of AlN compared to PZT, this bi-stable actuation approach features exceptionally high stroke levels with a correspondingly high overall sound pressure level. [2020-0104] [ABSTRACT FROM AUTHOR]