We demonstrate a method to repeatedly detach multiple thin layers from a single $4 \mathrm{H}-\text{SiC}$ wafer by electrochemical etching. Up to 13 porous $4 \mathrm{H}-\text{SiC}$ foils of $\sim 25 \mu ~\mathrm{m}$ thickness have been sequentially detached from a 4 -inch 4 H -SiC substrate piece. The detached layers are porous, but retain a single-crystalline $4 \mathrm{H}-\text{SiC}$ skeleton, making them suitable for applications ranging from chemically inert membranes to engineered MEMS and even substrates for power electronics. The process employs a tailored high-voltage pulse for initial pore nucleation, a moderate-voltage sequence to define layer thickness, and a final high-voltage pulse to initiate layer release. We characterised the donor wafer surface after each cycle, observing that surface roughness stabilises after the first few detachments at $\sim 200 ~\text{nm}$. This new technique fully exploits expensive SiC wafers by yielding multiple thin foils from one substrate, a significant advancement for SiC-based microfabrication.

Electrochemical etching (ECE) of silicon carbide is a powerful route to porous 4H‑SiC. Yet, reliable pore initiation on the Si-face typically requires additional sophisticated pre-conditioning (e.g. masked KOH etching, metal-assisted photochemical etching (MAPCE), focused ion beam (FIB) milling), limiting industrial adoption. We demonstrate a simple, CMOS‑compatible pre‑conditioning based on short reactive‑ion‑etching (RIE) steps (10–30 s, SF₆/O₂) that reproducibly nucleate pores on the Si‑face of highly doped 4H‑SiC (resistivity < 0.02 Ω·cm) and enable homogeneous ECE in HF/ethanol without UV illumination. Surface roughness increases modestly with RIE time (R a ≈ 1.3 nm to 4.0 nm), while subsequent ECE does not significantly degrade topography. SEM cross‑sections reveal continuous porous layers; image‑based quantification shows enhanced vertical pore alignment with longer RIE duration. A stepwise voltage program (11.5 V → 8.5 V → 11.5 V) yields stable current transients during etching. Eliminating noble metals and lithography reduces contamination risk. It improves process compatibility with front‑end manufacturing while remaining synergistic with our previously established ECE process flows and high‑temperature reorganisation of thin, porous SiC layers.

ABSTRACT Although thermal oxidation represents an essential method for growing high‐quality SiO2 on 4H‐SiC, it suffers from low growth rates and high thermal budgets, limiting its industrial relevance compared to deposited oxides such as TEOS‐based oxides. In this study, we investigate how oxygen plasma pre‐treatment affects the subsequent thermal oxidation and electrical performance of SiO2 layers on 4H‐SiC. A substantial enhancement in oxide growth rate (up to 84%) is observed, which we attribute to plasma‐induced surface modification that facilitates oxygen diffusion. However, this acceleration comes at the cost of reduced dielectric breakdown strength (∼18% lower) and a broadened transition region at the interface. Electrical measurements indicate that leakage is governed by Schottky and Poole‐Frenkel conduction mechanisms. Capacitance–voltage and conductance‐voltage analysis reveal lower interface state density (Dit) for samples with oxygen plasma pre‐treatment, indicating plasma‐induced modification of the SiO2/SiC interfacial defect structure. These findings suggest that plasma pre‐treatment introduces structural damage that promotes oxidation but degrades dielectric reliability. This work highlights both the potential and limitations of plasma‐enhanced oxidation for SiC‐based dielectrics and motivates further studies to optimise process parameters and mitigate reliability trade‐offs.

The fabrication of microelectromechanical systems (MEMS) devices comprises many steps, each of which adds to the tolerance, resulting in device performances that may fall outside the defined limits in the design process. Hence, it is important to know local thin film properties most accurately, directly affecting the performance of the MEMS device. Furthermore, the capability of monitoring and mapping the thin film thickness and stress across a wafer enables device statistics and the strengthening of scientific statements. Within this study, we used standard MEMS structures consisting of a cantilever and a step profile to perform automated and contactless characterization of the local thin film thickness and stress across six 4-inch (100 mm) wafers. For this purpose, we constructed a measurement setup combining white light interferometry (WLI) to measure the static deflection of the cantilevered beams and plates and the thickness of the thin film through a step profile etched into the thin film. Even more, an XYZ-stage positions hundreds of devices below the objective lens of the WLI. This leads to precise maps of the local thin film thickness and to the extraction of a mean stress and a gradient stress from the static deflection of slender beams. The beams are oriented parallel and perpendicular to the wafer flat so that the measurement of orientation-dependent stress values is possible.

Porous materials represent a versatile solution for several applications. Indeed, the recent development of a new material, named 3D-Graphene, which combines the exceptional characteristics of graphene with a three-dimensional structure, opens perspectives for applications where a high surface-to-volume ratio is beneficial. In this study, we explore the functionalization of 3D-Graphene with nickel (Ni)-nanoparticles as a strategy to enhance hydrogen storage capabilities, and we assess the influence of the NPs on hydrogen uptake and oxidation resilience. The morphology and structural properties of pristine and Ni-functionalized samples were characterized using Scanning Electron Microscopy. Additionally, X-ray Photoelectron Spectroscopy was employed to analyze the surface chemical composition of the functionalized samples. Samples have been hydrogenated supplying molecular or atomic hydrogen, and hydrogen storage performance was assessed through Thermal Desorption Spectroscopy. Afterwards, oxidation effects were systematically studied by exposing the samples to atmospheric oxygen, followed by further hydrogenation experiments. Our results indicate that Ni functionalization influences both hydrogen adsorption and oxidation behavior, with potential implications for improving the stability of the material, especially for hydrogen storage applications.

Step-controlled epitaxy enables high-quality homo- and hetero-epitaxial growth of single-crystalline semiconductors on silicon carbide (SiC). Optimizing this process requires a detailed understanding of step structures and thermodynamics to suppress defects, such as step bunching and nanofacet formation. However, calculating the energies of asymmetric steps and vicinal surfaces in compound semiconductors with intrinsic polarity remains challenging. In this work, the wedge-geometry approach is employed not only to calculate the absolute basal surface energy of zincblende SiC (3C-SiC) but also to determine the absolute vicinal surface energy by introducing tree-like and mountain-like wedge geometries. Step energies, specifically for asymmetric steps, are obtained from the energy differences between basal and vicinal surfaces. Five single-layer step configurations on both Si- and C-side vicinal surfaces are systematically evaluated, along with their dependence on the vicinal angle. The results show that step energy is almost independent on the vicinal angle for hydrogen-passivated steps. The correlation between vicinal surface energy and vicinal angle indicates that nanofacet formation is energetically favored on the Si-vicinal [1¯21¯] offcut surface, which can be suppressed by tuning hydrogen and carbon chemical potentials. The findings on 3C-SiC provide insights into step behavior across other SiC polytypes, and the method is applicable to other zincblende semiconductors.

Several intrinsic and extrinsic contributing loss mechanisms make the estimation of the total Q-factor Q of MEMS resonators challenging, as it is influenced by many parameters. Experimentally, however, only the total Q-factor of a vibrational mode can be measured; so for the study of environmental conditions, pressure and temperature sweeps are typically performed to provide knowledge about fluidic and thermo-elastic dissipation. However, the contributing amounts of intrinsic damping mechanisms cannot be split into their individual components. In this study, we explore the dynamics of many non-slender MEMS resonators while varying the width. We call this technique design-dependent Q-factor spectroscopy (DDQS). The use of hundreds of devices with several out-of-plane resonance modes within DDQS allows the separation of the total Q-factor into the different dissipation mechanisms in thin films and MEMS resonators. Experimental results discussed alongside theoretical predictions indicate how the variation of a geometrical parameter of the resonator allows access to frequency regions with different dominant dissipation mechanisms. Furthermore, we evaluate the impact of surface-related losses and fluidic damping, showing a two-fold improvement in Q by removing the native grown silicon dioxide layer under high vacuum conditions. Our results highlight the advantages of optimizing the design of MEMS resonators within DDQS to understand the contributions to energy dissipation and lead to a new MEMS design approach.

This study explores the application of Polycarbosilane (PCS) as an intermediate adhesive bonding technique for 4H-SiC substrates aiming to overcome the challenges of producing high-quality and cost-effective substrates for high-power electronics. Thin layers of PCS mixed with m-xylene and AIBN (azobisisobutyronitrile) were deposited onto 4H-SiC substrates via a spin coating. For demonstration purposes, these coated 4H-SiC substrates were then bonded with another 4H-SiC substrate. A defect-free, high-temperature stable bond is facilitated by annealing at high temperatures. Effusion measurements were conducted to characterise the PCS thin films and examine the organic-inorganic transitions and the resulting outgassing at high temperatures. SEM analysis confirmed the uniformity of the bonded layer. These results demonstrate PCS’s potential in high-temperature applications and will stimulate further research exploring doped SiC bonding layers and their electrical properties.

In our previous work, single-crystalline porous 4H-SiC thin foils were successfully released from a monocrystalline 4H-SiC wafer by photoelectrochemical etching (PECE). This technology is promising for the next-generation power device fabrication processes (e.g. cost-efficient engineered substrates) and micro-electromechanical systems. The surface terminations of the pore walls will affect the behavior in the further fabrication process and application, thus motivating the need for detailed investigations. This work based on DFT calculations focuses on the surface terminations of five 4H-SiC non-polar surfaces, i.e. {10-10}, {11-20}, {21-30}, {31-40} and {32-50}, which can well represent the walls of the C-face etched pores penetrating through the released foil along the [0001] direction. The surface energies of the stoichiometric surfaces are found to be in the sequence of {11-20} < {32-50} < {21-30} < {10-10} < {31-40}. All these surfaces have high chemical affinity to H2O and even more to HF. In particular, for the complete surface termination by HF, the relative stability of these crystal planes can be changed and depends on the HF chemical potential. For example, in the range of HF chemical potential from −4.10 to −1.70 eV, the 4H-SiC {10-10} becomes more stable than the {11-20}. This preliminary research provides insight into the surface chemistry of the 4H-SiC non-polar surfaces, especially the {21-30}, {31-40} and {32-50}, which have rarely been investigated.

A typical bulk acoustic wave-solidly mounted resonator (BAW-SMR) in filters and duplexers for today's radio frequency front end utilizes an acoustic mirror to trap the acoustic wave energy coupled into the device by the electric signal. The exploited Bragg reflection in the acoustic mirror is created by an alternation structure of low and high acoustic impedance (low-Z and high-Z) material thin films, as the ratio between the paired acoustic impedances directly correlates with the desired mirror reflectivity. Preferably, low-Z thin films consist of silicon dioxide (SiO2) with ∼13 MRayl, paired with high-Z material layers of tungsten (W), tantalum (Ta), or molybdenum (Mo) in between, featuring up to >100 MRayl for the acoustic impedance (in the case of W) and leading to a high impedance ratio of 8:1. However, an unwanted effect arises from metals as high-Z thin films, requiring photolithographic structuring steps to confine them within the active resonator regions and avoid electromagnetic feedthrough, which is detrimental to filter selectivity outside the desired passband. Hence, fully dielectric acoustic Bragg reflectors have been proposed by various groups, replacing metal thin films in acoustic Bragg reflectors with dielectric high-Z material systems. By the development of a-SiOCN:H as a low-Z material system with only 7.1 MRayl, pairing with a dielectric high-Z thin film of amorphous SiC (a-SiC, a-SiC:H), featuring 22.5 MRayl and, thus, an impedance ratio of 3:1, also becomes applicable. In this work, we present the design and manufacturing of this fully dielectric acoustic Bragg mirror with a-SiOCN:H and a-SiC:H, fabricated by an alternation of deposition parameters within a plasma-enhanced chemical vapor deposition process and reaching a state-of-the-art coupling coefficient of more than 6.6% in an AlN based BAW-SMR device.

Sensors that are sensitive to volatile organic compounds, and thus able to monitor the conservation state of food, are precious because they work non-destructively and allow avoiding direct contact with the food, ensuring hygienic conditions. In particular, the monitoring of rancidity would solve a widespread issue in food storage. The sensor discussed here is produced utilizing a novel three-dimensional arrangement of graphene, which is grown on a crystalline silicon carbide wafer previously porousified by chemical etching. This approach allows a very high surface-to-volume ratio. Furthermore, the structure of the sensor surface features a large number of edges, dangling bounds, and active sites, which make the sensor, on a chemically robust skeleton, chemically active, particularly to hydrogenated molecules. The interaction of the sensor with such compounds is read out by measuring the sensor resistance in a four-wire configuration. The sensor performance has been assessed on three hazelnut samples: sound, spoiled, and stink bug hazelnuts. A resistance variation of about ∆ R  = 0.13 ± 0.02 Ω between sound and damaged hazelnuts has been detected. Our measurements confirm the ability of the sensor to discriminate between sound and damaged hazelnuts. The sensor signal is stable for days, providing the possibility to use this sensor for the monitoring of the storage state of fats and foods in general. © 2023 Society of Chemical Industry.

In this paper, we demonstrate the impact of controlled gas flow changes with alternative supply deposition on the CTE-mismatch of 3C-SiC-Si heterostructures using LPCVD. Especially for MEMS systems it is of great interest to overcome the working temperature limitations given by classic Si applications. Silicon carbide, among other things, is known for its outstanding thermal properties. Thus, replacing or combining Si with SiC in key positions can increase the range of applications. However, the well-known issue of the CTE-mismatch of up to 31 % at 900 degrees C is impeding this promising progress. With our tailored polycrystalline 3C-SiC thin films it is possible to control the CTE-mismatch resulting in values as low as 3.8 % at 900 degrees C. For demonstration purposes, we applied two 3CSiC thin films with significant differently CTEs to micromachined 3C-SiC/Si-MEMS micro hotplate (mu HP) structures. Using tailored platinum micro heaters for thermal excitation, the deflection of the mu HPs was measured. Hereby mu HPs with a lower CTE-mismatch showed on average 3.6 times less deflection amplitudes for the same applied heating power. Theoretical considerations of the impact of the platinum on the total deflections are also provided. We emphasize the potential for MEMS applications, as either the thermal stress can be reduced, or the working temperature of such devices can be significantly increased without causing damaging malfunctions of the device.

Statistical analysis of microelectromechanical system (MEMS) resonator devices in an early stage of device fabrication is challenging since actuation and sensing of the frequency-dependent response characteristics are often impossible before electrical connections are established. Photo-thermal actuation and optical readout using laser Doppler vibrometry (LDV) are powerful techniques to overcome this problem, enabling a fast, contactless device characterization and thus generating a high amount of data for statistical analysis. This paper reports on a tailored measurement setup for the contactless characterization of pure, monocrystalline silicon MEMS resonators at the wafer level. The presented system combines a precision stage for the movement in all three dimensions, a lightweight vacuum chamber, a laser diode for actuation, and a laser Doppler vibrometer. Details on the hardware and software solutions are discussed, and the high potential of the described setup is demonstrated by measuring hundreds of devices fabricated on one silicon-on-insulator (SOI) wafer. First tests show that thickness variations in the silicon device layer influence the resonance frequency of devices across the wafer and that different loss mechanisms dominate different out-of-plane modes in plate-shaped MEMS resonators.

In this paper, we demonstrate the implementation of a doping scheme for 3C-SiC thin films using the alternating supply deposition (ASD) technique in a low-pressure chemical vapor deposition (LPCVD) system. The moment of introduction of the dopant is critical and resulted in different thin film resistivities. By synthesizing 3C-SiC thin films with the most promising dopant scheme and increasing ammonia (NH3) flow rates we provide insight of the capabilities of ASD doping. The electrical properties were characterized using the circular transfer length method (CTLM). Promising values for the specific contact resistance around 310(-6) Omega cm(2) were measured and resistivities of rho = 0.02 Omega cm, which is comparable to state-of-the-art thin film resistivities for polycrystalline 3C-SiC. The temperature dependence of undoped and highly doped thin films are compared from room temperature to 300 degrees C. For both cases a negative temperature coefficient was determined, which is explained by the effect of incomplete ionization of the dopant. Lowest resistivities of 0.014 Omega cm were measured at 300 degrees C. Chemical analysis demonstrates for elevated NH3 flow rates a change from highly <111> oriented poly 3C-SiC thin films to amorphous and highly insulating SiCN thin films of only 25 % of the maximum measured thickness. This can be explained by the competition of C and N atoms for Si bonds, which is dominated by nitrogen atoms at higher NH3 flow rates.

We demonstrate the first successful functionalization of epitaxial three-dimensional graphene with metal nanoparticles. The functionalization is obtained by immersing three-dimensional graphene in a nanoparticle colloidal solution. This method is versatile and demonstrated here for gold and palladium, but can be extended to other types of nanoparticles. We have measured the nanoparticle density on the top surface and in the porous layer volume by scanning electron microscopy and scanning transmission electron microscopy. The samples exhibit a wide coverage of nanoparticles with minimal clustering. We demonstrate that high-quality graphene promotes the functionalization, leading to higher nanoparticle density both on the surface and in the pores. X-ray photoelectron spectroscopy shows the absence of contamination after the functionalization process. Moreover, it confirms the thermal stability of the Au- and Pd-functionalized three-dimensional graphene up to 530 degrees C. Our approach opens new avenues for utilizing three-dimensional graphene as a versatile platform for catalytic applications, sensors, and energy storage and conversion. We report a new technique for fabricating metal-functionalized three-dimensional epitaxial graphene on porous SiC. The process is clean and scalable. The fabricated material exhibits high chemical and thermal stability, and versatility.

In this paper, we demonstrate the deposition of 3C-SiC thin films on SiO2 using the alternating supply deposition (ASD) technique in a low-pressure chemical vapor deposition (LPCVD) furnace. We provide data of the thin film properties showing strong dependencies on the process gas flow rates of silane, propane and hydrogen. For comparative reasons all gas flow compositions were performed on <100> silicon and SiO2 . A decreased rate of growth per cycle of similar to 37 % was discovered on SiO2 . X-ray photoelectron spectroscopy (XPS) depth profiling revealed an oxygen content of 7.5 % +/- 2.5 % throughout the entire thin film when grown on SiO2 . High resolution transmission electron microscopy (HRTEM) showed a 15 nm amorphous carbon layer at the 3C-SiC/Si interface. Conversely, on SiO2 a 10 nm graphite layer was determined as intermediate layer leading to prominent <111> 3C-SiC X-ray diffraction (XRD) peaks. Independent of the substrate type a similar microstructure is observed in cross-sectional analyses. Atomic force microscopy (AFM) surface roughness measurements showed for all SiO2 thin films lower values with a minimum of 4.9 nm (RMS), compared to 7 nm on Si. The electrical film resistivity was determined on SiO2 with CTLM analysis, depending on the process gas composition. The gained knowledge is beneficial for MEMS applications, where tailored 3C-SiC-on- SiO2 structures are desired.

Porosifying the surface of a single crystalline silicon carbide (4H-SiC) wafer with the means of metal assisted photo chemical etching (MAPCE) promotes the adhesion of an electroplated nickel (Ni) layer. By utilizing a mechanical peel-off process, a Ni layer with tailored mechanical stress is peeled off such that also a thin layer of 4H-SiC is teared apart from the wafer as well.

This paper reports on the impact of grain size on the quality factor of poly-crystalline-diamond (PCD) MEMS resonators. For this purpose, the grain size of each PCD thin film is tuned from tens of nm to several mu m via the methane flow rate during the chemical vapor deposition process on silicon substrates. In addition, a PCD stack, where the growth regime is changed during the deposition run, is studied. From these thin films purely mechanical plate-type resonators were fabricated and photo thermally actuated. The resonance characteristics are studied with Laser-Doppler vibrometry. Measurements are performed in a regime where material losses are the dominant dissipation mechanism and others like gas damping and thermo-elastic damping can be neglected. Furthermore, the resonator devices are assumed to have similar anchor losses across all thin films. It is shown, that quality factors of PCD MEMS-resonators can be increased by more than one order of magnitude when increasing the grain size in the investigated range.

The 5th generation (5G) wireless telecommunication standards with newly defined frequency bands up to 6 GHz are currently established around the world. While outperforming surface acoustic wave (SAW) filters above 1 GHz, bulk acoustic wave (BAW) resonators in multiplexers for radio-frequency front-end (RFFE) modules continuously face higher performance requirements. In contrast to free-standing bulk acoustic resonators (FBARs), solidly mounted resonator (SMR) technology uses an acoustic Bragg mirror, which has already been successfully applied for several GHz applications. In this work, we investigate the potential of amorphous hydrogenated silicon-oxycarbonitride (a-SiOCN:H) thin films synthesized with low-temperature plasma-enhanced chemical vapor deposition (PECVD) as a low acoustic impedance (low-Z) material. Compared to the state-of-the-art where in Bragg mirrors up to now SiO2 is used as standard, the acoustic impedance ratio against the high-Z material tungsten (W) is enhanced for a better device performance. To limit the expected increase in viscous loss when the acoustic impedance is reduced, to a minimum, predominantly the mass density was reduced while keeping the mechanical elasticity high. By doing so, acoustic impedance values as low as 7.1 MRayl were achieved, thereby increasing the impedance ratio of high-Z to low-Z materials from 8:1 up to 14:1.

In this paper, we will provide information on the growth mechanism of 3C-SiC using alternating supply deposition (ASD). SiH4 and C3H8 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.