3C-SiC — From Electronic to MEMS Devices

Since decades, silicon carbide (SiC) has been avowed as an interesting material for high-power and high-temperature applications because of its significant properties including its wide bandgap energy and high temperature stability. SiC is also professed as an ideal candidate for microsystem applications due to its excellent mechanical properties and chemical inertia, making it suitable for harsh environments. Among the 250 different SiC polytypes, only 4H, 6H and 3C-SiC are commercially available. The cubic structure, 3C-SiC, is the only one that can be grown on cheap silicon substrates. Hence, 3C-SiC is more interesting than any other polytype for reducing fabrication costs and increasing wafer diameter. This huge property has been evidenced for more than 30 years using chemical vapor deposition. Despite this key achievement and the growing interest for silicon carbide, no 3C-SiC-based devices can be found on the market whereas 4H-SiC-based devices are more and more largely commercialized. Even so, important headways have been reached for electrical and microelectromechanical systems (MEMS) applications. Therefore, the purpose of this chapter is to address concerns related to electronic applications and MEMS fabrication of 3C-SiC-based devices, trying to give a broad overview on specific issues and challenging solutions

Realization of minimum number of rotational domains in heteroepitaxied Si(110) on 3C-SiC( 001)

Structural and morphological characterization of a Si(110) film heteroepitaxied on 3C-SiC(001)/ Si(001) on-axis template by chemical vapor deposition has been performed. An antiphase domain (APD) free 3C-SiC layer was used showing a roughness limited to 1 nm. This leads to a smooth Si film with a roughness of only 3 nm for a film thickness of 400 nm. The number of rotation domains in the Si(110) epilayer was found to be two on this APD-free 3C-SiC surface. This is attributed to the in-plane azimuthal misalignment of the mirror planes between the two involved materials. We prove that fundamentally no further reduction of the number of domains can be expected for the given substrate. We suggest the necessity to use off-axis substrates to eventually favor a single domain growth

Screening and engineering of colour centres in diamond

We present a high throughput and systematic method for the screening of colour centres in diamond with the aim of searching for and reproducibly creating new optical centres down to the single defect level, potentially of interest for a wide range of diamond-based quantum applications. The screening method presented here should, moreover, help to identify some already indexed defects among hundreds in diamond (Zaitsev 2001 Optical Properties of Diamond (Berlin: Springer)) but also some promising defects of a still unknown nature, such as the recently discovered ST1 centre (Lee et al 2013 Nat. Nanotechnol. 8 487; John et al 2017 New J. Phys. 19 053008). We use ion implantation in a systematic manner to implant several chemical elements. Ion implantation has the advantage of addressing single atoms inside the bulk with defined depth and high lateral resolution, but the disadvantage of producing intrinsic defects. The implanted samples are annealed in vacuum at different temperatures (between 600 degrees C and 1600 degrees C with 200 degrees C steps) and fully characterised at each step in order to follow the evolution of the defects: formation, dissociation, diffusion, re-formation and charge state, at the ensemble level and, if possible, at the single centre level. We review the unavoidable ion implantation defects (such as the GR1 and 3H centres), discuss ion channeling and thermal annealing and estimate the diffusion of the vacancies, nitrogen and hydrogen. We use different characterisation methods best suited for our study (from widefield fluorescence down to subdiffraction optical imaging of single centres) and discuss reproducibility issues due to diamond and defect inhomogeneities. Nitrogen is also implanted for reference, taking advantage of the considerable knowledge on NV centres as a versatile sensor in order to retrieve or deduce the conditions and local environment in which the different implanted chemical elements are embedded. We show here the preliminary promising results of a long-term study and focus on the elements O, Mg, Ca, F and P from which fluorescent centres were found.Peer reviewe

Etude des propriétés électroniques et vibrationnelles des surfaces de graphite cristallin avant et après exposition à des espèces ioniques

Le travail présenté ici traite de l'apport de la spectroscopie de perte d'énergie d'électrons lents à haute résolution (HREELS) pour l'étude des propriétés électroniques et vibrationnelles des surfaces de graphite cristallin, avant et après traitement de la surface par bombardement ionique à l'argon et à l'hydrogène. Dans le cas des surfaces cristallines non bombardées, on a pu mettre en évidence un comportement atypique de la section efficace du mode plasmon basse énergie sur du graphite HOPG, contraire aux prévisions de la théorie diélectrique. Ce comportement se retrouve sur le mode phonon de Fuchs Kliewer, visible sur la reconstruction graphite du carbure de silicium, et s'accompagne d'une modification de la signature de perte entre cette reconstruction et la reconstruction 3x3 de ce matériau. On a montré que l'introduction, dans la fonction diélectrique du matériau, de termes associés aux transitions inter bandes, qui surviennent de part et d'autre du niveau de Fermi dans le schéma de bande du graphite, amène à une description qualitative de la forme des spectres dans le cas du HOPG mais aussi du SiC. Les résultats obtenus après bombardement des surfaces de graphite HOPG à l'argon et à l'hydrogène montre une forte sensibilité du mode plasmon basse énergie à la présence de défauts interstitiels. On a pu corréler les variations en terme de position et d'amortissement du plasmon avec la concentration et le type de défaut créé par le bombardement. Par ailleurs, les surfaces bombardées présentent une réactivité accrue aux espèces atomiques. Cela se traduit par l'observation des modes de vibration C-H, qui n'apparaissent qu'après bombardement puis exposition aux neutres. On interprète ces résultats comme étant dus à la présence de défauts de surfaces n'impliquant pas d'atomes d'hydrogène mais constituant des sites précurseurs de réactivité sur lesquels va s'initier l'érosion chimiqueAIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Oxygen isotope variations in Mg-rich olivines from type I chondrules in carbonaceous chondrites

International audienceUsing high-resolution cathodoluminescence (HR-CL) panchromatic imaging for the location of high-precision oxygen three-isotope analyses by secondary ion mass-spectrometry (SIMS), this study is aimed at characterizing the oxygen-isotope variations in Mg-rich olivines (≥Fo99) of selected type I chondrules from the Yamato (Y) -81020 CO3.05 (Ornans-type) carbonaceous chondrite. Cathodoluminescence being extremely sensitive to faint changes in CL activator/quencher concentrations (Al, Cr, Mn, Fe) allows us to describe various overlooked cycles of growth and dissolution in Mg-rich olivines, which strongly suggest an intimate relationship with their gaseous environment during their formation. The present study confirms significant Δ17O variations of ten ‰ in Mg-rich olivines but does not support the relationship previously found between Mg# [MgO/(MgO + FeO) × 100, mol%] and Δ17O among type I chondrules, nor the interpretation of redox changes that has been made of it. We instead show that Mg-rich olivines in Y-81020 chondrules exhibit a prominent 16O-enriched and 16O-depleted bimodal distribution, which is considered as the most primordial signature of type I chondrules from Y-81020 and very likely other carbonaceous chondrites. This signature is interpreted as a snapshot of the early stages of a mixing occurring between two clouds/environments in which chondrules formed and evolved by gas-melt interaction and mixed according to hydrodynamical instabilities imposed by the process responsible for the mixing. As far as this study allows, O-isotope variations of Mg-rich olivines seems to account for large scale dynamical instabilities while chemical variations highlighted by HR-CL (dissolution/growth) bear witness of smaller scale instabilities very likely occurring in the immediate vicinity of the chondrules. Without being able to decide on plausible astrophysical settings yet, we note however that processes like disruptive and vaporizing collisions between planetesimals offer a range of processes and physicochemical conditions, e.g., expansion, decompression, dynamical instabilities, that deserve to be explored in more detail, some of which resembling those highlighted in this study, e.g., gas-melt interaction, partial pressure fluctuations, heterogeneous materials, gas mixing

Direct Insight into Grains Formation in Si Layers Grown on 3C-SiC by Chemical Vapor Deposition

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Original 3C-SiC micro-structure on a 3C-SiC pseudo-substrate

International audienceAmong the different silicon carbide polytypes, 3C–SiC is very interesting for Micro-Electro-MechanicalSystems (MEMS) applications. This interest could benefit from the development of multi stacked Si/SiC heterostructures as illustrated by the achievement of a continuous silicon monocrystalline thin film on 3C–SiC epilayers deposited on (1 0 0) silicon substrates. Based on this recent result, an original monocrystalline 3C–SiC/Si/3C-SiC/Si hetero-structure has been developed by Low Pressure Chemical Vapor Deposition with a two-step process. This kind of structure allows the selective etching of the silicon epilayer in order to define an original 3C–SiC micro-structure. By wet etching, the remaining silicon film, used as a sacrificial layer, can be then etched, resulting in a monocrystalline 3C-SiC membrane on a 3C-SiC pseudosubstrate. This new and original approach opens the field for future MEMS devices

Toward high-quality 3C–SiC membrane on a 3C–SiC pseudo-substrate

International audienceThe cubic polytype of silicon carbide is an interesting candidate for Micro-Electro-Mechanical-Systems (MEMS) applications due to its tremendous physico-chemical properties. The recent development of multi-stacked Si/SiC heterostructures has demonstrated the possibility to obtain a (110)-oriented 3C–SiC membrane on a 3C–SiC pseudo-substrate, using a silicon layer grown by low pressure chemical vapor deposition as a sacrificial one. However, the (110) orientation of the 3C–SiC membrane led to a facetted and rough surface which could hamper its use for the development of new MEMS devices. Then, in this contribution, an optimized growth process is used to improve the surface quality of the 3C–SiC membrane. The progress relies on the mastering of a (111) orientation for the SiC film, resulting in a smooth surface. Such an optimized structure could be the starting point for the achievement of new MEMS devices in medical or harsh environment applications

Silicon-carbide-based MEMS for gas detection applications

Gas sensors are devices that can detect and/or discriminate gases in their surroundings. Some of these devices are based on vibrating structure covered with a coating sensitive to the species to detect. But such a layer can cause device failures issues like ageing, low reliability and high response time. Nonetheless, gas sensors are of importance for industrial environments in many applications. In addition, in some cases, the sensors must operate in harsh environments, that can lead to a severe degradation of the devices.In this paper, we propose to review different MEMS devices, without any sensitive layer, for gas detection applications. The objective is to measure a physical property of the gas in order to determine its concentration. With the microsystem devices, limits of detection as low as 0.2 % has been obtained, illustrating the capabilities of the structures elaborated. And in our case, due to the absence of sensitive film that must be adapted according to the species to detect, it leads to generic sensors, compatible with many different gases. Moreover, by combining the measures of 2 physical parameters, the discrimination of the gases, with their respective concentrations, is accessible

Turning the undesired voids in silicon into a tool: In-situ fabrication of free-standing 3C-SiC membranes

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