Low temperature growth of nanocrystalline diamond: Insight thermal property

One of the limitations of materials for high-power devices and structural coatings applications is heat dissipation. Diamond is a suitable material for heat distribution due to its high thermal conductivity. Nevertheless, it is usually grown at high temperature (800–1200 ◦C), which limits its use as a coating for substrates vulnerable to degradation at high temperatures. In this work, it is studied the effect of the distance between the plasma source and substrate on the growth of nanocrystalline diamond layers on silicon substrates at low temperature (<450 ◦C) by microwave linear antenna plasma enhanced chemical vapour deposition (MW-LA-PECVD) in pulse mode. The nanocrystalline diamond films have been analysed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. Finally, the superficial thermal conductivity of the diamond layers was determined by scanning thermal microscopy-AFM (SThM-AFM).6 página

Berkovich Nanoindentation on AlN Thin Films

Berkovich nanoindentation-induced mechanical deformation mechanisms of AlN thin films have been investigated by using atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM) techniques. AlN thin films are deposited on the metal-organic chemical-vapor deposition (MOCVD) derived Si-doped (2 × 1017 cm−3) GaN template by using the helicon sputtering system. The XTEM samples were prepared by means of focused ion beam (FIB) milling to accurately position the cross-section of the nanoindented area. The hardness and Young’s modulus of AlN thin films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option. The obtained values of the hardness and Young’s modulus are 22 and 332 GPa, respectively. The XTEM images taken in the vicinity regions just underneath the indenter tip revealed that the multiple “pop-ins” observed in the load–displacement curve during loading are due primarily to the activities of dislocation nucleation and propagation. The absence of discontinuities in the unloading segments of load–displacement curve suggests that no pressure-induced phase transition was involved. Results obtained in this study may also have technological implications for estimating possible mechanical damages induced by the fabrication processes of making the AlN-based devices

Diamond: a material for acoustic devices

Diamond has been foreseen to replace silicon for high power, high frequency electronic applications or for devices that operates in harsh environments. However, diamond electronic devices are still in the laboratory stage due to the lack of large substrates and the complexity of diamond doping. On another hand, surface acoustic wave filters based on diamond are commercially available. Diamond is especially suited for acoustic applications because of its exceptional mechanical properties. The other properties of diamond such as bio-inertness and chemical stability certainly make of diamond a key material for the next generation of acoustic sensors. In this article, we try to detail the interest of diamond films in composite acoustic applications and review the different type of acoustic devices/sensors

Growth of cubic boron nitride films by ibad and triode sputtering: development of intrinsic stress

Two methods are employed to evidenced the stress behavior in c-BN films. On the one hand, in depth stress profile of c-BN film, deposited by ion beam assisted evaporation, was performed by recording infrared spectra and substrate curvature after reactive ion etching (RIE) steps. It shows a peak of stress up to - 17 GPa in the h-BN basal layer and a stress relaxation when the cubic phase appears. On the other hand, dynamic stress profiles of c-BN films deposited by a triode sputtering system, are obtained by recording infrared spectra and substrate curvature after various c-BN deposition times, with the same experimental conditions. Likewise, a peak of stress of - 12 GPa is unmistakably observed in the h-BN basal layer followed by a stress release during c-BN nucleation, where an average value of - 12 GPa is observed in the c-BN film volume. These results provide a support for the stress model proposed by McKenzie even if along with a minimum stress a high level of densification of the layer is needed. (C) 2001 Elsevier Science B.V. All rights reserved

Hall Effect Characterization of 4H-SiC MOSFETs: Influence of Nitrogen Channel Implantation

International audienceEffect of a shallow nitrogen implantation in the channel region of n-channel 4H-SiC Hall bar MOSFETs on their electrical properties has been characterized by Hall effect. A significant improvement of Hall mobility in normally-off devices is observed with increasing nitrogen implantation dose up to 10 13 cm-2 with a peak Hall mobility of 42.4 cm 2 .V-1 .s-1. Coulomb scattering as dominant scattering mechanism up to room temperature is demonstrated using temperature dependent MOS-Hall effect characterization