However, the most common diamond pressure sensors typically exploit piezoresistive properties of boron-doped material. Indeed, due to aforementioned excellent mechanical characteristics, CVD diamond membranes are suitable for pressure sensors fabrication. For this reason, for several years, diamond has been considered a suitable material for pressure sensors used in harsh and aggressive environments. Nowadays, equipment able to measure pressure and pressure variations, even in aggressive media, is required. In this context, pressure has always been one of the most important and critical parameters to be measured in various fields, including automotive, industrial, biomedical, and aerospace. Such a pre-treatment provides homogeneous seeding with a nucleation density over 10 9 cm −2. In particular, crystalline silicon wafers are seeded with nanodiamond (ND) particles using an ultrasonic bath in water-based suspension of ND powder. For example, dry polishing allows a uniformly sown diamond layer to be obtained. Pre-treatment of substrates prior to diamond deposition significantly improves the nucleation density also for crystalline silicon. The use of a porous silicon layer demonstrated its effectiveness, providing nucleation sites by trapping the diamond seeds in its pores, thus, obtaining a good nucleation density and uniform diamond deposition. Over the years, many efforts have been made to improve nucleation efficiency with respect to the orientation of the nucleated diamond grains.
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A fundamental step is nucleation enhancement, because by this phase, it is possible to obtain different configurations with different mechanical, thermal, and electrical characteristics. Homogeneous diamond films with a low defect density are required in several applications. ĭiamond films with thicknesses ranging from a few microns to hundreds of microns are usually grown on silicon substrates by the microwave plasma-assisted CVD technique (MPCVD).
Moreover, overcoming the lack of efficient n-doping effect at room temperature of diamond, hence, the fabrication of p-n junction-based devices, post-treatments based on either laser- or ion beam-processing are able to induce a local transformation of diamond into graphite, representing a powerful methodology for the development of novel all-carbon devices for optoelectronics and photonics applications. For its high atomic volume density in lattice (10 23 atoms/cm 3) and its radiation hardness, it represents a key solution when used as an active material for the fabrication of miniaturized detectors for impinging charged particles, as well as for soft X-rays and UV detection. First of all, being a wide bandgap semiconductor (5.47 eV at room temperature), it offers a large number of advantages over other electronic materials, resulting particularly attractive for the realization of electronic devices used at temperatures in excess of 300 ☌. SC diamond of very high purity can be obtained having an electronic grade quality, while PCD display interesting characteristics in terms of mechanical, electronic, and optical properties combined with large film area. Modern CVD techniques are used for growth of single crystal (SC) and polycrystalline diamond (PCD) films. The proposed sensing system represents a valid alternative to conventional solutions, overcoming the drawback related to electromagnetic interference on the acquired weak signals generated by standard piezoelectric sensors. Preliminary characterizations demonstrate the feasibility of such diamond-on-Si membrane structure for pressure transduction. Exploiting the excellent properties of Chemical Vapor Deposition (CVD) diamond, in terms of high hardness, low thermal expansion, and ultra-high thermal conductivity, the realized sensors have been characterized up to 16.5 MPa at room temperature. Hence, pressure is evaluated by measuring the cavity length by an optoelectronic system coupled to the single mode fiber.
The FP cavity is defined by the end-face of a single mode fiber and the diamond diaphragm surface. The sensing element is based on a simple low-finesse Fabry–Pérot (FP) interferometer. Thin polycrystalline diamond films chemically vapor deposited on thinned silicon substrates were used as membranes for pressure sensor fabrication by means of selective chemical etching of silicon.
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