# High-Pressure Sensors Based on Laser-Manufactured Sintered Silicon Carbide
## 1 Introduction
In addition, when micro-sized features are required several technological issues can arise, e.g., low quality surfaces and cracks formation. In recent years, different unconventional techniques have been investigated to respond to the increasing demand of machining of advanced ceramic materials. Specifically, electrical discharge machining (EDM) and laser beam machining are the main alternatives investigated in the experimental works. However, materials can be machined by EDM whether their electrical conductivity is greater than \(10^{-2}\) S/cm [17]. Ceramics generally does not satisfy this requirement. In fact, SiC ceramics exhibit a typical electrical conductivity of about \(10^{-15}\) S/cm, even if it can be tailored to display very diverse values within a range from \(10^{-11}\) to \(10^{7}\) S/cm [18], but this is not the case. In order to allow EDM of these materials, an electrically conductive secondary phase is usually added to the insulating matrix [19]. On the other hand, focused pulsed lasers offer a virtual solution due to the fact that their effectiveness is independent of the mechanical and electrical properties of the machined materials [20]. MEMSs represent the field in which the peculiar physical properties of SiC and the versatility of laser treatments meet and several works also demonstrate the feasibility of miniature MEMS devices based on c-SiC [21]. Conventional methods of manufacturing SiC-based MEMS devices use the deep reactive ion etching and the electrochemical etching techniques [22]. In such cases, etching rate is very low and etching morphology is very poor. Conversely, laser manufacturing achieves higher etch rates and no additional mask material is necessary [23]. Moreover, laser ablation of SiC has been carried out with different pulse durations, from nanosecond to femtosecond regime, with higher etching rates [24]. Femtosecond lasers produce little contamination and low heat affected zone, but they are capable of slower removal rates if compared with nanosecond lasers [25]. Furthermore, the ns-pulsed lasers are machining systems cheaper than the fs-pulsed ones. Then, the most widely used laser system in practice is the nanosecond pulsed laser. In this context, SiC-based MEMS sensors find application in several industrial fields, from avionics to automotive, from spacecraft systems to turbines' parts. SiC has already been used for pressure sensors able to operate in high-temperature [26; 27] and MEMS-based sensors and actuators [28; 29], finding application in several fields, from automotive to aerospace, from healthcare to consumer electronics [30; 31]. Indeed, as aforementioned, SiC represents the elective material for the fabrication of mechanical components able to work under severe conditions. Pressure sensors able to work in harsh environments are fundamental for combustion chambers and gas turbine engines monitoring [32]. Crystalline-SiC (c-SiC) piezoresistive and capacitive pressure sensors, as well as c-SiC diaphragms on silicon have been reported in the literature [26; 33]. Moreover, polycrystalline SiC (poly-SiC) diaphragms on poly-SiC substrates for pressure sensors realization also demonstrated their effectiveness in high temperature conditions [34; 35]. In our research, S-SiC membranes, fabricated by means of laser treatment able to engrave cylindrical samples, have been used for pressure sensors fabrication. The technological steps necessary for the realization of the sensitive elements are mainly reduced to the laser treatment of S-SiC, overcoming difficulties related to complex etching processing of c-SiC, as well as lowering the costs related to the pristine material growth. Guaranteeing immunity to electromagnetic interference, fiber-optic pressure sensors [36] and Fabry-Perot (FP) interferometric sensors [37; 38; 39] have been proposed to operate in hostile and aggressive media. The feasibility of a low-finesse FP pressure sensor has been demonstrated for thin diamond membranes [39].