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Piezoresistive coefficients of materials are of great significance to the design of piezoresistance based devices. This paper proposed an in situ extraction method to determine the piezoresistive coefficients of n-type 4H-SiC, which requires no separate experimental study on the material properties and can directly obtain device-level parameters. Two types of all-SiC piezoresistive pressure sensors based on the SiC sealed cavity structure with different piezoresistor arrangements were fabricated and characterized. Through parameter fitting of the experimental data of pressure sensors and the numerical calculation results obtained by parameterization finite element analysis method, the longitudinal and transverse piezoresistive coefficients $\pi _{11}$ and $\pi _{12}$ that resulted in the best fit were found to be $- 3.4\times10$ −11 Pa−1 and $6.15\times10$ −11 Pa−1, respectively. The extracted parameters were also verified to prove the reliability of the extraction method. The above research has significant value for the understanding of piezoresistive effect in materials and provides guidance for the design and performance optimization of SiC-based sensors. [ABSTRACT FROM AUTHOR]

Silicon carbide has promising potential in high temperature pressure sensors due to its excellent material properties. This paper presents a piezoresistive n-type 4H-SiC absolute pressure sensor based on an all-SiC sealed cavity structure, which provides a new approach for the development of SiC pressure sensors. Firstly, the structural design of the pressure sensor with the measurement range of 10 MPa was conducted through the finite element method. After that, a SiC diaphragm with controllable thickness and high surface quality was achieved through grinding and chemical mechanical polishing process, which indicated that the root mean square surface roughness was 0.168 nm and the relative standard deviation of diaphragm thickness was 0.24%. A patterned SiC substrate with shallow grooves obtained by shallow etching process was directly bonded onto the SiC diaphragm to form the sealed cavity structure. Finally, the performance test of the fabricated sensor at 30 °C indicated that the sensitivity was 1.56 mV/V/MPa, the nonlinearity was 0.034% FS, and the accuracy was 0.29% FS. The temperature coefficient of sensitivity exhibited a negative value of −0.134% FS/°C at 250 °C. Moreover, the maximum temporal drift of zero pressure output at 250 °C was only 0.12 mV in 14 hours after several high temperature aging tests. The above research demonstrates the application potential of the proposed SiC sealed cavity structure in all-SiC pressure sensors, which provides a technical foundation for the development of high temperature pressure sensors. [ABSTRACT FROM AUTHOR]

In this paper, we adopt Ni-based ohmic contacts of n-type 4H-SiC (silicon carbide), basing its applications on SiC pressure sensors, to explore the manufacturability and high temperature reliability problems of SiC metallization process, including the adhesion of metal layers, the influence of surface treatment on ohmic contact formation way between metal and SiC wafers, the failure problem caused by the thermal stress between the metal and the SiC wafer at high temperature and the high temperature reliability of the ohmic contact metal structure. By optimizing the process details, the specific contact resistance (ρc) can reach 2.05E-5 Ω·cm2; moreover, both ohmic contact and metal wiring structure can keep stable performance in 300 °C 60 h air environment. [ABSTRACT FROM AUTHOR]