Silicon carbide (SiC) has promising potential for pressure sensing in a high temperature and harsh environment due to its outstanding material properties. In this work, a 4H-SiC piezoresistive pressure chip fabricated based on femtosecond laser technology was proposed. A 1030 nm, 200 fs Yb: KGW laser with laser average powers of 1.5, 3 and 5 W was used to drill blind micro holes for achieving circular sensor diaphragms. An accurate per lap feed of 16.2 μm was obtained under laser average power of 1.5 W. After serialized laser processing, the machining depth error of no more than 2% and the surface roughness as low as 153 nm of the blind hole were measured. The homoepitaxial piezoresistors with a doping concentration of 10¹⁹ cm⁻³ were connected by a closed-loop Wheatstone bridge after a rapid thermal annealing process, with a specific contact resistivity of 9.7 × 10⁻⁵ Ω cm². Our research paved the way for the integration of femtosecond laser micromachining and SiC pressure sensor chips manufacturing.

Femtosecond laser ablation has become one of the important structural processing methods for the third-generation semiconductor material, silicon carbide (SiC), and it is gradually being employed in the manufacture of microelectromechanical systems and microelectronic devices. Experimental study has been performed on infrared single and multiple pulses (1035 nm) femtosecond laser ablation of SiC at various processing parameters. Diameters of laser ablation spots on 4H-SiC were measured to estimate the absorption threshold for material modification and structural transformation, which were 2.35 J/cm² and 4.97 J/cm², respectively. In the multiple-pulse scribing ablation for microgrooves, the ablation threshold dropped to 0.70 J/cm² due to the accumulation effect when the effective pulse number reached 720. The calculated average of the thermally stimulated ablation depth of 4H-SiC is 22.4 nm, which gradually decreased with the raising of the effective pulse number. For obtaining square trenches with precise and controllable depths and a smooth bottom in 4H-SiC, the effects of processing parameters on the material removal rate and surface roughness are discussed. The ablation rate per pulse is almost constant, even if the effective pulse number varies. The reduction of laser spot overlapping ratio in x direction has a greater weakening effect on the material removal rate than that in y direction. The precise amount of material removal can still be controlled, while modulating the surface roughness of the ablated features by changing the hatch rotation angle. This research will help to achieve controllable, accurate, and high-quality machining results in SiC ablation, using infrared femtosecond laser.

Making full use of the availability and excellent performance of silicon carbide (SiC) substrates, SiC-based MEMS piezoresistive pressure sensors have been extensively investigated. In this article, a femtosecond laser was adopted instead of dry plasma etching technology to realize mass fabrication of 128 bulk SiC piezoresistive pressure sensor diaphragms from half a 4H-SiC wafer. These diaphragms were completed in 2 h with an average thickness error of less than 7.5% and a surface roughness of 108 nm. The 4H-SiC sensor was characterized with a nonlinear error of 0.13% FS and a repeatability error of 1.49% FS in the pressure range of 0–5 MPa at room temperature. The tolerance to temperature was measured in high and low temperature of −50 °C–300 °C with the temperature coefficient of sensitivity (TCS) of −0.11% FS°C at −50 °C and −0.16% FS°C at 300 °C. In addition, resistance measurement of the sensor in strongly alkaline corrosive solution proved the robustness with an average daily drift of only 1.61%. This integrated solution that combines femtosecond laser technology and MEMS processing provides exciting opportunities for rapid and large-scale manufacturing of bulk SiC pressure sensors.

This paper presents a SOI piezoresistive pressure sensor with the crossbeam membrane. The roots of the crossbeam were widened, which solved the problem of the poor dynamic performance of small-range pressure sensors working at a high temperature of 200 °C. A theoretical model was established to optimize the proposed structure, which combined the finite element and the curve fitting. Using the theoretical model, the structural dimensions were optimized to obtain the optimal sensitivity. During optimization, the sensor nonlinearity was also taken into consideration. The sensor chip was fabricated by MEMS bulk-micromachining technology, and Ti/Pt/Au metal leads were prepared to improve the sensor ability of high-temperature resistance over a long time. The sensor chip was packaged and tested, and the experimental results show the sensor achieved an accuracy of 0.241% FS, nonlinearity of 0.180% FS, hysteresis of 0.086% FS and repeatability of 0.137% FS at the high temperature. Given the good reliability and performance at the high temperature, the proposed sensor provides a suitable alternative for the measurement of pressure at high temperatures.

The widespread application of bulk silicon carbide in pressure sensing has been largely limited by the slow etching rate of traditional micromachining processes. This paper proposes a piezoresistive bulk 4H-SiC pressure sensor with diaphragm which has controllable thickness realized by femtosecond laser. A modified stress model was established by finite element analysis to fit the SiC circular diaphragm prepared by laser micromachining. The test results proved that the fabricated sensor with diaphragm thickness of $60 \mu \text{m}$ had sensitivity of 1.42 mV $/\text{V}/$ MPa under the applied pressure of up to 5 MPa at room temperature. Small hysterisis error of 0.17 %/FSO and nonlinearity of 0.20 % $/$ FSO was achieved. The sensor was able to work in a broad temperature range with the temperature coefficient of sensitivity of −0.23% FSO/°C at −50 °C and −0.10% FSO/°C at 300 °C. The dynamic response results exhibited that the resonance frequency of the sensor was 60.11 kHz and the rise time was $18 \mu \text{s}$ . The SiC pressure sensor also had the noise-limited resolution of 0.42 kPa and the dynamic range of 44.9 dB. The research demonstrates the prospect of employing the femtosecond laser technology to prepare bulk SiC pressure sensors for extreme temperature environment.

Due to material plastic deformation and current leakage at high temperatures, SOI (silicon-on-insulator) and SOS (silicon-on-sapphire) pressure sensors have difficulty working over 500 °C. Silicon carbide (SiC) is a promising sensor material to solve this problem because of its stable mechanical and electrical properties at high temperatures. However, SiC is difficult to process which hinders its application as a high-temperature pressure sensor. This study proposes a piezoresistive SiC pressure sensor fabrication method to overcome the difficulties in SiC processing, especially deep etching. The sensor was processed by a combination of ICP (inductive coupled plasma) dry etching, high-temperature rapid annealing and femtosecond laser deep etching. Static and dynamic calibration tests show that the accuracy error of the fabricated sensor can reach 0.33%FS, and the dynamic signal response time is 1.2 μs. High and low temperature test results show that the developed sensor is able to work at temperatures from −50 °C to 600 °C, which demonstrates the feasibility of the proposed sensor fabrication method.