Temperature sensors are widely used in industrial production, national defense and military fields. The traditional temperature sensors normally operate in a limited temperature range no more than 200 °C, which cannot be used for extreme high temperature detections. In this paper, a thermal protection method for the sensing graphene membrane is proposed and a graphene high temperature sensor has been fabricated and investigated. By growing a single silicon nitride (Si₃N₄) protective layer on top of graphene, our design not only solves the problem that graphene is easily oxidized at high temperature, but also prevents graphene from being polluted by impurities, which would lead to the degradation of graphene performance. We further explore the protective effect of Si₃N₄ layer with different thicknesses on the performance of the sensor. It has been found that the 400 nm Si₃N₄ protective layer gives the best protective capability. The sensor exhibits a positive temperature coefficient (PTC) from 50 to 600 °C and a maximal temperature coefficient of resistance (TCR) value of 0.29% °C⁻¹ at 150 °C is achieved. It has been demonstrated that our graphene high temperature sensor with protective layer structure maintains good stability not only at high temperature up to 600 °C, but also over a long-period of time under room temperature. In short, the high temperature sensor possesses a wide temperature measurement range with micro dimensions, a relatively high TCR and a smaller thermal hysteresis. The thermal protection approach proposed in this paper provides a new idea for the fabrication of high temperature pressure sensor, which is expected to be applied in aerospace engines and oil wells, etc.

The high-temperature pressure sensors have wide applications in aerospace, petroleum, geothermal exploration, automotive electronics, and other fields. However, the traditional silicon-based pressure sensors are restricted to pressure measurement under 120~{\circ }\text{C} and cannot be satisfied to measure the pressure of various gases or liquids in high temperature and other harsh environments. This article proposes a novel high-temperature pressure sensor based on graphene, in which a rectangular cavity is applied to improve the piezoresistive characteristics of the sensor. The unique of this sensor is that the graphene is coated by the silicon nitride (Si3N4) membrane, which could avoid the oxidation of graphene in high temperature and increase the temperature tolerance range. The sensor was placed at various temperatures ( 50~{\circ }\text{C} - 420~{\circ }\text{C} ) to explore the temperature characteristics, achieving a maximal temperature coefficient of resistance (TCR) of 0.322% {\circ }\text{C}{-{1}}. Moreover, the sensor with a 64 \times 9\,\,\mu \text{m}{{2}} cavity has a high pressure sensitivity of 5.32\times 10{-{4}} kPa {-{1}} , enabling a wide range from 100 kPa to 10 Pa. Experimental results indicate that the proposed sensor possesses superior pressure sensitivity, a wide pressure detection range, and a high-temperature tolerance of 420~{\circ }\text{C} , which provides new insight into fabricating high-temperature pressure sensors based on graphene and creates more applications in different fields.