Research On Key Technology Of Sapphire High Temperature Pressure Sensor

In-situ testing of pressure parameters has a wide range of needs in ultra-high temperature environments such as aerospace,environmental energy,mining and metallurgy,biomedical and other fields,especially in advanced engines.For example,the mesurement and extraction of in-situ pressure parameters in high temperature and harsh environments can improve the combustion efficiency of combustion chambers in turbine engines,ramjet engines and rocket engines.In addition,accurate pressure mesurements are of great significance for enhancing engine reliability,stability,safety,and extending working life.Sapphire is a single crystal?-Al₂O₃,and it has been considered as an ideal material for ultra-high temperature applications owing to its high melting point?²040°C?,high hardness,good mechanical properties,thermal stability,electrical insulation,chemical resistance and excellent optical properties.Research on sapphire high temperature pressure sensors is of great value in the development of high temperature pressure testing.For the test requirements of pressure parameters in high temperature and harsh environments,two kinds of sapphire pressure sensors suitable for high temperature environments were developed,namely wireless passive sapphire high temperature pressure sensor and al-sapphire fiber optic Fabry-Perot high temperature pressure sensor.In-depth research on the sensor structural design and the key technology of sensor preparation has been carried out.The main research contents include:?1?Structure and parameter design of sapphire high temperature pressure sensorAccording to the pressure diaphragm sensitive principle,combined with different signal transmission and extraction methods,a wireless passive sapphire high temperature pressure sensor based on LC resonance and an all-sapphire fiber optic high temperature pressure sensor based on Fabry-Perot interference structure were designed.According to the principle of sensitive diaphragm design and different signal testing,the structural parameters of the two sensors were designed and verified by finite element simulation.?2?Research on sapphire wafer bonding technologyThe sapphire wafer bonding process combined with oxygen plasma surface activation treatment and high temperature annealing was developed to solve the key problem of airtight chamber preparation in sapphire high temperature pressure sensor.The sapphire direct bonding technique and the sapphire indirect bonding technique with amorphous Al₂O₃ film as the intermediate layer were investigated.Firstly,the effect of oxygen plasma surface activation treatment on sapphire pre-bonding was analyzed and verified,the optimal high-temperature bonding process conditions were determined,and two different sapphire bonding structures including sapphire direct bonding structure and sapphire indirect bonding structure were realized.The bonding strength and interface quality of the two sapphire bonded structures were tested and compared by tensile test,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?.The results show that the interfaces of the two sapphire bonded structures were atomically connected and the bonding strength exceeded the strength of the sapphire substrate.The microscopic mechanism of sapphire wafer bonding was revealed by combining the contact angle test results of plasma activation treatment with the microscopic characterization results of the bonding interface.Finally,through airtight leak detection experiments and optical transmission characteristics studies,it is proved that the airtightness and light transmittance of the bonding interface can meet the needs of sensor applications.?3?Fabrication of sapphire high temperature pressure sensorFor the wireless passive sapphire high temperature pressure sensor,the sapphire sealed pressure cavity was prepared by investgating the key processes of sapphire etching,sapphire thinning,and direct bonding.The metal urgical integration of the capacitor plates and the inductor coils with the substrate was achieved by the screen printing process.For the al-sapphire fiber-optic Fabry-Perot high temperature pressure sensor,the sensitive head was fabricated by direct bonding of a three-layer structure,including a sapphire sensitive diaphragm,a sapphire etching wafer and a sapphire base.The as-fabricated sensors were tested by constructing a high temperature-pressure composite test system.For the wireless passive sapphire high temperature pressure sensor,the characterization in high-temperature pressure environments successfully demonstrates the sensing capabilities for pressures from 20 kPa to 600 kPa up to 600°C.At 600°C,the sensor sensitivity reaches as high as 10.37 kHz/kPa.Compared with other LC type high temperature pressure sensors,the wireless passive LC high temperature pressure sensor based on sapphire direct bonding technology proposed in this paper is simple in manufacturing process,compact in size and high in sensitivity,which can effectively avoid the deformation and collapse of the embedded cavity.For the al-sapphire fiber optic high temperature pressure sensor,the experimental results show that the sensor exhibits a good linear response in the temperature range of 25°C⁹00°C,and the sensor's sensitivity reaches 3.035 nm/kPa at 900°C,which has reached the domestic leading level.The two sapphire high temperature pressure sensors developed in this paper have outstanding application value in pressure testing under high temperature environments.