| Viscosity is one of the most important fluid properties and is used to characterize the ability of a fluid to resist positional changes.Viscosity sensors are used in a wide range of applications in the biomedical,petrochemical,and automotive industries.For example,in the automotive industry,lubricating oils are used as engine lubricants,and the viscosity of the oil must be maintained within a specified range to provide the desired function.Viscosity measurements are typically performed using complex,large instruments that require constant calibration and long wait times.Therefore,the development of sensors that are miniaturized,low-cost,and capable of real-time viscosity monitoring have an important role in the progress of high-end sensors.Resonant sensors based on Micro-Electro-Mechanical System?MEMS?processing are ideal for developing and manufacturing new miniaturized sensors due to their high sensitivity,small size,low cost,and the ability to read data in real time.In particular,aluminum nitride?AlN?thin film materials,due to their unique CMOS compatibility characteristics,have attracted great attention in recent years based on MEMS processing AlN resonant sensors.In order to solve the problem of miniaturization and low-cost of viscosity sensors,this thesis develops a resonant viscosity sensor based on an aluminum nitride piezoelectric film using MEMS processing technology.Committed to solving the problems of high quality AlN piezoelectric film materials and MEMS processing technology of devices.In the viscosity measurement,since the resonance type sensor is susceptible to frequency drift due to the influence of the ambient temperature,it is of great research value to realize temperature decoupling in the resonance type viscosity sensor.On the other hand,with the demand for miniaturization of sensors in the biomedical field,the focus is also on the MEMS-processed resonant sensors.Many biosensings can be converted to sensing the amount of viscosity,such as in human coagulation time measurements.The biomedical field typically requires precise temperature control,so integrating temperature sensing and viscosity sensing in a single device is of great research value.The main work of this thesis includes:?1?The propagation characteristics of acoustic waves in solids are discussed.The Rayleigh wave modes and Lamb wave modes are derived.The feasibility of simultaneously exciting Rayleigh waves and Lamb waves in a resonant sensor is theoretically demonstrated.The liquid viscosity sensing mechanism of the AlN resonant viscosity sensor was established by analyzing the interaction between the Lamb wave mode and the liquid.According to Rayleigh wave and Lamb wave theory,the AlN resonant viscosity sensor chip is designed.The electromechanical equivalent model of the resonant viscosity sensor chip is derived.The mechanism of viscosity and temperature on the sensor is analyzed from the model.The vibration mode of each mode of the sensor is analyzed by COMSOL finite element simulation software.The sensor chip with two modes is designed by theoretical model and simulation.A dual-mode temperature self-decoupling implementation scheme is designed.?2?A process for preparing AlN thin films based on pulsed DC magnetron sputtering was developed.The substrate parameters,substrate temperature,sputtering power,gas flow ratio,process vacuum,sputtering power and other process parameters were studied for effect on the quality of AlN piezoelectric film.A high quality AlN piezoelectric film was prepared and characterized by a piezoelectric coefficient of-7.4pC/N and a FWHM of less than 2°.A sensor chip processing technology based on MEMS processing was developed.Mainly involved in layout design,AlN film deposition,Mo interdigital transducer preparation,AlN etching,backside deep silicon etching and other processes.An AlN resonant sensor chip with excellent performance was successfully fabricated.?3?Developed a temperature self-decoupling aluminum nitride resonant viscosity sensor for temperature decoupling viscosity density product??·??0.5 sensing.The Lamb wave mode of the resonator is sensitive to both the viscosity density product and the ambient temperature,while the Rayleigh wave mode is only sensitive to ambient temperature and is not affected by liquid characteristics.The unique properties of these two resonant modes are due to the different spatial distribution of acoustic energy.Using the above features,a beat strategy is proposed to separate the temperature effect from the viscosity density product measurement to achieve temperature independent viscosity density product measurement in a single acoustic wave resonator chip.The experimental results show that the temperature-independent viscosity-density product of Newtonian fluid is measured over a wide temperature range of 20-80°C.The sensitivity of the sensor can reach-0.36 MHz/kg·m-2·s-0.5.This work is ideal for liquid characterization where environmental temperature fluctuations are high,such as oil and gas exploration,automotive and aerospace applications.?4?The use of aluminum nitride resonators for the kinetic analysis of human blood coagulation.A sensor system suitable for blood coagulation time detection is designed.The electrical parameter changes of the resonator caused by the increased plasma viscosity of the coagulation process can be used to monitor the coagulation process.Temperature monitoring is performed while measuring clotting time with a special sensor design.The viscosity sensitivity of the sensor is-0.1MHz/mPa·s,and the linearity decreases with increasing temperature,which is 0.9837 at 20°C.The viscosity measurement resolution decreases with increasing solution viscosity,which is 0.0568mPa·s at 1 mPa·s.The maximum jitter amplitude of the two modes of the sensor at each liquid concentration is less than 20 kHz.The sensor temperature monitoring sensitivity is-16 KHz/°C.The sensor system designed is designed to have a plasma sample volume of only 1.2?L.The clotting time and plasma temperature are provided by fitting a time-frequency curve.This work enables the monitoring of temperature fluctuations while measuring coagulation time in a single resonator,making it ideal for temperature-related biosensitivity-related sensing applications. |
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