【作者】 黄硕；

【导师】 傅新；

【作者基本信息】 浙江大学 ， 机械电子工程， 2009， 博士

【摘要】 本课题对微型热式气体流量传感器的稳态传热进行了系统研究。首先对薄膜材料热导率测量方法进行研究,建立了薄膜-衬底复合结构传热模型,以该模型为基础将基于拉曼光谱的薄膜热导率测量方法拓展到亚微米和纳米尺度,并使用该方法对传感器中的薄膜材料进行了热导率测量;其次,在准确获得微型热式气体流量传感器的材料热物性参数的基础上,对传感器的对流-导热耦合传热过程进行了研究,建立了传感器的稳态传热模型,并使用数值方法对传感器的工作传热过程进行了分析,以分析结果为基础提出了微型热式气体流量传感器的优化设计方法;再次,以优化设计方法为指导,对微型热式气体流量传感器进行了传感器工作模式设计、传感器材料选择和传感器结构参数设计工作;最后,结合实验室具体设备和工艺条件,制定了合适的传感器制做工艺路线,在工艺实验的基础上对传感器进行了制做,并对传感器进行了稳态工作性能实验测试,测试结果验证了提出的优化设计方法对提升传感器稳态工作性能的有效性。课题的主要研究工作如下:1.薄膜热导率测量方法的研究。针对高斯激光入射生热的情况对传统的基于拉曼光谱的薄膜热导率测量方法进行了修正,并以此为基础,对薄膜-衬底复合结构的传热进行了研究,分析了薄膜热导率、衬底热导率、薄膜/衬底接触面热阻对复合结构传热过程的影响,得到了薄膜热导率的解析表达式,从而实现了对基于拉曼光谱的薄膜热导率测量方法的拓展,使其可以被用来测量亚微米/纳米厚度薄膜的热导率。使用拓展的基于拉曼光谱的薄膜热导率测量方法对多孔硅薄膜试样、二氧化硅薄膜试样、氮化硅薄膜试样的热导率进行了测量,为分析传感器的稳态传热过程提供了准确的参数基础。2.微型热式气体流量传感器的稳态传热模型研究。对微型热式气体流量传感器的对流-导热耦合传热过程进行了分析,并对传感器的稳态传热过程进行了理论建模研究。在模型中,不仅考虑了流体通过对流传热对传感器稳态工作性能的影响,也充分考虑了传感器衬底导热作用的影响。使用有限差分的方法,对传感器的稳态传热理论模型进行了数值仿真分析。根据模型分析结果,以提升传感器的稳态工作性能为目的,分别就温敏元件的空间布置和加热元件的间隔距离提出了优化设计方法,为微型热式气体流量传感器的优化设计提供了理论基础。3.微型热式气体流量传感器的优化设计。对热分布型微型气体流量传感器的温度平衡工作模式进行了理论分析,得到了传感器输出信号与流量之间的关系式,从理论上证明了传感器输出信号具有高线性度。对传感器各元件的材料选择进行了研究,结合实验室本身设备和工艺条件,为提升传感器的工作性能,选择了合适的传感器衬底材料、绝缘层材料、加热元件材料、温度敏感元件材料和保护层材料,并根据提出的微型热式气体流量传感器优化设计方法,对传感器的结构参数进行了设计。4.微型热式气体流量传感器的制备工艺及实验测试研究。通过对各MEMS基本工艺的比较分析,并结合具体的实验室设备和工艺情况,针对设计的微型热式气体流量传感器进行了传感器衬底的制备工艺、绝缘层的制备工艺、加热元件的制备工艺、温度敏感元件和保护层的制备工艺实验研究,在工艺实验基础上制做了微型热式气体流量传感器。对制做的传感器进行了稳态性能实验测试,相关实验结果与传感器稳态传热建模仿真分析结果相符合,对提出的微型热式气体流量传感器稳态性能优化设计方法的有效性进行了验证。更多还原

【Abstract】 In this dissertation, the steady heat transfer of the micro thermal airflow sensor is systematically studied. Firstly, the thin film thermal conductivity measurement method is studied. A heat transfer model of the thin film-substrate structure is built to extend the original Raman method for the thermal conductivity measurement of the submicrometer- or nanometer-scale thin films. The extended Raman method is applied to the thin films used in the micro thermal airflow sensor to obtain their thermal conductivities. Secondly, based on the obtained material thermal parameters, the conjugate conduction-convection heat transfer of the micro thermal airflow sensor is studied, a steady heat transfer model is built and the numerical analysis is performed. Based on the analysis results, the optimal design criteria are proposed to enhance the steady performance of the micro thermal airflow sensor. Thirdly, based on the proposed optimal design criteria, the operation mode of the micro thermal airflow sensor is designed, the materials of the micro thermal airflow sensor are chosen and the structure of the micro thermal airflow sensor is designed to enhance the steady performance of the micro thermal airflow sensor. Fourthly, according to the present experimental devices and techniques of the lab, the applicable fabrication processes of the micro thermal airflow sensor are chosen, and the designed micro thermal airflow sensors are fabricated with the achievements of the fabrication processes experiments. The obtained micro thermal airflow sensors are test for their steady performance, and the test results have confirmed the validity of the proposed optimal design criteria.The main contents of this dissertation are briefly stated as the followings:1. The study on the thin film thermal conductivity measurement method. The original Raman method for the film thermal conductivity measurement is modified to adapt the Gaussian laser condition. Then, a heat transfer model of the thin film-substrate structure is built to analyze the effects of the thin film thermal conductivity, substrate thermal conductivity and the film/substrate interface thermal resistance. An analytical process is applied to the heat transfer model and thin film thermal conductivity equation is obtained, which means that the Raman method is extended for the thermal conductivity measurement of the submicrometer- or nanometer-scale thin films. The extended Raman method is applied to the porous silicon film, silicon dioxide film and the silicon nitride film to obtain their thermal conductivities. This study provides accurate thermal parameters of the materials used in the micro thermal airflow sensor for its steady heat transfer model. 2. The study on the steady heat transfer model of the micro thermal airflow sensor. The conjugate conduction-convection heat transfer of the micro thermal airflow sensor is analyzed, and the steady heat transfer model of the micro thermal airflow sensor is built. In this model, not only the effect of the heat transfer between the airflow and the sensor through the convection is described, but the heat transfer within the sensor through the conduction of the sensor substrate is also taken into account. The finite difference scheme is applied to the steady heat transfer model for the numerical analysis. Based on the analysis results, the optimal design criteria including the sensing elements positioning and the heating elements positioning are proposed to enhance the steady performance of the micro thermal airflow sensor. The proposed optimal design criteria lay the theoretical foundation for the design of the micro thermal airflow sensor.3. The study on the optimal design of the micro thermal airflow sensor. The temperature balance mode for the operation of the micro thermal airflow sensor is theoretical analyzed to describe the relationship between the sensor output signal and the flow rate. The high linearity of the sensor output signal is proved by the theoretical analysis. According to the practical condition of the experimental devices and techniques in the lab, the materials used in the micro thermal airflow sensor are studied and then chosen for the enhancement of the sensor performance, including the sensor substrate material, insulation layer material, heating element material, sensing element material and the passivation layer material. The structure of the micro thermal airflow sensor is designed according to the proposed optimal design criteria.4. The study on the fabrication processes and the steady performance test of the micro thermal airflow sensor. Based on the comparison of the different MEMS fabrication processes, and combined the practical condition of the experimental devices and techniques in the lab, the experiments are made separately for the fabrication of the sensor substrate, insulation layer, heating element, sensing element and passivation layer, and then the designed micro thermal airflow sensor is fabricated. The sensors are tested for their steady performance, and the test results have confirmed the validity of the proposed optimal design criteria.更多还原