基于非晶硅的双层微测辐射热计可靠性研究

发布时间：2019-01-02 15:10

【摘要】：非制冷型微测辐射热计具有功耗低、易携带及产量大等优势,在军事和民用两方面有着广泛的发展前景。然而,传统微测辐射热计都是采用单层微桥结构设计,热敏感层与红外吸收层都在同一个层面内,不利于器件性能的进一步提升。本文以双层微桥结构非晶硅微测辐射热计为研究对象,通过理论分析和仿真验证,探讨了热学及动力学基本性能,并针对MEMS微机电系统封装工艺,分析讨论了在稀薄气体环境下真空下降对器件性能的影响。最后,在大量仿真数据分析对比的基础上,提出了一种新型耐振动冲击的双层微桥结构非晶硅微测辐射热计设计。微桥结构热导值G的大小随着桥腿长度的减小以及桥腿宽度和厚度的增加而增加;热时间常数τ与桥腿长度成正比而与桥腿宽度成反比,并且相同结构尺寸的非晶硅微测辐射热计的热导值和热时间常数值,都比氧化钒微测辐射热计低。桥面结构温升?T正比于桥腿的长度而反比于其宽度和厚度。在相同的外界辐射条件下,非晶硅微测辐射热计的温升?T也比氧化钒器件的要高。谐响应分析结果表明,I型伞状双层微桥结构在经受外界振动激励时,桥面是形变量最大的地方,而集中应力最大的地方出现在热敏感层桥面与桥腿的连接处。当振动频率接近其共振频率时,X、Y、Z三个方向都出现了共振,其中最大位移形变量达到了0.031μm。如此大的位移形变很容易使微桥结构在振动过程中发生撕裂、坍塌,导致红外吸收层与热敏感层或者衬底与热敏感层发生永久性粘连而使探测器遭受损坏。当冲击峰值加速度为1000 g、脉冲宽度为1 ms时,微桥结构出现位移峰值的时刻与脉冲波的峰值点在时间上有大约0.2 ms的时间延迟,最大位移形变值为0.59μm,热敏感层与衬底之间的微腔厚度为1μm,如此大的振动位移变形,很有可能会导致热敏感层与衬底发生永久性沾粘。X方向振动时的最大应力为0.027 MPa,应力集中在桥腿与桥面的连接处;Y方向振动时的最大应力为0.07 MPa,应力集中在桥腿与桥面的连接处;Z方向振动时的最大应力比其它两个方向大了一个数量级,高达0.11 MPa,且应力集中在桥腿与桥面的连接处,该应力值已经超过结构处于张应力状态下的一阶屈曲值,此时微桥将会处于非常不稳定的状态。真空封装作为MEMS器件加工的一个重要环节,封装后腔体的真空度对微型芯片结构的可靠性有较大的影响。影响MEMS器件真空封装好坏的因素有很多,如封装工艺的缺陷、材料(比如粘接剂等化学用品)缓慢释放以及封装所用外壳的坚固程度等。一旦密封腔体发生真空泄漏导致少量气体混入其中,会使微桥结构在经受外界振动和冲击等激励作用时承受更大的压力。仿真研究表明,稀薄气体气压越高,对微桥结构所产生的压强也就越大。
[Abstract]:The uncooled microbolometer has the advantages of low power consumption, easy to carry and large output, so it has a wide development prospect in both military and civil fields. However, the traditional microbolometer is designed with single-layer microbridge structure. The thermal sensitive layer and infrared absorption layer are in the same layer, which is not conducive to the further improvement of device performance. In this paper, a double-layer microbridge amorphous silicon microbolometer is studied. The basic thermal and dynamic properties are discussed by theoretical analysis and simulation, and the encapsulation process of MEMS is discussed. The effect of vacuum drop on device performance in rarefied gas environment is analyzed and discussed. Finally, based on the analysis and comparison of a large number of simulation data, a new type of double-layer microbridge structure amorphous silicon microbolometer is proposed. The thermal conductivity G of the micro-bridge structure increases with the decrease of leg length and the increase of the width and thickness of the bridge leg. The thermal time constant 蟿 is directly proportional to the length of the bridge leg and inversely proportional to the width of the bridge leg, and the thermal conductivity and thermal time constant of the amorphous silicon microbolometer of the same structure are lower than that of the vanadium oxide microbolometer. The temperature rise of the deck structure is proportional to the length of the bridge leg and inversely to the width and thickness of the bridge leg. Under the same external radiation conditions, the temperature rise of amorphous silicon microbolometer is also higher than that of vanadium oxide device. The results of harmonic response analysis show that the bridge deck of type I umbrella microbridge structure is the place with the largest deformation when subjected to external vibration, while the maximum concentrated stress occurs at the junction between the bridge deck and the leg of the heat-sensitive layer. When the vibration frequency is close to its resonance frequency, all the three directions of XFY Z have resonance, in which the maximum displacement deformation reaches 0.031 渭 m. Such a large displacement deformation can easily tear the micro-bridge structure apart and collapse during vibration, resulting in the permanent adhesion between the infrared absorption layer and the thermosensitive layer or the substrate and the thermosensitive layer, thus causing damage to the detector. When the impact peak acceleration is 1000 g and the pulse width is 1 ms, the peak displacement of the bridge structure and the peak point of the pulse wave have a time delay of about 0.2 ms, and the maximum displacement deformation value is 0.59 渭 m. The thickness of the microcavity between the thermal sensitive layer and the substrate is 1 渭 m. Such a large vibration displacement deformation is likely to lead to permanent adhesion between the thermal sensitive layer and the substrate. The maximum stress in the X direction vibration is 0.027 MPa,. The stress is concentrated on the joint between the bridge leg and the bridge deck; The maximum stress of Y-direction vibration is 0.07 MPa, stress concentrated on the joint between the bridge leg and the bridge deck. The maximum stress in Z direction is an order of magnitude greater than that in the other two directions, and is up to 0. 11 MPa, and the stress is concentrated at the junction between the bridge leg and the bridge deck. The stress value has exceeded the first order buckling value of the structure under the state of tensile stress. At this point, the microbridge will be in a very unstable state. Vacuum packaging is an important part in the fabrication of MEMS devices. The vacuum degree of the cavity after packaging has a great influence on the reliability of microchip structure. There are many factors that influence the vacuum packaging of MEMS devices, such as the defects of packaging process, the slow release of materials (such as adhesives and other chemical supplies) and the firmness of the shells used in packaging. Once a small amount of gas is mixed into the sealed cavity due to vacuum leakage, the micro-bridge structure will be subjected to more pressure when it is subjected to external vibration and shock. The simulation results show that the higher the gas pressure, the greater the pressure on the micro bridge structure.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN215

【共引文献】