| Micro-bolometer has given us many opportunities in the field of civilian and military applications due to its less power consumption, light weight, low cost and being able of easily fabricated in mass production. However, the traditional micro bolometer is adopted a single micro-bridge design, in which the sensitive film and the absorbing film are integrated on a monolithic layer, which delays the performance of the device. Taking a double layer micro-bolometer as our main object, this thesis has discussed the basic thermal and dynamics properties through theoretical analysis and simulation verification. And for the MEMS packaging technology, the influence of the device performance due to vacuum reduction is also discussed. Finally, a new type of double-layer micro-bridge structure design has been proposed for amorphous silicon(a-Si) micro-bolometer.The thermal conductivity is inversely proportional to the leg length and directly proportional to the width and thickness. The thermal time constant is proportional to the bridge leg length and inversely proportional to the bridge leg width. And the thermal conductivity and thermal time constants of the a-Si micro-bolometer are lower than those of the vanadium oxide(VOx) micro-bolometer. Temperature rise of the bridge structure is proportional to the length of the legs and inversely proportional to the width and thickness, in which the a-Si micro-bolometer has a higher temperature rise than that of VOx micro-bolometer, if given a same radiation condition.Harmonic analysis results show that double micro-bolometer bridge with I type leg has the greatest deformation and the stress focuses mainly on the corner between the bridge and the leg. When the frequency is close to its resonant point, the bridge structure will have undergone resonance in the direction of X, Y, Z while the largest displacement is 0.031μm. Tearing and collapsing are very easily to happen in the micro-bolometer with so large displacement. The results indicate that the detectors will suffer damage due to the permanent adhesion of the infrared absorption layer and the heat sensitive layer, or adhesion of the heat sensitive layer and the substrate.When a peak acceleration impact is set at 1000 g, a time delay about 0.2ms happens between the maximum displacement and the pulse peak value, the maximum displacement is about 0.59μm. Then the heat sensitive layer and the substrate are easily to stick together because the gap between these layers is only 1 microns. At this condition, the maximum stresses in X, Y and Z direction are 0.027 MPa, 0.07 MPa and 0.11 MPa, respectively, which focus on the inner side of the corner between legs and pier. It is found that the bridge structure is not stable enough when the stress in Z direction is beyond the bending limit calculated though the use of Ansys software.Vacuum packaging is a key step in MEMS device processing, and the vacuum degree of the cavity has a big influence on the reliability of the microchip structure. There are many factors needed to be considered in the process of encapsulation, such as the defects come from packaging stage, the slow release of chemical materials and the stiffness degree of solid shell. Once the vacuum leak occurs and the device is objected to a certain vibration and shock excitation, the micro-bridge will be pressed under even more mechanical power. Our present simulation study shows that the micro-bridge will undergo a greater pressure with the rise of the rarefied gases inside the cavity of the bridge. |
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