Tham khảo tài liệu 'micromachining techniques for fabrication of micro and nano structures part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Release Optimization of Suspended Membranes in MEMS 189 Dealing with anisotropic etching there is a feature that is important to consider. When the motifs are aligned with 100 planes 100 walls will be obtained that are etched as the wafer surface. 4. Geometry and optimization of the suspended membranes A micro-hotplate was designed to be used in a monolithic CMOS gas sensor which was later fabricated by MOSIS. Then an anisotropic etching process was performed on the chip using TMAHW following several formulations that increase the selectivity of the TMAH to avoid damage to the exposed aluminium on the chip caused by the etching solution Fujitsuka et al. 2004 Sullivan et al 2000 Yan et al 2001 . The next figures show the fabricated chip after a TMAHW etching process. Fig. 4. Fabricated chip after etching. Fig. 5. Partially etched micro- hotplates. 190 Micromachining Techniques for Fabrication of Micro and Nano Structures It was found that the aluminium was sometimes still getting damaged by the solution in an unpredictable way and with a limited repeatability. The damage increased as the etching time was increased so if the etching time can be reduced by a significant amount the same applies to the damage of exposed aluminium. Figure 6 shows photographs from before left and after etching where the exposed aluminium is indicated. The damage can be seen. EXPOSED ALUMINUM DAMAGED ALUMINUM Fig. 6. Comparison between before left and after etching. This motivation is the main objective of this study which comprises etching and mechanics simulations and the etching of the resulting designs. It should be noted that the designs presented are of micro-hotplates with general applications as mentioned before. The most common geometry used for micro-hotplates and suspended membranes are shown in Fig. 7. It can be seen in this figure that the central part of the structure is aligned to 110 planes of the substrate while the supporting arms have an angle of 45 and 135 with respect
