13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- promising method for joining certain metals or semiconductors to alkali-ion-conductive glasses at decreased temperatures. Compared to other techniques, the main advantage of anodic bonding is that a strong junction interface can be achieved at a reduced bonding temperature by application of an electric field [7-9]. The temperature for anodic bonding is usually lower than the softening point of glass and the melting points of the materials selected for this purpose. Nowadays, there exists a demand for this straightforward and reliable bonding technique in connecting, packaging, or hermetic sealing of more complex micro/nano structures and integrated microcircuits in MEMS/NEMS devices. The promising applications of MEMS devices are still limited by the reliability of MEMS devices, especially in the applications for military and aerospace systems. Some previous studies [10, 11] show that one of the important structural failure mode is the stripping of micro anchors from its substrate in some type of MEMS devices. On the basis of the structure of these devices, in this paper, we report some mechanical tests on the micro anchors anodically bonded between Pyrex 7740 glass wafer and aluminum thin film coated on crystalline Si wafer. 2. Experimental 2.1. Specimen preparation The experimental specimens were made by die-level anodic bonding at different temperatures and voltages. The mesa structures are used to avoid the edge micro cracks due to the chip dicing process. Pyrex 7740 glass wafers of 500 μm thickness and 100 mm diameter were cut into 12 mm ×12 mm square chips. The chemical composition of Pyrex 7740 wafer includes 80.8 Mol% SiO2, 12.0 Mol% B2O3, 4.2 Mol% Na2O, 2.0 Mol% Al2O3, 0.6 Mol% K2O, 0.2 Mol% MgO, and 0.2 Mol% CaO, as shown in Table 1 [12]. Table 1. Chemical composition of Pyrex 7740 glass wafer (Mol%) SiO2 B2O3 Na2O Al2O3 K2O MgO CaO 80.8 % 12.0 % 4.2 % 2.0 % 0.6 % 0.2 % 0.2 % Si wafers were of 100 mm in diameter (double-side polished, p-type, and wafer surface plane (100), and were patterned into mesas with different-sized squares. There are four types of dice with different mesa spacing, as shown in Figure 2. These mesas were of 10 µm in height and were prepared with a deep reactive ion etch (DRIE) process. These patterned Si wafers were coated by an ARC-12M sputtering system with pure aluminum (99.999%). The coated aluminum thin films were of 500 Å, 950 Å, 1500 Å, and 2300 Å in thicknesses respectively. Then these Si wafers were also diced into squares of 12 mm ×12 mm. All square samples were cleaned by deionized water spray rinse in a 100-class clean room and dried by nitrogen gas under pressure. A pair of glass chip and well-coated crystalline silicon chip was placed between two stainless steel plates, which acted as plate electrodes, and then between two hot plates. The glass side was connected with the cathode, and the silicon side was connected with anode. The schematic of this bonding configuration is shown in Figure 3.
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