## 3 Performance Characterization and Reliability Assessment
### Shear Pull Test  
The shear tests were performed using a DAGE 4000 Plus bond tester (Nordson DAGE, Aylesbury, UK), a specialized instrument designed for mechanical reliability assessment of bonded interfaces. In this destructive test, a shear tool applies a lateral force to the edge of the bonded cap wafer at a constant speed until the bonding interface physically fractures. The instrument records the peak force in Newtons (N) required to cause this mechanical failure, which is reported as the shear strength. Figure 12 presents the critical mechanical reliability data from the new, more robust shear pull tests conducted in response to reviewer feedback. The figure is divided into two complementary parts that together provide a comprehensive view of the mechanical performance across different MEMS filter configurations. Figure 12a shows individual measurements for five samples (S1-S5) of each configuration, displayed as a line graph  
Figure 11: Cross-sectional SEM (Scanning Electron Microscope) images showing the bonding interfaces for the three configurations: L1 (10 \(\upmu\)m edge bonding), L2 (85 \(\upmu\)m resonator width with 220 \(\upmu\)m bottom width), and L3 (10.3 \(\upmu\)m bonding with matched resonator widths). with three distinct curves representing the L1 (fc = 17.5 GHz), L2 (fc = 17 GHz), and L3 (fc = 16.5 GHz) configurations. The data points demonstrate remarkably high consistency with minimal standard deviation across all samples, confirming the reliability of both the fabrication process and testing methodology. The L1 configuration (blue diamonds) maintains shear test values consistently around 8-9 kgf across all five samples, while the L3 configuration (green squares) shows similarly stable performance around 7-7.5 kgf. Most notably, the L2 configuration (orange triangles) exhibits consistently lower values around 2-3 kgf, with equally tight repeatability that reinforces the validity of this unexpected result. Figure 12b provides a consolidated view of the average shear test values in a bar chart format, which confirms the original trend with much higher statistical confidence. The quantitative results show that both L1 (average 8.86 kgf) and L3 (average 7.274 kgf) configurations achieved substantially superior bonding strength compared to the L2 configuration (average 2.374 kgf). The difference is particularly striking, with L1 showing approximately 3.7 times higher shear strength than L2, and L3 demonstrating roughly 3.1 times better performance than L2. These results reinforce the counterintuitive finding that the L2 configuration with intermediate, partial width matching exhibited weaker mechanical strength than even the L1 configuration, which lacked a top resonator entirely. This strongly suggests that the asymmetric, partial bonding interface in L2 may introduce stress concentration points that compromise the overall structural integrity of the bond. The incomplete overlap creates non-uniform stress distribution during mechanical loading, leading to premature failure at the interface boundaries where bonded and unbonded regions meet. The mechanical testing data conclusively establishes a direct correlation between maximized bonding area and mechanical robustness, with the L3 configuration providing the most complete bonding interface and the L1 configuration offering a simpler but more uniform bonding pattern. This validates that the L3 configuration delivers superior and reliable performance in both the electrical and mechanical domains, making it the optimal choice for applications requiring both high electrical performance and mechanical durability. The comprehensive dataset also demonstrates that partial bonding strategies should be approached with caution, as they may introduce unexpected mechanical vulnerabilities despite potential electrical advantages.