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Effects of Package Induced Stress on MEMS Device and Its Improvements  

Choa Sung-Hoon (삼성종합기술원)
Cho Yong Chul (삼성종합기술원)
Lee Moon Chul (삼성종합기술원)
Publication Information
Journal of the Korean Society for Precision Engineering / v.22, no.11, 2005 , pp. 165-172 More about this Journal
Abstract
In MEMS (Micro-Electro-Mechanical System), packaging induced stress or stress induced structure deformation becomes increasing concerns since it directly affects the performance of the device. In the decoupled vibratory MEMS gyroscope, the main factor that determines the yield rate is the frequency difference between the sensing and driving modes. The gyroscope, packaged using the anodic bonding at the wafer level and EMC (epoxy molding compound) molding, has a deformation of MEMS structure caused by thermal expansion mismatch. This effect results in large distribution in the frequency difference, and thereby a lower yield rate. To improve the yield rate we propose a packaged SiOG (Silicon On Glass) process technology. It uses a silicon wafer and two glass wafers to minimize the wafer warpage. Thus the warpage of the wafer is greatly reduced and the frequency difference is more uniformly distributed. In addition. in order to increase robustness of the structure against deformation caused by EMC molding, a 'crab-leg' type spring is replaced with a semi-folded spring. The results show that the frequency shift is greatly reduced after applying the semi-folded spring. Therefore we can achieve a more robust vibratory MEMS gyroscope with a higher yield rate.
Keywords
Package induced stress; Vibratory MEMS gyroscope; SiOG process; Wafer bowing;
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Times Cited By KSCI : 1  (Citation Analysis)
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