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Piezoresistive membrane deflection test structure for the evaluation of hermeticity in low cavity volume MEMS and microelectronic packages

This paper details the design, fabrication and characterisation of a piezoresistive membrane deflection test structure for the electrical evaluation of hermeticity in low cavity volume package. This test structure uses the 0-level silicon cap, defined in the MultiMEMS foundry service, as a deflecting membrane to electrically monitor changes in package cavity pressure over time. The hermeticity of the package can then be determined in real-time and low leak rates can be measured using a pressurisation stage, which also accelerates the test. The minimum detectable leak rate of the test structure without test acceleration is 6.9×10-12 atm.cm3.s-1, which is two orders of magnitude lower than the limit of the traditional helium fine leak test method.