MEMS ultra low leak detection methods: a review

Purpose - The purpose of this paper is to review traditional hermeticity test methods when applied to typical micro-electro-mechanical systems (MEMS) cavity volumes and to propose potential solutions. Design/methodology/approach - Standards for traditional testing have been applied to typical MEMS cavity volumes and the resulting issues of range and sensitivity discussed. In situ test structures have been designed and fabricated with access to the internal cavities to allow characterisation of the structures as a function of pressure. Findings - The ultra low leak rates necessary to guarantee hermeticity of MEMS cannot be measured using traditional methods. Optical test methods are possible although in situ test structures currently provide the greatest sensitivity. A portfolio of test techniques is required to allow accurate hermeticity testing of MEMS. Research limitations/implications - This paper provides a starting point for further investigation into several methods of MEMS hermeticity testing. Originality/value - This paper provides a review of the limitations of traditional testing and proposals for future testing as the trend towards smaller volume packaging continues.