Development of near hermetic silicon/glass cavities for packaging of integrated lithium micro batteries

A technology was developed for fabrication of very thin, chip-sized lithium secondary micro batteries. With help of wafer level processing the batteries can be directly integrated into silicon chips or MEMS devices. The batteries were packaged in 200 μm deep cavities of the silicon wafer and encapsulated with a glass substrate. Battery demonstrators were realized with 7 and 12 mm square and round foot prints. Near hermetic packaging was accomplished with the help of a UV curable epoxy seal that should ensure several years of battery lifetime. Bonding parameters, shear force and the water permeation rate of the adhesive were investigated. A capacity of 3 mAh/cm² and an energy density of 10 mWh/cm² were achieved. The electrical contact between the battery and the contact pads of the housing was investigated in detail. Electrical tests were made with encapsulated micro batteries and compared with macroscopic lithium polymer batteries. A reduction in capacity of approximately 10% was measured after 100 cycles.