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

A technology was developed for the fabrication of very thin, chip-sized lithium secondary micro batteries. Based on wafer level processing the batteries can be directly implemented into silicon chips, 3D chip stacks or MEMS devices. The batteries were packaged in 200 mum deep cavities of the silicon wafer and encapsulated with a glass substrate. Battery demonstrators with 7 and 12 mm² and round foot print were realized. Near hermetic packaging was accomplished using a UV curable epoxy sealing which should ensure several years of battery lifetime. Bonding parameters, shear force and water permeation rate of the adhesive were investigated. A capacity of 3 mAh/cm² and an energy density of 10 mWh/cm² have been 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 capacity reduction of approximately 10 % was measured after 100 cycles.