Assembly and hermetic encapsulation of wafer level secondary batteries
A new technology was developed for the construction and hermetic encapsulation of chip-size secondary lithium-ion batteries on wafer level. To reduce the size of the package and improve the handling and assembly of miniature batteries, we established a wafer level process that combines foil processing of Li batteries and wafer technologies for battery contacts and encapsulation. Parylene and thin film metal deposition was used for hermetic encapsulation of the batteries. With this technology, battery sizes between 1 mm² and 1 cm², and as thin as 250 µm, can be fabricated. A discharge capacity of 860 µAh/cm² was achieved with secondary lithium wafer-level batteries. The proportion of active material is thus increased to over 70 %, despite the system's very flat structure. The impact of the formation procedure on the battery performance was investigated. Electrical charge and discharge cycling tests have been carried out. The presented technology allows the transformation of the high energy density of cylindrical or prismatic cells to integrated micro batteries.