Thin film batteries
An ordinary battery consists of a number of electric cells connected either in series, to give a higher total voltage, or in parallel for larger capacity. Each of the cells consists of two, usually metal, electrodes separated by an electrolyte. To create a microbattery one needs to shrink the dimensions of such an electric cell to the order of a micrometer. Such a task can be performed with thin film technologies. These new solid-state micropower sources have unit cells of thickness of only 10 micrometers. They are composed of a positive titanium oxysulfide electrode, an amorphous lithium borate based electrolyte and a negative lithium electrode. All three are now in the form of thin films, one film deposited on top of the other. The films are deposited using sputtering and thermal evaporation technologies. The resulting microbattery has the ability to provide 100-200 microamperes per square centimetre and an average voltage of 2.3 volts. The patent holders are currently developing new materials for the electrolyte and the positive electrode in order to further increase the performance. To protect the miniature battery from air and moisture while keeping the thickness as small as possible, it has to be encapsulated by a tight barrier. A thin film of iron-phosphate based glass deposited on the battery by sputtering provides such a barrier. A machine capable of producing 500 microbatteries per week has been designed. These micropower sources can be integrated on small flat objects like tags, wireless electronic shelf edge labels or smart cards. Patent holders are seeking partners to introduce this innovative and useful product to the market.
