Article published Microbatteries
Smaller still and even more effective!
CEA LITEN has adapted the photolithography process to microbattery production. The process adopted can produce batteries that are 100 times smaller. A demonstrator version consisting of an array of 16 microbatteries with an output of 50 V and an RF switch, has now been successfully tested.
CEA was looking to design a very small power supply device capable of generating 50 V or so to provide energy to a switch intended for use in new-generation mobile telephones. LITEN's miniature energy source laboratory rose to the challenge. The team managed, for the first time ever, to produce an array of 16 series-mounted batteries on a surface with an area of less than one square millimetre. To do this, it made the microbattery manufacturing process compatible with photolithography. Microbatteries made using conventional methods contain liquid electrolytes which call for bulky packaging to avoid leaks. No liquid is needed with this technique, which makes it possible to produce batteries that are 100 times smaller. “For microelectronics applications, the photolithography process consists in depositing a silicon substrate on a succession of metal layers, which are then chemically treated to form the microbattery electrodes and electrolyte,” Raphaël Salot explains. To obtain this result, the researchers had to adapt chemical etching and material protection processes: “We needed products that were capable of effectively and specifically etching the metals used in making the microbatteries.” The manufacturing process is compatible with a standard clean room environment. As all the stages are carried out at temperatures below 200°C, the microbatteries can be made directly on the integrated circuits, with no risk to operation or performance. They can also be connected in series on a single silicon wafer directly during the manufacturing process. The 16-battery array was made to operate with a high-frequency switch. This part of the work involved cooperation with LETI. “The demonstrator passed tests with flying colours: not only did the battery operate the switch, it also proved to have a similar lifetime of at least a million cycles.” This development shows great promise as far as industrial applications are concerned. In particular, it could replace the button cells used on integrated circuits to back up data in the event of main battery failure. It could also be used to power the internal clocks on computers or stand-alone sensors in which the microbatteries could be connected to an energy recovery system (solar energy, thermal gradient energy, etc.).
