Solid-State Thin-Film Lithium Batteries for Integration in Microsystems

Abstract

The increasing miniaturization of electronic devices requires the miniaturization of devices that provide energy to them. Autonomous devices of reduced energy consumption are increasingly common and they have benefited from energy harvesting techniques. However, these devices often have peak power consumption, requiring storage of energy.This chapter presents the fabrication and characterization of thin-films for solid-state lithium battery. The solid-state batteries stand out for the possibility of all materials being solid and therefore ideal for microelectronics fabrication techniques. Lithium batteries are composed primarily of three materials, the cathode, the electrolyte and the anode. The positive electrode (cathode) and negative (anode) have high electrical conductivity and capacity for extraction and insertion of lithium ions. The electrolyte’s main features are the high ionic conductivity and high electrical resistivity. The materials chosen for the battery are lithium cobalt oxide (cathode), lithium phosphorus oxynitride (electrolyte), and metallic lithium (anode).The lithium cobalt oxide cathode (LiCoO2) was deposited by RF sputtering and characterized using the XRD, EDX, SEM techniques, and electrical resistivity. Fully crystalline \({\mathrm{LiCoO}}_{2}\) was achieved with an annealing of \(65{0}^{\circ }\mathrm{C}\) in vacuum for 2 h. Electrical resistivity of \(3.7\,\Omega \cdot \)mm was achieved.The lithium phosphorus oxynitride electrolyte (LIPON) was deposited by RF sputtering and characterized using the techniques EDX, SEM, ionic conductivity, DSC, and TGA. Ionic conductivity of \(6.3 \times 1{0}^{-7}\,\mathrm{S} \cdot {\mathrm{cm}}^{-1}\) for a temperature of \(2{6}^{\circ }\mathrm{C}\) was measured. The thermal stability of LIPON up to \(40{0}^{\circ }\mathrm{C}\) was also proved.The metallic lithium anode (Li) was deposited by thermal evaporation and its electrical resistance measured at four points during the deposition. Resistance of about 3. 5 Ω was measured for a thickness of 3 μm. The oxidation rate of the lithium in contact with the ambient atmosphere was evaluated. The patterning process of the battery was developed by means of shadow masks.