All‐Solid‐State Thin Film μ‐Batteries for Microelectronics

Continuous advances in microelectronics and micro/nanoelectromechanical systems enable the use of microsized energy storage devices, namely solid‐state thin‐film μ‐batteries. Different from the current button batteries, the μ‐battery can directly be integrated on microchips forming a very compact “system on chip” since no liquid electrolyte is used in the μ‐battery. The all‐solid‐state battery (ASSB) that uses solid‐state electrolyte has become a research trend because of its high safety and increased capacity. The solid‐state thin‐film μ‐battery belongs to the family of ASSB but in a small format. However, a lot of scientific and technical issues and challenges are to be resolved before its real application, including the ionic conductivity of the solid‐state electrolyte, the electrical conductivity of the electrode, integration technologies, electrochemical‐induced strain, etc. To achieve this goal, understanding the processing of thin films and fundamentals of ion transfer in the solid‐state electrolytes and hence in the μ‐batteries becomes utmost important. This review therefore focuses on solid‐state ionics and provides inside of ion transportation in the solid state and effects of chemistry on electrochemical behaviors and proposes key technology for processing of the μ‐battery. μ‐battery with its thickness in micrometer has gained increased attention in recent years due to reduced power consumption of modern microelectronics, and micro/nanoelectromechanical systems. However, there still exist tremendous issues to really integrate the μ‐battery into those microdevices. This review concentrates on the principle and challenges of the development of the μ‐batteries.