Novel atomic layer deposition of lithium-containing electrode and electrolyte thin films for 3D all-solid-state batteries

Atomic layer deposition (ALD) of lithium (Li)-containing films has aroused major interest in recent years. Promising applications are thin-film Li-ion batteries, protective particle coatings, interface model systems, and neuromorphic computing [1,2]. Here, we will focus on the development of processes for integrated 3D all-solid-state batteries to power upcoming autonomous sensor systems and ultralow-power internet of things devices. The experimental realization of the 3D battery concept to simultaneously increase power and energy density was recently demonstrated [3]. We focus on a concept to further increase footprint energy density by implementing an integration route adopted from an established 3D metal-insulator-metal device [4]. The stacking of these thinned 3D battery dies will enable capacities above 1 mAh/cm2 as system in package. The required conformal, pinhole-free deposition and stoichiometric control of nanometer thin films on highly structured surfaces are enabled by ALD. The vapor-phase technique based on sequential, self-limiting surface reactions is well understood, however deposition of Li-containing materials remains challenging [1]. In this work, we will demonstrate a novel, patented thermal three-step ALD process for Li-containing mixed oxides [5]. This process deals with the undesired hygroscopic nature of lithium hydroxide during deposition with water as co-reactant. Thereby, spinel lithium titanate (Li4Ti5O12) with low impurities is formed after rapid thermal processing, confirmed by X-Ray photoelectron spectroscopy and diffraction. This anode material is favorable for 3D substrates due to its zero-strain characteristics. Furthermore, thermal deposition, which is beneficial for 3D structures, of lithium phosphorousoxynitride (""LiPON"") electrolyte with high nitrogen content is achieved. Conformality and adhesion of a half cell layer stack will be demonstrated in a hole structure with a high aspect ratio of 20:1. First results of complementing functional films and electrochemical performance will be discussed.