Atomic Layer Deposition of Lithium Titanate on 3D-Structured 300 Mm Silicon Substrates

Abstract

Thin film battery technology delivers high added value for autonomous microsystems in e.g. wireless sensor networks, Internet of Things (IoT) applications and medical implants. The transition to solid state electrolytes means significant improvement of the battery safety and even opens possibilities for integration into silicon technology. The 3D micro battery concept, including deposition of functional layers on structured surfaces with high aspect ratio, has been shown to improve both, capacity and rate performance of all-solid-state batteries [1]. Our aim is the development and characterization of functional stacks allowing direct integration into microsystems. For CMOS compatible design and production, we manufacture functional electrode and electrolyte layers on 300 mm wafer using standard industrial thin film deposition equipment. Atomic layer deposition (ALD) is a vapor-phase technique based on sequential, self-limiting surface reactions enabling conformal deposition of thin films. In this work, alternate atomic layer deposition of titanium oxide and lithium carbonate is demonstrated. The formation of the desired spinel lithium titanate (LTO) is investigated by subsequent high temperature anneals. Although its comparatively low capacity LTO is a promising electrode material for 3D integration. It stands out due to its zero-strain characteristics and the three dimensionality of ion transport [2]. [1] Y. Wang, B. Liu, Q. Li, S. Cartmell. S. Ferrara, Z. Deng, and J. Xiao, Journal of Power Sources 286 (2015) 330-345. [2] V. Miikkulainen, O. Nilsen, M. Laitinen, and T. Sajavaara, RSC Advances 3 (2013) 7537.