Surface Dependent Performance of Ultrathin TiN Films as an Electrically Conducting Li Diffusion Barrier for Li-Ion Based Devices

In-depth understanding of lithium (Li) diffusion barriers is a crucial factor for enabling Li-ion based devices like 3D thin-film batteries and synaptic redox transistors integrated on silicon substrates. Diffusion of Li-ions into the silicon can damage surrounding components, detach the device itself, lead to battery capacity loss, and cause uncontrolled change of the transistor channel conductance. In this study, we analyze for the first time ultrathin 10 nm titanium nitride (TiN) films as bifunctional Li-ion diffusion barrier and current collector. Thermal atomic layer deposition (ALD) and pulsed chemical vapor deposition (pCVD) are employed for manufacturing. 10 nm ALD films demonstrate excellent blocking capability with an insertion of only 0.03 Li per TiN formula unit exceeding 200 galvanostatic cycles at 3 µA/cm2 between 0.05 and 3 V vs. Li/Li+. An ultra-low electrical resistivity of 115 µO cm is obtained. In contrast, a partial barrier breakdown is observed for 10 nm pCVD films. High surface quality with low contamination is identified as a key factor for the excellent performance of ALD TiN. Conformal deposition of 10 nm ALD TiN in 3D structures with high aspect ratios of up to 20:1 is demonstrated. The measured capacities of the surface area enhanced samples are in good agreement with the expected values. High-temperature blocking capability is proven for a typical electrode crystallization step. Ultrathin ALD TiN is an ideal candidate as an electrically conducting Li-ion diffusion barrier for Si-integrated devices.