An in-depth understanding of lithium (Li) diffusion barriers is a crucial factor for enabling Li-ion-based devices such as three-dimensional (3D) thin-film batteries and synaptic redox transistors integrated on silicon substrates. Diffusion of Li ions into silicon can damage the surrounding components, detach the device itself, lead to battery capacity loss, and cause an uncontrolled change of the transistor channel conductance. In this study, we analyze for the first time ultrathin 10 nm titanium nitride (TiN) films as a bifunctional Li-ion diffusion barrier and current collector. Thermal atomic layer deposition (ALD) and pulsed chemical vapor deposition (pCVD) are employed for manufacturing ultrathin films. The 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 versus Li/Li+. An ultralow electrical resistivity of 115 μΩ 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 for an electrically conducting Li-ion diffusion barrier for Si-integrated devices.

Lithium titanate (Li4Ti5O12) (LTO) has several promising properties with regard to energy storage. The most important is its low volume expansion during lithium (de-) intercalation enabling the material for complex three-dimensional battery anode designs. To employ this property at a small scale, e.g., for micro batteries (<100 nm active layer thickness), a highly conformal deposition process like atomic layer deposition (ALD) is needed. However, the ALD of lithium containing layers is quite ambitious. Particularly, thermally activated deposition of lithium containing layers with water as a coreactant is challenging due to the high reactivity and hygroscopic nature of many lithium compounds, e.g., lithium hydroxide. That is why a novel ALD process regime has been developed, which allows the deposition of highly conformal and single phase LTO layers with excellent step coverage and composition. The process uses two metalorganic precursors: one acting as lithium and another as a titanium source. In contrast to usual ALD processes, these two precursors are subsequently applied. The reactive pulse with water is applied after the two metal precursor pulses. In this work, this novel ALD process sequence has been introduced and successfully demonstrated on 200 mm wafers using standard industrial ALD equipment. The layers are transformed to single phase Li4Ti5O12 by rapid thermal processing as proven by crystal phase analysis. Elemental composition has been analyzed by time of flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy (XPS). Results show that the amounts of contaminants like carbon and chlorine are below the detection limits of XPS. Also, a uniform element distribution and stoichiometry in good agreement with theoretical expectations for lithium titanate could be shown.

Herein, growth kinetics, crystal structure, and the uniformity of titanium oxide (TiO2) thin films prepared using atomic layer deposition (ALD) and plasma‐enhanced ALD (PE‐ALD) are studied. TiO2 thin films are grown using titanium tetrachloride (TiCl4), water, and oxygen precursors. Using ALD, TiO2 is grown in the temperature range of 270–310 °C thermally and in the range of 300–400 °C with PE‐ALD. In spite of the plasma process yielding better uniformity on planar structures, the optimized thermal process provides a remarkable conformal step coverage within deep trenches. In addition, the change in the crystal structure and phase transitions of TiO2 is presented herein. This is attempted at using TiO2 as a component material to grow lithium titanate (LTO) as an electrode material in solid‐state lithium‐ion batteries (LIBs). Thereby, different substrates are used. In comparison to the silicon (Si) substrate, silicon oxide (SiO2) and titanium nitride (TiN) lead to crystal phase transformation while annealing. Measurements are performed using in situ high‐temperature X‐ray diffraction (HT‐XRD). It is also shown that when TiN is sandwiched between TiO2 and the silicon substrate, the TiO2 thin film (25 nm) gradually changes from an anatase to a rutile structure.

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autonomous sensors, wearable devices, and medical implants will grow up to 100 billion USD. [1,2] The shrinking device sizes of portable electronics require microsized on-chip energy storage solutions with high-energy and high-power capability. These demands are beyond the abilities of liquid lithium (Li)-ion batteries due to limited miniaturization potential and inherent risks of the liquid electrolyte such as flammability and leakage.TFBs with solid-state electrolytes and binder-free electrodes are a promising alternative. In general, interfaces are more pronounced in thin-film devices, which remains challenging in all-solid-state batteries. [3] TFBs provide high-power density, long cycle life, low self-discharge, high-temperature and chemical stability, on-chip integration, and miniaturization. [4] These properties pave the way for future replacement of standard on-chip supercapacitors. [5] However, the small form factor and short Li diffusion length of TFBs come at the cost of low energy density. So-called 3D TFBs can partially compensate this by increasing energy density per footprint area. Thereby the battery layer stack is coated over a microstructured substrate with an enhanced surface area. [6] A first functional full cell 3D TFB was recently demonstrated by Pearse et al. [7] Moitzheim et al. reported an extensive overview of the current state, challenges, and outlooks of 3D TFBs. [8] ALD is the ideal technique enabling the required conformal, pinhole-free deposition and stoichiometric control of nanometer-thin films on highly structured surfaces. The vapor-phase technique based on sequential, self-limiting surface reactions is well understood and an industrial standard in integrated circuit manufacturing. [9] However, the deposition of Li metal is not possible and Li compounds remain challenging. [10,11] Functional ALD films of cathode materials such as LiMn 2 O 4 [12] or LiCoO 2 [13] and solid-state electrolytes such as LiPON [14] or Li x Al y Si z O [15] were demonstrated. However, Li-containing anode materials directly fabricated by ALD were not yet electrochemically evaluated. Only closely related ALD TiO 2 anodes were successfully investigated and optimized. [16,17] Spinel Li 4 Ti 5 O 12 (LTO) is a well-suited anode for 3D TFBs. The material undergoes a phase transition to the rocksalt-like structure during lithiation by rearranging the Li atoms with minimal volume change below 0.1%. [18] This so-called "zero-strain"The "zero-strain" Li 4 Ti 5 O 12 is an attractive anode material for 3D solid-state thin-film batteries (TFB) to power upcoming autonomous sensor systems. Herein, Li 4 Ti 5 O 12 thin films fabricated by atomic layer deposition (ALD) are electrochemically evaluated for the first time. The developed ALD process with a growth per cycle of 0.6 Å cycle −1 at 300 °C enables high-quality and dense spinel films with superior adhesion after annealing. The short lithiumion diffusion pathways of the nanostructured 30 nm films result in excellent electrochemical properties. Planar films reveal 9...