Growth per cycle as a function of process table temperature for both plasma-assisted (squares) and thermal (circles) ALD processes.

All solid state 3D batteries are pursued for their increased safety and high power capabilities. At present conformal coating of the solid electrolyte remains one of the key hurdles for the implementation of such devices. In the present work we investigate atomic layer deposition (ALD) as means of conformal deposition of lithium phosphate (Li 3 PO 4 ) and nitrogen doped lithium phosphates (LiPON). These processes are characterized here to obtain the highest possible Li-ion conductivity. Li 3 PO 4 is shown to yield a conductivity of 10 -10 S/cm. On the other hand, an optimized LiPON process gave rise to a Li-ion conductivity of 5⋅10 -7 S/cm. In addition, good conformality of the LiPON process was shown on high aspect ratio pillars. Furthermore, a solid state battery device was fabricated comprising a Li 4 Ti 5 O 12 cathode, a 70 nm thick ALD LiPON solid electrolyte and a metallic lithium anode. The fabricated device is based on the thinnest solid electrolyte used so far as well as on the first ALD deposited solid electrolyte. 10.1149/07520.0061ecst ©The Electrochemical Society ECS Transactions, 75 (20) 61-69 (2017) 61 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.155.145.243 Downloaded on 2017-08-23 to IP

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Link to publication• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. All solid state 3D batteries are pursued for their increased safety and high power capabilities. At present conformal coating of the solid electrolyte remains one of the key hurdles for the implementation of such devices. In the present work we investigate atomic layer deposition (ALD) as means of conformal deposition of lithium phosphate (Li 3 PO 4 ) and nitrogen doped lithium phosphates (LiPON). These processes are characterized here to obtain the highest possible Li-ion conductivity. Li 3 PO 4 is shown to yield a conductivity of 10 -10 S/cm. On the other hand, an optimized LiPON process gave rise to a Li-ion conductivity of 5⋅10 -7 S/cm. In addition, good conformality of the LiPON process was shown on high aspect ratio pillars. Furthermore, a solid state battery device was fabricated comprising a Li 4 Ti 5 O 12 cathode, a 70 nm thick ALD LiPON solid electrolyte and a metallic lithium anode. The fabricated device is based on the thinnest solid electrolyte used so far as well as on the first ALD deposited solid electrolyte.

Quadrupole mass spectrometry was carried out to detect and identify the reaction products during atomic layer deposition (ALD) of lithium carbonate (Li 2 CO 3 ). We examined gas phase species for thermal ALD using a LiO t Bu precursor together with H 2 O and CO 2 and plasma-assisted ALD using the same lithium precursor combined with an O 2 plasma. For both processes it was concluded that in the first half-cycle the LiO t Bu chemisorbs on the surface by an association reaction of the complete precursor whereas in the second half-cycle the organic ligand is abstracted as tert-butanol. The differences between the two processes lie mainly in the formation of CO 2 and H 2 O reaction byproducts in the second half-cycle when an O 2 plasma is used as coreactant instead of H 2 O. The generation of CO 2 supports the fact that it is possible to deposit Li 2 CO 3 films directly by plasma-assisted ALD. Instead, in the case of thermal ALD, an additional CO 2 dose step is required to deposit Li 2 CO 3 and suppress LiOH or Li 2 O formation. The reaction with CO 2 appears to be reversible at higher deposition temperatures (T ≥ 250 °C) and by using extended plasma exposure times, and therefore the composition of the plasma-assisted ALD films can be varied between Li 2 CO 3 and Li 2 O.

High purity, uniform, and conformal aluminum phosphate (AlPxO y ) thin films were deposited by atomic layer deposition (ALD) between 25 and 300 °C using supercycles consisting of (i) PO­(OMe)3 dosing combined with O2 plasma exposure and (ii) AlMe3 dosing followed by O2 plasma exposure. In situ spectroscopic ellipsometry and mass spectrometry were applied to demonstrate the ALD self-limiting behavior and to gain insight into the surface reactions during the precursor and coreactant exposures, respectively. Compared to earlier reported AlPxO y ALD studies using H2O and O3 as coreactants or without using coreactans, the use of an oxygen plasma generally leads to higher growth per cycle values and promotes phosphorus incorporation in the film. Specifically, when using a 1:1 PO x :Al2O3 cycle ratio and a substrate temperature of 150 °C, the growth per supercycle is found to be 1.8 Å. The [P]:[Al] atomic ratio for this process is approximately 0.5 (∼AlP0.5O2.9) and can be tailored by changing the ratio between the two cycles or the substrate temperature. In literature reports where the same aluminum precursor was used, the [P]:[Al] atomic ratio was limited to 0.2 or a very high number of phosphorus cycles was needed in order to increase the phosphorus content. Instead, we demonstrate deposition of films with a composition close to AlPO4 by using a 2:1 PO x :Al2O3 cycle ratio. The limited incorporation of P in the film is suspected to derive from the steric hindrance of the relatively bulky phosphorus precursor. Mass spectrometry suggests that the PO­(OMe)3 precursor chemisorbs on the surface without the release of reaction products into the gas phase, whereas Al­(Me)3 already undergoes methyl ligand abstraction upon chemisorption.