Description
Lithium phosphorus oxynitride (LiPON) is a state-of-the-art solid electrolyte material for thin-film microbatteries (TFBs) [1]. LiPON as electrolyte material has low resistivity and high ionic conductivity for TFBs, even though the performance of TFBs is often more limited by the surface area of their active battery materials. This can be increased, without greatly increasing the dimensions of the batteries, by 3D-structuring the active materials. This creates a need for conformal thin films on high aspect ratio (AR) surfaces. Among the advanced thin-film fabrication methods, atomic layer deposition (ALD) is believed to stand out in terms of conformality [2]. Here, we have studied the conformality of thin ALD-grown LiPON films using lateral high-aspect-ratio test structures. Two different lithium precursors, lithium tert-butoxide (LiOtBu) and lithium bis(trimethylsilyl)amide (Li-HMDS), were investigated in combination with diethyl phosphoramidate (DEPA), the latter being the source of oxygen, phosphorus and nitrogen. The depositions were carried out in same reactor at a deposition temperature of 290 °C. The precursor temperatures were 130, 60 and 85 °C for LiOtBu, Li-HMDS and DEPA, respectively. Pulse and purge times were 5 s / 5 s for LiOtBu, and 3 s / 3 s for both Li-HMDS and DEPA.The results indicated that the film growth proceeded significantly deeper into the 3D cavities for the films grown from LiOtBu, while the Li-HMDS-based films grew more conformally initially, right after the cavity entrances. LiOtBu-based films were seen growing 3 times as deep as the Li-HMDS-based films. The penetration depth into the lateral cavities of the lateral high aspect ratio test structures was then converted to a dimensionless equivalent aspect ratio (EAR), that can be compared to the results from other 3D geometries, under similar experimental conditions. For the LiOtBu-based process, the visible film growth reached up to EAR = 316, which is highest among previously reported values [2,3]. Differences in precursor diffusion and reactivity can explain the observed results. The results also open possibilities for the use of LiPON as a solid electrolyte in batteries with high-surface-area electrodes. This could unlock faster charging and discharging for TFBs, as well as the use of thin-film techniques as suitable fabrication methods for microbatteries.
References
[1] Oudenhoven, J. F. M.; Baggetto, L.; Notten, P. H. L. All-Solid-State Lithium-Ion Microbatteries: A Review of Various Three-Dimensional Concepts. Adv. Energy Mater. 2011, 1, 10–33.
[2] Nisula, M.; Shindo, Y.; Koga, H.; Karppinen, M. Atomic Layer Deposition of Lithium Phosphorus Oxynitride. Chem. Mater. 2015, 27, 6987–6993.
[3] Put, B.; Mees, M. J.; Hornsveld, N.; Hollevoet, S.; Sepúlveda, A.; Vereecken, P. M.; Kessels, W. M. M.; Creatore, M. Plasma-Assisted ALD of LiPO(N) for Solid State Batteries. J. Electrochem. Soc. 2019, 166, A1239–A1242.
| Aikajakso | 2024 |
|---|---|
| Pidetty | European Materials Research Society-konferenssi, Ranska |