Atomic Layer Deposition of Lithium Phosphorus Oxynitride

Abstract

An atomic layer deposition (ALD) process is successfully developed for fabricating high-quality lithium phosphorus oxynitride (LiPON) thin films for a potential use as a conformal solid-state electrolyte coating in 3D Li-ion microbattery technology. In our ALD process the challenge of simultaneously incorporating phosphorus and nitrogen in the films is overcome by using a novel nitrogen-containing phosphorus precursor, diethyl phosphoramidate, together with lithium hexamethyldisilazide as the lithium precursor. A temperature window is found around 270−310°C, where homogeneous films are realized and the film growth is controlled in a digital manner by the number of ALD cycles at a rate of ∼0.7 Å/cycle. The process allows for a high N-to-P ratio in the films, which is beneficial for achieving the required high ionic conductivity. For a film deposited at 330°C with a composition of Li 0.95 PO 3.00 N 0.60 according to RBS/NRA analysis, an ionic conductivity value as high as 6.6 × 10 −7 S cm −1 is measured at 25°C.

Metal Fluorides as Lithium-Ion Battery Materials: An Atomic Layer Deposition Perspective

“…Recently, the deposition of LiPON was achieved both by thermal and plasma-enhanced ALD [108,109,130]. In the PEALD process, LiO t Bu was used as the lithium source combined with a pulsing sequence of water, TMPO and nitrogen plasma [109].…”

“…By using nitrogen plasma after the TMPO pulse, nitrogen could be incorporated into the films, causing the amorphization of the crystalline Li 3 PO 4 . In the thermal ALD process, the problems of nitrogen incorporation and nitrogen-phosphorous bond formation were resolved by using diethyl phosphoramidate, DEPA, a phosphate precursor with an amine group (Figure 9) [108]. By using DEPA with LiO t Bu, nitrogen contents as high as 9.7 at.% were achieved.…”

“…Both processes deposited conformal coatings on demanding substrates as required from a potential solid electrolyte material. In addition, very good electrochemical properties were realized with ionic conductivities of 1.45 × 10 −7 S/cm for the PEALD process (5 at.% nitrogen) and 6.6 × 10 −7 S/cm for the thermal ALD process (9.7 at.% nitrogen) [108,109]. The plasma-deposited LiPON has already been studied as a protecting layer for a conversion lithium-ion battery electrode.…”

“…Many materials, both crystalline and amorphous, have been deposited and ionic conductivities of the order of 10 −7 S/cm have been obtained with various materials. Of the traditional solid electrolytes, LiPON has been deposited using both ALD and PEALD [108,109]. Table 6.…”

Plasma - Assisted ALD of Lipo(N) for Solid State Batteries

“…Crystalline Li 3 PO 4 on the other hand only provides a conductivity of 10 -18 S/cm. Recently, ALD depositions of both Li 3 PO 4 and LiPON have been reported in literature (6)(7)(8)(9).…”