CRADA Final Report: Properties of Vacuum Deposited Thin Films of Lithium Phosphorous Oxynitride (Lipon) with an Expanded Composition Range Page: 4 of 9
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Thin films of an amorphous, solid-state, lithium electrolyte, referred to as "Lipon," were
first synthesized and characterized at ORNL in 1991. This material is typically prepared by
magnetron sputtering in a nitrogen plasma, which allows nitrogen atoms to substitute for part of
the oxygen ions of Li3PO4. Lipon is the key component in the successful fabrication of ORNL's
rechargeable thin film microbatteries. Cymbet and several other US Companies have licensed
this technology for commercialization. Optimizing the properties of the Lipon material,
particularly the lithium ion conductivity, is extremely important, yet only a limited range of
compositions had been explored prior to this program. The goal of this CRADA was to develop
new methods to prepare Lipon over an extended composition range and to determine if the film
properties might be significantly improved beyond those previously reported by incorporating a
larger N component into the film.
Cymbet and ORNL investigated different deposition processes for the Lipon thin films.
Cymbet's advanced deposition process not only achieved a higher deposition rate, but also
permitted independent control the O and N flux to the surface of the growing film. ORNL
experimented with several modified sputtering techniques and found that by using sectored
sputter targets, composed of Li3PO4 and Li3N ceramic disks, thin Lipon films could be produced
over an expanded composition range.
The resulting Lipon films were characterized by electrical impedance, infrared
spectroscopy, and several complementary analytical techniques to determine the composition.
When additional N plus Li are incorporated into the Lipon film, the lithium conductivity was
generally degraded. However, the addition of N accompanied by a slight loss of Li gave an
increase in the conductivity. Although the improvement in the conductivity was only very
modest and was a disappointing conclusion of this study, forcing a higher N content in the Lipon
may alleviate some of the run-to-run variations in the Lipon quality that have been problematical
Statement of Objectives:
The common objective for both participants of this crada was to synthesize and
characterize lipon thin films with nitrogen and lithium concentrations in excess of typical
compositions currently used at ORNL. This was accomplished. Although the results were
disappointing for the commercial applications of Lipon, a broader understanding of the effects of
composition and structural relaxation on the lithium conductivity was gained. In addition,
Cymbet has demonstrated that Lipon films of good quality can be deposited by a more
economical and practical high-deposition rate process.
The second objective for ORNL researchers was to investigate the oxygen-nitrogen
equilibrium for the lipon films during film deposition. Little progress was made on this
challenging undertaking to develop new approaches to monitor and control the oxygen partial
pressure within the plasma. Such a project would be worthy of additional effort in the future. If
successful it might advance our ability to reproducibly control the film stoichiometry for a
variety of thin film materials.
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Dudney, N.J. CRADA Final Report: Properties of Vacuum Deposited Thin Films of Lithium Phosphorous Oxynitride (Lipon) with an Expanded Composition Range, report, December 29, 2003; [Tennessee]. (digital.library.unt.edu/ark:/67531/metadc874987/m1/4/: accessed December 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.