Short communication Ion-implantation modification of lithium–phosphorus oxynitride thin-films Byoungsoo Kim a , Yoon Sang Cho b , Joon-Gon Lee a , Kyong-Hee Joo a , Kwang-Ok Jung a , Jeongmin Oh a , Byungwoo Park a,* , Hun-Joon Sohn a , Tak Kang a , Jaephil Cho b , Young-Shin Park c , Joo Yeol Oh c a School of Materials Science and Engineering, Seoul National University, Seoul 151-744, South Korea b Samsung SDI Co. Ltd., Kiheoung, Yongin city 449-901, South Korea c Samsung Advanced Institute of Technology, Suwon, Kyunggi-Do 440-600, South Korea Received 27 August 2001; accepted 10 January 2002 Abstract Among various solid electrolytes, the lithium–phosphorus oxynitride (Lipon) electrolyte synthesized by sputtering of Li 3 PO 4 in pure N 2 has a good ionic conductivity of 2ð1Þ 10 6 S cm 1 at 25 8C. As the nitrogen concentration increases in the Lipon electrolyte, the ionic conductivity is reported to increase as a result of a higher degree of cross-links. When Lipon films are deposited by sputtering, however, it is reported that the maximum nitrogen concentration saturates approximately at 6 at.%. By non-equilibrium processes, such as ion-implantation, nitrogen concentration can be controlled over 6 at.%. This study investigates the effect of nitrogen concentration on the ionic conductivity in Lipon films by using ion-implantation. Impedance measurements at 25 8C show that the nitrogen-implanted Lipon films enhance or retard the ionic conductivity over a wide range after nitrogen-implantation, when compared with as-deposited thin-films. # 2002 Elsevier Science B.V. All rights reserved. PACS: 84.60.Dn; 67.72.Ww Keywords: Ion-implantation; Lipon; Solid electrolyte; Ionic conductivity 1. Introduction With the development of electronic devices, thin-film solid-state batteries have received greater attention for the fabrication of batteries that can be completely integrated with microcircuits, such as microdevices, microsensors, and very-large-scale integration (VLSI). The operational accept- ability of such integrated devices is contingent on the high specific energy and low-power consumption of lithium-ion batteries [1–4]. Among all possible anode materials, lithium is the most attractive, since it has a favorable thermodynamic electrode potential with high specific capacity. Lithium metal, however, is very reactive with many solid-state electrolytes. Among various types of electrolytes, solid- sulfide electrolytes are excellent on account of their high ionic conductivity. Unfortunately, these materials typically form a resistive layer at the interface due to a reaction with the lithium metal, and the performance of a lithium battery starts to degrade [5,6]. Lithium–phosphorus oxynitride (Lipon) thin-film was first developed by Bates et al. [7]. Lipon has a good ionic conductivity, viz., 2ð1Þ 10 6 S cm 1 at 25 8C, and good electrochemical stability over 5 V(versus Li/Li þ ). Bates et al. suggested that the ionic conductivity of Lipon is increased by the enhancement of cross-links due to nitrogen incorporation, and reported that the nitrogen amount in as- deposited Lipon is saturated at approximately 6 at.% [7,8]. In sputtering, nitrogen atoms substitute for bridging (–O–) or non-bridging (=O) oxygen atoms in Li 3 PO 4 . This leads to two-coordinated (–N=) or three-coordinated (–N3) nitro- gen atoms, which cause higher cross-linked microstructures for increasing the ionic conductivity. Hence, it is considered that the ionic conductivity is closely related to the nitrogen concentration in Lipon. It was reported [7,8] that the typical composition of Lipon is Li 2.9 PO 3.3 N 0.46 , which has a max- imum nitrogen concentration of 6 at.%. There have been various attempts to increase the nitrogen concentration in oxynitride glass to incorporate more cross-links, but these Journal of Power Sources 109 (2002) 214–219 * Corresponding author. Tel.: þ82-2-880-8319; fax: þ82-2-885-9671. E-mail address: byungwoo@snu.ac.kr (B. Park). 0378-7753/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0378-7753(02)00036-8