Abstract
Nanoindentation has been used to characterize the elastic modulus and hardness of LiPON films ranging in
thickness from 1 to 10 μm. Four fully dense, amorphous films were deposited on glass and sapphire substrates
with one film annealed at 200 °C for 20 min. The modulus of LiPON is found to be approximately 77 GPa, and
argued to be independent of the substrate type, film thickness, and annealing. Based on the numerical analysis
of Monroe and Newman, this value may be sufficiently high to mechanically suppress dendrite formation at
the lithium/LiPON interface in thin film batteries [1]. Using Sneddon's stiffness equation and assuming the
modulus is 77 GPa, the hardness is found to be approximately 3.9 GPa for all but the annealed film. The
hardness of the annealed film is approximately 5% higher, at 4.1 GPa. Atomic force microscopy images of the
residual hardness impressions confirm the unexpected increase in hardness of the annealed film. Surprisingly,
the indentation data also reveal time-dependent behavior in all four films. This indicates that creep may also
play a significant role in determining how LiPON responds to complex loading conditions and could be
important in relieving stresses as they develop during service.
