Résumé
Innovative micro-supercapacitors (MSCs) such as LiPON based MSCs are emerging to address the technological challenges faced at higher frequencies (>kHz),especially energy harvesting and storage, which requires efficient materials coupled with improved microfabrication techniques to unlock the full potential of such devices. In this way, conformal and self-limiting surface reactions enabled by Atomic Layer Deposition (ALD) give great advantages to form and optimize Lithium based thin films compatible with complex geometries. Here in, a multidisciplinary approach was conducted to develop the thermal ALD process, characterize the physico-chemical properties and evaluate the electrical performances of nano-hybrid Solid State Electrolytes (SSE).The thermal ALD process for ultrathin LiPON films (<25nm) is realized using Li-Bistrimethylsilylamide (LiHMDS) and Diethylphosphoramidate (DEPA) precursors in a deposition temperature range 300-350°C. To further optimize LiPON’s electrochemical performances, Trimethyl Aluminium (TMA) and H2O were pulsed to incorporate Al2O3 in SSE films. Ellipsometry was used to calibrate the growth rate of LiPON-based films. The microstructure was analyzed by X-Ray Diffraction (XRD) to highlight the amorphous nature of the thin films, indicating that the Al2O3 incorporation preserves favorable amorphous structure, which is a key characteristic for achieving excellent electrochemical performances [1]. The XPS spectra show typical core peaks (Li1s, P2p, O1s, N1s, Al2p) corresponding to different LiPON based samples. The analysis reveals that Al2O3 insertion seems to impact the nitrogen environment. From N1s spectra (Fig.1), the peaks present two main components located at 397 eV and 399 eV, attributed respectively to a divalent nitrogen state (Nd) and a trivalent nitrogen state (Nt) [1], whose proportion evolves as a function of Al2O3 incorporation. Thus, the concentration of divalent nitrogen becomes predominant over trivalent nitrogen, inducing an increase in the Nd/Nt fraction when more Al2O3 is introduced. This variation has frequently been reported as a major factor in improving Li-ion mobility [1]. The Electrochemical Impedance Spectroscopy (Fig.2) addresses the changes in Li-ion conductivity of the LiPON films upon addition of Al2O3 concentration.This work provides a solid ALD approach with promising potential to optimize the electrical performances (ie Li+mobility, areal capacitance etc) in ultrathin SSE, shedding light on the application of such hybrid microstructures in several Lithionic devices such as micro-supercapacitors, micro-batteries and transistors.