On-Chip Microsupercapacitors Using Ultrathin Lipon Film

Abstract

On-chip solid-state micro-supercapacitors (MSCs) have been the center of massive researches over the recent years due to their wide range of applications (wearables, IoT, etc.), and the unremitting need for miniaturization and high electrical performances1. Moreover, MSC are known to gather high power density and extremely long cycle life2. In particular, the use of stable solid-state electrolytes in MSC is required to overcome safety issues (electrochemical and temperature instabilities) and enable easy packaging for on-chip integration3. Lithium phosphorous oxinitride (LiPON) solid-state electrolyte has aroused a growing interest for MSCs due to its well-known excellent electrochemical properties (ionic conductivity, potential and temperature stability, etc.)4. Furthermore, the recently proved feasibility of ultrathin and conformal films deposition5,6 makes LiPON a particularly interesting candidate for energy storage solutions with high aspect ratio architectures. To the best of our knowledge, no study has reported on the use of ALD LiPON for MSCs. In this work, we propose a thorough study of a 2D-planar ultrathin LiPON film for inorganic solid-state on-chip MSC. We obtained an uniform and homogeneous 10nm thick LiPON from the LiOtBu-DEPA chemical reaction. The elemental composition of the as deposited LiPON is determined by X-ray Photoelectron Spectroscopy as Li1.75PO2.5N0.6. The associated ionic conductivity is calculated around 10-8 S/cm at 25°C, and an activation energy of 0.62 eV is extracted using Electrochemical Impedance Spectroscopy within 20-50°C range. TiN/LiPON/Ti MIM structures have been considered to characterize our MSC. The fabricated device exhibits typical capacitance values as high as 100 µF/cm² for scan rates up to 1 V/s. The capacitive and faradaic dependences of MSC will be discussed. A good cycling ability (>103 cycles) within the 0 – 3V voltage range is also recorded by applying a constant current of 100 µA/cm². Rate dependence and voltage stability window of MSC will also be reported.