Novel Thin Film Solid State Ionic Device with Electrochemically Tunable Resistance Based on Lithium Plating/Stripping

Abstract

Electrochemically induced property tuning has recently emerged as a promising pathway to achieve accordable devices and reconfigurable circuits, in most cases making use of the change of one or several material properties with ion exchange or the local electroformation of conducting structures in an insulating material [1–3]. In the present work we report on the electrochemical tuning of a solid state ionic device impedance using lithium ion plating and stripping at a current collector/solid electrolyte interface [4,5]. The device presented a design with two actuation vertical metal electrodes separating a Cu/LiPON/Li multilayer, and two measurement interdigitated electrodes embedded in the LiPON layer. The measurement electrodes were isolated from the bottom actuation electrode by an Al2O3 dielectric layer (Fig1). The devices were microfabricated on silicon substrates with varied architectures including lithium plating surfaces ranging between 1µm² and 3000µm² (Fig.2). Upon chrono-potentiometric stimuli, lithium was plated between the measurement electrodes, thus changing significantly the impedance, and more particulary the electrical resistance. Fully reversible variation of the real part of the impedance (Re Z) over a range of more than 3 decades was observed by electrochemical impedance spectroscopy upon the formation and dissolution of nanometric lithium layer (Fig.3). Particular attention was put on the investigation of the influence of the current density during plating/stripping (plated lithium morphology), and the architecture (interdigitated electrodes design, plating surface) on the device performance.