Electrochemically controlled transport of lithium through ultrathin SiO2

Abstract

Monolithically integrating the energy supply unit on a silicon integrated circuit (IC) requires the development of a thin-film solid-state battery compatible with silicon IC fabrication methods, materials, and performance. We have envisioned materials that can be processed in a silicon fabrication environment, thus bringing local stored energy to silicon ICs. By incorporating the material directly onto the silicon wafer, the economic parallelism that silicon complementary metal-oxide-semiconductor (CMOS) technology has enjoyed can be brought to power incorporation in each IC on a processed wafer. It is natural to look first towards silicon CMOS materials, and ask which materials need enhancement, which need replacement, and which can be used “as is.” In this study, we begin by using two existing CMOS materials and one unconventional material for the construction of a source of electric power. We have explored the use of thermally grown silicon dioxide (SiO2) as thin as 9nm acting as an electrolyte material candidate in a solid-state power cell integrated on silicon. Other components of the thin-film cell consisted of rf-sputtered lithium cobalt oxide (LiCoO2) as the cathode and highly doped n-type polycrystalline silicon (polysilicon) grown by low-pressure chemical-vapor deposition as the anode. All structures were fabricated using conventional microelectronics fabrication technology. The charge and discharge behaviors of the LiCoO2∕SiO2∕polysilicon cells were studied. On the basis of the impedance measurements an equivalent circuit model of an ultrathin cell was inferred, and its microstructure was characterized by electron microscopy imaging. In spite of its high series resistance (∼4×107Ω), we have shown that an ultrathin layer of an as-deposited Li-free SiO2 is an interesting candidate for an electrolyte or controllable barrier layer in lithium-ion-based devices.

Electrochemical Thin Films at and above the Classical Limiting Current

“…This contradicts our macroscopic intuition about electrolytes, but, in very thin films, complete anion deplection might occur. For example, in a microbattery developed for on-chip power sources using the Li/SiO 2 /Si system, lithium ion conduction has recently been demonstrated in nano-scale films of silicon oxide, where there should not be any counter ions or excess electrons [6].…”

“…Thin-film technologies offer a promising way to construct rechargeable micro-batteries, which can be directly integrated into modern electronic circuits [1,2,3,4,5,6]. Due to the power-density requirements of many applications, such as portable electronics, micro-batteries are likely to be operated under at high current density, possibly exceeding diffusion limitation.…”

Polymer-based technology platform for robust electrochemical sensing using gold microelectrodes

“…As can be seen, this passivation process can be applied for materials where a low process temperature is crucial. Following literature references for the modeling of impedance of thin film electrodes [40,41], the equivalent circuit chosen (figure 4.b) gave the best fit results (chi-squared ≈ 10 -3 ) when modeled using numerical software analysis. This impedance model is similar to the Voigt's structure [42] and consists of a resistance, R e , and two RC circuits in series, in which the second capacitor is replaced by a diffusion-related constant phase element (CPE) (n = 0.5 ± ε, where 0 < ε ≤ 0.1).…”

Field-Limited Migration of Li-Ions in Li-Ion Battery

“…Low-dimensional Si-structures have been studied in rechargeable LIBs 3-7 to improve the cyclic performance and structural durability of Si-based anodes. The results from the studies 3-7 have demonstrated that low-dimensional Si-structures have the potential to offer high reversible capacity and long service life.Ariel et al 8 observed that the ability to store and deliver charge for electrochemical cells consisting of LiCoO 2 (cathode)/SiO 2 /Si(anode) was inversely proportional to current density. Zhou et al 9 suggested that the driving force for Li-migration was the gradient of electric potential and the concentration gradient of Li ions.…”

“…Ariel et al 8 observed that the ability to store and deliver charge for electrochemical cells consisting of LiCoO 2 (cathode)/SiO 2 /Si(anode) was inversely proportional to current density. Zhou et al 9 suggested that the driving force for Li-migration was the gradient of electric potential and the concentration gradient of Li ions.…”