To accommodate the down-scaling electronic industry, the energy storage changes into micro-scale or even nano-scale. Therefore, development of new methods and materials that can provide microwattsis highly needed. We focus on using thin-film solid-state micro-batteries that are basically relied on electrochemical potential difference of metals. Zinc and Copper are used as the electrodes and paper as a separator with an electrolyte layer. Two different methods were developed for the fabrication of paper batteries, physical vapor deposition (PVD) of thin films and the chemical sintering of metal microparticles. Zinc and Copper were chosen as proof-of-concept electrodes because the fabrication methods are fairly straightforward. Paper has been chosen as a separator applications mainly thanks to its high porosity and robust chemical and mechanical stability [1]. The popular ink printing technology has been explored and the results are promising including carbon nanotubes to the metal nanoparticles. Dispensing an ionic liquid using a special printer with the electrodes, researchers from UC Berkeley have achieved good results [2, 3].

We proposed the use of Copper (Cu) and Zinc (Zn) nanoparticles as the electrodes for thin-film microbatteries in the applications of micro-scale sensors. Compared to the widely used lithium-based batteries, Cu and Zn nanoparticles are less expensive, less prone to oxidation (thus involving simpler fabrication steps) and flammability, safe to use, and only requires very simple fabrication processes.Even though the voltage output is inherently smaller (∼1V) than conventional lithium-based batteries, it is sufficient for low-voltage Integrated Circuits (IC) technologies such as 130 nm and 90 nm channel length transistor processes. Commercial paper will be used as the separator to demonstrate the battery capacity. Paper that acts as the separator is slurry-casted with nanoparticles (30-40 nm in size) on both sides. The thickness of the metal nanoparticles-coated thin films and the paper separator are 1 μm and 100 μm, respectively. The electrodes were developed to achieve high conductivity (lower than 1 (Ω·cm)−1) with smooth surface, good adhesion, and flexibility. The metal nanoparticles will be formulated to slurry solutions for screen printing or ink-jet printing for the battery fabrication. For fabrication purposes, the slurries viscosity is approximately in the range of 10-12 cPs at the operating temperature, a surface tension between 28-33 dynes/cm. During the fabrication process including printing/coating and sintering, reductive environment is required to minimize the oxidation. AFM (Atomic Force Microscopy) and EDS (Energy Dispersive Spectroscopy) results will be employed to demonstrate the surface morphology as well as the percentages of metal oxides. Batteries will be tested with and without an ionic liquid for comparison. Humidity effects on the battery performance will also be discussed. Different geometries that are designed to make the batteries with higher voltage or charge will be proposed. Characterization results will include the open-circuit voltage, dielectric property, charging and discharging curve, capacitance and capacity, AFM of the surface test, EDS of the electrodes and the SEM (Scanning Electron microscopy) of the particles.Ourresearch suggest that conductive paper can be scalable and could make high-performance energy storage and conversion devices at low cost and would bring new opportunities for advanced applications.