Ag-doped polymer (polyethylene oxide: PEO) conductive-bridging-random-access-memory (CBRAM) cell using inert Pt electrodes is a potential electro-forming free CBRAM cells in which electro-forming and electro-breaking of nanoscale (16~22-nm in diameter) conical or cylindrical Ag filaments occurs after a set or reset bias is applied. The dependency of the morphologies of the Ag filaments in the PEO polymer electrolyte indicates that the electro-formed Ag filaments bridging the Pt cathode and anode are generated by Ag+ ions drifting in the PEO polymer electrolyte toward the Pt anode and that Ag dendrites grow via a reduction process from the Pt anode, whereas electro-breaking of Ag filaments occurs through the oxidation of Ag atoms in the secondary dendrites and the drift of Ag+ ions toward the Pt cathode. The Ag doping concentration in the PEO polymer electrolyte determines the bipolar switching characteristics; i.e., the set voltage slightly decreases, while the reset voltage and memory margin greatly increases with the Ag doping concentration.