NOVELTY - A flexible solid state thin film electrochemical device (10) comprises a flexible substrate (12); first (14) and second (18) electrodes; and an electrolyte (16) disposed between the electrodes, where the electrolyte is disposed on the flexible substrate. The first electrode is disposed on the electrolyte and the second electrode is buried between the electrolyte and the substrate.    USE - As flexible solid state thin film electrochemical device e.g. lithium ion battery for forming stack of thin film battery (claimed).    ADVANTAGE - The lithium materials deposited on flexible substrate provides flexible solid state lithium ion batteries having good structural and/or electrical or electrochemical characteristics. The flexible solid state thin film electrochemical device provides more compact constructions on flexible polymer substrates. The device exhibits increased power density per unit area of the substrate material by eliminating substrate materials and sharing current collectors. Arranging thin film battery structures using flexible thin films on thin, flexible substrates, allows stacking or rolling of thin film batteries in a way such that the storage density of battery can rival bulk batteries, while retaining the beneficial attributes (e.g. long cycle life and safety) of the thin film batteries. The device produces lithium based batteries which can be air stable. Low temperature processing (e.g. room temperatures) allows for use of polymer substrates.    DETAILED DESCRIPTION - A flexible solid state thin film electrochemical device (10) comprises a flexible polymeric substrate (12); first (14) and second (18) electrodes; and an electrolyte (16) disposed between the electrodes, where the electrolyte is disposed on the flexible substrate. The first electrode is disposed on the electrolyte and the second electrode is buried between the electrolyte and the substrate. At least one of the electrodes and the electrolyte are thin film layers. The device is in a rolled and/or a folded form. The device further comprises stacked layers of two additional electrodes and, an additional electrolyte disposed between the two additional electrodes; a flexible insulating layer; and at least one current collector. INDEPENDENT CLAIMS are included for the following:    (1) making a flexible solid state thin film electrochemical device involving depositing an electrolyte on a flexible supporting material; depositing an electrode on the electrolyte; and forming a buried electrode between the electrolyte and the flexible supporting material; and    (2) forming a flexible solid state thin film lithium ion battery structure from two stacked batteries of multiple layers upon a flexible substrate, where each of the two stacked batteries includes two lithium reactive electrodes and a lithium-based electrolyte, involving forming a first battery by forming an electrolyte layer on a flexible substrate, forming a first electrode layer on the electrolyte layer with a first current collector, and forming a second electrode layer buried beneath the electrolyte layer; forming a second battery on the first battery by forming a second electrolyte layer on the first current collector layer of the first battery; and forming a third electrode layer.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic isometric view of the thin film battery device.    Flexible solid state thin film electrochemical device (10)    Flexible substrate (12)    First electrode (14)    Electrolyte (16)    Second electrode (18)