TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Particles: The inorganic particles have dielectric constant of 5 or more, preferably 100 or more. The inorganic particles comprise piezoelectric particles, and have size of 0.001-10 mu m. The inorganic particles comprise barium titanate, lead-zirconium/titanium oxide (Pb(Zr,Ti)O3), lead lanthanum zirconium titanium oxide (Pb1-x'Lax'Zr1-y'Tiy'O3, where x' and y' are not defined), lead magnesium niobium oxide (Pb(Mg3Nb2/3)O3)-lead titanate (PbTiO3), hafnium oxide, strontium titanate, tin oxide, cerium oxide, magnesium oxide, nickel oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, alumina, titania, silicon carbide, lithium titanium phosphate (LiTi2(PO4)3) or their mixture, preferably barium titanate, lead magnesium niobium oxide-lead titanate, lead-zirconium/titanium oxide, lead lanthanum zirconium titanium oxide, alumina, lithium titanium phosphate or hafnium oxide, more preferably barium titanate. The inorganic particles consist of mixture of barium titanate and lithium titanium phosphate in weight ratio of 50:50, or mixture of barium titanate and alumina in weight ratio of 20:80. The inorganic particles comprise lithium phosphate, lithium titanium phosphorus oxide (LixTiy(PO4)3, where x is 0-2 and y is 0-3), lithium aluminum titanium phosphorus oxide (LiaAlbTic(PO4)3, where a is 0-2, b is 0-1 and c is 0-3), lithium aluminum titanium phosphorus oxide ((LiAlTiP)dOe, where d is 0-4 and e is 0-13) glass, lithium lanthanum titanium oxide (LifLagTiO3, where f is 0-2 and g is 0-3), lithium germanium phosphorus sulfide (LihGeiPjSk, where h is 0-4, i is 0-1, j is 0-1, and k is 0-5), lithium nitride (LilNm, where l is 0-4 and m is 0-2), silicon sulfide type glass, lithium silicon sulfide (LinSioSp, where n is 0-3, o is 0-2 and p is 0-4), phosphorus sulfide (P2S5) type glass, lithium phosphorus sulfide (LiqPrSs, where q is 0-3, r is 0-3, and s is 0-7), or their mixture. The inorganic particles comprise lithium oxide-alumina-titania-phosphorus pentoxide (14Li2O-9Al2O3-38TiO2-39P2O5) glass, lithium-germanium-phosphorus sulfide (Li3.25Ge0.25P0.75S4), lithium nitride (Li3N), lithium phosphorus oxide-lithium sulfide-silicon sulfide (Li3PO4-Li2S-SiS2) glass, lithium iodide-lithium sulfide-phosphorus sulfide (LiI-Li2S-P2S5) glass, or their mixture. The amount of inorganic particles with respect to total amount of porous film is 50-99 wt.%. The weight ratio of inorganic particles and binder polymer is 50:50-90:10.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The interstitial volumes have a curved shape defined by the shape of the interconnected inorganic particles. The binder polymer is interposed between adjacent inorganic particles of the interconnected inorganic particles, and the interstitial volumes are defined by the adjacent inorganic particles and the binder polymer. The binder has solubility parameter of between 15 MPa1/2 and 45 MPa1/2. The binder is chosen from polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethyl polyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxymethylcellulose, acrylonitrile-styrene-butadiene copolymer, polyimide, or their mixture, preferably polyvinylidene fluoride, polyvinylidene fluoride-hexafluoro propylene copolymer, or carboxymethylcellulose. The interstitial volume has size of 0.01-1 mu m. The composite porous film has porosity of 5-95%. The average size of interstitial volumes is less than average size of inorganic particles. The composite porous film is dimensionally stable at 120 degrees C or more, retains more than 10% of its original size when treated at 150 degrees C for 1 hour, and has thickness of 1-100 mu m. The binder polymer has a dielectric constant of 1-100, when measured at 1 kz. The composite porous film is provided on a porous substrate. The porous substrate is made of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetherether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, or their mixture.