The　SiO2/polymide　(PI)/SiO2　composite　films　were　deposited　by　a　combination　of　RF　magnetron　sputtering　and　chemical　solution　deposition.　The　microstructures　and　properties　of　the　composite　films　were　characterized　with　X-ray　diffraction　and　scanning　electron　microscopy.　The　impacts　of　the　deposition　conditions　on　quality　of　the　films　were　studied.　The　prototyped　under-gate　field　emission　display　(FED)　device　was　fabricated　with　the　SiO2/PI/SiO2　composite　films.　Various　properties　of　the　device,　including　the　breakdown　and　on-set　voltages,　peak　emission　current,　density,　luminous　intensity,　and　leakage　current,　were　measured.　The　results　show　that　the　SiO2/PI/SiO2　composite　film　is　a　potential　device-grade　FED　material　with　high　breakdown　voltage　and　low　leakage　current.　For　example,　at　an　anode　voltage　of　750　V　and　an　on-set　grid　voltage　of　91　V,　the　anode　and　grid　currents　were　found　to　be　384　μA　and　59　μA,　respectively,　with　a　luminous　intensity　of　600　cd/m2.