Solution　processed　metal　oxide　thin-film　transistors　(MO-TFTs)　have　gained　momentum　in　recent　years　and　opened　new　horizons　for　their　extended　applications　in　thin-film　optoelectronics.　Unfortunately,　the　relatively　high　processing　temperature　has　become　the　main　limitation　for　their　commercial　application　in　flexible　electronics.　In　this　work,　ultrashort　femtosecond　(fs)　laser　pulses　were　used　for　the　annealing　of　printed　InGaZnO　TFT　arrays　with　low　temperature　and　fast　processing.　The　high　transient　intensity　and　negligible　heat-affected　zone　is　beneficial　to　the　effective　conversion　of　precursor　to　metal-oxide　lattices,　which　was　also　verified　by　the　x-ray　photoelectron　spectroscopy　analysis.　Moreover,　for　the　first　time,　based　on　optical　engineering　method,　dielectric　mirrors　(DMs)　is　proposed　to　realize　reflection　of　photon　irradiation　and　protect　the　underlying　polymer　substrate.　TFTs　on　polyethylene　naphthalate　(PEN)　substrate　with　polymer　insulator　exhibited　a　mobility　of　4.24　cm2　V-1　s-1,　along　with　good　mechanical　stability.　The　mechanism　of　DMs　for　the　improvement　of　the　device　performance　was　systematically　investigated　based　on　laser-matter　interaction,　optical　structure　and　photon　transport.　DMs　can　reduce　laser-induced　pressure　and　variation　of　dielectric　properties　in　PEN　substrate　resulting　from　the　impact　ionization　due　to　a　strong　nonlinear　multi-photon　absorption.　Our　work　clearly　demonstrated　that　flexible　MO-TFTs　can　be　simply　fabricated　with　fs-laser　annealing.　More　importantly,　this　novel　method　is　applicable　for　a　wide　range　of　MO　and　polymer　substrates,　by　solving　the　incompatibility　of　solution　processed　MO　and　polymer　substrates　due　to　high　processing　temperature.　Therefore,　the　proposed　method　showed　tremendous　potential　to　be　applicable　in　flexible　electronics　such　as　sensors,　display　and　circuits.　©　2019　IOP　Publishing　Ltd.