Objective　The　precise　conductive　Cu　micropatterns　have　been　used　in　a　variety　of　electronic　devices.　Compared　to　other　traditional　fabrication　methods,　laser　direct　writing　is　more　efficient　and　reliable.　The　femtosecond　laser　direct　writing　technique,　in　particular,　is　used　to　construct　highly　conductive　Cu　microstructures.　Femtosecond　laser　with　ultrashort　pulse　duration　can　precisely　control　the　heat　input　resulting　in　the　reduction　of　Cu2+　in　the　laser　irradiation　zone　without　the　damage　of　substrate.　However,　the　intensity　is　as　high　as　10(11)　W　.　cm(-2)　and　the　scanning　speed　is　generally　lower　than　10　mm　.　s(-1)　to　achieve　the　necessary　reduction　temperature.　Si　nanoparticles　were　added　to　Cu2+　solution　in　this　study,　acting　as　photon-absorbing　nanoparticles　due　to　their　narrow　band-gap.　The　photon-absorbing　nanoparticles　reduced　the　volume　of　the　reduction　zone　by　decreasing　the　penetration　depth.　The　temperature　of　the　reduction　zone　was　rising,　resulting　in　more　efficient　and　less　expensive　direct　writing.　As　a　result,　the　conductive　Cu　microstructures　were　deposited　on　the　substrate　with　the　intensity　from　5.32　x　10(9)　to　8.51　x　10(9)　W　.　cm(-2)　and　the　scanning　speed　from　100　to　500　mm　.　s(-1).　The　intensity　was　two　orders　of　magnitude　lower,　and　the　direct　writing　efficiency　was　three　orders　of　magnitude　higher,　compared　to　previously　reported　work.　The　impacts　of　scanning　speed　and　intensity　on　the　morphology,　chemical　composition,　and　conductivity　of　Cu　microstructures　were　investigated.　The　lowest　sheet　resistance　was　0.28　Omega　.　sq(-1)　and　the　lowest　electrical　resistivity　was　4.67　x　10(-6)　Omega.m　at　the　intensity　of　5.32　x　10(9)　W　.　cm(-2)　with　a　scanning　speed　of　100　mm　.　s(-1),　respectively.　Methods　The　solvent　was　prepared　by　mixing　6　mL　of　ethylene　glycol　and　3　mL　of　deionized　water.　4　g　of　Cu(　NO3)(2)　.　3H(2)O　was　added　to　the　solvent　with　ultrasonication　for　at　least　30　min　to　thoroughly　dissolve　Cu(　NO3)(2)　.　3H(2)O.　For　2　minutes,　the　liquid　was　heated　to　170　degrees　C　.　The　solvent　received　100　mg　of　Si　nanoparticles.　To　obtain　the　suspension　liquid,　the　mixed　solution　was　ultrasonically　homogenized　for　1　h.　Glass　was　used　as　a　substrate　that　was　adhered　to　the　suspension　liquid　＇　s　surface.　The　laser　beam　scanning　was　controlled　by　a　femtosecond　laser　equipped　with　a　galvanometer　system.　After　the　femtosecond　laser　irradiation,　the　conductive　Cu　microstructure　was　formed　on　the　backside　of　the　substrate.　Then,　the　morphologies　of　the　Cu　microstructures　were　characterized　by　optical　microscopy　and　field　emission　scanning　electron　microscopy.　The　composition　of　the　Cu　microstructures　was　verified　using　X-ray　diffraction.　The　thickness　of　the　microstructures　was　measured　and　the　three-dimensional　topography　of　the　microstructures　was　depicted　using　a　surface　profiler.　Cu　microstructures＇　electrical　properties　were　measured　using　a　source　meter　based　on　the　four-point　probe　method.　Results　and　Discussions　The　continuity　of　laser-fabricated　microstructures　and　the　proportion　of　Cu　increased　with　the　increasing　intensity　(　Fig.　2　and　Fig.　3)　.　The　intensity　was　two　orders　of　magnitude　lower　than　that　in　previous　experiments.　The　addition　of　photon-absorbing　Si　nanoparticles　to　the　suspension　liquid　resulted　in　a　decrease　in　laser　penetration　depth　in　solution,　raising　the　temperature　of　the　laser-induced　reduction　zone　(Fig.　4)　.　The　more　metallic　Cu　was　obtained.　The　continuity　of　microstructures　and　the　proportion　of　Cu　also　increased　with　the　decreasing　scanning　speed　(　Fig.　5　and　Fig.　6　)　.　The　direct　writing　efficiency　was　one　to　three　orders　of　magnitude　higher　than　that　in　previous　work　(　Table　1　)　.　The　sheet　resistance　and　electrical　resistivity　of　asfabricated　Cu　microstructures　tended　to　decrease　with　increasing　intensity　or　decreasing　scanning　speed　(　Fig.　7)　.　The　Cu　microstructure　obtained　at　5.32　x　10(9)　W　.　cm(-2)　intensity　and　100　mm　.　s(-1)　scanning　speed　exhibited　the　lowest　sheet　resistance　of　0.28　Omega　.　sq(-1).　Moreover,　as　a　result　of　the　reduction　reaction　threshold,　the　microstructure＇　s　line　width　was　narrower　than　the　laser　spot＇　s　diameter.　As　a　result,　the　heat　input　to　the　irradiation　zone　was　precisely　controlled,　limiting　the　reduction　zone　area　and　resulting　in　finer　line　width　formation　(Fig.　9)　.　Conclusions　In　this　study,　highly　conductive　Cu　microstructures　were　formed　on　a　glass　substrate　using　femtosecond　laser　direct　writing.　As　photon-absorbing　nanoparticles,　Si　nanoparticles　were　added　to　the　precursor　solution.　With　the　intensity　ranging　from　5.32　x　10(9)　W　.　cm(-2)　to　8.51　x　10(9)　W　.　cm(-2)　and　the　scanning　speed　ranging　from　100　mm.s(-1)　to　500　mm　.　s(-1),　the　Cu　microstructures　were　formed　on　substrates.　Metallic　copper,　Cu2O,　and　minor　Si　were　found　in　the　copper　microstructures.　The　results　show　that　the　continuity　of　the　microstructure,　the　proportion　of　Cu,　and　the　conductivity　of　the　microstructures　all　increased　with　increasing　intensity　or　decreasing　scanning　speed.　At　the　scanning　speed　of　100　mm.s(-1)　,　the　lowest　sheet　resistance　of　0.28　Omega.　sq(-1)　and　the　lowest　electrical　resistivity　of　4.67　x　10(-6)　Omega　.　m　were　obtained.　The　intensity　was　two　orders　of　magnitude　lower　than　that　in　previous　work,　and　the　direct　writing　efficiency　was　one　to　three　orders　of　magnitude　higher　than　that　in　previous　work.　Moreover,　the　line　width　of　the　microstructure　was　significantly　smaller　than　the　diameter　of　the　laser　spot.