A　metal-catalyst-free　method　for　the　direct　growth　of　patterned　graphene　on　an　insulating　substrate　is　reported　in　this　paper.　Parylene　N　is　used　as　the　carbon　source.　The　surface　molecule　layer　of　parylene　N　is　cross-linked　by　argon　plasma　bombardment.　Under　high-temperature　annealing,　the　cross-linking　layer　of　parylene　N　is　graphitized　into　nanocrystalline　graphene,　which　is　a　process　that　transforms　organic　to　inorganic　and　insulation　to　conduction,　while　the　parylene　N　molecules　below　the　cross-linking　layer　decompose　and　vaporize　at　high　temperature.　Using　this　technique,　the　direct　growth　of　a　graphene　film　in　a　large　area　and　with　good　uniformity　is　achieved.　The　thickness　of　the　graphene　is　determined　by　the　thickness　of　the　cross-linking　layer.　Patterned　graphene　films　can　be　obtained　directly　by　controlling　the　patterns　of　the　cross-linking　region　(lithography-free　patterning).　Graphene-silicon　Schottky　junction　photodetectors　are　fabricated　using　the　as-grown　graphene.　The　Schottky　junction　shows　good　performance.　The　application　of　direct-grown　graphene　in　optoelectronics　is　achieved　with　a　great　improvement　of　the　device　fabrication　efficiency　compared　with　transferred　graphene.　When　illuminated　with　a　792　nm　laser,　the　responsivity　and　specific　detectivity　of　the　detector　measured　at　room　temperature　are　275.9　mA/W　and　4.93　x　10(9)　cm　Hz(1/2)/W,　respectively.