Hafnium　oxide　thin　films　were　deposited　on　silicon　substrates　by　RF　reactive　magnetron　sputtering.　The　effects　of　oxygen　partial　pressure,　tuned　by　the　O-2/Ar　flow　ratio,　on　the　microstructure　and　electrical　properties　were　characterized.　All　HfOx,　thin　films　exhibit　monoclinic　phases.　As　the　increase　of　O-2/Ar　flow　ratio　from　0.08　to　0.33,　the　crystallinity　is　improved　accompanied　with　the　decreases　of　flat　band　voltage　and　leakage　current　density.　However,　when　the　O-2/Ar　flow　ratio　further　increases　to　0.5,　the　crystallinity　becomes　worse　with　the　increase　of　flat　band　voltage　and　leakage　current.　The　HfOx,　based　resistive　random-access　memory　(RRAM)　has　been　fabricated　and　its　storage　properties　were　also　investigated.