Try to find 2001 Nights if you can, it's just 3 volumes.
Half the volumes of Tezuka's Phoenix (2, half of 3, 5, 6, parts of 9 and 11) are all pretty great sci-fi.
Nausicaä of the Valley of the Wind is set in a future where everything in nature has evolved to a new form and humanity has been left behind, no longer fit to live.
The Puma Blues is definitely sci-fi even if the characters spend all their time in a national park.
Pluto by Naoki Urasawa is a great thriller set in a future full of robots
/shelf/ thread
Liam Ramirez