The sentence against 26-year-old Swiss activist Luca Christos Bernasconi and Italians Constantino Alfonso Ragusa, 34 and Silvia Ragusa Guerini, 29, is higher than what the prosecutor had sought.
A Bellinzona-based court found the three guilty "of plotting a criminal act of arson ... (and) the concealment and assembly of explosives," said the ruling.
The trio was arrested on April 15th, 2010 with explosives and other components for building a bomb, and have been held in preventive detention since then, according to the Swiss attorney general's office.
They had also carried 31 handwritten letters in German, claiming responsibility for a bomb attack on the IBM facility, on behalf of the "ELF Switzerland Earth Liberation Front," added the attorney general.
The late 2010 bomb attacks on the Swiss embassies in Athens and Rome were launched in retaliation for their arrest, according to the Swiss Federal Intelligence Service.
The Earth Liberation Front, born in Britain in the 1990s, is made up of numerous autonomous cells around the world.
During congressional testimony in 2004, FBI deputy assistant director John Lewis had said that the group had "emerged as a serious domestic terrorist threat."
The targetted IBM nanotechnology research centre, in the small suburb of Rüschlikon some five miles south of Zurich, focuses on "novel nanoscale structures and devices to advance energy and information technologies," according to its website.
Friday's ruling can be appealed.