A tricobalt device is a powerful explosive weapon that Captain Janeway used to destroy the Caretaker's array in the Delta Quadrant in 2371.
Tricobalt devices are heavy explosives whose detonation can tear a large hole through ordinary space and subspace, making them far more destructive than most ship weapons. Their use is closely watched because of the damage they cause.
Voyager used tricobalt devices to destroy the array built by the Caretaker, ensuring that the technology could not be seized by the Kazon and used against the Ocampa. The decision stranded Voyager in the Delta Quadrant, setting the course of the entire series.