This power module substrate includes a copper plate that is formed of copper or a copper alloy and is laminated on a surface of a ceramic substrate 11; a nitride layer 31 that is formed on the surface of the ceramic substrate 11 between the copper plate and the ceramic substrate 11; and an AgCu eutectic structure layer 32 having a thickness of 15 m or less that is formed between the nitride layer and the copper plate.

Novel methods of preparing a metal bonded substrate. A method may include providing a ceramic substrate, the ceramic substrate comprising a ceramic body. The method may include bonding a thick metal sheet to the ceramic substrate, wherein the bonding comprises forming a metal oxide layer by powder deposition on a metal surface, and bringing the ceramic substrate and thick metal sheet together, wherein the metal oxide layer and the thick metal sheet interact to form an interface layer between the thick metal sheet and the ceramic substrate, after the bonding.