A packaging structure including at least one hermetically sealed cavity in which at least one microelectronic device is arranged, the cavity being formed between a substrate and at least one cap layer through which several release holes are formed. Several separated portions of metallic material are provided such that each of the separated portions of metallic material is arranged on the cap layer above and around one of the release holes and forms an individual and hermetical plug of said one of the release holes. At least one diffusion barrier layer including at least one non-metallic material is arranged on the cap layer and forms a diffusion barrier against an atmosphere outside the cavity at least around the release holes. Parts of the diffusion barrier layer are not covered by the portions of metallic material.