Substrate employing core with cavity embedding reduced height electrical device(s), and related integrated circuit (IC) packages and fabrication methods

A substrate, comprising:

• a first metallization structure comprising one or more first metallization layers;
• a second metallization structure comprising one or more second metallization layers;
• and
• a core between the first metallization structure and the second metallization structure in a first direction, the core having a first height in the first direction, the core comprising:
• a cavity;
• and
• an embedded electrical device structure having a second height of at least the first height in the first direction, the embedded electrical device structure disposed in the cavity and comprising:
• a first electrical device adjacent to the first metallization structure, wherein the first electrical device comprises:
• a first front side adjacent to the first metallization structure;
• a first back side opposite the first front side in the first direction;
• and
• one or more first metal interconnects each exposed from the first front side and coupled to the first metallization structure;
• and
• a second component adjacent to the first electrical device and the second metallization structure, the second component comprising a spacer structure;
• wherein the spacer structure comprises:
• a second front side adjacent to the first back side of the first electrical device;
• and
• a second back side opposite the second back side in the first direction, the second front side adjacent to the second metallization structure.