Built-in-coil substrate

A built-in-coil substrate comprising:

• a substrate body including a plurality of ceramic insulating layers stacked on top of one another;
• a plurality of coil elements respectively arranged between sets of insulating layers, which are not mutually adjacent insulating layers, and so as to extend in a substantially circumferential direction around an imaginary central axis that extends in a stacking direction in which the insulating layers of the substrate body are stacked;
• an interlayer connection conductor that penetrates through the insulating layers and connects the coil elements to one another;
• and
• a cavity disposed inside of the substrate body;
• wherein
• the coil elements include first coil elements that are superposed with one another when viewed in perspective in the stacking direction, and second coil elements that are superposed with one another inside the inner periphery of the first coil elements, which are superposed with one another when viewed in perspective in the stacking direction;
• the cavity is continuous between at least one of the coil elements and one of the insulating layers that is in contact with the coil element, and another one of the insulating layers that opposes the coil element, such that the coil element is exposed;
• and
• the cavity has an annular shape and extends further inward than outer peripheries of the first coil elements, which are superposed with each other when viewed in perspective in the stacking direction, an interval being provided between the cavity and the outer peripheries, and further outward than the inner peripheries of the second coil elements, which are superposed with each other.