Inductor and DC-DC converter

An inductor comprising:

• a coil electrode section;
• and
• a magnetic layer section,
• the coil electrode section including:
• a first spiral electrode;
• a second spiral electrode lying in substantially a same plane as the first spiral electrode and wound in substantially a same direction as the first spiral electrode;
• a connection electrode arranged to connect an outer end of the second spiral electrode and an outer end of the first spiral electrode;
• a first protrusion electrode disposed at an inner end of the first spiral electrode and extending in a direction substantially perpendicular to the plane;
• and
• a second protrusion electrode disposed at an inner end of the second spiral electrode and extending in a direction substantially perpendicular to the plane;
• wherein
• the first protrusion electrode and the second protrusion electrode define opposite end electrodes of the coil electrode section;
• the magnetic layer section sandwiches the coil electrode section and is disposed such that the first protrusion electrode and the second protrusion electrode are exposed at and extend from a main surface of the magnetic layer section that extends substantially parallel to the plane in which the first and second spiral electrodes lie;
• the magnetic layer section includes a first magnetic layer and a second magnetic layer, the first magnetic layer and the second magnetic layer being arranged to sandwich the first spiral electrode, the second spiral electrode, and the connection electrode from directions substantially perpendicular to the plane in which the first and second spiral electrodes lie;
• the first magnetic layer includes a through hole arranged such that each of the first and second protrusion electrodes pass therethrough;
• the second magnetic layer includes a depression arranged to accommodate the first spiral electrode, the second spiral electrode, and the connection electrode;
• the second magnetic layer includes a projection at a central region of winding of each of the first spiral electrode and the second spiral electrode, the projection having a height at which the projection is in contact with or adjacent to the first magnetic layer;
• when a central three-dimensional region includes the projection, a first three-dimensional region in which a plane region of the projection virtually extends along a length in a thickness direction of the first magnetic layer, and a second three-dimensional region in which the plane region of the projection virtually extends along a length in a thickness direction of the second magnetic layer exclusive of the projection, the following relationship is satisfied:
• 0.1<Sv/Sh<0.65
• where Sv is an area of a side surface of the magnetic layer section that is substantially parallel with the thickness direction and crossing the first magnetic layer or the second magnetic layer exclusive of the projection in the central three-dimensional region, a location of the side surface of the magnetic layer section corresponding to a location of the first spiral electrode or the second spiral electrode, and Sh is an area of a cross section along a central cross section in the thickness direction of the first spiral electrode or the second spiral electrode in the central three-dimensional region.