Disclosed is an implantable device including: a first insulation layer； a second insulation layer arranged on the first insulation layer； a first semiconductor layer arranged between the first and second insulation layers； a second semiconductor layer doped into the first semiconductor layer, with the second semiconductor layer forming a closed loop as seen in a top view； a metal layer disposed on the second insulation layer, with the metal layer forming an electrode； a third insulation layer covering the metal layer； and an insulation region including the first and second semiconductor layers.
