The present invention relates to an implantable electrode device comprising a carrier made of a polymer material, wherein the carrier is flexible and electrically isolating, at least one measurement electrode formed by an electrically conducting pad located on the carrier, wherein the electrically conducting pad has a contact surface, at least one electrically conducting trace, and at least one electrically conducting terminal, wherein the trace electrically connects the measurement electrode and the terminal. Implantable electrode devices of this type are not suitable to remain implantable over a long time. In order to provide an implantable electrode device which may remain in a patient's body the present invention suggest to further develop the implantable electrode such that the implantable electrode device further comprises a barrier layer enclosing the carrier by covering all surfaces thereof, wherein the contact surface of the conducting pad is exposed to an outside environment, and wherein a surface of the electrode device on a side on which the measurement electrode is located has a maximum valley depth or a maximum peak height between the contact surface of the measurement electrode and a meanline of the surface of the electrode device excluding the measurement electrodes being equal to or smaller than 60 micrometres or wherein a surface of the electrode device on a side on which the measurement electrode is located has a maximum valley depth or a maximum peak height between the contact surface of the measurement electrode and a meanline of the surface of the electrode device excluding the measurement electrodes being larger than 60 micrometres and wherein the maximum linear extension of the contact surface is equal to or less than 100 micrometres.
