Graphene based magnetoresistance sensors

A magnetic field sensor comprising:

• a graphene structure on a base layer;
• a substrate layer;
• and
• a plurality of electrodes positioned in parallel on top of the graphene structure and in contact with a top layer of the graphene, wherein the graphene structure lies between the electrodes and a base layer;
• wherein the graphene structure comprises:
• at least two graphene layers disposed on the substrate layer, wherein each graphene layer consists of a single layer of carbon atoms arranged in a honey-comb fashion, the at least two graphene layers having gate electrodes fabricated thereon and comprising a gate voltage tuned graphene layer and an effective graphene layer, the effective graphene layer comprising one or more graphene layers,
• wherein each layer of the graphene structure has a three dimensional (3D) carrier density and a charge mobility;
• wherein the charge mobility of the gate voltage tuned graphene layer is higher than the charge mobility of the effective graphene layer;
• wherein a magnetoresistance ratio of the graphene structure is determined by a difference in the charge mobility or the carrier density between the gate voltage tuned graphene layer and the effective graphene layer, and wherein the charge mobility or the carrier density of the gate voltage tuned graphene layer is tunable by a gate voltage applied to the graphene structure through the gate electrodes, and wherein the gate electrodes are in contact with the gate voltage tuned graphene layer;
• and
• wherein a largest magnetoresistance ratio is obtained when the gate voltage of the graphene structure is at a charge neutrality point (CNP), and wherein equal number of electrons and holes exist at the charge neutrality point.