Single-package bridge-type magnetic field sensor

#The present invention relates to the field of magnetic field measurement using a magnetic tunnel junction (MTJ, Magnetic Tunnel Junction) or giant magnetoresistance (GMR Giant Magnetoresistance) device, in particular, relates to the integration of MTJ or GMR chips into a standard semiconductor package.

#Magnetic sensors are widely used in modem systems to measure or detect physical parameters including but not limited to magnetic field strength, current, position, motion, orientation, and so forth. There are many different types of sensors in the prior art for measuring magnetic field and other parameters. However, they all suffer from various limitations well known in the art, for example, excessive size, inadequate, inadequate sensitivity and/or dynamic range, cost, reliability and other factors. Thus, there continues to be a need for improved magnetic sensors, especially sensors that can be easily integrated with semiconductor devices and integrated circuits and manufacturing methods thereof.

#Magnetic tunnel junction (MTJ) sensors have the advantages of high sensitivity, small size, low cost, and low power consumption. Although MTJ devices are compatible with standard semiconductor fabrication processes, methods for building high sensitivity devices with sufficient yield for low cost mass production have not been adequately developed. In particular, yield issues due to difficulty in MTJ process and backend packaging process, and difficulty in matching the magnetoresistive response of MTJ elements when combined to form bridge sensors have proven difficult.

#FIG. 1—A schematic drawing of the magnetoresistive response of a spin-valve sensing element with the reference layer magnetization pointing in the negative H direction.

#FIG. 2—A schematic drawing of a half-bridge with a fixed reference resistor and a sensing resistor.

#FIG. 3—An embodiment of a half-bridge in a magnetoresistive sensor chip where both reference resistor and sensing resistor made of plural MTJ elements arranged in row arrays and bar-shape permanent magnets are used to bias the MTJ elements.

#These sensor elements are configured as spin valves, where one of the magnetic layers has a magnetization with an orientation that is fixed in order to serve as a reference. This fixed layer can be a single magnetic layer or a synthetic antiferromagnetic structure composed of a pinned ferromagnetic layer exchange coupled to a reference ferromagnetic layer, wherein the pinned ferromagnetic layer is made magnetically insensitive by exchange coupling it to an antiferromagnetic layer. The other magnetic layer, the so called free layer, rotates in response to an applied magnetic field. The resistance of the spin valve varies in proportion to the relative difference in the orientation of the magnetization of the free and pinned ferromagnetic layers. Because the free layer rotates in response to the applied magnetic field, the sensor is sensitive to the applied magnetic field. In a MTJ element, the free layer and fixed layer are separated by a tunnel barrier. Electrical current flows through the tunnel barrier. In a GMR element, the free layer and the pinned layer are separated by a non-magnetic metallic layer. Electrical current can flow either in the plane of the multilayer thin film or perpendicular to the plane.

#The general form of the magnetoresistive transfer curve of a GMR or MTJ magnetic sensor element suitable for linear magnetic field measurement is shown schematically in FIG. 1. The transfer curve depicted in the figures saturates at low 1 and high 2, resistance values, RL and RH, respectively. In the region between saturation, the transfer curve is linearly dependent on the applied magnetic field, H.

#In non-ideal cases, the transfer curves is not symmetric about the H=0 point in the plot. The saturation fields 4 and 5 are typically offset by an amount that is determined by the interlayer coupling between the free layer and the pinned layer. A major contributor to the interlayer coupling, so called Neel coupling or “orange-peel” coupling, is related to roughness of the ferromagnetic films within the GMR and MTJ structures, and it is dependent on materials and manufacturing processes.