Magnetoresistive Sensor with Substrate-Integrated Compensating Coil
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Solution Overview
Problem
Magnetic sensors with traditional compensating coils suffer from poor space utilization and high costs due to large device areas, and existing solutions do not effectively address magnetic hysteresis and dynamic range improvements.
Innovation Solution
A magnetoresistive sensor with a serpentine compensating coil is formed directly on a wafer using deposition and etching, integrated with parallel rectangular soft ferromagnetic flux concentrators and a push-pull sensor bridge, allowing for efficient space utilization and compact structure without increasing the substrate size, featuring an alternating arrangement of current straps and flux concentrators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a large serpentine compensating coil is placed on top of a sensor chip substrate, then the sensor can be operated in a closed loop mode, but the space utilization becomes poor and the actual sensor size becomes much larger than desired
Solution Approach 1:
The patent moves the compensating coil from the chip surface (2D plane) to the substrate layer (different dimension), allowing the coil to be formed in the substrate beneath the chip. This dimensional relocation enables the coil to occupy space that would otherwise be unused, achieving closed loop operation without increasing the chip footprint.
Solution Approach 2:
The compensating coil is nested within the substrate structure, with the sensor chip positioned above it. This nesting arrangement allows the coil to be contained within the overall device footprint without adding to the chip area, as the coil and chip occupy different spatial layers within the same footprint.
2Measurement precision
If an AMR sensor chip uses a bias strip and reset coil to generate orthogonal magnetic field, then sensitivity and linearity are improved, but the device area becomes large and cost increases
Solution Approach 1:
The patent combines the compensating coil function with the substrate structure itself, rather than using separate bias strips and reset coils on the chip surface. This merging of functions into a single integrated coil reduces the overall device area while maintaining the ability to improve sensitivity and linearity through closed loop operation.
Solution Approach 2:
The substrate serves multiple functions: it provides mechanical support for the sensor chip and simultaneously houses the compensating coil for closed loop operation. This multi-functionality eliminates the need for separate dedicated components, reducing device area and cost.
3Stability of the object's composition
If a spiral initialization coil is disposed on the package substrate, then magnetic hysteresis and drift are reduced, but the overall device complexity increases
Solution Approach 1:
The patent merges the initialization coil function with the compensating coil by using the same serpentine coil structure on the substrate for both purposes. This single coil performs dual functions: initializing the magnetic state and providing closed loop compensation, thereby reducing device complexity compared to having separate initialization and compensating coils.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in a smaller, lower-cost sensor with improved linearity, reduced hysteresis, and enhanced dynamic range, enabling easy operation in a closed loop mode while maintaining compact size.
Implementation Method 1
a serpentine compensating coil... for controlling magnetic hysteresis
Implementation Method 2
parallel rectangular soft ferromagnetic flux concentrators
Implementation Method 3
collection of MR sensor units... interconnected in order to form a push-pull sensor bridge
Data Source
Figure 1~8
Figure 2
Figure 3~5
AI summary
A magnetoresistive sensor with a compensating coil comprising a silicon substrate (1), a collection of MR sensor units (6) disposed on the silicon substrate (1), a collection of rectangular soft ferromagnetic flux concentrators (4), a serpentine compensating coil (7), a connecting circuit, and a collection of bond pads (16) used for electrical connections. The MR sensor units (6) are interconnected in order to form a push-pull sensor bridge. The collection of MR sensor units (6) is disposed below the gap between two adjacent soft ferromagnetic flux concentrators (4). The serpentine compensating coil (7) has a positive current strap over the MR sensor units (6) and a negative current strap under the soft ferromagnetic flux concentrators (4). The MR sensor bridge and the serpentine compensating coil (7) are connected through bond pads (16) and covered with an encapsulation structure. The magnetoresistive sensor also comprises a spiral initialization coil which is placed on a substrate which is within the encapsulating structure. A sensor chip is disposed on the initialization coil, which is used for reducing magnetic hysteresis. This magnetoresistive sensor has smaller size, lower cost, increased dynamic range, improved linearity, and decreased magnetic hysteresis. The design allows the magnetic sensor to be easily operated in a closed loop mode.