Magnetic Sensor Bridge Offset Reduction via MR Element Grouping
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Solution Overview
Problem
Magnetic sensors with Wheatstone bridge circuits face variations in magnetoresistive element dimensions due to photoresist mask thickness variations, leading to offset issues in detection signals, especially when substrates have stepped sections.
Innovation Solution
The magnetic sensor design groups magnetoresistive elements into specific groups based on top surface areas and positions them on a support member with distinct regions to balance resistance and reduce signal offset, using a configuration where each resistor section is composed of elements from different groups to minimize variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If magnetoresistive elements are formed using photolithography with photoresist mask, then manufacturing process is simplified, but dimensions of magnetoresistive elements vary due to photoresist mask thickness variations
Solution Approach 1:
The magnetoresistive elements are divided into multiple groups (first group, second group, third group, fourth group) based on their top surface areas. Each group contains elements with specific area characteristics, allowing the system to accommodate dimensional variations by strategically assigning groups to different resistor sections rather than requiring all elements to have identical dimensions.
Solution Approach 2:
Different resistor sections are assigned different groups of magnetoresistive elements with specific area characteristics. For example, the first resistor section receives elements from the first group, the second resistor section receives elements from the second group, and so on. This local optimization ensures that each section has the appropriate element characteristics needed for bridge balance while accommodating manufacturing variations.
2Device complexity
If magnetoresistive element dimensions vary, then manufacturing tolerance is relaxed, but offset occurs in detection signal
Solution Approach 1:
The invention changes the parameter of top surface area as the key differentiating characteristic among magnetoresistive element groups. By categorizing elements into groups based on their area parameters (with each group having a maximum area larger than the minimum area of subsequent groups), the system can compensate for dimensional variations and maintain bridge balance, thereby preventing offset in the detection signal despite relaxed manufacturing tolerances.
3Ease of manufacture
If photoresist layer thickness varies, then deposition process becomes simpler, but interference pattern changes affect photoresist mask dimensions
Solution Approach 1:
The invention performs preliminary classification of magnetoresistive elements into groups based on their top surface areas before they are assigned to resistor sections. This preliminary action allows the system to anticipate and compensate for dimensional variations caused by photoresist thickness variations, ensuring that elements with similar area characteristics are grouped together and appropriately distributed to maintain bridge balance.
4Device complexity
If all magnetoresistive elements are designed with same dimensions, then design process is simplified, but actual dimensions vary due to manufacturing variations
Solution Approach 1:
Instead of designing all magnetoresistive elements with the same dimensions and hoping for consistency, the invention inverts the approach by deliberately designing elements with different top surface areas and categorizing them into groups. This inversion transforms manufacturing variations from a problem into a manageable characteristic, where the system is designed to accommodate and utilize the variations rather than fight against them.
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
This approach effectively reduces signal offset and maintains balance in resistor sections, preventing deviations in output potentials due to stress and temperature variations, while avoiding the complexity of increasing the number of partial resistor sections.
Implementation Method 1
a detection signal depending on an external magnetic field is generated using a magnetoresistive element (hereinafter also referred to as an MR element) whose resistance is variable depending on the external magnetic field
Data Source
AI summary
A magnetic sensor includes first to fourth resistor sections and a plurality of MR elements. Each of the plurality of MR elements belongs to any of first to fourth groups. The first to fourth groups are defined based on the areas of top surfaces of the MR elements. The first resistor section, the second resistor section, the third resistor section, and the fourth resistor section are constituted of the first group, the second group, the third group, and the fourth group, respectively; the second group, the first group, the fourth group, and the third group, respectively; the first group, the fourth group, the third group, and the second group, respectively; or the third group, the second group, the first group, and the fourth group, respectively.