Magnetic Sensor With Buffer Coat Layer To Reduce Offset Voltage
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Solution Overview
Problem
Conventional magnetic sensors with Hall elements and magnetic flux concentrators face issues such as stress generation, sensitivity variations, and instability due to adhesive problems, thermal expansion differences, and magnetic saturation, which affect their accuracy and reliability.
Innovation Solution
A magnetic sensor design with a circular or polygonal magnetic substance and base layer, featuring a controlled thickness and thermal expansion matching, and a tapered side surface to balance sensitivity and prevent saturation, along with a polyimide layer replacing epoxy adhesive to prevent wafer warping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If epoxy adhesive is used to adhere the magnetic tape onto the semiconductor substrate, then the magnetic flux concentrator can be positioned close to the Hall elements, but stress is generated at the Hall elements causing offset voltage and sensitivity variations
Solution Approach 1:
The patent removes the epoxy adhesive layer entirely from the structure. Instead of using adhesive to bond the magnetic flux concentrator to the substrate, the design allows the concentrator to be positioned close to the Hall elements through direct placement or alternative bonding methods that do not introduce stress-generating adhesive layers between the magnetic tape and semiconductor substrate.
Solution Approach 2:
The patent introduces a buffer coat layer (polyimide or silicon oxide) as an intermediary between the magnetic flux concentrator and the Hall elements. This buffer layer serves as a stress-isolating medium that prevents stress transmission from the magnetic concentrator to the Hall elements, while still allowing the magnetic flux to be effectively concentrated and detected.
2Measurement precision
If the magnetic flux concentrator thickness is increased to improve magnetic amplification, then the magnetic field detection capability is enhanced, but magnetic saturation occurs reducing linearity
Solution Approach 1:
The patent optimizes the thickness parameter of the magnetic flux concentrator to a specific range (1μm to less than 15μm, preferably 5μm to 14μm). This parameter optimization balances the magnetic amplification effect with the avoidance of magnetic saturation, ensuring both high sensitivity and linear output characteristics across the operating range.
3Measurement precision
If the distance between Hall elements and magnetic flux concentrator is reduced to improve sensitivity, then detection capability is enhanced, but stress and offset voltage increase
Solution Approach 1:
The buffer coat layer acts as a stress-isolating intermediary that enables close positioning of the magnetic flux concentrator to the Hall elements without direct stress transmission. The buffer layer physically separates the two components while maintaining magnetic coupling, thus achieving high sensitivity without the harmful stress and offset voltage that would result from direct contact.
4Strength
If adhesive layer thickness is increased to improve bonding strength, then the magnetic flux concentrator is securely attached, but wafer warping and sensitivity variations occur
Solution Approach 1:
The patent eliminates the adhesive layer entirely from the magnetic flux concentrator assembly. By removing the epoxy adhesive that causes warping and sensitivity variations, the design achieves secure attachment through alternative means (such as the buffer coat layer or direct placement) without the harmful effects of adhesive-induced stress and non-uniformity.
5Ease of manufacture
If thermal expansion coefficients of different layers are mismatched, then the manufacturing process is simplified, but stress and offset voltage are generated during temperature changes
Solution Approach 1:
The patent selects materials for the buffer coat layer and magnetic flux concentrator with carefully matched thermal expansion coefficients. The buffer coat layer is made of polyimide or silicon oxide, and the magnetic flux concentrator uses amorphous metal or soft magnetic thin films, with their thicknesses and material properties optimized to ensure their thermal expansion characteristics are compatible, preventing stress generation during temperature variations.
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 provides a magnetic sensor with stable magnetic characteristics, reduced offset voltage, and balanced sensitivity across axes, while preventing stress and saturation, enhancing measurement precision and reliability.
Implementation Method 1
a magnetic flux concentrator 115, having a magnetic amplification function
Implementation Method 2
Hall elements 112a and 112b that are embedded
Data Source
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AI summary
The present invention relates to a magnetic sensor with which magnetic characteristics are made extremely stable by consideration of an area of contact of a base layer of a magnetic substance and a semiconductor substrate. On a semiconductor substrate (111) a plurality of Hall elements (112a, 112b) are embedded so as to be coplanar to a top surface of the semiconductor substrate while being mutually spaced apart by a predetermined distance, and above the Hall elements and the semiconductor substrate, a base layer (114), having coefficient of thermal expansion differing from that of the Hall elements and partially covers a region of each Hall elements, is formed via a protective layer (113), and a magnetic flux concentrator (115), having an area larger than the base layer and with magnetic amplification, is formed on the base layer. An area of contact of the base layer of the magnetic substance and the semiconductor substrate is made small to lessen the generation of an offset voltage.