GMR Angle Sensor TaN Hard Mask Oxidation
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Solution Overview
Problem
Current magnetic field angle sensors lack a monolithic, low-cost design with improved sensitivity and accuracy, and suffer from electrical shunting effects due to the use of conventional hard masks.
Innovation Solution
A GMR-based magnetic field angle sensor is fabricated using a reactive ion etching technique with a carefully controlled tantalum nitride hard mask, which is partially oxidized to increase its sheet resistance and minimize shunting effects, while maintaining the mask within the structure to prevent damage and enhance device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional hard mask is used in the fabrication process, then the manufacturing process is simple, but electrical shunting effects occur that reduce device performance
Solution Approach 1:
The patent applies parameter changes by modifying the physical and chemical properties of the TaN hard mask through controlled oxidation. The oxidation process changes the sheet resistance from conventional low values to high values (exceeding 1 kΩ/sq), transforming the hard mask from a conductive to a highly resistive layer. This parameter change eliminates electrical shunting effects while maintaining the hard mask's structural function throughout the fabrication process.
2Ease of manufacture
If the hard mask is removed after patterning, then the structure is clean, but the sensor is damaged during removal
Solution Approach 1:
The patent applies the self-service principle by making the hard mask serve dual functions: it provides mechanical protection to the sensor during fabrication and simultaneously acts as an electrical barrier against shunting effects. The oxidized TaN hard mask remains in the final structure, continuously protecting the sensor from damage while blocking electrical current paths. The hard mask serves itself by maintaining its protective function throughout the device's operational life.
3Measurement precision
If the GMR stack has high aspect ratio for improved sensitivity, then the sensor accuracy improves, but the structure becomes more complex and difficult to fabricate
Solution Approach 1:
The patent applies parameter changes by transforming the electrical properties of the hard mask through oxidation, changing it from a conductive barrier to a highly resistive layer. This parameter change in the hard mask's sheet resistance enables the fabrication of high-aspect-ratio GMR stacks by preventing electrical shunting that would otherwise occur along the mask layer. The high resistivity allows the sensor to achieve improved accuracy through high-aspect-ratio structures without suffering from parasitic current paths.
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 achieves high sensitivity, accuracy, and reduced shunting effects, allowing for a high-aspect-ratio GMR stack with minimal electrical interference, resulting in improved device performance and increased areal density.
Implementation Method 1
when the photoresist used to pattern the TaN (for later use as a hard mask) is stripped in an oxygen plasma, most of the TaN is converted to TaO/TaON so that the hard mask's sheet resistance is increased
Implementation Method 2
FIELD OF THE INVENTION relates to GMR based magnetic field angle sensors with particular reference to their fabrication using a particular reactive ion etching (RIE) technique
Data Source
AI summary
A high-amplitude magnetic angle sensor is described along with a process for its manufacture. A thin tantalum nitride hard mask, used to pattern the device, is left in place within the completed structure but, by first converting most of it to tantalum oxide, its effect on current shunting is greatly reduced.