Selective Magnesium Oxide Etching Using Aqueous Ammonia
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Solution Overview
Problem
Current methods fail to selectively etch magnesium oxide films adjacent to metal layers using wet etching, which is necessary for manufacturing magnetic heads with high sensitivity and output characteristics, as existing etchants like tetramethylammonium hydroxide are ineffective for magnesium oxide.
Innovation Solution
A method involving an etchant with an aqueous ammonia solution, potentially containing ammonium persulfate, is used to selectively etch magnesium oxide films, maintaining a pH range of 9.0 to 10.0, ensuring the metal layers are not etched while the magnesium oxide films are removed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etchants like tetramethylammonium hydroxide are used, then the etching process can be performed, but the magnesium oxide film cannot be effectively etched
Solution Approach 1:
The patent changes the chemical parameters of the etchant by using aqueous ammonia solution with controlled pH (9.0-10.0) and specific concentration ranges, which enables effective etching of magnesium oxide film while maintaining selectivity against metal layers. This parameter optimization resolves the contradiction between etching effectiveness and selectivity.
Solution Approach 2:
The patent replaces conventional organic-based etchants (tetramethylammonium hydroxide) with an inorganic-based aqueous ammonia solution, substituting the chemical mechanism to achieve both effective magnesium oxide removal and metal layer protection simultaneously.
2Manufacturing precision
If wet etching is used to remove magnesium oxide film, then continuous film removal is achieved, but the metal layer may be damaged by conventional etchants
Solution Approach 1:
The etchant exhibits different etching rates for different materials: it effectively etches magnesium oxide film while having minimal effect on metal layers. This local quality difference in chemical reactivity allows precise film removal without damaging the metal layer.
Solution Approach 2:
The aqueous ammonia solution acts as a selective intermediary that facilitates the removal of magnesium oxide film through chemical reaction while being inert or minimally reactive toward metal layers, thus protecting them from damage.
3Productivity
If the pH is increased to improve etching rate, then magnesium oxide etching improves, but metal layer etching may increase
Solution Approach 1:
The patent optimizes the pH parameter to a specific range (9.0-10.0) where the etching rate of magnesium oxide is sufficiently high while the etching rate of metal layers remains negligible. This precise parameter control resolves the contradiction between etching rate and selectivity.
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 allows for the precise removal of unwanted magnesium oxide films, preventing continuity failures between magnetic elements and electrodes, thereby enhancing the manufacturing process of magnetoresistive devices and thin-film magnetic heads.
Implementation Method 1
wet etching a magnesium oxide film that lies adjacent to a metal layer by using an etchant containing an aqueous ammonia solution
Implementation Method 2
an etchant containing an aqueous ammonia solution
Data Source
AI summary
A magnetoresistive device includes an MR element including a metal layer, and an insulating portion made of magnesium oxide and in contact with the MR element. A method of manufacturing the magnetoresistive device includes the step of removing an unwanted magnesium oxide film that is formed by the magnesium oxide in the process of forming the insulating portion. In this step, the unwanted magnesium oxide film is wet etched by using an etchant containing an aqueous ammonia solution.