Resistance Change Element Tunnel Current Prevention
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Solution Overview
Problem
Resistance change elements suffer from property deterioration due to tunnel currents caused by the proximity of hard-bias layers and thin interlayer insulating films, leading to unstable performance in magnetic sensors and nonvolatile memory devices.
Innovation Solution
A resistance change element with a first lead electrode, a resistance change layer, and a second lead electrode, where the second material with a higher work function is unevenly distributed in a second region, preventing tunnel currents by increasing the work function and using a bias magnetic field generator between the electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hard-bias layer is provided close to the side surface of the resistance change layer to stabilize magnetization direction, then the initial magnetization direction of the magnetization free layer can be made a prescribed direction, but the bottom surface of the hard-bias layer and the top surface of the lower lead electrode become close, causing tunnel currents to flow and deteriorating the properties of the resistance change element
Solution Approach 1:
An injection layer made of a second material with higher work function than the first lead electrode is introduced as an intermediary between the first lead electrode and the resistance change layer. This injection layer acts as a mediator that prevents electron tunneling from the first lead electrode to the resistance change layer, thereby blocking the harmful tunnel current while allowing the hard-bias layer to remain close to the resistance change layer for magnetization stabilization.
Solution Approach 2:
The work function parameter is changed by introducing a second material with higher work function than the first lead electrode. By selecting materials with different work function values, the energy barrier for electron tunneling is increased, preventing tunnel current flow. Specifically, the first lead electrode has a lower work function material while the injection layer has a higher work function material, creating an energy barrier that blocks electron tunneling.
2Device complexity
If the interlayer insulating film is made thin to reduce device complexity, then manufacturing is simplified, but tunnel currents may flow between the first lead electrode and second lead electrode, deteriorating the properties of the resistance change element
Solution Approach 1:
The injection layer serves as an intermediary barrier between the first lead electrode and the resistance change layer, preventing tunnel current even when the interlayer insulating film is thin. By introducing this intermediate layer with higher work function, the structure allows for reduced interlayer insulating film thickness while maintaining electrical isolation and preventing harmful tunnel currents.
Solution Approach 2:
The work function parameter is strategically changed by introducing a second material with higher work function at the interface between the first lead electrode and the resistance change layer. This parameter change creates an energy barrier that prevents electron tunneling, allowing the interlayer insulating film to be made thinner without causing tunnel current issues.
3Object-affected harmful factors
If the second material with higher work function is uniformly distributed throughout the first lead electrode, then tunnel currents would be prevented, but the work function increase would affect the entire electrode including the region under the resistance change layer, potentially affecting electrical connection
Solution Approach 1:
The second material with higher work function is not uniformly distributed throughout the first lead electrode, but is localized specifically in the injection layer at the interface region between the first lead electrode and the resistance change layer. This local concentration of the high work function material provides tunnel current prevention exactly where needed, while leaving the bulk of the first lead electrode with its original electrical properties intact, ensuring good electrical connection.
Solution Approach 2:
The first lead electrode structure is segmented into two functional regions: the bulk first lead electrode material that provides electrical connection, and the injection layer made of second material that provides tunnel current prevention. This segmentation allows each region to perform its specific function optimally without interfering with the other.
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 stabilizes the properties of the resistance change element, preventing tunnel currents and ensuring accurate detection in magnetic sensors and reliable operation in nonvolatile memory devices.
Implementation Method 1
the second material has a work function that is larger than that of a first material that configures the first lead electrode
Implementation Method 2
a hard-bias layer of a permanent magnet or the like is provided on the side surface of the resistance change film in order to make the initial magnetization direction of the magnetization free layer a prescribed direction
Implementation Method 3
a resistance change element (for example, a GMR element, a TMR element or the like) having a resistance change film in which the resistance changes accompanying change in the magnetization direction of the magnetization free layer in accordance with an external magnetic field
Data Source
AI summary
A resistance change element includes a first lead electrode, a resistance change layer provided on the first lead electrode, and a second lead electrode provided on the resistance change layer. The surface of the first lead electrode on the resistance change layer side includes a first region in which the resistance change layer is provided, and a second region that is a region other than the first region. In the second region, a second material having a work function that is larger than that of a first material configuring the first lead electrode is unevenly distributed.