IGZO Selector Device Mitigates Memory Sneak Paths
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Solution Overview
Problem
High-density memory arrays, such as MRAM arrays, suffer from the sneak path problem due to cross-talk interference between adjacent memory cells, which is exacerbated by the difficulty in forming reliable Schottky contacts in double-sided IGZO Schottky diodes during the deposition of the top electrode, leading to Ohmic contacts instead.
Innovation Solution
A method for forming a selector device with a double-sided Schottky diode using a semiconductor material like IGZO, where the semiconductor material is deposited after forming an opening in the second electrode layer and oxide, ensuring Schottky interfaces are maintained by keeping defects away from these interfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a plasma-assisted process (PVD) is used to deposit the top electrode, then the top electrode can be formed, but the IGZO channel is damaged and defects are created, resulting in Ohmic contacts instead of Schottky contacts
Solution Approach 1:
The patent applies preliminary action by depositing the top electrode material (platinum) before forming the IGZO channel. The IGZO channel is then deposited conformally over the electrode, ensuring that the Schottky interface is formed without subsequent plasma damage. This sequence prevents the plasma-assisted PVD process from damaging the IGZO and creating defects that would lead to Ohmic contacts.
Solution Approach 2:
The patent inverts the conventional fabrication sequence by depositing the electrode layer first and then forming the IGZO channel on top of it. This reverse approach ensures that the IGZO material is not exposed to damaging plasma processes after the Schottky interface is created, thereby maintaining the integrity of the Schottky contact.
2Reliability
If the plasma power is reduced to protect the IGZO channel, then less damage occurs, but the deposition process becomes insufficient to form a good Schottky contact
Solution Approach 1:
The patent resolves this contradiction by performing the electrode deposition before IGZO channel formation. Since the IGZO channel is not yet formed, it cannot be damaged by plasma. The electrode is deposited with appropriate plasma power to ensure good Schottky contact properties, and subsequent low-power or non-plasma processes are used for IGZO deposition to maintain channel integrity.
3Reliability
If selector devices are inserted next to memory cells to mitigate the sneak path problem, then read-out signals are protected, but the fabrication complexity increases due to the need for reliable double-sided Schottky contacts
Solution Approach 1:
The patent simplifies the overall device fabrication by using preliminary electrode deposition before IGZO channel formation. This approach ensures reliable Schottky contacts on both sides of the IGZO channel without requiring complex subsequent processing steps, thereby reducing fabrication complexity while maintaining read-out signal protection.
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 effectively mitigates the sneak path problem by creating reliable Schottky contacts between the semiconductor material and the electrode layers, maintaining diode behavior for device selection and reducing the impact of defects on electrical performance.
Implementation Method 1
a plasma-assisted process (e.g. Physical Vapor Deposition (PVD) that is typically involved in the deposition of the top electrode 91, damages the IGZO 93)
Data Source
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AI summary
The present invention presents a selector device for a memory array, and a method for forming the selector device. The selector device comprises a first electrode layer embedded in an oxide; a second electrode layer arranged above the first electrode layer and separated from the first electrode layer by the oxide; and a semiconductor material forming a semiconductor layer on the top surface of the second electrode layer, and extending through the second electrode layer and the oxide onto the top surface of the first electrode layer, wherein the semiconductor material contacts the first electrode layer and the second electrode layer. The selector device helps to solve the sneak path problem in the memory array it is inserted into.