Nitrogen-Doped GeSbTe Phase Change Memory for Solder Reflow Stability
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Solution Overview
Problem
Phase change memory devices based on materials like the GST-225 family suffer from undesired data loss due to their low crystallization temperature, which causes transformation from the amorphous reset state to the crystalline set state at elevated temperatures, such as during solder reflow in embedded system applications.
Innovation Solution
Development of a phase change material family, GewSbxTeyNz, with a crystallization temperature greater than 410°C, and a method for programming memory devices using pre-coding operations involving specific reset and set pulses to maintain data integrity at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If GST-225 family materials are used for phase change memory, then the memory can be programmed and read with random access, but the low crystallization temperature causes undesired transformation from amorphous reset state to crystalline set state at elevated temperatures
Solution Approach 1:
The patent modifies the material composition parameters by adding nitrogen to the GeSbTe system, creating GewSbxTeyNz alloys. This compositional parameter change increases the crystallization temperature from approximately 150°C in GST-225 to above 410°C in the nitrogen-doped materials, thereby preventing undesired phase transformation at elevated temperatures while preserving programmability
Solution Approach 2:
The patent creates a composite phase change material by incorporating nitrogen into the GeSbTe alloy system. The resulting GewSbxTeyNz composite material combines the desirable programmable properties of chalcogenide materials with the high thermal stability of nitrogen-doped structures, achieving both ease of operation and reliability
2Productivity
If pre-coding is performed before mounting, then data can be stored in memory chip, but the elevated temperature of solder reflow process causes data loss in GST-225 based memory devices
Solution Approach 1:
By changing the crystallization temperature parameter from 150°C to above 410°C through nitrogen doping, the material can withstand the 260°C solder reflow temperature without undergoing undesired crystallization, thus preserving pre-coded data through the mounting process
3Ease of operation
If high current density pulse is applied to melt or breakdown crystalline structure, then reset operation can be performed, but the low crystallization temperature causes quick transformation back to crystalline state during cooling
Solution Approach 1:
The patent changes the crystallization temperature parameter by incorporating nitrogen into the phase change material, raising it from 150°C to above 410°C. This parameter change ensures that during the cooling phase after reset operation, the material remains stable in the amorphous state and does not spontaneously crystallize, thereby improving phase state stability
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 high crystallization temperature of GewSbxTeyNz materials prevents unwanted data loss during thermal cycles, ensuring data preservation in memory devices even after mounting and solder reflow, and allows for effective programming of memory cells with a large read margin.
Implementation Method 1
Phase change memory materials, like chalcogenide based materials and similar materials, can be caused to change phase between an amorphous state and a crystalline state by application of electrical current
Implementation Method 2
The change from the amorphous to the crystalline state, referred to as set herein, is generally a lower current operation
Implementation Method 3
The change from crystalline to amorphous state, referred to as reset herein, is generally a higher current operation, which includes a short high current density pulse to melt or breakdown the crystalline structure
Implementation Method 4
The relatively low crystallization temperature of materials in the GST-225 family (e.g., Tx ̃150° C.) can cause phase change memory cells fabricated from materials in the GST-225 family undergo undesired transformation from the amorphous reset state to the crystalline set state at elevated temperatures
Data Source
AI summary
A family of phase change materials GewSbxTeyNz having a crystallization temperature greater than 410° C., wherein a Ge atomic concentration is within a range from 43% to 54%, a Sb atomic concentration is within a range from 6% to 13%, a Te atomic concentration is within a range from 14% to 23%, and a N atomic concentration is within a range of 15% to 27%, is described. A method for programming a memory device including such phase change materials is also described.