Semiconductor Device Reset Gate Pillar Structure
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Solution Overview
Problem
Existing semiconductor devices face challenges in achieving a reset operation with a small memory cell size due to high reset currents required, which lead to increased IR drop and difficulty in connecting multiple transistors to word lines, and require complex high-temperature processes.
Innovation Solution
A semiconductor device with a pillar-shaped resistance-changing layer and a reset gate that surrounds the resistance-changing layer, allowing for a reset operation without high current flow through selection elements, and enabling a metal gate last process for both metal gate and high-temperature processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high reset current is used to achieve reset operation, then the reset operation can be performed, but the memory cell size becomes large and IR drop increases
Solution Approach 1:
The invention divides the heater function into two separate heaters: a first heater for set operation and a second heater for reset operation. This segmentation allows each heater to be optimized for its specific function, enabling reset operation with lower current density and smaller memory cell size without requiring a single high-current heater
Solution Approach 2:
The invention applies different heater structures and materials locally optimized for their specific functions. The first heater uses a specific resistance value optimized for set operation, while the second heater uses different material composition or structure optimized for reset operation, allowing efficient reset with reduced current requirements
2Ease of operation
If a single source line is selected with a diode, then memory cell selection is achieved, but electric currents of all connected memory cells flow through the source line causing increased IR drop
Solution Approach 1:
The invention segments the current path by using separate source lines for different operational modes. One source line is dedicated for set operation while another is dedicated for reset operation, preventing current from all memory cells from flowing simultaneously through a single source line, thereby reducing IR drop
3Power
If bipolar transistors are used as selection elements, then high current can be handled, but it is difficult to connect many transistors to word lines
Solution Approach 1:
The invention replaces the mechanical/electrical complex transistor structure with a simpler heater-based selection mechanism. The heater elements directly control the phase change material state through resistive heating, eliminating the need for complex bipolar transistor connections while maintaining high current handling capability through the heater's intrinsic resistance
4Adaptability or versatility
If metal gate last process is used to perform both metal gate and high-temperature processes, then both processes can be integrated, but the process becomes complex with multiple steps
Solution Approach 1:
The invention merges the metal gate formation process with the high-temperature process by using a polysilicon gate that can withstand high temperatures. The polysilicon gate is formed first, then high-temperature processes are performed, and finally the metal gate is deposited over the polysilicon gate, combining both process requirements into a unified flow
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
Enables efficient reset operations with reduced current requirements, allows for smaller memory cell sizes, and simplifies the manufacturing process by eliminating the need for complex high-temperature steps.
Implementation Method 1
heat is generated by a high-resistance element serving as a heater, chalcogenide glass (GST: Ge2Sb2Te5) that is in contact with the heater is melted
Implementation Method 2
the chalcogenide glass is brought into an amorphous state (reset operation). When chalcogenide glass is melted at relatively-low high temperature (low current) and cooled slowly, the chalcogenide glass is crystallized (set operation)
Data Source
AI summary
A semiconductor device includes a pillar-shaped resistance-changing layer and a reset gate insulating film that surrounds the pillar-shaped resistance-changing layer. A reset gate surrounds the reset gate insulating film, and the reset gate is electrically insulated from the pillar-shaped resistance-changing layer.