Steep Slope FET With Impact Ionization Channel for pMTJ
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Solution Overview
Problem
The scaling of perpendicular magnetic tunnel junctions (pMTJs) is limited by the size of the access transistor, which struggles to handle large programming currents, and the reliability of the access transistor is compromised due to stringent reliability requirements for memory applications.
Innovation Solution
The implementation of a steep slope field-effect transistor (FET) with an impact ionization channel (i-channel) and a pMTJ structure, where the gate layer is positioned closer to the drain than the source, enhancing current drivability and reliability by utilizing impact ionization phenomena to provide additional current drive capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional access transistors are used in pMTJ, then the device structure is simple, but the current drivability is insufficient and reliability is compromised
Solution Approach 1:
The channel layer is segmented into distinct regions: a first channel region adjacent to the source electrode and a second channel region adjacent to the drain electrode, with different doping concentrations. This segmentation allows each region to be optimized for its specific function - the source-side region for carrier injection and the drain-side region for impact ionization, thereby improving reliability without requiring a completely new device architecture
Solution Approach 2:
Different regions of the channel are assigned different doping concentrations to create local quality variations. The first channel region has a first doping concentration while the second channel region has a second doping concentration, enabling localized optimization of electrical properties. This allows the transistor to achieve high current drivability and reliability through spatially varying material properties rather than uniform structure
2Power
If larger programming currents are handled by access transistor, then current drivability improves, but transistor size must increase which limits pMTJ scaling
Solution Approach 1:
The invention changes the electrical parameters of the channel by implementing different doping concentrations in different channel regions. The first channel region has a first doping concentration optimized for carrier injection, while the second channel region has a second doping concentration optimized for impact ionization. This parameter variation enables the transistor to achieve high current drivability within a compact footprint, allowing pMTJ scaling without sacrificing programming current capability
Solution Approach 2:
The invention replaces the conventional approach of increasing transistor physical dimensions to handle larger currents with a field-effect mechanism. By using impact ionization in the second channel region, the device generates additional carriers through electrical field effects rather than relying on increased channel cross-section. This substitution of mechanical scaling with field-based current multiplication enables high current capability in a scaled-down device
3Productivity
If impact ionization channel is implemented, then current drivability and reliability improve, but device structure becomes more complex
Solution Approach 1:
The channel is divided into functionally distinct segments: a first channel region for carrier injection and a second channel region for impact ionization. This segmentation is achieved through different doping concentrations in adjacent regions, allowing each segment to perform its designated function efficiently. The segmented structure enables high current drivability through impact ionization while maintaining a relatively simple planar device geometry
Solution Approach 2:
The invention merges multiple functions into a single continuous channel layer. The same channel layer serves both as the injection region (first channel region) and the impact ionization region (second channel region), rather than requiring separate structures. This merging is achieved through lateral variation in doping concentration within the channel, combining carrier injection and impact ionization functions in one integrated structure, thereby improving productivity without excessive complexity
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 configuration enables bidirectional programmability and improves the reliability of the pMTJ, allowing for larger current drivability and extended lifetime suitable for memory systems like MRAM, while maintaining low operating voltage and avoiding saturation of drain current.
Implementation Method 1
forming an impact ionization channel (i-channel) layer above the source layer in the film thickness direction
Data Source
AI summary
According to one embodiment, a method includes forming a bottom electrode layer above a substrate in a film thickness direction, forming a source layer above the bottom electrode layer in the film thickness direction, forming an impact ionization channel (i-channel) layer above the source layer in the film thickness direction, forming a drain layer above the i-channel layer in the film thickness direction, forming an upper electrode layer above the drain layer in the film thickness direction to form a stack that includes the bottom electrode layer, the source layer, the i-channel layer, the drain layer, and the upper electrode layer, and forming a gate layer positioned on sides of the i-channel layer along a plane perpendicular to the film thickness direction in an element width direction. The gate layer is formed in a position closer to the drain layer than the source layer.