Passing Word Line Isolation for DRAM Leakage Reduction
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Solution Overview
Problem
Conventional volatile memory cells, such as DRAM cells, experience sub-threshold leakage current even when in the 'off' state, leading to charge loss and increased refresh rates, which in turn increase power consumption and affect device performance.
Innovation Solution
The implementation of active and passing word line structures with recessed access devices and isolation structures formed within a semiconductive material, where the passing word line structures are partially within an insulative material to reduce charge leakage, and the use of pillars with varying dimensions and dielectric materials to enhance leakage reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional volatile memory cells are used with standard word line structures, then the device can operate with simple structure, but sub-threshold leakage current occurs causing charge loss and increased power consumption
Solution Approach 1:
The word line structure is segmented into active word line portions and passing word line portions. The active word lines are positioned above the semiconductive layer and connected to memory cells, while the passing word lines extend into the isolation structure to avoid inducing leakage in unselected cells. This segmentation allows selective activation and reduces unwanted electrical coupling.
Solution Approach 2:
Different regions of the word line structure are assigned different functions and properties. Active word line regions are configured for strong electrical coupling to memory cells, while passing word line regions are positioned within the isolation structure to provide electrical isolation. The isolation structure itself has varying dielectric properties to optimize both coupling and isolation requirements in different spatial locations.
2Productivity
If voltage is applied to passing word lines adjacent to unselected memory cells, then adjacent word lines can be accessed, but leakage current is induced from the capacitor through the drain of the unselected memory cell
Solution Approach 1:
The isolation structure acts as an intermediary between the passing word lines and the unselected memory cells. When voltage is applied to passing word lines, the isolation structure (comprised of dielectric materials with appropriate breakdown voltages and thicknesses) prevents the voltage from inducing significant leakage current in unselected cells, thereby mediating the interaction between passing and active word lines.
Solution Approach 2:
The passing word lines are extended into the vertical dimension by positioning them within the isolation structure rather than solely in the lateral plane. This three-dimensional configuration increases the distance and reduces the electrical coupling between passing word lines and unselected memory cells, thereby reducing leakage current while maintaining access functionality.
3Ease of manufacture
If the isolation structure has uniform cross-section, then manufacturing is simpler, but it cannot effectively reduce charge leakage from unselected memory cells
Solution Approach 1:
The isolation structure is designed with an asymmetric cross-sectional profile, featuring a widened portion rather than a uniform cross-section. This asymmetric geometry creates enhanced electrical isolation in critical regions where passing word lines are positioned, effectively reducing charge leakage from unselected memory cells while remaining manufacturable using standard semiconductor fabrication techniques.
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 reduces charge leakage from unselected memory cells, thereby increasing the time between refresh operations and improving the overall performance of microelectronic devices by minimizing the disturb effect from adjacent word lines.
Implementation Method 1
The insulative material may be located between the dielectric material of the passing word line structure and the semiconductive material. The insulative material may reduce leakage of charge from the storage structure of the memory cell when a voltage is applied to the passing word line structure.
Implementation Method 2
A dielectric material of the passing word line structure may be located adjacent to an insulative material and the passing word line structure may include a dielectric material having an effective thickness greater than a thickness of a corresponding dielectric material of the active word line structures.
Data Source
AI summary
A microelectronic device comprises a first pillar of a semiconductive material, a second pillar of the semiconductive material adjacent to the first pillar of the semiconductive material, an active word line extending between the first pillar and the second pillar, and a passing word line extending on a side of the second pillar opposite the active word line, the passing word line extending into an isolation region within the semiconductive material, the isolation region comprising a lower portion and an upper portion having a substantially circular cross-sectional shape and a larger lateral dimension than the lower portion. Related microelectronic devices, electronic systems, and methods are also described.