Buried Word Line Work Function Tuning for DRAM Row Hammer Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The row hammering issue in DRAM cells causes intermittent failures due to charge migration and data corruption, which existing solutions attempt to address by limiting access or reducing refresh time, but these methods impact performance and have physical limitations.
Innovation Solution
A semiconductor structure is developed with an n-type work function metal layer, including titanium and titanium nitride, to tune the work function of the buried word line, preventing leakage to adjacent rows, comprising a substrate, trench, gate dielectric, and buried word line with a gradually increasing titanium nitride to titanium ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of accesses per row per refresh cycle is limited to address row hammer failure, then data corruption is reduced, but system performance deteriorates
Solution Approach 1:
An intermediate layer (first work function metal layer) is introduced between the bit line contact and the buried channel array transistor to prevent direct charge migration. This intermediary structure blocks the harmful electron flow path while allowing normal memory operations, thus protecting data integrity without limiting access frequency.
Solution Approach 2:
The patent converts the harmful effect of repeated row access (which causes charge migration) into a beneficial protective mechanism. By designing the work function metal layer with specific properties, the structure that would normally be vulnerable to row hammering is transformed into an active defense mechanism that prevents charge migration while maintaining normal access operations.
2Reliability
If the bottom critical dimension in the buried channel array transistor is decreased to address row hammer failure, then charge migration is reduced, but manufacturing complexity increases
Solution Approach 1:
Instead of changing the critical dimensions of the transistor, the patent changes the material parameters of the work function metal layer. By adjusting the work function and material composition (using titanium nitride and titanium in specific ratios), the patent achieves charge migration prevention through electrical property modification rather than geometric dimension changes, avoiding increased manufacturing complexity.
3Reliability
If the time between refreshes is decreased to prevent row hammering, then data corruption is reduced, but refresh overhead increases
Solution Approach 1:
The protective work function metal layer structure is built in advance during manufacturing, providing inherent protection against row hammering before any access operations occur. This preliminary structural defense eliminates the need for frequent refresh operations or access limiting, as the charge migration path is blocked by design rather than by operational constraints.
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 solution effectively prevents row hammering without significantly altering the DRAM or DIMM design, maintaining performance while reducing data corruption and failure rates.
Implementation Method 1
an n-type work function metal layer to tune the work function of the buried word line, thereby preventing the row hammering issue resulted from the word line leakage to a non-accessed physically adjacent row
Data Source
AI summary
A method of manufacturing a semiconductor device for preventing row hammering issue in DRAM cell, including the steps of providing a substrate, forming a trench in the substrate, forming a gate dielectric conformally on the trench, forming an n-type work function metal layer conformally on the substrate and the gate dielectric, forming a titanium nitride layer conformally on the n-type work function metal layer, and filling a buried word line in the trench.