Dual-bit Memory Trench Isolation Near Bit Line Contacts
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Solution Overview
Problem
Conventional dual-bit flash memory devices experience increased parasitic leakage current as cell size shrinks, leading to higher programming currents and affecting read and verification operations, especially in low power applications like portable electronics.
Innovation Solution
Incorporating trench isolation material near bit line contact areas to prevent current flow between adjacent bit lines, using techniques like LOCOS or STI to form isolation trenches that block leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cell size is shrunk to increase storage density, then storage capacity per unit area is improved, but parasitic leakage current between bit lines increases
Solution Approach 1:
The patent divides the continuous substrate into isolated regions by introducing trench isolation structures between adjacent bit lines. This segmentation physically separates the bit lines, preventing parasitic leakage current while maintaining high storage density through compact cell design.
Solution Approach 2:
The trench isolation material acts as an intermediary barrier between adjacent bit lines. This intermediate structure blocks the harmful leakage current path without interfering with the normal operation of the memory cells, effectively mediating between the need for high density and low leakage.
2Object-generated harmful factors
If trench isolation material is added to reduce leakage current, then parasitic leakage current is reduced, but device complexity and manufacturing steps increase
Solution Approach 1:
The trench isolation structure is merged with the existing bit line contact formation process. The same etching and filling steps used to create contact holes are utilized to form the isolation trenches, combining two functions into a single integrated process sequence.
Solution Approach 2:
The trench isolation structure serves multiple functions simultaneously: it provides electrical isolation between bit lines, acts as a mechanical support structure, and defines the lateral boundaries of the active regions. This multi-functionality reduces the need for additional dedicated isolation structures.
3Productivity
If trench isolation material is added to reduce leakage current, then programming efficiency is improved, but manufacturing cost and process steps increase
Solution Approach 1:
The trench isolation structures are formed preliminarily during the early stages of device fabrication, before the final memory cell programming operations. This preliminary action ensures that the isolation structures are already in place to prevent leakage during subsequent programming cycles, improving programming efficiency without requiring post-fabrication modifications.
Data Source
AI summary
A dual-bit memory device is provided which includes trench isolation material disposed near bit line contact areas. For example, in one implementation a semiconductor memory device is provided in which each memory cell can store two bits of information. The memory device comprises a substrate, first and second buried bit lines in the substrate, a first bit line contact on the first buried bit line, a second bit line contact on the second buried bit line, and an insulator region disposed in the substrate between the first buried bit line and the second buried bit line. The insulator region prevents a current from flowing between the first buried bit line and the second buried bit line.