TCAM Bitcell With Programmable Resistive Elements
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Solution Overview
Problem
Ternary content addressable memory (TCAM) systems face challenges in reducing the size and transistor count of bitcells while maintaining high voltage tolerance for resistive RAM technology, which requires dual gate oxide transistors that are not compatible with low voltage logic transistors.
Innovation Solution
Implementing a TCAM bitcell configuration with programmable resistive elements in a gain-cell configuration, using a resistance ratio to drive the match line output and isolating low voltage transistors from high voltage operations, and reducing the number and size of transistors in each bitcell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dual gate oxide transistors are used to withstand high voltages in RRAM, then voltage tolerance is improved, but device complexity and transistor size increase
Solution Approach 1:
The transistor gate oxide is segmented into two layers with different thicknesses - a thicker first gate oxide layer for withstanding high programming voltages and a thinner second gate oxide layer for low-voltage logic operations. This segmentation allows the same transistor to handle both high voltage tolerance and low voltage complexity requirements simultaneously.
2Loss of energy
If RRAM technology is integrated into TCAM, then non-volatility and low power consumption are improved, but compatibility with low voltage transistors deteriorates
Solution Approach 1:
Different regions of the gate oxide have different thicknesses tailored to different functional requirements. The thicker first gate oxide layer provides high voltage tolerance for RRAM programming operations, while the thinner second gate oxide layer enables compatibility with low voltage logic transistors. This local quality variation resolves the voltage compatibility issue while maintaining energy efficiency.
3Area of moving object
If bitcell size is reduced, then TCAM density is improved, but maintaining high voltage tolerance becomes more difficult
Solution Approach 1:
The patent merges the high voltage tolerance function and low voltage logic function into a single dual gate oxide transistor structure. This consolidation allows the bitcell to maintain voltage tolerance capabilities while reducing overall size, as the segmented gate oxide provides both functions without requiring separate transistor types.
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 approach allows for a non-volatile, low power consumption TCAM with smaller bitcells, enabling efficient search operations and maintaining high voltage tolerance, thus addressing the compatibility issues between RRAM technology and low voltage transistors.
Implementation Method 1
The programmable resistive element is made of a dielectric solid-state material whose resistance can be changed using an appropriate voltage. Each programmable resistive element implements at least two levels of resistance: a high resistive state (HRS) and a low resistive state (LRS).
Data Source
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AI summary
A content addressable memory device includes a first memory cell having three programmable resistive elements coupled in parallel. The first terminals of the first, second, and third programmable resistive elements are coupled to a first node, the second terminal of the first programmable resistive element coupled to a first source line voltage, the second terminal of the second programmable resistive element coupled to a second source line voltage, and the second terminal of the third programmable resistive element coupled to a first supply voltage. A first access transistor includes a first current electrode coupled to a bit line; a second current electrode coupled to the first node, and a control electrode coupled to a word line. A match line transistor includes a first current electrode coupled to a match line; a second current electrode coupled to a second supply voltage and a control electrode coupled to the first node.