Memory Cell Array Field Stopper Elimination
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Solution Overview
Problem
High voltage transistors in semiconductor memory devices require a junction breakdown voltage of at least 15V, leading to increased transistor size and chip area, as existing solutions struggle to balance high voltage requirements with compact design needs.
Innovation Solution
The semiconductor device incorporates a p-type impurity region formed on the entire surface of the substrate where bit line connect transistors are formed, with a shared gate electrode and lightly doped drain structure, eliminating the need for a field stopper in the isolation region, thereby reducing the transistor size and chip area while maintaining the necessary breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate length and distance between gate electrode and contact are increased to raise the breakdown voltage of the transistor, then the junction breakdown voltage reaches at least 15V, but the size of the transistor becomes larger and the chip area increases
Solution Approach 1:
The patent applies different impurity concentrations at different locations: high concentration in the channel region to maintain low threshold voltage and small transistor size, and low concentration in the drain region to increase breakdown voltage. This local differentiation of impurity quality resolves the contradiction between small size and high breakdown voltage.
Solution Approach 2:
The patent changes the impurity concentration parameter spatially - high concentration (1×10^19 to 1×10^21 atoms/cm³) in the channel and low concentration (1×10^16 to 1×10^18 atoms/cm³) in the drain region. This parameter variation allows the transistor to simultaneously achieve low threshold voltage and high breakdown voltage without increasing size.
2Device complexity
If conventional transistors are used in isolation regions without field stoppers, then the structure is simpler, but substrate floating effects occur and breakdown voltage requirements cannot be met
Solution Approach 1:
The patent extracts and eliminates the field stopper structure from the isolation region, replacing it with a simplified structure where the low-concentration impurity region in the drain extends to the isolation region boundary. This removal of the field stopper simplifies the structure while maintaining breakdown voltage control through the extended low-concentration region.
Solution Approach 2:
The low-concentration impurity region serves multiple functions: it increases breakdown voltage at the drain, controls substrate potential to prevent floating effects, and eliminates the need for separate field stopper structures. This multi-functionality resolves the contradiction between structural simplicity and reliability.
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 allows for high-density transistor arrangement with reduced chip area, maintaining the required breakdown voltage and preventing substrate floating effects, thus enabling efficient high-voltage operations without the need for large transistors.
Implementation Method 1
a first-conductivity-type impurity region which is formed in the region of the semiconductor substrate where said plurality of first transistors are formed in such a manner that the depth of the first-conductivity-type impurity region is greater than the depth of the first and second diffused layers of said plurality of first transistors to control the threshold voltage of the first transistors
Implementation Method 2
isolation regions which are formed in the semiconductor substrate and isolate said plurality of first transistors from one another
Data Source
AI summary
A plurality of first transistors formed on a substrate share a gate electrode. Isolation regions isolate the plurality of first transistors from one another. In the region where the plurality of first transistors, an impurity region is formed in such a manner that it includes the source and drain regions of the plurality of first transistors and that the depth of the impurity region is greater than the depth of the source and drain regions. The impurity region sets the threshold voltage of the first transistors.