Optical Fuse Redundancy Circuit for Semiconductor Memory
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Solution Overview
Problem
Conventional semiconductor memory devices face challenges with the reliability of electrical fuses and anti-fuses due to variations in manufacturing processes, leading to inconsistent resistance and programming reliability, which affects the integration density and reprogrammability of redundancy circuits.
Innovation Solution
A redundancy circuit is designed with a fuse set circuit comprising transistors of different contact resistances, a fuse control circuit that manages power supply voltages based on operation modes, and a redundancy control unit to generate enable signals for programming and repairing defective memory cells, allowing for efficient replacement of defective cells with redundancy cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If electrical fuse is used for redundancy circuit, then reprogrammability is improved, but reliability deteriorates due to resistance variation from manufacturing process changes
Solution Approach 1:
The patent changes the physical state of the fuse from electrical (conductive) to optical (absorptive). The optical fuse uses a material that changes its optical properties when exposed to laser beam, creating a permanent non-volatile memory state. This resolves the contradiction by providing both reprogrammability through laser exposure and reliability through stable optical state, avoiding the resistance variation issues of electrical fuses.
Solution Approach 2:
The patent replaces the electrical fuse mechanism with an optical fuse mechanism. Instead of using electrical current to create or break conductive paths, the invention uses laser beam to alter the optical properties of a material, creating a permanent state change. This substitution eliminates the reliability issues associated with electrical fuse resistance variation while maintaining reprogrammability.
2Adaptability or versatility
If anti-fuse is used for redundancy circuit, then reprogrammability is improved, but reliability deteriorates due to incomplete programming and resistance variation
Solution Approach 1:
The patent replaces the electrical anti-fuse mechanism with an optical fuse mechanism. Instead of using high voltage to create electrical conduction, the invention uses laser beam to induce permanent optical absorption changes in the material. This provides stable, non-volatile memory states that are immune to the resistance variation and incomplete programming issues of electrical anti-fuses, while maintaining reprogrammability.
Solution Approach 2:
The patent changes the programming mechanism from electrical (voltage-based) to optical (laser-based). The optical fuse uses materials whose optical properties permanently change when exposed to laser beam, creating stable non-volatile memory states. This resolves the contradiction by providing both reprogrammability and reliability, avoiding the electrical programming inconsistencies.
3Reliability
If laser fuse is used for redundancy circuit, then reliability is improved, but integration density deteriorates due to required interval between fuses
Solution Approach 1:
The patent replaces the laser fuse with an optical fuse that uses a different physical mechanism. Instead of requiring physical spacing to prevent laser damage, the optical fuse uses materials that change their optical properties when exposed to laser beam, allowing for tighter spacing and higher integration density while maintaining the reliability benefits of non-volatile programming.
4Adaptability or versatility
If electrical fuse is used for redundancy circuit, then reprogrammability is improved, but device complexity increases due to large control driver
Solution Approach 1:
The patent replaces the electrical fuse control mechanism with an optical control mechanism. Instead of requiring complex electrical drivers to generate high currents for fuse programming, the invention uses laser beam to directly alter the optical properties of the fuse material. This dramatically simplifies the control circuitry while maintaining reprogrammability and reliability.
Data Source
AI summary
A redundancy circuit includes at least one fuse set circuit and a fuse control circuit. The at least one fuse set circuit includes a plurality of fuse cells, each of the plurality of fuse cells having a first transistor and a second transistor having same sizes. The first transistor has a first contact resistance and the second transistor has a second contact resistance different from the first contact resistance. Each of the plurality of fuse cells stores a fuse address indicating a defective cell in a repair operation and outputs a repair address corresponding to the stored fuse address. The fuse control circuit, connected to the plurality of fuse cells, controls the plurality of fuse cells in response to a program signal and a precharge signal such that the corresponding fuse address is stored in each of the fuse cells.