Companion Controller for Flash Memory Column Redundancy
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Solution Overview
Problem
Existing memory systems face increasing complexity and manufacturing costs due to on-chip redundancy circuitry, which is undesirable for larger memory structures, and there is a need to minimize control logic and memory pins for interfacing with host interfaces.
Innovation Solution
A separate companion control chip is used to provide column redundancy for a FLASH memory chip by transferring normal and redundant data bytes, checking for defective memory locations, and combining data to provide corrected bytes for external users, thereby reducing the need for on-chip control logic and minimizing memory pins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If on-chip redundancy circuitry is used for larger memory structures, then memory reliability is improved, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent extracts the redundancy control logic from the memory chip itself and places it in a separate companion controller chip. The memory chip contains only the memory array and basic I/O circuitry, while the companion controller handles all redundancy management, address remapping, and defective cell identification. This separation reduces the complexity of the memory chip while maintaining reliability through external redundancy circuitry.
Solution Approach 2:
The system is divided into two independent functional segments: the memory chip and the companion controller chip. Each chip has a specialized function - the memory chip for data storage and the companion controller for redundancy management. This segmentation allows each component to be optimized independently, reducing overall system complexity while maintaining reliability.
2Reliability
If on-chip redundancy circuitry is used for larger memory structures, then memory reliability is improved, but manufacturing costs increase
Solution Approach 1:
By extracting the redundancy control logic to a separate companion controller chip, the patent enables simpler memory chip manufacturing processes. The memory chip can be produced using standard, well-established fabrication techniques without the need for complex redundancy circuit integration, thereby reducing manufacturing costs while maintaining reliability through the external controller.
3Reliability
If on-chip redundancy circuitry is used, then replacement of defective memory cells is enabled, but the number of memory pins required increases
Solution Approach 1:
The patent extracts the pin management complexity for redundancy operations to the companion controller chip. The memory chip uses a reduced set of pins for basic operations, while the companion controller handles the additional signaling requirements for redundancy management, address remapping, and defective cell identification, thereby reducing the pin count on the memory chip itself.
Data Source
AI summary
Column redundancy is provided outside of a FLASH memory chip using a separate companion controller chip. The companion chip initially receives and stores fuse address information from the FLASH memory chip for defective memory cells in the FLASH memory. In a read mode of operation, the companion control chip detects receipt of a defective address from the FLASH memory and stores in a redundant shift register redundant data that is downloaded from the FLASH memory chip. The redundant data is used to provide correct FLASH memory data to an external user that interfaces with the companion control chip. In a program mode of operation, the companion control chip provides redundant bits that are stored in redundant columns in the FLASH memory chip. The companion control chip provides flexibility by readily providing a number of different redundancy schemes for bits, nibbles, or bytes without requiring additional logic circuits in the FLASH memory chip itself. Data is transferred between the FLASH memory chip and the companion control chip a byte at a time.