OTP Memory Testing Without Erase Circuits
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Solution Overview
Problem
Existing methods for testing one-time-programmable (OTP) memory devices, such as oxide-nitride-oxide read only memory (NROM) devices, are unreliable and degrade the quality and increase the size and cost of the memory device due to the need for multiple program-and-erase cycles and additional erase circuits.
Innovation Solution
A method where each memory cell is programmed to a first threshold voltage higher than its initial maximum value, allowing for direct user programming without the need for erase operations, thereby reducing the program margin and improving memory cell quality and device size and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple program-and-erase cycles are performed to test the memory device, then the reliability of testing is improved, but the quality of the memory device deteriorates due to increased charge loss and the need for ten times cycling margins
Solution Approach 1:
The patent applies preliminary action by performing a test program operation that programs memory cells to a first threshold voltage higher than the maximum initial threshold voltage. This preliminary programming establishes a known good state before user programming, eliminating the need for subsequent erase operations and reducing the required cycling margins while maintaining testing reliability.
2Ease of operation
If erase operations are performed after program operations to clear memory cells, then the memory cells are prepared for user programming, but the size and cost of the memory device increase due to extra erase circuits
Solution Approach 1:
The patent extracts and eliminates the erase function from the memory device by designing a test method that programs memory cells to a threshold voltage higher than the maximum initial value. This extraction removes the need for erase circuits entirely, as the test program operation directly establishes the state needed for user programming without requiring subsequent erase operations.
Solution Approach 2:
The test program operation serves multiple functions: it tests the memory cells, programs them to a known good state, and prepares them for user programming all in one operation. This multi-functionality eliminates the need for separate erase operations and the associated erase circuits.
Data Source
AI summary
An OTP memory device and method for testing the same is disclosed. The memory device includes a number of memory cells and each memory cell has an initial threshold voltage. Each memory cell is programmed to have a first threshold voltage larger than a maximum value of the initial threshold voltages in the test program operation. When the memory device is test pass, the memory device is directly provided for a user program operation without need of an erase operation.