OTP Memory Built-In Self-Test Using Low-Amplitude Verification Current
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Solution Overview
Problem
One-time-programmable memory systems often malfunction due to defective memory or programming circuitry, which is typically detected only at the time of programming, leading to increased defect rates, as existing methods do not allow for pre-programming verification of their functionality.
Innovation Solution
A method and apparatus for testing one-time-programmable memory that uses a test current less than the threshold to verify the functionality of programming circuitry without actually programming the memory, employing a low amplitude signal to check the integrity of fuses and programming circuitry, and producing output signals indicating success or failure, allowing for built-in self-testing without damaging the circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high current is applied to the fuse to verify programming circuitry functionality, then the programming circuitry can be tested, but the fuse will blow and the memory cannot be programmed
Solution Approach 1:
The patent applies preliminary action by testing the programming circuitry and fuse integrity before actual programming occurs. A test mode is enabled that activates the programming circuitry with limited current to verify functionality without permanently changing the fuse state. This allows defect detection prior to programming, ensuring the memory can be programmed successfully without requiring the fuse to be blown during testing.
Solution Approach 2:
The patent changes the current parameter during testing by applying a limited test current that is sufficient to activate the programming circuitry and detect defects but insufficient to blow the fuse. The test current is controlled to be below the fuse blowing threshold, allowing the circuit to be tested without causing permanent damage to the memory structure.
2Ease of manufacture
If no testing is performed before programming, then the memory and circuitry remain intact for programming, but defective units are not detected until after programming
Solution Approach 1:
The patent implements preliminary testing before programming by enabling a test mode that activates the programming circuitry and fuse with limited current. This preliminary action identifies defective units before they are programmed, allowing for early detection and isolation of faulty memory or circuitry while maintaining the integrity of the memory structure for subsequent programming operations.
3Reliability
If the fuse is tested with threshold current to verify functionality, then the programming circuitry can be validated, but the memory location cannot be programmed
Solution Approach 1:
The patent performs preliminary validation of the programming circuitry and fuse integrity before programming occurs. By testing with limited current in a test mode, the system validates that the programming circuitry functions correctly without causing the fuse to blow. This ensures that subsequent programming operations can proceed successfully without requiring retesting or revalidation.
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
Enables effective pre-programming verification of one-time-programmable memory and its programming circuitry, reducing defect rates and ensuring system reliability by identifying functional issues before actual programming, thus improving overall system performance.
Implementation Method 1
Limiting current flow through the one-time-programmable memory may involve imposing a high impedance between a voltage source and the memory
Implementation Method 2
The test current is less than a threshold current needed to change the state of the circuit element, e.g., blow a fuse
Data Source
AI summary
An apparatus and method of testing one-time-programmable memory provides one-time-programmable memory having one or more memory locations for storing data and corresponding programming circuitry for each memory location. In addition, each programming circuitry has a circuit element configured to permanently change state to store the data in the memory. The method also reads each memory location to verify that the memory location is unprogrammed and activates the programming circuitry for each memory location, which applies a test current to the programming circuitry. The test current is less than a threshold current needed to permanently change the state of the circuit element. The method then determines whether the programming circuitry is functioning properly.