Silicide Fuse Programming Circuit Using Voltage Reference
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Solution Overview
Problem
Existing one-time programmable (OTP) memory circuits face issues with unreliable programming due to variations in temperature and process variations, leading to under- or over-programming, which affects yield and reliability, and require large die areas, increasing costs.
Innovation Solution
A circuit and method that uses a programming circuit with a control element to form a programming current proportional to a reference voltage, utilizing a current mirror and transistors to control the programming current, which includes an amplifier and a current mirror to ensure reliable programming by controlling the resistivity of fuse elements through electro-migration of silicide material, thereby adjusting the resistance without forming an open circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed external reference current is used to form the programming current, then the programming process is simplified, but the programming reliability deteriorates due to temperature variations causing current variation
Solution Approach 1:
The patent changes the reference from a fixed current to a voltage reference (Vref) that is less sensitive to temperature variations. By using a voltage reference combined with a programmable resistor, the system achieves temperature compensation because the voltage reference can be designed to have minimal temperature coefficient, and the programmable resistor's temperature effects are compensated through the feedback mechanism.
Solution Approach 2:
The patent implements a feedback mechanism where the programming current is continuously adjusted based on the actual resistance value of the programmable resistor. The control circuit monitors the resistance and dynamically adjusts the current to achieve the target resistance value, compensating for temperature drift and process variations. This closed-loop control ensures reliable programming despite environmental changes.
2Reliability
If a programming current is formed by a current through another resistor with similar construction, then process variations are compensated, but the die area increases due to large reference circuits
Solution Approach 1:
The patent changes from using a physical resistor-based reference to a voltage-based reference system. This parameter change allows the reference to be implemented with much smaller circuit elements, significantly reducing the die area while maintaining the ability to compensate for process variations through the voltage reference's stability.
Solution Approach 2:
The patent uses a voltage reference that can be replicated across multiple memory cells without requiring large physical areas. The Vref signal serves as a compact template that can be distributed to numerous cells, enabling consistent programming across the array without proportionally increasing the total die area.
3Reliability
If a high programming current is applied to ensure reliable programming, then programming reliability improves, but the risk of over-programming increases which adversely affects yield
Solution Approach 1:
The patent employs a dynamic programming current that adjusts in real-time during the programming process. The current starts at a higher level to ensure reliable programming initiation, then automatically reduces as the programmable resistor approaches the target resistance value. This dynamic adjustment prevents over-programming while ensuring adequate programming stimulus, optimizing both reliability and precision.
Solution Approach 2:
The feedback mechanism continuously monitors the resistance value during programming and adjusts the current accordingly. When the target resistance is approached, the feedback signal reduces the programming current, preventing over-programming. This closed-loop control ensures precise termination of the programming process, improving manufacturing precision without sacrificing 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
The solution provides reliable programming of OTP memory circuits by compensating for temperature and process variations, improving yield and reliability while reducing the area required on the die, thus lowering costs and enhancing the consistency of the programming process.
Implementation Method 1
utilizing a current mirror and transistors to control the programming current, which includes an amplifier and a current mirror to ensure reliable programming by controlling the resistivity of fuse elements through electro-migration of silicide material
Data Source
AI summary
In one embodiment, a programming circuit is configured to form a programming current for a silicide fuse element by using a non-silicide programming element.