OTP Bitcell Diode Under Anti-Fuse for Reliable Programming
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Solution Overview
Problem
Advanced CMOS processes face challenges with one-time programmable (OTP) memory bitcells due to issues with gate oxide rupture reliability, trap density, and the need for two gate oxides of different thicknesses, which are not always available, leading to inefficiencies in programming and manufacturing costs.
Innovation Solution
A one-time programmable memory device with a single gate and a diode under the gate oxide, where the diode is formed by doped regions, allowing for selective programming and isolation of bitcells without a select device, using a floating P+ region to prevent unintended ruptures and leveraging Fowler-Nordheim tunneling voltages for efficient programming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a select device is used in the OTP bitcell, then selective programming and reading can be achieved, but the device complexity increases and the bitcell area expands
Solution Approach 1:
The patent extracts and removes the select device from the OTP bitcell structure, replacing it with a diode formed by doped regions. This extraction eliminates the need for the select device while maintaining selective programming capability through the diode's inherent selectivity, thereby reducing device complexity and bitcell area.
Solution Approach 2:
The patent merges the select function with the diode structure formed by doped regions. The diode combines the functions of selection and isolation that were previously performed by separate select devices, simplifying the overall bitcell architecture while maintaining operational capability.
2Reliability
If two gate oxides of different thicknesses are used, then the anti-fuse can be reliably ruptured, but the manufacturing process complexity increases and additional process steps are required
Solution Approach 1:
The patent changes the parameter of gate oxide thickness from having two different values to a single uniform thickness. This parameter change simplifies the manufacturing process while maintaining rupture reliability through the diode-assisted voltage distribution mechanism that ensures sufficient electric field across the gate oxide during programming.
Solution Approach 2:
The diode structure acts as an intermediary that enables reliable gate oxide rupture with a single thickness gate oxide. The diode mediates the voltage distribution, ensuring that sufficient voltage is applied across the gate oxide during programming without requiring the gate oxide to be specially engineered with dual thicknesses.
3Ease of manufacture
If a single gate oxide thickness is used, then the manufacturing process is simplified, but the ability to sustain programming voltage and achieve reliable rupture is compromised
Solution Approach 1:
The diode serves as an intermediary that enables the single thickness gate oxide to sustain programming voltage reliably. The diode's voltage characteristics ensure proper voltage distribution across the bitcell, allowing the gate oxide to achieve sufficient electric field for rupture while maintaining manufacturing simplicity.
Solution Approach 2:
The patent changes the operational parameters of the single thickness gate oxide by introducing the diode structure, which modifies the voltage distribution and timing characteristics. This allows the gate oxide to function reliably for rupture despite having uniform thickness, compensating for the simplified manufacturing through parameter optimization.
4Productivity
If high current is applied to rupture the gate oxide, then programming is achieved, but unintended bitcells may be damaged and self-heating effects occur
Solution Approach 1:
The patent applies local quality by using the diode to create localized current confinement. The diode ensures that high current is applied only to the selected bitcell's gate oxide while preventing current flow to adjacent bitcells, thereby enabling fast programming without damaging unintended cells.
Solution Approach 2:
The diode acts as an intermediary that controls current flow paths. It mediates between the programming voltage source and the gate oxide, ensuring that high current is directed only where needed for rupture while protecting other bitcells from harmful current effects and self-heating.
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
This solution enables reliable and efficient programming of OTP bitcells by eliminating the need for two gate oxides, reducing programming time and costs, and ensuring long-term memory retention by using a diode structure that prevents accidental bitcell damage during programming.
Implementation Method 1
the diode is formed by two doped regions layered under the gate
Implementation Method 2
The voltage applied to the conductive portion is independent from the voltage applied to the first doped region
Implementation Method 3
leveraging Fowler-Nordheim tunneling voltages for efficient programming
Data Source
AI summary
A one-time programmable memory device includes a first doped region in a semiconductor substrate, a second doped region implanted within the first doped region, and a gate positioned over the second doped region. The first doped region and second doped regions form a diode. A first contact is coupled to the first doped region for applying a voltage to the first doped region. The gate includes a dielectric portion that is capacitively coupled to the second doped region. The gate also includes a conductive portion that is coupled to a second contact for applying a voltage to the conductive portion. The voltage applied to the conductive portion is independent from the voltage applied to the first doped region. The memory device is programmed by forming a rupture in the dielectric portion of the gate.