OTP PUF Unit Cell Programming and Reading Path Separation
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Solution Overview
Problem
Existing Physically Unclonable Function (PUF) technologies require complex sensing amplifiers to compare source and drain side gate oxide leakage currents for programming and reading, leading to increased expense, circuitry complications, and higher chances of error.
Innovation Solution
A semiconductor device with a PUF unit cell that uses a different path for programming and reading, utilizing channel current instead of gate leakage current, where the bit line and source line are coupled during programming and decoupled during reading to determine '1' or '0' states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate oxide leakage current is used for reading PUF cells, then the PUF function can be implemented, but complex sensing amplifiers are required to compare source and drain side currents
Solution Approach 1:
The patent extracts the reading function from the complex sensing amplifier comparison process and implements it through a simplified current path selection mechanism. By using select transistors to choose between source-side and drain-side reading paths, the system eliminates the need for complex current comparison amplifiers while maintaining PUF identification accuracy.
Solution Approach 2:
Instead of comparing both source and drain currents simultaneously as in conventional approaches, the patent inverts the approach by selectively reading only one side (either source or drain) at a time through controlled transistor switching. This inversion simplifies the reading circuitry while preserving the PUF function.
2Manufacturing precision
If soft breakdown of gate oxide is used for encoding, then PUF states can be created, but complicated sensing is required to detect the small leakage currents
Solution Approach 1:
The patent introduces select transistors as intermediary components that mediate between the encode transistor and the reading circuitry. These intermediaries enable the system to detect the encoded state without requiring direct measurement of small leakage currents, thereby simplifying the detection process while maintaining encoding precision.
3Loss of information
If all cell currents are read and compared with reference current, then PUF code can be generated, but complicated reading steps are required
Solution Approach 1:
The patent segments the reading process into distinct phases controlled by select transistors: first selecting which encode transistor to read, then selecting whether to read from the source or drain side. This segmentation breaks down the complicated simultaneous comparison process into simpler sequential steps while preserving PUF code accuracy.
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 approach simplifies the reading process by using consistently high '1' state channel current and small '0' state channel current, reducing variations and errors, and eliminates the need for complex sensing amplifiers.
Implementation Method 1
Soft breakdown of oxide on top of either the source or drain of the encoding transistor is introduced by applied voltage or process plasma damage
Implementation Method 2
The channel current, instead of gate leakage current, for read has a great advantage in that the state '1' bit current is the transistor 'on' current that is consistently high
Data Source
AI summary
A semiconductor device includes at least a one-time programmable (OTP) physically unclonable function (PUF) unit cell with the PUF unit cell coupled to a bit line and a source line and includes an encode transistor is proposed. An encode enable transistor directly couples the bit line and the source line. A path programming the encode transistor is different from a path reading the encode transistor.