Non-Volatile Memory PUF Using Threshold-Voltage Differential Reading
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Solution Overview
Problem
Existing physical unclonable functions (PUFs) within integrated circuits are not robust enough to withstand temperature variations and aging, are sensitive to attacks, and have a large surface footprint, making them difficult to produce and distinguish reliably.
Innovation Solution
A PUF device comprising non-volatile memory cells with depletion-type state transistors and a processing circuit that generates a unique, unpredictable code by reading the effective threshold voltages of these transistors, organized in symmetric matrix sub-assemblies to enhance dispersion and reliability, with a second assembly for reliability information storage and differential reading methods to ensure robustness and security.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PUF structures are used, then the device can generate unique codes, but the device is not robust against temperature variations and aging
Solution Approach 1:
The patent uses depletion-type state transistors whose threshold voltages are inherently less sensitive to temperature variations and aging effects compared to enhancement-type transistors. This parameter change in transistor type fundamentally alters the physical characteristics to achieve desired robustness while maintaining code uniqueness
Solution Approach 2:
The patent employs non-volatile memory cells with depletion-type state transistors that maintain their characteristics over long periods without requiring refresh operations. These cells are designed to be inherently stable and resistant to environmental degradation, effectively creating long-lived stable objects rather than short-lived vulnerable ones
2Reliability
If PUF structures are made robust against environmental variations, then the code stability improves, but the random variations become harder to identify
Solution Approach 1:
The patent changes the operating parameter regime by using depletion-type transistors with negative threshold voltages. This allows the system to operate in a regime where small random variations in threshold voltage (caused by manufacturing variations) remain identifiable while the overall structure is robust against larger environmental variations. The differential reading technique further enhances this by comparing matched pairs, amplifying the small random differences while canceling out environmental effects
3Reliability
If existing PUF devices are implemented, then unique codes are generated, but the surface footprint is penalizing
Solution Approach 1:
The patent merges the PUF functionality with standard non-volatile memory cell structures that already exist in the technology portfolio. By combining the depletion-type state transistor (providing robustness) with the floating gate memory cell (providing non-volatility and compactness), the design achieves unique code generation in a compact footprint without requiring separate dedicated PUF circuitry
Solution Approach 2:
The patent creates a multi-functional structure where the same memory cell array serves both as storage (using floating gate) and as the PUF source (using depletion-type state transistor threshold voltage variations). This universal structure eliminates the need for separate PUF and memory circuits, significantly reducing the overall surface footprint
4Area of stationary object
If PUF structures are made compact, then the surface footprint reduces, but the device becomes more sensitive to attacks
Solution Approach 1:
The patent incorporates reliability information storage and differential reading mechanisms that are built into the structure from the beginning. By preliminarily establishing matched pairs of memory cells and storing reliability metadata, the system is pre-configured to detect and resist attacks before they can compromise the PUF functionality, making the compact structure inherently secure rather than vulnerable
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 a robust, secure, and compact PUF device that is resistant to temperature changes and attacks, with a unique code suitable for encryption, while being easy to produce and distinguish, and has a reduced surface footprint.
Implementation Method 1
the state transistors of the memory cells of the first assembly are of the depletion type and have a control gate and a floating gate that are electrically connected
Data Source
AI summary
An embodiment system comprises a physical unclonable function device, wherein the device comprises a first assembly of non-volatile memory cells each having a selection transistor embedded in a semiconductor substrate and a depletion-type state transistor having a control gate and a floating gate that are electrically connected, the state transistors having respective effective threshold voltages belonging to a common random distribution, and a processing circuit configured to deliver, to an output interface of the device, a group of output data based on a reading of the effective threshold voltages of the state transistors of the memory cells of the first assembly.