SRAM PUF Circuits Using Non-Volatile Resistance Elements
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Solution Overview
Problem
Conventional physically unclonable function (PUF) circuits based on static random access memory (SRAM) bit cells face reproducibility issues due to transistor noise caused by temperature, voltage variations, and aging effects, leading to inconsistent PUF output responses.
Innovation Solution
The integration of passive non-volatile resistance elements, such as magnetic tunnel junctions (MTJs), replaces pull-up or pull-down transistors in the PUF circuit, providing a constant resistance that maintains imbalance between cross-coupled transistors, reducing transistor noise and enhancing PUF output reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SRAM bit cells are used for PUF circuits, then the circuit structure is simple and manufacturing is easy, but transistor noise from temperature, voltage variations, and aging effects causes poor reproducibility of PUF outputs
Solution Approach 1:
The patent changes the physical parameters of the circuit by replacing volatile transistors with non-volatile resistance elements (such as magnetic tunnel junctions or phase change memory). This substitution fundamentally alters the circuit's operational characteristics, eliminating transistor noise while maintaining the cross-coupled feedback structure. The non-volatile elements provide stable resistance values that are insensitive to temperature, voltage, and aging, thereby improving PUF output reproducibility without requiring complete redesign of the circuit topology.
Solution Approach 2:
The patent creates a hybrid circuit structure that combines non-volatile resistance elements (such as MTJs or PCMs) with standard CMOS transistors. The non-volatile elements serve as the core storage and feedback components, while CMOS transistors provide control and readout functionality. This composite approach leverages the stability of non-volatile materials and the maturity of CMOS technology, achieving improved reproducibility while maintaining manufacturing compatibility.
2Reliability
If passive non-volatile resistance elements are integrated to replace transistors, then PUF output reproducibility improves and transistor noise is reduced, but device complexity and manufacturing complexity increase
Solution Approach 1:
The patent designs the non-volatile resistance elements to serve multiple functions: they act as both the storage element and the feedback element in the cross-coupled configuration. The same MTJ or PCM device provides both the stable resistance for noise reduction and the non-volatile storage capability. This multi-functionality reduces the need for additional components and simplifies the manufacturing process by consolidating functions into single devices.
Solution Approach 2:
The patent introduces control circuitry and readout mechanisms that act as intermediaries between the non-volatile resistance elements and the external environment. These intermediary components translate the resistance states of the non-volatile elements into usable digital signals while protecting the sensitive non-volatile devices from direct stress during readout operations. This mediation approach enables the use of emerging non-volatile technologies with current CMOS manufacturing processes.
3Reliability
If cross-coupled transistors are used in SRAM bit cells, then the circuit is compact and fast, but threshold voltage imbalance and transistor noise lead to inconsistent PUF responses
Solution Approach 1:
The patent changes the physical state and material properties of the feedback elements from volatile transistor channels to non-volatile resistance materials. This parameter change eliminates the threshold voltage variations and hot carrier effects that plague conventional transistors, providing stable and consistent PUF responses. The non-volatile resistance elements maintain their electrical characteristics over time and across environmental conditions, ensuring response consistency.
Solution Approach 2:
The patent creates a simplified version of the conventional SRAM cross-coupled structure by replacing the complex transistor-based feedback path with simpler non-volatile resistance elements. This copied structure maintains the essential feedback mechanism and stability characteristics of the original SRAM design while eliminating the noisy transistor components. The non-volatile elements effectively copy the functional behavior of transistor feedback without the associated noise and variability.
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 results in improved reproducibility of PUF outputs, reducing bit error rates and stabilizing PUF responses across temperature and voltage variations, while supporting write-back operations for memory state storage and reset functionality.
Implementation Method 1
The integration of passive non-volatile resistance elements, such as magnetic tunnel junctions (MTJs), replaces pull-up or pull-down transistors in the PUF circuit, providing a constant resistance that maintains imbalance between cross-coupled transistors
Implementation Method 2
where the added passive NV resistance elements are phase change memory (PCM) materials
Data Source
AI summary
Transistor noise tolerant, non-volatile (NV) resistance element-based static random access memory (SRAM) physically unclonable function (PUF) circuits and related systems and methods. In exemplary aspects, a transistor and its complementary transistor, such as a pull-up transistor and complement pull-down transistor or pull-down transistor and complement pull-up transistor, of the PUF circuit are replaced with passive NV resistance elements coupled to the respective output node and complement output node to enhance imbalance between cross-coupled transistors of the PUF circuit for improved PUF output reproducibility. The added passive NV resistance elements replacing pull-up or pull-down transistors in the PUF circuit reduces or eliminates transistor noise that would otherwise occur if the replaced transistors were present in the PUF circuit as a result of changes in temperature, voltage variations, and aging effect. The bit error rate of the PUF circuit is reduced by the reduction in transistor noise thereby improving PUF output reproducibility.