Digital Circuit Reverse Engineering Resistance via Threshold Voltage Asymmetry
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Solution Overview
Problem
Reverse engineering of integrated circuits poses a significant threat to the semiconductor industry, as attackers can steal and replicate circuit designs, and existing countermeasures are often costly and inefficient, requiring process technology extensions or increased area and energy consumption.
Innovation Solution
The method involves forming and connecting field effect transistors in a digital circuit such that the output signal has an undefined logic state when threshold voltages are equal, and setting these voltages to achieve a predetermined defined logic state, using differently doped transistors to create metastable states that are shifted to stable states, thereby making the circuit resistant to reverse engineering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional countermeasures against reverse engineering are implemented (such as process technology extensions, increased area, or increased energy consumption), then security against reverse engineering is improved, but manufacturing complexity, area, and energy consumption increase
Solution Approach 1:
The patent changes the electrical parameters of existing transistors by adjusting threshold voltages through doping modifications. By creating transistors with different threshold voltage characteristics (e.g., first transistor with threshold voltage Vth1, second transistor with threshold voltage Vth2 where Vth1 ≠ Vth2), the circuit develops metastable states that are difficult to reverse engineer without requiring process technology extensions or additional circuit components
2Ease of manufacture
If threshold voltages of field effect transistors are set to be equal for symmetry, then manufacturing simplicity is improved, but security against reverse engineering deteriorates because the circuit becomes predictable and easier to analyze
Solution Approach 1:
The patent applies local quality by creating specific doping regions within the transistor structure to modify threshold voltages of individual transistors. By introducing doping regions with different doping concentrations or doping types in specific locations, the circuit achieves asymmetric threshold voltage characteristics while maintaining overall manufacturing simplicity and using standard CMOS process steps
3Ease of manufacture
If standard CMOS process is used without modifications, then ease of manufacture is improved, but the ability to create metastable states for security purposes is limited
Solution Approach 1:
The patent enables the standard CMOS process to serve dual purposes: manufacturing regular circuits and simultaneously creating security features through doping-modified transistors. The same fabrication process that creates the functional circuit also introduces doping regions that generate threshold voltage differences, allowing the circuit to self-generate metastable states without requiring separate process steps or additional manufacturing complexity
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 increases the difficulty and effort for reverse engineering, providing robust and dynamic characteristics that conceal the circuit's nature, even under security IC attack scenarios, without requiring process changes or significant resource expenditure.
Implementation Method 1
connecting the field effect transistors such that an output signal of the digital circuit in response to a predetermined input has an undefined logic state when the threshold voltages of the field effect transistors are equal and setting the threshold voltages of at least one of the field effect transistors such that the output signal of the digital circuit in response to the predetermined input has a predetermined defined logic state
Implementation Method 2
using differently doped transistors to create metastable states that are shifted to stable states
Data Source
AI summary
A method for manufacturing a digital circuit is described comprising forming two field effect transistors, connecting the field effect transistors such that an output signal of the digital circuit in response to a predetermined input has an undefined logic state when the threshold voltages of the field effect transistors are equal and setting the threshold voltages of at least one of the field effect transistors such that the output signal of the digital circuit in response to the predetermined input has a predetermined defined logic state.