Wheatstone Bridge IC Identification Using Insulated Resistors
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Solution Overview
Problem
Existing methods for identifying integrated circuit chips based on physical parameters are unstable over time and sensitive to temperature changes, and require additional manufacturing steps or modifications.
Innovation Solution
The use of identical diffused resistors connected as Wheatstone bridges, surrounded by an insulating region and covered only with insulator up to the second interconnect level, which generates a unique identifier through imbalance values that are temperature-stable and resistant to technological dispersions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electric parameters are measured for chip identification, then a unique identifier can be obtained, but the identifier varies over time and is sensitive to temperature changes
Solution Approach 1:
The patent changes the physical parameter being measured from electrical parameters (voltage, current) to optical parameters (reflectivity, absorption). Optical parameters are used because they remain stable over time and are not sensitive to temperature variations, unlike electrical parameters which drift. This parameter substitution resolves the contradiction by maintaining measurement precision for identification while achieving reliability through temporal and thermal stability.
2Adaptability or versatility
If additional identification elements are added to provide unique identifiers, then chip identification capability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent makes the existing interconnect levels and insulating layers serve a dual function: their primary function for circuit connectivity is maintained, and they simultaneously function as the identification element. The reflectivity or absorption characteristics of these existing layers provide the unique identifier without requiring any additional manufacturing steps. This universality principle resolves the contradiction by achieving identification capability using already-present structures, thereby avoiding increased manufacturing complexity.
3Ease of manufacture
If electrical parameters are used for identification, then identification can be implemented, but the features are sensitive to parasitic dispersions and temperature
Solution Approach 1:
The patent substitutes electrical measurement systems with optical measurement systems. Instead of measuring electrical parameters like resistance or voltage that are affected by temperature and parasitic effects, the invention uses optical properties (reflectivity, absorption) of the interconnect levels and insulating layers. Optical measurements are inherently less sensitive to temperature variations and parasitic electrical dispersions, thus resolving the contradiction by replacing the measurement domain while maintaining ease of implementation.
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 provides a stable and unique identification for integrated circuit chips without requiring additional manufacturing steps, with the identifier being resistant to temperature variations and maintaining good technological dispersion over time.
Implementation Method 1
element for identifying an integrated circuit chip, comprising identical diffused resistors (220, 221, 222, 223) connected as a Wheatstone bridge (20)
Implementation Method 2
the value differences forming the identifier of a chip are by nature very small. They range within the margin of inaccuracy linked to the manufacturing
Implementation Method 3
the diffused resistors are surrounded with an insulating region... the integrated circuit is covered with a stack of interconnect levels and of insulating layers, the resistors being only covered with insulator
Data Source
AI summary
Wheatstone bridges, each formed of four identical resistors, are used as integrated circuit identification elements. An identification circuit including an assembly of Wheatstone bridges and comparators is formed in a substrate. Since the resistors forming the bridges are sensitive to technological dispersions, the output voltages of the bridges are not identical. Each comparator compares the outputs of two bridges and provides a bit of an identification number of the chip. Preferably, the resistors are covered with insulator only, at least up to a second interconnect level from the substrate.