Differential BTI Transistor Pair Sensing for Chip Age Metering
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Solution Overview
Problem
Existing methods for determining the age of integrated circuits are inaccurate and lack a reliable metric, as they rely on bias temperature instability (BTI) which fluctuates and lacks an absolute starting value, making it difficult to assess the age of chips effectively.
Innovation Solution
The use of differential sensing on pairs of matching transistors, where one transistor is continuously stressed during operation and the other serves as a reference, to determine the threshold voltage difference, providing a controlled metric for age assessment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bias temperature instability is used to determine chip age, then age assessment can be performed, but the measurement is inaccurate due to fluctuations and lack of absolute starting value
Solution Approach 1:
The patent divides the single transistor into two separate transistors: a stressed transistor that operates continuously and a reference transistor that remains unused. This segmentation allows independent measurement of BTI degradation in the stressed transistor against a stable reference, eliminating the fluctuation problem and providing an absolute starting value for age determination.
Solution Approach 2:
The reference transistor serves as an intermediary that mediates the measurement process. By comparing the threshold voltage shift of the stressed transistor against the stable reference transistor, the system obtains a reliable differential measurement that compensates for process variations and provides accurate age assessment.
2Measurement precision
If a reference transistor is added to create a differential measurement system, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent combines the age determination function with the existing transistor structure by adding only one additional transistor and its associated switching circuitry. The metering circuit integrates the reference transistor and differential sensing into the existing chip architecture, achieving accurate measurement without significant complexity increase.
Solution Approach 2:
The reference transistor and its associated switching circuitry serve multiple functions: providing a stable reference for differential measurement, enabling absolute starting value determination, and compensating for process variations. This multi-functionality justifies the added components by delivering substantial measurement improvement.
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 allows for accurate determination of the age of integrated circuits by leveraging BTI degradation in a controlled manner, ensuring reliable age monitoring and preventing unwanted variations in the transistors.
Implementation Method 1
usage metering by bias temperature instability
Implementation Method 2
differential current sense circuit determines a threshold voltage (Vt) difference between the reference transistor and the stressed transistor
Data Source
AI summary
Techniques for usage metering by bias temperature instability with differential sensing on pairs of matching transistors are provided. In one aspect, a usage metering device includes: at least one metering circuit on a chip, the at least one metering circuit having a pair of matching transistors, and a differential current sense circuit connected to the pair of matching transistors, wherein the pair of matching transistors includes a reference transistor which is unused during regular operation of the chip, and a stressed transistor that is on continuously during the regular operation of the chip, and wherein the differential current sense circuit determines a Vt difference between the reference transistor and the stressed transistor. A method for usage metering and a method of forming a usage metering device are also provided.