Wheatstone Bridge Temperature Sensor with Metal Line Stress Amplification
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Solution Overview
Problem
Existing temperature measurement devices for integrated circuit chips are not very precise due to inaccuracies in resistor manufacturing processes, leading to variations in resistance values between chips from the same or different semiconductor wafers.
Innovation Solution
A device using a Wheatstone bridge with resistors implanted in the substrate, where opposing resistors are covered with networks of metal lines parallel to different directions, amplifying stress variations and enhancing temperature sensitivity, while being producible using standard CMOS fabrication steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistor is formed in the substrate to measure temperature, then temperature measurement is enabled, but measurement precision deteriorates due to manufacturing inaccuracies causing resistance value variations
Solution Approach 1:
The single resistor measurement approach is segmented into a Wheatstone bridge configuration with four resistors. By dividing the measurement system into multiple components (R1, R2, R3, R4) arranged in a bridge circuit, the patent enables differential measurement that cancels out common manufacturing variations, thereby improving temperature measurement precision despite resistor manufacturing inaccuracies
Solution Approach 2:
The patent changes the measurement parameter from absolute resistance value to resistance ratio or bridge unbalance voltage. By measuring the relative difference between resistors in the Wheatstone bridge rather than absolute values, the system becomes insensitive to manufacturing variations in individual resistors, thus improving measurement precision
2Measurement precision
If metal lines are added to amplify stress variations, then temperature sensitivity improves, but device complexity increases
Solution Approach 1:
The patent utilizes thermal expansion by placing metal lines (which have higher thermal expansion coefficients than silicon) over the resistors. As temperature changes, the metal lines expand or contract, inducing stress in the underlying resistors that amplifies the piezoresistive effect. This natural physical phenomenon enhances temperature sensitivity without requiring complex active sensing mechanisms
Solution Approach 2:
The metal lines act as an intermediary element between the temperature field and the resistor. Instead of directly measuring temperature, the metal lines mediate by converting temperature changes into mechanical stress on the resistors, which then produces measurable electrical signals. This intermediary approach simplifies the overall sensing mechanism while improving sensitivity
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
Achieves precise temperature measurement by amplifying stress variations related to temperature changes, resulting in significant output voltage variations (5-25%) that accurately determine substrate temperature, independent of manufacturing inaccuracies and additional production steps.
Implementation Method 1
since silicon has piezoresistive properties, the value of a resistor formed in a silicon substrate depends on the mechanical stresses undergone by the substrate. The temperature variations causing stress variations in the substrate, it follows that the value of the resistance is linked to the temperature of the substrate.
Implementation Method 2
each of two first opposed resistances of the bridge is covered with a network of metal lines parallel to a first direction, the first direction being such that a variation of the stresses of the substrate along this direction causes a variation of the unbalance value of the bridge
Data Source
Figure 1~2B
Figure 3A~4
Figure 5
AI summary
The invention relates to a device for detecting temperature variations of the substrate of an integrated circuit chip, comprising, in the substrate, implanted resistors (41, 43, 45, 47) connected in a Wheatstone bridge, in which each of the first two opposite resistors (45, 47) of the bridge is covered with a network of metallic lines parallel to a first direction, the first direction being such that a variation of the stresses of the substrate along this direction causes a variation of the unbalance value (VOUT) of the bridge.