Vertical Reference Resistor for Stress-Independent Temperature Compensation
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Solution Overview
Problem
Existing stress sensing circuits in semiconductor devices face challenges in accurately determining mechanical stress components due to confusion between temperature and stress effects, often caused by reference resistors with different temperature coefficients and sensitivity to in-plane stresses.
Innovation Solution
The implementation of a vertical reference resistor with the same temperature coefficient as sensing resistors, featuring deep trenches orthogonal to the surface and a buried layer for symmetrical current flow, which reduces stress direction dependencies and ensures accurate stress component measurement by producing a voltage difference signal indicative of in-plane stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference resistor is used to compare resistance from sensing resistors, then stress components can be determined, but temperature and stress effects become confused due to different temperature coefficients
Solution Approach 1:
The reference resistor is designed with a specific three-dimensional structure (vertical orientation with lateral extensions) that gives it different local properties: it has the same temperature coefficient as sensing resistors but different stress sensitivity characteristics, allowing it to serve as an effective reference that compensates for temperature effects while enabling stress measurement
Solution Approach 2:
The reference resistor transitions from a conventional planar structure to a three-dimensional structure with vertical orientation and lateral extensions. This dimensional change allows the reference resistor to have the same temperature coefficient as sensing resistors while being less sensitive to in-plane stresses, thereby resolving the confusion between temperature and stress effects
2Device complexity
If a conventional reference resistor is used, then resistance comparison is simple, but the reference resistor is influenced by in-plane stresses masking the correct magnitude of stress components
Solution Approach 1:
The reference resistor is oriented vertically with respect to the substrate surface, transitioning from a two-dimensional planar structure to a three-dimensional structure. This vertical orientation reduces sensitivity to in-plane stresses while maintaining temperature coefficient matching, thereby improving stress measurement precision without excessive complexity
Solution Approach 2:
The reference resistor structure exhibits asymmetric orientation (vertical vs. lateral sensing resistors) which creates different stress sensitivity characteristics. The lateral extensions provide symmetry in the horizontal plane but the overall vertical structure breaks the symmetry with respect to stress direction, allowing the reference resistor to be less sensitive to in-plane stresses
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 enables precise determination of stress components by distinguishing between temperature-induced and stress-induced changes, allowing for appropriate adjustments in semiconductor devices, thereby improving the accuracy of stress compensation in integrated circuits.
Implementation Method 1
The layer is doped to promote current flow in the plane. The first and second trenches are doped to impede current flow in the vertical direction.
Implementation Method 2
Some circuit parameters like bandgap voltage and oscillator frequency respond differently to stress in the x direction than stress in the y direction. Determining the magnitude and direction of stress components allows proper compensation for mechanical stresses on the chip.
Data Source
AI summary
An integrated circuit comprises a semiconductor substrate having a surface. A lateral resistor is arranged in a first plane parallel to the surface of the substrate. A vertical reference resistor comprises a layer arranged in a second plane parallel to the surface of the substrate and deeper than the first plane. This layer is doped to promote current flow in the second plane. The vertical reference resistor further comprises a first trench and a second trench coupled between the layer and the surface of the substrate. The first and second trenches are arranged in a vertical direction orthogonal to the first and the second planes and are doped to impede current flow in the vertical direction. A cross-section of the first and second trenches is two-fold rotationally symmetric around the vertical direction, and the lateral resistor and the first and second trenches have the same temperature coefficient.