Integrated Circuit Thermal Sensor Using Suspended Metallization
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Solution Overview
Problem
Existing integrated circuits (ICs) with thermal conductivity sensors face challenges such as substrate area compromise and limited sensitivity due to the formation of polysilicon coils, which are not ideal for semiconductor device density and sensitivity.
Innovation Solution
An integrated circuit design incorporating a metallization stack with a cavity that suspends conductive portions, allowing for a thermal conductivity sensor without substrate area sacrifice, using suitable conductive materials and configurations like interdigitated heating and sensing elements for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polysilicon coils are formed in the substrate to create thermal conductivity sensors, then sensor functionality is achieved, but substrate area is compromised and device density is reduced
Solution Approach 1:
The patent transitions from planar coil structures to vertically suspended conductive elements within a cavity. This dimensional change allows the sensor to occupy three-dimensional space rather than consuming valuable two-dimensional substrate area, resolving the contradiction between achieving sensor functionality and preserving substrate real estate
Solution Approach 2:
The conductive elements are nested within a cavity structure that is formed in the substrate. This nesting approach allows the sensor components to be contained within the substrate volume rather than extending across the substrate surface, thereby maintaining substrate area while achieving sensor functionality
2Ease of manufacture
If both coils are formed of polysilicon with the same temperature coefficient of resistance, then manufacturing is simplified, but sensor sensitivity is limited
Solution Approach 1:
The patent employs different materials for the first and second conductive elements, where each material has a distinct temperature coefficient of resistance. This local differentiation of material properties enables the sensor to detect thermal conductivity changes with higher sensitivity, as the differential response between the two elements amplifies the measurement signal
Solution Approach 2:
The sensor structure utilizes composite materials with different thermal and electrical properties for the two conductive elements. This composite approach allows optimization of each element's characteristics for its specific function, improving overall sensor sensitivity while maintaining compatibility with standard semiconductor manufacturing processes
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
Enables the integration of thermal conductivity sensors in ICs without compromising substrate area, enhancing sensitivity and accuracy through flexible design and material choices, suitable for various applications including smart buildings and medical devices.
Implementation Method 1
The sensing coil essentially is operated by the determination of the resistance of the coil at a given current through the coil, which is temperature-dependent. The determination of the resistance and hence the temperature of the coil can be used to determine the heat transfer from the active coil to the passive coil, as R=R0(1+a(T+T0))
Implementation Method 2
The heat transfer from the active to the passive coil is measured, with the amount of heat transfer being governed by the thermal conductivity of the gas in between the two coils
Data Source
AI summary
Disclosed is an integrated circuit comprising a substrate (10) including semiconductor devices and a metallization stack (20) over said substrate for interconnecting said devices, the metallization stack comprising a cavity (36), and a thermal conductivity sensor comprising at least one conductive portion (16, 18) of said metallization stack suspended in said cavity. A method of manufacturing such an IC is also disclosed.