Capacitive Humidity Sensor Electrografting CMOS Integration
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Solution Overview
Problem
Existing methods for integrating capacitive humidity sensors into CMOS structures face challenges such as difficulty in integration with testing electronics and require significant processing modifications, including the need for complex electrode configurations and sensitive material placement between metal layers.
Innovation Solution
A post-CMOS approach using electrografting to attach a moisture-sensitive polymer layer to a metal substrate, forming a capacitive humidity sensor with a low-temperature process, and integrating it with MEMS-CMOS substrates through wafer bonding, allowing for enhanced functionality and simplified fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sandwich structure with two electrode surfaces or interdigitated structure with comb electrodes is used, then the capacitive humidity sensing function is achieved, but the integration with CMOS structures becomes difficult and requires significant processing modifications
Solution Approach 1:
The patent extracts the sensitive polymer layer from between two metal electrodes and places it on only one metal electrode surface. This eliminates the need for complex processing to deposit and pattern metal layers above and below the polymer, while maintaining the capacitive sensing function. The polymer is applied directly to the CMOS-compatible metal electrode using electrostatic deposition, simplifying the manufacturing process.
Solution Approach 2:
Instead of placing the polymer between two metal layers (traditional approach), the patent inverts the structure by placing the polymer on one metal layer only, with the CMOS substrate serving as the reference electrode. This inversion simplifies the fabrication process while achieving the same sensing functionality.
2Ease of manufacture
If interdigitated metal electrodes are coated with chemical-sensitive polymer, then integration is simplified, but a large parallel capacitance is created through the substrate under the electrodes
Solution Approach 1:
The patent removes the problematic parallel capacitance path by using a single metal electrode structure instead of interdigitated electrodes that extend over the substrate. The polymer-coated metal electrode is positioned such that the substrate beneath does not create a significant parallel capacitance, thereby improving measurement precision while maintaining ease of integration.
3Reliability
If the dielectric of CMOS is selectively etched to expose core metal layer, then integrated chemical capacitance sensor is produced, but the CMOS process flow requires modification
Solution Approach 1:
The patent eliminates the need for selective dielectric etching and core metal layer exposure by applying the polymer directly to the existing metal electrode layer in the CMOS structure. This approach maintains the standard CMOS process flow without requiring modifications to etch the dielectric or access core metal layers, thereby reducing device complexity while achieving reliable sensor integration.
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
The solution enables the integration of capacitive humidity sensors into CMOS structures with improved ease and minimal processing modifications, providing a stable and sensitive humidity sensing capability with a linear capacitance response over a wide range of relative humidity.
Implementation Method 1
the absorbed water vapor occupies free spaces between polymer molecules, and the dielectric permittivity of the polymer is linearly changed proportionally to the amount of absorbed water
Implementation Method 2
A post-CMOS approach using electrografting to attach a moisture-sensitive polymer layer to a metal substrate
Implementation Method 3
Capacitive type humidity sensors thus provide a measure of the humidity based on the amount of absorption or desorption of water molecules and the resultant variation of the dielectric constant of the sensing material, and thus changes in its capacitance
Data Source
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AI summary
A semiconductor device composed of a capacitive humidity sensor comprised of a moisture-sensitive polymer layer electrografted to an electrically conductive metal layer situated on an CMOS substrate or a combined MEMS and CMOS substrate, and exposed within an opening through a passivation layer, packages composed of the encapsulated device, and methods of forming the capacitive humidity sensor within the semiconductor device, are provided.