Capacitive Pressure Sensor Diaphragm Step Design
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Solution Overview
Problem
Electrostatic capacitance type pressure sensors face zero-point shifts due to non-uniform film deposition on the diaphragm, leading to measurement errors, as the existing solutions assume uniform film formation which is not always feasible, especially in semiconductor manufacturing processes where Atomic Layer Deposition (ALD) is used, resulting in deviations in film thickness and stress distribution.
Innovation Solution
The pressure introducing holes are positioned near the step part of the diaphragm to intentionally form a thick film with deposits, alleviating the bending moment caused by film stress, thus suppressing zero-point shifts regardless of film uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a filter is used to prevent deposition components from entering the vacuum gauge, then adhesion and accumulation of deposition on the diaphragm is reduced, but it is impossible to completely eliminate deposition components
Solution Approach 1:
The diaphragm is designed with non-uniform thickness, creating different local properties: the central portion has thinner thickness and lower rigidity, while the peripheral edge portion has greater thickness and higher rigidity. This local quality differentiation allows the peripheral region to resist deposition-induced stress while the central region maintains sensing functionality.
Solution Approach 2:
The diaphragm is segmented into functionally distinct regions by the step part: a first region (central portion) with thinner thickness for pressure sensing and a second region (peripheral edge) with greater thickness for structural support and stress resistance. This segmentation allows each region to perform its specific function optimally.
2Ease of manufacture
If the diaphragm thickness is made uniform, then manufacturing is simpler, but deposition causes bending and zero-point shift
Solution Approach 1:
Instead of uniform thickness, the diaphragm employs local quality variation with a step part creating two distinct thickness zones. The peripheral edge portion has greater thickness to counteract deposition stress, while the central portion remains thinner for pressure sensitivity, resolving the contradiction between manufacturing simplicity and measurement precision.
Solution Approach 2:
The diaphragm transitions from symmetric uniform thickness to asymmetric non-uniform thickness with the step part. This asymmetric design places the step part at a specific position to create the thickness differential, allowing the structure to asymmetrically distribute stress and maintain zero-point stability despite deposition.
3Measurement precision
If the central portion thickness is reduced to lower rigidity, then deposition-induced bending is suppressed, but structural strength may be compromised
Solution Approach 1:
The diaphragm implements local quality optimization by reducing thickness only in the central sensing portion while maintaining greater thickness at the peripheral edge. This creates a rigidity gradient where the central region is compliant enough to respond to pressure while the peripheral region provides structural strength and resists deposition-induced bending.
Solution Approach 2:
The thicker peripheral edge portion acts as a counterweight to the thinner central portion. The increased rigidity and mass at the periphery counterbalance the reduced rigidity at the center, providing overall structural stability and preventing excessive bending while allowing the central region to remain sensitive to pressure changes.
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 effectively reduces zero-point shifts by controlling the film stress distribution, maintaining measurement accuracy even with non-uniform film deposition, and is applicable to both uniform and non-uniform film systems.
Implementation Method 1
an electrostatic capacitance type pressure sensor provided with a pressure sensor chip having a diaphragm structure for detecting an electrostatic capacitance in accordance with the pressure of a medium to be measured
Implementation Method 2
the deposition adhered on the diaphragm generates an internal stress such as a compressive stress or tensile stress in response to the components of the deposition
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An electrostatic capacitance type pressure sensor comprises a diaphragm (21) having a step part (21 c) between a peripheral edge part and a center part on the side of the pressure introduction chamber (27). The diaphragm (21) is divided into a region on the center part side and a region on the peripheral edge side at the step part (21c) as a boundary. A thickness of the region on the center part side is formed thinner than that of the region on the peripheral edge side. The cover plate (1) has a plurality of pressure introducing holes (10) adapted to introduce the medium to be measured into the pressure introduction chamber (27) from a direction crossing the surface of the diaphragm (21). Openings (10a) of the plurality of pressure introducing holes (10) facing the pressure introduction chamber (27) are positioned in the vicinity of the step part (21c) of the diaphragm (21) in the direction parallel to the surface of the diaphragm (21).