Capacitive MEMS Pressure Transducer With Controlled Membrane Geometry
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing capacitive MEMS pressure transducers face challenges in controlling the area of the electrode formed by the membrane, leading to inaccuracies in pressure detection, and are susceptible to mechanical stresses due to humidity and thermal expansion differences.
Innovation Solution
The capacitive MEMS pressure transducer features a membrane with a controllable shape defined by an anchoring portion and a dielectric structure that reduces mechanical stresses, using polysilicon layers and a passivation layer to protect against humidity, and a buried cavity to decouple mechanical stress from the membrane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If chemical etch is used to form the cavity, then the cavity can be formed and membrane released, but the area of the electrode formed by the membrane is not very controllable
Solution Approach 1:
The membrane area is defined in advance by the anchoring portion geometry before the etching process. The sacrificial layer is patterned with the anchoring portion that pre-determines the final membrane dimensions, so the membrane area is controlled by the anchoring portion design rather than being dependent on etching parameters.
Solution Approach 2:
The sacrificial layer acts as an intermediary element that is removed to form the cavity while simultaneously defining the membrane boundaries through the anchoring portion. This intermediary structure enables both cavity formation and precise membrane area control in the same process step.
2Device complexity
If single wafer manufacturing is used, then manufacturing is simplified, but the membrane area control remains poor
Solution Approach 1:
The membrane area is predetermined by the anchoring portion geometry defined in the design stage, before manufacturing begins. This preliminary definition of dimensions through the anchoring portion structure allows precise area control to be achieved within the single-wafer process without requiring additional control steps.
Solution Approach 2:
The membrane area is controlled by changing the geometric parameters of the anchoring portion (such as its lateral dimensions and shape) rather than relying on etching parameters. This parameter change approach decouples area control from the etching process, enabling precise control within the simplified single-wafer manufacturing framework.
3Ease of manufacture
If membrane is exposed to humidity, then manufacturing is simplified, but the membrane is susceptible to mechanical stresses from thermal expansion differences
Solution Approach 1:
The sacrificial layer is extracted and removed to form the cavity, creating a suspended membrane structure that is released from the substrate. This extraction eliminates the mechanical constraint from the substrate, allowing the membrane to be less susceptible to thermal expansion stresses while maintaining manufacturing simplicity.
Solution Approach 2:
The membrane is formed from a uniform polysilicon layer with consistent material properties throughout. This material homogeneity ensures uniform thermal expansion characteristics, reducing internal stresses caused by thermal expansion differences while maintaining ease of manufacture through standard deposition 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
This design enhances the accuracy of pressure detection by controlling membrane dimensions and reduces mechanical stresses, improving sensitivity and reliability.
Implementation Method 1
at least one portion of the sacrificial region is selectively removed through the porous material layer, to form a cavity
Implementation Method 2
an electrode formed by a membrane, which delimits a cavity and deforms as a function of pressure
Implementation Method 3
pressure variations are transduced into capacitance variations, which may be detected electronically
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
MEMS pressure transducer (1) including: a semiconductor body (2); a lower dielectric region (4,6), arranged above the semiconductor body (2); a fixed electrode region (12) and a lower anchoring region (14), which are formed by conductive material, are arranged on the lower dielectric region (4,6) and are laterally separated from each other; a membrane (55) of conductive material, which is suspended above the fixed electrode region (12), so as to delimit a cavity (39) upwardly, the fixed electrode region (12) facing the cavity, the membrane (55) being deformable as a function of pressure and forming a variable capacitor together with the fixed electrode region (12); and an upper anchoring region (37") of conductive material, which laterally delimits the cavity (39) and is interposed, in direct contact, between the membrane (55) and the lower anchoring region (14).