MEMS Capacitive Button Structure for Waterproof Wearable Interfaces
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Solution Overview
Problem
Existing user interface elements in portable and wearable electronic devices, such as smartphones and smartwatches, face challenges in providing impermeability to moisture and liquids while being complex, prone to wear, and having high energy consumption and implementation difficulties.
Innovation Solution
A microelectromechanical button device with a deformable package and detection structure, integrated within the device's case, that uses capacitive variation to detect button presses, ensuring hermetic sealing and low energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hermetic gaskets and O-rings are used to ensure water tightness, then waterproof performance is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The button element is integrated directly into the housing structure, eliminating the need for separate hermetic gaskets and O-rings. The housing itself forms the hermetic barrier, merging the button mechanism with the waterproof enclosure to reduce component count and assembly complexity.
Solution Approach 2:
The housing serves multiple functions: it provides structural support, forms the hermetic seal against water penetration, and integrates the button element. This multi-functionality eliminates the need for dedicated sealing components while maintaining waterproof performance.
2Reliability
If traditional sealed buttons with flange portions and retainer elements are used, then waterproof performance is improved, but manufacturing complexity and assembly difficulty increase
Solution Approach 1:
The button element and housing are designed as integrated components where the button is directly formed within the housing structure. This eliminates the need for separate retainer elements and flange interlocking mechanisms, significantly simplifying assembly while maintaining the hermetic seal.
3Ease of operation
If inductive elements (coils) are used for button detection, then button press detection is enabled, but energy consumption increases
Solution Approach 1:
The inductive detection mechanism using coils is replaced with a capacitive detection system. The capacitive sensor detects button presses through changes in capacitance caused by the deformation of the button element, eliminating the need for continuous electrical power consumption associated with inductive coils.
4Volume of moving object
If reduced dimensions are used for portable devices, then device portability is improved, but implementation of physical buttons becomes more difficult
Solution Approach 1:
The button element is integrated directly into the housing structure as a monolithic or closely coupled component. This integration eliminates the need for separate mounting features and reduces the overall space required for the button mechanism, enabling implementation in compact portable devices.
Solution Approach 2:
The button element utilizes a flexible or deformable membrane structure that can be actuated with minimal space. This thin-film approach allows the button to function within reduced dimensions while maintaining tactile feedback and detection capability.
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 provides a waterproof user interface with reduced energy consumption, low manufacturing complexity, high detection accuracy, and cost-effectiveness, overcoming the limitations of traditional methods.
Implementation Method 1
uses capacitive variation to detect button presses
Implementation Method 2
package of a microelectromechanical button device, having a first main surface extending in a horizontal plane and being hermetically sealed
Data Source
Figure 1~3
Figure 4A~4B
Figure 5A~5C
AI summary
A microelectromechanical button device (5) is provided with a detection structure (14) having: a substrate (22) of semiconductor material with a front surface (22a) and a rear surface (22b); a buried electrode (28) arranged on the substrate; a mobile electrode (32), arranged in a structural layer (30) overlying the substrate and elastically suspended above the buried electrode at a separation distance so as to form a detection capacitor (Cd); and a cap (46) coupled over the structural layer and having a first main surface (46a) facing the structural layer and a second main surface (46b) that is designed to be mechanically coupled to a deformable portion (3) of a case (2) of an electronic apparatus (1) of a portable or wearable type. The cap has, on its first main surface, an actuation portion (48) arranged over the mobile electrode and configured to cause, in the presence of a pressure applied on the second main surface, a deflection of the mobile electrode and its approach to the buried electrode, with a consequent capacitive variation of the detection capacitor, which is indicative of an actuation of the microelectromechanical button device.