MEMS Button Cap Structure for Waterproof Capacitive Input
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Solution Overview
Problem
Existing user interface elements for portable and wearable electronic devices, such as smartphones and smartwatches, face challenges in providing waterproof physical buttons that are complex to implement, prone to wear and damage, and have high energy consumption due to the use of inductive elements in limited spaces.
Innovation Solution
A microelectromechanical button device with a detection structure comprising a semiconductor substrate, a buried electrode, a mobile electrode suspended above the buried electrode, and a cap that deflects the mobile electrode upon pressure, causing capacitive variation indicative of actuation, which is intrinsically hermetic and reduces energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hermetic gaskets and O-rings are used to ensure waterproofing, then water tightness is improved, but device complexity increases
Solution Approach 1:
The patent merges the button structure with the waterproof sealing structure into a single integrated unit. The button element itself forms part of the hermetic seal through its flange portions that interlock with the retainer element, eliminating the need for separate gaskets and O-rings. This integration reduces the number of components and simplifies assembly while maintaining waterproof integrity.
Solution Approach 2:
The button cap serves multiple functions simultaneously: it provides the physical button interface for user input, structural support through its flange portions, and contributes to the hermetic seal formation. The retainer element also serves dual purposes by both retaining the button assembly and participating in the waterproof sealing mechanism through its complementary flanges.
2Ease of operation
If inductive elements are used for button detection, then button functionality is achieved, but energy consumption increases
Solution Approach 1:
The patent replaces inductive detection mechanisms with a direct mechanical-capturing approach. The button element's physical displacement when pressed is directly captured through its structural connection to the retainer element and housing, eliminating the need for energy-consuming inductive sensors. The mechanical action of button pressing is directly transduced into a detectable state change without requiring active electromagnetic fields.
3Reliability
If sealed coupling mechanisms are implemented, then waterproofing is improved, but manufacturing complexity increases
Solution Approach 1:
The button assembly is segmented into distinct modular components: the button cap with its flange portions, the retainer element with complementary flanges, and the button element. Each component can be manufactured separately using standard manufacturing processes, and then assembled through simple interlocking flange connections. This segmentation allows for easier manufacturing and quality control compared to creating complex integrated sealed structures in single manufacturing steps.
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, low-energy, and cost-effective user interface element with reduced complexity in manufacturing, offering high accuracy and speed in detection, overcoming the limitations of traditional solutions.
Implementation Method 1
a mobile electrode, arranged in a structural layer overlying the substrate and elastically suspended above the buried electrode at a separation distance so as to form a detection capacitor; and a cap coupled over the structural layer and having a first main surface facing the structural layer and a second main surface that is designed to be mechanically coupled to a deformable portion of a case of an electronic apparatus of a portable or wearable type. The cap has, on its first main surface, an actuation portion 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
Data Source
AI summary
A microelectromechanical button device is provided with a detection structure having: a substrate of semiconductor material with a front surface and a rear surface; a buried electrode arranged on the substrate; a mobile electrode, arranged in a structural layer overlying the substrate and elastically suspended above the buried electrode at a separation distance so as to form a detection capacitor; and a cap coupled over the structural layer and having a first main surface facing the structural layer and a second main surface that is designed to be mechanically coupled to a deformable portion of a case of an electronic apparatus of a portable or wearable type. The cap has, on its first main surface, an actuation portion 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.