Acceleration Sensor Through Hole Gap for Cavity Pressure Control
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Solution Overview
Problem
Existing acceleration sensors face challenges in maintaining a reduced pressure state within their cavities, which affects their sensitivity and noise levels, especially when exposed to heat treatments and subsequent processes.
Innovation Solution
The design incorporates a through hole structure with a wide portion not filled with the first film, filled with a second film, and a gap that maintains a reduced pressure state by allowing air leakage, ensuring the cavity remains at a pressure lower than atmospheric pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cavity is hermetically sealed by joining a wafer with a concave portion in a reduced-pressure atmosphere, then the cavity is sealed, but the pressure in the cavity rises due to heat load during heat treatment process and subsequent processes
Solution Approach 1:
The patent introduces a pressure equalization hole that allows the cavity to communicate with the external atmosphere during heat treatment and subsequent processes. This preliminary structural design prevents pressure buildup by enabling pressure equalization before final sealing, resolving the contradiction between maintaining seal integrity and preventing pressure rise.
Solution Approach 2:
The patent creates a localized pressure management system by introducing a pressure equalization hole at a specific location in the cavity structure. This local modification allows pressure to be managed only in the cavity region without affecting the overall sealing structure, enabling selective pressure control where needed while maintaining sealing elsewhere.
2Measurement precision
If the cavity pressure is reduced to improve sensitivity and reduce mechanical noise, then the S/N ratio improves, but the pressure in the cavity rises during heat treatment and subsequent processes
Solution Approach 1:
The pressure equalization hole is designed to remain open during heat treatment and subsequent processes, allowing pressure to equalize with the external atmosphere. This preliminary pressure management prevents pressure-induced sensitivity degradation, enabling the cavity to be evacuated to the desired low pressure after manufacturing without suffering from pressure buildup during processing.
3Reliability
If the through hole is completely filled with insulating film to provide electrical isolation, then electrical insulation is improved, but the reduced pressure state in the cavity cannot be maintained
Solution Approach 1:
The patent applies different filling strategies to different regions of the through hole. The lower portion of the through hole is filled with insulating film to provide electrical isolation between the movable electrode and the substrate, while the upper portion remains open to serve as a pressure equalization channel. This localized differentiation of filling status resolves the contradiction between electrical insulation and pressure management.
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 configuration enhances the sensitivity and reduces mechanical noise of the acceleration sensor, improving its S/N ratio and maintaining a consistent reduced pressure state during manufacturing and operation.
Implementation Method 1
the wide portion has a gap not filled with the first film, and the gap is filled with a second film
Data Source
AI summary
Airtightness in a cavity of an inertial sensor (acceleration sensor) is increased to achieve high sensitivity. In the acceleration sensor having movable electrodes VE1, VE2 and fixed electrodes FE1, FE2, the fixed electrodes are formed by portions surrounded by a through hole TH1 provided in a cap layer CL, and the through hole is filled with an insulating film IF1 and polysilicon P and has a wide portion (WP). The wide portion has a gap SP that is not filled with the insulating film IF1 and the polysilicon P, and the gap SP is filled with the interlayer insulating film ID. With such a configuration, degassing can be exhausted through the gap (airway) SP in a pressure reducing step.