Embedded Surrounding Wall for MEMS Cavity Release Etching

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Solution Overview

Problem

In the production of electronic devices with MEMS elements, the thin guard rings and side walls tend to collapse during release etching, leading to insufficient mechanical strength and a narrow time margin for the process, and the titanium layer etching complicates the removal of the interlayer insulating layer in unintended regions.

Innovation Solution

The electronic device design includes a surrounding wall embedded in the underlayer opening, with a titanium layer positioned away from the cavity to prevent etchant contact, and an asperity on the lower surface for enhanced mechanical strength and a longer etchant path during release etching, facilitating a larger process margin.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If a thin guard ring is used to form a cavity, then the device size is reduced, but the side wall collapses during release etching and mechanical strength becomes insufficient

Engineering Contradiction:

Improvedevice sizeVSAvoidmechanical strength

Core Design Contradiction:

Volume of moving objectVSStrength

Solution Approach 1:

The surrounding wall is embedded in the underlayer opening, creating a nested structure where the surrounding wall fits into the underlayer. This nesting provides mechanical support to the thin side walls during release etching, preventing collapse while maintaining the reduced device size.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Volume of moving object

If a thin guard ring is used to form a cavity, then the device size is reduced, but the time margin for release etching becomes narrow

Engineering Contradiction:

Improvedevice sizeVSAvoidtime margin for release etching

Core Design Contradiction:

Volume of moving objectVSLoss of time

Solution Approach 1:

The surrounding wall embedded in the underlayer opening creates a longer etchant path during release etching. The etchant must travel through the opening and around the embedded surrounding wall, which slows down the etching process and provides a larger time margin for controlled release etching.

Inventive Principle:

Principle #7Nested doll (Nesting)

3Reliability

If a titanium layer is formed on the side wall to improve junction, then the electrical connection is improved, but the titanium layer is etched during release etching causing interlayer insulating layer removal in unintended regions

Engineering Contradiction:

Improvejunction qualityVSAvoidetching precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The titanium layer is extracted from the side wall surface and repositioned on the lower surface of the surrounding wall. This extraction removes the harmful effect of titanium etching during release etching, as the titanium is now positioned away from the cavity region where etchant flows.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The titanium layer is moved from a vertical position on the side wall to a horizontal position on the lower surface. This dimensional change places the titanium in a location that is not exposed to the etchant flow during release etching, preventing unwanted etching of the interlayer insulating layer.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS9190954B2Electronic device, method for producing the same, and oscillator

Publication Date: 2015.11.17 SEIKO EPSON CORP

AI summary

An electronic device according to an aspect of the invention include: a substrate; an underlayer having an opening and being formed on the substrate; a functional element provided on the underlayer; and a surrounding wall forming a cavity that accommodates the functional element, at least a part of the surrounding wall being disposed in the opening.