BAW Filter Release Hole Layout for Compact Low-Parasitic Resonators

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Solution Overview

Problem

The challenge in fabricating bulk acoustic wave filters is to achieve a smaller size while maintaining the high frequency and light weight requirements, which is difficult due to the small thickness of bulk acoustic resonators and the need for multiple resonators in close proximity, leading to interference and increased chip size.

Innovation Solution

The design includes two adjacent bulk acoustic wave resonators with a boundary structure and a release hole in the piezoelectric layer, allowing for reduced chip area and cost by minimizing the need for additional release holes, with the resonators connected in series or parallel configurations to optimize electrode overlap and etching solution release.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If multiple bulk acoustic wave resonators are disposed adjacent to each other to reduce chip size, then the chip area is reduced, but parasitic capacitance increases and interference occurs between resonators

Engineering Contradiction:

Improvechip areaVSAvoidparasitic capacitance

Core Design Contradiction:

Area of stationary objectVSObject-generated harmful factors

Solution Approach 1:

The boundary structure is segmented with a disconnection region that divides the boundary into separate sections. This segmentation allows the boundary to provide electrical isolation between adjacent resonators while maintaining mechanical support, thereby reducing parasitic capacitance between closely spaced resonators

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The boundary structure acts as an intermediary element between adjacent resonators. By positioning the boundary structure between resonators and creating a disconnection region, it provides electrical isolation to minimize parasitic capacitance while still maintaining the compact chip layout

Inventive Principle:

Principle #24Intermediary (Mediator)

2Strength

If the boundary structure is continuous to provide structural support, then mechanical strength is maintained, but etching solution release becomes difficult

Engineering Contradiction:

Improvestructural supportVSAvoidetching solution release

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The boundary structure is divided into separate sections by the disconnection region, creating segments that are connected only at specific points. This segmentation allows etching solution to pass through the disconnection region while the boundary segments maintain structural support for the resonators

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A disconnection region is extracted from the continuous boundary structure, creating a gap that allows etching solution to release from between adjacent resonators. The boundary structure is taken out at this specific location to enable manufacturing while maintaining support elsewhere

Inventive Principle:

Principle #2Taking out (Extraction)

3Ease of manufacture

If release holes are added to enable etching solution release, then manufacturing is facilitated, but chip area and cost increase

Engineering Contradiction:

Improveetching solution releaseVSAvoidchip area

Core Design Contradiction:

Ease of manufactureVSArea of stationary object

Solution Approach 1:

The boundary structure's disconnection region is merged with the function of a release hole. The gap in the boundary structure serves dual purposes: providing structural segmentation for support and creating a pathway for etching solution release, eliminating the need for separate release holes

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The boundary structure with its disconnection region performs multiple functions: it provides mechanical support for the resonators, enables electrical isolation between adjacent resonators, and facilitates etching solution release. This multi-functionality eliminates the need for additional dedicated release holes

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 reduces parasitic capacitance, minimizes chip size, and lowers manufacturing costs by allowing for efficient etching solution release through strategically placed release holes, enhancing the performance and compactness of the filter.

Implementation Method 1

a first bulk acoustic wave resonator including, in an order from bottom to top, a first cavity, a first bottom electrode, a first segment of a piezoelectric layer, and a first top electrode

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11616489B2Bulk acoustic wave filter having release hole and fabricating method of the same

Publication Date: 2023.03.28 SHENZHEN NEWSONIC TECH CO LTD

AI summary

A bulk acoustic wave filter includes: a first bulk acoustic wave resonator including, in an order from bottom to top, a first cavity, a first bottom electrode, a first segment of a piezoelectric layer, and a first top electrode; a second bulk acoustic wave resonator disposed adjacent to the first bulk acoustic wave resonator, and including, in the order from bottom to top, a second cavity, a second bottom electrode, a second segment of the piezoelectric layer, and a second top electrode; a boundary structure surrounding the first cavity and the second cavity, the boundary structure including a boundary portion extending between and separating the first cavity and the second cavity, and the boundary portion being disconnected at a disconnection region; and a first release hole formed in the piezoelectric layer, and overlapping the disconnection region.