Bubble-Shaped Glass Caps for Hermetic MEMS Packaging

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Solution Overview

Problem

Current packaging technologies for three-dimensional MEMS devices are costly and require sophisticated fabrication steps, making them unsuitable for standard wafer-level packaging due to the limited thickness of sacrificial layers and the need for deep cavities, which increases the complexity and expense of packaging.

Innovation Solution

A microglass-blowing process is used to fabricate 'bubble-shaped' glass structures on a wafer level, allowing for hermetic sealing of three-dimensional MEMS devices by bonding a glass cap wafer with metal traces to a handle wafer, followed by flip-chip bonding and vacuum sealing, enabling cost-effective and flexible packaging for various shapes and form factors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If standard wafer-level packaging is used for three-dimensional MEMS devices, then manufacturing cost is reduced, but the limited thickness of sacrificial layers and need for deep cavities makes the process infeasible

Engineering Contradiction:

Improvemanufacturing costVSAvoidfabrication process complexity

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The packaging process is divided into two distinct levels: wafer-level fabrication of the glass structure with integrated cavities, and device-level assembly of MEMS components. This segmentation allows the complex three-dimensional packaging to be achieved through simpler, standardized wafer-level processes followed by modular device assembly, reducing both cost and fabrication complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention transitions from traditional planar wafer-level packaging to three-dimensional packaging by forming cavities and structures within the glass wafer itself. The glass wafer is transformed from a flat substrate into a multi-level structure with internal cavities that can accommodate three-dimensional MEMS devices, enabling cost-effective packaging without requiring deep external cavities or thick sacrificial layers.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If customized hermetic packages are used for MEMS devices, then vacuum sealing and environmental protection are achieved, but manufacturing cost increases significantly

Engineering Contradiction:

Improvehermetic sealingVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The glass wafer structure serves multiple functions simultaneously: it provides the hermetic seal, contains the vacuum environment, houses the MEMS devices through integrated cavities, and enables wafer-level batch processing. This multi-functional design eliminates the need for separate custom packaging components for each MEMS device, achieving reliable hermetic sealing while maintaining cost-effectiveness through standardized wafer-level fabrication.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Volume of moving object

If deep cavities are created in handle wafers for three-dimensional MEMS devices, then device accommodation is improved, but fabrication complexity and expense increase

Engineering Contradiction:

Improvedevice cavity volumeVSAvoidcavity fabrication complexity

Core Design Contradiction:

Volume of moving objectVSDevice complexity

Solution Approach 1:

The cavities are formed within the glass wafer structure during the wafer fabrication process itself, before MEMS devices are assembled. This preliminary formation of three-dimensional cavities allows subsequent device assembly to proceed with simple placement operations rather than requiring complex post-fabrication cavity creation, reducing overall fabrication complexity while maintaining adequate cavity volume for three-dimensional devices.

Inventive Principle:

Principle #10Preliminary action

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 method provides a cost-effective and flexible hermetic packaging solution for three-dimensional MEMS devices, reducing the need for customized packages and complex fabrication steps, while maintaining a high vacuum seal and accommodating devices of varying shapes and sizes.

Implementation Method 1

heating the cap-handle wafer stack as to allow pressure buildup within the cavity causing plastic deformation of the cap wafer

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

bonding a glass cap wafer with metal traces to a handle wafer, followed by flip-chip bonding and vacuum sealing

Methodology Applied

Scientific EffectThermal bonding: Welding

Data Source

PatentUS10167190B2Low cost wafer level process for packaging MEMS three dimensional devices

Publication Date: 2019.01.01 RGT UNIV OF CALIFORNIA

AI summary

An apparatus and method for wafer-level hermetic packaging of MicroElectroMechanical Systems (MEMS) devices of different shapes and form factors is presented in this disclosure. The method is based on bonding a glass cap wafer with fabricated micro-glassblown “bubble-shaped” structures to the substrate glass/Si wafer. Metal traces fabricated on the substrate wafer serve to transfer signals from the sealed cavity of the bubble to the outside world. Furthermore, the method provides for chip-level packaging of MEMS three dimensional structures. The packaging method utilizes a micro glass-blowing process to create “bubbleshaped” glass lids. This new type of lids is used for vacuum packaging of three dimensional MEMS devices, using a standard commercially available type of package.