Oriented Ceramic Substrate for Composite Wafer Bonding

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Solution Overview

Problem

Single-crystal supporting substrates face challenges with high cost and susceptibility to cracking during processing, which affects the surface flatness and bonding strength in composite substrates used for surface acoustic wave elements and semiconductor applications.

Innovation Solution

A ceramic supporting substrate with an oriented crystal structure, achieving an orientation degree of 50% or more and a controlled aspect ratio of crystal grains, is used to enhance surface flatness and prevent cracking, similar to single-crystal substrates while maintaining high strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a single-crystal supporting substrate is used, then surface flatness is improved, but cost increases and susceptibility to cracking during processing worsens

Engineering Contradiction:

Improvesurface flatnessVSAvoidsusceptibility to cracking

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent uses a composite substrate structure where a functional layer (single-crystal piezoelectric material) is bonded to a supporting substrate (polycrystalline ceramic with oriented crystal grains). This composite structure allows the functional layer to provide the required surface flatness while the supporting substrate provides mechanical strength and crack resistance, resolving the contradiction between surface quality and structural reliability.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If a single-crystal supporting substrate is used, then surface flatness is improved, but processing difficulty increases due to cracking

Engineering Contradiction:

Improvesurface flatnessVSAvoidprocessing difficulty

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent divides the substrate system into two separate components: a functional layer that provides surface flatness and a supporting substrate that provides mechanical strength. This segmentation allows each component to be optimized independently - the functional layer can be processed to achieve high surface flatness while the supporting substrate can be manufactured with appropriate mechanical properties, avoiding the processing difficulties of single-crystal substrates.

Inventive Principle:

Principle #1Segmentation

3Manufacturing precision

If ceramic with high orientation degree is used, then surface flatness is improved, but crystal grain structure becomes more complex

Engineering Contradiction:

Improvesurface flatnessVSAvoidcrystal grain structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent applies local quality by orienting crystal grains in specific directions within the ceramic supporting substrate. The crystal grains are oriented to provide surface flatness in the bonding direction while maintaining random orientation in other directions. This localized orientation approach achieves the required surface quality without requiring complete crystallographic control throughout the entire material structure.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS10332958B2Supporting substrate for composite substrate and composite substrate

Publication Date: 2019.06.25 NGK INSULATORS LTD

AI summary

A supporting substrate for a composite substrate comprises a ceramic and has a polished surface for use in bonding. An orientation degree of the ceramic forming the supporting substrate at the polished surface is 50% or higher, and an aspect ratio of each crystal grain included in the supporting substrate is 5.0 or less.