Engineered Substrates for Free-Standing MEMS Microstructures

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Current surface micromachining processes for forming free-standing microstructures in MEMS devices face challenges such as residual strain and surface roughness due to the use of polycrystalline materials like polysilicon, which affect signal integrity and require additional processing steps and equipment.

Innovation Solution

The development of engineered substrates with a sacrificial intermediate layer of varying silicon- or germanium-based material composition, allowing for the growth of monocrystalline films with reduced residual strain and surface roughness, enabling the formation of free-standing microstructures without the need for extensive polishing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If surface micromachining processes use polycrystalline materials like polysilicon to form free-standing microstructures, then the microstructures can be formed through selective removal of sacrificial layers, but residual strain and surface roughness are introduced that affect signal integrity

Engineering Contradiction:

Improveease of manufactureVSAvoidsurface roughness

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent changes the material parameter from polycrystalline to monocrystalline silicon, fundamentally altering the crystal structure to eliminate grain boundaries and associated surface roughness while maintaining the manufacturability of the device

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a sacrificial intermediate layer of silicon-germanium that is intentionally designed to be removed after serving its temporary purpose of enabling monocrystalline film growth, allowing the formation of high-precision microstructures without permanent complex equipment

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Ease of manufacture

If surface micromachining processes use polycrystalline materials like polysilicon to form free-standing microstructures, then the microstructures can be formed through selective removal of sacrificial layers, but additional processing steps and equipment are required to address residual strain and surface roughness

Engineering Contradiction:

Improveease of manufactureVSAvoidprocessing steps

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The patent performs preliminary action by growing the monocrystalline silicon film on the sacrificial intermediate layer before final device assembly, pre-establishing the desired crystal structure to avoid subsequent complex processing steps for strain and roughness correction

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The sacrificial intermediate layer acts as an intermediary that enables monocrystalline film growth on a compatible substrate, then is removed to leave the desired free-standing microstructure without requiring additional processing equipment

Inventive Principle:

Principle #24Intermediary (Mediator)

3Manufacturing precision

If monocrystalline silicon film is grown over silicon-germanium sacrificial intermediate layer with varying composition, then residual strain and surface roughness are reduced, but the intermediate layer requires precise composition control and sequential sublayer growth

Engineering Contradiction:

Improvesurface roughnessVSAvoidcomposition control

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent segments the intermediate layer into multiple sublayers with progressively varying silicon-germanium compositions, allowing controlled strain management during monocrystalline film growth while maintaining overall compositional control

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by varying the silicon-germanium composition at different depths within the intermediate layer, with each sublayer having a specific composition optimized for its position to control strain and enable high-quality monocrystalline growth

Inventive Principle:

Principle #3Local quality

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 approach results in free-standing microstructures with reduced residual strain and surface roughness, enhancing the sensitivity and accuracy of MEMS devices by eliminating the need for additional processing steps and equipment, thus improving manufacturing efficiency and device performance.

Implementation Method 1

growing an intermediate layer of monocrystalline silicon- or germanium-based material over a silicon substrate

Methodology Applied

Scientific EffectEpitaxy: Epitaxy

Implementation Method 2

The silicon- or germanium-based material may have a lattice constant different from a lattice constant of the silicon substrate

Methodology Applied

Scientific EffectLattice constant matching:

Data Source

PatentUS20240190694A1Engineered substrates, free-standing semiconductor microstructures, and related systems and methods

Publication Date: 2024.06.13 LAWRENCE SEMICON RES LAB

AI summary

An engineered substrate comprises a base substrate, a monocrystalline sacrificial intermediate layer epitaxially grown over the base substrate, and a monocrystalline top layer epitaxially grown over the monocrystalline sacrificial intermediate layer. The engineered substrate may be used to form a free-standing microstructure comprising the engineered substrate by removing at least a portion of the intermediate layer from between the base substrate and the top layer.