Piezoelectric Actuator Protection Layer Design

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Solution Overview

Problem

The existing fluid ejection devices face inefficiencies due to the passivation layer's high Young's modulus and low Poisson's ratio, which stiffen the membrane and limit deformation capabilities of the piezoelectric actuator, essential for fluid ejection processes.

Innovation Solution

A low-stress protection layer with a Young's modulus lower than the passivation layer, made of organic or hybrid inorganic-organic materials like silicone, is applied partially or fully over the piezoelectric actuator to protect against humidity without interfering with deformation, using techniques like spin-coating or printing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a passivation layer with high Young's modulus is used to protect the piezoelectric actuator from humidity, then the protection against humidity is improved, but the deformation capability of the piezoelectric actuator deteriorates

Engineering Contradiction:

Improveprotection against humidityVSAvoiddeformation capability

Core Design Contradiction:

Object-affected harmful factorsVSStrength

Solution Approach 1:

The protective coating is divided into multiple layers: a first protective coating layer with low elastic modulus applied directly to the piezoelectric actuator, and a second protective coating layer with high elastic modulus applied over the first layer. This segmentation allows the first layer to maintain deformation capability while the second layer provides enhanced humidity protection.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the protective coating structure have different mechanical properties tailored to their specific functions. The first protective coating layer has low elastic modulus specifically at the interface with the piezoelectric actuator to allow deformation, while the second protective coating layer has high elastic modulus for structural protection and humidity barrier.

Inventive Principle:

Principle #3Local quality

2Object-affected harmful factors

If a passivation layer with high Young's modulus is used to protect the piezoelectric actuator, then the protection against humidity is improved, but the electric power consumption increases

Engineering Contradiction:

Improveprotection against humidityVSAvoidelectric power consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The protective coating is segmented into layers with different mechanical properties, allowing the piezoelectric actuator to deform more efficiently with lower energy input while still maintaining comprehensive humidity protection through the multi-layer structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The elastic modulus parameter of the protective coating is optimized by using a low elastic modulus material for the first protective coating layer, reducing the energy required for membrane deformation and thus lowering electric power consumption while maintaining protection functionality.

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If a passivation layer with high Young's modulus is used, then the protection against humidity is improved, but the intrinsic stress impact during manufacturing increases

Engineering Contradiction:

Improveprotection against humidityVSAvoidintrinsic stress impact

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The protective coating is applied in multiple stages with different material properties. The first protective coating layer with low elastic modulus is applied first to establish a compliant base layer, then the second protective coating layer with high elastic modulus is applied afterward, distributing and reducing the overall intrinsic stress impact during the manufacturing process.

Inventive Principle:

Principle #1Segmentation

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 solution effectively protects the piezoelectric actuator from humidity while maintaining its deformation capabilities, optimizing electric power consumption and chemical resistance to inks, and reducing the impact of intrinsic stress during manufacturing.

Implementation Method 1

a piezoelectric actuator 3, coupled to the membrane 7

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

using techniques like spin-coating or printing

Methodology Applied

Scientific EffectSpin-coating: Spin Coating

Data Source

PatentUS10974508B2Fluid ejection device with piezoelectric actuator and manufacturing process thereof

Publication Date: 2021.04.13 STMICROELECTRONICS SRL

AI summary

A fluid ejection device, comprising: a chamber; a membrane, with a first side and a second side opposite to one another, where the first side faces the chamber; an actuator, of a piezoelectric type, which extends on the second side of the membrane and is operatively coupled to the membrane for causing, in use, a vibration of the membrane; a passivation layer, which extends only alongside, or partially on, the actuator; and a protection layer, which extends on the actuator at least in surface portions of the latter that are free from the passivation layer, and has a Young's modulus lower than the Young's modulus of the passivation layer.