Inorganic Planarization Layer for Micro-Fluid Ejection Heads

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Solution Overview

Problem

Conventional micro-fluid ejection head substrates face challenges with planarization and corrosion protection due to the sensitivity of organic planarization layers to processes like grit blasting, deep reactive ion etching, and solvent washing, leading to residue issues and manufacturing difficulties.

Innovation Solution

A substantially inorganic planarization layer composed of alternating dielectric compounds and spin-on-glass (SOG) layers, with a hard mask material, is deposited over the micro-fluid ejection head substrate to provide improved planarization and resistance to aggressive treatments, allowing for cleaner contact areas and reduced cracking.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an organic planarization layer (epoxy photoresist material) is applied to provide planarization and passivation functions, then the device surface is planarized and protected from corrosion, but the organic material is sensitive to aggressive processes (grit blasting, DRIE, solvent washing) used to remove photoresist mask material, resulting in residue remaining on critical areas

Engineering Contradiction:

Improvecorrosion protectionVSAvoidphotoresist mask material residue

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The planarization layer material composition is changed from organic (epoxy photoresist) to inorganic (spin-on-glass and dielectric compounds). This parameter change makes the material resistant to aggressive removal processes while maintaining planarization and passivation functions, thereby eliminating residue issues on bond pads and other critical areas.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The planarization layer is constructed as a composite structure with multiple inorganic sub-layers including spin-on-glass and dielectric compounds. This composite inorganic structure provides both corrosion protection and resistance to aggressive processing, solving the contradiction between reliability and harmful residue generation.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If a thick planarization layer is applied to ensure adequate planarization, then the device surface is sufficiently planarized for lamination, but the layer tends to crack during subsequent handling and ejection head processing

Engineering Contradiction:

Improvesubstrate planarizationVSAvoidcrack resistance

Core Design Contradiction:

Manufacturing precisionVSStrength

Solution Approach 1:

The planarization layer is segmented into multiple thin inorganic sub-layers (spin-on-glass and dielectric compounds) rather than a single thick organic layer. This segmentation maintains adequate planarization capability while reducing the tendency to crack during handling and processing.

Inventive Principle:

Principle #1Segmentation

3Ease of manufacture

If photoresist mask material is removed using aggressive processes (grit blasting, DRIE, solvent washing) to ensure complete removal, then photoresist is thoroughly removed, but the organic planarization layer is damaged and residue remains on bond pads where good electrical connection is essential

Engineering Contradiction:

Improvephotoresist mask material removalVSAvoidelectrical connection quality

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

Changing the planarization layer from organic to inorganic material allows aggressive photoresist removal processes to be used without damaging the planarization layer. The inorganic material is resistant to grit blasting, DRIE, and solvent washing, enabling complete photoresist removal while preserving the planarization layer and ensuring good electrical connections on bond pads.

Inventive Principle:

Principle #35Parameter changes

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

The inorganic planarization layer ensures uniformity and robustness, enabling more effective removal of photoresist mask materials and minimizing residue on critical areas, thus enhancing the manufacturing process and product reliability.

Implementation Method 1

at least one spin on glass (SOG) layer

Methodology Applied

Scientific EffectSpin coating: Spin Coating

Implementation Method 2

A first sub-layer derived from a dielectric compound is deposited over a device surface

Methodology Applied

Scientific EffectPhysical vapor deposition: Physical Vapour Deposition

Data Source

PatentUS7905569B2Planarization layer for micro-fluid ejection head substrates

Publication Date: 2011.03.15 BRADY WORLDWIDE INC

AI summary

A substantially inorganic planarization layer for a micro-fluid ejection head substrate and method therefor. The planarization layer includes a plurality of layers composed of one or more dielectric compounds and at least one spin on glass (SOG) layer having a total thickness ranging from about 1 microns to about 15 microns deposited over a second metal layer of the micro-fluid ejection head substrate. A top most layer of the planarization layer is selected from one or more of the dielectric compounds and a hard mask material.