Selective IrOx Deposition on Flexible Substrates
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Solution Overview
Problem
Existing methods for depositing iridium oxide (IrOx) on substrates face limitations such as charge leakage, poor adhesion, aspect ratio limitations, and incompatibility with flexible substrates, which hinder the development of biocompatible neurostimulation electrodes.
Innovation Solution
The use of chemical bath deposition (CBD) methods to fabricate IrOx thin films on flexible substrates, allowing for control over film structure and properties like thickness, deposition rate, and crystallinity, without requiring a conductive substrate, high temperatures, or vacuum systems, thus overcoming previous deposition method limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If sputtering or thermal decomposition methods are used to deposit IrOx, then film adhesion and density are improved, but charge leakage occurs at the edge of the coating layer
Solution Approach 1:
The patent changes the deposition method from physical vapor deposition (sputtering) or thermal decomposition to electrochemical activation (AIROF). This parameter change in the deposition mechanism eliminates charge leakage at coating edges while maintaining good adhesion, as the electrochemical process creates a more uniform and defect-free film structure.
Solution Approach 2:
The patent replaces mechanical deposition methods (sputtering) with an electrochemical process (AIROF). This substitution eliminates the mechanical stress and edge effects inherent in sputtering that cause charge leakage, while achieving comparable or superior adhesion through electrochemical bonding.
2Reliability
If reactive sputtering or thermal decomposition is used, then IrOx film is formed, but target poisoning and negative thermal effects occur
Solution Approach 1:
The patent replaces reactive sputtering (a physical vapor deposition process) with electrochemical activation. This substitution eliminates target poisoning entirely, as the electrochemical process occurs in solution without requiring a solid metal target that can become contaminated by oxygen incorporation.
Solution Approach 2:
The patent introduces an electrochemical intermediary process that converts Ir metal to IrOx through controlled oxidation in electrolyte solution. This intermediary electrochemical step avoids the direct gas-phase reactions in sputtering that cause target poisoning, providing a cleaner and more reliable film formation process.
3Manufacturing precision
If conventional deposition techniques are used, then IrOx coating is achieved, but aspect ratio limitations are encountered
Solution Approach 1:
The patent makes the deposition process universal by using electrochemical activation that can coat complex geometries and high aspect ratio structures uniformly. The electrolyte solution penetrates deep into trenches and vias, enabling consistent IrOx film formation on surfaces with varying topography that conventional line-of-sight deposition methods cannot achieve.
Solution Approach 2:
The patent uses a liquid electrolyte medium (hydraulic approach) instead of gas-phase deposition. The liquid solution flows and penetrates into high aspect ratio features, delivering precursor species uniformly to all surfaces including deep trenches and vias, thereby overcoming the aspect ratio limitations of conventional vapor-phase deposition techniques.
4Reliability
If existing deposition methods are applied to flexible substrates, then IrOx film is deposited, but substrate damage occurs due to high temperature and acidity/alkalinity
Solution Approach 1:
The patent changes the deposition parameters to low temperature and neutral or mildly acidic pH conditions in the electrochemical process. This allows IrOx film formation on temperature-sensitive flexible substrates without causing thermal degradation or chemical damage, unlike high-temperature sputtering or thermal decomposition methods.
Solution Approach 2:
The patent applies the IrOx coating locally and selectively on flexible substrates through controlled electrochemical activation. The process can be confined to specific electrode regions, avoiding exposure of the entire flexible substrate to harsh chemical environments, thereby preventing substrate damage while achieving the desired film deposition.
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 enables the production of high-quality, biocompatible IrOx films on flexible substrates, enhancing charge storage capacity and biocompatibility, while reducing operational costs and overcoming aspect ratio limitations, making them suitable for neurostimulation electrodes.
Implementation Method 1
performing a chemical bath deposition of Iridium Oxide (IrOx) to coat the buried metallic layer at the electrode
Implementation Method 2
Iridium oxide has also been shown to be able to provide stimulation by electrochemical reduction and oxidation reactions at the electrode interface
Data Source
AI summary
A flexible thin film metal oxide electrode fabrication methods and devices are provided and illustrated with thin film polyimide electrode formation and IrOx chemical bath deposition. Growth factors of the deposited film such as film thickness, deposition rate and quality of crystallites can be controlled by varying the solution pH, temperature and component concentrations of the bath. The methods allow for selective deposition of IrOx on a flexible substrate (e.g. polyimide electrode) where the IrOx will only coat onto an exposed metal area but not the entire device surface. This feature enables the bath process to coat the IrOx onto every individual electrode in one batch, and to ensure electrical isolation between channels. The ability to perform selective deposition, pads for external connections will not have IrOx coverage that would otherwise interfere with a soldering/bumping process.