TiW Electrode Stress Compensation in Piezoelectric Inkjet Print Heads
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Solution Overview
Problem
High-temperature annealing of lead zirconate titanate (PZT) films in ink jet print heads results in significant tensile stress, leading to inherent deflection of the actuator membrane and limited pressure generation ability.
Innovation Solution
A Titanium-Tungsten (TiW) upper electrode is used to counteract the tensile stress, providing compressive stress that compensates for the substrate and piezoelectric actuator stresses, resulting in a flat multilayer package and enhanced deflection efficiency, while reducing energy consumption and improving stability and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature annealing is applied to PZT films, then piezoelectric properties are improved, but tensile stress increases causing inherent deflection
Solution Approach 1:
The patent applies composite materials by combining PZT piezoelectric layer with a TiW (titanium-tungsten) stress compensation layer. This composite structure allows the TiW layer to counteract the tensile stress generated during PZT annealing, maintaining a flat actuator membrane while preserving piezoelectric properties. The TiW layer is specifically designed with compressive stress to balance the tensile stress in the PZT layer.
Solution Approach 2:
The patent changes the stress state parameter by introducing a TiW layer with controlled thickness and material properties. By adjusting the TiW layer thickness (typically 50-200 nm) and its inherent compressive stress, the overall stress balance of the multilayer structure is optimized to eliminate deflection while maintaining the piezoelectric functionality of the PZT layer.
2Force
If PZT film thickness is increased, then pressure generation ability improves, but inherent deflection increases
Solution Approach 1:
The patent uses composite materials where the TiW stress compensation layer is integrated with the PZT piezoelectric layer. This composite structure enables thicker PZT films to be used for enhanced pressure generation while the TiW layer compensates for the increased stress and deflection that would otherwise result from greater PZT thickness.
Solution Approach 2:
The TiW layer acts as a counterweight to the tensile stress generated by the PZT layer. By positioning the TiW layer adjacent to the PZT layer and controlling its thickness and stress state, it provides an opposing compressive force that balances the tensile stress, allowing thicker PZT films to be used without excessive deflection.
3Shape
If stress compensation layer is added, then deflection is reduced, but device complexity increases
Solution Approach 1:
The patent merges the stress compensation function with the electrode structure by integrating the TiW layer as part of the upper electrode assembly. This merging approach allows the TiW layer to serve dual purposes: providing stress compensation and functioning as an electrode, thereby reducing device complexity compared to adding a separate dedicated stress compensation layer.
Solution Approach 2:
The TiW layer is designed to perform multiple functions simultaneously: it serves as both a stress compensation layer to counteract tensile stress and as an upper electrode for applying electric fields to the PZT layer. This multi-functionality reduces the overall device complexity by eliminating the need for separate stress compensation and electrode structures.
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 TiW film ensures a flat non-actuated state, increases deflection efficiency, and maintains high printing quality over time by balancing stresses within the multilayer package, thereby improving the pressure generation ability of the ink jet print head.
Implementation Method 1
a piezoelectric actuator is arranged to be used in a deflection mode for deflecting an actuator membrane in order to pressurize ink in a pressure generation chamber
Implementation Method 2
When thin PZT films are deposited on a substrate, the final processing step for the PZT material is usually annealing at a high temperature of e.g. approximately 600° C. to 700° C. Because of the high temperature, the PZT film shrinks considerably. This results in tensile stress in the PZT film.
Data Source
AI summary
An ink jet print head, having a pressure generation chamber arranged for being in communication with a print head nozzle and an actuator membrane for delimiting the pressure generation chamber. The actuator membrane has a substrate and a piezoelectric actuator provided on the substrate, said piezoelectric actuator having a lower electrode, an upper electrode and at least one piezoelectric layer arranged between the lower electrode and the upper electrode; the substrate and the upper electrode are arranged on opposite sides of the piezoelectric layer, and the upper electrode has a Titanium-Tungsten film.