CMOS-Integrated Piezoelectric Droplet Ejector With Low-Temperature Actuators
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Solution Overview
Problem
Existing piezoelectric inkjet printheads face challenges in integrating CMOS control circuits due to incompatibility with high-temperature processing required for PZT actuators, leading to degraded CMOS components and the inability to form PZT actuators with CMOS circuits on the same substrate.
Innovation Solution
Integrate a CMOS control circuit with a piezoelectric actuator using low-temperature processable materials like aluminium nitride or zinc oxide, which are deposited and annealed below 450°C, allowing for efficient droplet ejection without damaging the CMOS components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PZT piezoelectric actuators are used with high-temperature processing (>450°C), then piezoelectric performance is improved, but CMOS control circuits are damaged
Solution Approach 1:
The patent changes the temperature parameter from high-temperature processing (>450°C for PZT) to low-temperature processing (<450°C) to enable CMOS-compatible manufacturing. This parameter change allows the use of alternative piezoelectric materials that can be processed at lower temperatures without degrading CMOS circuits.
Solution Approach 2:
The patent replaces expensive, temperature-sensitive PZT materials with alternative piezoelectric materials that are compatible with low-temperature CMOS processing. While these alternatives may have different performance characteristics, they enable integration without requiring high-temperature processing that would damage CMOS circuits.
2Reliability
If PZT actuators are deposited by physical vapour deposition with annealing, then piezoelectric properties are enhanced, but processing temperature exceeds CMOS survival threshold
Solution Approach 1:
The patent changes the processing temperature parameter from >450°C to <450°C, enabling CMOS-compatible manufacturing. This requires using alternative piezoelectric materials that achieve adequate piezoelectric properties at lower temperatures through modified deposition and annealing processes.
Solution Approach 2:
The patent substitutes PZT with alternative piezoelectric materials that do not require high-temperature annealing (>450°C). These materials can be processed at lower temperatures compatible with CMOS survival, even though they may require different processing methodologies.
3Measurement precision
If high-density piezoelectric actuators are integrated with separate control circuits, then resolution is maximized, but number of electrical connections increases
Solution Approach 1:
The patent merges the control circuit and piezoelectric actuator onto a single substrate, eliminating the need for numerous external electrical connections. This integration is enabled by using low-temperature processable piezoelectric materials that are compatible with CMOS fabrication, allowing both components to be manufactured together on the same substrate.
Solution Approach 2:
The substrate serves multiple functions: it acts as both the mechanical support for the piezoelectric actuators and the platform for integrating CMOS control circuits. This multi-functional substrate reduces the need for separate components and interconnections while maintaining high-density actuator arrays for fine resolution.
4Reliability
If lead-containing PZT materials are used, then piezoelectric efficiency is high, but CMOS foundry manufacturing is prohibited
Solution Approach 1:
The patent replaces lead-containing PZT materials with lead-free alternative piezoelectric materials that are compatible with CMOS foundry manufacturing processes. While PZT offers superior piezoelectric efficiency, the alternative materials enable integration in standard CMOS facilities without requiring special handling for lead-containing materials.
Solution Approach 2:
The patent changes the material composition parameter by eliminating lead from the piezoelectric material. This substitution with lead-free alternatives maintains adequate piezoelectric efficiency while enabling manufacturing in standard CMOS foundries that prohibit lead-containing materials.
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 integration reduces the need for external connections, increases nozzle density, improves manufacturing yield, and enhances reliability while maintaining effective droplet ejection performance.
Implementation Method 1
a piezoelectric actuator element (which is deformable in use) formed by one or more said layers and comprising a piezoelectric body and first and second electrodes in contact with the piezoelectric body
Implementation Method 2
PZT may be deposited by physical vapour deposition but this requires subsequent annealing and/or poling steps at a temperature of greater than 450° C.
Implementation Method 3
PZT may be deposited by physical vapour deposition but this requires subsequent annealing and/or poling steps at a temperature of greater than 450° C.
Data Source
AI summary
A droplet ejector assembly for a printhead comprises a substrate, the substrate comprising a CMOS control circuit, a plurality of layers on the first surface of the substrate, a fluid chamber having a droplet ejection outlet, and a piezoelectric actuator element formed by one or more said layers and comprising first and second electrodes in contact with a piezoelectric body. The piezoelectric actuator element defines part of the fluid chamber. At least one said electrode electrically is connected to the CMOS control circuit. The droplet ejector comprises a fluid chamber having a droplet ejection outlet. The piezoelectric actuator element is separate to the droplet ejection outlet and the piezoelectric body is formed of one or more piezoelectric materials processable at a temperature below 450° C. Thus, a CMOS control circuit is integrated with a droplet ejector assembly. The CMOS control circuit may receive both an analogue actuator ejection pulse and serial digital controls signals and use the serial digital control signals to determine which piezoelectric actuator elements are connected to and driven by individual actuator ejection pulses.