Thermal Inkjet Printhead Buffer Layer Mitigates Thermal Shock
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Solution Overview
Problem
Thermal inkjet printhead chip structures face a short lifespan due to thermal shock caused by transient high temperatures generated by the resistive layer, which can crack the substrate and dielectric layers, leading to reduced durability.
Innovation Solution
A thermal inkjet printhead chip structure is designed with a buffer layer between the dielectric and resistive layers to mitigate thermal shock, comprising a substrate, oxide layer, driver circuitry, dielectric layer, buffer layer, resistive layer, and conductive layer, where the buffer layer is made of materials like titanium nitride or tungsten nitride and the resistive layer of tantalum aluminide or Hafnium Boride, with a resistance coefficient significantly higher than the resistive layer, reducing power density and contact resistances to minimize temperature transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a resistive layer is formed directly on the substrate and dielectric layer, then the heating function is achieved, but thermal shock causes cracking and shortens lifespan
Solution Approach 1:
A buffer layer made of titanium nitride or tungsten nitride is introduced between the resistive layer and the dielectric layer. This intermediary layer absorbs and dissipates the thermal shock generated by the resistive layer during heating operations, preventing direct thermal stress transmission to the dielectric layer and substrate, thereby avoiding cracking and extending device lifespan.
Solution Approach 2:
The patent employs a composite structure consisting of multiple layers with different material properties: the buffer layer (titanium nitride or tungsten nitride) combined with the resistive layer (tantalum aluminide or Hafnium Boride). This composite structure leverages the high thermal stability and shock resistance of the buffer layer materials to protect the underlying dielectric layer while maintaining the heating functionality of the resistive layer.
2Reliability
If a metal barrier layer is used to improve electrical conductivity, then electrical performance is enhanced, but thermal conductivity increases thermal shock to the dielectric layer
Solution Approach 1:
The patent changes the material parameter selection for the buffer layer, choosing titanium nitride or tungsten nitride instead of conventional metal barrier layers. These materials provide sufficient electrical conductivity for device operation while having lower thermal conductivity compared to pure metals, thereby reducing thermal shock transmission to the dielectric layer while maintaining acceptable electrical performance.
3Ease of manufacture
If BPSG material is used between resistive and silicon dioxide layers, then manufacturing is simplified, but stress issues cause easy cracking at high temperature
Solution Approach 1:
The patent changes the material composition parameter of the buffer layer from BPSG (boron-phosphorus doped silicate glass) to titanium nitride or tungsten nitride. This material substitution eliminates the inherent stress issues associated with BPSG at high temperatures, providing a buffer layer that maintains structural integrity and crack resistance under thermal stress while still being compatible with standard manufacturing processes.
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 buffer layer effectively reduces thermal shock on the dielectric layer, extending the lifespan of the thermal inkjet printhead chip by buffering the transient high temperatures and reducing the risk of cracking, while also simplifying manufacturing processes and reducing costs.
Implementation Method 1
The heating area of the thermal inkjet printhead chip structure would instantly generate an extremely high temperature when the driver circuitry is in operation, which would result in the substrate and the insulating oxide layer underneath the heating area becoming cracked. Such a phenomenon is termed as thermal shock
Implementation Method 2
a resistive layer formed on the substrate and directly electrically connected to a source and a drain of the driver circuitry. The area of the resistive layer that is not covered by the conductive layer functions as a heating area
Data Source
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AI summary
A thermal inkjet printhead chip structure includes a substrate, an oxide layer formed on the substrate, at least one driver circuitry each including a source, a drain and a gate and formed on the substrate and further surrounded by the oxide layer, a dielectric layer, a buffer layer, a resistive layer and a conductive layer. The dielectric layer is formed on the driver circuitry and has openings formed therethrough to expose the source and drain. The buffer layer is formed on the dielectric layer, covering the source and drain and connected to the source and drain. The resistive layer is formed on the buffer layer and has at least one heating area. The resistive layer extends above the source and drain and is connected to the source and drain. The conductive layer is formed on the resistive layer and exposes the heating area. A manufacturing method also is provided.