Inkjet Printhead Low-Loss Contact for Thermal Actuators
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Solution Overview
Problem
Thermal inkjet printheads face issues with resistive losses and early failure due to high current density and hot spots in the electrical connections between thermal actuators and drive circuitry, particularly when the resistive heater film is deposited on non-planar topography, leading to oxidation and electro-migration, and the use of additional low resistivity layers to mitigate this increases energy requirements and complicates material selection.
Innovation Solution
The solution involves supporting the heater on a planar surface with metallic vias connecting the contacts to the underlying CMOS, minimizing current density and parasitic resistance, and using a laminate insulating layer to maintain efficient electrical connections without the need for additional coatings or complex etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the resistive heater film is deposited on non-planar topography to connect thermal actuators to drive circuitry, then electrical connection is established, but high current density and hot spots occur leading to oxidation and electro-migration
Solution Approach 1:
The electrical connection path is segmented into multiple layers: a lower conductive layer deposited on non-planar topography, an insulating layer, and an upper conductive layer with metallic vias. This segmentation distributes the electrical connection function across different structural levels, preventing current concentration in a single non-planar path.
Solution Approach 2:
The solution transitions from a two-dimensional planar connection to a three-dimensional stacked architecture. Conductive layers are separated by an insulating layer in the vertical dimension, with metallic vias providing vertical interconnection. This dimensional change allows electrical connections to bypass the harmful effects of non-planar topography by distributing current paths through multiple spatial levels.
2Reliability
If additional low resistivity layers are deposited to mitigate high current density, then current distribution improves, but energy requirements increase and material selection becomes complex
Solution Approach 1:
The insulating layer is applied selectively in the contact regions where current density needs to be managed, rather than uniformly across the entire heater structure. This localized application of the insulating layer provides current distribution benefits precisely where needed (at the electrical contacts) while leaving the active heating regions unaffected, thus avoiding additional energy requirements.
Solution Approach 2:
The insulating layer acts as an intermediary between the lower and upper conductive layers. It provides electrical isolation while allowing thermal and mechanical coupling, enabling the upper conductive layer to distribute current effectively without requiring additional low resistivity materials that would increase energy consumption.
3Reliability
If additional low resistivity layers are used to reduce current density, then electrical performance improves, but device complexity increases due to coating and etching requirements
Solution Approach 1:
The insulating layer serves multiple functions simultaneously: it provides electrical isolation between conductive layers, acts as a structural support for the upper conductive layer, and facilitates thermal management. This multi-functionality eliminates the need for separate specialized layers, reducing manufacturing complexity while maintaining electrical performance.
Solution Approach 2:
The solution merges the functions of electrical isolation and structural support into a single insulating layer, rather than requiring separate layers for each function. This consolidation reduces the number of deposition and etching steps needed, thereby reducing device complexity while achieving the desired electrical performance.
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 reduces resistive losses, prevents hot spots, and maintains energy efficiency by ensuring reliable electrical connections while avoiding the limitations of additional low resistivity layers, thus enhancing the operational lifespan and energy efficiency of the printhead.
Implementation Method 1
a heater on the insulating layer configured to vaporize some ink in the ink chamber such that a droplet of ink is ejected through the nozzle
Implementation Method 2
at least one metallic via in each of the contacts respectively, the metallic vias extending through the insulating layer to establish an electrical connection between the conductive layer and the contacts
Data Source
AI summary
An inkjet printhead that has a supporting substrate, a conductive layer deposited in a pattern on one side of the supporting substrate, an insulating layer deposited such that the conductive layer is between the insulating layer and the supporting substrate, an ink chamber supported on the supporting substrate such that the conductive layer is between the ink chambers and the supporting substrate, a nozzle in fluid communication with the ink chamber, a heater on the insulating layer configured to vaporize some ink in the ink chamber such that a droplet of ink is ejected through the nozzle, the heater having a resistive element extending between a pair of contacts and, at least one metallic via in each of the contacts respectively, the metallic vias extending through the insulating layer to establish and electrical connection between the conductive layer and the contacts. The insulating layer has a planar surface on which the heater is supported.