Piezoelectric Liquid Jet Head Electrode Insulation
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Solution Overview
Problem
Piezoelectric elements in liquid jet heads are prone to breakdown due to humidity, and existing solutions like covering the piezoelectric layer with an upper electrode can lead to dielectric breakdown between electrodes.
Innovation Solution
A liquid jet head design featuring a flow passage forming substrate with piezoelectric elements and a joining substrate that includes a piezoelectric element preserver, where the lower electrode is narrower than the pressure generating chamber, and the upper electrode is continuously formed, with the adhesive insulating the exposed portions of the electrodes to prevent dielectric breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the piezoelectric layer is covered with an upper electrode to prevent breakdown due to humidity, then the piezoelectric element is protected from humidity, but dielectric breakdown occurs between the upper electrode and lower electrode
Solution Approach 1:
The patent introduces an adhesive layer as an intermediary substance between the upper electrode and lower electrode. This adhesive layer acts as a mediator that provides both mechanical bonding and electrical insulation, preventing direct contact between the electrodes while maintaining the protective coverage over the piezoelectric layer.
Solution Approach 2:
The patent employs a thin film adhesive layer that flexibly covers the electrode interfaces. This thin film structure provides continuous insulation without adding significant thickness or rigidity, effectively preventing dielectric breakdown while maintaining the compact structure of the piezoelectric element.
2Shape
If the lower electrode is made narrow to fit within the pressure generating chamber, then the piezoelectric element structure is optimized, but the electrode needs additional protection at exposed areas
Solution Approach 1:
The patent merges the protective function with the bonding function by using the adhesive layer for both purposes. The same adhesive that bonds the upper electrode to the substrate also protects the exposed areas of the lower electrode, eliminating the need for separate protective structures.
Solution Approach 2:
The adhesive layer serves multiple functions simultaneously: it provides mechanical bonding between electrodes, electrical insulation to prevent dielectric breakdown, and environmental protection for exposed electrode areas. This multi-functionality resolves the contradiction by addressing both structural optimization and protective requirements through a single element.
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 configuration enhances the durability of the liquid jet head by preventing dielectric breakdown and protecting the piezoelectric elements from humidity without the need for additional protective films, thereby improving the reliability and longevity of the device.
Implementation Method 1
piezoelectric elements which are formed on one surface of the flow passage forming substrate and each includes a lower electrode, a piezoelectric layer, and an upper electrode
Implementation Method 2
a joining substrate which is adhered onto the one surface of the flow passage forming substrate by an adhesive
Data Source
AI summary
An upper surface of a piezoelectric layer in an area opposed to a pressure generating chamber and a side surface of the piezoelectric layer in an arrangement direction of the piezoelectric elements are covered with an upper electrode. In addition, on one end in a longitudinal direction of the piezoelectric element, the piezoelectric layer extends up to an adhesive area of a flow passage forming substrate to which a circumferential portion of a piezoelectric element preserver of a joining substrate is adhered, and the lower electrode extends up to the outside of an end portion of the piezoelectric layer to form a terminal section in an end portion of the lower electrode.