Liquid Ejecting Head Substrate ESD Protection via Intermediary Conductive Layer
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Solution Overview
Problem
Existing liquid ejecting head element substrates are prone to electro-static discharge (ESD) damage, particularly due to surface discharge occurring at positions away from the pad or grounded-gate MOS, leading to damage at the protective film between the anticavitation layer and the heating resistor, especially in long liquid ejecting heads with large distances between these components.
Innovation Solution
An element substrate configuration featuring a conductive layer disposed between the exterior side surface of the discharge port forming member and the element forming layer, which attracts and directs ESD current to the substrate, reducing the likelihood of damage by grounding the ESD current externally and utilizing a protective film with high electrical insulating properties to cover the heating resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the distance between the pad and the heating resistor is increased (as in long liquid ejecting heads), then the liquid ejecting head can accommodate longer recording media, but the ESD damage risk to the protective film increases
Solution Approach 1:
The invention introduces an intermediary conductive layer between the insulating discharge port forming member and the element forming layer. This conductive layer acts as a mediator to intercept and redirect ESD current, preventing it from reaching the protective film and heating resistor. The conductive layer is positioned at the exterior side surface of the discharge port forming member, creating an intermediate protection zone that resolves the contradiction between increased length and ESD damage resistance.
2Power
If the electrode thickness is increased to reduce resistance, then the electrical performance improves, but the insulating properties of the protective film are compromised and ESD damage risk increases
Solution Approach 1:
The conductive layer serves as an intermediary protection mechanism that allows the use of thicker electrodes for better electrical performance without compromising the protective film's insulation. By positioning the conductive layer between the exterior side surface and the element forming layer, it intercepts ESD current before it can reach the protective film, thus resolving the contradiction between power delivery and insulation reliability.
3Reliability
If a dummy MOS is connected in parallel with the heating resistor to prevent ESD damage, then the heating resistor is protected, but the ESD current may still damage the protective film between the dummy MOS and the heating resistor
Solution Approach 1:
The invention applies preliminary protection by placing the conductive layer at the exterior side surface of the discharge port forming member, which is the first point of contact for ESD current. This preliminary interception prevents ESD current from reaching both the dummy MOS and the protective film, thereby protecting the heating resistor while also preventing damage to the protective film that would occur with dummy MOS alone.
Solution Approach 2:
The conductive layer acts as an intermediary barrier between the external environment and the internal components (dummy MOS and heating resistor). It intercepts ESD current at the exterior side surface, preventing the current from reaching the protective film and the dummy MOS-heating resistor interface, thus resolving the issue of protective film damage while maintaining heating resistor protection.
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 significantly reduces ESD damage occurrences by effectively redirecting ESD current away from critical components, maintaining the insulating properties of the protective film, and preventing damage even when the insulating properties are compromised by increased electrode thickness or wiring layer resistance.
Implementation Method 1
the element substrate may have ESD damage... configured to prevent ESD damage to the element substrate... attracts and directs ESD current to the substrate
Implementation Method 2
utilizing a protective film with high electrical insulating properties to cover the heating resistor... maintaining the insulating properties of the protective film
Data Source
AI summary
An element substrate for a liquid ejecting head includes a substrate, an element forming layer on the substrate, and a discharge port forming member formed of an insulating member on the element forming layer. The element forming layer includes an energy generating element configured to provide energy to a liquid for ejection. The discharge port forming member includes a discharge port forming surface having discharge ports through which the liquid is ejected and an exterior side surface positioned between the discharge port forming surface and the element forming layer. The exterior side surface has a first edge facing the element forming layer. The element substrate further includes a conductive layer disposed between the first edge and the element forming layer and grounded.