Su-Ho Shin

T-jet: a novel thermal inkjet printhead with monolithically fabricated nozzle plate on SOI wafer

A novel thermal inkjet printhead with monolithically fabricated nickel nozzle plate on SOI wafer has been proposed for the first time. A chamber and a restrictor are implemented on the 40 /spl mu/m thick top-silicon layer, and a nozzle plate covering heater layers are monolithically fabricated on them. Unlike the general back-shooters, the inkjet printhead reported here is a kind of back-shooter, which has a chamber and a restrictor with arbitrary shape by utilizing the silicon dioxide etch-stop layers in the bottom and sidewalls of chamber. Moreover, nozzle plating mold process, followed by placing the chamber underneath the heater layer, is performed on a planar surface, resulting in more uniform and reliable control of nozzle size. The new design was applied for monochrome inkjet printhead, which has 56 nozzles in 2 columns with real 600NPI(nozzle per inch), and showed good performances such as a drop velocity of 12 m/s, a drop volume of 30 pl, and a maximum firing frequency of 12 kHz for single nozzle ejection. From nozzle by nozzle inspection, we observed the uniformity variation of less than 4% in drop speed as well as drop volume. The monolithic fabrication process resulted in a good uniformity and is expected to have superior manufacturing yield to the nozzle assembly process.

Firing frequency improvement of back shooting inkjet printhead by thermal management

This paper presents a firing frequency improvement of a backshooter type inkjet printhead, DomeJet, with an optimized thermal design. DomeJet is a thermally driven monolithic inkjet printhead that consists of dome-shaped ink chambers and omega-shaped heaters over the chambers. As the firing frequency increases, the residual heat accumulated in heater layer causes unstable droplet ejection. In a roofshooter architecture printhead, a silicon substrate with a layer of silicon dioxide between the substrate and the heater is an excellent thermal reservoir. Compared to a roofshooter, a backshooter type head has disadvantage in heat release since the heater is confined to a thin film which has low thermal conductivity. In this study, two models are proposed. Model I has an aluminum metal layer over the heater that forms heat passage to the substrate, and Model II has thick nickel nozzle plate in contact with the metal layer to enhance heat dissipation capability. The result gives a head being operated at a frequency of 40 kHz.

Lumped Modeling of Crosstalk Behavior of Thermal Inkjet Print Heads

This paper presents a lumped model to predict crosstalk characteristics of thermally driven inkjet print heads. The model is based on a heat conduction equation, an empirical pressure-temperature equation, and a nonlinear hydraulic flow-pressure equation. It has been simulated through the construction of a Kirchhoffian R-L-C network, and subsequently analyzed using SIMULINK and an electronic circuit simulation tool. Using the lumped R-C model, heating characteristics of the head are predicted to be in agreement with IR temperature measurements. The inter-channel crosstalk is simulated using the lumped R-L network. The values of viscous flow resistance, R and flow inertance, L of the inter-channels are adjusted to accord with the 3-D numerical simulation results of three adjacent jets. The crosstalk behaviors of a back shooter head as well as a top shooter head have been investigated. Predictions of the proposed lumped model of the meniscus oscillations are consistent with numerical simulations. Comparison of the lumped model with experimental results identifies that abnormal two-drop ejection phenomena are related to the increased meniscus oscillations because of the more severe crosstalk effects at higher printing speeds. Our model can be used as a design tool for a better design of thermal inkjet print heads to minimize crosstalk effects.Copyright

Effects of Meniscus Motion on Ejection Performance in Thermal Inkjet Print Heads by 3-D Numerical Simulation and 1-D Lumped Modeling

Undesired meniscus motion at the nozzle exti can cause detrimental effects on ejection performance of an inkjet print head, resulting in degradation of printing quality at high frequency operation. In this study, visulization of droplet ejection and meniscus motion was performed experimentally, and the results were compared with those of numerical simulations. Effects of design factors on themeniscus motion, such as material properties of ink and geometric dimensions of head structure, were investigated by three-dimensional (3-D) numerical simulations. The result demonstrated that the ejection performance and the following menicus motion might be affected significantly due to changes in the design factors. For simple and fast computation, one-dimensional (1-D) lumped model was constructed, and its results were meaningful for the intuitive understanding of ejection performance and meniscus oscillation. Also, effects of different meniscus conditions on the subsequent ejection were investigated by 3-D numerical computations. The results showed that a stabilizing time, e.g., 70μs, was needed for uniform reproducible ejection. The results of this study will be helpful for development of the inkjet print heads of higher performance.Copyright