You may have seen the Business Week article in which Antonio Perez said that when he peered into a microscope in the Rochester, NY, Research & Development lab in 2003, he realized that Kodak "had it all here ... The Holy Grail of Inkjet Printing." Part of what Antonio was looking at during that visit was Kodak's internally developed MEMS printhead technology.

The capabilities of our KODAK EASYSHARE printers depend in large part on the innovative design of the printhead. In this posting, we will describe the technology behind the printhead with its 3,840 firing chambers, each comprising a heater, expansion chamber and nozzle. The challenge for the Kodak design team was to come up with a printhead that could deliver the ink very precisely onto the paper (or other media), handling photos and text with the same excellent quality. To further complicate our task, the printhead needed to be very durable and last through many ink tank changes while maintaining superb image quality. This would make replacement ink cartridges far less expensive, since they would not have to include the costly printhead (it could stay on the printer). Early work in Kodak Research on Micro-Electro-Mechanical Systems (MEMS) provided us with the foundations to design and build a unique thermal inkjet drop ejector. It provides very high quality photos and text, at good printing speeds.

Cross-Section of Inkjet Printhead

The printhead uses heat to control the formation and delivery of the ink droplet:

• When the heater is pulsed on, it heats the ink and causes a vapor bubble to expand. This pushes ink out of the nozzle, where surface tension pulls it into a droplet.
• After the heater is pulsed off, the bubble is vented to atmosphere and the chamber refills with ink.
• The chamber is now ready to be fired again.

Thermal profile of a firing chamber

In most thermal inkjet printers, the ink in the nozzle that is not ejected collapses back onto the heater with substantial force, wearing it out over time. In our design, the vapor bubble vents to the atmosphere, so there is essentially no mechanical wear on the heater. In addition, the material forming the heater does not change over time as much as most thin film heater materials. Because of this, the heater not only lasts though many ink tank changes, but in addition the characteristics of the drops are very stable over long lifetimes.

Most inkjet printheads have a separate nozzle plate attached to the integrated circuit silicon, forming a sandwich with fluid passages in between. These components need to be aligned with great precision, which is inherently difficult. Misalignment results in dot placement errors. By building nozzles directly into our printhead, we eliminated this problem and gained precision. Our nozzles are formed using only thin film semiconductor fabrication processes; a monolithic structure, which allows alignment tolerances that would be impossible for the traditional two-plate systems. We chose to make our nozzles out of glass, an inorganic material, because it can be shaped very precisely and uniformly. Since the layer is homogeneous, nothing wears down and print quality remains constant. Using this state of the art silicon fabrication technology, Kodak is able to place dots on paper with very high precision which, when combined with Kodak's nano-particle pigment ink and microporous media technologies, results in Kodak lab-quality photos.

Exploded view of printhead and ink tanks

Very fast printing speed

We chose a nozzle layout to provide high frequency firing, and warming pulses that would vary to maintain uniform drop size as the printhead heats up. In this way image quality remains consistent when printing in different room conditions or during long print jobs.

PRINTHEAD AND INK TANK ASSEMBLY

MEMS Fabrication Technology Thermal Inkjet Printhead. Our goals of unsurpassed photo quality, excellent quality black text, and very fast printing speed, as well as providing industry leading ease of use and cost per print, led us to a printhead architecture, featuring a 3840 nozzle printhead that is part of the printer, not part of the replaceable ink supply. We utilize a total of 6 inks, one for text black, four photo colors - cyan, magenta, yellow and photo black - and a clear protective ink. The text black is provided in a separate tank, and the 5 photo inks are provided in a single color tank. We also utilize two different nozzle sizes resulting in 2.7 pico-liter and 6.5 pico-liter drop sizes. Both tanks are mounted on the printhead at all times, so the KODAK EASYSHARE All-in-One Printer, with its two paper trays, can print photos, text or mixed graphics documents any time, without any swapping of tanks.

Working on this project was a great experience. An inkjet writing system is a complex integration of multiple technologies. Kodak has the unique situation of having expertise in all of these areas. This allowed us to integrate the subsystems and make tradeoffs between the technologies to optimize the product for the customer. This Rochester, NY-based team was hand selected and is comprised of experts in media development, pigment ink technology, ink jet physics, MEMS fabrication, image science, and printhead design. The team has incredible scientists and capabilities, allowing the technology to be developed in record time. It has been a personally rewarding experience to work with such a high-powered and cooperative team.

We hope that you enjoy using this technology as much as we enjoyed developing it!

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