MEMS Goes Mainstream

HP has it; so do Kodak, Fujifilm Dimatix (formerly Spectra), Silverbrook and others. I'm referring to the next disruptive technology hitting inkjet head technology, the Holy Grail for manufacturers: single-pass inkjet for the masses.

While the concept and execution of single-pass inkjet printing is not new, the increasing advances in head design certainly are. There are many printers on the market that have multiple heads aligned in an array to cover the substrate width. This single-pass model uses full-size piezo heads, and has inherent issues of alignment and interlacing artifacts, not to mention the sheer number and cost of multiple heads aligned in a fixture plate.

Some years ago, many companies started to research ways of manufacturing inkjet heads using the same processes that currently are used for integrated-circuit production. This process is known as MEMS Fabrication Techniques. (See Figure 1.)

Micro-Electro Mechanical Systems (MEMS) is the technology of the very small, and merges at the nanoscale into “Nano-Electro Mechanical Systems” (NEMS) and nanotechnology. MEMS generally range in size from a micrometer (a millionth of a meter) to a millimeter (thousandth of a meter). The scale of MEMS is such that it permits larger and denser arrays of smaller ink orifices, increasing resolution and printing speed.

At these size scales, the standard constructs of classical physics do not always hold true. Some of the other benefits of silicon MEMS fabrication techniques feature sub-micron accuracy, robust material set and the ability for high-volume manufacturing. MEMS really shine in creating nozzles, holes, manifolds and channel structures in the inkjet head design.

MEMS inkjet heads can be fabricated using modified semiconductor fabrication technology, laser ablation, photolithography, molding and plating, wet etching and dry etching, electro-discharge machining (EDM) and other technologies capable of manufacturing very small devices.

A 10.79 cm (4.25 in.) HP Edgeline Technology print head is shown in Figure 2. It uses five silicon print head chips (called die), each with 2,112 nozzles placed in a staggered configuration. This arrangement is called a multi-die module. Each print head prints two colors of ink and has 10,560 nozzles — 5,280 per color.

FujiFilm Dimatix has been busy, as well. They have a different take on head construction. Look at the size difference for an equivalent nozzle configuration (Figure 3).

The definition in the internal structures is amazing. Fifty nanometers is about two millionths of an inch, and the columns are half that width (Figure 4).

The Kodak MEMS print head uses heat to control the formation and delivery of the ink droplet (Figure 5).

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 the atmosphere and the chamber refills with ink. The chamber is now ready to be fired again.

Silverbrook, an R&D facility from Australia, has an incredibly dense array of MEMS produced heads (Figure 6). These heads are for water-based ink, and called “Suspended-heater thermal bubble” nozzle. Other head types for solvent and UV-curable are under development.

Print heads have five pairs of rows and are 20 mm in length. 20 mm sections are joined by the insertion of a specially designed, wedge-shaped piece. A 20.3 cm (8 in.) wide print head has 70,400 nozzles. Yikes!

Silverbrook has demonstrated working, single-pass, A4 (60 ppm) and photo (4 × 6) printers operating at one print every two seconds.
Source: americanprinter