Micro Piezo Printhead Manufacturing Technology

PrecisionCore and a Convergence of Innovative Manufacturing Technology

Technology Clearing the Path

Inkjet printers create output by ejecting droplets of ink directly onto a sheet of paper or other media. Broadly speaking, there are two systems for ejecting ink, piezo and thermal. Piezo systems use piezoelectric elements ("piezo elements") that contract under an applied voltage to eject the ink. Thermal systems heat the ink to cause it to bubble out. Epson's PrecisionCore printheads are a piezo system.

Ejecting up to 50,000 perfectly controlled droplets of ink per second from each of the hundreds of independently controlled nozzles, these phenomenally precise and accurate printheads are core components in Epson's inkjet printers. Piezo systems are able to more precisely control the volume of ink ejected and the size of individual ink droplets than thermal systems, but piezo printheads are also structurally more complex and difficult to produce.

To maximize printhead quality and productivity, we invested 40 billion yen to build advanced, fully automated production lines in Japan. Outfitted with Epson's own industrial robots, these lines employ a combination of inkjet technology fine-tuned over two decades and MEMS* microfabrication techniques that allow us to process parts on a submicron level.

* Micro-electro-mechanical systems, or MEMS, is a technology for fabricating microstructures, microsensors, microactuators, and microelectronics on a single silicon substrate, glass substrate, or organic material. MEMS also refers to devices that are fabricated in this way.

Printheads That Cannot Be Replicated

It would be extremely difficult for another company to replicate Epson's PrecisionCore printheads.

That is because only Epson owns the following three innovative technologies that are essential for the manufacture and assembly of MicroTFP print chips, the heart of our PrecisionCore printheads.

  1. Thin-film piezo technology
  2. MEMS technology
  3. Ultra-precision assembly technology

MicroTFP Print Chip Manufacturing

MicroTFP print chips are manufactured at Epson's Suwa Minami Plant, in Nagano prefecture in Japan. Three silicon chips - a TFP actuator, an ink channel, and a nozzle plate - are bonded together. Ink that enters through the ink flow path of the ink channel is ejected from the nozzles by pump-like action of the TFP actuator. Epson's innovative thin-film piezo technology is used to produce the TFP actuators; its innovative MEMS technology is used to make the chip components.

1. Thin Film Piezo (TFP) technology

A TFP actuator is an extremely thin piezo element formed on a silicon substrate. The piezo element contracts when a voltage is applied to it. This movement provides the power to drive ink, which flows into the ink flow path, from the nozzle plate.

Thin film piezo technology is used to form piezo elements on a silicon wafer in uniform, one-micrometer-thick films. High-quality ceramic crystals that have consistent orientation are formed by sintering using Epson's own crystallization process.

These TFP actuators provide extremely precise control over droplet size and placement and astonishingly accurate prints. That is because their uniform crystal structure means that they maintain uniform displacement when they contract and because the extreme thinness of the piezo film allows for larger contractions and, thus, larger displacement.

Epson manufactures the material for the piezo elements themselves. We also independently developed the chemical reaction process used to synthesize the materials as well as the synthesizing equipment. Having access to the best piezoelectric materials to meet the performance requirements of the piezo elements is a huge advantage for Epson.

2. MEMS technology

High-accuracy, 3D submicron photolithography is a source of Epson's MEMS process strength. In ordinary semiconductor fabrication the dimensional accuracy required for planar processing is high, but the accuracy required for thicknesses is not all that high. Industrial equipment used in the photolithography step normally has several percent variation, but Epson is able to limit this variation anywhere from one-fifth to one-tenth.

This level of accuracy exceeds conventional systems and is among the best in the industry. And it is this that enables us to form extremely fine and intricate TFP actuators, ink channels, and nozzle plates. These are what provide the picoliter-level control over ejected ink volume and the extraordinary precision of dot placement on media.

The nozzles in thermal heads produced on photosensitive resin are only about several microns in length. In contrast, nozzles in MicroTFP print chips produced on silicon wafers may be more than 10 times that length, and this greater nozzle length translates into far more accurate ink droplet placement.

Ultra-Precision, Fully Automated Assembly Line

3. Ultra-precision assembly technology

PrecisionCore printheads are assembled on fully automated manufacturing lines at two Epson sites in Japan, Tohoku Epson and Akita Epson. The MicroTFP print chips are made by connecting them to a base film that carries driver ICs and then assembling them together with a component that has the ink flow path structures and a case. This is where the third innovative technology, ultra-precision assembly, comes into play.

Epson originally produced its own robots for use on automated watch assembly lines. Over the decades, this technology evolved into the ultra-precision robotic systems that made the automated printhead lines possible.

Epson's fully automated printhead assembly lines require only minimal operator intervention, allowing the company to minimize manufacturing costs.

In addition, people are a source of particles, so with few people in the manufacturing area, particulation is negligible. This, plus the fact that the chips are not shipped internationally over long distances and thus are not exposed to the risk of contamination, means that consistent quality can be maintained.

Maintaining Quality

The innovative technologies used for PrecisionCore printheads are also used in the inspection of MicroTFP print chips.

We created high-speed automated inspection systems for MicroTFP print chips by drawing on the ultra-precision robotics technology that went into our fully automated printhead assembly lines and on image processing technologies developed for LCDs and printers. These inspection systems allow us to reduce personnel needs on the chip manufacturing lines while sorting defectives and assuring quality.

PrecisionCore printheads are produced from start to finish in Japan, with both quality and productivity pushed to the limit. Underpinning this quality control is a production and quality control and technology analysis support system that was developed entirely in-house to control wafer processing for the chips. By coordinating this system with the printer production and quality control system, we are able to perform end-to-end quality and technology analyses and ensure traceablity from finished printer to printhead to chip (wafer).

Control over Production Allows Us to Exceed Customer Expectations

Everything from piezo element production to printhead assembly are performed by Epson on manufacturing lines that themselves are produced by Epson.

We will further evolve and extend these technologies to achieve PrecisionCore printheads that have even greater accuracy and higher density.