An ink-jet printer includes one or more cartridges that contain a reservoir of ink. The reservoir is connected by a conduit to a printhead that is mounted to the body of the cartridge.
The printhead is controlled for ejecting minute droplets of ink from the printhead to a printing medium, such as paper, that is advanced through the printer. The ejection of the droplets is controlled so that the droplets form images on the paper.
In a typical printhead, the ink droplets are expelled through orifices that are formed in an orifice plate that covers most of the printhead. The orifice plate is usually electroformed with nickel and coated with a precious metal for corrosion resistance. Alternatively, the orifice plate is made from a laser-ablated polyimide material.
The orifice plate is bonded to an ink barrier layer of the printhead. This barrier layer is made from photosensitive material that is laminated onto the printhead substrate, exposed, developed, and cured in a configuration that defines ink chambers. The chambers have one or more channels that connect the chambers with the reservoir of ink. Each chamber is continuous with one of the orifices from which the ink droplets are expelled.
The ink droplets are expelled from each ink chamber by a heat transducer, such as a thin-film resistor. The resistor is carried on the printhead substrate, which is preferably a conventional silicon wafer upon which has been grown an insulation layer, such as silicon dioxide. The resistor is covered with suitable passivation and other layers, as is known in the art and is described, for example, in U.S. Pat. No. 4,719,477, hereby incorporated by reference.
To expel an ink droplet, the resistor is driven (heated) with a pulse of electrical current. The heat from the resistor is sufficient to form a vapor bubble in the surrounding ink chamber. The rapid expansion of the bubble instantaneously forces a droplet through the associated orifice. The chamber is refilled after each droplet ejection with ink that flows into the chamber through the channel(s) that connects with the ink reservoir.
In the past, the orifice plate and barrier layer were mechanically aligned and bonded together, usually in a high-temperature and high-pressure environment. Inasmuch as the orifice plate and barrier layers are made of different material, the need for precisely aligning these two components is complicated by the differences in their coefficients of thermal expansion. Also, this approach to constructing a printhead limits the minimum thickness of the bonded components to about 25 μm, which thus prevents the use of very small droplet volumes with the attendant high resolution and thermal efficiencies such use would permit.
Currently, the notion of an integrally formed orifice plate and barrier layer has been considered. For clarity, an integrated orifice plate and barrier layer will be hereafter referred to as a droplet plate, which is a unitary plate defining both the ink chambers and orifices (the orifices hereafter referred to as nozzles). It will be appreciated that such a plate eliminates the problems associated with the orifice plate and barrier layer construction just mentioned.
Manufacture of such a droplet plate may be carried out using photolithographic techniques, which techniques generally offer a high degree of design latitude. It is desirable, however, to arrive at a simple, reliable fabrication process that has very precise dimension control as well as one that results in materials that are robust and inert.