Coating processes – Direct application of electrical – magnetic – wave – or... – Chemical vapor deposition
Patent
1996-03-14
1998-03-24
Pianalto, Bernard
Coating processes
Direct application of electrical, magnetic, wave, or...
Chemical vapor deposition
2041921, 427 58, 427237, 427249, 4272553, 427294, 4274192, 427586, 427595, C23C 800
Patent
active
057310483
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to improvements in or relating to ceramic piezoelectric ink jet print heads of the kind having an ink channel for connection to an ink ejection nozzle and to a reservoir for the ink, and a piezoelectric wall actuator which forms part of the channel and is displaceable in response to a voltage pulse thereby generating a pulse in liquid ink in the channel due to a change of pressure therein which causes ejection of a liquid droplet from the channel. Such print heads are referred to hereafter as piezoelectric ceramic ink jet print heads.
BRIEF DESCRIPTION OF THE DRAWINGS
Examples of print heads as described, for example, in EP-A-277703, EP-A-278590 and EP-A-364136 are shown in FIGS. 1, 2, 3 and 4.
FIGS. 1 and 2 are different sectional views of the same ink jet printhead, and
FIG. 3 is a view similar to that of FIG. 1 showing another form of printhead.
FIG. 4 is a greatly enlarged view of an ink channel defined by walls in such a print head.
BACKGROUND OF THE INVENTION
One form of ink jet printhead 10 comprises a multiplicity of parallel ink channels 12 forming an array in which the channels are mutually spaced in an array direction perpendicular to the length of the channels. The channels are formed at a density of two or more channels per mm. in a sheet 14 of piezoelectric material, suitably PZT, poled in the direction of arrows 15 and are defined each by side walls 16 and a bottom surface 18, the thickness of the PZT being greater than the channel depth. The side walls 16 are generally at an angle of no more than 10.degree. from the normal to the bottom wall. The channels 12 are open topped and in the printhead are closed by a top sheet 20 of insulating material which is thermally matched to the sheet 14 and is disposed parallel to the surfaces 18 and bonded by a bonding layer 21 to the tops 22 of the walls 16. The channels 12 on their side wall surfaces are lined with a metallised electrode layer 34. It will be apparent therefore that when a potential difference of similar magnitude but opposite sign is applied to the electrodes on opposite faces of each of two adjacent walls 16, the walls will be subject to electric fields in opposite senses normal to the poling direction 15. The walls are in consequence deflected in shear mode.
Referring now to FIG. 2, the channels 12 therein are provided on facing walls 16 thereof with metallised electrodes 34 which extend from the edges of the tops 16 of the walls down the walls to a location well short of the bottom surface 18 of the channels. There is an optimum metallisation depth which gives maximum wall displacement at about the mid-height of the walls depending on the distribution of wall rigidity. In this form the walls are of the so-called cantilever type.
In FIG. 2, it will be seen that the channels 12 comprise a forward part 36 of uniform depth which is closed at its forward end by a nozzle plate 38 having formed therein a nozzle 40 from which droplets of ink in the channel are expelled by activation of the facing actuator walls 16 of the channel. The channel 12 rearwardly of the forward part 36 also has a part 42 of lesser depth extending from the tops 22 of the walls 16 than the forward part 36. The metallised plating 34 which is on opposed surfaces of the walls 16 occupies a depth approximately one half that of the channel side walls but greater than the depth of the channel part 42 so that when plating takes place the side walls 16 and bottom surface 18 of the channel part 42 are fully covered whilst the side walls in the forward part 36 of the channel are covered to approximately one half the channel depth in that part. One suitable electrode metal used is an alloy of nickel and chromium, i.e. nichrome. Alternatively, aluminium provides a high conductivity electrode and the metal track in the part 42 is suitable for applying a wire bond connection. Aluminium in particular requires to be coated with a layer of passivation to inhibit electrolysis and bubble formation or corrosion which could occur if the
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Eldridge, et al., "Passivation of Silicon Ink Jet Structures," IBM Technical Disclosure Bulletin, p. 220, vol. 23, No. 6 (Nov. 1980).
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Ashe James
Phillips Christopher David
Speakman Stuart
Pianalto Bernard
XAAR Limited
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