Substrate for recording head and recording head

Abstract: An electricity-heat converter can be provided by a substrate (11) for recording head, a recording head and a recording device equipped with an electricity-heat converter capable of generating heat energy for discharging liquid by causing the state change of liquid for recording by heat to occur and a wiring (6, 7, 8) which is sandwiched on both sides between insulating layers (9) comprising an organic material and connected electrically to said electricity-heat converter through at least one contact portion formed at said insulating layer (9).

Description: This invention is applicable to recording devices such as output printers of copying device, word processor, facsimile, video, computer, etc. In particular, it concerns substrate for a recording head and a recording head incorporating such substrate. More particularly, it relates to a recording head to which the liquid jet recording method, which performs recording by discharging liquid for recording through a discharging port, is applicable. An example of liquid jet recording head of the prior art is shown in Fig. 1A and 1B. Fig 1A is a schematic plan view of the substrate for recording head. Fig. 1B is a schematic sectional view of the recording head along the line B-B' in Fig. 1A. The on-demand type recording head of the prior art has an electrode heat converter which generates heat energy to be utilized for discharging liquid (ink) by formation of a heat generating resistance layer 1 comprising HfB₂, TaAl, etc. and an electroconductive layer 2 for formation of electrodes comprising Al, etc. arranged at predetermined intervals formed on a substrate 11 comprising a semiconductor such as silicon or an insulating material such as glass, etc., and on the heat generating portion 1a of the electricity-heat converter are formed a discharging port and a liquid channel communicated thereto. And, a plurality of discharging ports are provided at a ratio of 8 or more per 1 mm for the purpose of high resolution recording, and electricity-heat converters are arranged at high density so as to correspond thereto. Here, 3, 4 and 5 are protective layers. The liquid supplied from a liquid vessel not shown is supplied into the common liquid chamber as a part of liquid channel, and further fills the parts such as heat-acting portions, etc. corresponding respectively to the discharging ports of the liquid channels with liquid. Recording by way of liquid jetting generates bubbles by causing the state of change in the liquid on the heat-generating portion 1a in the heat acting portion by the heat energy generated from the heat-generating portion 1a by applying recording signals on the electrodes, thereby discharging liquid through the pressure of volume expansion of the bubbles to form flying liquid droplets. The method for preparation of such recording head of the prior art is to be described. First, an HfB₂ film 1 as the heat-generating resistance layer for formation of an electricity-heat converter and Al as the electrode 2 are formed by sputtering, etc. and then subjected to patterning. Next, SiO₂ as the oxidation resistant film 3 for the electricity-heat converter and Ta as the cavitation resistant film 4 are formed by sputtering, etc. and subjected to patterning. And, a photosensitive polyimide is coated as the ink resistant film 5 and subjected to patterning. Further, Al, Ni and Cu of the the second layer are subjected to film forming patterning, and Cu is plated to about 10 µm for increasing conductivity to make a common electrode 10. Here, SiO₂ represented by the symbol 3 which the layer beneath the common electrode 10 and the photosensitive polyimide represented by the symbol 5 serve as the interlayer insulating layer. Then, a ceiling plate 14 having a wall portion for sectionalizing the common liquid chamber 12 and individual liquid chambers 13 as the liquid channels for the recording liquid is plastered and a wiring connected to the driving circuit for supplying electrical signals is electrically connected (not shown) to prepare a liquid jet recording head. However, in the above prior art example, since the common electrode 10 exists externally of the ceiling plate 14 (namely outside the liquid channel of the recording head), the length of the electrode 2 on the common electrode side is required to be ℓ₂ as shown in Fig. 1A, whereby a considerable length of high density wiring is required at the electrode. For this reason, other than the shortcomings in production such as lowered yield caused by short circuit, wire breaking, etc., short circuit or wire breaking sometimes occurs when driving is performed by passing large currents, whereby the durability of the recording head is lowered. In the aforesaid example the common electrode portions of the heat converters are connected to a common electrode 10 by via connections. An alternative arrangement is described in European Patent Application EP-A-0258606 where via connections are made to electroconductive layer wiring and spring lead contacts then are made to this layer wiring. A surface pattern of polymer material, in the immediate vicinity of the via connections, is applied to provide a protective layer or shield. The present invention is intended as a remedy to the problem aforesaid. The substrate for a recording head constructed in accordance with the present invention has, in common with the substrate disclosed in the above reference: a multiplicity of electricity-heat converter elements each capable of generating heat for discharging ink liquid by causing a change of state in the ink liquid, each element including a resistive portion and first and second electrode portions leading from the resistive portion; and electrode wiring located between upper and lower layers of electrically insulative ink resistant material, which electrode wiring is connected to each first electrode via through-holes defined in the lower layer of ink resistant material. In accordance with the present invention the aforesaid substrate is characterised in that: electrode wiring consists in layers of electro-conductive material, which layers, located between said upper and lower layers extend over each through-hole and are connected to each first electrode. The substrate defined above can then be assembled with a channelled cover member to produce a recording head with ink chamber, with the through-holes and a portion of the electro-conductive wires, effectively sealed by the upper and lower insulative layers, lying within the ink chamber. In this way the common electrode portion of each converter element can be foreshortened. The probability of short circuit and wire breakage occurring during production and during use is in each case therefore much reduced with consequent improvements in yield and product life time, respectively. High yield can be obtained even with dense integration i.e. with fine geometry converter electrodes since only short length common electrode portions are required. In the drawings: Fig. 1A is a schematic plan view showing the recording head substrate of a prior art example; Fig. 1B is a schematic sectional view of the recording head along the line B-B' in Fig. 1A; Fig. 2 is a schematic plan view showing a recording head substrate embodying the present invention; Fig. 3 is a schematic sectional view of a recording head along the line A-A' in Fig. 2; Fig. 4 is a schematic perspective view of the recording head according to the present invention; Fig. 5 is a schematic illustration of the liquid jet recording device according to the present invention; Fig. 6 is a schematic perspective view of the recording head according to another embodiment of the present invention. To facilitate better understanding of the invention, a preferred embodiment thereof will be described hereinbelow. The following description is given by way of example only. Fig. 2 is a schematic plan view of a recording head substrate embodying the present invention, and Fig. 3 is a schematic sectional view of this recording head along a line A-A' in Fig. 2. First, on a substrate 11 are provided an HfB₂ layer as a heat generating layer 1 and an Al layer as the electrode 2 of an electricity-heat converter for forming an electricity-heat member, and a first layer wiring is formed. An Si0₂ layer as the oxidation resistant protective film 3 of the electricity-heat converter and a Ta layer as the cavitation resistant protective film 4 are formed. As the ink resistant protective film 5, a photosensitive polyimide 5 is coated. A part of the wiring portion as a second electroconductive wiring consists of multiple layers with different materials, and the uppermost layer 8 as the second electroconductive layer 8 and the lowest layer 6 comprise the same material so as to sandwich the first electroconductive layer 7 above and beneath thereof. Here, 6 is a Ti layer, 7 a Cu layer and 8 a Ti layer. On the above second layer wirings (6, 7, 8), as a protective layer 9 comprising an organic material, is coated a photosensitive polyimide. For formation of plated electrodes by etching of Ti of the second electroconductive layer, Cu is exposed and Cu, which is of higher conductivity, is formed as the external common electrode 10. The respective layer constitutions are described in detail. They can be easily understood by referring to the enlarged portion in Fig. 3. The heat generating resistance layer 1 and the electrode 2 are terminated respectively within the liquid chamber 12, and a SiO₂ layer 3 and a photosensitive polyimide 5 are arranged thereon. Here, after formation of the first opening by patterning of the SiO₂ layer 3, the polyimide 5 is formed and the second opening with smaller size than the first opening is formed by patterning. By doing so, the SiO₂ is covered at the end portion with the thru-hole portion. Through the thru-hole, Ti layer 6 Cu layer 7 and Ti layer 8 are successively formed, patterned and finally the photosensitive polyimide 9 is formed so as to cover over these to constitute a connecting portion. A grooved ceiling plate 14 is laid down to complete construction of a common liquid container chamber 12 and the individual liquid channels 13 formed thereon on the substrate, and the wiring for connection to the main device side is electrically connected to constitute the liquid jet recording head 15 (Fig. 4). 16 Is a discharging port, 17 is a liquid channel wall, and 18 is a port for supplying recording liquid. Here, Ti, Cu and Ti forming the second layer wiring have respectively the following functions: Ti which constitutes the lowest layer 6 of the second electroconductive layer has good adhesion to the photosensitive polyimide which constitutes the ink resistant protective film 5. Here, other than Ti, Cr, etc. may be available. Cu which constitutes the intermediate layer 7 as the first electroconductive layer enhances the conductivity of the second layer wiring, serving as the plating subbing layer during preparation of the external common electrode 10, and here, other than Cu, Ni, Au, Sn, etc. may be suitably available. Also, Ti which constitutes the uppermost layer 8 of the second electroconductive layer has good adhesion to the photosensitive polyimide constituting the protective film 9 of the second layer wiring, and also at the same time functions as the oxidation resistant protective film for preventing oxidation of Cu which is one of the constituent materials during thermal curing in the preparation steps of the photosensitive polyimide. Also here, for Ti, Cr, etc. may be substituted. The liquid recording head 15 as described above is mounted on the carriage 19 as shown in Fig. 5, to be used for the liquid jet recording device. The recording head is scanned along the shaft 21 by means of the wire 20 for transmitting the driving force. The recording paper 22 as the recording medium is conveyed by the paper delivery roller 24 in contact with the conveying means, namely the platen 23. 25 is a discharging restoration system. Other than the recording heads which performs discharging in substantial the horizontal direction relative to the heat generating surface of the electricity-heat converter as shown in Fig. 4, the present invention is also applicable to the type which performs discharging in the direction crossing with the heat-generating surface as shown in Fig. 6. This comprises an orifice plate 26 having a discharging orifice 16 and a liquid channel wall 17 in combination on a heater substrate 11, and 18 shows the supplying inlet of recording liquid. As described above, the recording head embodying the present invention is suited to miniaturization and denser integration. It can be provided integrally with a liquid vessel and made detachable relative to the carriage of a recording apparatus. Of course, since denser integration of the electricity-heat converter can be accomplished with better reliability, the present invention can be preferably applied to the full-line type wherein some hundred to some thousand electricity-heat converters are arranged at a high density of 8 or more per 1 mm, whereby considerable cost reductions can be achieved. As described above, by making a structure using respective layers of insulating material above and beneath electroconductive layers; the connective common electrode wiring can be located within the liquid chamber, and the length of high density electrodes can be made shorter, wherein the occurrence of short circuit and wire breaking can be extremely reduced to result in a significant improvement in yield.

Claims: A substrate for a recording head, said substrate comprising: a multiplicity of electricity-heat converter elements (1,2) each capable of generating heat for discharging ink liquid by causing a change of state in said ink liquid, each element (1,2) including a resistive portion (1) and first and second electrode portions (2) leading from said resistive portion (1); and electrode wiring (6,7,8) located between upper and lower layers (9,5) of electrically insulative ink resistant material, which electrode wiring (6,7,8) is connected to each first electrode (2) via through-holes defined in said lower layer (5) of ink resistant material; which substrate is characterised in that said electrode wiring (6,7,8) consists in layers (6,7,8) of electro-conductive material, which layers, located between said upper and lower layers (9,5), extend over each through-hole and are connected to each first electrode (2). A substrate as claimed in claim 1 wherein said electrode wiring (6,7,8) comprises a layer (7) of a first electroconductive material, which layer (7) is sandwiched between layers (6,8) of a second electroconductive material. A substrate as claimed in claim 2 wherein said second electroconductive material (6,8) exhibits a better adhesion, than said first electroconductive material (7), to said electrically insulative ink resistant material (5,9). A substrate as claimed in either one of claims 2 or 3 wherein said first electroconductive material (7) is of lower electrical resistivity than said second electroconductive material (6,8). A substrate as claimed in any one of claims 2 to 4 wherein said second electroconductive material (6,8) is of titanium (Ti) or chromium (Cr) or both. A substrate as claimed in any one of claims 2 to 5 wherein said first electroconductive material (7) is of any one of the materials: copper (Cu), nickel (Ni), gold (Au), tin (Sn) or any combination thereof. A substrate as claimed in any one of the preceding claims wherein said electrically insulative ink resistant material (5,9) comprises an organic material. A substrate as claimed in claim 7 wherein said organic material (5,9) is of polyimide. A substrate as claimed in any one of the preceding claims wherein said electrically insulative ink resistant material is of light sensitive material. A substrate as claimed in any one of the preceding claims wherein said electrode wiring (6,7,8) has a layer thickness greater than the first and second electrode (2) of each electricity-heat converter (1,2). A substrate as claimed in any one of the preceding claims wherein said electricity-heat converters (1,2) are provided at a density of at least eight per millimetre. A recording head comprising: a substrate (1 to 11) as claimed in any of claims 1 to 11; and a cover member (14) in which is defined a plurality of channels (13) each located over a respective one of said electricity-heat converter elements (1,2), each channel (13) leading from a common ink chamber (12) also defined in said cover member (14), wherein said through-holes and a portion of said layers (6,7,8), located between upper and lower layers (9,5), are located within said chamber (12).

Inventors: TAMURA HIDEO CANON TAMAGAWARYO, TAMURA, HIDEO, CANON TAMAGAWARYO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1990
Main classification: B41J2
IPC codes: H05K3, B41J2