EP0852539B1 - Ink-jet printing head and method of manufacturing it - Google Patents

Abstract

The proposed ink-jet printing head has a plurality of parallel channels (K; K1; K2;...) which are etched isotropically through apertures (O) in a first layer (6) overlying the channels (K; K1; K2;...). After the etching process, the apertures (O) in the first layer (6) are closed off by the deposition on the first layer (6) of a second layer (7) which covers the apertures (O), the latter having a diameter of, for example, 1 νm. The apertures (O) produced in the first layer (6) by photolithography and subsequent dry etching are arranged in such a way that the desired channels (K; K1; K2;...) beneath the first layer (6) are exposed by the etching process. Advantages: no adjustment-related costs, formation of closed channels without bonding or adhesive techniques, possibility of integrating the trigger circuit and printing head on a single substrate.

Description

The invention relates to an inkjet printhead arranged parallel to each other within a substrate and channels separated by partitions, which with a Cover plate and at one of its ends with one Exit opening are provided, as well as with each Channel assigned thermal or piezoelectric Element which, when excited and within the channel located ink liquid an ejection of a Causes ink droplets from the orifice, as well as a Method of making one Inkjet printhead.

Inkjet printheads are now widely used in inkjet printers used. The inkjet print head is working mostly according to the known and for example in DE 30 12 698 C2 described drop-on-demand method, or DoD method for short called. This is used to create a point a medium to be printed, e.g. B. paper, from a channel an ink droplet is ejected from the inkjet printhead, as soon as a thermal or piezoelectric assigned to the channel Element with a suitable current pulse a control circuit is controlled. The suggestion is made e.g. B. by a current pulse of 2µs to 10µs duration, with a thermal energy of about 15 to 50 µ joules is released. This heating leads to local evaporation the ink liquid (bubble formation), the liquid column from the corresponding channel outlet opening is pushed without first touching. After completing the Current pulse collapses the bubble over the thermal element. As a result, part of the liquid column is withdrawn, with an ink drop outside the channel outlet openings pinches off and according to the momentum conservation law moved on. This ink droplet creates on black paper in the case of black ink Pressure point. The typical emission frequency is around 5 kHz.

To create a character, e.g. B. a letter the thermal or piezoelectric elements of the parallel adjacent channels in a suitable manner from the Drive circuit with current pulses are supplied so that the points on paper for that letter visible through the impact of appropriate drops of ink become.

Due to the very small channel diameter and narrow Grid distances between the channels (or nozzles) become Manufacture of inkjet printheads from the Semiconductor technology known processing methods for Fine structures used. Examples of such Processing methods are in EP 0 359 417 A2, EP 0 434 946 A2 as well as in the publication IEEE Transactions on Electron Devices, Volume 26, 1979, page 1918. in the Contrary to the production of integrated Semiconductor circuits based on a single substrate are formed in the known methods for Manufacturing inkjet printheads always two different substrates necessary. Be on a substrate Partitions formed between channels and these with one a second substrate manufactured cover plate, the is manufactured separately, closed.

In the known methods for thermal excitation Heating resistors can be arranged on or in the duct. The Channels are often etched in by orientation a silicon substrate. The heating resistors can attached to the channels by bonding. As Cover plate can be used for example a glass plate by anodic bonding on the channel plate and so that is applied in the first substrate.

As known from EP 0 443 722 A2, the channels of the Inkjet printhead are also formed by the fact that a first substrate, which is provided with heating resistors, a cover plate provided with partitions is adjusted. Instead of the cover plate provided with partition walls also a flat cover plate on the first substrate be stuck on if the mentioned in the first substrate Channels each in the form of channel floors and two Channel side walls are already incorporated. The glued cover plate then forms the in these channels Sewer ceiling.

DE-A-3 917 434 discloses a multilayer ink print head with ink channels created by selective etching. The ink print head points for receiving the ink channels and / or the drive chambers of the Transducer areas on a substrate layer with a cover layer arranged above. There are openings in the cover layer corresponding to the course of the generating ink supply channels arranged. The ink channels are generated by selective etching of the substrate layer through the openings. The Openings are dimensioned so that after filling the ink channels with Ink the ink closes the openings capillary. In one embodiment After etching out the ink channels, the openings of the cover layer are also closed with a glued-on lid.

Problematic with these known methods of manufacture integrable inkjet printheads is the imperative Use of two substrates to be joined together. This requires a complicated adjustment, the fine Channels before gluing the two substrates Contamination must be protected, which additional Effort means.

The invention has for its object a Inkjet printhead and a method of making one Specify inkjet printhead, which is a complicated Adjustment and a gluing or bonding of two separately manufactured substrates is not necessary.

This task is for an inkjet printhead type mentioned solved in that the cover plate consists of at least two layers that immediately on the channel one with a variety of over the channel arranged first layer provided openings, and that on the surface facing away from the channel of the first Layer is arranged a second layer, the openings covers.

Further developments of the inkjet print head are in the Subclaims 2 to 14 specified.

• Bereitstellen eines die Höhe der Kanalseitenwände bestimmenden Substrates, welchem thermische oder piezoelektrische Elemente im Bereich der späteren Kanäle zugeordnet sind;
• Abscheidung einer ersten Schicht auf diesem Substrat;
• Strukturierung dieser ersten Schicht mit einer Vielzahl von Öffnungen oberhalb der späteren Kanäle;
• isotrope Ätzung des Substrates durch die Öffnungen in der ersten Schicht solange, bis die Kanäle freigelegt sind;
• Abscheidung einer zweiten Schicht auf die erste Schicht solange bis die Öffnungen verschlossen sind;
• Bildung von Austrittsöffnungen an jeweils einem Ende der Kanäle.

A method for producing such an inkjet printhead has the following method steps:

• Providing a substrate which determines the height of the channel side walls and to which thermal or piezoelectric elements in the region of the later channels are assigned;
• Depositing a first layer on this substrate;
• Structuring of this first layer with a large number of openings above the later channels;
• isotropic etching of the substrate through the openings in the first layer until the channels are exposed;
• Depositing a second layer on the first layer until the openings are closed;
• Formation of outlet openings at each end of the channels.

Further developments of this manufacturing process are in the Claims 16 to 24 specified.

Figur 1

Eine ausschnittsweise Schnittdarstellung durch einen Tintenstrahlkopf im Bereich des thermische Elementes eines Kanales in Längserstreckung des Kanales,

Figur 2

eine ausschnittsweise Schnittdarstellung durch den Tintenstrahlkopf von Figur 1 im Bereich des thermischen Elementes, jedoch orthogonal zur Längserstreckung des Kanales,

Figur 3

eine Draufsicht auf die Oberseite des in den Figuren 1 und 2 dargestellten Tintenstrahldruckkopfes, bei welchem die zweite Schicht der Deckelplatte noch nicht aufgebracht ist,

Figur 4

eine ähnliche Darstellung wie Figur 1, jedoch mit innerhalb des Kanalraumes angeordneten thermischen Element,

Figur 5

eine Schnittdarstellung des Tintenstrahldruckkopfes von Figur 4 entlang der dortigen Schnittlinie E-F,

Figur 6

die ausschnittsweise Darstellung von zwei Kanalenden eines Tintenstrahldruckkopfes mit orthogonal zur Längserstreckung der Kanäle angeordneten Austrittsöffnungen,

Figur 7

eine ausschnittsweise schematische Darstellung des Tintenstrahldruckkopfes mit integriertem Transistor auf Siliziumsubstrat.

The ink jet print head according to the invention and its production method is explained in more detail below in connection with exemplary embodiments. In the exemplary embodiments, the inkjet print head and its production method are described using a print head with thermal excitation. However, it is equally possible to produce a printhead with piezoelectric excitation. The invention therefore also relates to such printheads with piezoelectric excitation. Show it:

Figure 1

A sectional view through an ink jet head in the region of the thermal element of a channel in the longitudinal extension of the channel,

Figure 2

2 shows a sectional view through the ink jet head from FIG. 1 in the area of the thermal element, but orthogonal to the longitudinal extent of the channel,

Figure 3

1 shows a plan view of the top of the ink jet print head shown in FIGS. 1 and 2, in which the second layer of the cover plate has not yet been applied,

Figure 4

1 shows a representation similar to FIG. 1, but with a thermal element arranged inside the channel space,

Figure 5

3 shows a sectional illustration of the ink jet print head from FIG. 4 along the section line EF there,

Figure 6

2 shows a section of two channel ends of an ink jet print head with outlet openings arranged orthogonally to the longitudinal extent of the channels,

Figure 7

a fragmentary schematic representation of the inkjet printhead with an integrated transistor on a silicon substrate.

Designate in the following figures, unless otherwise indicated, same reference numerals, same parts with the same Meaning.

The structure of a possible embodiment of an ink jet print head according to the invention from a Summary of Figures 1, 2 and 3 clearly. Of the Inkjet printhead is in plan view in Figure 3 shown schematically in sections, the im individual second layer 7 of a still to be explained Cover plate is removed for clarity. Of the Inkjet printhead has a variety of parallel adjacent channels K1, K2, K3, K4, the for example, can have a width of 50 µm. Between the individual channels K1, K2 or K2, K3 or K3, K4 are partitions 10 with a width of, for example 30µm arranged. The channels K1, K2, K3 and K4 are on their in Figure 3 ends drawn still closed. The Channels K1, K2, K3 and K4 can have a total of one, for example Have a length of 1 cm and end at the bottom in a reservoir R, which is used to hold ink liquid is provided. This reservoir R can with support points S be provided, which the floor and ceiling wall of the Reservoirs R to increase the stability with each other connect. In addition, a feed channel can be placed in the reservoir R. Z open, over which the ink liquid from a Storage container is fed.

Each of the channels K1, K2, K3 and K4 has an area an assigned thermal element 2, in order to known DOD methods when stimulated by a suitable current pulse an ink droplet from the front Eject end of each channel K1, K2, K3 and K4. For this, in a manufacturing step, that in FIG. 3 illustrated inkjet printhead on the section line S1 to separate. The z. B. in the separation of integrates manufacturable inkjet heads by sawing or Sawing, etching or breaking along the cutting line S1 respectively.

The ink jet printhead is along in Figures 1 and 2 the section line A-B and C-D shown in Figure 3 Area of the thermal element 2 is shown enlarged.

The thermal element 2 is, for example, one on one upper main surface of a substrate 1 arranged beams Polysilicon. The bar extends orthogonally to Longitudinal direction of the channel K, has a width of about 1.5 to 2µm and a length that is slightly shorter than the width of a Channel K is. The thermal elements 2 of each Channels K1, K2, K3, K4 are, as shown in FIG. 3, preferably arranged side by side to the from the respective channels K1, K2, K3, K4 emerging Ink droplets when the respective thermal is excited Element 2 with the same energy and thus with same speed from the outlet openings that in FIG. 3 is designated by the reference number 15, let it come out.

The thermal element 2 serves as a heating resistance zone. The substrate 1 may e.g. B. contain a complete integrated drive circuit on a silicon substrate. A sufficiently thick heat-storing layer is preferably to be arranged below the thermal element 2, which prevents the main part of the thermal energy generated in the thermal element 2 from flowing off when a current pulse is applied in the substrate 1 and the liquid ("ink") in the channel K not being reached . The heat storage layer is e.g. B. SiO ₂ with a thickness greater than or equal to about 1.0 microns. When integrating with an electronic control circuit on a silicon substrate, z. B. a field oxide, preferably with an additional layer of plasma oxide or TEOS, can be used.

On the substrate 1 is a protective layer 3, the z. B. from 300 nm plasma oxide and 600 nm plasma nitride can exist arranged. This protective layer 3 can be the upper main surface completely cover the substrate 1 and serves for protection of the thermal element 2 from erosion by the imploding bubbles in the ink liquid. Furthermore can this protective layer 3 also to protect an inside of the substrate 1 integrated control circuit before mobile Ions that may be in the ink liquid can be serve.

A further protective layer 4, which protects against erosion, is preferably provided in the area of the thermal element 2. This protective layer 4 extends, as can be seen from FIGS. 2 and 3, completely beyond the outer contour of the thermal element 2 and additionally beyond the width of the channel K. This additional protective layer 4 can, for. B. consist of sputtered tantalum (Ta), which is structured by photolithography and a CF ₄ / O ₂ plasma dry etching.

A further substrate 5 with a thickness of preferably 5 to 50 μm is arranged over the substrate 1 thus prepared on the main surface. This substrate 5 determines the depth of the channels K and thus the height of the side walls of the channel K. The substrate 5 can, for. B. consist of plasma oxide (SiO ₂ ), so-called spin-on glasses (SOG), polysiloksanes or polyimide.

On the substrate 5, which is initially unstructured a first layer 6, which has a plurality of openings O is provided, applied by deposition. This layer 6 can e.g. B. consist of plasma nitride or polysilicon and have a thickness of approximately 1 to 3 μm. The openings O, the by photolithography and then dry etching can be formed, are arranged in the layer 6, that in a subsequent isotropic etching process for the Channels K1, K2, K3, K4 and the reservoir R necessary Cavities are formed in the substrate 5. The openings O have for example a diameter of 1 µm and are one row in the area of channels K1, K2, K3 and K4 with each other and lie in the area of the reservoir, except for the mentioned support points S, in a large number side by side and with each other.

Furthermore, a layer for the Feed channel Z are etched out of Fig. 3.

The channels K1, K2, K3 and K4 as well as the reservoir R (see FIG. 3) are etched by an isotropic etching, which must be sufficiently selective to the layers 3, 4 and 6 mentioned. In the event that the substrate 5 consists of plasma oxide or SOG and the layer 6 consists of polysilicon or silicon nitride, the isotropic etching can be carried out dry with a fluorine-containing plasma, in HF steam or wet with BHF (buffered HF). In the event that the substrate 5 consists of polyamide or another organic material, the isotropic etching can be carried out using an O ₂ plasma.

After the desired structuring of the channels K1, K2, K3, K4 etc. and the reservoir and thus also the undercutting of the layer 6 (see FIG. 2) has been achieved, a second layer 7 is applied to the layer 6, e.g. B. again by deposition. This layer 7 should preferably be sufficiently non-compliant. A complete closure of the openings O is thereby facilitated. The layer 7 is deposited until the openings O are closed (for example plasma Si ₃ N ₄ deposition) or is ended beforehand (for example CVD deposition of boron-phosphorus-silicate glass BPSG) ). The sealing with BPSG is preferably accomplished by a subsequent flow process at high temperatures.

Closed channels K and reservoirs R using only one Substrate are generated using a mechanical assembly process of two components as in the prior art no longer necessary is.

If necessary, for further stabilization or as Protection on layer 7 another layer or more Layers are applied. Can mass produce of course, a variety of those shown in Fig. 3 Structures simultaneously on a common substrate are produced and then separated.

Instead of that described in FIGS. 1 to 3 Embodiments of an ink jet print head according to the Invention, in which the thermal elements 2 in the range the channel bottom of the channels K are arranged, it is also possible, as shown in FIGS. 4 and 5, the thermal element 2 to be arranged within the channel K.

For this purpose, as can be seen from FIG. 4, a resistance layer is arranged within the substrate 5, which is then structured by photolithography and etching. In the exemplary embodiment in FIG. 4, the resistance layer of the thermal element 2 is arranged at approximately half the height of the substrate 5. For this purpose, the substrate 5 is first deposited on a base plate (not shown in FIG. 4) in order to achieve its desired half thickness. The resistance layer is then deposited on the substrate 5 and structured, as shown in FIG. 5. The thermal element 2 is designed in such a way that a thin bar 2 _a hangs within the channel K, which is suspended on the edge side over wider webs within the substrate 5. The thermal element 2 is thus not in contact with the substrate 1, but is suspended within the channel K, so that the energy generated by the thermal element 2 can advantageously be released exclusively to the ink liquid within the channel K. As mentioned, this presupposes that the substrate 5 is deposited in two steps. When the substrate 5 is isotropically etched, the thermal element 2 is automatically exposed. 5, which shows a plan view from above along the section line EF in FIG. 4, to the left and right of the beam 2a, are used as resistance connections and can be contacted either from above or below. Since, in contrast to the embodiment of FIGS. 1 and 2, the thermal element 2 is exposed to the ink liquid, it is recommended that the thermal element 2 be made of an erosion-resistant material, e.g. B. tantalum. After the deposition and structuring of the resistance layer forming the thermal element 2, the second part of the substrate 5 is deposited.

In connection with Fig. 3 it was explained that the upper Ends of the channels K1, K2, K3 and K4 with outlet openings 15 are provided, which on the end faces of the respective Channels K1, K2, K3 and K4 are arranged. The in Embodiment of Fig. 6 shown in detail Channels K1, K2 of an inkjet printhead face at their Channel ends also have outlet openings 15. This However, outlet openings 15 are on the upper channel wall formed by circular openings. The outlet openings 15 are located in layer 6, which is above substrate 5 is arranged. So that the outlet openings 15 at the subsequent layer 7 deposition not mentioned are closed, are the diameters of the Outlet openings 15 chosen so large that the openings O the outlet openings are securely closed during the isotropic etching process 15 itself certainly not closed become. The outlet openings 15 are in the Embodiment of Fig. 6 parallel to Substrate surface. The outlet openings 15 are preferably larger than 1.0 µm. The expediently Diameters between 5 and 50 µm selected. The essential The advantage of these outlet openings 15 is their circular shape To see shape, the emergence of a circular Droplets allowed, creating a dot on the paper with exactly circular outer contour can be formed. It is also advantageous in this embodiment that the Outlet openings 15 not only in a row, but can be arranged flat in a matrix. Of Another is not sawing or breaking like in Embodiment of Fig. 3 necessary, whereby a Contamination of the outlet opening 15 can be avoided.

7 shows a detail of the inkjet printhead in the region of a thermal element 2 consisting of polysilicon with an integrated transistor on a silicon substrate. The already known reference symbols stand for the known parts. For the sake of clarity, the representation of the channel K and the layers 6 and 7 has been omitted. The thermal element 2 made of low-doped polysilicon is contacted at the edge by highly doped polysilicon. The highly doped polysilicon sections are marked with the reference symbol 31. The two highly doped polysilicon sections 31 are contracted by metal tracks 30 which act as leads. Two heat-storing layers 20, 21 are arranged below the thermal element 2. The layer 20, which consists for example of TEOS-SiO ₂ , is located directly below the thermal element 2. Below this layer 20 there is a further heat-storing layer 21 which, for. B. consists of FOX-SiO ₂ .

The metal path 30, which adjoins the right high-doped polysilicon section 31, contacts with its other end an n ⁺ -doped layer which, for example, forms the source connection of a MOS transistor. The metal track 30 can consist of aluminum or bismuth. The protective layer 3 already known from FIG. 1 consists of plasma SiO ₂ and a layer of plasma Si ₃ N ₄ , which extends over the metal track 30 in the region of the MOS transistor.

Claims (24)

1. Ink-jet print head having channels (K; K1; K2...), which are arranged parallel to one another within a substrate (5) and are separated by partitions (10) and are provided with a cover plate (6, 7) and in each case with an outlet opening (15) at one of their ends, and also having a thermal or piezoelectric element (2) assigned to each channel (K; K1, K2...), which element, upon excitation and with ink liquid situated within the channel (K; K1, K2...), causes an ink droplet to be ejected from the outlet opening (15),
   characterized in that the cover plate (6, 7) comprises at least two layers (6, 7), in that a first layer (6) produced by deposition is arranged directly on the channel (K; K1, K2...), which first layer is provided with a multiplicity of openings (O) lying above the channel (K; K1, K2...), and in that a second layer (7) produced by deposition is arranged on the surface of the first layer (6) remote from the channel (K; K1, K2...), which second layer is made of borophosphorus silicate glass or Si₃N₄ and covers the openings (O).
2. Ink-jet print head according to Claim 1, characterized in that an electronic drive circuit (A) is integrated within the substrate (5).
3. Ink-jet print head according to Claim 1 or 2, characterized in that the thermal element (2) is arranged at the bottom of the channel (K; K1, K2...) as a heating resistor formed by a polysilicon layer.
4. Ink-jet print head according to Claim 3, characterized in that at least one protective layer (3, 4) is arranged between the bottom of the channel and the polysilicon layer.
5. Ink-jet print head according to Claim 1 or 2, characterized in that the thermal or piezoelectric element (2) is arranged within the channel (K; K1, K2...) and is suspended from the side walls of the channel at the edges, and in that the thermal or piezoelectric element (2) is formed from erosion-resistant material.
6. Ink-jet print head according to Claim 3 or 4, characterized in that a heat-storing layer (20, 21), preferably a layer made of silicon oxide (SiO₂), is arranged on that surface of the chemical element (2) which is opposite to the bottom of the channel.
7. Ink-jet print head according to Claim 6, characterized in that the heat-storing layer (20, 21) has a thickness > about 1.0 µm.
8. Ink-jet print head according to Claim 3, 4, 6 or 7, characterized in that at least one protective layer (3, 4) is arranged between the bottom of the channel and the thermal element (2).
9. Ink-jet print head according to Claim 8, characterized in that the protective layer (3) is composed of plasma oxide with a thickness of preferably 300 nm and plasma nitride with a thickness of preferably 600 nm.
10. Ink-jet print head according to Claim 8, characterized in that a further protective layer (4), which is preferably composed of sputtered Ta, is arranged over the first protective layer (3).
11. Ink-jet print head according to one of the preceding claims, characterized in that the channel has channel side walls with a height of about 5 µm to 50 µm.
12. Ink-jet print head according to one of the preceding claims, characterized in that the channel side walls are formed from plasma oxide, polysiloxanes or polyimide.
13. Ink-jet print head according to one of the preceding claims, characterized in that the first layer (6) of the cover plate, which first layer is provided with openings (O), is a patterned plasma nitride or polysilicon layer.
14. Ink-jet print head according to one of the preceding claims, characterized in that the second layer (7) is composed of borophosphorus silicate glass or Si₃N₄.
15. Method of manufacturing an ink-jet print head according to one of Claims 1 to 14, having the following method steps:

    provision of a substrate (5), which determines the height of the channel side walls and to which thermal or piezoelectric elements (2) are assigned in the region of the subsequent channels (K; K1, K2...);

    deposition of a first layer (6) on this substrate (5);

    patterning of this first layer (6) with a multiplicity of openings (O) above the subsequent channels (K; K1, K2...);

    isotropic etching of the substrate (5) through the openings (O) in the first layer (6) until the channels (K; K1, K2...) are uncovered;

    deposition of a second layer (7) onto the first layer (6) until the openings (O) are closed off;

    formation of outlet openings (15) in each case at one end of the channels (K; K1, K2...).
16. Method according to Claim 15, characterized in that the substrate (5) is deposited in the form of plasma oxide, polysiloxanes or polyimide with a thickness of about 5 µm to 50 µm onto a baseplate.
17. Method according to Claim 15 or 16, characterized in that the first layer (6) is patterned by photolithography with subsequent dry etching.
18. Method according to one of Claims 15 to 17, characterized in that the substrate (5) is composed of plasma oxide or polysiloxanes and the first layer (6) is composed of polysilicon or silicon nitride, and the first layer (6) is patterned by photolithography with subsequent isotropic etching, dry using a fluorine-containing plasma in HF vapour or wet using BHF.
19. Method according to one of Claims 15 to 17, characterized in that the substrate (5) is composed of polyimide or another organic material, and the first layer (6) is patterned by photolithography with subsequent isotropic etching by means of an O₂ plasma.
20. Method according to one of Claims 15 to 19, characterized in that a deposition with plasma Si₃N₄ or a CVD deposition of borophosphorus silicate glass is effected as the second layer.
21. Method according to Claim 20, characterized in that after the second layer (7) has been deposited onto the first layer (6), a flow process at high temperatures is carried out.
22. Method according to one of Claims 15 to 21, characterized in that, in a first step, the substrate (5) is deposited approximately up to half of the desired thickness of the substrate (5), in that, in a subsequent step, a resistive layer is applied and this resistive layer is patterned, and in that, in a further step, the second half of the substrate is deposited onto the resistive layer.
23. Method according to Claim 22, characterized in that the resistive layer is an erosion-resistant layer.
24. Method according to one of Claims 15 to 21, characterized in that an opening (A) is arranged in the first layer (6) in each case at one end of the channels, which opening is large enough that it is not closed off during the subsequent process of depositing the second layer (7), and these openings (A) serve as outlet openings (15).

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