Patent Application
20160009088
1. Field of the Invention
The present application relates to a substrate for an ink jet recording head adapted to record information by ejecting an ink onto an ink jet recording medium, and a method for manufacturing the same. This substrate is hereinafter referred to as the ink jet recording head substrate. The present application also relates to an ink jet recording head including the ink jet recording head substrate.
2. Description of the Related Art
A thermal ink jet recording head has recently been desired which can operate at low power with reliability. A thermal ink jet recording head (hereinafter simply referred to as the ink jet recording head) includes an element substrate for the ink jet recording head, and a liquid flow channel member having an ink chamber and ink ejection openings communicating with the ink chamber. The element substrate is provided with a heating resistor that applies heat for generating bubbles in an ink that are the energy for ejecting the ink. The heating resistor is provided with a protective layer thereon for preventing the heating resistor from coming into contact with the ink. In addition, an insulating layer is disposed between the base member, such as a silicon substrate, of the element substrate and the heating resistor. It is effective in operating the ink jet recording head at low power to reduce the thermal conductivity of the insulating layer disposed between the heating resistor and the semiconductor substrate, or base member. The insulating layer on the semiconductor substrate is generally made of silicon oxide having a thermal conductivity of 1.3 W·m−1·K−1. An insulating layer having a lower thermal conductivity than silicon oxide, that is, a heat accumulation layer is desired.
In the case of using a heat accumulation layer having a low thermal conductivity, heat generated from the heating resistor does not easily dissipate in the direction of the semiconductor substrate through the heat accumulation layer. This is efficient in increasing the temperature of the thermal operation portion, which will come into contact with the ink, on the heating resistor, accordingly reducing the energy applied for bubbling the ink. Consequently, the resulting recording head can operate at low power.
The ink jet recording head disclosed in U.S. Pat. No. 7,390,078 includes an insulating layer 28, a heat accumulation layer (low thermal diffusivity film) 32, a heating resistor layer 26, a covering layer (electroconductive metal layer) 60 and a protective layer 30 on a substrate 22, as shown in
According to an aspect of the application, there is provided an ink jet recording head substrate includes a base substrate, a heat accumulation layer overlying the base substrate, a heating resistor layer overlying the heat accumulation layer and including an electrothermal conversion portion, a wiring layer electrically connected to the heating resistor layer, and an insulating protective layer covering the heating resistor layer and the wiring layer. The heat accumulation layer includes a porous cyclic siloxane film formed by a gas-phase process.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The aerogel forming the heat accumulation layer 32 disclosed in U.S. Pat. No. 7,390,078 is prepared by a sol-gel process using a reaction, such as hydrolysis or polycondensation, of the material solution. The aerogel is applied onto a base substrate, and is then heat-treated to remove the remaining solvent in the coating, thus being densified.
In this process, however, it is difficult to completely remove the solvent. The solvent can remain to some extent. In particular, in the case of forming a heat accumulation layer on a substrate having semiconductor elements or the like, long-time heat treatment, which can adversely affect the semiconductor elements, is limited. If such a residual solvent remains in the heat accumulation layer, the residual solvent can be evaporated by the heat of the heat accumulation layer generated when the ink jet recording head has been operated. The evaporation of the residual solvent causes the heat accumulation layer to expand and contract and thus breaks the heat accumulation layer. Consequently, the heating resistor layer might be broken, and the head might not work due to an open circuit.
Accordingly, an aspect of the present application provides an ink jet recording head that can operate at low power with reliability.
Exemplary embodiments of the application will now be described in detail with reference to the drawings. Ink Jet Recording Apparatus
In
The ink jet recording head substrate 100 having the above-described structure is provided with a liquid flow channel member 120 thereon. The liquid flow channel member 120 has ink ejection openings 121 corresponding to the positions of the thermal operation portions 117, and a liquid flow channel 116 continuing from an ink supply port 107 passing through the ink jet recording head substrate 100, to the ink ejection openings 121 via the thermal operation portions 117. The ink jet recording head 1 thus includes the ink jet recording head substrate 100 and the liquid flow channel member 120.
The heat accumulation layer 102 formed in the present embodiment includes a cyclic siloxane film. The cyclic siloxane film is formed by a gas-phase process, such as plasma chemical vapor deposition (plasma CVD or P-CVD). The heat accumulation layer 102 may further include an insulating film formed of silicon oxide, silicon nitride or the like on the surface of the base substrate 101. In the following description, the cyclic siloxane film may be referred to simply as the heat accumulation layer 102.
The P-CVD process will now be described with reference to
The heat accumulation layer 102 is formed using at least one process gas (material gas) capable of forming a cyclic siloxane film. The material gas for forming the cyclic siloxane skeleton is introduced into the P-CVD chamber shown in
The cyclic siloxane mentioned herein is the general term of compounds having a cyclic skeleton expressed by (—Si—O—)n formed with siloxane units (n represents an integer), where Si atoms are bound to O and other atoms. Atoms other than O include H, C, N, and F. Although a normal silicon oxide film also has a —Si—O— cyclic structure, the atoms bound to Si are only O. Some of the glass materials contain Na, Ca or Al. The Na, Ca or the like is however merely held in the SiO cyclic structure, and Al is bound to O. The cyclic siloxane skeleton may have a single cyclic structure or a plurality of cyclic structures. Alternatively, a plurality of cyclic structures may be connected to each other with a linkage structure. The number n of siloxane units of the cyclic siloxane skeleton is preferably 3 to 20. When n is less than 3, the cyclic skeleton is difficult to form. In contrast, when n exceeds 20, the mechanical strength of the film is reduced and results in reduced durability to thermal stress. If the cyclic skeleton contains partially has a —SiNR— or —SiCR—O-bond in the molecule thereof, the siloxane unit may contain these bonds, and the number n of the siloxane units includes the siloxane units containing these bonds.
Process gases capable of forming the cyclic siloxane film include silicon compounds capable of supplying Si, oxidizing gases capable of supplying O, and compounds capable of supplying H, C, N, F, or any other element to the side chain, the cyclic skeleton or the linkage structure. The process gas for introducing such an element may be a single compound gas or a combination of a plurality of gases. A gas having a cyclic siloxane structure may be used as a process gas.
The cyclic siloxane film formed by a gas phase process is porous and has pores of 0.1 nm to 3 nm in size. The pore size can be controlled by selecting the raw material gas used in the gas phase process and the deposition conditions.
In the gas phase process, the structure and porosity of the resulting cyclic siloxane film vary depending on the process gas, the flow rate of the process gas, and deposition conditions including deposition temperature. The variation in porosity affects the physical properties of the resulting film. As the porosity is increased, the thermal conductivity decreases; and as the porosity is reduced, the durability to thermal stress increased. There is a trade-off between the thermal conductivity and the durability to thermal stress. In the present embodiment, it is advantageous for good balance between them to control the porosity of the cyclic siloxane film in a specific range. The porosity may be in the range of 20% to 70%. The optimum porosity depends on the composition of the cyclic siloxane. When it contains Si, O, C and H (hereinafter referred to as SiOCH siloxane), the advantageous porosity is in the range of 30% to 60%. The cyclic siloxane may contain Si, O, F and H (hereinafter referred to as SiOFH siloxane), Si, O, C, H and F (SiOCHF siloxane), or Si, O, C, H, N and F (SiOCHNF siloxane). Advantageously, these cyclic siloxanes have porosities in the range of 30% to 65%. The porosity may be controlled by thermal treatment performed independently after the deposition.
The cyclic siloxane film of the heat accumulation layer 102 may have a thickness of 0.3 μm to 10.0 μm, such as 0.5 μm to 2.0 μm.
If the heating resistor layer 104 or the wiring layer 105 is formed on the thus formed porous cyclic siloxane film (heat accumulation layer 102), the flatness of these layers overlying the cyclic siloxane film may be reduced depending on the pore size of the cyclic siloxane film, and accordingly, the thermal efficiency may be reduced. The material of the overlying layer having a high thermal conductivity may be trapped in the pores, thereby increasing the thermal conductivity of the heat accumulation layer 102. This reduces the effect of the heat accumulation layer 102. It is therefore advantageous that the pores be sealed at the surface of the film so as to ensure the flatness of the heat accumulation layer 102 and prevent foreign matter from entering the pores. For this sealing of the pores, an insulating film (pore-sealing film 103), such as a silicon oxide film or a silicon nitride (SiN) film, may be formed on the surface of the cyclic siloxane film (heat accumulation layer 102), as shown in
The invention will be further described in detail with reference to Examples. The Application is not however limited to the disclosed examples.
The process will now be described which was performed in the present Example for manufacturing an ink jet recording head substrate and an ink jet recording head.
In the following process, the base substrate 101 may be a simple Si substrate or a substrate including driving elements such as switching transistors for selectively operating the electrothermal conversion portions 108 or other semiconductor elements. For the sake of simplicity, the drawings used in the following description show a simple Si substrate as the base substrate 101.
A heat accumulation layer 102 is formed of a cyclic siloxane to a thickness of 1.5 μm on the base substrate 101 by a gas phase process under the conditions of any one of 1A to 1E shown in Table 1 (
The cyclic siloxane formed from the material gases expressed by formulas (A) and (B) may have the structure as shown in formula (C).
In formula (C), R1 and R2 each represent H, group containing a carbon atom, such as CH3 or C2H5, or a site bound to another cyclic siloxane structure, such as —CH2— or —O—. Since O, C and H are bound directly to the Si atom, this cyclic siloxane is represented as SiOCH. According to observation through a transmission electron microscope, the pore size was in the range of 0.1 nm to 3 nm. The number n of siloxane units in the cyclic skeleton was estimated in the range of 3 to 20 from the pore size.
Then, a TaSiN heating resistor layer 104 was formed to a thickness of about 50 nm on the heat accumulation layer 102 by reaction sputtering, and, subsequently, an Al layer was formed to a thickness of about 285 nm as the wiring layer 105 by sputtering. The heating resistor layer 104 and the wiring layer 105 were subjected to dry etching using a photolithography technique. In the present Example, the dry etching was performed by reactive ion etching (RIE).
For forming electrothermal conversion portions 108, the Al wiring layer 105 was further removed, in part, by etching using a photolithography technique in such a manner that the heating resistor layer 104 was exposed in the removed portions, as shown in
Then, a silicon nitride insulating protective layer 106 was formed to a thickness of about 300 nm, as shown in
Subsequently, a liquid flow channel member 120 in which a liquid flow channel 116 was to be formed was formed on the ink jet recording head substrate 100, and ink ejection openings 121 were formed in the liquid flow channel member 120 corresponding to the positions of the thermal operation portions 117, as shown in
The porosity of the porous SiOCH heat accumulation layer 102 formed on the base substrate 101 was measured by observation through a transmission electron microscope. Also, the thermal conductivity of the heat accumulation layer 102 was estimated by the 3ω method. The results are shown in Table 1.
The electrothermal conversion portions 108 of the ink jet recording head 1 produced through the above-described process were operated under the following conditions, and the durability to thermal stress was estimated by applying breaking pulses.
The durability to thermal stress was evaluated according to the following criteria:
Bad: broken by less than 3.0×109 pulses
The samples were comprehensively evaluated in terms of thermal conductivity and durability to thermal stress according to the following criteria:
Good: When having a thermal conductivity of less than 1.00 W·K−1·m−1 and broken in the test for durability to thermal stress using pulses in the range of 3.0×109 to less than 5.0×109, or when having a thermal conductivity in the range of 1.00 W·K−1·m−1 to less than 1.30 W·K−1·m−1 and being durable to thermal stress of 5.0×109 pulses or more.
Bad: Cases other than the above cases
The results are shown in Table 1 together. For comparison, a SiO film formed by the sol-gel process disclosed in U.S. Pat. No. 7,390,078 and a known SiO film formed by thermal CVD using silane and oxygen gas were evaluated.
In terms of durability to thermal stress, the SiOCH films formed under the conditions of 1A to 1D shown in Table 1 were evaluated as excellent, and the SiOCH film formed under the conditions of 1E shown in Table 1 was evaluated as good. These results suggest that the samples formed under these conditions are sufficiently durable to thermal stress. The reason why the sample of conditions 1E was evaluated as good is probably that the mechanical strength thereof was reduced due to the high porosity thereof. The heat accumulation layer formed by the sol-gel process disclosed in U.S. Pat. No. 7,390,078 was evaluated as bad. This is probably because the heating resistor layer was broken by the thermal expansion and contraction of the heat accumulation layer resulting from the evaporation of the residual solvent from the layer.
The comprehensive evaluation in terms of thermal conductivity and durability to thermal stress were excellent for 1B, 1C and 1D, and good for 1A and 1E.
These results suggest that the SiOCH films of the present Example are porous, and have lower thermal conductivities and higher durabilities to thermal stress than heat accumulation layers of SiO formed by a known CVD process. The results of the comprehensive evaluation show that the desirable porosity of the SiOCH film is in the range of 30% to 60%. Hence, in the case of the present Example, the gas flow rate of formula (A) to formula (B) is desirably in the range of 10:90 to 50:50. Unlike the case of the sol-gel process, the heat accumulation layers of the present Example, which were formed by P-CVD being a gas phase process, do not contain a residual solvent. Such a heat accumulation layer is unlikely to release solvent vapor when the ink jet recording head is operated, and accordingly there is little risk of expansion and contraction of the heat accumulation layer. Accordingly, the problem is reduced that the heating resistor on the accumulation layer is broken and results in open circuit in the head.
Thus, an ink jet recording head substrate is provided which can operate at low power with reliability.
Heat accumulation layers 102 were formed under the deposition conditions of 2A to 2F shown in Table 2 using tetrafluorosilane (SiF4), oxygen gas and hydrogen gas as raw material gases instead of those used in Example 1. Each of the resulting heat accumulation layers is assumed to be a porous SiOFH film having a cyclic siloxane structure expressed by the following formula (D).
In formula (D), X represents F or H, or a linkage bound to another cyclic siloxane structure via —O—. According to observation through a transmission electron microscope, the pore size was in the range of 0.1 nm to 3 nm. The number n of siloxane units in the cyclic skeleton was estimated in the range of 3 to 20 from the pore size. Then, ink jet recording heads were produced in the same process as in Example 1.
The ink jet recording head substrates and ink jet recording heads produced in the above process were subjected to measurements for the porosity and thermal conductivity of the heat accumulation layer 102 in the same manner as in Example 1, and the heat accumulation layer was comprehensively evaluated together with the durability to thermal stress. The results are shown in Table 2.
In terms of durability to thermal stress, the SiOFH films formed under the conditions of 2A to 2E were evaluated as excellent, and the SiOFH film formed under the conditions of 2F was evaluated as good. These results suggest that the samples formed under these conditions are sufficiently durable to thermal stress. The reason why the sample of conditions 2F was evaluated as good is probably that the mechanical strength thereof was reduced due to the high porosity thereof.
The sample of 2E, whose porosity was 65%, was evaluated as excellent. This is because the mechanical strength thereof was higher than that of the SiOCH film (1E) in Example 1 having the same porosity. In view of mechanism for increasing the mechanical strength of the heat accumulation layer, it is assumed that the film density (density of the entirety of the film except pores) of the SiOFH film is increased to more than that of the SiOCH film having Si—C bonds by increasing the number of Si—F bonds. Consequently, the mechanical strength of the SiOFH film was increased to more than that of the SiOCH film of Example 1. The comprehensive evaluations were excellent for 2B to 2E shown in Table 2, and good for 2A and 2F shown in Table 2.
These results suggest that the SiOFH films of the present Example containing a cyclic siloxane are porous, and have lower thermal conductivities and higher durabilities to thermal stress than heat accumulation layers of SiO formed by a known CVD process. The results also show that the desirable porosity of the SiOFH film is in the range of 30% to 65%. In the present Example, hence, it is desirable that tetrafluorosilane, hydrogen gas and oxygen gas be used in the proportions in which the flow rates of hydrogen gas and oxygen gas are 50 to 15 sccm and 40 to 12 sccm, respectively, relative to the flow rate of tetrafluorosilane of 50 sccm.
Heat accumulation layers 102 were formed under the deposition conditions of 3A to 3F shown in Table 3 using tetrafluorosilane (SiF4), trimethylsilane (3MS) and oxygen gas as raw material gases instead of those used in Example 1. Each of the resulting heat accumulation layers is assumed to be a porous SiOCHF film having a cyclic siloxane structure expressed by the following formula (E).
In formula (E), X1 and X2 each represent H, F, CH3, or a linkage bound to another cyclic siloxane via —CH2— or —O—. According to observation through a transmission electron microscope, the pore size was in the range of 0.1 nm to 3 nm. The number n of siloxane units in the cyclic skeleton was estimated in the range of 3 to 20 from the pore size. Then, ink jet recording heads were produced in the same process as in Example 1.
The ink jet recording head substrates and ink jet recording heads produced in the above process were subjected to measurements for the porosity and thermal conductivity of the heat accumulation layer 102 in the same manner as in Example 1, and the heat accumulation layer was comprehensively evaluated together with the durability to thermal stress. The results are shown in Table 3.
In terms of durability to thermal stress, the SiOCHF films formed under the conditions of 3A to 3E were evaluated as excellent, and the SiOCHF film formed under the conditions of 3F was evaluated as good. These results suggest that the samples formed under these conditions are sufficiently durable to thermal stress. The reason why the sample of conditions 3F was evaluated as good is probably that the mechanical strength thereof was reduced due to the high porosity thereof.
The sample of 3E, whose porosity was 65%, was evaluated as excellent. This is because the mechanical strength thereof was higher than that of the SiOCH film (1E) in Example 1 having the same porosity. As with Example 2, the increase in mechanical strength of the SiOCHF film results from the addition of F.
The comprehensive evaluations were excellent for 3B to 3E, and good for 3A and 3F. These results suggest that the SiOCHF films of the present Example have lower thermal conductivities and higher durabilities to thermal stress than heat accumulation layers of SiO formed by a known CVD process. The SiOCHF film formed in the present Example exhibits good performance when the porosity is in the range 30% to 65%.
Heat accumulation layers 102 were formed to a thickness in the range of 0.5 μm to 2 μm under the deposition conditions of 4A to 4F shown in Table 4 using trimethylsilane (3MS), nitrogen trifluoride (NF3) and oxygen gas as raw material gases instead of those used in Example 1. Each of the resulting heat accumulation layers is assumed to be a porous SiOCHNF film having a cyclic siloxane structure expressed by the following formula (F).
In formula (F), Y1 and Y2 each represent H, F, CH3, NH2, NHF or NF2, or a linkage bound to another cyclic siloxane via —CH2—NH—, —NF— or —O—. Z Represents O, NH or NF, and at least one of Z′s in the skeleton is O. The pore size was 0.1 nm to 3 nm, and the number n of the siloxane units was 3 to 20. Then, the ink jet recording heads were produced in the same process as in Example 1.
The ink jet recording head substrates and ink jet recording heads produced in the above process were subjected to measurements for the porosity and thermal conductivity of the heat accumulation layer 102 in the same manner as in Example 1, and the heat accumulation layer was comprehensively evaluated together with the durability to thermal stress. The results are shown in Table 4.
In terms of durability to thermal stress, the SiOCHNF films formed under the conditions of 4A to 4E were evaluated as excellent, and the SiOCHNF film formed under the conditions of 4F was evaluated as good. These results suggest that the samples formed these conditions are sufficiently durable to thermal stress. The reason why the sample of conditions 4F was evaluated as good is probably that the mechanical strength thereof was reduced due to the high porosity thereof.
The sample of 4E, whose porosity was 65%, was evaluated as excellent. This is because the mechanical strength thereof was higher than that of the SiOCH film (1E) in Example 1 having the same porosity. In the mechanism for increasing the mechanical strength of the SiOCHNF film, the number of Si—F or Si—N bonds is increased and some of the —Si—O— units are substituted with —Si—N—, by adding N and F to the film. The film density (density of the entirety of the film except pores) of the SiOCHNF film is thus increased, and consequently, the mechanical strength thereof is increased to more than that of the films to which N and F are not added.
The comprehensive evaluations were excellent for 4B to 4E, and good for 4A and 4F. These results suggest that the SiOCHNF films of the present Example have lower thermal conductivities and higher durabilities to thermal stress than heat accumulation layers of SiO formed by a known CVD process. The SiOCHNF film formed in the present Example exhibits good performance when the porosity is in the range 30% to 65%.
A process will now be described for manufacturing an ink jet recording head substrate according to another embodiment.
A heat accumulation layer 102 was formed of a porous cyclic siloxane film on the base substrate 101 in the same manner as in Examples 1 to 4 (
Then, the heating resistor layer 104, the wiring layer 105, the insulating protective layer 106 and the liquid flow channel member 120 for the liquid flow channel 116 were further formed over the pore-sealing film 103 in the same manner as in Example 1, and a through hole was formed for the ink supply port 107 (
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-140397, filed Jul. 8, 2014, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-140397 | Jul 2014 | JP | national |
