Patent Application
20160009090
1. Field of the Invention
The present invention relates to an inkjet printhead substrate for making a record on a record medium by ejecting ink by an inkjet process, a method of manufacturing the inkjet printhead substrate, and an inkjet printhead including the inkjet printhead substrate.
2. Description of the Related Art
In recent years, thermal inkjet printheads which can be driven with low power consumption and which have high reliability have been demanded. A thermal inkjet printhead (hereinafter also simply referred to as “inkjet printhead”) is mainly composed of a device substrate for printheads and a channel-forming member having an ink chamber and ink ejection ports communicating with the ink chamber. The device substrate is provided with a heat-generating resistor (electrothermal transducing portion) generating heat that is energy for bubbling ink to eject ink. The heat-generating resistor is provided with a protective layer for avoiding the contact with ink. An insulating layer is placed between the heat-generating resistor and a semiconductor substrate such as a silicon substrate. Reducing the thermal conductivity of the insulating layer, which is placed between the heat-generating resistor and the semiconductor substrate, is effective in driving the inkjet printhead with low power consumption. Hitherto, an insulating layer on a semiconductor substrate has been made of silicon oxide (hereinafter referred to as SiO). SiO has a thermal conductivity of 1.3 Wm−1K−1 and therefore cannot sufficiently prevent heat from escaping into the semiconductor substrate. This has hindered the reduction of power consumption. Therefore, an insulating layer with a thermal conductivity less than the thermal conductivity of SiO, that is, a heat storage layer is demanded.
When the thermal conductivity of the heat storage layer is low, heat generated from a heat-generating resistor is unlikely to escape toward a substrate through the heat storage layer, the temperature of a heat application portion which is placed on the heat-generating resistor and which is contacted with ink rises efficiently, and input energy necessary to bubble ink is small. As a result, a printhead capable of being driven with low power consumption can be obtained.
The present invention provides an inkjet printhead substrate including a base plate, a heat storage layer placed on the base plate, a heat-generating resistive layer which is placed on the heat storage layer and which includes an electrothermal transducing portion, a wiring layer electrically connected to the heat-generating resistive layer, and an insulating protective layer covering the heat-generating resistive layer and the wiring layer. The heat storage layer includes a porous cyclic silazane film formed by a vapor phase process.
The present invention provides a method of manufacturing an inkjet printhead substrate. The method includes a step of forming a heat storage layer on a base plate, a step of forming a heat-generating resistive layer including an electrothermal transducing portion on the heat storage layer, a step of forming a wiring layer electrically connected to the heat-generating resistive layer, and a step of forming an insulating protective layer covering the heat-generating resistive layer and the wiring layer. The step of forming the heat storage layer includes a sub-step of forming a porous cyclic silazane film by a vapor phase process.
Furthermore, the present invention provides an inkjet printhead including the above inkjet printhead substrate and a channel-forming member which has an ink ejection port located at a position corresponding to the heat application portion and which forms a liquid channel that extends from an ink supply port, extending through the inkjet printhead substrate, to the ink ejection port through the heat application portion.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The aerogel making up the heat storage layer 32 described in Patent Document is prepared by a sol-gel process in such a manner that a material solution is subjected to a chemical reaction such as hydrolysis or polycondensation. Thereafter, the following process is used: a process in which the aerogel is applied to a substrate and is then densified in such a manner that a remaining solvent is removed by heat treatment.
However, in the above process, it is difficult to completely remove the solvent by heat treatment; hence, the solvent may possibly remain. Driving the printhead heats the heat storage layer 32 to high temperature and therefore the solvent remaining in the heat storage layer 32 may possibly be gasified. The heat storage layer 32 is expanded by the gasification of the remaining solvent and is contracted by degassing. The repetition of such expansion and contraction cracks the heat storage layer 32, whereby the heat-generating resistive layer 26, which is placed on the heat storage layer 32, is also cracked. Hence, the printhead may possibly become non-functional because of disconnection.
It is an object of the present invention to provide an inkjet printhead which can be driven with low power consumption and which has high reliability.
Embodiments of the present invention will now be described with reference to the attached drawings.
Referring to
A channel-forming member 120 is placed on an inkjet printhead substrate 100 having the above configuration. The channel-forming member 120 has ink ejection ports 121 located at positions corresponding to the heat application portions 117 and forms a liquid channel 116 which extends from an ink supply port 107, extending through the inkjet printhead substrate 100, to the ink ejection ports 121 through the heat application portions 117. The inkjet printhead 1 includes the inkjet printhead substrate 100 and the channel-forming member 120.
The heat storage layer 102 includes the cyclic silazane film. The cyclic silazane film is formed by, for example, a vapor phase process such as a plasma-enhanced chemical vapor deposition (PECVD) process. The heat storage layer 102 may include an insulating layer, made of SiO or SiN, lying on the base plate 101. In descriptions below, the cyclic silazane film is referred to as the heat storage layer 102 in some cases.
The PECVD process is described below with reference to
In the present invention, the heat storage layer 102 is formed using a process gas (source gas) capable of forming the cyclic silazane film. Gas which is a material for forming the skeleton of cyclic silazane is introduced into the PECVD chamber shown in
The term “cyclic silazane” as used herein is a collective term for compounds with a cyclic skeleton having a silazane unit represented by the formula —(Si—N)n—, where n is an integer. The compounds may have a monocyclic structure or a polycyclic structure. The cyclic silazane film is made of a material containing a plurality of such cyclic skeletons. Herein, the bond number n of silazane units forming a cyclic skeleton is preferably 3 to 20. This is because when the bond number n is less than 3, it is difficult to form the cyclic skeleton and when the bond number n is more than 20, the mechanical strength is low and the durability to thermal stress or the like is deteriorated. The bond number n is not limited to 1. Various bond numbers n of cyclic structures may be contained.
A mixture of a silicon compound capable of supplying Si and an amine compound capable of supplying N can be used a process gas capable of forming cyclic silazane. An aminosilane compound containing both Si and N may be used. Furthermore, a compound with a cyclic silazane structure can be used a process gas. In this case, the bond number n of the silazane units can be adjusted in the stage of raw materials.
The porous cyclic silazane film, which is formed by the vapor phase process, preferably has a pore size of 0.1 nm to 3 nm. The pore size varies depending on the bond number n of the silazane units forming the cyclic skeleton or the length of linking groups linking cyclic skeletons and can be adjusted by selecting raw materials or deposition conditions in the case of using the vapor phase process.
In the vapor phase process, the composition and porosity of the cyclic silazane film vary depending on deposition conditions such as the type and flow rate of a process gas and deposition temperature. The change in porosity of the cyclic silazane film affects properties thereof. As the porosity is high, the thermal conductivity is low. As the porosity is low, the durability to thermal stress is high. That is, the thermal conductivity and the durability to thermal stress are in a trade-off relationship. In the present invention, in order to well balance the thermal conductivity and the durability to thermal stress, the porosity is preferably adjusted within a predetermined range. The porosity can be selected from the range of 20% to 70%. In particular, the porosity preferably ranges from 30% to 60%. The porosity can be adjusted by heat treatment after the cyclic silazane film is formed. The cyclic silazane film preferably has a thickness of 50 nm to 5,000 nm and more preferably 100 nm to 3,000 nm.
In the case of forming the heat-generating resistive layers 104 and the wiring layer 105 on the porous cyclic silazane film (heat storage layer 102) as described above, the flatness of the cyclic silazane film may possibly decrease depending on the size of pores in the cyclic silazane film or the thermal conductivity of the heat storage layer 102 may possibly increase because a material with high thermal conductivity enters the pores. Therefore, it is preferred that the flatness of the heat storage layer 102 is ensured and pore-sealing treatment for preventing a foreign substance from entering the pores is performed by sealing surface pores. The pore-sealing treatment is performed in such a manner that an insulating layer (also referred to as “pore-sealing film 103”) such as an SiO film or a silicon nitride (SiN) film is formed on the cyclic silazane film (heat storage layer 102) as shown in
The present invention is further described below in detail with reference to examples. The present invention is not limited to the examples. Modifications can be made within the scope of the present invention.
Exemplary steps of manufacturing an inkjet printhead substrate and inkjet printhead according to an embodiment of the present invention are described below.
The manufacturing steps are performed for each base plate 101 made of Si or a substrate including driving elements, fabricated in advance, including semiconductor elements such as switching transistors, for selectively driving electrothermal transducing portions 108. However, for the sake of convenience, the base plate 101, which is made of Si, is shown in figures below (
A heat storage layer 102 made of cyclic silazane was formed on the base plate 101 by a vapor phase process under Deposition Conditions A, B, C, D, or E shown in Table so as to have a thickness of 0.5 μm to 2.0 μm as shown in
This compound is a known compound with CAS No. 5505-72-6 and is commercially available.
In cyclic silazane formed from the compound represented by Formula (A), for example, vinyl groups are radially polymerized to form a structure represented by the following formula:
The structure represented by Formula (B) contains methyl groups bonded to Si atoms and methylene chains linking the Si atoms. The methylene chains, which link the Si atoms, are not necessarily only butylene groups formed by the polymerization of vinyl groups but also may possibly be ethylene or propylene groups formed by the elimination of some of methylene groups in plasma. As shown in Table below, as the deposition temperature is high, this tendency is significant and the pore size is small. Therefore, the porosity may probably be low. In the present invention, a cyclic silazane structure containing an alkyl group such as a methyl group in the form of a side chain and a methylene chain in the form of a linking group, that is, cyclic silazane containing a side chain and/or a linking group containing a carbon atom is denoted as SiCN. In a cyclic skeleton represented by the formula —(Si—N)n—, the bond number represented by n is 3 in the case of the structure represented by Formula (B). A plurality of cyclic skeletons in which n is 3 are linked through linking groups to form macrocyclic structures. The macrocyclic structures become large-sized pores.
The heat storage layer 102 formed as described above was porous and had a pore size of 0.1 nm to 3 nm.
Next, heat-generating resistive layers 104 made of TaSiN or the like were formed on the heat storage layer 102 by reactive sputtering so as to have a thickness of about 50 nm. Furthermore, an Al layer for forming a wiring layer 105 was formed over the heat-generating resistive layers 104 so as to have a thickness of about 285 nm. The heat-generating resistive layers 104 and the wiring layer 105 were dry-etched together by photolithography. In this example, dry etching used was reactive ion etching (RIE).
Next, in order to form electrothermal transducing portions 108, the wiring layer 105 was partly etched off by photolithography again as shown in
Thereafter, an insulating protective layer 106 made of SiN was formed by a PECVD process as shown in
Next, a channel-forming member 120 forming a liquid channel 116 was formed on the inkjet printhead substrate 100 as shown in
The porosity of the heat storage layer 102, made of porous SiCN, formed on the base plate 101 under Deposition Conditions A, B, C, D, or E in a step shown in
The inkjet printhead 1, which was formed through the above steps, was evaluated for durability to thermal stress using destructive pulses in such a manner that the electrothermal transducing portions 108 were driven under conditions below.
Driving frequency: 10 kHz
Driving pulse width: 2 μs
Driving voltage: 1.3 times the bubbling voltage required to eject ink.
Herein, the durability to thermal stress was rated in accordance with judgmental standards below.
A: One durable to 5.0×109 or more pulses.
B: One broken by 3.0×109 pulses to less than 5.0×109 pulses.
C: One broken by less than 3.0×109 pulses.
Furthermore, the thermal conductivity and the durability to thermal stress were comprehensively rated in accordance with judgmental standards below.
A: One which has a thermal conductivity of less than 1.00 Wm−1K−1 and which is durable to 5.0×109 or more pulses as determined by the evaluation of durability to thermal stress.
B: One which has a thermal conductivity of less than 1.00 Wm−1K−1 and which is broken by 3.0×109 pulses to less than 5.0×109 pulses or one which has a thermal conductivity of 1.00 Wm−1K−1 1.30 Wm−1K−1 and which is durable to 5.0×109 or more pulses as determined by the evaluation of durability to thermal stress.
C: One other than the above.
The above results are summarized in Table. For comparison, the following films were also rated: an SiO film prepared by a sol-gel process described in Patent Document and a conventional SiO film prepared by a thermal CVD process using silane and oxygen.
In the evaluation of durability to thermal stress, the cyclic silazane films each prepared under Deposition Conditions A, B, C, or D were rated A and the cyclic silazane film prepared under Deposition Conditions E was rated B as shown in Table. These results show that the cyclic silazane films are sufficiently durable to thermal stress under all conditions. The reason why the cyclic silazane film prepared under Deposition Conditions E was rated B is probably due to the fact that the porosity thereof is high and therefore the mechanical strength thereof is low. The SiO film prepared by the sol-gel process described in Patent Document was rated C. This is probably due to the fact that heat-generating resistive layers were cracked because the SiO film was expanded and contracted by the gasification of a solvent remaining in the SiO film.
In the comprehensive rating of thermal conductivity and durability to thermal stress, the cyclic silazane films each prepared under Deposition Conditions B, C, or D were rated A and the cyclic silazane films each prepared under Deposition Conditions A or E were rated B.
The above results show that the cyclic silazane films prepared in this example are porous, are lower in thermal conductivity than the conventional SiO film prepared by the thermal CVD process, and are sufficiently durable to thermal stress. Results of the comprehensive rating show that the cyclic silazane films preferably have a porosity of 30% to 60%. That is, in the case of using the compound represented by Formula (A), the deposition temperature preferably ranges from 100° C. to 300° C. A heat storage layer according to the present invention is formed by a PECVD process that is a vapor phase process. Therefore, unlike a sol-gel process, a film contains no residual solvent. Hence, in the case of driving an inkjet printhead, concerns about degassing are little and the heat storage layer is unlikely to be expanded or contracted. Thus, the following problem is slight: a problem that a heat-generating resistor on the heat storage layer is cracked and is broken.
As described above, an inkjet printhead substrate which can be driven with low power consumption and which has high reliability is provided.
Exemplary steps of manufacturing an inkjet printhead substrate according to another embodiment of the present invention are described below.
First, as shown in
Furthermore, as shown in
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. 2014-142363, filed Jul. 10, 2014, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-142363 | Jul 2014 | JP | national |
