Patent Application
20250144935
The present disclosure relates to an actuator, a liquid discharge head, and a production method of the actuator.
A piezoelectric film, which changes its shape by an electric field being applied thereto, is applied to various industrial products as a means for moving or vibrating an object minutely and accurately. For example, the piezoelectric film is used for a small-size speaker, a hard disk drive, a printer (liquid discharge apparatus), or the like. In these apparatuses, there are some printers that employ a piezoelectric film as a driving element of a liquid discharge head that discharges liquid. In such a liquid discharge head, the piezoelectric film is driven to discharge liquid, by applying an electric field via electrodes (upper electrode and lower electrode) formed to sandwich the piezoelectric film from above and below. At this time, a voltage required for sufficiently displacing the piezoelectric film is several tens of volts, which is relatively high for a semiconductor device. On the other hand, the discharge port density of the liquid discharge head becomes higher to print a high-resolution image, and wiring lines and electrodes having different potentials are arranged densely on a substrate including a driving element.
The liquid discharge head including the actuator having such a piezoelectric film may be prone to failure caused by a short-circuit between wiring lines or between a wiring line and a lower electrode due to a creepage effect on the device surface, or a wiring line corrosion. For this reason, sufficiently covering the wiring lines with an insulation layer (passivation film) is important, but covering the step portions of side surfaces of the wiring lines resulting from the thicknesses of the wiring lines without the insulation layer being cracked is not easy. One solution for this issue is that the film thickness of the insulation layer may be simply increased. However, increasing the thickness of the layer sometimes causes a distortion of the substrate (wafer) due to a film stress, or an unnecessarily longer processing time when etching the insulation layer thereafter, which is not desirable.
For the above issue, Japanese Patent Application Laid-open No. 2005-032919 discusses a configuration for improving the coverage property of the insulation layer on the wiring lines in a semiconductor device including a semiconductor film and wiring lines on a substrate. The coverage property of the insulation layer contacting and covering the wiring lines is improved by providing cross-sectional shape tapers to the wiring lines. In Japanese Patent Application Laid-open No. 2005-032919, the taper shape is obtained by providing a multilayer structure to the wiring line, and changing the processing conditions of etching. Thus, a film deposition apparatus and a plurality of materials for forming a plurality of layers are required, and also the management of a forming process for each layer becomes necessary. Further, there may be a case where the degree of freedom of materials that can be used to compose the wiring lines reduces. It is because a material that can form a desired taper shape while satisfying conditions such as adhesiveness with an underlaying film on which the wiring lines are formed, easiness of etching, electric resistivity, atomic diffusion rate to a film in contact with the wiring lines, and the like, needs to be selected.
Another method for forming cross-sectional taper shapes of the wiring lines is a method of providing taper shapes to the ends of the resist film used when the wiring lines are etched, and transferring the shapes to the etched portions. However, to achieve the desired shapes of the taper portions of the resist film, the materials for the resist film is limited and the management of a process becomes complicated when patterning the resist film, which may become factors of reducing the yield. Examples of the process management factors when patterning the resist film include an exposure amount of light irradiation, a temperature, an exposure time, a flow control of exhaust air and air in an exposure apparatus.
As described above, with the method of providing tapers to the cross-section shapes of the wiring lines to increase the covering property of the insulation layer that contacts and covers the wiring lines, there is an issue in selectivity of the material, and that the process control tends to become complicated.
The present disclosure is directed to a piezoelectric actuator with a wiring line therein sufficiently covered by an insulation layer, and having a high electric reliability.
According to some embodiments, an actuator includes a piezoelectric element including a first electrode, a piezoelectric layer, and a second electrode on a substrate in this order, a wiring line electrically connected to at least one of the first electrode and the second electrode, and an insulation layer arranged to contact and cover the wiring line, wherein a thickness of the wiring line is less than a thickness of the insulation layer in a direction perpendicular to the substrate, and the thickness of the insulation layer is 500 nm or less.
Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Various exemplary embodiments, features, and aspects of the present disclosure will be described with reference to the attached drawings. The components having the same functions are assigned the same symbols, and redundant descriptions thereof may sometimes be omitted. Hereinbelow, examples of applying the present disclosure to a piezoelectric actuator used in a liquid discharge head provided in a liquid discharge apparatus serving as an inkjet printer will be described. However, the present disclosure is not limited to the exemplary embodiments described below, and can be changed within the range which those skilled in the art can conceive and achieve, such as other exemplary embodiments, additions, modifications, and removals. Any of the embodiments should be included in the range of the present disclosure, as long as the embodiment achieves an action and an effect of the present disclosure.
In addition, as described above, each of the liquid discharge heads 4 according to the present exemplary embodiment is the one-pass type head having a length corresponding to a width (size in a direction orthogonal to a conveyance direction of the recording medium 1) of the recording medium 1, which is so-called a page-wide type head. However, the present disclosure can be applied to a liquid discharge head, so-called serial type liquid discharge head, that performs recording while scanning the liquid discharge head across a recording medium. Examples of the serial type liquid discharge head include a liquid discharge head having a configuration with an element substrate for black ink and an element substrate for color ink mounted thereon. Examples other than that include a liquid discharge head having a configuration with a width shorter than the recording medium 1, in which several element substrates are arranged so that discharge ports overlap each other in a discharge port array direction.
As illustrated in
The flow path substrate 11 includes a supply port 15 for supplying liquid to be discharged from the discharge port 19 to a pressure chamber 17, and an outlet port 16 for flowing out liquid from the pressure chamber 17. In this way, the element substrate 10 is configured so as to be able to circulate liquid between the inside and the outside of the pressure chamber 17. In addition, the piezoelectric actuator according to the present disclosure can be suitably applied even to a liquid discharge head having no circulation flow path configuration with no outlet port 16 in the flow path substrate 11. Further, the liquid discharge head 4 may be configured so as to supply liquid from both the supply port 15 and the outlet port 16 in
The actuator substrate 12 is joined to the flow path substrate 11. The actuator substrate 12 includes a substrate (substrate 100, see
The pressure chamber substrate 13 is joined to a surface of the actuator substrate 12 opposite to the surface to which the flow path substrate 11 is joined. The pressure chamber 17 is provided in the pressure chamber substrate 13 so as to correspond to the piezoelectric element 110. Similar to the flow path substrate 11, any material and any production method may be used to form the pressure chamber substrate 13 according to the present exemplary embodiment by, for example, etching the silicon substrate.
The discharge port substrate 14 is joined to a surface of the pressure chamber substrate 13 opposite to the actuator substrate 12. The discharge port 19 is provided in the discharge port substrate 14. In the liquid discharge unit 7, liquid is supplied from the supply port 15 to the pressure chamber 17, and discharged from the discharge port 19 by driving of the piezoelectric element 110 to deform the actuator substrate 12.
In addition, a protection layer may be provided so as to cover an inner wall of a liquid flow path communicating from the supply port 15 to the pressure chamber 17, the discharge ports 19, and the outlet port 16. An effect of improving a long-term reliability of the liquid discharge unit 7 can be obtained by forming, on the inner wall of the liquid flow path, the protection layer using a material having a resistance to the discharging liquid higher than the silicon configuring the flow path substrate 11, the pressure chamber substrate 13, and the like.
In a case where the flow path substrate 11 and the pressure chamber substrate 13 are configured of silicon substrates, for example, silicon dioxide (SiO2), silicon carbide (SiC), aluminum oxide (Al2O3), hafnium oxide (HfO2), tantalum oxide (TaO), and diamond-like carbon (DLC) can be used for the protection layer.
Next, the actuator substrate 12 serving as the piezoelectric actuator will be described in detail. Note that components described in the following exemplary embodiments are merely examples, and the components are not intended to limit the range of the present disclosure only thereto.
In the liquid discharge head 4, in many cases, a configuration in which a plurality of the piezoelectric elements 110 is arranged is employed. Further, to achieve a high-resolution printing, the piezoelectric elements 110 are arranged on a substrate at high density.
An upper wiring line (second wiring line) 140 and a lower wiring line (first wiring line) 150 are connected to each of the piezoelectric elements 110, and a pad 170 and a pad 180 for applying a voltage to each of the piezoelectric elements 110 are connected thereto. In addition, the pads 170 and 180 in the present disclosure are electrically connected to the respective wiring lines (upper wiring line 140 and lower wiring line 150), are areas with their surfaces not covered by a passivation film described below, and are portions to be connected with an electric wiring substrate such as a flexible printed circuit (FPC) substrate outside the piezoelectric actuator, with wiring lines or the like.
The liquid discharge head 4 includes the pressure chamber 17 (see
The substrate 100 desirably has a flat surface, and its material can be appropriately selected. For example, materials such as silicon, silicon carbide, quartz, gallium nitride, gallium arsenide, indium phosphide, and sapphire can be suitably used. To easily form the pressure chamber 17, a Silicon On Insulator (SOI) substrate can be used as a substrate serving as both the substrate 100 and the pressure chamber substrate 13. In general, the SOI substrate has a layered structure in which a silicon oxide layer (BOX layer) is formed on a silicon substrate and a silicon layer is further formed thereon. For example, in the SOI substrate, a thicker silicon substrate can be used as the pressure chamber substrate 13, and a thinner silicon substrate and the BOX layer can be used as the substrate 100. The BOX layer can be formed to have a thickness between several tens of nanometers and several hundreds of micrometers, and the film thickness of the silicon layer on the BOX layer can be selected relatively arbitrarily. Only silicon can be removed by combining these film thicknesses appropriately, and performing selective etching using the BOX layer as an etching stop layer. In the case where the pressure chamber 17 is formed using such etching, since the bottom portion of the pressure chamber 17 is a surface of the BOX layer, an extremely flat bottom portion can be obtained.
In a case where the substrate 100 is formed with a silicon substrate or the like and electrically conductive, it is desirable to provide an insulation layer 101 between the lower electrode 111 and the substrate 100. For example, commonly used insulator materials, such as a silicon oxide film, a silicon nitride film, a silicon acid nitride film, and an aluminum oxide film, can be used for the insulation layer 101.
Since there may be a case where the lower electrode 111 is exposed to high temperatures of several hundred degrees Celsius in a firing process of the piezoelectric layer 112 thereafter, the lower electrode 111 is desirably formed of a material with a high melting temperature. Examples of the material include copper, platinum, gold, chrome, cobalt, titanium, and their alloys. Further, in a case where the piezoelectric layer 112 is formed so as to contact the surface of the lower electrode 111, the lower electrode 111 may also serve as a film for controlling the crystal orientation of the piezoelectric layer 112. In this case, a material having an appropriate crystal structure may be selected for the lower electrode 111. For example, in a case where lead zirconate titanate (PZT) is used for the piezoelectric layer 112, platinum can be used for the lower electrode 111 serving also as the crystal orientation control film. A generally used film formation method such as magnetron sputtering can be used for the platinum film formation, and the film thickness is appropriately adjusted so as to be able to obtain a desired orientation. Further, to increase the adhesiveness between the lower electrode 111 and the insulation layer 101 serving as an underlaying film, a thin film such as a titanium film and a chrome film may be further included as an adhesion layer. In this case, it is desirable to appropriately select a material having an appropriate crystal structure for the adhesion layer so as to be able to obtain a desired crystal orientation of the piezoelectric layer 112.
Further, examples of the material for the piezoelectric layer 112 include an oxidized material containing lithium and niobium or lithium and tantalum as main materials (e.g., lithium niobate or lithium tantalate), an oxidized material containing lead and titanium as main materials (e.g., lead titanate), an oxidized material with zirconium further added thereto (e.g., lead zirconate titanate), an oxidized material containing lead and niobium as main materials, an oxidized material including barium and titanium as main materials (e.g., barium titanate), an inorganic material such as zinc oxide, quartz, and aluminum nitride, and an organic material such as polylactic acid and polyvinylidine fluoride. Among the above-described materials, the lead zirconate titanate (PZT), which is an oxidized material mainly containing lead, zirconium, and titanium as main materials that are high in displacement efficiency, can be suitably used. The thickness of the piezoelectric layer 112 is determined based on a applied voltage to obtain a desired displacement amount and a piezoelectric characteristic, and in general, it is about 1 to 2 micrometers (μm).
The upper electrode 113 is formed on the piezoelectric layer 112, and for example, platinum, titanium, tungsten, and their alloys can be used for the upper electrode 113. Similar to the lower electrode 111, to increase the adhesiveness between the upper electrode 113 and the piezoelectric layer 112, a thin film made of titanium or chrome may be provided between the upper electrode 113 and the piezoelectric layer 112 as an adhesion layer.
In order to apply a desired voltage between the lower electrode 111 and the upper electrode 113 to displace the piezoelectric layer 112, the lower wiring line 150 is electrically connected to the lower electrode 111, and the upper wiring line 140 is electrically connected to the upper electrode 113. In this way, a potential difference based on an electrical signal transmitted from the outside can be applied to the piezoelectric layer 112. The materials forming the upper wiring line 140 and the lower wiring line 150 may be the same, or different. The materials used for the upper wiring line 140 and the lower wiring line 150 only need to be conductive members, but it is desirable to use a material having a low electric resistance to reduce the occurrence possibility of wire breakage caused by the electromigration. Examples of the material include aluminum, copper, and gold. Further, an alloy consisting of two or more materials from these materials may be used. Further, to increase the adhesiveness of the wiring lines, titanium or chrome films may be provided between the lower wiring line 150 and a film contacting the lower wiring line 150, and between the upper wiring line 140 and a film contacting the upper wiring line 140.
In the present exemplary embodiment, a silicon oxide film serving as the insulation layer (second protection layer) 130 is formed between the lower wiring line 150 and the lower electrode 111, between the upper wiring line 140 and the lower electrode 111, and between the upper wiring line 140 and the piezoelectric layer 112. In addition, the silicon oxide film is merely an example, and similar to the insulation layer 101, the material of the insulation layer 130 can be appropriately selected from commonly used insulation materials such as silicon nitride, silicon oxynitride, and aluminum oxide. The insulation layer 130 may be a layered film with two or more kinds of different films layered. To form the insulation layer 130, for example, a commonly used film formation method, such as a chemical vapor deposition (CVD) method or a sputtering method, can be used. In the present exemplary embodiment, the silicon oxide film was formed as the insulation layer 130 using the CVD method because the CVD method is excellent in production rate.
In the piezoelectric element 110 used for the liquid discharge head 4, a relatively large potential difference for a semiconductor device is applied between the upper electrode 113 (upper wiring line 140) and the lower electrode 111 (lower wiring line 150), to sufficiently displace the piezoelectric layer 112. To obtain a sufficient displacement amount, a potential difference of about 30 V or more is applied to the piezoelectric layer 112 in the film thickness direction. In a case where the insulation layer 130 is a silicon oxide film produced using the CVD method, the dielectric breakdown strength is about 7 megavolts per centimeter (MV/cm). Accordingly, for example, to achieve the dielectric strength of 50 V, a failure probability can be reduced by setting the film thickness of the insulation layer 130 to 72 nanometers (nm) or more. Further, the insulation layer 130 plays a role of a moisture prevention film for the lower layer thereof (first protection layer 120 described in detail below). To secure the moisture resistance for the underlaying film of the silicon oxide film, the film thickness is desirably 200 nm or more. On the other hand, if the film is too thick, since the displacement characteristic of the piezoelectric element deteriorates, the film thickness of the insulation layer 130 is desirably 1.5 μm or less. Accordingly, the film thickness of the insulation layer 130 is desirably 200 nm or more and 1.5 μm or less.
Further, to increase the adhesiveness of the insulation layer 130, a titanium or chrome thin film (not illustrated) may be provided between the insulation layer 130 and the upper wiring line 140, and between the insulation layer 130 and the lower wiring line 150.
When the silicon oxide film serving as the insulation layer 130 is formed, there is a possibility that the piezoelectric layer 112 is damaged to deteriorate the piezoelectric characteristic. In response, in the present exemplary embodiment, an aluminum oxide film serving as the first protection layer 120 is formed on the surface of the piezoelectric layer 112, as a protection layer to prevent the damage to the piezoelectric layer 112. On the other hand, the surface of the aluminum oxide film deteriorates when exposed to moisture at high temperature. In a case where a formation process of a contact hole (hereinbelow, also referred to as a lower through-hole) 131 and a contact hole (hereinbelow, also referred to as an upper through-hole) 132 (described below) or a formation process of the upper wiring line 140 and the lower wiring line 150 is performed in a state where the aluminum oxide film is exposed on the outermost surface in the middle of a production process, there may be a case where the surface of the aluminum oxide film is exposed to moisture at a time of cleaning after patterning. There is a case where the surface of the aluminum oxide film deteriorates when the moisture remaining on the surface of the aluminum oxide film becomes high in temperature at a time of etching or ashing. There may be a case where if the deteriorated aluminum oxide film is present on the piezoelectric layer 112, the insulation resistance property may deteriorate, which may cause a failure. For this reason, the silicon oxide film serving as the insulation layer 130 is desirably formed so as to contact and cover the aluminum oxide film serving as the first protection layer 120.
The first protection layer 120 desirably has a bare minimum thickness, from a viewpoint of reducing the influence on the displacement characteristic of the piezoelectric element and the formation of the contact holes 131 and 132. More specifically, the thickness of the first protection layer 120 is desirably 50 nm or less, and more desirably 25 nm or less. Further, for example, to achieve the dielectric strength of 50 V or more, the thickness of the aluminum oxide film serving as the first protection layer 120 is desirably 5 nm or more, in consideration of the step coverage property for the piezoelectric layer 112 having a micrometer order thickness. More specifically, the film thickness of the first protection layer 120 is desirably 5 nm or more and 50 nm or less, and more desirably 5 nm or more and 25 nm or less. Similarly, in a case where an aluminum oxide film is used for the first protection layer 120, an atomic layer deposition (ALD) method is desirably used, from a viewpoint of the step coverage property to the piezoelectric layer 112, e.g., introducing a precursor molecule to the substrate surface, purging an excess precursor, introducing a reactant molecule that reacts with the adsorbed precursor, purging the reaction byproducts, repeating this cycle to build up a layer-by-layer film with precise thickness control, each cycle resulting in the deposition of a single atomic layer.
Further, in the present exemplary embodiment illustrated in
As described above, a relatively high voltage is applied to the piezoelectric actuator used for the liquid discharge head 4 to obtain a sufficient displacement amount to discharge liquid, and in a case where the discharge ports 19 are arranged at high density, the area density of the piezoelectric elements 110 on the element substrate 100 is high. Under these conditions, and in an environment with high humidity caused by the piezoelectric actuator discharging ink, current may flow on the surface of the piezoelectric actuator, which may cause a failure. In the piezoelectric actuator used for the liquid discharge head 4 for discharging liquid such as ink, in particular, the existence of the liquid largely affects the piezoelectric actuator. For this reason, the upper wiring line 140 and the lower wiring line 150 are covered by the insulation layer 160 serving as a passivation film high in moisture resistance and insulation property. A silicon oxide film, a silicon nitride film, a silicon acid nitride film, and the like can be used for the insulation layer 160. In particular, a passivation film containing a silicon nitride film in a part of the film is higher in moisture resistance than the silicon oxide film, and can achieve the sufficient moisture resistance and the insulation property even with a thinner film thickness than the film thickness in the case of forming the passivation film with the silicon oxide film, which gives less bad influence on the displacement characteristic of the piezoelectric actuator, and is desirable. In addition, the insulation layer 160 desirably has a higher moisture resistance than the second protection layer 130. The moisture resistances of the two layers may be compared using a commonly used moisture resistance evaluation method such as a moisture intrusion evaluation.
From a viewpoint of the insulation property, the insulation layer 160 is desirably arranged to cover at least the lower wiring line 150, the upper wiring line 140, and the peripheral edges of the piezoelectric layer 112, viewed from the direction perpendicular to the substrate 100. The insulation layer 160 desirably has a bare minimum thickness, from a viewpoint of reducing the influence on the displacement characteristic of the piezoelectric element 110 and the formation of the contact holes 131 and 132. On the other hand, in the piezoelectric actuator according to the present exemplary embodiment, it is impossible to refill the piezoelectric layer 112 with the insulation layer 160 or the like and flatten the upper and lower wiring lines 140 and 150 formed thereon using a chemical mechanical polishing (CMP) method or the like, to prevent the displacement characteristic from being damaged. Thus, since the shapes of the upper wiring line 140 and the lower wiring line 150 take over the step shapes caused by the piezoelectric element 110, the insulation layer 160 needs to have a film thickness determined in consideration of the step coverage property for the piezoelectric layer 112, and the upper and lower wiring lines 140 and 150. The desirable thickness of the second protection layer 130 excellent in wiring line coverage property will be described below. In addition, to achieve a sufficient insulation resistance property of the piezoelectric actuator to which a high voltage of several tens of volts is applied, the thickness of the insulation layer 160 is desirably 100 nm or more.
In the piezoelectric actuator for the liquid discharge head 4 according to the present exemplary embodiment, as illustrated in
In consideration of the above-described issue, the present disclosing party performed examinations to make the film thickness of the wiring line thin. First, when a voltage of an effective value 40 V and frequency 100 kilohertz (kHz) was applied to an element having an effective electrode area of about 0.05 mm2, which was an area at which the upper electrode and the lower electrode overlap, viewed from the direction perpendicular to the substrate surface, the current flowing through the wiring line was less than 1 microamps (μA). Based on this value, as a result of producing wiring lines with several different cross-sectional areas and performing durability tests, it was found that the wiring line had an enough lifetime when the cross-sectional area of the wiring line had 165 nm2 or more. Accordingly, the cross-sectional area at a position at which the cross-sectional area of the wiring line on a surface perpendicular to the substrate surface is smallest, which is normally a cross-sectional area in a width direction of the wiring line, was desirably 165 nm2 or more. When the cross-sectional area of the wiring line was less than 165 nm2, a wire breakage that may be due to an electromigration was found. Accordingly, it was found that even if the wiring lines (upper wiring line 140 and lower wiring line 150) were made thin to a film thickness that can maintain the film shape, i.e., to a degree not to become an island-like shape, the piezoelectric actuator was usable as a piezoelectric actuator.
Since the film thickness of the wiring line not to become the island-like shape depends on the material of the film in contact with the wiring line from a bottom side, and the film formation method, in a case where the film thickness of the wiring line is desired to be thin as much as possible, it is desirable to check the thickness of the wiring line after the process is completed.
Further, as for the upper limit of the film thickness of the wiring line, the thickness of the wiring line was made thinner than that of the insulation layer 160, and it was found that the wiring line was able to be easily and sufficiently covered by the insulation layer 160, in particular by making the thickness of the wiring line 200 nm or less, more desirably 100 nm.
Based on the above-described results, the piezoelectric actuator according to the present exemplary embodiment has a silicon nitride film with a thickness of 200 nm as the insulation layer 160 so as to be able to sufficiently cover the piezoelectric layer 112 with a thickness of 2 μm, and the lower wiring line 150 and the upper wiring line 140 with a thickness of 100 nm, as an example.
The film thicknesses of the wiring lines (upper wiring line 140 and lower wiring line 150) and the insulation layer 160 are approximately the same in an area formed on a uniformly flat plane surface.
Further, the film thickness of the wiring line (upper wiring line 140 or lower wiring line 150) is desirably thinner than that of the insulation layer 160 in the direction perpendicular to the substrate 100 at any position in the piezoelectric actuator so that the insulation layer 160 has an enough coverage property even in a configuration in which the film thickness of the wiring line is not uniform depending on the position, such as a case where the wiring line is formed along an edge surface of the piezoelectric layer 112. In addition, in a case where the insulation layer 160 has a layered structure consisting of a plurality of layers, the total thickness of all the plurality of stacked layers may be regarded as the thickness of the insulation layer 160.
With reference to
Subsequently, as illustrated in
The lower electrode 111 can be formed using, for example, a sputtering method. In addition, in a case where the piezoelectric layer 112 is made of lead zirconate titanate (PZT), platinum is desirably used for the lower electrode 111 serving also as a crystal orientation control film. In the present exemplary embodiment, a platinum film with a film thickness of about 100 nm is formed, as an example. A titanium or chrome thin film may be formed as an adhesion layer to increase an adhesive force between the lower electrode 111 and the insulation layer 101.
The piezoelectric layer 112 is formed by applying a starting material such as sol-gel liquid on the lower electrode 111 and firing it to have a desired crystal orientation, using a sol-gel method. In the present exemplary embodiment, a PZT film with a film thickness of 2 μm is formed, as an example.
Subsequently, the upper electrode 113 is formed using a sputtering method or the like. In the present exemplary embodiment, for example, a titanium and tungsten alloy film with a film thickness of about 100 nm is formed.
Subsequently, after forming a resist pattern (not illustrated) in such a manner that the upper electrode 113 and the piezoelectric layer 112 have a desired pattern by a photolithography method, the upper electrode 113 and the piezoelectric layer 112 are patterned as illustrated in
Subsequently, after forming a resist pattern (not illustrated) in such a manner that the lower electrode 111 has a desired pattern using a photolithography method, the lower electrode 111 is patterned as illustrated in
Subsequently, as illustrated in
Subsequently, as illustrated in
Next, as illustrated in
Subsequently, the upper and lower wiring lines 140 and 150 are formed using a commonly used semiconductor process. A wiring line layer to become the upper wiring line 140 and the lower wiring line 150 is formed on the insulation layer 130 using a sputtering method. In the present exemplary embodiment, a titanium film (not illustrated) serving as an adhesive layer is formed on the surface of the insulation layer 130 using sputtering or vapor-deposition, and an aluminum and copper alloy film serving as the wiring line layer is formed on the titanium film. Then, the titanium film and the wiring line layer are patterned by a photolithography method that uses a resist pattern, to form the upper wiring line 140 and the lower wiring line 150 as illustrated in
Subsequently, as illustrated in
Then, the pressure chamber substrate 13 and the discharge port substrate 14 respectively including the pressure chamber 17 and the discharge port 19, and the flow path substrate 11 including the flow path for supplying liquid to the pressure chamber 17 are prepared and joined with the actuator substrate 12 to form the liquid discharge head (see
In the following exemplary embodiments, different points from the above-described first exemplary embodiment will be mainly described, and descriptions of configurations similar to those described above are omitted.
In a second exemplary embodiment, the thicknesses of the wiring lines are further thinner than those in the first exemplary embodiment. The thicknesses of the upper wiring line 140 and the lower wiring line 150 are determined to be 5 nm, and other configurations are determined to be the same as those of the first exemplary embodiment. By making the film thicknesses of the wiring lines extremely thin, the coverage property by the insulation layer 160 further increases. However, in a case where the film thickness of the piezoelectric layer 112 is thick, a part of the upper wiring line 140 formed along the edge surface of the piezoelectric layer 112 may be affected by the unevenness of the edge surface of the piezoelectric layer 112, to be broken.
In the present exemplary embodiment, an ALD method is used to form a wiring line film to be the upper and lower wiring lines 140 and 150, as a method to prevent the breakage of the thin upper wiring line 140. In this case, as a material of the wiring lines, any material is usable as long as the upper and lower wiring lines 140 and 150 can be formed using the ALD method. The upper wiring line 140 and the lower wiring line 150, which are a wiring line layer in the present exemplary embodiment, are made of copper with a film thickness of 5 nm, as an example. For the wiring line with an extremely thin film thickness, a layered film including a plurality of stacked layers may be usable. For example, using a layered film formed by continuously stacking a 3 nm titanium film and a 2 nm tungsten film as the upper wiring line 140 and the lower wiring line 150 may be conceivable.
The piezoelectric element 110 in the present disclosure has a piezoelectric layer 112 sandwiched by two electrodes (lower electrode 111 and upper electrode 113), but in this configuration, the lower and upper electrodes 111 and 113 and the piezoelectric layer 112 have a thin film form in many cases. In addition, the film thicknesses thereof are almost uniform, and the lower and upper electrodes 111 and 113 and the piezoelectric layer 112 are made to be desired sizes by an etching process or the like. Accordingly, the edge surfaces thereof each become an approximately perpendicular surface to the surface of the film. Further, in a case where the upper wiring line 140 and the lower wiring line 150 are located at a same position in the direction perpendicular to the substrate 100 as illustrated in
Accordingly, the pad 170 connected to the upper wiring line 140 is formed vertically above the piezoelectric layer 112 in the direction perpendicular to the substrate 100. In addition, the pad 170 is desirably formed at a position at which the piezoelectric layer 112 is difficult to deform, i.e., at a position not overlapping the pressure chamber 17 in the direction perpendicular to the surface of the substrate 100. In addition, the pad 170 is desirably arranged not to intersect with the edge surface 112b of the piezoelectric layer 112 in the direction perpendicular to the surface of the substrate 100, and the shape of the piezoelectric layer 112 may be appropriately adjusted based on the shapes and arrangements of the upper wiring line 140 and the pad 170.
Further, in a case where a plurality of the piezoelectric elements 110 is arranged in a piezoelectric actuator, the piezoelectric layers 112 of two or more of the piezoelectric elements 110 may be connected in part. In other words, in the two or more of the piezoelectric elements 110, the piezoelectric layers 112 may be integrally formed, and the lower electrode 111 and the upper electrode 113 may be provided for each of the piezoelectric elements 110.
In addition, since the lower wiring line 150 electrically connected to the lower electrode 111 is never formed along the edge surface 112b of the piezoelectric layer 112, and even if formed using a film formation method such as sputtering or vapor-deposition, the possibility that the film thickness thereof becomes extremely thin to cause the breakage of the line is not high. In
With reference to
When the piezoelectric actuator according to the present exemplary embodiment is produced, in the process of forming the upper through-hole 132 and the lower through-hole 131 illustrated in
Further, as illustrated in
The present disclosure will be described in more detail using a practical example and a comparison example, but the present disclosure is not limited by the following examples, within the gist of the present disclosure.
The piezoelectric actuator having the configuration illustrated in
A silicon substrate was used for the substrate 100, a 500 nm thick silicon thermal oxide film was used for the insulation layer 101, a 100 nm thick platinum film was used for the lower electrode 111, a 2 μm thick PZT was used for the piezoelectric layer 112, and a 100 nm thick titanium and tungsten alloy was used for the upper electrode 113. An aluminum and copper alloy film was used for the upper wiring line 140 and the lower wiring line 150, and its thickness was 30 nm, its width (length in shorter side direction) was 5 μm, and its cross-sectional area in the shorter side direction was 150,000 nm2. In addition, a titanium adhesion film was formed on a surface of the insulation layer 130 opposite to the substrate 100. A 200 nm thick silicon nitride film was used for the insulation layer 160.
As a result of observing the degree of corrosion by soaking the piezoelectric actuator produced as described above in the solution containing sodium hydroxide, the corrosion was not found on the upper wiring line 140 and the lower wiring line 150. Further, in high-temperature and high-humidity conditions, even after continuously applying a voltage of 40 V for 1,000 hours, the breakage of the wiring line was not found, and a result indicating a good actuation was obtained.
While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure 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 priority from Japanese Patent Application No. 2023-189033, filed Nov. 6, 2023, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-189033 | Nov 2023 | JP | national |
