JP2015056453A - Piezoelectric actuator and droplet discharge head, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric actuator that can prevent the occurrence of a pin hole in a Pt film of an upper electrode to avoid the occurrence of the floating of film on an interface, and thereby holding good piezoelectric characteristics of a piezoelectric thin film.SOLUTION: A piezoelectric actuator includes a diaphragm 23, a lower electrode 18 provided on the diaphragm 23, a piezoelectric thin film 17 provided on the lower electrode 18, and an upper electrode 16 provided on the piezoelectric thin film 17, where the upper electrode 16 includes conductive oxide and a platinum film formed on the conductive oxide, and the platinum film has the average particle diameter in the lateral direction smaller than the thickness.

Description

  The present invention relates to a piezoelectric actuator, a droplet discharge head including the piezoelectric actuator, and an image forming apparatus equipped with the droplet discharge head.

  In general, an image recording apparatus such as a printer, a facsimile, or a copying apparatus is provided with an ink jet head as a droplet discharge head. Such an inkjet head includes a nozzle that ejects ink droplets, an ink liquid chamber in which ink is stored, a vibration plate that forms part of the wall surface of the ink liquid chamber, and a pressure for pressurizing ink in the ink liquid chamber. And an actuator element (piezoelectric element). Then, by driving the actuator element and pressurizing the ink liquid chamber through the vibration plate, ink droplets are ejected from the nozzle.

  For example, there are two known types of piezo-type ink jet heads, one using a longitudinal vibration mode piezoelectric actuator that extends and contracts in the axial direction of the piezoelectric element and one using a bend mode piezoelectric actuator. Among these, a thin film piezoelectric actuator obtained by further thinning the latter bend mode piezoelectric actuator is a thin film device in which film formation and patterning of various thin film layers on a substrate are repeated to form a multilayer film formation.

  Therefore, in a thin film piezoelectric actuator, it is important to control the adhesion at the interface of the laminated film. If the cleanliness of the interface is poor or the adhesion of the film is low, interface peeling may occur.

  In the piezoelectric actuator in which the diaphragm is formed on the substrate and the lower electrode, the piezoelectric thin film, and the upper electrode are formed on the diaphragm, in order for the upper electrode to sufficiently cover the piezoelectric thin film, It has been proposed that the thickness of the upper electrode be 0.5 to 2 times the surface roughness (Rmax) of the piezoelectric thin film (see, for example, Patent Document 1).

However, in the above conventional technique, due to low adhesion in each layer, or high stress due to the film itself or structure, at the interface between the upper electrode and the insulating protective film (Al ₂ O ₃ ) covering the upper surface of the upper electrode, There is a problem that film floating or film peeling (hereinafter referred to as film floating or the like) occurs.

  When the part where the film floating or the like occurs is confirmed in detail, a pinhole of several tens of nm level exists in the Pt film of the upper electrode. Once a photoresist or stripping solution enters such a fine pinhole, it is difficult to remove it, and it becomes a cause of film floating and the like.

Further, in the technique of Patent Document 1, only the relationship between the thickness of the upper electrode and the surface roughness of the piezoelectric thin film is defined, and there is no problem with respect to the problem that pinholes are generated in the Pt film of the upper electrode. It has not been solved. As a result, in the technique of Patent Document 1, there is a risk that film floating or the like may occur at the interface between the upper electrode of the piezoelectric thin film element and the insulating protective film (Al ₂ O ₃ ).

  An object of the present invention is to avoid the occurrence of film floating at the interface by preventing the occurrence of pinholes in the Pt film of the upper electrode, and to maintain the piezoelectric characteristics of the piezoelectric thin film satisfactorily Is to provide.

  The present invention also provides a liquid droplet ejection head that can maintain a good ink ejection characteristic by maintaining the piezoelectric characteristics of the piezoelectric thin film, and can obtain a stable ink ejection characteristic even when continuously ejected, and Another object is to realize an image forming apparatus equipped with a droplet discharge head.

  In order to solve the above problems, the present invention provides a diaphragm, a lower electrode provided on the diaphragm, a piezoelectric thin film provided on the lower electrode, and an upper part provided on the piezoelectric thin film. A piezoelectric actuator provided with an electrode, wherein the upper electrode has a conductive oxide and a platinum film formed on the conductive oxide, and the platinum film has an average particle diameter in a lateral direction. Is smaller than the film thickness.

  According to the present invention, the platinum film of the upper electrode is set such that the average particle diameter in the lateral direction is smaller than the film thickness, and the particle diameter of platinum atoms is small. As a result, platinum atoms can be filled without gaps, so that pinholes can be avoided in the Pt film of the upper electrode, and a piezoelectric actuator that maintains the piezoelectric characteristics of the piezoelectric thin film can be obtained.

1 is an exploded perspective view of a piezoelectric actuator according to Example 1. FIG. It is sectional drawing along the SA-SA line of FIG. It is sectional drawing which shows a mode that the diaphragm was formed on the silicon substrate. It is sectional drawing which shows a mode that the lower electrode, the piezoelectric material thin film, and the upper electrode were formed on the diaphragm. It is sectional drawing which shows a mode that the resist pattern was formed on the upper electrode. It is sectional drawing which shows a mode when performing litho etching. It is sectional drawing which shows a mode that the actuator element was formed on the upper electrode. It is sectional drawing which shows a mode that the insulating protective film was formed on the actuator element and the diaphragm. It is sectional drawing which shows a mode that the metal wiring was formed on the insulating protective film. It is sectional drawing which shows a mode that the passivation film was formed in metal wiring. It is sectional drawing which shows a mode that the adhesive agent was apply | coated to the sub-frame junction part of a sub-frame board | substrate. It is sectional drawing which shows a mode that the sub-frame junction part of the sub-frame board | substrate was joined to the joint surface level | step difference of an actuator board | substrate. It is sectional drawing which shows a mode that the lower surface of the silicon substrate was grind | polished and the resist pattern was formed in the grind | polished surface. It is sectional drawing which shows a mode that the etching was given and the partition was formed in the downward position of the joint surface level | step difference. It is sectional drawing which shows a mode that the nozzle substrate was joined to the partition of an actuator substrate. It is a figure which shows the cross section of Pt film | membrane of an upper electrode, and a mode that the pinhole produced. It is the figure which shows the longitudinal cross-section of Pt film | membrane of an upper electrode, and shows a mode that the pinhole produced. It is a figure which shows the cross section of Pt film | membrane of an upper electrode, and a mode that the pinhole has not arisen. FIG. 3 is an overall configuration diagram when an image forming apparatus according to a second embodiment is viewed from a side. It is a top view which shows the principal part of the image forming apparatus of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

The piezoelectric actuator according to this embodiment has an actuator element, and this actuator element has a structure in which a lower electrode, a piezoelectric thin film (PZT film), and an upper electrode are laminated and patterned. The lower electrode is laminated with TiO ₂ / Pt / SRO (SrRuO ₃ : strontium ruthenate) as an electrode material, and the upper electrode is laminated with Pt / SRO (SrRuO ₃ ) as an electrode material. Furthermore, the piezoelectric thin film is formed of a polycrystalline body. Thus, the piezoelectric actuator has a configuration in which the lower electrode / piezoelectric body / upper electrode are stacked on the substrate.

One of the problems of the piezoelectric actuator configured as described above is low adhesion at each layer interface of the lower electrode / piezoelectric thin film / upper electrode, or film floating at each layer interface due to high stress. In addition, there is a problem that film adhesion or the like occurs at the interface between the upper electrode and the insulating protective film (Al ₂ O ₃ ) covering the upper surface of the upper electrode with low adhesion.

  In the process of searching for causes such as film floatation, it has been found that if the cleanliness of the interface is poor, the adhesiveness is lowered and interface peeling occurs. Specifically, when the photoresist or the photoresist stripping liquid component remains and the cleanliness of the interface is deteriorated, film floating or the like occurs.

  When the part where the film floating etc. occurred was confirmed, for example, in the upper electrode, it was found that pinholes of several tens of nm level existed in the Pt film. Then, once a photoresist or a photoresist stripping solution enters a small pinhole on the order of several tens of nm, it is very difficult to remove it. That is, there is a problem that pinholes of several tens of nm level or less exist in the Pt film of the upper electrode.

  Therefore, in this embodiment, in order to eliminate pinholes in the Pt film of the upper electrode, the average grain size in the lateral direction of the Pt film is made equal to or less than the film thickness of the Pt film, thereby reducing the piezoelectric thin film (PZT film). The generation of film floating or the like is prevented while the piezoelectric characteristics are kept good.

  Thus, by making the average particle size in the lateral direction of the Pt film equal to or less than the film thickness, the piezoelectric characteristics of the piezoelectric thin film (PZT film) are improved, the ink ejection characteristics can be maintained well, and the ink is continuously ejected. Even if it is made, it is possible to obtain stable ink ejection characteristics.

  Next, the piezoelectric actuator in this embodiment and the droplet discharge head provided with the piezoelectric actuator will be described.

Example 1
1 and 2 show a droplet discharge head according to the first embodiment, and here, an inkjet head 10 is shown as an example of the droplet discharge head. The ink jet head 10 includes a subframe substrate 11, an actuator substrate 12 disposed below the subframe substrate 11, and a nozzle substrate 13 disposed below the actuator substrate 12. The sub-frame substrate 11 and the nozzle substrate 13 are bonded to the actuator substrate 12 with an adhesive, respectively, and the inkjet head 10 has a structure in which the sub-frame substrate 11, the actuator substrate 12, and the nozzle substrate 13 are stacked. .

  The sub-frame substrate 11 is made of silicon, and an actuator protection cavity 14 and a sub-frame bonding portion 15 are provided on the side of the bonding surface with the actuator substrate 12 (the lower surface side in the drawing). Although not shown, the sub-frame substrate 11 is also provided with an ink supply hole for supplying ink from the outside, an opening for routing the electric wiring to the outside, an alignment mark with the actuator substrate 12, and the like.

  The actuator substrate 12 is also made of silicon, and an actuator element having a laminated structure of an upper electrode 16, a piezoelectric thin film (PZT film) 17, and a lower electrode 18 on one side surface (upper surface in the drawing) of the actuator substrate 12. 19 is provided.

  Further, on the upper surface of the actuator substrate 12, in addition to the actuator element 19, as a basic configuration, an insulating protective film 20, a metal wiring 21 for transmitting a signal from an external drive circuit, and a passivation film 22 for protecting the metal wiring 21. Is formed. The insulating protective film 20 is formed so as to cover the upper surface of the actuator substrate 12 and the outer surface of the actuator element 19, and the metal wiring 21 is disposed on the insulating protective film 20.

  A vibration plate 23 is provided on the other surface (lower surface in the drawing) of the actuator substrate 12, and a plurality of partition walls 24 are formed on the lower surface of the vibration plate 23. A nozzle substrate 13 having nozzle holes 25 is provided on the lower surface of the partition wall 24. An ink liquid chamber 26 is formed by the diaphragm 23, the left and right partition walls 24, and the nozzle substrate 13, and the ink liquid chamber 26 communicates with the outside through the nozzle holes 25 of the nozzle substrate 13.

  In the actuator substrate 12, the joint surface step 27 made of the metal wiring 21 and the passivation film 22 is disposed above the position where the partition wall 24 is provided. The upper surface of the bonding surface step 27 is bonded to the lower surface of the subframe bonding portion 15 of the subframe substrate 11 with an adhesive 28.

  The nozzle substrate 13 has nozzle holes 25 formed by a known press process or Ni electroforming method, and is bonded to the partition wall 24 of the actuator substrate 12 with an adhesive.

  In the present embodiment, the upper electrode 16, the piezoelectric thin film (PZT film) 17, the actuator element 19 including the lower electrode 18, and the diaphragm 23 constitute a piezoelectric actuator.

  Next, a method for manufacturing the inkjet head 10 according to the present embodiment will be described with reference to the drawings.

  First, as shown in FIG. 3A, the diaphragm 23 is formed on the silicon substrate 24 '. As the silicon substrate 24 ′, a silicon wafer having a thickness of <100> 625 μm is used. The diaphragm 23 has a structure in which a silicon oxide film, a silicon nitride film, and a polysilicon film are laminated by thermal oxide film and CVD.

Next, as shown in FIG. 3B, the upper electrode layer 16 ′, the piezoelectric thin film layer 17 ′, and the lower electrode layer 18 ′ are formed on the vibration plate 23. As the lower electrode layer 18 ′, a Ti layer, a Pt layer, and a SrRuO ₃ layer (SRO layer) are formed by sputtering. A piezoelectric thin film layer 17 ′ is laminated on the lower electrode layer 18 ′, and a PZT film having a desired thickness is formed on the piezoelectric thin film layer 17 ′ by a sol-gel method. Further, an SRO layer and a Pt layer are formed as the upper electrode layer 16 ′ on the PZT film of the piezoelectric thin film layer 17 ′.

In the lower electrode layer 18 ′, the film quality of the SRO layer (that is, the SrRuO ₃ film) varies depending on the sputtering conditions. In particular, in order to place the SrRuO ₃ film in the (111) orientation following the Pt (111) with emphasis on the crystal orientation, the substrate is heated at a film formation temperature of 450 to 600 ° C. to form a film. preferable. Regarding SRO film formation conditions, film formation may be performed at room temperature, and then thermal oxidation may be performed at a crystallization temperature (650 ° C.) by RTA treatment.

The SrRuO ₃ film is sufficiently crystallized and has a sufficient specific resistance as an electrode. However, as the crystal orientation of the film, (110) is likely to be preferentially oriented, and PZT formed thereon is formed. As for (110), it becomes easy to orient.

  Regarding SRO crystallinity produced on Pt (111), since the lattice constants of Pt and SRO are close to each other, in the normal θ-2θ measurement, the 2θ positions of SRO (111) and Pt (111) are overlapped, so that discrimination is possible. difficult. With respect to Pt, diffraction lines cancel each other at a position where 2θ tilted by Psi = 35 ° is about 32 ° due to the disappearance rule, and no diffraction intensity is observed. Therefore, it is possible to confirm whether the SRO is preferentially oriented to (111) by tilting the Psi direction by about 35 ° and judging from the peak intensity where 2θ is about 32 °.

  Note that the SRO layer of the upper electrode 16 is also preferably formed by heating the substrate at a deposition temperature of 450 to 600 ° C.

  Here, formation of the Pt layer in the upper electrode 16 which is a characteristic part of the present embodiment will be described.

  The Pt layer of the upper electrode 16 is preferably formed by heating the substrate at 250 to 600 ° C. When the Pt layer of the upper electrode 16 is formed at a temperature lower than 250 ° C., film floating or the like tends to occur at the interface between the Pt layer and the SRO layer in the upper electrode 16.

  Therefore, in this embodiment, the particle size of the Pt layer (Pt film) in the upper electrode 16 is greatly changed. In order to greatly change the particle size of the Pt film of the upper electrode 16, it can be changed by the substrate heating temperature. Specifically, the higher the substrate heating, the larger the particle size of the Pt film of the upper electrode 16. The thickness of the Pt film of the upper electrode 16 is controlled by the film formation time.

  Next, as shown in FIG. 3C, a resist pattern 31 is formed on the upper electrode layer 16 '. Then, as shown in FIG. 3D, lithographic etching is performed to form an actuator element 19 having a pattern in which the peripheral portion is cut as shown in FIG. 3E. The actuator element 19 has a structure in which a lower electrode 18, a piezoelectric thin film (PZT film) 17, and an upper electrode 16 are laminated.

Next, as shown in FIG. 3F, an insulating protective film 20 is formed on the patterned actuator element 19. The insulating protective film 20 has a two-layer structure composed of an Al ₂ O ₃ film formed by the ALD method and a silicon oxide film formed by the CVD method.

  Next, as shown in FIG. 3G, metal wirings 21 are arranged on both sides of the actuator element 19 as wirings for propagating signals of an external circuit, thereby forming a desired pattern. Here, the metal wiring 21 is intended to provide a junction step between the subframe substrate 11 and the subframe junction 15 (see FIGS. 1 and 2), and does not have a function as an electric circuit. . Further, these metal wirings 21 are located above the partition walls 24 (see FIGS. 1 and 2).

  Then, as shown in FIG. 3H, a passivation film 22 is formed around the upper surface, the side surface, and the lower portion of the side surface of the metal wiring 21 as insulation protection for the metal wiring 21. In this embodiment, in order to increase the displacement efficiency of the actuator element 19, the passivation film 22 around the upper surface, the side surface, and the lower portion of the side surface of the actuator element 19 is removed. In the process of the present embodiment, a silicon nitride film (SiN) is formed as the passivation film 22 by plasma CVD. This film forming method is a process having the highest processing temperature (340 ° C.).

  Here, the film adhesion at the interface of the upper electrode 16 was evaluated by the scratch method. The surface of the sample was scratched while applying a load to the diamond indenter, and the adhesion was evaluated by the magnitude of the vertical load (peeling critical load) when the film peeled.

  In this example, the vertical load when the film peeled at the interface between the Pt film and the PZT film was 4 mN or more. The conventional inkjet head has a configuration in which the upper electrode SRO film below the passivation film is not removed. In such a configuration, the vertical direction when the film peels off at the interface between the Pt film and the SRO film. The load was about 2.5 mN. Thus, it can be seen that the adhesion of the inkjet head 10 of this example is improved as compared with the conventional inkjet head.

In addition, the piezoelectric performance was calculated by measuring the amount of deformation by applying an electric field (150 kV / cm) with a laser Doppler vibrometer and fitting it by simulation. After evaluating the initial properties were carried out (the characteristic immediately after the repeated application voltage added 10 ¹⁰ times) Evaluation durability. The ink jet head 10 according to this example had the same characteristics as a general ceramic sintered body with respect to the initial characteristics and the results after the durability test (residual polarization Pr: 20 to 25 uC / cm ² , piezoelectric constant). Is -130 to -160 pm / V).

  On the other hand, the subframe substrate 11 uses a silicon wafer of <100> 400 μm, and the pattern of the actuator protection cavity 14 and the subframe joint 15 having a space corresponding to the actuator element 19 as a gap is formed by lithography. . In addition to the above, an ink supply hole (not shown) for supplying ink from the outside and an opening area (not shown) for mounting a drive IC are formed.

  Next, a procedure for joining the sub-frame substrate 11 to the actuator substrate 12 formed as described above will be described.

  First, as shown in FIG. 4A, an adhesive 28 is applied to the lower end surface of the subframe joining portion 15 of the subframe substrate 11. The adhesive 28 is applied only to the lower end surface of the subframe joint 15 by a known flexographic printing technique. Here, the coating thickness of the adhesive 28 is set to 3 μm (μm).

  Then, the sub-frame substrate 11 and the actuator substrate 12 are aligned so that the lower end surface of the sub-frame bonding portion 15 matches the bonding surface step 27 of the actuator substrate 12 (see FIG. 1).

  Next, as shown in FIG. 4B, the lower end surface of the sub-frame bonding portion 15 is bonded to the upper surface of the bonding surface step 27 of the actuator substrate 12 (see FIG. 1) by the wafer bonding apparatus. The frame substrate 11 is integrated.

  Next, as shown in FIG. 4C, polishing is performed on the lower surface of the silicon substrate 24 ', and a resist pattern 32 is formed on the polished surface. Thereafter, as shown in FIG. 4D, etching is performed to form the partition wall 24 below the joint surface step 27, and the ink liquid chamber 26 is formed between the adjacent partition walls 24. The partition wall 24 is not formed below the actuator element 19, but is formed below the joint surface step 27 including the metal wiring 21 and the passivation film 22. That is, the partition wall 24 is configured to support the joint surface step 27 to which the subframe joint portion 15 of the subframe substrate 11 is joined from below. The polishing process for the lower surface of the silicon substrate 24 ′ is performed to adjust the height of the silicon substrate 24 ′ so that the ink liquid chamber 26 has a desired size.

  Finally, as shown in FIG. 4E, the nozzle substrate 13 in which the nozzle holes 25 are formed is bonded to the lower surface of the partition wall 24 of the actuator substrate 12. As described above, the inkjet head 10 is manufactured.

Next, samples as in Experimental Examples 1 to 4 and Comparative Examples 1 to 3 were produced under the conditions shown in Table 1. For each sample of Experimental Examples 1 to 4 and Comparative Examples 1 to 3, it was examined whether or not a pinhole was generated in the Pt film of the upper electrode after the upper electrode was formed. Also, with respect to the samples of each of Experimental Examples 1 to 4 and Comparative Examples 1 to 3, is there a film floating or the like on the Pt film of the upper electrode at the interface between the upper electrode and the insulating protective film (Al ₂ O ₃ )? I investigated whether or not. In addition, the measurement of the adhesive force was performed by the scratch test using a nano indenter. The greater the adhesion, the more the adhesion can be maintained.

  In Comparative Example 1, the deposition temperature of the upper electrode film is 150 ° C., the average particle diameter of the Pt film is 48 nm, and the film thickness of the Pt film is 40 nm. At this time, the adhesion was 3 mN, and the Pt film of the upper electrode was “existent” both with pinholes and film floating.

  In Experimental Example 1, the deposition temperature of the upper electrode film is 150 ° C., the average particle diameter of the Pt film is 50 nm, and the film thickness of the Pt film is 60 nm. At this time, the adhesive force was 15 mN, and the Pt film of the upper electrode was “none” for both pinholes and film floating.

  In Experimental Example 2, the deposition temperature of the upper electrode film is 150 ° C., the average particle diameter of the Pt film is 53 nm, and the film thickness of the Pt film is 125 nm. At this time, the adhesion was 17 mN, and the Pt film of the upper electrode was “none” for both pinholes and film floating.

  In Comparative Example 2, the deposition temperature of the upper electrode film is 300 ° C., the average particle diameter of the Pt film is 94 nm, and the film thickness of the Pt film is 80 nm. At this time, the adhesion was 5 mN, and the Pt film of the upper electrode was “existent” both with pinholes and film floating.

  In Experimental Example 3, the deposition temperature of the upper electrode film is 300 ° C., the average particle diameter of the Pt film is 105 nm, and the film thickness of the Pt film is 125 nm. At this time, the adhesion was 24 mN, and the Pt film of the upper electrode was “none” for both pinholes and film floating.

  In Comparative Example 3, the deposition temperature of the upper electrode film is 500 ° C., the average particle diameter of the Pt film is 156 nm, and the film thickness of the Pt film is 125 nm. At this time, the adhesion was 4 mN, and the Pt film of the upper electrode was “existent” both with pinholes and film floating.

  In Experimental Example 4, the deposition temperature of the upper electrode film is 500 ° C., the average particle diameter of the Pt film is 160 nm, and the film thickness of the Pt film is 200 nm. At this time, the adhesion was 28 mN, and the Pt film of the upper electrode was “none” for both pinholes and film floating.

As is clear from Table 1, by making the lateral particle size of the Pt film equal to or less than the film thickness, pin holes are eliminated in the Pt film of the upper electrode, and the upper electrode and the insulating protective film (Al ₂ O ₃ ) Occurrence of the upper electrode film floating at the interface can be reliably prevented.

  5 and 6 show the state of the Pt film of the upper electrode according to the prior art. FIG. 5 shows a cross section of the Pt film of the upper electrode, and it can be seen that a plurality of pinholes (portions surrounded by circular broken lines) are generated in the Pt film. FIG. 6 shows a longitudinal section of the Pt film of the upper electrode, and it can be seen that a pinhole is similarly generated.

  On the other hand, FIG. 7 shows a state of the Pt film of the upper electrode according to the present example. As shown in FIG. 7, it can be seen that no pinhole is generated in the Pt film of the upper electrode, and the effect of this example is remarkably exhibited.

  According to the present embodiment, the average particle diameter in the lateral direction of the Pt film of the upper electrode 16 is set smaller than the film thickness, and the particle diameter of platinum atoms is small. As a result, platinum atoms can be filled without gaps, so that pinholes can be avoided in the Pt film of the upper electrode 16, and film floating and the like can be prevented without deteriorating the characteristics of the piezoelectric thin film 17. it can.

  Further, the average particle diameter of 50 nm or more in the lateral direction of the platinum film is an average particle diameter range in which the adhesion can be further improved, and the adhesion of the film can be enhanced at the interface to further prevent film floating and the like. .

In addition, according to the present embodiment, by using SrRuO ₃ as the conductive oxide, it is possible to maintain good ink discharge characteristics and obtain stable ink discharge characteristics even when continuously discharged.

  In addition, since the platinum film is formed at a temperature of 250 to 500 ° C., the adhesion of the film at the interface is further enhanced, and in this respect also, film floating and the like can be further prevented.

Example 2
Next, an image forming apparatus equipped with the inkjet head 10 of Example 1 will be described with reference to FIGS. 8 is an overall configuration diagram when the image forming apparatus 100 is viewed from the side, and FIG. 9 is a plan view showing a main part of the image forming apparatus 100.

  In the image forming apparatus 100, side plates (not shown) are provided on the front side and the heel side in FIG. 8, respectively, and a guide rod 101 and a guide rail 102 are spanned between these side plates. A carriage 103 is slidably supported on the guide rod 101 and the guide rail 102. The carriage 103 slides in the left-right direction (main scanning direction) in FIG. 9 along the guide rod 101 and the guide rail 102 when the rotational force of the main scanning motor 104 is transmitted via the timing belt 105. To do.

  The carriage 103 is provided with, for example, four recording heads 107 that eject ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). The recording head 107 is mounted such that a plurality of ink ejection openings are arranged in a direction crossing the main scanning direction, and the ink droplet ejection direction is directed downward. The recording head 107 is the same as the inkjet head 10 shown in the first embodiment, and includes a piezoelectric actuator such as a piezoelectric element.

  In addition, a sub tank 108 for supplying ink of each color to the recording head 107 is mounted on the carriage 103. The sub tank 108 is supplementarily supplied with ink from a main tank (ink cartridge) via an ink supply tube (not shown).

  A paper feed cassette 110 is provided in the lower part of the image forming apparatus 100, and paper 112 is loaded on a paper stacking unit (pressure plate) 111 such as the paper feed cassette 110. Near the end of the paper stacking unit 111, a half-moon roller (paper feed roller) 113 and a separation pad 114 are provided to face the paper feed roller 113. The separation pad 114 is made of a material having a large friction coefficient and is urged toward the paper feed roller 113 side. The sheet feeding roller 113 separates the sheets 112 from the sheet stacking unit 111 one by one, and feeds the separated sheets 112 to a guide 115 provided connected to the separation pad 114.

  The paper 112 fed to the guide 115 is sent to the transport belt 121 via the counter roller 122 and the transport guide 123. The counter roller 122 is for sandwiching and transporting the paper 112 fed to the guide 115 with the transport belt 121. The conveyance guide 123 is for causing the sheet 112 fed substantially vertically upward between the counter roller 122 and the conveyance belt 121 to change the direction by approximately 90 ° to follow the conveyance belt 121. Further, a tip pressure roller 125 urged toward the conveying belt 121 by the pressing member 124 and a charging roller 126 for charging the surface of the conveying belt 121 are provided. The transport belt 121 transports the paper 112 by electrostatic adsorption.

  The conveyor belt 121 is an endless belt and is stretched between the conveyor roller 127 and the tension roller 128. The conveyance roller 127 is rotated from the sub-scanning motor 131 via the timing belt 132 and the timing roller 133, and is configured to circulate in the belt conveyance direction (sub-scanning direction) in FIG. Note that a guide member 129 is disposed on the back side of the conveyance belt 121 so as to correspond to an image forming area formed by the recording head 107.

  As shown in FIG. 8, a slit disk 134 is attached to the shaft of the transport roller 127, and the slit of the slit disk 134 is detected by a sensor 135 (see FIG. 9). Thereby, the rotation amount of the conveyance roller 127 (the movement amount of the conveyance belt 121) can be detected. Note that the slit disk 134 and the sensor 135 constitute an encoder 136.

  The charging roller 126 is disposed so as to come into contact with the surface layer of the transport belt 121 and to rotate following the rotation of the transport belt 121. A pressure of 2.5 N is applied to both ends of the charging roller 126 shaft.

  Further, as shown in FIG. 9, an encoder scale 142 having slits is provided on the front side of the carriage 103, and an encoder sensor 143 including a transmission type photosensor for detecting the slits is provided on the front side of the carriage 103. It has been. The encoder scale 142 and the encoder sensor 143 constitute an encoder 144 for detecting the position of the carriage 103 in the main scanning direction (position with respect to the home position).

  Further, in order to discharge the paper 112 recorded by the recording head 107, a separation unit for separating the paper 112 from the conveying belt 121, a paper discharge roller 152 and a paper discharge roller 153, and a paper 112 to be discharged. And a paper discharge tray 154 for stocking.

  A double-sided paper feeding unit 161 is detachably attached to the back of the image forming apparatus 100 (left side in the figure). The double-sided paper feeding unit 161 takes in the paper 112 returned by the reverse rotation of the conveying belt 121, reverses it, and feeds it again between the counter roller 122 and the conveying belt 121.

  In the image forming apparatus 100 configured as described above, the sheets 112 are separated and fed one by one from the sheet stacking unit 111, and the sheet 112 fed substantially vertically upward is guided by the guide 115, and the conveyance belt 121. It is sandwiched between the counter roller 122 and conveyed. Further, the front end of the paper 112 is guided by the transport guide 123 and pressed against the transport belt 121 by the front end pressure roller 125, and the transport direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately applied to the charging roller 126 from a high voltage power source of a control circuit (not shown), that is, an alternating voltage is applied. As a result, the conveying belt 121 is alternately charged in a strip shape with a predetermined width in the sub-scanning direction that is the rotating direction, that is, plus and minus in the alternating charging voltage pattern. When the paper 112 is fed onto the conveyance belt 121 charged alternately with plus and minus, the paper 112 is attracted to the conveyance belt 121 by electrostatic force, and the paper 112 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 121. Is done.

  Therefore, by driving the recording head 107 according to the image signal while moving the carriage 103, ink droplets are ejected onto the stopped paper 112 to record one line, and after the paper 112 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 112 has reached the recording area, the recording operation is finished, and the paper 112 is discharged onto the paper discharge tray 154.

  In the case of duplex printing, when recording on the front surface (surface to be printed first) is completed, the recording sheet 112 is fed into the duplex feeding unit 161 by rotating the conveyance belt 121 in the reverse direction. In the double-sided paper feeding unit 161, the paper 112 is reversed (the back side becomes the printing surface), and is fed again between the counter roller 122 and the transport belt 121. Then, timing control is performed, and the sheet is conveyed onto the conveyor belt 121 and recorded on the back surface in the same manner as described above, and then discharged onto the sheet discharge tray 154.

  Although the embodiments of the present invention have been described in detail with reference to the drawings, each of the above embodiments is only an example of the present invention, and the present invention is not limited only to the configuration of each of the above embodiments. . Needless to say, changes in design and the like within the scope of the present invention are included in the present invention.

  For example, the image forming apparatus 100 according to the second exemplary embodiment can be applied to a printer, a facsimile machine, a copying machine, and a multifunction machine of these.

  The present invention can also be applied to a droplet discharge head or droplet discharge device that discharges a liquid other than ink, such as a DNA sample, a resist, or a pattern material, or an image forming apparatus including these.

10 Inkjet head (droplet discharge head)
11 Subframe substrate 12 Actuator substrate 13 Nozzle substrate 14 Actuator protection cavity 15 Subframe junction 16 Upper electrode 16 'Upper electrode layer 17 Piezoelectric thin film (PZT film)
17 'Piezoelectric thin film layer 18 Lower electrode 18' Lower electrode layer 19 Actuator element 20 Insulating protective film 21 Metal wiring 22 Passivation film 23 Diaphragm 24 Partition wall 24 'Silicon substrate 25 Nozzle hole 26 Ink liquid chamber 27 Joint surface step 28 Adhesive 31 resist pattern 32 resist pattern 100 image forming apparatus

Japanese Patent No. 3209082

Claims (8)

A diaphragm,
A lower electrode provided on the diaphragm;
A piezoelectric thin film provided on the lower electrode;
A piezoelectric actuator provided with an upper electrode provided on the piezoelectric thin film,
The upper electrode has a conductive oxide and a platinum film formed on the conductive oxide, and the platinum film has a lateral average particle size smaller than the film thickness. Piezoelectric actuator.   2. The piezoelectric actuator according to claim 1, wherein an average particle diameter in a lateral direction of the platinum film is 50 nm or more. The piezoelectric actuator according to claim 1, wherein the conductive oxide is strontium ruthenate (SrRuO ₃ ).   The piezoelectric actuator according to claim 1, wherein the piezoelectric thin film is made of a polycrystalline body.   A droplet discharge head comprising the piezoelectric actuator according to claim 1.   An image forming apparatus comprising the droplet discharge head according to claim 5. A diaphragm,
A lower electrode provided on the diaphragm;
A piezoelectric thin film provided on the lower electrode;
With an upper electrode provided on the piezoelectric thin film,
The upper electrode is a method of manufacturing a piezoelectric actuator comprising a conductive oxide and a platinum film formed on the conductive oxide,
A method of manufacturing a piezoelectric actuator, wherein the platinum film is formed at a temperature of 250 to 500 ° C., and an average particle diameter in a lateral direction of the platinum film is made smaller than a film thickness. The method for manufacturing a piezoelectric actuator according to claim 7, wherein the conductive oxide is strontium ruthenate (SrRuO ₃ ), and the strontium ruthenate is formed by sputtering at 450 to 600 ° C.