JP2015082541A - Electromechanical conversion element, manufacturing method thereof, liquid droplet discharge head with electromechanical conversion element, ink cartridge, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromechanical conversion element with excellent piezoelectric characteristics, configured by arranging a lower electrode (a metal oxide layer formed on an electrode), an electromechanical conversion film, and an upper electrode on a vibration plate, and configured to prevent hillock from being formed on the lower electrode, without reducing pressure resistance or increasing leak current.SOLUTION: An electromechanical conversion element includes: a lower electrode 403 arranged on a vibration plate 402, formed of a platinum film which has been rapidly heated after deposition, having a (111) preferential plane orientation, and configured so that an X-ray diffraction peak position 2θ derived from the (111) plane may be controlled within a range of 39.90°-40.10°; an electromechanical conversion film 404 formed of a lead zirconate titanate (PZT), and controlled so that an orientation rate of plane orientation (100) of the PZT is 70% or more, and a half width of a rocking curve in plane orientation (200)/(002)of the PZT is controlled to be equal to or less than 10°; and an upper electrode 405. The electromechanical conversion element is formed by arranging a metal oxide layer 403(b) on the lower electrode 403.

Description

  The present invention relates to an electro-mechanical conversion element that is provided in an ink jet image forming apparatus and discharges a droplet of ink or the like, a method for manufacturing the electro-mechanical conversion element, a liquid droplet ejection head including the electro-mechanical conversion element, an ink cartridge, and an image forming apparatus. About.

Piezoelectric elements are also used in various semiconductor devices, capacitors, and the like, and research has been actively conducted on manufacturing methods thereof (see, for example, Patent Document 1). In particular, inkjet recording of printers, facsimiles, copying machines, and the like. An electro-mechanical conversion element is used for a droplet discharge head provided in an image forming apparatus of a type, and various manufacturing methods and configurations have been proposed in order to obtain good piezoelectric characteristics (for example, Patent Documents 2 to 5). Reference 7).
The droplet discharge head includes a nozzle that discharges ink droplets, a pressure chamber that communicates with the nozzle, (also referred to as an ink flow path, a pressure liquid chamber, a discharge chamber, and a liquid chamber), and a pressure chamber. An electro-mechanical conversion element such as a piezoelectric element that pressurizes the ink of the ink, or an electro-thermal conversion element such as a heater, or a vibration plate that forms the wall surface of the ink flow path and an energy generation means comprising an electrode facing the diaphragm. Thus, the ink droplets are ejected from the nozzles by pressurizing the ink in the pressurized chamber with the energy generated by the energy generating means. Piezoelectric (piezo type) liquid droplet ejection heads (also called ink jet recording heads) use longitudinal vibration mode piezoelectric actuators that expand and contract in the axial direction of the piezoelectric elements, and bend mode. Two types using a piezoelectric actuator are already known. Further, it is already known that a thin film piezoelectric actuator obtained by further thinning the actuator of the latter bend mode piezoelectric element can improve the displacement characteristics of the actuator by controlling the crystal orientation of the piezoelectric body (piezo) to (100). Various studies have been conducted on techniques for controlling orientation.
However, when a ferroelectric thin film is formed on an electrode such as platinum in the production of a piezoelectric element, a capacitor, a semiconductor element, etc., hillocks (minute protrusions) are generated, and the piezoelectric characteristics and characteristics as a ferroelectric substance are deteriorated. Various suppression methods and coping methods have been proposed (for example, see Patent Documents 8 to 15).

A liquid droplet ejection head provided in an image forming apparatus such as a printer, a facsimile machine, or a copying apparatus includes a plurality of nozzle openings, a flow path forming substrate having a pressurized liquid chamber (pressurizing chamber) communicating with each nozzle opening, A diaphragm that forms one surface of the pressure chamber, and an electro-mechanical conversion element is provided on the diaphragm, and the electro-mechanical conversion element includes a lower electrode, an electro-mechanical conversion film, An upper electrode is provided and configured. In order to obtain an electro-mechanical conversion element with high piezoelectricity, lead zirconate titanate (PZT) is preferably used as an electro-mechanical conversion film made of a piezoelectric material. For example, an adhesion layer (TiOx), It is effective to sequentially form a lower electrode (platinum: Pt), a buffer layer (TiOx), an electromechanical conversion film (PZT), and an upper electrode.
The buffer layer is composed of a metal oxide layer such as TiOx and avoids the influence of the lower electrode having different orientation plane orientation [platinum electrode: plane orientation (111)], and the crystal of the electromechanical conversion film (PZT). It plays a role not to hinder growth [plane orientation (100)]. The buffer layer preferably plays a role as a so-called seed layer that promotes (100) crystal growth of PZT.
As described above, a method of controlling the crystal orientation and crystal shape of a piezoelectric body has been proposed in order to obtain good piezoelectric characteristics. For example, in Patent Document 2 (Japanese Patent Laid-Open No. 11-191646), a piezoelectric thin film made of a polycrystalline material is sandwiched between an upper electrode and a lower electrode, and becomes a nucleus of a piezoelectric crystal at a crystal grain boundary of the lower electrode. Piezoelectric characteristics are improved by a configuration in which titanium is formed in an island shape.
However, when only a thin layer (40 to 60 mm) of crystal source (Ti) is formed on the lower electrode (for example, platinum electrode), Ti diffuses into the lower electrode, and Ti is formed into a thin layer (oxidation treatment). There is a problem that hillocks are generated in the platinum electrode. That is, when the piezoelectric thin film is formed on the lower electrode in which the crystal source (Ti → TiOx) is formed in an island shape, deterioration of the piezoelectric characteristics is inevitable. When the electromechanical conversion element does not have a sufficient piezoelectric constant, there arises a problem that the ejection characteristics required for the droplet ejection head cannot be satisfied.
That is, a titanium layer (Ti layer) is formed on the lower electrode (Pt) in order to make the electro-mechanical conversion film (PZT) an orientation film having a plane orientation (100) excellent in piezoelectric characteristics, and the Ti layer In order to prevent diffusion into the electromechanical conversion film (PZT), the Ti layer is preferably heat treated (oxidized) to form a metal oxide layer (TiOx). In the metal oxide layer forming process by the oxidation treatment, there is a problem that fine protrusions, that is, hillocks are generated on the lower electrode. An example in which hillocks are generated on the lower electrode is shown in the SEM photograph of FIG.
If hillocks exist in the lower electrode, local concentration of the electric field occurs when voltage is applied, causing dielectric breakdown (decrease in pressure resistance), increasing current leakage (increasing leakage current), or forming a film on the lower electrode. There is a problem that reliability is adversely affected by penetrating various layers (for example, an insulating protective film described later).
The present invention has been made in view of the above prior art, and includes an electric electrode having a lower electrode, an electro-mechanical conversion film, and an upper electrode on a diaphragm, and having a metal oxide layer on the lower electrode. -In mechanical conversion elements, even if an oxidation treatment is performed during the formation of the metal oxide layer, the generation of hillocks on the lower electrode is suppressed, and there is no decrease in withstand voltage or increase in leakage current. -An object is to provide a mechanical conversion element.

In the process of investigating the cause of the above problem, the present inventors generate hillocks on the lower electrode when a titanium oxide layer (TiOx) is formed by oxidation treatment of the titanium layer (Ti layer) during the formation of the metal oxide layer. Occurs by the combination of the presence of residual stress in the lower electrode (platinum film: Pt film) and the phenomenon that titanium / oxygen atoms diffuse into the Pt film during the oxidation treatment of the titanium layer (Ti layer). I found out that
In order to solve the problem, the residual stress in the Pt film is reduced by simply increasing the film formation temperature of the lower electrode (Pt film) (for example, 500 ° C.). -The crystallinity of the plane orientation (100) of the mechanical conversion film (PZT) was lowered and the piezoelectric properties were reduced.
On the other hand, before a Ti layer for forming a metal oxide layer is formed on the surface of the Pt film [plane orientation is (111)], the Pt film is subjected to rapid heating treatment (also referred to as RTA treatment) and remains. By reducing the stress, it was found that an electromechanical conversion element having a good hillock-free and simultaneously good piezoelectric characteristics was obtained, and the present invention was achieved. By rapid heating treatment (also referred to as RTA treatment), the X-ray diffraction peak position 2θ derived from the preferential orientation plane orientation (111) of the Pt film is restored to around 40 °, which is the original Pt without distortion due to residual stress ( In the present invention, it is preferably 39.90 ° to 40.10 °).
That is, the above-described problem is an electro-mechanical conversion element including a lower electrode, an electro-mechanical conversion film, and an upper electrode on a diaphragm, and having a metal oxide layer on the lower electrode,
The lower electrode is made of a platinum film that has been subjected to rapid heating treatment (RTA treatment) after film formation, and the preferred orientation plane orientation of the lower electrode is (111), and an X-ray diffraction peak derived from the (111) plane The position 2θ is in the range of 39.90 ° to 40.10 °;
The electro-mechanical conversion film is made of PZT, the orientation ratio of the plane orientation (100) of the PZT is 70% or more, and the half width of the rocking curve in the plane orientation (200) / (002) of the PZT is 10 °. This is solved by an electromechanical conversion element characterized by the following.

  According to the present invention, the residual stress of the lower electrode (platinum film) is released by the rapid heating process (RTA process) before the metal oxide layer is formed. Occurrence of hillocks is suppressed, and there is no decrease in pressure resistance or increase in leakage current due to local concentration of electric field, and an electro-mechanical transducer having excellent piezoelectric characteristics in which the plane orientation of PZT is preferentially oriented to (100) is provided. The

It is a SEM photograph which shows a mode that a hillock generate | occur | produces on a lower electrode in a metal oxide layer formation process. It is a schematic sectional drawing which shows the structural example of the droplet discharge head provided with the electromechanical conversion element of this invention. It is a schematic sectional drawing which shows the structural example of the electromechanical conversion element of this invention. It is a schematic diagram explaining the factor which a hillock generate | occur | produces on a lower electrode when not performing RTA process to a lower electrode (platinum). It is a schematic diagram explaining the state in which hillock generation | occurrence | production does not generate | occur | produce on a lower electrode when an RTA process is performed to a lower electrode. It is the side view and top view which show another structure of the electromechanical conversion element of this invention containing an insulation protective film and extraction wiring. It is a figure which shows the typical PE hysteresis curve at the time of performing the characteristic evaluation of the electromechanical conversion element of this invention. It is a figure for demonstrating the state before the polarization process of the electromechanical conversion element of this invention (a), and after the polarization process (b). FIG. 3 is another schematic cross-sectional view showing a configuration example of a droplet discharge head configured by arranging a plurality of electro-mechanical conversion elements shown in FIG. 2. It is a perspective explanatory view showing an example of an image forming apparatus provided with a droplet discharge head of the present invention. It is side surface explanatory drawing of the mechanism part of the image forming apparatus shown in FIG. It is a flowchart which shows the formation process of the contact | adherence layer, lower electrode, and metal oxide layer which were formed in the Example. 13 is an AFM photograph of a platinum film having a metal oxide film formed on the surface according to the flowchart of FIG. 12 ((a) tapping mode, (b) PM mode). The change of XRD peak position 2 (theta) before and after the RTA process measured about the platinum film | membrane of an Example is shown. It is a figure explaining the half value width of the rocking curve in the surface orientation (200) / (002) of PZT.

As described above, the electro-mechanical conversion element of the present invention includes a lower electrode, an electro-mechanical conversion film, and an upper electrode on a diaphragm, and an electro-mechanical apparatus having a metal oxide layer on the lower electrode. A conversion element,
The lower electrode is made of a platinum film that has been subjected to rapid heating treatment (RTA treatment) after film formation, and the preferred orientation plane orientation of the lower electrode is (111), and an X-ray diffraction peak derived from the (111) plane The position 2θ is in the range of 39.90 ° to 40.10 °;
The electro-mechanical conversion film is made of lead zirconate titanate (PZT), the orientation ratio of the plane orientation (100) of the PZT is 70% or more, and rocking in the plane orientation (200) / (002) of the PZT The half width of the curve is 10 ° or less.

The electro-mechanical conversion element of the present invention has a configuration including an electro-mechanical conversion film made of PZT preferentially oriented in the plane orientation (100), and the platinum film of the lower electrode is subjected to rapid thermal annealing (RTA). Since the residual stress is released by the treatment, generation of hillocks in the platinum film is suppressed in the metal oxide layer formation process. Similarly, generation of hillocks in the platinum film is also suppressed in the crystallization process when forming the electromechanical conversion film. Since the generation of hillocks is prevented, there is no decrease in pressure resistance due to local concentration of electric field or increase in leakage current, and the electro-mechanical conversion element having excellent piezoelectric characteristics in which the plane orientation of PZT is preferentially oriented to (100) Is provided.
If the electro-mechanical conversion element has a PZT plane orientation preferentially oriented to (100), a piezoelectric constant equivalent to that of the ceramic sintered body (for example, about -130 to -160 pm / V) can be maintained. If a droplet discharge head is configured using such an electro-mechanical conversion element, it is excellent in discharge stability and durability, and can be applied to various image forming apparatuses.

The electro-mechanical conversion element of the present invention has a configuration in which a high piezoelectric constant is ensured without lowering the pressure resistance when a voltage is applied or an increase in leakage current, and the basic configuration is as follows. The structure includes a lower electrode (platinum film), an electro-mechanical conversion film (PZT), and an upper electrode, and has a metal oxide layer on the lower electrode, and the layers are stacked and patterned.
As will be described later, the metal oxide layer preferably contains titanium as a constituent component, and the formed titanium layer is oxidized (for example, 650 ° C. to 800 ° C.). By forming such a metal oxide layer, it is possible to suppress the diffusion of metal particles during the formation of PZT and prevent the deterioration of the piezoelectric constant and electrical characteristics of PZT. Furthermore, by including titanium as a constituent component of the metal oxide layer, PZT (100) having excellent piezoelectric characteristics can be grown, and by using titanium, which is a component element of the electro-mechanical conversion film, by diffusion. Deterioration of piezoelectric characteristics can be prevented. Because of such effects, in the present invention, the metal oxide layer can be referred to as a buffer layer.
However, since hillocks are generated on the lower electrode in the step of oxidizing the titanium layer, the lower electrode needs to be subjected to rapid heating treatment (RTA treatment) after film formation as described below.

The rapid heating treatment (RTA treatment) in the present invention is a heating to a predetermined temperature (for example, 650 ° C. to 850 ° C. is preferable for the treatment of a platinum film) at a temperature rising rate of 10 ° C./second or more. The holding treatment is performed for a predetermined time (for example, 1 to 5 minutes is preferable in the treatment of a platinum film) at a temperature of 5 ° C.
If the treatment temperature of the platinum film is less than 650 ° C., the stress cannot be sufficiently relaxed. If the treatment temperature exceeds 850 ° C., the orientation to Pt (111) is too strong, so that (100) grows at the time of PZT formation. Is inhibited.
That is, the lower electrode is made of a platinum film that has been subjected to rapid heating treatment (RTA treatment) after film formation, the preferred orientation plane orientation of the lower electrode is (111), and X-ray diffraction derived from the (111) plane The peak position 2θ is in the range of 39.90 ° to 40.10 °.
The X-ray diffraction peak position 2θ of the original Pt (111) orientation plane of platinum is observed at around 40 °. However, when the crystal lattice is distorted due to stress or the like, the X-ray diffraction peak position 2θ is shifted. That is, the distortion of the crystal lattice can be known by measuring the 2θ deviation from around 40 °.
In the present invention, the RTA treatment releases the distortion of the crystal lattice due to the residual stress to obtain the original Pt (111) orientation of platinum, and then the metal oxide layer (for example, the formed titanium layer is oxidized). As a result, it is possible to prevent the occurrence of hillocks in the platinum film as the lower electrode, there is no decrease in pressure resistance or increase in leakage current, and the electro-mechanical conversion with excellent piezoelectric properties in which the plane orientation of PZT is preferentially oriented to (100) It can be set as an element.
By releasing the residual stress of the lower electrode by the RTA treatment, generation of hillocks can also be prevented in the crystallization process (heat treatment) when forming the electro-mechanical conversion film (PZT).

The platinum film subjected to the RTA treatment preferably has a particle size in the range of 60 nm to 280 nm. When the particle size is 60 nm to 280 nm, an electromechanical conversion element having good piezoelectric characteristics in which the plane orientation (100) of the electromechanical conversion film (PZT) is preferentially oriented can be obtained.
The surface roughness Rz of the lower electrode is preferably 50 nm or less. When Rz exceeds 50 nm, it corresponds to the presence of hillocks on the lower electrode, which causes problems such as a decrease in pressure resistance and an increase in leakage current. Rz is measured by an atomic force microscope (AFM).

  In addition, since the adhesiveness between the base (Si substrate) which is a vibration plate and the lower electrode (Pt film) is not necessarily good, it is preferable to provide an adhesion layer between them. Any material that does not affect the piezoelectric characteristics and has good adhesion can be used without particular limitation, but a film (crystalline film) made of a metal oxide (for example, titanium oxide) is preferably used as described later.

In the electromechanical conversion element of the present invention, in order to ensure a high piezoelectric constant, the electromechanical conversion film was PZT preferentially oriented in the plane orientation (100). When the electro-mechanical conversion film does not have a sufficient piezoelectric constant, for example, ejection characteristics required for a droplet ejection head used in an inkjet recording type image forming apparatus (for example, the displacement amount of the electro-mechanical conversion film or the continuous There is a problem that the displacement amount after discharge is not satisfied.
Here, it is preferable that the orientation ratio of the plane orientation (100) of the PZT is 70% or more and the full width at half maximum of the rocking curve in the plane orientation (200) / (002) is 10 ° or less.
By preferentially orienting the surface orientation (100) of PZT, the piezoelectric characteristics of the electromechanical conversion film can be improved, and a high piezoelectric constant can be obtained if the orientation rate is 70% or more.
FIG. 15 is a diagram for explaining the full width at half maximum of the rocking curve in the vicinity of the plane orientation (200) / (002) of PZT [2θ = 44.7 °]. Since the plane orientation (200) and the plane orientation (002) have close diffraction angles, they are collectively described as (200) / (002).
The rocking curve is a diffraction intensity curve measured when X-rays are incident on a sample crystal and rotated at a constant speed in the vicinity of the X-ray incident angle on the sample satisfying the Bragg condition. The full width at half maximum at the peak in the diffraction curve is the full width at half maximum of the rocking curve. Therefore, the rocking curve half-width indicates the uniaxiality of the crystal with respect to the substrate. If the PZT has sufficient uniaxiality, that is, if the rocking curve half width of (200) / (002) is 10 ° or less, sufficient deterioration resistance can be provided.

That is, the electromechanical transducer of the present invention is
An adhesion layer forming step, a lower electrode forming step, a metal oxide layer forming step, an electromechanical conversion film forming step, and an upper electrode forming step;
The lower electrode forming step includes
Forming a platinum film on the adhesion layer;
A step of heating the formed platinum film to 650 ° C. to 850 ° C. at a temperature rising rate of 10 ° C./second or more and performing rapid heating treatment (RTA treatment) for 1 minute to 5 minutes,
The metal oxide layer forming step includes
Including a step of forming a titanium layer on the surface of the platinum film subjected to RTA treatment, and forming a metal oxide layer by oxidation treatment at a temperature of 650 ° C. to 800 ° C.
The electro-mechanical conversion film forming step includes:
Including a step of applying a PZT precursor solution on the metal oxide layer to form a laminate;
The upper electrode forming step is preferably obtained by a manufacturing method including a step of forming a metal electrode film or a metal oxide electrode film and a metal electrode film.

  Here, the adhesion layer forming step, the lower electrode forming step, and the metal oxide layer forming step can be performed in accordance with a flowchart (see FIG. 12) shown in an example described later. Note that the adhesion layer forming step in FIG. 12 shows an example in which a titanium layer is formed and oxidized.

The present invention will be further described in detail with reference to the drawings.
FIG. 2 is a schematic cross-sectional view showing a configuration example of a droplet discharge head including an electro-mechanical conversion element.
In the configuration of FIG. 2, a nozzle 102 that ejects ink droplets, a pressure chamber 101 that communicates with the nozzle, a base (vibration plate) 105, and an electro-mechanical conversion element 109 that pressurizes ink in the pressure chamber. I have. The electro-mechanical conversion element 109 includes an electro-mechanical conversion film (PZT) 107 and an upper electrode 108 on a lower electrode (platinum film) 106, and has a metal oxide layer (not shown) on the lower electrode.
That is, the electromechanical conversion element of the present invention includes a flow path forming substrate [pressure chamber substrate (Si substrate) having a plurality of nozzle openings (nozzles 102) and a pressurized liquid chamber (pressure chamber 101) communicating with each nozzle opening. 104] and a lower electrode 106, an electro-mechanical conversion film 107, and an upper electrode 108 on the vibration plate of the droplet discharge head having a base (vibration plate) 105 that forms one surface of the pressurized liquid chamber. And a metal oxide layer (not shown) is provided on the lower electrode. If necessary, it is preferable to provide an adhesion layer [for example, titanium oxide (TiOx)] (not shown) between the diaphragm 105 and the lower electrode (platinum film) 106.
The electro-mechanical conversion element 109 is energy generating means, and ejects ink droplets from the nozzle 102 by pressurizing ink in the pressure chamber 101 with energy generated by the electro-mechanical conversion element. In FIG. 2, a voltage is applied to the lower electrode (106) and the upper electrode (108) to vibrate the electromechanical conversion film 107 to generate the energy. In FIG. 2, reference numeral 103 denotes a nozzle plate.

As described above, a silicon substrate (Si substrate) is preferably used for the flow path forming substrate (pressure chamber substrate), an electro-mechanical conversion element is formed on one surface, and on the electro-mechanical conversion element, As a basic configuration, an interlayer insulating film (not shown), a metal wiring for transmitting a signal from an external drive circuit, and a passivation protective film for protecting the metal wiring are formed.
ing. Further, a pressure chamber is formed on the other surface of the Si substrate via a vibration plate. The electro-mechanical conversion element configured as described above has a junction surface step (formed by an interlayer insulating film, a metal wiring, a passivation protection film, etc., not shown) formed on the partition wall and a subframe junction surface. It is configured to be joined by an adhesive.
The nozzle substrate 103 has nozzle holes formed by a known press process or Ni electroforming method, and is bonded to the pressure chamber 101 surface of the pressure chamber substrate (Si substrate) 104 with an adhesive.

A configuration example of the electromechanical conversion element of the present invention is shown in a schematic cross-sectional view of FIG.
3 includes a substrate 401, a diaphragm 402, an adhesion layer 403 (a), a lower electrode 403, a metal oxide layer 403 (b), an electro-mechanical conversion film 404, and an upper electrode 405.
Here, with respect to the upper electrode, it is preferable to provide a conductive layer capable of obtaining a sufficient specific resistance value electrically. Further, in order to suppress a decrease in displacement or the like during continuous driving when the electro-mechanical conversion element is operated as an actuator, the upper electrode 403 on the side in contact with the electro-mechanical conversion film 404 is made of a conductive oxide electrode layer. It is preferable to include.
In the electromechanical conversion element of the present invention, the lower electrode is obtained by subjecting a platinum film formed before the formation of the metal oxide layer to RTA treatment. The preferred orientation plane orientation of the lower electrode is (111), and the X-ray diffraction peak position 2θ derived from the (111) plane is controlled in the range of 39.90 ° to 40.10 °.
The electromechanical conversion film is made of lead zirconate titanate (PZT). The orientation ratio of the PZT plane orientation (100) is controlled to 70% or more, and the rocking curve half width at the ratio ((200) / (002)) of the plane orientation (200) to the plane orientation (002) is controlled to 10 ° or less. The

As described above, the electro-mechanical conversion element according to the present invention includes an adhesion layer forming step, a lower electrode forming step, a metal oxide layer forming step, an electro-mechanical conversion film forming step, and an upper electrode forming step. Is obtained.
Here, the lower electrode forming step includes a step of forming a platinum film on the adhesion layer, and the formed platinum film is heated to 650 ° C. to 850 ° C. at a temperature rising rate of 10 ° C./second or more for 1 minute to 5 minutes. The process includes a minute rapid heating process (RTA process). Further, the metal oxide layer forming step includes a step of forming a metal oxide layer by forming a titanium layer on the surface of the platinum film subjected to the RTA treatment, and oxidizing at a temperature of 650 ° C. to 800 ° C. Further, the electro-mechanical conversion film forming step includes a step of applying a PZT precursor solution on the metal oxide layer to form a laminate. The upper electrode forming step includes a step of forming a metal electrode film or a metal oxide electrode film and a metal electrode film.
Although not particularly limited, an exemplary embodiment will be described with reference to FIG.
As shown in FIG. 3, the diaphragm 402 is formed on the substrate 401. The substrate 401 is a silicon wafer having a plane orientation (111) (for example, about 625 μm), and the diaphragm 402 is a thermal oxide film of the substrate (Si substrate), and a silicon oxide film, a silicon nitride film, a polysilicon film by a CVD method. Etc. are formed in a desired configuration.
Next, on the diaphragm 402, an adhesion layer 403 (a), a lower electrode 403, a metal oxide layer (for example, a layer containing titanium: TiOx) 403 (b), an electro-mechanical conversion film (PZT) 404, an upper portion An electrode 405 is formed.
Although not limited, it is preferable that an adhesion layer (for example, a layer containing titanium: TiOx) 403 (a) is provided between the diaphragm 402 and the lower electrode 403 as shown in FIG. The adhesion layer and the metal oxide layer can be regarded as being integrated with the lower electrode, and can be formed by a sputtering method and subjected to necessary heat treatment.
The electro-mechanical conversion film is formed to have a desired thickness by, for example, a sol-gel method using a PZT precursor solution.
On the electro-mechanical conversion film (PZT), for example, a strontium ruthenate (SrRuO ₃ : SRO) layer and a platinum layer (Pt layer) are laminated to form the upper electrode 405.

When titanium (Ti) is used in the formation of the adhesion layer and the metal oxide layer, respectively, in order to prevent diffusion of the formed Ti film in the adhesion layer and the metal oxide layer, heat treatment is performed to obtain TiOx. preferable. As the heat treatment, the RTA treatment as described above can be preferably applied. The Ti layer formed in the formation of the adhesion layer and the metal oxide layer is RTA-treated at 650 ° C. to 800 ° C. (for example, about 730 ° C.) to form a TiOx film.
Electricity composed of the aforementioned diaphragm / adhesion layer (TiOx) / lower electrode (Pt) / metal oxide layer (TiOx) / electro-mechanical conversion film (PZT) / upper electrode (SRO layer / Pt layer) The mechanical conversion element structure is an effective layer structure for obtaining an electro-mechanical conversion film having high piezoelectricity, that is, PZT (100) preferentially oriented with a plane orientation (100) orientation ratio of 70% or more.
In such a configuration, if a step of forming a metal oxide layer (TiOx) as it is without performing RTA treatment on the lower electrode (Pt film) formed by sputtering or the like, that is, a Ti film is formed. When heat treatment (RTA treatment) for forming a metal oxide layer (TiOx) is performed, hillocks (see FIG. 1) are generated on the lower electrode. If hillocks occur on the lower electrode, the reliability is adversely affected by decreasing the withstand voltage due to local concentration of the electric field, increasing the leakage current, and penetrating the film formed on the lower electrode as described above. Give rise to the problem of giving.

As a result of studying such problems, the present inventors have formed a metal oxide layer and a factor due to residual stress in the lower electrode (Pt) Pt film (platinum crystal grains) as shown in the schematic diagram of FIG. It has been found that the cause of the problem is that the Ti film is diffused by the heat treatment (RTA treatment) at the same time.
Here, when the Pt film is formed by sputtering or the like, even if the residual stress is reduced by simply raising the film forming temperature of the Pt film, the particle size of the Pt film becomes large and the electro-mechanical There is a problem that the piezoelectric characteristics of the conversion film (PZT) deteriorate.

  On the other hand, as shown in the schematic diagram of FIG. 5, a rapid heating process (RTA process) is performed after the Pt film as the lower electrode is formed before the heat treatment to turn the Ti film into a metal oxide layer (TiOx). By releasing the residual stress, it was possible to prevent hillocks from being generated on the lower electrode. Thus, even if a metal oxide layer (TiOx) is formed on the lower electrode in which the generation of hillocks is suppressed, there is no decrease in breakdown voltage or increase in leakage current due to local concentration of the electric field, and there is no formation on the upper part of the lower electrode. Reliability is improved because damage to a constituent film (for example, an insulating protective film) to be formed is eliminated. If an electro-mechanical conversion film (PZT) is formed on the lower electrode having such a metal oxide layer, an electro-mechanical conversion element having excellent piezoelectric characteristics preferentially oriented in the plane orientation (100) can be obtained. .

The schematic cross-sectional view of FIG. 2 shows an example of the configuration of the electromechanical conversion element according to the present invention. FIG. 6 further includes an insulating protective film and an extraction wiring of the electromechanical conversion element according to the present invention. An example is shown.
In the electromechanical conversion element shown in FIG. 6, an adhesion layer 181 (a), a first electrode (lower electrode) 181, a metal oxide layer 181 (b), a second electrode ( An upper electrode 182 and an electromechanical conversion film 183 are formed.
The first insulating protective film 184 has a contact hole 189, the first electrode (lower electrode) 181 and the third electrode 185 (a) are electrically connected, and the second electrode (upper electrode) 182. And the fourth electrode 185 (b) are electrically connected. At this time, using the third electrode 185 (a) as a common electrode and the fourth electrode 185 (b) as an individual electrode, a second insulating protective film 186 that protects the common electrode and the individual electrode is formed and partially opened. And configured as an electrode PAD. The electrode prepared for the common electrode is referred to as a common electrode PAD 188, and the electrode manufactured for the individual electrode is referred to as an individual electrode PAD 187.
Below, each constituent material and construction method of the electromechanical conversion element of this invention are demonstrated concretely.

〔substrate〕
As the substrate, it is preferable to use a silicon single crystal substrate, and it is usually preferable to have a thickness of 100 μm to 600 μm [for example, the pressure chamber substrate (Si substrate) in FIG. 2]. There are three types of plane orientations, (100), (110), and (111), but (100) and (111) are generally widely used in the semiconductor industry. A single crystal substrate having a plane orientation of 100) was used. In addition, when a pressure chamber as shown in FIG. 2 is manufactured, a silicon single crystal substrate is processed using etching. In this case, it is common to use anisotropic etching as an etching method. Is.
Anisotropic etching utilizes the property that the etching rate differs with respect to the plane orientation of the crystal structure. For example, in anisotropic etching immersed in an alkaline solution such as KOH, the (111) plane has an etching rate of about 1/400 compared to the (100) plane. Therefore, while a structure having an inclination of about 54 ° can be produced in the plane orientation (100), a deep groove can be removed in the plane orientation (110), so that the arrangement density is increased while maintaining rigidity. In this configuration, it is possible to use a single crystal substrate having a (110) plane orientation. However, in this case, SiO ₂ which is a mask material is also etched, so this area is also used with attention.

[Vibration version]
As shown in FIG. 2, upon receiving the force generated by the electro-mechanical conversion film, the base (vibrating plate) is deformed and displaced, and ink droplets in the pressure chamber are ejected. Therefore, it is preferable that the base has a predetermined strength. Examples of the material include Si, SiO ₂ , and Si ₃ N ₄ produced by the CVD method. Furthermore, it is preferable to select a material close to the linear expansion coefficient of the lower electrode and the electromechanical conversion film as shown in FIG. In particular, as an electro-mechanical conversion film, lead zirconate titanate (PZT) is generally used as a material, so that a linear expansion coefficient close to 8 × 10 ⁻⁶ (1 / K) is 5 A material having a linear expansion coefficient of 10 × 10 ⁻⁶ to 10 × 10 ⁻⁶ (1 / K) is preferable, and further has a linear expansion coefficient of 7 × 10 ^{−6 to} 9 × 10 ⁻⁶ (1 / K). More preferred is the material.
Specific examples of the material include aluminum oxide, zirconium oxide, iridium oxide, ruthenium oxide, tantalum oxide, hafnium oxide, osmium oxide, rhenium oxide, rhodium oxide, palladium oxide, and compounds thereof. It can be produced by a spin coater using a Sol-gel method. The film thickness is preferably 0.1 μm to 10 μm, and more preferably 0.5 μm to 3 μm. If the film thickness is less than 0.5 μm, it is difficult to process the pressure chamber as shown in FIG. 2, and if the film thickness is more than 10 μm, the substrate is difficult to deform and displace, and ink droplet ejection becomes unstable.

[Lower electrode]
As the lower electrode (first electrode in FIG. 6), platinum having high heat resistance and low reactivity is preferably used. As described above, platinum (Pt) is formed by a thin film formation method, and rapid heating processing (RTA processing) is performed after the film formation. The metal oxide layer is formed after controlling the X-ray diffraction peak position 2θ derived from the preferred orientation plane orientation (111) of the lower electrode to a range of 39.90 ° to 40.10 ° by RTA treatment. Although the lower electrode is formed on the diaphragm, it is desirable to provide an adhesion layer between the lower electrode and the diaphragm to suppress peeling and the like.
As a method for producing the Pt film, vacuum film formation such as sputtering or vacuum deposition is generally used. As a film thickness, 80 nm-200 nm are preferable, and 100 nm-150 nm are preferable. If the film thickness is less than 80 nm, a sufficient current cannot be supplied as a common electrode, and a problem occurs when ink is ejected. Furthermore, if the film thickness is thicker than 200 nm, the cost increases due to the use of platinum. When platinum is used as the material, the surface roughness increases as the film thickness increases. This affects the surface roughness and crystal orientation of the metal oxide layer and electro-mechanical conversion film (PZT) to be produced, and causes a problem that sufficient displacement for ink ejection cannot be obtained.

[Adhesion layer]
The adhesion layer can be formed by forming a metal film on the diaphragm and then heat-treating (for example, RTA treatment) to form a film (crystal film) made of a metal oxide. Titanium (Ti) is preferably used as the metal.
In the case of using Ti, Ti is formed on the diaphragm by a thin film forming method such as sputtering to form a titanium layer, and then RTA (Rapid Thermal).
Annealing equipment is heated in an oxygen (O ₂ ) atmosphere (for example, a heating rate of 10 ° C./second or more) and held at a temperature of 650 ° C. to 800 ° C. for 1 to 30 minutes to thermally oxidize the titanium layer. Then, the adhesion layer is formed by converting into a titanium oxide (TiOx) layer.
To form the titanium oxide layer, reactive sputtering may be used, but a thermal oxidation method at a high temperature of the titanium film is desirable. The production by reactive sputtering requires a special sputtering chamber configuration because the silicon substrate needs to be heated at a high temperature. Furthermore, the crystallinity of the titanium oxide film is better in the oxidation by the RTA apparatus than in the oxidation by a general furnace. This is because, according to oxidation in a normal heating furnace, a titanium film that is easily oxidized forms several crystal structures at a low temperature, and thus it is necessary to break it once. Therefore, oxidation by RTA having a high temperature rising rate is advantageous in order to form better crystals. As materials other than Ti, materials such as Ta, Ir, and Ru are also preferably used.
The film thickness of the adhesion layer is preferably 10 nm to 50 nm, and more preferably 15 nm to 30 nm. If the film thickness is less than 10 nm, there is a concern that sufficient adhesion cannot be obtained. If the film thickness is more than 50 nm, the surface roughness of the lower electrode increases and the adhesion with the electromechanical conversion film decreases. . As a result, the crystallinity of the electro-mechanical conversion film is adversely affected, the piezoelectric characteristics are lowered, and a problem that a sufficient displacement for ink ejection cannot be obtained occurs.

[Metal oxide layer]
Titanium (Ti) is preferably used as a material for forming the metal oxide layer. The Ti film can be formed by sputtering, for example. An oxidation treatment is required to make the Ti film a metal oxide layer, but the method can be carried out using an RTA apparatus in the same manner as the production of the adhesion layer. For example, a titanium layer is formed on the surface of a platinum film subjected to RTA treatment, oxidized at a temperature of 650 ° C. to 800 ° C. for 1 minute to 30 minutes in an oxygen (O ₂ ) atmosphere, and made of a metal oxide (TiO x). It can be formed by using a crystal film. The reason is the same as that described in the section of the adhesion layer. The thickness of the metal oxide layer to be formed is preferably 5 nm to 15 nm. If the film thickness is less than 5 nm, the crystal growth of PZT (110) / (111) is promoted and the piezoelectric constant decreases, and if it exceeds 15 nm, the PZT orientation becomes amorphous and it is difficult to control the orientation. It is.
In addition to Ti, Ti / Ir, PbO / TiOx, LNO, PbTiO _{3 and the} like are preferably used as the sputtering film forming material.

[Electro-mechanical conversion membrane]
Examples of the electro-mechanical conversion film include materials composed of complex oxides, but lead zirconate titanate (PZT) was mainly used.
PZT is a solid solution of lead zirconate (PbZrO ₃ ) and titanic acid (PbTiO ₃ ), and the characteristics differ depending on the ratio. In general, a composition exhibiting excellent piezoelectric characteristics is obtained when the ratio of PbZrO ₃ and PbTiO ₃ is 53:47, and is expressed as Pb (Zr _0.53 , Ti _0.47 ) O _{3 in} the chemical formula. It is indicated as PZT (53/47).

As a method for producing the electro-mechanical conversion film, it can be produced by a spin coater using a sputtering method or a Sol-gel method. In that case, since patterning is required, a desired pattern is obtained by photolithography etching or the like.
When PZT is produced by the Sol-gel method, PZT precursor solution can be produced by using lead acetate, zirconium alkoxide, and titanium alkoxide compounds as starting materials and dissolving them in methoxyethanol as a common solvent to obtain a uniform solution. . Since the metal alkoxide compound is easily hydrolyzed by moisture in the atmosphere, an appropriate amount of a stabilizer such as acetylacetone, acetic acid or diethanolamine may be added to the precursor solution as a stabilizer.

When a PZT film is formed on the entire surface of the base substrate, a PZT film can be obtained by forming a coating film by a solution coating method such as spin coating and performing heat treatments such as solvent drying, thermal decomposition, and crystallization. Since the transformation from the coating film to the crystallized film involves volume shrinkage, it is necessary to adjust the precursor concentration so that a film thickness of 100 nm or less can be obtained in one step in order to obtain a crack-free film.
The film thickness of the electromechanical conversion film is preferably 0.5 μm to 5 μm, more preferably 1 μm to 2 μm. If the film thickness is less than 0.5 μm, sufficient displacement cannot be generated, and if the film thickness is more than 5 μm, the number of steps increases due to the lamination of multiple layers, resulting in a problem that the process time becomes long. is there.
The relative dielectric constant of the electromechanical conversion film is preferably 600 or more and 2000 or less, and more preferably 1200 or more and 1600 or less. When the relative dielectric constant is less than 600, sufficient displacement characteristics cannot be obtained, and when the relative dielectric constant exceeds 2000, polarization treatment is not sufficiently performed, and sufficient characteristics cannot be obtained for displacement deterioration after continuous driving. Such a problem occurs.

[Upper electrode]
As the upper electrode (second electrode in FIG. 6), a metal electrode film made of metal or a metal oxide electrode film made of metal oxide and a metal electrode film made of metal are laminated. The electrode made is preferred. Details of the metal oxide electrode film and the metal electrode film are described below.
(Metal oxide electrode film)
As a material, SrRuO ₃ (SRO) is preferably used. Other than the left, Sr _x (A) _(1-x) Ru _y O _(1-y) , [A = Ba, Ca, B = Co, Ni, x, y = 0 to 0.5] Such materials are also mentioned. The film forming method is produced by sputtering. The film thickness of the SRO film is preferably 20 nm to 80 nm, and more preferably 40 nm to 60 nm. If the film thickness is less than 20 nm, sufficient characteristics cannot be obtained for the initial displacement and displacement deterioration characteristics. When the film thickness is greater than 80 nm, the withstand voltage of the deposited PZT is very poor and leaks easily.
(Metal electrode film)
As the metal electrode film, platinum is preferably used like the lower electrode. If necessary, platinum group elements such as iridium and platinum-rhodium, and alloy films thereof can be used.
The thickness of the metal electrode film is preferably 30 nm to 200 nm, more preferably 50 nm to 120 nm. When the film thickness is less than 30 nm, it is impossible to supply a sufficient current as the individual electrode, and a problem occurs when ink is ejected. Further, if the film thickness is greater than 200 nm, when using an expensive platinum group element material, the cost increases. When using platinum as the material, the surface roughness increases as the film thickness increases. When the fourth electrode is manufactured through the insulating protective film, process defects such as film peeling are likely to occur.

[First insulating protective film]
As the first insulating protective film shown in FIG. 6, it is necessary to select a material that prevents damage to the electromechanical conversion element due to the film formation / etching process and is difficult to transmit moisture in the atmosphere. A dense inorganic material is preferable. Organic materials are not suitable because it is necessary to increase the film thickness in order to obtain sufficient protection performance. If the insulating protective film is thick, the vibration displacement of the diaphragm is significantly hindered, resulting in a droplet discharge head with low discharge performance.
In order to obtain high protection performance with a thin film as the first insulating protective film, it is preferable to use an oxide, nitride, or carbonized film, but an electrode material, an electro-mechanical conversion film (PZT) serving as a base of the insulating film It is necessary to select a material having high adhesion to the diaphragm material. In addition, it is necessary to select a film forming method that does not damage the piezoelectric element. That is, a plasma CVD method in which a reactive gas is turned into plasma and deposited on a substrate, or a sputtering method in which a film is formed by causing a plasma to collide with a target material and flying away is not preferable. Examples of a preferable film forming method include a vapor deposition method and an ALD method, but an ALD method with a wide choice of usable materials is preferable. Preferable materials include oxide films used for ceramic materials such as Al ₂ O ₃ , ZrO ₂ , Y ₂ O ₃ , Ta ₂ O ₃ , and TiO ₂ . In particular, by using the ALD method, a thin film having a very high film density is produced and damage in the process is suppressed.

The film thickness of the first insulating protective film needs to be thin enough to ensure the protection performance of the electromechanical conversion element, and at the same time, it needs to be as thin as possible so as not to hinder the displacement of the diaphragm. . The film thickness of the preferable first insulating film protection is in the range of 20 nm to 100 nm. If it is thicker than 100 nm, the displacement of the diaphragm is reduced, so that a droplet discharge head with low discharge efficiency is obtained. On the other hand, when the thickness is less than 20 nm, the function of the piezoelectric element as a protective layer is insufficient, so that the performance of the piezoelectric element is deteriorated as described above.
A configuration in which the first insulating protective film has two layers is also conceivable. In this case, in order to increase the thickness of the second insulating protective film, a configuration in which the second insulating protective film is opened in the vicinity of the second electrode so as not to significantly impede the vibration displacement of the diaphragm can be cited. At this time, as the second insulating protective film, any oxide, nitride, carbide, or a composite compound thereof can be used, but SiO ₂ generally used in semiconductor devices can be used.
Arbitrary methods can be used for the film formation, and a CVD method and a sputtering method can be exemplified, and it is preferable to use a CVD method capable of forming isotropically in consideration of the step coverage of the pattern forming portion such as the electrode forming portion. The thickness of the second insulating protective film needs to be a thickness that does not cause dielectric breakdown by the voltage applied to the lower electrode and the individual electrode wiring. That is, it is necessary to set the electric field strength applied to the insulating film within a range not causing dielectric breakdown. Furthermore, considering the surface properties of the base of the insulating film 2, pinholes, etc., the film thickness needs to be 200 nm or more, and more preferably 500 nm or more.

[Third electrode, fourth electrode]
The third electrode and the fourth electrode shown in FIG. 6 are each preferably a metal electrode material made of Ag alloy, Cu, Al, Au, Pt, or Ir. As a method for manufacturing the third electrode and the fourth electrode, a metal film is manufactured using a sputtering method, a spin coating method, or the like, and then a desired pattern is obtained by photolithography etching or the like.
The film thickness of each electrode is preferably 0.1 μm to 20 μm, more preferably 0.2 μm to 10 μm. If the film thickness is less than 0.1 μm, the resistance increases and it becomes impossible to pass a sufficient current through the electrode, and the discharge of the droplet discharge head becomes unstable. If the film thickness is more than 20 μm, the process time is long. There is a problem of becoming.
Further, the contact resistance at the contact hole portion (10 μm × 10 μm) as the common electrode and the individual electrode is preferably 10Ω or less as the common electrode, 1Ω or less as the individual electrode, and more preferably 5Ω or less as the common electrode. The electrode is 0.5Ω or less. If the contact resistance exceeds 10Ω for the common electrode and 1Ω for the individual electrode, a sufficient current cannot be supplied, and a problem occurs when ink is ejected from the droplet ejection head.

[Second insulating protective film]
The function as the second insulating protective film shown in FIG. 6 is a passivation layer having the function of a protective layer for individual electrode wiring and common electrode wiring. As shown in FIG. 6, the second insulating protective film covers the individual electrode and the common electrode except for the individual electrode lead portion and the common electrode lead portion (not shown). This makes it possible to use inexpensive Al or an alloy material mainly composed of Al as the electrode material. As a result, a low-cost and highly reliable droplet discharge head can be obtained.
As the material of the second insulating protective film, any inorganic material or organic material can be used, but it is necessary to use a material with low moisture permeability. Examples of the inorganic material include oxides, nitrides, and carbides, and examples of the organic material include polyimide, acrylic resin, and urethane resin. However, in the case of an organic material, it is necessary to form a thick film, which is not suitable for patterning described later. Therefore, it is preferable to use an inorganic material that can exhibit a wiring protection function with a thin film. In particular, it is preferable to use Si ₃ N ₄ on the Al wiring because it is a proven technology for semiconductor devices.

The thickness of the second insulating protective film needs to be 200 nm or more, and more preferably 500 nm or more. When the film thickness is small, a sufficient passivation function cannot be exhibited, so that disconnection due to corrosion of the wiring material occurs, and stable ink discharge from the droplet discharge head cannot be performed, and the reliability of the ink jet is lowered.
A structure having openings on the electromechanical conversion element and on the surrounding diaphragm is preferable. This is the same reason that the individual liquid chamber region of the first insulating protective film is thinned. As a result, a highly efficient and highly reliable droplet discharge head can be obtained.

Since the electromechanical conversion element is protected by the first insulating protective film and the second insulating protective film, photolithography and dry etching can be used to form the opening. In addition, the area of the PAD part is preferably 50 × 50 μm ² or more, and more preferably 100 × 300 μm ² or more. If the value is less than this value, sufficient polarization processing cannot be performed, and there arises a problem that sufficient characteristics cannot be obtained for displacement deterioration after continuous driving.

As described above, it is composed of diaphragm / adhesion layer (TiOx) / lower electrode (Pt) / metal oxide layer (TiOx) / electro-mechanical conversion film (PZT) / upper electrode (SRO layer / Pt layer). The electromechanical conversion element has high piezoelectricity and exhibits, for example, a PE hysteresis curve as shown in FIG.
In addition, it is preferable that the electromechanical conversion element manufactured with the above-mentioned structure is polarized by injection of electric charges generated by corona discharge. The state of the polarization treatment can be determined from the PE hysteresis curve.
Polarized electrical - in P-E hysteresis when applying an electric field strength of ± 150 kV / cm in the transducer, it is preferable maximum polarization Pm value is 30 .mu.C / cm ² or more 40 .mu.C / cm ² or less.
Further, as shown in FIG. 8, a hysteresis loop is measured with an electric field strength of ± 150 kV / cm, and the polarization at the time of the first 0 kV / cm is Pini, 0 kV / cm when the voltage is returned to 0 kV / cm after applying +150 kV / cm. When the polarization at cm is Pr, the value of Pr−Pini is defined as the polarizability, and the quality of the polarization state can be judged from this polarizability.
Here polarizability Pr-Pini is preferably at 6.0μC / cm ² or less, and more preferably 3.0μC / cm ² or less. When the polarizability Pr-Pini exceeds 6.0 μC / cm ² , sufficient characteristics cannot be obtained for displacement deterioration after continuous driving as an electro-mechanical conversion film of PZT.

The droplet discharge head of the present invention is characterized by including the above-described electro-mechanical conversion element. That is, it has a plurality of nozzle openings, a flow path forming substrate having a pressurized liquid chamber communicating with each nozzle opening, and a diaphragm that forms one surface of the pressurized liquid chamber, and electro-mechanical conversion on the diaphragm An element is provided, and the electro-mechanical conversion element is configured by providing a lower electrode, an electro-mechanical conversion film, and an upper electrode on a vibration plate.
If the droplet discharge head is configured using the electromechanical conversion element of the present invention, the ink droplet discharge characteristics can be maintained with the same driving force as that of the ceramic sintered body, and stable ink droplet discharge characteristics can be obtained even when continuously discharged. Can be maintained.

By including the droplet discharge head of the present invention, an ink cartridge can be configured. FIG. 9 shows a configuration in which a plurality of droplet discharge head configurations shown in FIG. 2 are arranged.
According to the present invention, an electro-mechanical conversion element having performance equivalent to that of bulk ceramics can be formed, and then etching is removed from the back surface for forming a pressure chamber, and a droplet is obtained by joining a nozzle plate having nozzle holes. A discharge head is formed. In the figure, descriptions of liquid supply means, flow paths, and fluid resistance are omitted. In FIG. 9, reference numeral 901 is a pressure chamber, 902 is a nozzle, 903 is a nozzle plate, 904 is a pressure chamber substrate (Si substrate), 905 is a vibration plate, 906 is an adhesion layer, and 907 is an electro-mechanical conversion element.
If the droplet discharge head of the present invention is used, the discharge stability, durability, and image quality are good, so that it can be applied to image forming apparatuses such as printers and MFPs used in offices and personal computers.

  An example of an image forming apparatus equipped with the droplet discharge head of the present invention will be described with reference to FIGS. 10 is a perspective view of the recording apparatus, and FIG. 11 is a side view of a mechanism portion of the image forming apparatus.

  The image forming apparatus shown in FIGS. 10 and 11 includes a carriage 93 movable in the main scanning direction inside a recording apparatus main body 81, a droplet discharge head 94 embodying the present invention mounted on the carriage 93, and the droplet discharge head. A paper feed cassette (or a paper feed cassette) that accommodates a number of sheets 83 from the front side in the lower part of the recording apparatus main body 81 is stored. 84 may be detachably mounted, and the manual feed tray 85 for manually feeding the paper 83 can be unfolded and fed from the paper feed cassette 84 or the manual feed tray 85. The sheet 83 is taken in, a required image is recorded by the printing mechanism unit 82, and then discharged to a discharge tray 86 mounted on the rear side.

  The printing mechanism 82 holds a carriage 93 slidably in the main scanning direction by a main guide rod 91 and a sub guide rod 92 which are guide members horizontally mounted on left and right side plates (not shown). The droplet discharge head 94 of the present invention that discharges ink droplets of each color (Y), cyan (C), magenta (M), and black (Bk) crosses a plurality of ink discharge ports (nozzles) with the main scanning direction. The ink droplets are mounted with the ink droplet discharge direction facing downward. In addition, each ink cartridge 95 for supplying ink of each color to the droplet discharge head 94 is replaceably mounted on the carriage 93.

  The ink cartridge 95 has an air port that communicates with the atmosphere upward, a supply port that supplies ink to the droplet discharge head 94 below, and a porous body filled with ink inside. The ink supplied to the droplet discharge head 94 is maintained at a slight negative pressure by the capillary force. Further, although the droplet discharge heads 94 for the respective colors are used here as the recording heads, a single droplet discharge head having nozzles for discharging the ink droplets of the respective colors may be used.

  Here, the carriage 93 is slidably fitted to the main guide rod 91 on the rear side (downstream side in the paper conveyance direction), and is slidably mounted on the sub guide rod 92 on the front side (upstream side in the paper conveyance direction). doing. In order to move and scan the carriage 93 in the main scanning direction, a timing belt 100 is stretched between a driving pulley 98 and a driven pulley 99 that are rotationally driven by a main scanning motor 97, and the timing belt 100 is moved to the carriage 93. The carriage 93 is driven to reciprocate by forward and reverse rotation of the main scanning motor 97.

  On the other hand, in order to convey the paper 83 set in the paper feed cassette 84 to the lower side of the droplet discharge head 94, the paper feed roller 101 and the friction pad 102 for separating and feeding the paper 83 from the paper feed cassette 84, and the paper 83 A guide member 103 that guides the sheet 83, a conveyance roller 104 that conveys the fed sheet 83 in a reversed manner, a conveyance roller 105 that is pressed against the circumferential surface of the conveyance roller 104, and a feed angle of the sheet 83 from the conveyance roller 104. A leading end roller 106 is provided. The transport roller 104 is rotationally driven by a sub-scanning motor 107 through a gear train.

  A printing receiving member 109 is provided as a sheet guide member for guiding the sheet 83 fed from the conveying roller 104 below the droplet discharge head 94 in accordance with the movement range of the carriage 93 in the main scanning direction. . A conveyance roller 111 and a spur 112 that are rotationally driven to send the paper 83 in the paper discharge direction are provided on the downstream side of the printing receiving member 109 in the paper conveyance direction, and the paper 83 is further delivered to the paper discharge tray 86. A roller 113 and a spur 114, and guide members 115 and 116 that form a paper discharge path are disposed.

  During recording, the droplet discharge head 94 is driven according to the image signal while moving the carriage 93, thereby ejecting ink onto the stopped paper 83 to record one line, and transporting the paper 83 by a predetermined amount. After that, the next line is recorded. Upon receiving a recording end signal or a signal that the trailing edge of the paper 83 has reached the recording area, the recording operation is terminated and the paper 83 is discharged.

  Further, a recovery device 117 for recovering the ejection failure of the droplet ejection head 94 is disposed at a position outside the recording area on the right end side in the movement direction of the carriage 93. The recovery device 117 includes a cap unit, a suction unit, and a cleaning unit. While waiting for printing, the carriage 93 is moved to the recovery device 117 side and the droplet discharge head 94 is capped by the capping unit, and the discharge port portion is kept in a wet state to prevent discharge failure due to ink drying. Further, by ejecting ink that is not related to recording during recording or the like, the ink viscosity of all the ejection ports is made constant and stable ejection performance is maintained.

  When ejection failure occurs, the capping means seals the ejection port (nozzle) of the droplet ejection head 94, sucks out bubbles and the like from the ejection port with the suction means through the tube, and adheres to the ejection port surface. The dust and the like are removed by the cleaning means, and the ejection failure is recovered. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed at the lower part of the main body and absorbed and held by an ink absorber inside the waste ink reservoir.

  As described above, in the image forming apparatus of the present invention, since the liquid droplet ejection head manufactured using the electro-mechanical conversion element of the present invention is mounted, there is no ink droplet ejection failure due to vibration plate drive failure, and stability. Ink droplet ejection characteristics can be obtained and image quality is improved.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these Examples at all.

[Examples 1-2, Comparative Examples 1-3]
A thermal oxide film (film thickness: 1 μm) was formed on a 6 inch silicon wafer (Si substrate) to constitute a diaphragm. Next, an adhesion layer was formed on the diaphragm. The adhesion layer was formed by depositing titanium (Ti) on the vibration plate of the Si substrate with a sputtering apparatus (film thickness: 50 nm) and then thermally oxidizing at 730 ° C. using an RTA apparatus to form titanium oxide (TiOx). Is. Subsequently, in order to form a lower electrode on the adhesion layer, a platinum film (film thickness 160 nm) was first formed by sputtering. Film formation was performed while maintaining the Si substrate heating temperature at 300 ° C. during sputtering film formation. The formed platinum film was heated at a rate of 10 ° C./second or more, and then subjected to rapid heating treatment (RTA treatment) at the following predetermined temperature for 3 minutes. An example in which the RTA treatment is not performed is shown in Comparative Example 3 of Table 1.
RTA treatment temperature described in Table 1 (Comparative Example 1): 570 ° C
RTA treatment temperature described in Table 1 (Comparative Example 2): 650 ° C
RTA treatment temperature described in Table 1 (Example 1): 730 ° C
RTA treatment temperature described in Table 1 (Example 2): 810 ° C
Table 1 (Comparative Example 3) No RTA treatment Note that the comparative example and the example are classified as follows: the orientation ratio of the PZT plane orientation (100) is 70% or more, and the plane orientation (200) and plane orientation (002). It is judged including whether or not the rocking curve half-value width in the ratio [(200) / (002)] is 10 ° or less.
In order to form a metal oxide layer on the surface of the platinum film subjected to RTA treatment, a titanium layer was formed by a sputtering apparatus, and was thermally oxidized at 730 ° C. using an RTA apparatus to form a metal oxide layer (TiOx). The thickness of the metal oxide layer was 10 nm. According to the flowchart shown in FIG. 12, the formation of the adhesion layer, the formation of the lower electrode, and the formation of the metal oxide layer were sequentially performed. FIG. 13 shows an image of a platinum film (Example 1) having a metal oxide layer formed on the surface according to the flowchart of FIG. 12 and observed with an atomic force microscope (AFM). FIG. 13A shows the tapping mode, and FIG. 13B shows the PM mode.
Next, an electro-mechanical conversion film made of PZT was formed on the lower electrode having the metal oxide layer. That is, a solution (precursor coating solution) adjusted to Pb: Zr: Ti = 114: 53: 47 was prepared, and this solution was applied onto the lower electrode having the metal oxide layer by spin coating. Filmed.

  For the synthesis of a specific precursor coating solution, lead acetate trihydrate, isopropoxide titanium and isopropoxide zirconium were used as starting materials. Crystal water of lead acetate was dissolved in methoxyethanol and then dehydrated. The lead amount is excessive with respect to the stoichiometric composition. This is to prevent crystallinity deterioration due to so-called lead loss during heat treatment. Isopropoxide titanium and isopropoxide zirconium were dissolved in methoxyethanol, the alcohol exchange reaction and the esterification reaction were advanced, and the PZT precursor solution was synthesized by mixing with the methoxyethanol solution in which the lead acetate was dissolved. The PZT concentration was 0.5 mol / l. Using this liquid, a film was formed by spin coating, and after the film formation, thermal decomposition was performed by heating from 120 ° C. (dry) to 500 ° C. After thermal decomposition treatment of the third layer, crystallization heat treatment (temperature: 750 ° C.) was performed by RTA (rapid heat treatment). At this time, the film thickness of PZT was 240 nm. This process was performed a total of 8 times (24 layers) to obtain PZT having a film thickness of about 2 μm.

  An SRO film (film thickness: 20 nm) and a platinum film (film thickness: 125 nm) are sequentially formed on an electro-mechanical conversion film (PZT) by sputtering to form an upper electrode (second electrode). The electromechanical conversion elements of 1-2 and Comparative Examples 1-3 were produced.

  Table 1 shows the processing conditions, the platinum film (Pt) state, and the PZT crystallinity of the electromechanical transducers of Examples 1-2 and Comparative Examples 1-3 formed under the above conditions. Specifically, the deposition temperature of the platinum film (Pt), the X-ray diffraction peak position 2θ after the deposition of Pt (111), the RTA treatment temperature after the deposition, the same treatment time, and the Pt (111) after the RTA treatment X-ray diffraction peak position 2θ, surface roughness Rz of lower electrode having metal oxide layer, orientation ratio of PZT (100), peak intensity, rocking curve (RC) half width at (200) / (002) Is shown in Table 1.

As shown in Table 1, in both Example 1 and Example 2 of the present invention, the preferential orientation plane orientation of the lower electrode is (111), and the X-ray diffraction peak position 2θ derived from the (111) plane is It is in the range of 39.90 ° to 40.10 °, and the orientation ratio of the plane orientation (100) of the electro-mechanical conversion film (PZT) is 70% or more, and at (200) / (002) The full width at half maximum of the rocking curve is 10 ° or less.
For example, FIG. 14 shows changes in the XRD peak position 2θ before and after the RTA process of the example. As shown in FIG. 14, the peak position 2θ of 39.82 before the RTA process is shifted to about 40 after the RTA process. This indicates that the residual stress in the platinum film is released. That is, when the residual stress in the platinum film is released, the generation of hillocks can be prevented during formation of the metal oxide layer (oxidation treatment of the titanium layer), and the surface roughness of the lower electrode having the metal oxide layer Rz is in the range of about 24 nm to 27 nm. And it was confirmed that there was no crystallinity fall of PZT and the outstanding piezoelectric characteristic was hold | maintained.
In Comparative Examples 1 and 2, the XRD peak position 2θ before and after the RTA treatment is changed, but the rocking curve (RC) half-width at (200) / (002) exceeds 10 °, and the crystallinity of PZT As a result, the piezoelectric characteristics deteriorated.
In Comparative Example 3, the residual stress was not released and the generation of hillocks could not be prevented.
As described above, as a result of changing the RTA treatment temperature from 570 ° C. to 810 ° C., PZT (electro-mechanical conversion film) having excellent crystallinity of (100) plane orientation is obtained particularly at 730 ° C. to 810 ° C. It was.
In each of Examples 1 and 2, the generation of hillocks in the platinum film is suppressed, there is no decrease in pressure resistance or increase in leakage current due to local concentration of electric field, and the PZT plane orientation is preferentially oriented to (100). An excellent electromechanical conversion element was provided.

[Examples 3-5, Comparative Examples 4-5]
In the configuration of Example 1, the electromechanical devices of Examples 3 to 5 and Comparative Examples 4 to 5 were the same as Example 1 except that the film thickness of the metal oxide layer was changed as follows. A conversion element was produced.
Film thickness of the metal oxide layer described in Table 2 (Comparative Example 4): 5.8 nm
Film thickness of metal oxide layer described in Table 2 (Example 3): 8.0 nm
Film thickness of the metal oxide layer described in Table 2 (Example 4): 10.2 nm
Film thickness of metal oxide layer described in Table 2 (Example 5): 12.2 nm
Film thickness of the metal oxide layer described in Table 2 (Comparative Example 5): 14.1 nm

  Example 3-5 formed under the above conditions, the film formation temperature of the platinum film (Pt) of the electromechanical conversion element of Comparative Examples 4-5, the film thickness of the metal oxide layer (TiOx), the metal oxide layer Table 2 shows the surface roughness Rz, the orientation ratio of PZT (100), the peak intensity, and the rocking curve (RC) half width at the same (200) / (002).

In Table 2, since the orientation rate of PZT (100) was less than 70% (50.7%) in Comparative Example 4, excellent piezoelectric characteristics could not be obtained.
In Comparative Example 5, the full width at half maximum of the rocking curve in [(200) / (002)] exceeded 10 °, the crystallinity of PZT was lowered, and the piezoelectric characteristics were lowered.
In all of Examples 3 to 5 of the present invention, the preferred orientation plane orientation of the lower electrode is (111), and the X-ray diffraction peak position 2θ derived from the (111) plane is 39.90 ° to 40.40. Further, the orientation ratio of the plane orientation (100) of the electro-mechanical conversion film (PZT) is 70% or more, and the rocking curve half width at (200) / (002) is also 10 °. It is as follows. However, in Example 3, the surface roughness Rz of the lower electrode having the metal oxide layer was slightly large, but unlike the hillock accompanying the residual stress of the so-called lower electrode, the crystallinity degradation of PZT was limited. In Examples 4 and 5, there was no decrease in the crystallinity of PZT. That is, an electromechanical conversion film having good PZT (100) crystallinity was obtained when the thickness of the metal oxide layer (TiOx) was 10.2 nm to 12.2 nm.
As a film thickness of the metal oxide layer, it is judged that a range of about 5 nm to 15 nm is preferable comprehensively from various experiments.
In all of Examples 3 to 5, the generation of hillocks in the platinum film is suppressed, there is no decrease in pressure resistance due to local concentration of the electric field, and there is no increase in leakage current, and the PZT plane orientation is preferentially oriented to (100). An electromechanical transducer having excellent characteristics has been provided.

[Comparative Examples 6-8]
In the configuration of Example 1, the Si substrate heating temperature (Pt film formation temperature) at the time of sputtering film formation when forming the platinum film was as follows, except that the Pt film was formed and the RTA treatment was not performed. In the same manner as in Example 1, the electromechanical conversion elements of Comparative Examples 6 to 8 were produced.
Pt deposition temperature described in Table 3 (Comparative Example 6): 300 ° C
Pt deposition temperature described in Table 3 (Comparative Example 7): 400 ° C
Pt deposition temperature described in Table 3 (Comparative Example 8): 500 ° C

Film formation temperature of the platinum film (Pt) of the electromechanical conversion elements of Comparative Examples 6 to 8 formed under the above conditions,
The peak position, the same peak intensity, the Pt particle size, the surface roughness Rz of the lower electrode having the metal oxide layer, the orientation ratio of PZT (100), the same peak intensity, the same (200) / The rocking curve (RC) half width at (002) is shown in Table 3.

In each of Comparative Examples 6 and 7, hillocks (see FIG. 1) occurred, which caused problems with a decrease in pressure resistance and an increase in leakage current. In addition, with the generation of hillocks, the piezoelectric properties of PZT deteriorated.
Although no hillock occurred when the Pt film formation temperature of Comparative Example 8 was 500 ° C., the crystallinity of PZT (100) was lowered and the piezoelectric characteristics were reduced because the Pt particle size increased and Pt (111) increased. Declined.

That is, the electromechanical conversion element of the present invention suppresses generation of hillocks on the lower electrode even when an oxidation treatment is performed at the time of forming the metal oxide layer, and does not cause a decrease in pressure resistance or an increase in leakage current. Excellent characteristics. For this reason, the characteristics (piezoelectric constant) equivalent to those of the ceramic sintered body are maintained, and the displacement of the electro-mechanical conversion film is sufficiently ensured to maintain the ink ejection characteristics satisfactorily. Deterioration is sufficiently suppressed, and stable ink ejection characteristics can be obtained.
If a droplet discharge head is configured using such an electro-mechanical conversion element, it has excellent discharge stability and durability, so that it can be applied to office, personal printers, MFPs, and other image forming apparatuses. Application to three-dimensional molding technology is also possible.

(Reference in FIG. 2)
101 Pressure chamber 102 Nozzle 103 Nozzle plate 104 Pressure chamber substrate (Si substrate)
105 Ground (diaphragm)
106 Lower electrode 107 Electro-mechanical conversion film 108 Upper electrode 109 Electro-mechanical conversion element (reference numeral in FIG. 3)
401 Substrate 402 Diaphragm 403 (a) Adhesion layer 403 Lower electrode 403 (b) Metal oxide layer 404 Electric-mechanical conversion film 405 Upper electrode (reference numeral in FIG. 6)
181 First electrode (lower electrode)
181 (a) Adhesion layer 181 (b) Metal oxide layer 182 Second electrode (upper electrode)
183 Electro-mechanical conversion film 184 First insulating protective film 185 (a), (b) Third and fourth electrodes 186 Second insulating protective film 187 Individual electrode PAD
188 Common electrode PAD
189 Contact hole (reference numeral in FIG. 9)
901 Pressure chamber 902 Nozzle 903 Nozzle plate 904 Pressure chamber substrate (Si substrate)
905 Diaphragm 906 Adhesion layer 907 Electro-mechanical conversion element (reference numerals in FIGS. 10 and 11)
81 Recording Device Body 82 Printing Mechanism Unit 83 Paper 84 Paper Feed Cassette 85 Tray 86 Paper Discharge Tray 91 Main Guide Rod 92 Subordinate Guide Rod 93 Carriage 94 Head 95 Ink Cartridge 97 Main Scanning Motor 98 Drive Pulley 99 Driven Pulley 100 Timing Belt 101 Feed Paper roller 102 Friction pad 103 Guide member 104 Transport roller 105 Transport roller 106 Front roller 107 Sub-scanning motor 109 Printing receiving member 111 Transport roller 112 Spur 113 Discharge roller 114 Spur 115 Guide member 116 Guide member 117 Recovery device

Japanese Patent No. 4543545 JP 11-191646 A JP 2008-244201 A Japanese Patent No. 4530615 Japanese Patent No. 3842279 Japanese Patent No. 4207167 Japanese Patent No. 3541877 JP 2006-287161 A JP 2003-45873 A Japanese Patent Laid-Open No. 11-45984 JP 2008-227115 A Japanese Patent No. 3892424 Japanese Patent No. 5179714 JP 2012-15505 A JP 2011-238774 A

Claims (11)

An electro-mechanical conversion element comprising a lower electrode, an electro-mechanical conversion film, and an upper electrode on the diaphragm, and having a metal oxide layer on the lower electrode,
The lower electrode is made of a platinum film that has been subjected to rapid heat treatment after film formation, and the preferred orientation plane orientation of the lower electrode is (111), and the X-ray diffraction peak position 2θ derived from the (111) plane is 39. In the range of 90 ° to 40.10 °,
The electro-mechanical conversion film is made of PZT, the orientation ratio of the plane orientation (100) of the PZT is 70% or more, and the half width of the rocking curve in the plane orientation (200) / (002) of the PZT is 10 °. An electro-mechanical conversion element characterized by the following.   2. The electromechanical conversion element according to claim 1, wherein the lower electrode having the metal oxide layer has a surface roughness Rz of 50 nm or less.   The electromechanical conversion element according to claim 1, wherein the metal oxide layer contains titanium as a constituent component.   The electro-mechanical transducer according to any one of claims 1 to 3, wherein the metal oxide layer has a thickness of 5 nm to 15 nm.   5. The electromechanical conversion element according to claim 1, wherein the metal oxide layer is obtained by oxidizing a formed titanium layer at a temperature of 650 ° C. to 800 ° C. 6.   6. The electromechanical conversion element according to claim 1, wherein a particle diameter of the platinum film subjected to the rapid heating treatment is in a range of 60 nm to 280 nm.   The rapid heating treatment is characterized in that the platinum film is heated to 650 ° C. to 850 ° C. at a temperature rising rate of 10 ° C./second or more for 1 minute to 5 minutes before forming the metal oxide layer. The electromechanical transducer according to any one of claims 1 to 6. A method for producing an electromechanical conversion element according to any one of claims 1 to 7,
An adhesion layer forming step, a lower electrode forming step, a metal oxide layer forming step, an electromechanical conversion film forming step, and an upper electrode forming step;
The lower electrode forming step includes
Forming a platinum film on the adhesion layer;
Heating the formed platinum film to 650 ° C. to 850 ° C. at a temperature rising rate of 10 ° C./second or more and performing a rapid heat treatment for 1 minute to 5 minutes,
The metal oxide layer forming step includes
Including a step of forming a titanium layer on the surface of the platinum film subjected to the rapid heating treatment and forming a metal oxide layer by oxidation treatment at a temperature of 650 ° C. to 800 ° C.
The electro-mechanical conversion film forming step includes:
Including a step of applying a PZT precursor solution on the metal oxide layer to form a laminate;
The method of manufacturing an electromechanical conversion element, wherein the upper electrode forming step includes a step of forming a metal electrode film or a metal oxide electrode film and a metal electrode film.   A liquid droplet ejection head comprising the electro-mechanical conversion element according to claim 1.   An ink cartridge comprising the droplet discharge head according to claim 9.   An image forming apparatus comprising the droplet discharge head according to claim 9.