JP5998534B2 - Piezoelectric film structure, electric-mechanical conversion element, droplet discharge head, and droplet discharge apparatus - Google Patents

Description

  The present invention relates to a droplet discharge head using a piezoelectric film structure, an electromechanical conversion element having the structure, and a droplet discharge apparatus having the droplet discharge head.

As the piezoelectric ceramic material, ABO ₃ type perovskite oxide is used. Particularly in ferroelectric ceramic materials, lead zirconate titanate (PZT) is the mainstream material.

  However, since the PZT film contains lead (Pb), it is considered that there is a problem in terms of worker safety and environment. Therefore, research and development of lead-free piezoelectric materials that do not contain lead are widely performed.

Barium titanate (BaTiO ₃ ) is known as a lead-free ferroelectric ceramic material. Non-Patent Document 1 discloses that the electric characteristics of barium titanate relate to the particle size. The optimum size is about 1 μm.

Conventionally, since PZT can crystallize at 800 ° C. or less, as shown in Patent Document 1, platinum (Pt) lower electrode and the silicon oxide film of titanium between the (SiO ₂₎ (Ti) or titanium oxide (TiO ₂₎ Is usually used as an adhesion layer.

  Non-Patent Document 2 discloses that the particle size of barium titanate relates to the processing temperature. In order to form a large particle size, a high temperature process at 1000 ° C. or higher is preferable.

According to Non-Patent Document 3, when the heat treatment is performed at 1000 ° C., the surface of the Pt film having a titanium oxide adhesion layer is deteriorated, and a part of the Pt film is separated from the substrate. The Pt film having a structure having an (Al ₂ O ₃ ) adhesion layer does not leave the substrate, and the surface has no film defects such as hillocks and voids.

  However, as shown in the SEM observation results of Non-Patent Document 3, so-called grain growth was observed in which the particle size of the Pt film after heat treatment was several times larger than that before treatment. Along with this change, residual stress is generated in the Pt film.

  Furthermore, the thermal expansion coefficient of the alumina film differs from that of the silicon oxide film by about one digit. Since the alumina film is formed directly on the silicon oxide film, a large thermal stress is generated due to the coefficient of thermal expansion, and when an actuator is formed with such a structure, the electrostrictive characteristics are stressed. There is a problem with device uniformity.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to improve the heat-resistant adhesion between the diaphragm and the lower electrode and to provide a stable piezoelectric film structure and electro-mechanical conversion element. Another object is to provide a droplet discharge head and a droplet discharge device.

  In order to achieve this object, the present invention has the following features.

Piezoelectric film structure according to the present invention, a silicon oxide film on a silicon substrate, at least a silicon nitride film the film thickness is less than the silicon thermal expansion coefficient than the silicon substrate formed in the oxide film on the size KuKatsu silicon oxide film A film structure including one layer, an alumina film formed on the film structure, having a thermal expansion coefficient larger than that of the film structure and smaller than the film structure , a lower electrode provided on the alumina film, and the lower part A piezoelectric film provided on the electrode and an upper electrode provided on the piezoelectric film are provided.

  According to the present invention, it is possible to provide a piezoelectric film structure, an electromechanical conversion element, a droplet discharge head, and a droplet discharge device that have improved heat-resistant adhesion between the diaphragm and the lower electrode and that are also stable.

It is a figure which shows the structure of the piezoelectric film structure which concerns on this embodiment. It is a figure which shows the starting material of the CSD method which concerns on this embodiment, a common solvent, and a stabilizer. It is a figure which shows the structure of the piezoelectric film structure which concerns on this embodiment. It is a figure which shows the droplet discharge head which has an electronic device structure concerning this embodiment. 1 is a perspective explanatory view of an ink jet recording apparatus according to an embodiment. It is side surface explanatory drawing of the mechanism part of the inkjet recording device which concerns on this embodiment.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram showing a configuration of a piezoelectric film structure according to the present embodiment. As shown in FIG. 1, a silicon oxide film (SiO ₂ ) 2 having a thickness of about 600 nm is formed on a silicon (Si, 001) substrate 1, and a silicon nitride film (SiN) is formed thereon by LPCVD (Low Pressure Chemical Vapor Deposition). _x , 200 nm) 3, silicon oxide film (50 nm) 4 by LPCVD, alumina (Al ₂ O ₃ , 50 nm) adhesion layer 5 by RF sputtering, platinum (Pt, 200 nm) lower electrode 6, and then by CSD method A lead-free composite oxide BST (Ba (Sn _x Ti _1-x ) O ₃ ) piezoelectric film 7 is deposited.

The main component of the alumina adhesion layer 5 is Al ₂ O ₃ , and inevitable impurity elements such as Ti and Fe may exist.

  The film structure having a thermal expansion coefficient larger than that of the silicon substrate 1 formed on the silicon oxide film 2 is a single layer or multi-layer structure, and includes at least one silicon nitride film structure. The silicon nitride film 3 and the silicon oxide film 4 It consists of. The thermal expansion coefficient of the film structure having a larger thermal expansion coefficient than that of the silicon substrate 1 is smaller than the thermal expansion coefficient of the alumina film 5.

  The film structure composed of the silicon oxide film 2, the silicon nitride film 3, the silicon oxide film 4, and the alumina adhesion layer 5 is a diaphragm. The lower electrode is a heat-resistant material having a melting point of 1000 ° C. or higher, and includes at least platinum (Pt), iridium (Ir), rhodium (Rh), or one of these alloys.

  Next, a piezoelectric film is a thinned material that gives mechanical change (displacement) to electrical input, and is generally a material that exhibits a piezoelectric effect or a material that exhibits an electrostrictive effect. Piezoelectric generates strain proportional to the input electric field strength, and electrostriction generates strain proportional to the square of the electric field strength.

Piezoelectric film is a ABO ₃ type oxide containing no ABO ₃ type oxides or lead containing lead (Pb). Here, the procedure of the manufacturing method for the BST piezoelectric film 7 will be described. FIG. 2 is a diagram showing starting materials, common solvents, and stabilizers for the CSD method.

A predetermined amount of Ba (OEt) ₂ , Ti (O ⁱ Pr) ₄ , and Sn (O ⁱ Pr) ₄ is dissolved in EGMME. The dissolution temperature is obtained by refluxing at 100 to 124 ° C. for 18 hours. In addition, MEA as a stabilizer is added in an amount twice as much as the alkoxide group of the starting material. In order to increase the solubility of Ba (OEt) ₂ , methanol is added after the completion of the reaction, and reflux at 80 ° C. for 6 hours is added. The precursor solution is adjusted to a concentration of 0.3M.

  A precursor solution is formed on the Pt film by spin coating (rotation speed: 2500 rpm, 30 seconds), and then dried at 120 ° C. for 1 minute, followed by thermal decomposition treatment. This process can be estimated from the TG-DTA measurement of the dried gel produced from the precursor solution. In this embodiment, the process is performed at 400 ° C. for 10 minutes. Subsequently, crystallization is performed.

  The film after pyrolysis is an amorphous material, and a crystallized film can be obtained by performing a heat treatment at 700 ° C. or higher in order to make the electrostrictive characteristics appear. In this embodiment, the treatment was performed at 1000 ° C. for 1 hour. The film thickness that can be deposited by this operation was 50 nm.

  When used as an actuator, the generated force deforms the diaphragm, and the amount of deformation eliminates ink in the ink chamber, so a film thickness of approximately 0.5 to 2 microns is required. Accordingly, the spin coating, drying, thermal decomposition, and crystallization are repeated for the desired film thickness. In this embodiment, this operation was performed 10 times to form a film of about 0.5 microns.

  Next, a Pt (100 nm) upper electrode 8 is deposited on the BST piezoelectric film 7 by RF sputtering to form a film structure as shown in FIG. This structure has high reliability and can be used as a lead-free electromechanical conversion element. The electro-mechanical conversion element is an element having a structure in which the material that gives the electric strain is thinned and electrode films are arranged on the upper and lower surfaces of the film for electric field input.

(Embodiment 2)
As shown in FIG. 3, a silicon oxide film 12 having a thickness of about 600 nm is formed on a silicon (001) substrate 11, and a silicon nitride film (100 nm) 13 is formed thereon by LPCVD (Low Pressure Chemical Vapor Deposition). An alumina film (25 nm) 14 and Pt (200 nm) 15 are sequentially formed by RF sputtering. This silicon wafer is heat-treated at 900 ° C. for 30 minutes. The film structure composed of the silicon oxide film 12, the silicon nitride film 13, and the alumina adhesion layer 14 is a diaphragm.

  Next, an SRO film (60 nm) 16 is formed on the Pt film 15 by RF sputtering. The Pt film 15 and the SRO film 16 are lower electrodes. Further, a lead zirconate titanate (PZT) film 17 is formed as a piezoelectric film on the SRO 16 by the CSD method.

  In the synthesis of the precursor coating solution for the PZT film 17, 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 10 mol% excess relative 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 above lead acetate was dissolved. The PZT concentration was 0.1 mol / l.

  A PZT precursor solution is applied on the SRO film 16 by using this solution with a spin device. The film thickness obtained by one film formation is preferably around 100 nm, and the precursor concentration is optimized from the relationship between the film formation area and the amount of applied precursor. This is subjected to 300 ° C. treatment as first heating (solvent drying) and then calcined at 500 ° C. The PZT film thickness at this time was 110 nm.

  After applying the PZT precursor solution, it was dried at 300 ° C., and the process of calcining at 500 ° C. was repeated three times to obtain a 330 nm PZT film 17, followed by 730 ° C. crystallization main firing at RTA. Defects such as cracks did not occur in the film. Further, after applying the PZT precursor solution three times, it was dried at 300 ° C., calcined at 500 ° C., and then subjected to 730 ° C. crystallization main firing treatment. Defects such as cracks did not occur in the film. The film thickness reached 1000 nm.

  Next, an SRO film (200 nm) 18 and a Pt film (100 nm) 19 were formed by sputtering as the upper electrode to form an electronic device structure as shown in FIG. The electronic device thus formed has a small leakage current and can improve fatigue resistance as an actuator.

(Embodiment 3)
FIG. 4 is a view showing a droplet discharge head 21 having the electronic device structure as shown in FIG. 1 or FIG. FIG. 4A is a diagram illustrating a configuration of a one-nozzle droplet discharge head. FIG. 4B is a diagram illustrating a configuration of a droplet discharge head in which a plurality of nozzles 22 are arranged. In the figure, descriptions of the liquid supply means, the flow path, and the fluid resistance are omitted. First, the pressure chamber 23, the pressure chamber plate 24, the nozzle 22 and the nozzle plate 25 shown in FIG. 4 will be described.

<Pressure chamber 23, pressure chamber plate 24 (Si substrate)>
The pressure chamber 23 is formed by communicating with the nozzle 22, and is divided by a pressure chamber plate 24 that forms a side surface, a nozzle plate 25 that forms a lower surface, and a vibration plate 26 that forms an upper surface. A piezoelectric layer (electronic device) for pressurizing the liquid in the pressure chamber 23 via the vibration plate 26 is provided. The pressure chamber plate 24 is formed by a method such as etching a silicon wafer.

<Nozzle plate 25, nozzle 22>
The nozzles 22 are formed on the nozzle plate 25 in a straight line in two rows. The nozzle plate 25 is made of, for example, Ni electroforming, but is not limited thereto.

<Preparation of droplet discharge head 21>
4A, the device structure shown in FIG. 1 or FIG. 3 is patterned by dry etching to form individual ink jet actuators. The upper part of the droplet discharge head 21 includes an upper electrode 27, a piezoelectric film 28, and a lower electrode 29.

  When the pressure chamber 23 under the droplet discharge head as shown in FIG. 4A is manufactured, the silicon single crystal substrate is processed using etching. In this case, the etching method is different. It is common to use isotropic etching. 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. Thereafter, the nozzle plate 25 having the nozzle holes is joined, and the droplet discharge head 21 is formed.

(Embodiment 4)
Next, an example of an ink jet recording apparatus equipped with the ink jet head according to the present embodiment will be described with reference to FIGS. 5 is an explanatory perspective view of the ink jet recording apparatus, and FIG. 6 is an explanatory side view of a mechanism portion of the ink jet recording apparatus.

  This ink jet recording apparatus includes a carriage movable in the main scanning direction inside the recording apparatus main body 81, a recording head composed of an ink jet head embodying the present invention mounted on the carriage, an ink cartridge for supplying ink to the recording head, and the like. A sheet feeding cassette (or a sheet feeding tray) 84 on which a large number of sheets 83 can be stacked from the front side is detachably attached to the lower part of the apparatus main body 81. The manual feed tray 85 for manually feeding the paper 83 can be opened, the paper 83 fed from the paper feed cassette 84 or the manual feed tray 85 is taken in, and the printing mechanism 82 After recording a required image, the image is discharged to a paper 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 head 94 composed of the ink jet head according to the present embodiment that ejects ink droplets of each color (Y), cyan (C), magenta (M), and black (Bk) has a plurality of ink ejection openings (nozzles) in the main scanning direction. And are mounted with the ink droplet ejection direction facing downward. In addition, each ink cartridge 95 for supplying ink of each color to the 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 inkjet head below, and a porous body filled with ink inside, and the capillary force of the porous body. Thus, the ink supplied to the inkjet head is maintained at a slight negative pressure. Further, although the heads 94 of the respective colors are used here as the recording heads, a single head having nozzles for ejecting 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). It is location. 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 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 are guided. A guide member 103, a conveyance roller 104 that reverses and conveys the fed paper 83, a conveyance roller 105 that is pressed against the circumferential surface of the conveyance roller 104, and a tip that defines a feed angle of the paper 83 from the conveyance roller 104 A roller 106 is provided. The transport roller 104 is rotationally driven through a gear train by a sub-scanning motor.

  A printing receiving member 109 is provided as a paper guide member that guides the paper 83 sent from the transport roller 104 below the recording 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.

  At the time of recording, the recording head 94 is driven according to the image signal while moving the carriage 93, thereby ejecting ink onto the stopped sheet 83 to record one line, and after conveying the sheet 83 by a predetermined amount, Record the next line. 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 defective ejection of the 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. The carriage 93 is moved to the recovery device 117 side during printing standby and the head 94 is capped by the capping means, and the ejection port portion is kept in a wet state to prevent ejection 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 a discharge failure occurs, the discharge port (nozzle) of the head 94 is sealed with a capping unit, and bubbles and the like are sucked out from the discharge port with the suction unit through the tube. Is 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.

  Thus, in this ink jet recording apparatus, since the ink jet head produced in the third embodiment is mounted, there is no ink droplet ejection failure due to diaphragm drive failure, and stable ink droplet ejection characteristics are obtained. Image quality is improved.

  Although the present embodiment has been described above, the present embodiment is not limited thereto. For example, it can be applied to a semiconductor memory.

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Silicon oxide film 3 Silicon nitride film 5 Alumina adhesion layer 6 Platinum 7 BST piezoelectric film 21 Droplet discharge head

JP 2007-35883 A "Dielectric properties of fine-grained barium titanate ceramics", Journal of Applied Physics, 58, 1619 (1985) "Size effect of nanograined BaTiO3 ceramics fabricated by aerosol deposition method", Japanese Journal of Applied Physics, 49, 09MC02 (2010) "Enhanced stability of platinized silicon substrates using an unconventional adhesion layer deposited by CSD for high temperature dielectric thin film deposition", Applied Physics A: Materials Science & Processing, 87, 705 (2007)

Claims (7)

And a silicon oxide film on a silicon substrate, a layered structure including one layer of at least a silicon nitride film thickness is smaller than the silicon thermal expansion coefficient greater than the silicon substrate formed in the oxide film on KuKatsu the silicon oxide film An alumina film formed on the film structure, having a higher coefficient of thermal expansion than the film structure and having a smaller film thickness than the film structure , a lower electrode provided on the alumina film, and provided on the lower electrode A piezoelectric film structure comprising a piezoelectric film and an upper electrode provided on the piezoelectric film.   2. The piezoelectric film structure according to claim 1, wherein the film structure having a larger coefficient of thermal expansion than the silicon substrate comprises a single layer or a multilayer structure. 3. The piezoelectric film structure according to claim 1, wherein the lower electrode is a heat-resistant material having a melting point of 1000 ° C. or more and includes at least platinum, iridium, rhodium, or an alloy thereof. The piezoelectric film structure according to any one of claims 1 to 3 , wherein the piezoelectric film is an ABO ₃ type oxide or a lead-free ABO ₃ type oxide containing lead. An electro-mechanical conversion element comprising the piezoelectric film structure according to any one of claims 1 to 4 . A droplet discharge head comprising the electro-mechanical conversion element according to claim 5 . A droplet discharge apparatus comprising the droplet discharge head according to claim 6 .

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