JP5728925B2 - Piezoelectric element, printer head and inkjet printer - Google Patents

Description

  The present invention relates to a piezoelectric element having an electromechanical conversion function, a printer head using the piezoelectric element, and an ink jet printer using the printer head.

  Conventionally, a piezoelectric element used for a printer head of an ink jet printer is known (see Patent Document 1).

  Such a piezoelectric element includes a substrate, a lower electrode layer formed on the substrate, a piezoelectric layer formed on the lower electrode layer, and an upper electrode layer formed on the piezoelectric layer. And have.

  This piezoelectric element becomes a thin film actuator by applying an electric field to the piezoelectric layer via the upper and lower electrodes, and these are used for an ink jet head.

  Incidentally, lead zirconate titanate (abbreviated as PZT) -based thin films have high piezoelectricity and are used for piezoelectric elements such as piezoelectric sensors and piezoelectric actuators.

  When a PZT thin film is formed by the CSD method, element characteristics vary depending on the type of electrode material, and in recent years, oxide electrodes have attracted attention from the viewpoint of reliability.

  Thin film of lanthanum strontium cobaltate, strontium ruthenate or lanthanum nickelate is known as an oxide electrode candidate. A lanthanum nickelate thin film is particularly promising because the constituent elements are simple and expensive elements are not used.

  Lanthanum nickelate is a material described by the chemical formula NiLaO3, and its crystal has a perovskite type. This perovskite structure is represented by the general formula ABO3.

  Conventionally, platinum is used as an electrode of a PTZ piezoelectric element. PTZ film formation by the CSD (Chemical Solution Deposition) method yields a PZT crystallized film exhibiting piezoelectricity by heat treatment at about 650 to 750 ° C. on the Pt electrode.

  In general, as the crystallization temperature rises, the piezoelectricity is improved, saturated at 750 ° C., and when the temperature rises, the lead of the PZT component evaporates out of the film system as lead oxide, and the characteristics deteriorate. These are called so-called lead removal.

  Since lead loss is accompanied by oxygen, oxygen defects are generated in the PZT film, which is a problem regarding reliability.

Lowering the treatment temperature is effective as a measure to prevent lead loss in crystallization treatment, and if the specific oxide electrode film has the same crystal structure as PZT or the reactivity with low lead, trace the underlying crystal structure. A phenomenon of crystallization at low temperatures has been confirmed.
The specific oxide electrode is lanthanum nickelate (LaNiO3: hereinafter abbreviated as LNO).
Lanthanum strontium cobaltate ((La, Sr) CoO3: hereinafter abbreviated as LSCO)
Strontium ruthenate (SrRuO3: hereinafter abbreviated as SRO)
There is.

  Conductive oxides mainly composed of LNO include LNO and materials in which a part of nickel is replaced with other genera, such as LaNiO3 / LaFeO3 based material replaced with iron, LaNiO3 / LaAlO3 based material replaced with aluminum , LaNiO3 / LaMnO3 materials substituted with manganese, and LaNiO3 / LaCoO3 materials substituted with cobalt.

  If it describes with a general formula, it will be ABO3, A site corresponds to La, B site corresponds to Ni, Al, Mn, Co.

  It is a conductive oxide mainly composed of LNO, and the ratio of A site to B site is generally 1: 1.

  By the way, when a PZT thin film is composed of an LNO electrode as an actuator, the characteristics are improved as compared with a conventional Pt electrode. However, in terms of reliability (piezoelectric characteristics deteriorate as the number of repeated electric field applications increases). It was insufficient.

  An object of the present invention is to provide a piezoelectric element capable of sufficiently improving reliability, a printer head using the piezoelectric element, and an ink jet printer using the printer head.

The invention of claim 1 includes a substrate, a lower electrode layer formed on the substrate, a piezoelectric layer formed on the lower electrode layer, and an upper electrode formed on the piezoelectric layer. A piezoelectric element comprising a layer,
The lower electrode layer is made of a conductive oxide having a chemical formula ABO3 and a ratio of A site to B site (A / B) of 1.1 to 1.6 .
The chemical formula ABO3 is lanthanum nickelate,
The A site is lanthanum, the B site is nickel,
The piezoelectric layer is made of a perovskite oxide ferroelectric material mainly composed of lead zirconate titanate formed by the CSD method.

  According to the present invention, the reliability of the piezoelectric element can be improved.

1 is a perspective view showing an appearance of a main part of an ink jet recording apparatus according to the present invention. It is sectional drawing which showed the structure of the inkjet recording device shown in FIG. It is sectional drawing which showed the structure of the inkjet head of the inkjet recording device using a piezoelectric material element. It is explanatory drawing which showed the structure which integrated the inkjet head shown in FIG. Table 1 is a table showing the relationship between the target composition and the film composition (ratio). Table 2 shows the ratio of the film composition and the evaluation (change rate) of the piezoelectric characteristics. It is the table | surface which showed the starting material ratio, film | membrane composition, and evaluation (change rate) of a piezoelectric characteristic. It is explanatory drawing which showed the preparation flow of the LNO film.

  Hereinafter, an example which is an embodiment of an ink jet recording apparatus (ink jet printer) using a piezoelectric element according to the present invention will be described with reference to the drawings.

[First embodiment]
[Inkjet recording apparatus]
An ink jet recording apparatus 80 shown in FIGS. 1 and 2 includes a printing mechanism portion 82 provided inside the apparatus main body 81. The printing mechanism 82 includes a carriage 93 that can move in the main scanning direction, a recording head (printer head) 94 that is an ink jet head mounted on the carriage 93, an ink cartridge 95 that supplies ink to the recording head 94, and the like. have.

  A paper feed cassette (or a paper feed tray) 84 on which a large number of sheets 83 can be stacked from the front side is detachably attached to the lower portion of the apparatus main body 81. In addition, a manual feed tray 85 for manually feeding the paper 83 is attached to the front portion of the apparatus main body 81 so that the paper 83 can be turned over.

  The paper 83 fed from the paper feed cassette 84 or the manual feed tray 85 is taken into the apparatus main body 81, and after a required image is recorded by the printing mechanism unit 82, the paper 83 is discharged to the paper discharge tray 86 mounted on the rear side. It has come to be.

  The printing mechanism 82 is slidably held in the main scanning direction by the main guide rod 91 and the sub guide rod 92 which are guide members horizontally mounted on left and right side plates (not shown), and the main guide rod 91 and the sub guide rod 92. The carriage 93 is provided. A plurality of recording heads 94 that are ink jet heads that eject ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk) are mounted on the carriage 93. Has ink discharge ports (nozzles) arranged in a direction crossing the main scanning direction, and the ink droplet discharge direction is directed downward.

  In addition, ink cartridges 95 for supplying inks of the respective colors to the recording heads 94 are mounted on the carriage 93 in a replaceable manner.

  The ink cartridge 95 has an atmosphere port (not shown) communicating with the atmosphere at the upper side, and a supply port (not shown) for supplying ink to the inkjet head at the lower side, and the inside is filled with ink. A porous body is provided, and the ink supplied to the inkjet head is maintained at a slight negative pressure by the capillary force of the porous body.

  Here, each color head 94 is used as a recording head, but a single head having nozzles for ejecting ink droplets of each color may be used.

  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 fixed to the carriage 93. ing. Then, 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 transport roller 104 that reverses and transports the fed paper 83, a transport roller 105 that is pressed against the peripheral surface of the transport roller 104, and a leading end that defines a feed angle of the paper 83 from the transport roller 104 A roller 106 is provided on the apparatus main body 81.

  The transport roller 104 is rotationally driven by a sub-scanning motor 107 via a gear train (not shown).

  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. Record the 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 to recover the ejection failure. 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, since this inkjet recording apparatus is equipped with an inkjet head using a piezoelectric element, which will be described later, there is no ink droplet ejection failure due to diaphragm drive failure, and stable ink droplet ejection characteristics are obtained. Image quality will be improved.
[Inkjet head]
FIG. 3 shows a configuration of a recording head 94 which is an ink jet head. The recording head 94 includes a pressure chamber substrate 200 that forms a pressure chamber 221 and has a U-shaped cross section that is open at the bottom, and a nozzle plate 210 that closes the opening at the bottom of the pressure chamber substrate 200. The chamber substrate 200 is formed of an Si substrate and has a diaphragm (substrate) 230 made of the Si substrate. The nozzle plate 210 is formed with nozzle holes 211 that are ink discharge ports.

  An adhesion layer 241 is formed on the vibration plate 230, and a lower electrode layer 242 is formed on the adhesion layer 241. A piezoelectric layer 243 is formed at the central portion on the lower electrode layer 242, and a SAM (Self-Assembled Monolayer) film 421 is formed around the piezoelectric layer 243, and the piezoelectric layer 243 is piezoelectric. An upper electrode layer 244 is formed on the body layer 243.

  The diaphragm 230, the lower electrode layer 242, the piezoelectric layer 243, and the upper electrode layer 244 constitute a piezoelectric element 240, and the lower electrode layer 242, the piezoelectric layer 243, and the upper electrode layer 244 perform electro-mechanical conversion. An element is configured.

FIG. 4 shows an example in which the inkjet head (single bit) shown in FIG. 3 is integrated.
[Piezoelectric layer]
The PTZ forming the piezoelectric layer 243 has a perovskite structure, and lead is arranged at the A site, and zirconium and titanium are arranged at the B site.

  From the relationship of the element ion radius in the crystal structure, lanthanum constituting LNO is an element that can be substituted for the A site of PTZ.

  As indicated by PLZT (lead lanthanum zirconate titanate) known as an electro-optic material, there exists a solid solution in which La is substituted at the A site. La substitution contributes to lowering the crystallization temperature. It also reduces the degree of lead loss.

  The latter contributes to increasing the process margin of the crystallization process. The former has the function of lowering the conventional heat treatment temperature, thereby reducing the occurrence of lead loss defects.

When a PZT film is formed on the LNO that is the lower electrode layer 242 by the CSD method (chemical solution method), La diffuses into the PZT and is taken into the PZT crystal. Therefore, rather than forming LNO with a stoichiometric composition (the ratio of A site to B site is 1: 1), the La ratio is intentionally increased (in other words, the Ni amount is decreased), and the LNO is increased. In the subsequent crystallization of the PZT film by the CSD method, the lower temperature can be reduced by reacting excess La with PZT.
[Lower electrode layer]
In the lower electrode layer 242, at least the uppermost film is LNO, and the composition is made La rich with the composition.

  The LNO film that is the lower electrode layer 242 is formed by sputtering. An LNO sintered target is used as a sputtering target used in this sputtering method. Experiments have shown that if the target composition is La rich, the LNO film can be La rich.

  Specifically, La / Ni = 1.5 / 1.0, 1.25 / 1.0, 1.0 / 1.0 (stoichiometric composition), 1.0 / 1.25, 1.0 /1.5 LNO sintering target is prepared.

  Then, an Ar / O2 mixed gas was introduced into the sputtering apparatus, an LNO film was formed at a substrate temperature of 300 ° C. with each LNO sintering target, and the composition analysis of each LNO film was quantified and measured by fluorescent X-ray analysis. . The results are shown in Table 1 in FIG.

  Here, the substrate on which the LNO film is formed is obtained by forming a titanium adhesion film on a Si wafer with a thermal oxide film and further stacking a Pt film thereon.

As can be seen from the results in Table 1, the composition of the LNO film also changes according to the target composition, and in order to make the film composition (La / Ni) “1” or more, the target composition is La / Ni = 1.0 / What is more than 1.0 may be used.
[Formation of PZT film]
The PZT film is formed by a generally known CSD method (chemical solution method).
In this CSD method, a coating solution having the same composition as that of the conventional one is dropped on a substrate to form a uniform film (coating film) by a spin coating method, and then the solvent contained in the coating film is removed. The coating film is dried at a temperature of about 200 ° C. Furthermore, in order to remove the organic component contained in the dried coating film, heat treatment is performed at a temperature of about 400 to 500 ° C. Thereafter, crystallization is performed by heat treatment at a temperature of about 700 to 750 ° C. for about 1 to 60 minutes. By repeating these processes a plurality of times, a desired PTZ film is obtained.

  Table 2 in FIG. 6 shows the results of creating piezoelectric elements for each composition of each LNO film and evaluating the piezoelectric characteristics of these piezoelectric elements.

  The piezoelectric characteristics are evaluated by measuring a PE hysteresis curve (curve of polarization amount with respect to electric field strength, electric field strength on the horizontal axis and polarization amount on the vertical axis), and using the residual polarization value as a substitute characteristic. Then, both electric fields of ± 15 kV / cm are applied to the initial value, the change rate of the remanent polarization value with respect to the number of times of application (the change rate with respect to the initial remanent polarization value) is obtained, and the case where a Pt electrode is used as a comparative example I write.

  As can be seen from Table 2, by using the lower electrode of the LNO film, it can be confirmed that the characteristics are improved as compared with the Pt electrode. It can also be seen that the rate of change is further reduced if the ratio of La / Ni is 1.1 or more. That is, it can be seen that the La / Ni ratio is 1.1 or more, and the reliability of the piezoelectric layer (piezoelectric element) is improved.

That is, it was found that when lanthanum nickelate was used for forming the PZT film, the piezoelectric characteristics of the PTZ film were improved when it was slightly shifted from A / B = 1: 1 (in the case of La rich).
[Second Embodiment]
The case of an electrode in which an LNO film is produced by the CSD method will be described.

  FIG. 8 shows a flow of producing an LNO film by the CSD method.

  First, nickel acetylacetonate dihydrate is dried under reduced pressure to form nickel acetylacetonate. Next, isopropoxide lanthanum and nickel acetylacetonate are dissolved in 2-methoxyethanol.

  This is refluxed at 130 ° C. to adjust the LNO precursor solution (concentration 0.1 to 0.5 mol / liter).

  This adjusted LNO precursor solution is applied onto a Pt / Ti / SiO2 / Si substrate by spin coating. The coating film is solvent-dried at 200 ° C., thermally decomposed at 400 to 500 ° C., and subjected to crystallization heat treatment at 700 to 750 ° C.

  Using the precursor solution concentration of 0.1 mol / liter, the above film forming process is repeated three times to produce an LNO film having a thickness of 120 nm.

  The LNO composition after film formation was changed by changing the ratio of Ni and La starting materials, and the piezoelectric characteristics of these LNO films were obtained in the same manner as in Example 1. The results are shown in Table 3 in FIG.

  As can be seen from Table 3, by changing the starting material ratio, the LNO composition can be changed, and when the La / Ni ratio is 1.0 or more (1.4 in Table 3), there is a significant difference in the change rate. It can be seen that the rate of change is small, that is, the reliability of the piezoelectric layer (piezoelectric element) is improved.

  The present invention is not limited to the above-described embodiments, and design changes and additions are permitted without departing from the scope of the claimed invention.

80 Inkjet recording device (inkjet printer)
94 Recording head (printer head)
230 Substrate (diaphragm)
240 Piezoelectric element (electro-mechanical conversion element)
242 Lower electrode layer 243 Piezoelectric layer 244 Upper electrode layer

JP 2009/54934 A

Claims (6)

A piezoelectric body comprising a substrate, a lower electrode layer formed on the substrate, a piezoelectric layer formed on the lower electrode layer, and an upper electrode layer formed on the piezoelectric layer An element,
The lower electrode layer is made of a conductive oxide having a chemical formula ABO3 and a ratio of A site to B site (A / B) of 1.1 to 1.6 .
The chemical formula ABO3 is lanthanum nickelate,
The A site is lanthanum, the B site is nickel,
A piezoelectric element made of a perovskite oxide ferroelectric material mainly composed of lead zirconate titanate, wherein the piezoelectric layer is formed by a CSD method. The piezoelectric element according to claim 1, wherein the conductive oxide is lanthanum nickelate which is an LNO film. Piezoelectric element according to claim 2, characterized in that the LNO film is deposited by sputtering. Piezoelectric element according to claim 2, characterized in that the LNO film is formed in the CSD method.   A printer head for an ink jet printer, comprising the piezoelectric element according to any one of claims 1 to 4.   An ink jet printer comprising the printer head according to claim 5.