JP2015147332A - Liquid ejection head, driving method of the same and liquid ejection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid ejection head capable of improving ejection characteristics.SOLUTION: A liquid ejection head I comprises: a flow passage formation substrate 10 formed with pressure generating chambers 12; a diaphragm 50 provided on the flow passage formation substrate 10 so as to cover the pressure generating chambers 12; and a piezoelectric element 300 having a first electrode 60, a piezoelectric layer 70 and a second electrode 80 provided on the diaphragm 50. In a driving method of the liquid ejection head I, the diaphragm 50 has deflection causing opposite sides to the pressure generating chambers 12 to protrude in a state that an electric field is not applied to the piezoelectric element 300. In the piezoelectric element 300, relaxation time of polarization of the piezoelectric layer 70 is less than an oscillation period of media in the pressure generating chambers.

Description

  The present invention relates to a liquid ejecting head, a driving method thereof, and a liquid ejecting apparatus.

  Conventionally, an ink jet recording head is known as a typical example of a liquid ejecting head mounted on a liquid ejecting apparatus such as an ink jet printer. In the ink jet recording head, a part of the pressure generating chamber communicating with the nozzle opening is configured by a diaphragm, and this is displaced by applying a voltage to the piezoelectric element, pressurizing the pressure generating chamber, and supplying ink from the nozzle opening. It comes to inject.

  In this type of ink jet recording head, the two electrodes constituting the piezoelectric element are configured as a common electrode common to the pressure generation chamber and an individual electrode for each pressure generation chamber, and a predetermined drive waveform is used for the drive. Applied. For example, the drive waveform supplied to the individual electrode is a waveform in which the voltage is increased or decreased with reference to the intermediate voltage, and a reference voltage higher than the intermediate voltage is applied to the common electrode. (For example, refer to Patent Document 1).

  As a driving mode of such an ink jet recording head, there are a pushing mode in which the volume of the pressure generating chamber is decreased from the initial value, a pulling mode in which the volume of the pressure generating chamber is once increased from the initial value, and then decreased. Are known. In any driving mode, the piezoelectric layer is polarized by applying a voltage to the piezoelectric element, and the electromechanical conversion characteristics corresponding to this polarization and the compliance of the diaphragm (ease of displacement with respect to a predetermined stress) are achieved. Accordingly, the volume of the pressure generating chamber is changed, so that liquid such as ink is ejected.

JP2013-159081A

  However, in Patent Document 1, when polarization is maintained in the piezoelectric layer by applying a drive waveform, the stress state acting on the piezoelectric element changes due to the polarization, and the piezoelectric element and the diaphragm are convex downward (pressure generation chamber). It may be in a bent state (convex to the side). And even after the application of the drive waveform is stopped, such a downwardly convex state is maintained, and the diaphragm can only be displaced so as to pass through a region where the compliance such as the diaphragm is small, and the displacement efficiency is lowered. However, there is a possibility that the injection characteristics are adversely affected.

  Such a problem exists not only in the ink jet recording head, but of course in other liquid ejecting apparatuses and liquid ejecting heads that eject droplets other than ink. This also exists in the liquid ejecting head.

  SUMMARY An advantage of some aspects of the invention is that it provides a liquid ejecting head, a driving method thereof, and a liquid ejecting apparatus capable of improving ejection characteristics.

  An aspect of the present invention that solves the above problems includes a flow path forming substrate in which a pressure generation chamber is formed, a vibration plate provided on the flow path formation substrate so as to close the pressure generation chamber, and the vibration plate. And a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode, wherein the diaphragm is a pressure generating chamber in a state where an electric field is not applied to the piezoelectric element. The liquid ejecting head is characterized in that the opposite side has a convex bend, and the piezoelectric element has a polarization relaxation time equal to or less than a vibration period of a medium in the pressure generating chamber.

  According to this aspect, since the diaphragm has a bent state that is convex upward (convex on the side opposite to the pressure generating chamber), the diaphragm is displaced downward so as to pass through a region where the compliance of the diaphragm is large. And the displacement efficiency can be substantially increased. Since a predetermined piezoelectric element is used, the piezoelectric element and the diaphragm that are displaced downward by applying the drive waveform can be returned to the upward protrusion before the next drive waveform is applied. Accordingly, the vibration plate and the like can be displaced so as to pass through a region where the compliance of the vibration plate is large every drive cycle of the liquid jet head, and a state in which the displacement efficiency is improved can be secured. The injection efficiency can be improved.

  Here, it is preferable that the piezoelectric layer is made of a composite oxide having a perovskite structure containing bismuth, iron, barium, and titanium. According to this, it becomes easy to obtain a piezoelectric element in which the relaxation time of polarization of the piezoelectric layer is equal to or less than the vibration period of the medium in the pressure generating chamber, and the liquid ejecting head can be easily provided.

  The piezoelectric layer is preferably made of a composite oxide having a mixed crystal perovskite structure of bismuth ferrate and barium titanate. According to this, it becomes easier to obtain a piezoelectric element in which the relaxation time of polarization of the piezoelectric layer is equal to or less than the vibration period of the medium in the pressure generating chamber, and the liquid ejecting head can be provided more easily.

  Another aspect of the present invention that solves the above problems includes a flow path forming substrate in which a pressure generation chamber is formed, a vibration plate provided on the flow path formation substrate so as to close the pressure generation chamber, and the vibration plate. And a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode, and a polarization direction of the piezoelectric layer is reversed at each driving period of the liquid ejecting head. In the method of driving a liquid jet head, a voltage to be applied is applied to drive the piezoelectric element.

  According to this aspect, in order to apply a predetermined voltage every driving cycle of the liquid ejecting head, a diaphragm or the like that is displaced downward by applying the driving waveform is made convex upward before the next driving waveform is applied. Can be returned. Accordingly, the vibration plate and the like can be displaced so as to pass through a region where the compliance of the vibration plate is large every drive cycle of the liquid jet head, and a state in which the displacement efficiency is improved can be secured. The injection efficiency can be improved.

  Here, it is preferable to use a voltage in the vicinity of the coercive voltage of the piezoelectric layer as the voltage for reversing the polarization direction of the piezoelectric layer. According to this, the polarization of the piezoelectric layer can be surely depolarized, and the driving method of the liquid ejecting head can be reliably provided.

  Moreover, it is preferable that the time for holding the voltage for reversing the polarization direction is an integral multiple of the vibration period of the medium in the pressure generating chamber. According to this, it is possible to apply a voltage for pressurizing the pressure generating chamber at a timing that is advantageous for the injection characteristics by using the vibration of the medium in the pressure generating chamber. Therefore, it is possible to provide a method of driving the liquid ejecting head that can further improve the ejecting characteristics.

  According to still another aspect of the invention for solving the above-described problem, a liquid ejecting apparatus using the liquid ejecting head according to any one of the above or a driving method thereof is provided. According to this aspect, the vibration plate and the like can be displaced so as to pass through a region where the compliance of the vibration plate is large every drive cycle of the liquid jet head, and a state in which the displacement efficiency is improved can be ensured. As a result, the injection efficiency can be improved.

FIG. 2 is a diagram illustrating a schematic configuration of a recording apparatus according to the first embodiment. FIG. 3 is an exploded perspective view illustrating the recording head according to the first embodiment. FIG. 3 is a plan view illustrating the recording head according to the first embodiment. FIG. 3 is a cross-sectional view illustrating the recording head according to the first embodiment. FIG. 3 is a diagram for explaining functions and the like of a recording head according to the first embodiment. FIG. 3 is a diagram illustrating an example of a driving waveform for a recording head according to the first embodiment. The figure which shows the relationship between the drive voltage which concerns on Embodiment 1, the pressure of a pressure generation chamber, and a polarizability. FIG. 4 is a diagram for explaining characteristics related to a recording head according to the first embodiment. FIG. 4 is a diagram for explaining a manufacturing example of a recording head according to the first embodiment. FIG. 4 is a diagram for explaining a manufacturing example of a recording head according to the first embodiment. FIG. 4 is a diagram for explaining a manufacturing example of a recording head according to the first embodiment. FIG. 9 is a diagram for explaining a recording head driving method according to a second embodiment. The figure which shows the relationship between the drive voltage which concerns on Embodiment 2, and a polarizability.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
FIG. 1 shows a schematic configuration of an ink jet recording apparatus which is an example of a liquid ejecting apparatus according to Embodiment 1 of the invention. As shown in the figure, in the ink jet recording apparatus II, recording head units 1A and 1B having ink jet recording heads are detachably provided in cartridges 2A and 2B constituting ink supply means. The carriage 3 on which the recording head units 1A and 1B are mounted is provided on a carriage shaft 5 attached to the apparatus main body 4 so as to be axially movable, and ejects a black ink composition and a color ink composition, respectively. ing.

  In the ink jet recording apparatus II, the driving force of the driving motor 6 is transmitted to the carriage 3 via a plurality of gears and a timing belt 7 (not shown), so that the carriage 3 on which the recording head units 1A and 1B are mounted becomes a carriage shaft. Move along 5. On the other hand, the apparatus main body 4 is provided with a conveyance roller 8 as a conveyance means, and a recording sheet S which is a recording medium such as paper is conveyed by the conveyance roller 8. The conveying means for conveying the recording sheet S is not limited to the conveying roller 8 and may be a belt, a drum, or the like.

  Next, an ink jet recording head, which is an example of a liquid ejecting head mounted on the ink jet recording apparatus II of this embodiment, will be described in detail. FIG. 2 is an exploded perspective view of the ink jet recording head of this embodiment, and FIG. 3 is a plan view of FIG. 4A is a cross-sectional view corresponding to the line AA ′ in FIG. 3, and FIG. 4B is a cross-sectional view corresponding to the line BB ′ in FIG. 4A.

  As shown in the drawing, a pressure generating chamber 12 is formed in the flow path forming substrate 10, and a plurality of nozzle openings 21 for discharging ink of the same color are arranged in parallel in the pressure generating chamber 12 partitioned by a plurality of partition walls 11. Are arranged along the direction. Hereinafter, this direction is referred to as a direction in which the pressure generating chambers 12 are arranged in parallel, or a first direction X, and a direction orthogonal to the first direction X is referred to as a second direction Y.

  An ink supply path 13 having an opening area reduced by narrowing one side of the pressure generation chamber 12 from the first direction X on one end side in the second direction Y of the pressure generation chamber 12 of the flow path forming substrate 10; A communication passage 14 having substantially the same width as the pressure generation chamber 12 in the first direction X is partitioned by a plurality of partition walls 11. On the outside of the communication path 14 (on the side opposite to the pressure generation chamber 12 in the second direction Y), a communication portion 15 that forms a part of the manifold 100 serving as a common ink chamber for each pressure generation chamber 12 is formed. ing. That is, the flow path forming substrate 10 is formed with a liquid flow path including a pressure generation chamber 12, an ink supply path 13, and a communication portion 15.

  On one side of the flow path forming substrate 10, that is, the surface where the liquid flow path such as the pressure generation chamber 12 opens, a nozzle plate 20 having a nozzle opening 21 communicating with each pressure generation chamber 12 is provided with an adhesive. Or a heat-welded film or the like. Nozzle openings 21 are arranged in the nozzle plate 20 in the first direction X.

  A diaphragm 50 is formed on the other surface side of the flow path forming substrate 10. The diaphragm 50 of the present embodiment has a bend that is upwardly convex (the side opposite to the pressure generation chamber 12 is convex). Such a diaphragm 50 can be constituted by, for example, an elastic film 51 formed on the flow path forming substrate 10 and an insulator film 52 formed on the elastic film 51, but is not limited to the above example. It is also possible to process a part of the flow path forming substrate 10 thinly and use it as an elastic film.

  On the insulator film 52, for example, a first electrode 60 having a thickness of about 0.2 μm and a thickness of about 3.0 μm or less, preferably about 0.5 μm, with an adhesion layer made of titanium, for example. A piezoelectric element 300 including a piezoelectric layer 70 having a thickness of ˜1.5 μm and a second electrode 80 having a thickness of about 0.05 μm is formed. These thicknesses are examples and are not limited to the above examples.

  The adhesion layer may be omitted. In the present embodiment, the diaphragm 50 and the first electrode 60 act as a diaphragm, but the present invention is not limited to this. Only one of the first electrodes 60 may act as a diaphragm without providing either or both of the elastic film 51 and the insulator film 52. Further, the piezoelectric element 300 itself may substantially serve as a diaphragm. When the first electrode 60 is directly provided on the flow path forming substrate 10, the first electrode 60 can be protected with an insulating protective film or the like so that the first electrode 60 and the ink are not conducted.

  The first electrode 60 constituting the piezoelectric element 300 is configured as an individual electrode separated for each pressure generation chamber 12. The material of the 1st electrode 60 will not be specifically limited if it is a material which has electroconductivity, For example, noble metals, such as platinum (Pt) and iridium (Ir), are used suitably. Such a first electrode 60 is formed with a width narrower than the width of the pressure generation chamber 12 in the first direction X of the pressure generation chamber 12. That is, in the first direction X of the pressure generation chamber 12, the end portion of the first electrode 60 is located inside the region facing the pressure generation chamber 12. In other words, the first electrode 60 is configured independently for each active part 310. The active portion 310 in this specification is a portion sandwiched between the first electrode 60 and the second electrode, and is a portion where piezoelectric distortion occurs due to potential supply to the first electrode 60 and the second electrode 80.

  In the second direction Y, both end portions of the first electrode 60 are formed to the outside of the pressure generating chamber 12, respectively, and on one end side thereof (on the side opposite to the communication path 14 in the second direction Y), A lead electrode 90 made of gold (Au) or the like is connected.

  In the piezoelectric element 300, generally, one of the electrodes is a common electrode, and the other electrode is an individual electrode by patterning for each pressure generating chamber 12. In the present embodiment, the first electrode 60 is an individual electrode, and the second electrode 80 is a common electrode. However, there is no problem even if this is reversed for the convenience of a drive circuit and wiring. In the present embodiment, the second electrode 80 is formed continuously over the plurality of pressure generating chambers 12 to constitute a common electrode.

  The piezoelectric layer 70 is continuously provided in the first direction X. Further, the width of the piezoelectric layer 70 in the second direction Y is wider than the length of the pressure generation chamber 12 in the second direction Y and is provided to the outside of the pressure generation chamber 12. In the second direction Y, the end of the piezoelectric layer 70 on the ink supply path 13 side (the right end in FIG. 4A) is located outside the end of the first electrode 60, and the first An end portion of the electrode 60 is covered with the piezoelectric layer 70. On the other hand, the nozzle layer 21 side (left side of FIG. 4A) of the piezoelectric layer 70 is located inside the end of the first electrode 60 and is not covered with the piezoelectric layer 70.

  Such a piezoelectric layer 70 is polarized by voltage application, and is deformed, for example, by bending based on the electromechanical conversion characteristics corresponding to the polarization. The time during which the piezoelectric layer 70 maintains the polarization can be adjusted by the piezoelectric material, and the delay time (relaxation time) from when the polarization is generated in the piezoelectric layer 70 until the polarization substantially disappears is also the piezoelectric material. Can be adjusted.

In particular, in the present embodiment (Embodiment 1), the piezoelectric layer 70 is configured so that the polarization relaxation time of the piezoelectric layer 70 is equal to or less than the vibration period of the medium in the pressure generation chamber 12. As a piezoelectric material for realizing such a piezoelectric layer 70, a composite oxide having a perovskite structure including bismuth (Bi), iron (Fe), barium (Ba), and titanium (Ti) can be used. In the A site of the perovskite structure, that is, the ABO ₃ type structure, oxygen is 12-coordinated, and in the B site, oxygen is 6-coordinated to form an octahedron. Bi and Ba are located at the A site, and Fe and Ti are located at the B site.

  The composite oxide having a perovskite structure containing Bi, Fe, Ba, and Ti is a composite oxide having a perovskite structure of a mixed crystal of bismuth ferrate and barium titanate, or bismuth ferrate and barium titanate are uniform. Although it is also expressed as a solid solution in solid solution, it may be a composition deviated from the composition expressed as a mixed crystal or a solid solution. Even in the composition expressed as a mixed crystal or a solid solution, bismuth ferrate and barium titanate are not detected alone in the X-ray diffraction pattern.

  According to such a complex oxide, it is easy to realize a configuration in which the relaxation time is relatively short from when the polarization is generated in the piezoelectric layer 70 to when the polarization substantially disappears. Therefore, it is easy to obtain the piezoelectric element 300 in which the relaxation time of the polarization of the piezoelectric layer 70 is equal to or less than the vibration period of the medium in the pressure generation chamber 12, which is one preferred embodiment.

Bismuth ferrate and barium titanate are piezoelectric materials having a perovskite structure and have various compositions. For example, as bismuth ferrate or barium titanate, in addition to BiFeO ₃ and BaTiO ₃ , some elements (Bi, Fe, Ba, Ti and O) are partially lost or excessive, or some of the elements are other Some have been replaced by elements. In the present invention, when expressed as bismuth ferrate or barium titanate, those that deviate from the stoichiometric composition due to deficiency or excess, or those in which some of the elements are replaced with other elements are bismuth ferrate or titanate. It shall be included in the range of barium. The ratio of bismuth ferrate to barium titanate can also be changed variously.

  The composition of the piezoelectric layer 70 made of a complex oxide having such a perovskite structure is represented, for example, as a mixed crystal represented by the following general formula (1). Formula (1) can also be represented by the following general formula (1 '). The description of the general formula (1) and the general formula (1 ′) is a composition notation based on the stoichiometry, and as described above, as long as the perovskite structure can be taken, the inevitable composition due to lattice mismatch, oxygen deficiency, etc. Of course, partial substitution of elements and the like are allowed. For example, if the stoichiometric ratio is 1, the range of 0.85 to 1.20 is allowed. In addition, even when the general formulas are different as described below, those having the same ratio of the A-site element to the B-site element may be regarded as the same composite oxide.

(1-x) [BiFeO ₃ ] -x [BaTiO ₃ ] (1)
(0 <x <0.40)
(Bi _1-x Ba _x ) (Fe _1-x Ti _x ) O ₃ (1 ′)
(0 <x <0.40)

  In addition, the composite oxide constituting the piezoelectric layer 70 of the present embodiment may further include an element other than Bi, Fe, Ba, and Ti. Examples of other elements include Mn, Co, and Cr. Also in the case of a complex oxide containing these other elements, it is preferable to have a perovskite structure.

  When the piezoelectric layer 70 contains Mn, Co, and Cr, Mn, Co, and Cr are complex oxides having a structure located at the B site of the perovskite structure. For example, when Mn is included, the composite oxide constituting the piezoelectric layer 70 has a structure in which part of Fe in a solid solution in which bismuth ferrate and barium titanate are uniformly dissolved, is substituted with Mn, or ferric acid It is expressed as a composite oxide having a mixed crystal perovskite structure of bismuth manganate and barium titanate. The basic characteristics are the same as those of the composite oxide having a mixed crystal perovskite structure of bismuth ferrate and barium titanate, but the leakage characteristics are improved. Also, when Co or Cr is included, the leakage characteristics may be improved in the same manner as Mn. In the X-ray diffraction pattern, bismuth ferrate, barium titanate, bismuth ferrate manganate, bismuth ferrate cobaltate, and bismuth ferrate chromate are not detected alone.

  Although Mn, Co, and Cr have been described as examples, leakage characteristics may be improved in the same manner when two other transition metal elements are included at the same time, and these can also be used as the piezoelectric layer 70. Furthermore, other additives may be included to improve the properties. The piezoelectric layer 70 made of a complex oxide having a perovskite structure including Mn, Co, and Cr in addition to Bi, Fe, Ba, and Ti is, for example, a mixed crystal represented by the following general formula (2). Formula (2) can also be expressed by the following general formula (2 '). In general formula (2) and general formula (2 '), M is Mn, Co, or Cr.

  The description of the general formula (2) and the general formula (2 ′) is a composition notation based on stoichiometry, and as described above, as long as a perovskite structure can be obtained, an inevitable composition shift due to lattice mismatch, oxygen deficiency, etc. Is acceptable. For example, if the stoichiometric ratio is 1, one in the range of 0.85 to 1.20 is allowed. In addition, even when the general formulas are different as described below, those having the same ratio of the A-site element to the B-site element may be regarded as the same composite oxide. In addition, the composite oxide which comprises the piezoelectric material layer 70 is not restrict | limited to the said example, As shown in embodiment mentioned later, you may make it comprise a piezoelectric material layer using the composite oxide containing lead.

(1-x) [Bi (Fe _{1- y My} ) O ₃ ] -x [BaTiO ₃ ] (2)
(0 <x <0.40, 0.01 <y <0.10)
_{(Bi 1-x Ba x)} ((Fe 1-y M y) 1-x Ti x) O 3 (2 ')
(0 <x <0.40, 0.01 <y <0.10)

  On the flow path forming substrate 10 on which such a piezoelectric element 300 is formed, that is, on the first electrode 60, the elastic film 51, the insulator film 52 provided as necessary, and the lead electrode 90, the manifold 100 is provided. A protective substrate 30 having a manifold portion 32 constituting at least a part is bonded through an adhesive 35. The manifold part 32 penetrates the protective substrate 30 in the thickness direction and is formed across the width direction of the pressure generating chamber 12, and communicates with the communication path 14 of the flow path forming substrate 10 as described above. A manifold 100 serving as an ink chamber common to the pressure generation chamber 12 is configured.

  Alternatively, the communication path 14 of the flow path forming substrate 10 may be divided into a plurality of pressure generation chambers 12 and only the manifold portion 32 may be used as a manifold. Further, for example, only the pressure generating chamber 12 is provided in the flow path forming substrate 10 and a member interposed between the flow path forming substrate 10 and the protective substrate 30 (for example, an elastic film 51, an insulator film 52 provided if necessary), etc. An ink supply path 13 that communicates the manifold 100 with each pressure generating chamber 12 may be provided.

  A piezoelectric element holding portion 31 having a space that does not hinder the movement of the piezoelectric element 300 is provided in a region facing the piezoelectric element 300 of the protective substrate 30. The piezoelectric element holding part 31 should just have the space of the grade which does not inhibit the motion of the piezoelectric element 300, and the said space may be sealed or not sealed. The protective substrate 30 can be made of substantially the same material as the thermal expansion coefficient of the flow path forming substrate 10, for example, glass or ceramic material. In this embodiment, a silicon single crystal made of the same material as the flow path forming substrate 10 is used. It formed using the board | substrate.

  The protective substrate 30 is provided with a through hole 33 that penetrates the protective substrate 30 in the thickness direction. The vicinity of the end portion of the lead electrode 90 drawn from each piezoelectric element 300 is provided so as to be exposed in the through hole 33. A drive circuit 120 for driving the piezoelectric elements 300 arranged side by side is fixed on the protective substrate 30. As the drive circuit 120, for example, a circuit board, a semiconductor integrated circuit (IC), or the like can be used. The drive circuit 120 and the lead electrode 90 are electrically connected via a connection wiring 121 made of a conductive wire such as a bonding wire.

  A compliance substrate 40 including a sealing film 41 and a fixing plate 42 is bonded onto the protective substrate 30. The sealing film 41 can be made of a material having low rigidity and flexibility, and one surface of the manifold portion 32 is sealed by the sealing film 41. The fixed plate 42 is made of a relatively hard material. Since the region of the fixing plate 42 facing the manifold 100 is an opening 43 that is completely removed in the thickness direction, one surface of the manifold 100 is sealed only with a flexible sealing film 41. ing.

  With respect to the recording head I as described above, the inventor of the present application has found that the apparent rigidity k when the diaphragm 50 and the like are further displaced downward changes according to the displacement state of the diaphragm 50 and the like. It was. FIG. 5 is a graph showing the relationship between the apparent rigidity k in the downward convex direction of the vibration plate 50 and the like mounted on the recording head I and the displacement of the vibration plate 50 and the like. In the figure, when x is positive, the state of the diaphragm 50 or the like corresponds to upward convexity, and when x is negative, the state of the diaphragm 50 or the like corresponds to downward convexity.

  As shown in the figure, in the recording head I of this embodiment, when the x becomes a predetermined value xm in the negative range, the apparent rigidity k takes the minimum value km, and x increases or decreases more than this. Accordingly, the apparent rigidity k in the downward convex direction of the diaphragm 50 or the like increases (more energy is required to displace the diaphragm 50 or the like in the downward convex direction). When attention is paid to the existence of such a relationship, it is generated by applying a voltage to the piezoelectric element 300 by displacing the diaphragm 50 and the like in a range where the apparent stiffness k is small (an area where the compliance of the diaphragm 50 is large). It is understood that much of the energy that is generated can be distributed for the displacement of the diaphragm 50 and the like, and as a result, the displacement of the diaphragm 50 can be increased and the pressure generating chamber 12 can be pressurized appropriately.

  In the present embodiment, the diaphragm 50 has an initial deflection state in which the displacement is, for example, x1 (x1> 0 ≧ xm), and the diaphragm 50 is held upward. Then, by applying a voltage to the piezoelectric element 300, the diaphragm 50 or the like is placed so as to stride over a predetermined value xm that gives the apparent minimum value km of the stiffness k, that is, to pass through a region where the compliance of the diaphragm 50 is large. It can be displaced up to x2 (xm> x2). Such a displacement X1 (| x1 | + | x2 |) of the diaphragm 50 or the like in this embodiment is, for example, a state in which the diaphragm or the like is held excessively upward even if it includes a predetermined value xm. The displacement is larger than the displacement X3 (| x3 | + | x4 |) when bent downward from the top, and it must be further bent downward while the diaphragm is maintained downward. This is larger than the displacement X5 (| x5 | + | x6 |) when it is necessary.

  Note that the relationship between the apparent rigidity k in the downward convex direction and the displacement of the diaphragm 50 and the like as shown in FIG. 5 is merely an example, and may vary depending on the configuration of the recording head, but may be experimentally performed in advance. Can be determined based on If the recording head has such a relationship that the apparent rigidity when the diaphragm or the like is further displaced downward according to the displacement state of the diaphragm or the like, the scope of the invention is not changed. In this case, the present invention can be applied.

  The operation of the ink jet recording head I described above is as follows. That is, after taking ink from an ink inlet connected to an external ink supply means (not shown) and filling the interior from the manifold 100 to the nozzle opening 21 with ink, according to a recording signal (driving signal) from the driving circuit 120, A voltage is applied between the first electrode 60 and the second electrode 80 corresponding to the pressure generation chamber 12. When the voltage is applied, the piezoelectric layer 70 is polarized, and the piezoelectric element 300 is bent and deformed based on the electromechanical conversion characteristics corresponding to the polarization. As a result, the piezoelectric element 300 and the diaphragm 50 are displaced in the direction of the pressure generating chamber 12. . As a result, the pressure in the pressure generating chamber 12 is increased and ink is ejected from the nozzle opening 21.

  6A to 6C are examples of drive waveforms representing drive signals (COM) input to such a piezoelectric element 300. FIG. Among these, FIG. 6A shows a driving waveform in a pushing mode in which ink is ejected by reducing the capacity of the pressure generating chamber 12 from the initial value. FIG. 6B shows a striking mode in which ink is ejected by contracting the volume of the pressure generating chamber 12 as necessary, and then reducing the capacity of the pressure generating chamber 12 from the initial value after being once expanded. A drive waveform is shown. FIG. 6C is an example of a driving waveform in which pushing and striking are combined. In the figure, Vm represents an intermediate voltage, and Vc represents a coercive voltage that gives an electric field at which the polarization becomes zero when the polarization and voltage hysteresis loops of the piezoelectric layer 70 are evaluated.

  The driving waveform 201 shown in FIG. 6A includes a step P01 for maintaining the minimum voltage Vmin1 for a certain time, a contraction step P02 for increasing the voltage to the maximum voltage Vmax1, a step P03 for maintaining the maximum voltage Vmax1 for a certain time, and a minimum voltage Vmin1. And a process P05 following the next process P01 (Vmax1> Vmin1> Vc).

  According to the drive waveform 201, the meniscus in the nozzle opening 21 is largely pushed out from the pressure generation chamber 12 side by the piezoelectric element 300 being deformed in the direction of decreasing the volume of the pressure generation chamber 12 in the contraction process P02. Ink is ejected from the nozzle openings 21.

  In this embodiment, since the diaphragm has a predetermined deflection that is convex upward (convex on the side opposite to the pressure generation chamber), the diaphragm is displaced so as to pass through a region where the compliance of the diaphragm is large, and the displacement efficiency is improved. Improvements are being made. Therefore, ink can be suitably ejected from the nozzle opening 21.

  In addition, the driving waveform 202 shown in FIG. 6B includes an expansion process P12 for decreasing the voltage to the minimum voltage Vmin2 following the process P11 to which the maximum voltage Vmax2 is applied, and a process P13 for maintaining the minimum voltage Vmin2 for a certain period of time. A contraction process P14 for raising the voltage to the maximum voltage Vmax2 and a process P15 subsequent to the next process P11 (Vmax2> Vmin2> Vc).

  According to the driving waveform 202, the piezoelectric element 300 is displaced in the direction of increasing the volume of the pressure generating chamber 12 by the expansion process P12, and the meniscus of the nozzle opening 21 is drawn. Next, the piezoelectric element 300 is deformed in the direction of decreasing the volume of the pressure generating chamber 12 by the contraction process P14, and the meniscus of the nozzle opening 21 is rapidly drawn to the pressure generating chamber 12 side. Thereafter, the piezoelectric element 300 decreases the capacity of the pressure generating chamber 12, for example, by displacing the capacity of the pressure generating chamber 12 so as to return it from the expanded state to the initial value, so that the pressure generating chamber 12 is pressurized and the nozzle Ink is ejected from the opening 21.

  In the pulling mode (FIG. 6B), the amount of expansion of the pressure generating chamber 12 in the expansion step P12 is larger than that in the pressing mode (FIG. 6A), and the pressure generating chamber from an external ink supply means (not shown). Pressure fluctuations are likely to occur due to ink being supplied into the interior 12. If such a pressure fluctuation is utilized to displace the diaphragm 50 at a timing at which pressure is easily applied in the direction of the nozzle opening 21, the injection characteristics can be further improved.

  The drive waveform 203 shown in FIG. 6C is decreased to the minimum voltage Vmin3 that is opposite in polarity to the process P21 to which the intermediate voltage Vm is applied and is larger than the coercive voltage Vc of the piezoelectric layer 70. Expansion step P22, step P23 for maintaining the minimum voltage Vmin3 for a certain period of time, contraction step P24 for increasing the maximum voltage Vmax3 higher than the intermediate voltage Vm, step P25 for maintaining the maximum voltage Vmax3 for a certain period of time, and decrease to the intermediate voltage Vm And a process P27 following the next process P21 (Vmax3> Vm> Vmin3> Vc).

  According to the drive waveform 203, the piezoelectric element 300 is displaced in the direction of increasing the volume of the pressure generating chamber 12 by the expansion process P22, and the meniscus in the nozzle opening 21 is drawn to the pressure generating chamber 12 side. Thereafter, in the contraction process P24, the piezoelectric element 300 is deformed in the direction of decreasing the volume of the pressure generating chamber 12, whereby the meniscus in the nozzle opening 21 is largely pushed out from the pressure generating chamber 12 side, and ink is ejected from the nozzle opening 21. Be injected.

  In this mode (FIG. 6C), since the expansion amount of the pressure generation chamber 12 in the expansion step P22 is smaller than that in the pulling mode (FIG. 6B), the pressure generation chamber is supplied from an external ink supply means (not shown). Pressure fluctuation due to ink being supplied into the ink 12 is unlikely to occur.

  FIG. 7 illustrates the relationship between the driving voltage shown in the example of FIG. 6B when the recording head I is driven, the pressure in the pressure generation chamber 12 in the expansion process, and the polarizability of the piezoelectric layer 70. It is a time chart. In the figure, T1 represented by time t1 to time t2 represents the polarization relaxation time of the piezoelectric layer 70, and Tc represented by time t1 to time t3 represents the period of vibration of the medium in the pressure generation chamber 12. Represents.

  At time t1, the voltage applied to the piezoelectric element 300 decreases. As a result, the expansion of the pressure generating chamber 12 causes the medium in the pressure generating chamber 12 to vibrate, and the pressure in the pressure generating chamber 12 changes at a predetermined vibration cycle (hereinafter also simply referred to as “cycle”) Tc. Displacement of the diaphragm 50 at a timing at which pressure is easily applied in the direction of the nozzle opening 21 by using pressure fluctuations that change at the cycle Tc is advantageous for the injection characteristics.

  The period Tc can be appropriately designed so as to realize a desired printer speed. Such a cycle Tc varies depending on the volume of the pressure generating chamber 12, the rigidity of the diaphragm, the ink flow path, and the like. In FIG. 7, the period Tc is represented by the time point t1 to the time point t3 as described above. For example, a value within the range of 1 to 50 μs can be determined. In this embodiment, 8 μs is adopted.

  Here, in the present embodiment, the piezoelectric element 300 is used in which the polarization relaxation time T1 of the piezoelectric layer 70 is equal to or shorter than the vibration period of the medium in the pressure generation chamber 12 (Tc ≧ T1). The relaxation time T1 is a time period from time t1 when voltage is applied to the piezoelectric element 300 and polarization is maintained in the piezoelectric layer 70 to time t2 when the polarization substantially disappears. At the time point t2, the polarization of the piezoelectric element 300 that has been displaced downwardly at the time point t1 decreases to such an extent that it returns to the initial position having the upward convex deflection. As a result, the pressing force applied to the pressure generating chamber 12 side is substantially eliminated, and the diaphragm 50 returns to the upward convex, which is the initial position.

  Therefore, the bending position of the diaphragm 50 can be ensured in an upwardly convex state for each vibration period of the medium in the pressure generating chamber 12, and the injection efficiency can be improved. As described above, if a composite oxide containing Bi, Fe, Ba, and Ti and having a perovskite structure is used as the piezoelectric layer 70, it is easy to obtain an ink jet recording head I having a polarization relaxation time T1 of a period Tc or less. Become.

  Here, in order to further improve the jetting characteristics of the ink jet recording head I, attention was paid to dividing the elements relating to the ease of displacement of the piezoelectric element 300 and the diaphragm 50 and evaluating them separately.

  FIGS. 8A and 8B are diagrams for explaining the relationship between the initial bending position and the ease of displacement of the diaphragm 50 in the thickness direction. Among these, FIG. 8A is a diagram showing an evaluation result regarding the ease of displacement (Δtc) of the diaphragm 50 and the like when a pressing force is applied from the pressure generating chamber 12 to the diaphragm 50 side. . FIG. 8B shows the evaluation results regarding the ease of displacement (Δvh) of the diaphragm 50 and the like when a pressing force is applied in the direction of the pressure generating chamber 12 by bending and deforming the piezoelectric element 300. FIG. In the figure, 100% of Δtc and Δvh is obtained when the period Tc is 8 μs. An example of the relationship between the initial deflection position and Δtc and vh will be described here based on the drawings.

  As shown in FIG. 8A, when the diaphragm 50 is convex downward, the diaphragm 50 is relatively easily displaced when a pressing force is applied from the pressure generation chamber 12 to the diaphragm 50 side. , Δtc takes a large value. On the other hand, when the diaphragm 50 or the like is convex, the diaphragm 50 is relatively difficult to displace when a pressing force is applied from the pressure generation chamber 12 to the diaphragm 50 side, and Δtc takes a small value. It becomes like this.

  For example, when the initial deflection position is about 115 nm on the upper side (the side opposite to the pressure generation chamber 12), it can be seen that Δtc is about 65%. When Δtc is smaller than 100%, that is, when the diaphragm 50 and the like are convex upward, the Young's modulus of each film such as the diaphragm 50 is hardly changed, but the compliance of the diaphragm 50 and the like is reduced, The period Tc is small. Although the cycle Tc is small, it is advantageous in terms of the printing speed of the printer. However, when the design specification cycle is 8 μs, the compliance of the diaphragm 50 and the like is increased, and the cycle Tc is within the range of the design specification cycle. A method of improving the injection characteristics even when the size is increased can be employed.

  At this time, the film thickness and the like of the piezoelectric element 300 and the diaphragm 50 are adjusted to increase the compliance (broken line shown in FIG. 8A). Then, Δtc increases, and a configuration that matches the design specification period can be realized. In addition, when the compliance of the diaphragm 50 or the like is increased, the diaphragm 50 or the like can be greatly displaced when a pressing force is applied in the direction of the pressure generating chamber 12 by bending and deforming the piezoelectric element 300. (The broken line shown in FIG. 8B).

  As described above, the two types of compliances Δtc and Δvh are independently evaluated for the ease of displacement of the piezoelectric element 300 and the diaphragm 50 in the thickness direction. At this time, the characteristics of the two types of compliance are different. If used, the configuration of the piezoelectric element 300 and the diaphragm 50 having higher ejection characteristics can be adjusted, and the ejection characteristics can be further improved.

  Next, a method for manufacturing the ink jet recording head of this embodiment will be described. 9 to 11 are cross-sectional views showing a method for manufacturing an ink jet recording head.

  First, as shown in FIG. 9A, an elastic film 51 is formed on the surface of a flow path forming substrate wafer 110 that is a silicon wafer. In the present embodiment, the elastic film 51 made of silicon dioxide is formed by thermally oxidizing the flow path forming substrate wafer 110. The formation method of the elastic film 51 is not limited to thermal oxidation, and may be formed by a sputtering method, a CVD method, a spin coating method, or the like. Next, as shown in FIG. 9B, an insulator film 52 made of zirconium oxide is formed on the elastic film 51. Examples of a method for forming the insulator film 52 include a sputtering method, a CVD method, and a vapor deposition method.

  Next, as shown in FIG. 9C, the first electrode 60 is formed on the entire surface of the diaphragm 50. As a material of the first electrode 60, a metal such as platinum or iridium, a conductive oxide such as iridium oxide or lanthanum nickel oxide, or a laminated material of these materials is preferably used. The first electrode 60 can be formed by, for example, a vapor phase film formation such as a sputtering method, a PVD method (physical vapor deposition method), a laser ablation method, or a liquid phase film formation such as a spin coating method.

  Next, a piezoelectric layer 70 made of a composite oxide containing Bi, Fe, Ba, and Ti and having a perovskite structure is formed. In the present embodiment, a so-called sol-gel method is used in which a so-called sol in which a metal complex is dissolved and dispersed in a solvent is applied, dried, gelled, and further fired at a high temperature to obtain a piezoelectric layer 70 made of a metal oxide. Thus, the piezoelectric layer 70 is formed. The method for manufacturing the piezoelectric layer 70 is not limited to the sol-gel method, and for example, a PVD method such as a MOD method, a sputtering method, or a laser ablation method may be used.

  As shown in FIG. 10A, when the first piezoelectric film 74 is formed on the first electrode 60, the first electrode 60 and the first piezoelectric film 74 are patterned at the same time. Then, as shown in FIG. 10B, a piezoelectric layer 70 composed of a plurality of layers of piezoelectric films 74 is formed by laminating the second and subsequent layers of piezoelectric films 74. Incidentally, the second and subsequent piezoelectric films 74 are continuous over the diaphragm 50, on the side surfaces of the first electrode 60 and the first piezoelectric film 74, and over the first piezoelectric film 74. Formed.

  As shown in FIG. 10C, the piezoelectric layer 70 is patterned to form the recesses 71 and the like. In the present embodiment, patterning is performed by so-called photolithography, in which a mask (not shown) having a predetermined shape is provided on the piezoelectric layer 70, and the piezoelectric layer 70 is etched through the mask. The patterning of the piezoelectric layer 70 may be, for example, dry etching such as reactive ion etching or ion milling, or wet etching using an etching solution.

  Next, over the one surface side of the flow path forming substrate wafer 110 (the surface side on which the piezoelectric layer 70 is formed), the patterned side surface of the piezoelectric layer 70, the vibration plate 50, and the first electrode 60. The second electrode 80 is formed over the top and patterned. Then, as shown in FIG. 11A, a protective substrate wafer 130 which is a silicon wafer and serves as a plurality of protective substrates 30 is attached to the flow path forming substrate wafer 110 on the piezoelectric element 300 side with an adhesive (FIG. After joining via 35) shown in a), the flow path forming substrate wafer 110 is thinned to a predetermined thickness.

  Next, as shown in FIG. 11B, a mask film 53 is newly formed on the flow path forming substrate wafer 110 and patterned into a predetermined shape. Then, as shown in FIG. 11C, the flow path forming substrate wafer 110 is subjected to anisotropic etching (wet etching) using an alkali solution such as KOH through the mask film 53, whereby the piezoelectric element 300 is obtained. The pressure generation chamber 12 corresponding to the above is formed. At this time, the diaphragm 50 has a bend in which the opposite side to the pressure generation chamber 12 is convex.

  Thereafter, unnecessary portions of the outer peripheral edge portions of the flow path forming substrate wafer 110 and the protective substrate wafer 130 are removed by cutting, for example, by dicing. The nozzle plate 20 having the nozzle openings 21 formed on the surface of the flow path forming substrate wafer 110 opposite to the protective substrate wafer 130 is bonded, and the compliance substrate 40 is bonded to the protective substrate wafer 130. The ink jet recording head I of the present embodiment is obtained by dividing the flow path forming substrate wafer 110 and the like into a single chip size flow path forming substrate 10 and the like as shown in FIGS.

(Embodiment 2)
The method for driving an ink jet recording head, which is an example of a liquid jet head according to the second embodiment of the present invention, is different from the first embodiment in that a voltage that reverses the polarization of the piezoelectric layer is applied every driving cycle of the ink jet recording head. Different. In the following, the same members are denoted by the same reference numerals, and redundant description will be omitted, and detailed description will be made focusing on different portions.

  12A and 12B are diagrams for explaining a method of driving the ink jet recording head of the present embodiment. Of these, FIG. 12A shows an example of the drive waveform of the present embodiment, that is, a voltage waveform that reverses the polarization of the piezoelectric layer for each drive cycle, and FIG. 12B shows the relationship between the voltage and the polarizability. It is a figure explaining.

  As shown in the figure, this embodiment is basically the same as the drive waveform of FIG. 6C of the first embodiment, but before the step P24 for raising the voltage to the maximum voltage Vmax3, the drive potential is set to the coercive voltage Vc. Step P22a for reducing the resistance voltage V2 and Step P23a for maintaining the coercive voltage Vc for a certain period of time are performed. As a result, as shown in FIG. 12B, the polarization of the piezoelectric layer 70 is forced to be close to 0, and the pressing force applied to the pressure generating chamber 12 side is substantially eliminated, so that the diaphragm It is possible to return to the upward convex state where 50 is the initial position.

  In the process P22a and the process P23a, the driving potential is not limited to the coercive voltage Vc, but may be a voltage in the vicinity of the coercive voltage Vc (plus or minus 3v). The time for maintaining the coercive voltage Vc is preferably an integral multiple of the vibration period Tc of the medium in the pressure generating chamber 12. According to this, it is possible to apply the maximum voltage Vmax3 for pressurizing the inside of the pressure generation chamber 12 at a timing advantageous for the ejection characteristics by using the vibration of the medium.

  FIG. 13 is a time chart for explaining the relationship between the change in drive voltage when the ink jet recording head I is driven and the polarizability of the piezoelectric layer 70. Each process P21 to P27 of the drive waveform 203 in FIG. 13 corresponds to each process in FIG.

  In the present embodiment, the voltage in the vicinity of the coercive voltage Vc (plus or minus 3 v) for reversing the polarization of the piezoelectric layer 70 at every drive period (steps P21 to P27) of the ink jet recording head I as shown in FIG. Apply. For example, in the example of the present embodiment, the drive voltage starts to decrease from the intermediate voltage Vm from the time point t1 and reaches the vicinity of the coercive voltage Vc at the time point t2. As a result, the polarization of the piezoelectric layer 70 can be depolarized, and the piezoelectric element 300 and the diaphragm 50 that are displaced downward by applying a drive waveform in order to pressurize the pressure generation chamber 12 and eject ink. Can be returned to an upward convex before the next application of the drive waveform (for example, time t3). Therefore, the ejection efficiency can be improved for each drive cycle of the ink jet recording head I.

  Furthermore, in the present embodiment, the piezoelectric layer 70 has a polarization relaxation time exceeding the vibration period of the medium in the pressure generation chamber 12, in other words, the piezoelectric layer 70 that holds polarization generated by voltage application. Can be used, and the degree of freedom of material selection is high.

  The manufacturing method can be basically the same as that of the first embodiment. The control portion such as the drive circuit 120 may be configured to apply a voltage that reverses the polarization of the piezoelectric layer 70 every drive cycle of the ink jet recording head I.

(Other embodiments)
The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the first embodiment, the recording head I on which the piezoelectric layer 70 using a complex oxide not containing lead has been described. However, a piezoelectric layer is formed using a complex oxide containing lead, You may make it mount. As a material constituting the piezoelectric layer containing lead, a ferroelectric material such as lead zirconate titanate (PZT) and a metal oxide such as niobium oxide, nickel oxide, magnesium oxide and lanthanum oxide are added thereto. Additions etc. are mentioned. Specifically, lead zirconate titanate (Pb (Zr, Ti) O ₃ ), barium zirconate titanate (Ba (Zr, Ti) O ₃ ), lead lanthanum zirconate titanate ((Pb, La) ( Zr, Ti) O ₃ ) or lead magnesium niobate zirconium titanate (Pb (Zr, Ti) (Mg, Nb) O ₃ ).

  In addition, the present invention is widely intended for a driving method for a liquid ejecting head in general, for example, a recording head such as various ink jet recording heads used in an image recording apparatus such as a printer, and a color filter such as a liquid crystal display. It is also applied to driving methods for color material ejection heads used in the manufacture of electrodes, electrode material ejection heads used in electrode formation for organic EL displays, FEDs (field emission displays), and bio-organic matter ejection heads used in biochip production. be able to.

  Furthermore, the present invention can be similarly applied to driving methods of various sensors and actuator devices that use the piezoelectric element 300 that is a thin film and is driven in a bending deformation mode.

  I ink jet recording head (liquid ejecting head), II ink jet recording apparatus (liquid ejecting apparatus), 10 flow path forming substrate (substrate), 11 partition, 12 pressure generating chamber, 13 ink supply path, 14 communication path, 15 communication Part, 20 nozzle plate, 21 nozzle opening, 30 protective substrate, 31 piezoelectric element holding part, 32 manifold part, 33 through hole, 35 adhesive, 40 compliance board, 41 sealing film, 42 fixing plate, 43 opening part, 50 Diaphragm, 51 Elastic film, 52 Insulator film, 60 First electrode, 70 Piezoelectric layer, 71 Recess, 80 Second electrode, 90 Lead electrode, 100 Manifold, 120 Drive circuit, 300 Piezoelectric element

Claims (7)

A flow path forming substrate in which a pressure generating chamber is formed;
A diaphragm provided on the flow path forming substrate so as to close the pressure generating chamber;
A piezoelectric element having a first electrode, a piezoelectric layer and a second electrode provided on the diaphragm;
In a liquid jet head comprising:
The diaphragm has a bend in which a side opposite to the pressure generation chamber is convex in a state where an electric field is not applied to the piezoelectric element,
The piezoelectric element is characterized in that a polarization relaxation time of the piezoelectric layer is less than or equal to a vibration period of a medium in the pressure generating chamber.   The liquid jet head according to claim 1, wherein the piezoelectric layer is made of a composite oxide having a perovskite structure including bismuth, iron, barium, and titanium.   3. The liquid jet head according to claim 1, wherein the piezoelectric layer is made of a composite oxide having a mixed crystal perovskite structure of bismuth ferrate and barium titanate. 4. A flow path forming substrate in which a pressure generating chamber is formed;
A diaphragm provided on the flow path forming substrate so as to close the pressure generating chamber;
A piezoelectric element having a first electrode, a piezoelectric layer and a second electrode provided on the diaphragm;
In a method for driving a liquid jet head comprising:
A driving method of a liquid ejecting head, wherein a voltage that reverses the polarization direction of the piezoelectric layer is applied every driving cycle of the liquid ejecting head to drive the piezoelectric element.   5. The method of driving a liquid jet head according to claim 4, wherein a voltage in the vicinity of a coercive voltage of the piezoelectric layer is used as the voltage for reversing the polarization direction of the piezoelectric layer.   The method of driving a liquid jet head, wherein a time for holding the voltage for reversing the polarization direction is an integral multiple of a vibration period of a medium in the pressure generating chamber.   A liquid ejecting apparatus using the liquid ejecting head according to claim 1 or a driving method thereof.

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