JP2013244663A - Piezoelectric diaphragm and inkjet recording head including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure adhesion of a piezoelectric thin film 4 by reducing peeling stress of the piezoelectric thin film 4 at an end part in a long axis direction, in a structure where an outer shape of a pressure chamber 1a having different cross sectional aspect ratios includes a curve part 12.SOLUTION: A piezoelectric diaphragm 10 includes a substrate 1 with a pressure chamber 1a formed thereon, and a piezoelectric thin film 4 which is arranged on the substrate 1 and is partially positioned above the pressure chamber 1a. Aspect ratios of cross sections of the pressure chamber 1a are different from each other. At least a part of an outer shape of the cross section of the pressure chamber 1a includes a curve part 12 projected to the outside of the pressure chamber 1a. At least a part of the piezoelectric thin film 4 is formed along the curve part 12 of the pressure chamber 1a, above the pressure chamber 1a. When a distance between a sidewall 1b of the pressure chamber 1a and the piezoelectric thin film 4 in an X axis direction as a long axis direction of the cross section of the pressure chamber 1a is dμm, and a distance between the sidewall 1b of the pressure chamber 1a and the piezoelectric thin film 4 in a Y axis direction as a short axis direction is dμm, d>dis satisfied.

Description

  The present invention relates to a piezoelectric diaphragm having a piezoelectric thin film on a substrate on which a pressure chamber is formed, and an ink jet recording head including the piezoelectric diaphragm.

  Ink jet recording heads having actuators (diaphragms) for ejecting ink have recently been required to have a higher level of performance, and higher density, higher speed, and lower cost of printing have been further required. To increase the density of printing, it is effective to reduce the size and density of the diaphragm, and to reduce the cost, it is effective to reduce the size, increase the density, and reduce the driving voltage. The use of a thin film piezoelectric element (piezoelectric thin film) for the diaphragm is an effective means for reducing the size, density, and driving voltage of the diaphragm. Therefore, a diaphragm using such a piezoelectric thin film (piezoelectric diaphragm) Each company is committed to development.

  One such piezoelectric diaphragm is disclosed in Patent Document 1, for example. In the piezoelectric diaphragm of Patent Document 1, in a configuration in which a piezoelectric thin film is provided on a substrate on which a pressure chamber is formed, the cross-sectional shape of the pressure chamber in a plane perpendicular to the thickness direction of the substrate is a horizontally long rectangle (aspect ratio). Different rectangles).

Japanese Patent Laid-Open No. 11-77998 (see claim 1, FIG. 1, FIG. 3, etc.)

  However, in Patent Document 1, since the corners are present at the four corners of the pressure chamber by making the cross-sectional shape of the pressure chamber to be a quadrangle, the ink flow tends to stagnate in the vicinity of the corners, and there is a bubble at the corner. As a result, the ink discharge performance deteriorates. In order to avoid such a drop in the ink ejection performance, the outer shape of the cross section of the pressure chamber includes a curved portion having a convex shape on the outside of the pressure chamber, and a corner portion where ink and bubbles stay is formed. It is effective to eliminate them.

  On the other hand, in a piezoelectric diaphragm, the adhesion between the piezoelectric thin film and the substrate often becomes a problem. In general, the adhesion of the piezoelectric thin film can be improved by adjusting the film forming conditions of the piezoelectric thin film or by forming an adhesion layer between the substrate and the piezoelectric thin film. However, it is very difficult to adjust the film forming conditions of the piezoelectric thin film to improve the adhesion, and a slight change in the film forming conditions often causes a decrease in piezoelectric performance. In addition, since the adhesion and the piezoelectric performance often have a trade-off relationship, the effect of improving the adhesion by adjusting the film forming conditions cannot be expected so much. In addition, since the piezoelectric thin film is affected by the lower layer at the time of film formation, when the adhesion layer is formed, the adhesion layer adversely affects the piezoelectric thin film, which may lead to a decrease in performance of the piezoelectric thin film. Further, an increase in the number of new layers called adhesion layers or an increase in the number of steps for forming adhesion layers leads to an increase in cost.

  Furthermore, in general, the peeling stress of a piezoelectric thin film when a piezoelectric diaphragm is driven tends to be larger than the peeling stress of a bulk piezoelectric body (the peeling stress is proportional to the electric field strength (applied voltage per unit thickness)). Therefore, a thin piezoelectric film tends to be disadvantageous to peeling.

  In addition, the piezoelectric thin film positioned above the pressure chamber is generally formed so as to be along the outer shape inside the outer shape (side wall) of the pressure chamber from the viewpoint of driving efficiency. When the aspect ratios of the pressure chambers are different, the distance (clearance) between the piezoelectric thin film and the side wall of the pressure chamber is set appropriately in the major axis direction (longitudinal direction) and the minor axis direction (short direction) of the cross section of the pressure chamber. Otherwise, it has been experimentally known that the peeling stress of the piezoelectric thin film becomes larger at the end in the long axis direction than at the end in the short axis direction, and the piezoelectric thin film is easily peeled off at the end in the long axis direction.

  In particular, as described above, when the outer shape of the pressure chamber includes a curved portion and at least a part of the piezoelectric thin film is formed by a curved portion along the curved portion of the pressure chamber, the piezoelectric thin film does not include the curved portion. It is known that the adhesiveness of the piezoelectric thin film is further reduced as compared with the above, and the piezoelectric thin film is more easily peeled off at the end portion in the long axis direction.

  Therefore, in a configuration in which a curved portion is included in the outer shape of the pressure chamber having different cross-sectional aspect ratios and at least a part of the piezoelectric thin film is formed along the curved portion of the pressure chamber, the piezoelectric performance is reduced and the cost is increased. Without inviting, it is desirable to reduce the peeling stress of the piezoelectric thin film at the end portion in the major axis direction to ensure the adhesion of the piezoelectric thin film.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to include a curved portion in the outer shape of a pressure chamber having different cross-sectional aspect ratios, and at least a part of the piezoelectric thin film is a curve of the pressure chamber. Even when it is formed along the edge, the peeling stress of the piezoelectric thin film at the end portion in the long axis direction can be reduced, thereby reducing the adhesiveness of the piezoelectric thin film without causing a decrease in piezoelectric performance or an increase in cost. It is an object of the present invention to provide a piezoelectric diaphragm capable of ensuring the above and an ink jet recording head including the piezoelectric diaphragm.

A piezoelectric diaphragm according to an aspect of the present invention includes a substrate on which a pressure chamber is formed, and a piezoelectric thin film provided on the substrate and at least a part of which is positioned above the pressure chamber. The cross section perpendicular to the thickness direction of the substrate is different in aspect ratio, and at least a part of the outer shape of the cross section of the pressure chamber is a piezoelectric diaphragm including a curved portion protruding outward from the pressure chamber. Above the pressure chamber, at least a part of the piezoelectric thin film is formed along the curved portion of the pressure chamber, and the pressure chamber in the major axis direction of the cross section of the pressure chamber. When the distance between the side wall and the piezoelectric thin film is d ₁ μm, and the distance between the side wall of the pressure chamber and the piezoelectric thin film in the minor axis direction of the cross section is d ₂ μm,
d ₁ > d ₂
It is.

The aspect ratio of the cross section of the pressure chamber is different, at least a part of the outer shape of the pressure chamber includes a convex curve portion outside the pressure chamber, and at least a part of the piezoelectric thin film extends along the curve portion of the pressure chamber above the pressure chamber. In the configuration thus formed, by satisfying d ₁ > d ₂ , the major axis of the cross section of the pressure chamber can be obtained without adjusting the film forming conditions of the piezoelectric thin film or providing an adhesion layer under the piezoelectric thin film. The peeling stress of the piezoelectric thin film at the direction end can be reduced. Thereby, the adhesiveness of the piezoelectric thin film can be ensured without lowering the piezoelectric performance due to the adjustment of the film forming conditions or increasing the cost due to the provision of the adhesive layer.

In the above configuration, when the width in the major axis direction of the pressure chamber is L ₁ μm and the width in the minor axis direction is W ₁ μm,
1 <L ₁ / W ₁ <2
It is desirable that

By satisfying L ₁ / W ₁ <2, it is possible to avoid a rapid decrease in the driving efficiency of the diaphragm due to a rapid decrease in the displacement volume of the pressure chamber. Since the aspect ratio of the cross section of the pressure chamber is different, 1 <L ₁ / W ₁ is necessarily satisfied.

In the above configuration,
d ₁ <W _1/4
It is desirable that

as d ₁ is increased, it is possible to reduce the peel stress of the piezoelectric thin film in the long axis direction end, the d ₁ is W _1/4 or more, while the effect of reducing the peeling stress is reduced, a predetermined discharge The driving voltage for obtaining the quantity increases rapidly, and the driving efficiency decreases. Therefore, by satisfying the above conditional expression, it is possible to avoid a decrease in driving efficiency while obtaining a great effect of reducing the peeling stress.

  In the above configuration, an outer shape of the cross section of the pressure chamber includes two straight portions that are parallel to the major axis direction and face each other, and the curved portion is one end of the two straight portions. The structure containing the 1st curve part which connects parts and the 2nd curve part which connects the other edge parts may be sufficient.

In this configuration, the curved portions (the first curved portion and the second curved portion) of the pressure chamber are positioned so as to intersect the major axis of the pressure chamber. Therefore, a part of the piezoelectric thin film is positioned so as to cross the long axis along the curved portion of the pressure chamber. In such a configuration, by satisfying d ₁ > d ₂ , it is possible to reduce peeling stress at a portion (curved portion) that intersects the long axis of the piezoelectric thin film.

In particular, when the first curved portion and the second curved portion of the pressure chamber are semicircular, a part of the piezoelectric thin film is also semicircular along the curved portion of the pressure chamber. In such a configuration, by satisfying d ₁ > d ₂ , it is possible to reduce the peeling stress in the semicircular portion of the piezoelectric thin film.

  In the above-described configuration, the outer shape of the cross section of the pressure chamber is formed by alternately connecting the straight portions and the curved portions, and the straight portions are positioned in parallel to the major axis direction and face each other. Two first straight line portions and a second straight line portion that is parallel to the short axis direction or that is inclined with respect to both the long axis direction and the short axis direction may be included.

In this configuration, the outer shape of the cross section of the pressure chamber is substantially polygonal. In the configuration having such a pressure chamber, by satisfying d ₁ > d ₂ , the peeling stress of the piezoelectric thin film at the end portion in the long axis direction is satisfied. Can be reduced.

The said structure WHEREIN: The external shape of the said cross section of the said pressure chamber may all be formed in the said curve part. In this case, the entire piezoelectric thin film is formed in a shape along the curved portion of the pressure chamber above the pressure chamber. In the configuration having the pressure chamber and the piezoelectric thin film having such a shape, by satisfying d ₁ > d ₂ , the peeling stress of the piezoelectric thin film at the end portion in the long axis direction can be reduced.

In particular, when the pressure chamber has an elliptical shape, the piezoelectric thin film also has an elliptical shape, and satisfies d ₁ > d ₂ , thereby reducing the peeling stress at the end of the elliptical piezoelectric thin film in the long axis direction. can do.

The said structure WHEREIN: The said piezoelectric thin film may be pulled out from the upper side of the said pressure chamber above the side wall of the one end side of the said major axis direction of the said pressure chamber. In this way, even in the configuration in which the piezoelectric thin film is drawn from the upper side of the pressure chamber to the upper side of the side wall, the distance between the end of the piezoelectric thin film opposite to the drawing side and the side wall of the pressure chamber in the major axis direction is d ₁ . by satisfying _1> d _2, it is possible to reduce the peel stress at the end portion of the piezoelectric thin film.

  An ink jet recording head according to an aspect of the present invention includes the piezoelectric diaphragm having the above-described configuration and a nozzle substrate on which nozzle holes for discharging ink accommodated in the pressure chambers of the piezoelectric diaphragm are formed.

  According to the above-described piezoelectric diaphragm, the adhesiveness of the piezoelectric thin film can be ensured without lowering the piezoelectric performance due to the adjustment of the film forming conditions of the piezoelectric thin film or increasing the cost due to the provision of the adhesive layer. Therefore, by using such a piezoelectric diaphragm, it is possible to realize an ink jet recording head with high performance, low cost, and high reliability.

In a configuration in which the aspect ratio of the cross section of the pressure chamber is different and at least a part of the outer shape of the pressure chamber includes a curved portion, d ₁ > d ₂ is satisfied, thereby reducing the peeling stress of the piezoelectric thin film at the end portion in the long axis direction can do. Thereby, even when at least a part of the piezoelectric thin film is formed along the curved portion of the pressure chamber, the piezoelectric performance is reduced by adjusting the film forming conditions, and the cost is increased by providing the adhesion layer. The adhesion of the piezoelectric thin film can be ensured without incurring.

It is the top view and sectional drawing which show the structure of the outline of the piezoelectric diaphragm which concerns on embodiment of this invention. It is explanatory drawing which plotted the relationship between the drive voltage required for ink discharge, and the amplitude of the peeling stress of a piezoelectric thin film. It is a graph which shows the relationship between the application time of a drive voltage, and the peeling stress of a piezoelectric thin film. And L ₁ / W ₁ is the ratio of the width L ₁ and width W ₁ of the Y-axis direction of the X-axis direction of the pressure chamber is a graph showing the relationship between the displacement volume of the pressure chamber. The distance d ₁ between the sidewall and the piezoelectric thin film of the pressure chamber in the X-axis direction, with showing the relationship between the amplitude of the peeling stress of the piezoelectric thin film is a graph showing the relationship between the distance d ₁ and the driving voltage. (A)-(d) is sectional drawing which shows a part of manufacturing process in the manufacturing method of the inkjet recording head which has the said piezoelectric diaphragm. (A)-(d) is sectional drawing which shows the remaining one part of the manufacturing process in the manufacturing method of the said inkjet recording head. (A)-(c) is sectional drawing which shows a part further remaining of the manufacturing process in the manufacturing method of the said inkjet recording head. (A) And (b) is sectional drawing which shows the remainder of the manufacturing process in the manufacturing method of the said inkjet recording head. It is the top view and sectional drawing which show the other structure of the said piezoelectric diaphragm. It is a top view which shows other structure of the said piezoelectric diaphragm. It is a top view which shows other structure of the said piezoelectric diaphragm. It is a top view which shows other structure of the said piezoelectric diaphragm.

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

[1. Configuration of piezoelectric diaphragm
FIG. 1 shows a plan view and a cross-sectional view showing a schematic configuration of a piezoelectric diaphragm 10 according to the present embodiment. The piezoelectric diaphragm 10 is configured by laminating an insulating film 2, a lower electrode 3, a piezoelectric thin film 4, and an upper electrode 5 in this order on a substrate 1.

  The substrate 1 is composed of a semiconductor substrate made of a single crystal Si (silicon) or an SOI (Silicon on Insulator) substrate. A concave portion is formed in the substrate 1, and the concave portion serves as a pressure chamber 1 a that stores ink as an ejection medium. The upper wall of the pressure chamber 1a, that is, the thinned portion of the substrate 1 forms a diaphragm. In the substrate 1, the periphery of the pressure chamber 1a is a side wall 1b, and the pressure chamber 1a is surrounded by the side wall 1b.

The insulating film 2 is made of, for example, SiO ₂ (silicon oxide), and is formed for the purpose of protecting and insulating the substrate 1. The insulating film 2 may be a natural oxide film or a film formed by thermal oxidation of the substrate 1.

  The lower electrode 3 is configured by laminating layers made of Ti (titanium) and Pt (platinum) in this order. The Ti layer is formed in order to improve the adhesion between the insulating film 2 and the Pt layer. The Pt layer is an electrode on which the piezoelectric thin film 4 is formed, that is, an electrode serving as a base for the piezoelectric thin film 4.

  The piezoelectric thin film 4 is made of PZT (lead zirconate titanate) having a perovskite crystal structure. The piezoelectric thin film 4 is provided on the lower electrode 3 and is located above the pressure chamber 1a.

  The upper electrode 5 is configured by laminating layers made of Cr (chromium) and Au (gold) in this order, and is formed inside the formation region of the piezoelectric thin film 4. The Cr layer is formed for the purpose of improving the adhesion between the upper Au layer and the piezoelectric thin film 4. Note that Ti may be used instead of Cr, and Pt may be used instead of Au. The upper electrode 5 and the lower electrode 3 are electrically connected to a control circuit (not shown).

  In the above configuration, when an electric signal is applied from the control circuit to the lower electrode 3 and the upper electrode 5 sandwiching the piezoelectric thin film 4, the piezoelectric thin film 4 expands and contracts in the left-right direction, and the piezoelectric thin film 4 and the pressure chamber 1a The diaphragm on the upper wall curves up and down. Therefore, if ink is stored in the pressure chamber 1a, the ink can be ejected to the outside, and the piezoelectric diaphragm 10 can be used as an actuator of the ink jet recording head 50 (see FIG. 9B). .

[2. Pressure chamber and piezoelectric thin film shape setting)
Next, the setting of the shape of the pressure chamber 1a and the piezoelectric thin film 4 will be described. In this embodiment, the aspect ratio of the cross section of the pressure chamber 1a is different. Here, the cross section of the pressure chamber 1a refers to a cross section perpendicular to the thickness direction of the substrate 1, and will be used in this sense hereinafter. Further, the fact that the aspect ratio of the cross section of the pressure chamber 1a is different means that the maximum width (diameter and inner diameter) of the pressure chamber 1a is different in two directions perpendicular to each other in the cross section of the pressure chamber 1a.

That is, in FIG. 1, when two directions perpendicular to each other in the cross section of the pressure chamber 1a are defined as the X-axis direction and the Y-axis direction, the width L ₁ (μm) in the X-axis direction and the Y-axis direction in the pressure chamber 1a. Are different from each other in the width W ₁ (μm), and in this embodiment, L ₁ > W ₁ . Since the width L ₁ and the width W ₁ have such a relationship, in this embodiment, the direction of the width L ₁ (X-axis direction) is also referred to as the major axis direction or the longitudinal direction, and the X axis is the major axis. Also called. Further, the direction of the width W ₁ (Y-axis direction) is also referred to as a short-axis direction or a short-side direction, and the Y-axis is also referred to as a short axis.

  In the broad sense, the X axis and the Y axis are perpendicular to the axis (Z axis (not shown)) passing through the center O of the cross section of the pressure chamber 1a and perpendicular to each other. Two axes. Therefore, the expressions of the X axis and the Y axis can be used not only for the pressure chamber 1a but also for the piezoelectric thin film 4, for example.

  Moreover, at least a part of the outer shape of the cross section of the pressure chamber 1a includes a curved portion. More specifically, the outer shape of the cross section of the pressure chamber 1a is composed of a straight portion 11 and a curved portion 12 having a shape protruding outward from the pressure chamber 1a (side wall 1b side). The straight portion 11 is composed of two straight portions 11a and 11b that are positioned in parallel to the X-axis direction and face each other. The curved portion 12 includes two semicircular curved portions 12a (first curved portion) and 12b (second curved portion) positioned symmetrically with respect to the Y axis. The curved portion 12a connects one ends of the two straight portions 11a and 11b, and the curved portion 12b connects the other ends of the two straight portions 11a and 11b. Accordingly, the curved portions 12a and 12b are positioned so as to intersect the X axis. Further, the curved portions 12a and 12b are respectively positioned so as to protrude outward in the X-axis direction (on the side opposite to the Y-axis side).

Above the pressure chamber 1a, at least a part of the piezoelectric thin film 4 is formed along the curved portion 12 of the pressure chamber 1a. In the present embodiment, the piezoelectric thin film 4 is entirely smaller than the outer shape of the pressure chamber 1a and is formed along the outer shape. The aspect ratio of the piezoelectric thin film 4 (P ₁ and W ₂ described later) The ratio is also different from the pressure chamber 1a.

  Such a piezoelectric thin film 4 includes a straight portion 21 and a curved portion 22. The straight portion 21 is composed of two straight portions 21a and 21b that are located in parallel to the X-axis direction and face each other along the straight portion 11 of the pressure chamber 1a. The curved portion 22 includes two semicircular curved portions 22a and 22b that are positioned symmetrically with respect to the Y axis along the curved portion 12 of the pressure chamber 1a. The curved portion 22a connects one ends of the two straight portions 21a and 21b, and the curved portion 22b connects the other ends of the two straight portions 21a and 21b. Therefore, the curved portions 22a and 22b are positioned so as to intersect the X axis. The curved portions 22a and 22b are positioned so as to protrude outward in the X-axis direction.

  From the plan view of FIG. 1, it can be seen that the outer shape of the pressure chamber 1a and the outer shape of the piezoelectric thin film 4 are symmetrical (line symmetric) with respect to both the X axis and the Y axis.

Here, the distance between the side wall 1b of the pressure chamber 1a and the piezoelectric thin film 4 in the X-axis direction is d ₁ μm, and the distance between the side wall 1b of the pressure chamber 1a and the piezoelectric thin film 4 in the Y-axis direction is d ₂ μm. In this embodiment,
d ₁ > d ₂
The shapes of the pressure chamber 1a and the piezoelectric thin film 4 are set so that More specifically, assuming that the length of the linear portions 21a and 21b of the piezoelectric thin film 4 is L ₂ (μm) and the width of the piezoelectric thin film 4 in the Y-axis direction is W ₂ (μm), L ₁ = 330 μm, W ₁ = 230 μm, L ₂ = 76 μm, W ₂ = 190 μm. At this time, the width P ₁ (μm) in the X-axis direction of the piezoelectric thin film 4 is represented by L ₂ + W ₂ and is 266 μm. Therefore, d ₁ = (L ₁ −P ₁ ) / 2 = 32 μm and d ₂ = (W ₁ −W ₂ ) / 2 = 20 μm (that is, d ₁ > d ₂ ). Note that a numerical example of this embodiment is referred to as Example 1.

FIG. 2 is an explanatory diagram in which the relationship between the drive voltage necessary for ink ejection (voltage applied between the upper and lower electrodes) and the amplitude of the peeling stress of the piezoelectric thin film 4 is plotted. For comparison with Example 1, FIG. 2 also shows the relationship between the drive voltage and the amplitude of the peeling stress in the piezoelectric diaphragms of Comparative Examples 1 to 3 manufactured by changing numerical values such as L ₁ . Incidentally, the cross-sectional shape of the pressure chamber 1a in the comparative examples 1 and 3 is a perfect circle (the aspect ratio is 1), and the cross-sectional shape of the pressure chamber 1a in the comparative example 2 is long in the X-axis direction as in the first embodiment. It is a scale (a shape with an aspect ratio larger than 1). Specific numerical values such as L ₁ in Comparative Examples 1 to 3 are as follows.

Comparative Example 1: L ₁ = W ₁ = 230 μm, P ₁ = W ₂ = 210 μm, d ₁ = d ₂ = 10 μm
Comparative Example 2: L ₁ = 330 μm, W ₁ = 230 μm, P ₁ = 290 μm, W ₂ = 190 μm, d ₁ = d ₂ = 20 μm
Comparative Example 3: L ₁ = W ₁ = 230 μm, P ₁ = W ₂ = 170 μm, d ₁ = d ₂ = 30 μm

Here, FIG. 3 is a graph showing the relationship between the application time and the peel stress of the piezoelectric thin film 4 when a sine wave is applied as the drive voltage. The peeling stress of the piezoelectric thin film 4 is represented by the sum of the initial stress Δσ ₀ of the piezoelectric thin film 4 (stress applied to the piezoelectric thin film 4 when no voltage is applied) and the peeling stress generated by applying the drive voltage. The amplitude Δσ of the peeling stress on the vertical axis in FIG. 2 corresponds to a change amount of the peeling stress generated by the application of the drive voltage, that is, a portion obtained by subtracting the initial stress Δσ ₀ from the entire peeling stress of the piezoelectric thin film 4.

  FIG. 2 shows that the amplitude Δσ of the peel stress is smaller in Comparative Example 2 and Example 1 having different cross-sectional aspect ratios than in Comparative Examples 1 and 3 in which the cross-sectional shape of the pressure chamber 1a is a perfect circle. Therefore, it can be said that the pressure chamber 1a desirably has a shape having a different cross-sectional aspect ratio, that is, a shape including the straight portion 11 and the curved portion 12.

Next, when the aspect ratio of the cross section of the pressure chamber 1a is different, the peeling stress (amplitude Δσ) of the piezoelectric thin film 4 in the X-axis direction and the Y-axis direction in each of d ₁ = d ₂ and d ₁ > d ₂ The size of was examined. At this time, for the X-axis direction, the end stress A in the X-axis direction (see FIG. 1) is used as an evaluation point, and the peeling stress of the piezoelectric thin film 4 at the end A is examined. Using the end B (see FIG. 1) as an evaluation point, the peeling stress of the piezoelectric thin film 4 at the end B was examined. The results are shown in Table 1 (when d ₁ = d ₂ ) and Table 2 (when d ₁ > d ₂ ).

  Here, patterns I, II, and III in Table 1 are obtained by setting each dimension as follows.

Pattern I: L ₁ = 330 μm, W ₁ = 230 μm, P ₁ = 290 μm, W ₂ = 190 μm, d ₁ = d ₂ = 20 μm
Pattern II: L ₁ = 330 μm, W ₁ = 230 μm, P ₁ = 290 μm, W ₂ = 190 μm, d ₁ = d ₂ = 20 μm (The above dimensions are the same as pattern I, but the dimensions of the upper electrode 5 are 20 μm smaller than I)
Pattern III: L ₁ = 330 μm, W ₁ = 230 μm, P ₁ = 270 μm, W ₂ = 170 μm, d ₁ = d ₂ = 30 μm

  In addition, patterns IV, V, and VI in Table 2 have respective dimensions set as follows.

Pattern IV: L ₁ = 330 μm, W ₁ = 230 μm, P ₁ = 270 μm, W ₂ = 190 μm, d ₁ = 30 μm, d ₂ = 20 μm
Pattern V: L ₁ = 330 μm, W ₁ = 230 μm, P ₁ = 270 μm, W ₂ = 190 μm, d ₁ = 30 μm, d ₂ = 20 μm (the above dimensions are the same as those of the pattern IV, but the dimensions of the upper electrode 5) Is 20 μm smaller than Pattern IV)
Pattern VI: L ₁ = 330 μm, W ₁ = 230 μm, P ₁ = 244 μm, W ₂ = 170 μm, d ₁ = 43 μm, d ₂ = 30 μm

From Table 1, it can be seen that when d ₁ = d ₂ , the peeling stress at the end A in the X-axis direction always increases. Therefore, in this case, peeling occurs from the end A in the X-axis direction of the piezoelectric thin film 4. On the other hand, it can be seen from Table 2 that when d ₁ > d ₂ , the peeling stress at the end A can be reduced. Therefore, by setting d ₁ > d ₂ , peeling of the piezoelectric thin film 4 during driving of the diaphragm can be suppressed. In addition, Example 1 mentioned above is close to the shape of the pattern V of Table 2.

As described above, in the configuration in which the aspect ratio of the cross section of the pressure chamber 1a is different and at least a part of the outer shape of the pressure chamber 1a includes the curved portion 12, by satisfying d ₁ > d ₂ , The peeling stress of the piezoelectric thin film 4 in the part A can be reduced as compared with the case of d ₁ = d ₂ . Therefore, in reducing the peeling stress of the piezoelectric thin film 4, it is not necessary to adjust the film forming conditions of the piezoelectric thin film 4 or to provide an adhesion layer under the piezoelectric thin film 4.

When the piezoelectric thin film 4 is formed so as to follow the outer shape of the pressure chamber 1a above the pressure chamber 1a, the piezoelectric thin film 4 includes a curved portion 22 along the curved portion 12 of the pressure chamber 1a. Even in such a configuration, by satisfying d ₁ > d ₂ , the adhesiveness of the piezoelectric thin film 4 is not caused without lowering the piezoelectric performance due to the adjustment of the film forming conditions or increasing the cost due to the provision of the adhesive layer. Can be secured. As a result, the reliability of the ink jet recording head using the piezoelectric diaphragm 10 can be improved.

  In addition, by using a thin piezoelectric body (piezoelectric thin film 4), the piezoelectric diaphragm 10 can be reduced in size, increased in density, and driven at a lower voltage. Therefore, by applying the piezoelectric diaphragm 10 to an ink jet recording head, In addition, the ink jet recording head can be reduced in size, density, and cost. And since the ink of a small diameter dot can be discharged with a low voltage, the high density of printing, high definition, and cost reduction can also be achieved.

  Furthermore, it is not necessary to rely only on the film forming conditions for improving the adhesion of the piezoelectric thin film 4, and in setting the film forming conditions for the piezoelectric thin film 4, it is possible to focus on improving only the piezoelectric characteristics. Thereby, the condition setting range for improving the piezoelectric performance is widened, and as a result, it becomes easy to produce a high-quality film.

Further, in the present embodiment, in the configuration in which the aspect ratio of the cross section of the pressure chamber 1a is different, the curved portions 12a and 12b of the pressure chamber 1a are positioned so as to cross the X axis, and the curved portions 22a and 22b of the piezoelectric thin film 4 are also X Located so as to cross the axis. Therefore, by setting d ₁ > d ₂ , it is possible to reduce the peeling stress at the curved portions 22a and 22b intersecting with the X axis. In particular, in the configuration in which the curved portions 22a and 22b of the piezoelectric thin film 4 are semicircular, the above effect can be obtained.

[3. For the desired range of L ₁ / W _1]
FIG. 4 shows the displacement volume (ink discharge amount) of L ₁ / W ₁ and the pressure chamber 1a when L ₁ / W ₁ is changed in the pattern V (d ₁ = 30 μm, d ₂ = 20 μm) in Table 2. It is a graph which shows the relationship. At this time, the area of the cross section of the pressure chamber 1a is constant, and the driving voltage is also constant. Further, the displacement volume on the vertical axis in FIG. 4 is shown normalized by assuming that the displacement volume when the aspect ratio of the cross section of the pressure chamber 1a is 1.

From this figure, it can be seen that when L ₁ / W ₁ is 2 or more, the displacement volume decreases rapidly, and the driving efficiency of the diaphragm rapidly decreases. Thus, L at ₁ / W ₁ is 2 or more, since the driving efficiency is rapidly reduced, at the same drive voltage as that of L ₁ / W ₁ = _1, the same displacement as that of L ₁ / W ₁ = ₁ If the volume is to be generated, it is necessary to increase the area of the cross section of the pressure chamber 1a as compared with the case of L ₁ / W ₁ = 1. Therefore, when the pressure chamber has an elongated shape as in Patent Document 1 described above, it is necessary to increase the area of the pressure chamber in order to obtain the same displacement volume as in the present embodiment.

  On the other hand, the ink that is the ejection medium has an action of compressing itself and absorbing (losing) the pressure when it receives pressure. For this reason, when the area of the cross section of the pressure chamber is increased as described above, the amount of ink that receives pressure increases (the amount of ink that absorbs pressure also increases), and ink ejection efficiency decreases.

Therefore, in order to avoid a sudden drop in drive efficiency due to a sudden drop in displacement volume and a drop in discharge efficiency due to ink compression, it is desirable that L ₁ / W ₁ <2. In this embodiment, since the aspect ratio of the cross section of the pressure chamber 1a is different, L ₁ / W ₁ > 1. Therefore, when these are put together, it can be said that it is desirable to satisfy 1 <L ₁ / W ₁ <2.

In FIG. 4, even when L ₁ / W ₁ is 4 or more, the displacement volume gradually decreases. For example, when L ₁ / W ₁ = 16, the displacement volume is L ₁ / W ₁ = 1. Is about 0.2. That is, in FIG. 4, the displacement volume is not asymptotic to 0.4.

[4. for the desired range of d _1]
FIG. 5 shows the d ₁ and the peel stress of the piezoelectric thin film 4 at the end A in the X-axis direction when d ₁ is changed in the pattern V (L ₁ = 330 μm, W ₁ = 230 μm) in Table 2. 6 is a graph showing a relationship between amplitude Δσ and a relationship between d ₁ and a driving voltage necessary for ejecting a predetermined amount of ink droplets.

From the figure, as the d ₁ is increased, it is possible to reduce the peel stress of the piezoelectric thin film 4 at the end A, the d ₁ is W _1/4 or more, the effect of reducing the peeling stress is reduced, while As a result, the driving voltage for obtaining a predetermined discharge amount increases rapidly, and the driving efficiency decreases. Therefore, while obtaining a large reduction effect of peeling stress, in order to avoid a decrease in driving efficiency, it would be desirable to satisfy the d ₁ <W _1/4.

[5. Inkjet recording head manufacturing method]
Next, a method for manufacturing the ink jet recording head 50 having the above-described piezoelectric diaphragm 10 will be described. 6 to 9 are cross-sectional views showing respective manufacturing steps in the method for manufacturing the ink jet recording head 50. Note that the numerical values such as the film thickness shown below are all examples, and are not limited to these numerical values.

First, as shown in FIG. 6A, a substrate 1 (thickness: 200 μm) made of Si having a thermal oxide film (thickness: 2 μm) on both sides is prepared as an insulating film 2. Then, as shown in FIG. 6B, an insulating film 2a made of SiO ₂ (thickness 2 μm) is formed on the back surface of the substrate 1 using TEOS-CVD, that is, tetraethoxysilane (TEOS) as a source gas. The film is formed by the conventional CVD (Chemical Vapor Deposition) method.

Subsequently, as shown in FIG. 6C, a resist is applied on the insulating film 2 a on the back surface side of the substrate 1, and exposure and development are performed to obtain a resist pattern 7. This resist pattern 7 is a pattern for processing and forming the pressure chamber 1a in a process described later. Then, as shown in FIG. 6D, using the resist pattern 7 as a mask pattern, the insulating films 2 and 2a are formed using trifluoromethane (CHF ₃ ) gas in a RIE (Reactive Ion Etching) apparatus. Is dry-etched to remove the SiO ₂ layer not protected by the resist.

  Next, as shown in FIG. 7A, Ti (thickness 20 nm) and Pt (thickness 100 nm) layers are sequentially formed on the surface of the substrate 1 (the surface opposite to the insulating film 2a) by sputtering. A lower electrode 3 is formed by forming a film. Further, as shown in FIG. 7B, PZT (thickness 5 μm) is formed on the lower electrode 3 by a sputtering method at a temperature of 600 ° C. to form the piezoelectric thin film 4. The formed film (PZT film) has a perovskite phase that provides good piezoelectric characteristics, and is oriented in the <100> direction perpendicular to the surface of the substrate 1.

  Subsequently, as shown in FIG. 7C, a lift-off resist pattern 8 for patterning the upper electrode 5 is formed on the piezoelectric thin film 4. Then, as shown in FIG. 7D, each layer of Cr (thickness 10 nm) and Au (thickness 90 nm) is deposited on the resist pattern 8 and the piezoelectric thin film 4 on which the resist pattern 8 is not formed by vapor deposition. The upper electrode 5 is formed by sequentially forming a film.

  Thereafter, as shown in FIG. 8A, the substrate 1 is immersed in a stripping solution, and the resist pattern 8 is stripped. As a result, the upper electrode 5 patterned by lift-off is obtained. Next, as shown in FIG. 8B, a resist pattern 9 for patterning the piezoelectric thin film 4 is formed so as to cover the upper electrode 5. And as shown in FIG.8 (c), the board | substrate 1 is immersed in hydrofluoric acid, the piezoelectric thin film 4 is etched, and it patterns.

  Next, as shown in FIG. 9A, the substrate 1 is deeply processed by the Bosch process of an ICP (Inductively Coupled Plasma) apparatus using the pattern of the insulating films 2 and 2a on the back surface of the substrate 1 as a mask. The pressure chamber 1a is produced. Thereby, the piezoelectric diaphragm 10 is completed.

  Finally, the substrate 1 of the piezoelectric diaphragm 10 and the glass substrate 31 (thickness 200 μm) are bonded together by anodic bonding, and the glass substrate 31 and the nozzle substrate (thickness 300 μm) made of an Si substrate are bonded together by anodic bonding. Thus, the ink jet recording head 50 is completed. The glass substrate 31 has a hole 31a having a diameter of 100 μm, and the nozzle substrate 32 has a diameter of 50 μm and a diameter of 20 μm as nozzle holes 32a for ejecting ink contained in the pressure chamber 1a. Two-stage holes are formed. The ink in the pressure chamber 1a is discharged to the outside through the hole 31a of the glass substrate 31 and the nozzle hole 32a of the nozzle substrate 32.

  According to the configuration of the piezoelectric diaphragm 10 described above, the adhesion of the piezoelectric thin film 4 can be ensured without causing a decrease in piezoelectric performance due to adjustment of the film forming conditions of the piezoelectric thin film 4 or an increase in cost due to the provision of the adhesion layer. Can do. Therefore, by using such a piezoelectric diaphragm 10, it is possible to realize an ink jet recording head 50 with high performance, low cost, and high reliability.

[6. Other configurations of piezoelectric diaphragm]
FIG. 10 is a plan view and a cross-sectional view showing another configuration of the piezoelectric diaphragm 10. As shown in the figure, the piezoelectric thin film 4 may be drawn from above the pressure chamber 1a to above the side wall 1b on one end side in the X-axis direction of the pressure chamber 1a. In this configuration, the upper electrode 5 formed on the piezoelectric thin film 4 can be pulled out from the upper side of the pressure chamber 1a to the upper side wall 1b on the one end side in the X-axis direction of the pressure chamber 1a.

In such a configuration, the distance between the side wall 1b of the end A and the pressure chamber 1a of the opposite side as d ₁ is the lead side of the piezoelectric thin film 4 in the X-axis direction, by satisfying the d _1> d _2, It is possible to reduce the peeling stress of the piezoelectric thin film 4 at the end A on the side opposite to the drawing side.

In particular, in the configuration of FIG. 10, in order to draw the piezoelectric thin film 4 from the upper side of the pressure chamber 1a to the upper side of the side wall 1b, not only the entire piezoelectric thin film 4, but only a part of the outer shape (curved portion 12) of the pressure chamber 1a. In this case, the above effect can be obtained by satisfying d ₁ > d ₂ .

  In the configuration of FIG. 10, there is no point at which the peeling stress is concentrated at the end portion on the lead-out side of the piezoelectric thin film 4, unlike the end portion A on the opposite side, so that the peeling stress is larger than the end portion A. There is no. Therefore, only the peeling stress at the end A needs to be considered for the peeling stress.

  In the piezoelectric diaphragm 10 described above, the curved portion 12 of the pressure chamber 1a and the curved portion 22 of the piezoelectric thin film 4 are examples located on the X axis. However, the curved portion 12 and the curved portion 22 are located on the X axis. You don't have to.

  11 and 12 are plan views showing still another configuration of the piezoelectric diaphragm 10. As shown in these drawings, the outer shape of the cross section of the pressure chamber 1 a may be formed by alternately connecting the straight portions 13 and the curved portions 12. The straight portion 13 is parallel to the two first straight portions 13a and 13a and is parallel to the X-axis direction, and is parallel to the Y-axis direction, or both the X-axis direction and the Y-axis direction. It may include the 2nd straight part 13b located so that it may incline. Here, the 1st linear part 13a shall be longer than the 2nd linear part 13b.

  Note that the number of the second linear portions 13b is not particularly limited, and as shown in FIG. 11, there may be only two positioned parallel to the Y axis, or as shown in FIG. There may be a total of six, which are two parallel to each other, plus four that are inclined (at an angle other than 90 °) with respect to both the X-axis and the Y-axis. May be the number. The outer shape of the pressure chamber 1a has a substantially polygonal shape (a shape in which each corner of the polygon is rounded) according to the number of the second linear portions 13b, and the piezoelectric thin film 4 also follows the outer shape of the pressure chamber 1a. It becomes a substantially polygonal shape. That is, the outer shape of the piezoelectric thin film 4 has a shape in which the straight portions 21 and the curved portions 22 are alternately connected along the outer shape of the pressure chamber 1a.

Even with such a configuration, the peeling stress of the piezoelectric thin film 4 at the end in the X-axis direction can be reduced by satisfying d ₁ > d ₂ .

  FIG. 13 is a plan view showing still another configuration of the piezoelectric diaphragm 10. As shown in the figure, the outer shape of the cross section of the pressure chamber 1 a may be entirely formed by a curved portion 12. In FIG. 13, the curved portion 12 has an elliptical shape.

In this case, above the pressure chamber 1a, the outer shape of the piezoelectric thin film 4 is also formed by an elliptical curved portion 22 along the outer shape of the pressure chamber 1a. Intersect. In such a configuration, by satisfying d ₁ > d ₂ , it is possible to reduce the peeling stress at the end of the piezoelectric thin film 4 that intersects the X axis. In particular, when the curved portion 12 of the pressure chamber 1a is elliptical and the curved portion 22 of the piezoelectric thin film 4 is elliptical, the above effect can be obtained by satisfying d ₁ > d ₂ .

In the configuration of FIGS. 10 to 13, further 1 <and L ₁ / W ₁ <2, by satisfying d1 <W _1/4, the effect described above can be obtained is of course possible.

  Of course, the configuration shown in FIG. 10 in which the piezoelectric thin film 4 is drawn from above the pressure chamber 1a to above the side wall 1b can be applied to the configurations shown in FIGS.

  The piezoelectric diaphragm of the present invention can be used for an ink jet recording head, for example.

DESCRIPTION OF SYMBOLS 1 Substrate 1a Pressure chamber 1b Side wall 4 Piezoelectric thin film 10 Piezoelectric diaphragm 11 Linear part 11a Linear part 11b Linear part 12 Curved part 12a Curved part 12b Curved part 13 Linear part 13a First linear part 13b Second linear part 32 Nozzle substrate 32a Nozzle hole 50 Inkjet recording head

Claims (10)

A substrate on which a pressure chamber is formed;
A piezoelectric thin film provided on the substrate and at least partially positioned above the pressure chamber;
The aspect ratio of the cross section of the pressure chamber perpendicular to the thickness direction of the substrate is different, and at least a part of the external shape of the cross section of the pressure chamber includes a curved portion having a shape protruding outward from the pressure chamber. A piezoelectric diaphragm,
Above the pressure chamber, at least a part of the piezoelectric thin film is formed along the curved portion of the pressure chamber,
The distance between the side wall of the pressure chamber and the piezoelectric thin film in the major axis direction of the cross section of the pressure chamber is d ₁ μm, and the distance between the side wall of the pressure chamber and the piezoelectric thin film in the minor axis direction of the cross section. When d ₂ μm,
d ₁ > d ₂
Piezoelectric diaphragm characterized by being. When the width in the major axis direction of the pressure chamber is L ₁ μm and the width in the minor axis direction is W ₁ μm,
1 <L ₁ / W ₁ <2
The piezoelectric diaphragm according to claim 1, wherein: d ₁ <W _1/4
The piezoelectric diaphragm according to claim 2, wherein: An outer shape of the cross section of the pressure chamber includes two linear portions that are parallel to the major axis direction and face each other;
2. The curved portion includes a first curved portion that connects one ends of the two straight portions, and a second curved portion that connects the other ends. 4. The piezoelectric diaphragm according to any one of 3 above.   The piezoelectric diaphragm according to claim 4, wherein the first curved portion and the second curved portion are semicircular. The external shape of the cross section of the pressure chamber is formed by alternately connecting a straight portion and the curved portion,
The straight portion is parallel to the short-axis direction and inclined with respect to both the long-axis direction and the short-axis direction, and two first straight-line portions positioned parallel to the long-axis direction and facing each other. The piezoelectric diaphragm according to any one of claims 1 to 3, further comprising a second linear portion positioned so as to perform.   The piezoelectric diaphragm according to any one of claims 1 to 3, wherein the outer shape of the cross section of the pressure chamber is entirely formed by the curved portion.   The piezoelectric diaphragm according to claim 7, wherein the curved portion has an elliptical shape.   The piezoelectric diaphragm according to any one of claims 1 to 8, wherein the piezoelectric thin film is drawn from above the pressure chamber to above a side wall on one end side in the major axis direction of the pressure chamber. A piezoelectric diaphragm according to any one of claims 1 to 9,
An ink jet recording head comprising: a nozzle substrate having nozzle holes for discharging ink accommodated in the pressure chambers of the piezoelectric diaphragm.

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