Piezoelectric vibration substrate and piezoelectric vibration element

Abstract

The present application can suppress cracks or notches caused by heating, ultrasonic vibration, and application of weight at the time of mounting the piezoelectric vibration element.[0012]The piezoelectric vibration element 11 includes a piezoelectric layer 2A formed of a block-shaped piezoelectric material, a lower electrode 3 on a first surface 2a of the piezoelectric layer 2A, and a support substrate 5 bonded to the lower electrode 3.

Description

TECHNICAL FIELD

[0001] The present application relates to a piezoelectric vibration substrate and element which can be preferably used for a MEMS scanner or the like. BACKGROUND

[0002] A head-up display (HUD) refers to a device which "superimposes necessary information on a field of view in a state where a line of sight is kept in front". In automobile driving, it is possible to recognize information in a state where a line of sight is kept in front, compared to a case where information on an instrument panel or a console panel is viewed, and thus, it is effective for preventing side driving, and in addition, since a focus of an eye moves less, it is possible to achieve fatigue reduction and safety improvement of a driver.

[0003] As to a principle of the HUD, an image of a fluorescent tube, a CRT, or a liquid crystal display is mapped on a windshield or a transparent screen (combiner) of a vehicle. The HUD has the following 2 modes according to a difference in optical structure.

[0004] (1) A direct projection mode which directly projects an image on a screen such as a windshield

[0005] (2) A virtual imaging mode which makes a windshield or the like function as a mirror to image on a retina of a driver

[0006] The biggest difference between the above modes is a sense of distance when a driver sees an image. In the direct projection mode, an image is recognized on a screen (combiner) as in a common projector, and in the virtual imaging mode, an image is recognized in a space several meters away from a line of sight of a driver. In either mode, compared to a case where the HUD is not used, a line of sight between a front field of view of a driver and an instrument panel or a console panel is extremely reduced. However, in the virtual imaging mode, a focus of a field of view with respect to driving is also less moved, and thus, it is possible to concentrate more on driving, and fatigue is less. In the virtual imaging mode, a new mode which draws by scanning a laser beam is being developed in recent years.

[0007] As to a laser scanning type display, RGB 3 color laser beams are combined by an optical element called a combiner, and this one beam is reflected by a minute mirror to be scanned two-dimensionally, and thus, drawing is performed. This mode is similar to scanning of an electron beam of a CRT, but instead of exciting a phosphor, a pulse width and output of each laser are controlled at a position corresponding to a pixel on a horizontal scanning line, a color and a brightness are changed, and a pixel is drawn in a point shape at high speed. A resolution which can be achieved depends on a vibration frequency of a mirror and a modulation frequency of a laser.

[0008] Main advantages brought by this mode are as follows.

[0009] (1) Since the number of components is less, miniaturization, cost reduction, and reliability improvement are achieved.

[0010] (2) Since the laser is lit at the luminance required for each pixel, low power consumption can be achieved.

[0011] (3) Since a laser that has been collimated (parallel light) is used, no focus adjustment is required.

[0012] For a micro-mirror that is a core component of a laser scanning type display, Si is processed using MEMS (Micro Electro Mechanical System) technology, and metal is evaporated. The driving method of the MEMS mirror includes an electrostatic method in which electrostatic attraction is used for driving, an electromagnetic method in which electromagnetic force is used for driving, and a piezoelectric method in which a piezoelectric element is used for driving. As advantages of the piezoelectric method, high-speed driving, low power consumption, and large driving force can be cited. As a disadvantage of the piezoelectric method, it is difficult to form a piezoelectric film.

[0013] Conventionally, in order to manufacture a piezoelectric vibration element used in a MEMS mirror or the like, a piezoelectric film such as PZT is formed on a silicon substrate by a sputtering method or the like (Patent Literature 1).

[0014] Prior Art Documents

[0015] Patent Literature

[0016] Patent Literature 1: Japanese Patent Application Laid-Open (kokai) No. 2014-225596

[0017] Patent Literature 2: Japanese Patent Application Laid-Open (kokai) No. 2014-086400 SUMMARY

[0018] In the future, a HUD is required to be large-scaled and wide-angled, and is required to be expanded to a maximum of 20 degrees with respect to the current angle of 7 to 8 degrees. In order to achieve large-scale and wide-angle, the frequency, amplitude, and reliability of the piezoelectric vibration element of the MEMS mirror need to be improved. However, as described in Patent Literature 1, it is found that in the conventional piezoelectric vibration element in which a piezoelectric layer is formed on a silicon substrate by a film formation method, a piezoelectric vibration element having such high frequency, amplitude, and reliability cannot be achieved.

[0019] In particular, when the piezoelectric vibration element is mounted to a package or a substrate and electrically connected, wire bonding or flip-chip bonding is performed. In the bonding process, the piezoelectric vibration element needs to be subjected to a load such as heating, ultrasonic vibration, and load. At this time, it is found that if a method of improving the frequency, amplitude, and reliability of the piezoelectric vibration element is adopted, the heating, ultrasonic vibration, and load increase, and a crack or a notch is easily generated in the piezoelectric vibration element. Accordingly, the yield of the piezoelectric vibration element is reduced.

[0020] The present application can suppress cracks or notches caused by heating, ultrasonic vibration, and weight application at the time of mounting a piezoelectric vibration element.

[0021] The invention according to the first aspect includes a piezoelectric vibration substrate characterized by comprising:

[0022] a piezoelectric layer formed of a block-shaped piezoelectric material and having a first surface and a second surface on the opposite side of the first surface;

[0023] a lower electrode on the first surface of the piezoelectric layer; and

[0024] a support substrate joined to the lower electrode.

[0025] The invention according to the first aspect includes a piezoelectric vibration element characterized by comprising:

[0026] the piezoelectric vibration substrate, and

[0027] an upper electrode on the piezoelectric layer.

[0028] The invention according to the second aspect includes a piezoelectric vibration substrate characterized by comprising:

[0029] a piezoelectric layer formed of a block-shaped piezoelectric material and having a first surface and a second surface on the opposite side of the first surface;

[0030] a lower electrode on the first surface of the piezoelectric layer;

[0031] a high-rigidity ceramic plate joined to the lower electrode; and

[0032] a support substrate joined to the high-rigidity ceramic plate.

[0033] The invention according to the second aspect includes a piezoelectric vibration element characterized by comprising:

[0034] the piezoelectric vibration substrate, and

[0035] an upper electrode on the second surface of the piezoelectric layer.

[0036] Effects of the Invention

[0037] The inventors of the present application have studied the reason why cracks or notches are generated in a piezoelectric vibration element due to heating, ultrasonic vibration, and weight application at the time of mounting the piezoelectric vibration element to a package or a substrate and electrically connecting it. As a result, it has been found that, in the case where a piezoelectric film such as PZT is formed by various film formation methods such as sputtering, the crystalline quality of the piezoelectric film is poor, which constitutes the reason for cracks or notches.

[0038] Therefore, the inventors of the present application have also studied that a piezoelectric vibration plate is manufactured by thin-filmizing a piezoelectric material substrate in a bulk form. However, the piezoelectric material substrate in a bulk form has a tendency that, if the thickness is thinned by processing to, for example, 50 μm or less, it is cracked due to insufficient strength, and thus it is difficult to be used as a piezoelectric vibration element.

[0039] Based on these insights, the inventors of the present application have found that, by directly bonding a piezoelectric material substrate in a bulk form to another support substrate with the aid of a lower electrode and an intermediate layer, and thinning the piezoelectric material substrate by polishing to a desired thickness suitable for high frequency vibration, a piezoelectric vibration layer having a thin thickness and good crystallinity is successfully formed, and thus cracks or notches of the piezoelectric vibration element caused by heating, ultrasonic vibration and application of weight can be suppressed.

[0040] Further, the inventors of the present application have found that, in the piezoelectric vibration element of the above-described form, by providing another high-rigidity ceramic plate between the lower electrode provided on the first face of the piezoelectric layer and the support substrate, cracks or notches of the piezoelectric vibration element caused by heating, ultrasonic vibration and application of weight can be further reduced.

[0041] As a result, by the present application, a piezoelectric actuator device having excellent piezoelectric characteristics and durability can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 In the figure, (a) indicates a laminate of the piezoelectric body 2, the lower electrode 3 and the intermediate layer 4, (b) indicates the support substrate 5, and (c) indicates a bonded body obtained by directly bonding the intermediate layer 4 and the support substrate 5.

[0043] Figure 2 In the figure, (a) indicates a state where the intermediate layer 8 is provided on the first face of the high-rigidity ceramic body 7, (b) indicates the support substrate 5, (c) indicates a state where the high-rigidity ceramic plate 7A is bonded to the support substrate 5, and (d) indicates a state where the lower electrode 3 and the intermediate layer 4 are provided on the piezoelectric body 2. Figure 1 (c) indicates a bonded body obtained by processing the piezoelectric body in the bonded body of (c), and (b) indicates a piezoelectric vibration element 11 having a piezoelectric layer 2A, an upper electrode 1, a lower electrode 3, an intermediate layer 4, an amorphous layer 6 and a support substrate 5.

[0044] Figure 3 In the figure, (a) indicates a state where the intermediate layer 8 is provided on the first face of the high-rigidity ceramic body 7, (b) indicates the support substrate 5, (c) indicates a state where the high-rigidity ceramic plate 7A is bonded to the support substrate 5, and (d) indicates a state where the lower electrode 3 and the intermediate layer 4 are provided on the piezoelectric body 2.

[0045] Figure 4 In the figure, (a) indicates a bonded body of the support substrate 5, the lower electrode 3, the high-rigidity ceramic plate 7A and the piezoelectric body 2, (b) indicates a state where the piezoelectric body 2 is processed in the bonded body of (a) to form a piezoelectric layer 2A, and (c) indicates a piezoelectric vibration element 12. Figure 4 (c) indicates a bonded body obtained by processing the piezoelectric body in the bonded body of (c), and (b) indicates a piezoelectric vibration element 11 having a piezoelectric layer 2A, an upper electrode 1, a lower electrode 3, an intermediate layer 4, an amorphous layer 6 and a support substrate 5.

[0046] Figure 5 is a transmission electron microscope (TEM) photograph of the vicinity of the interface of the support substrate and the intermediate layer in the embodiment of the present application.

[0047] Figure 6 is a cross-sectional transmission electron microscope (TEM) photograph showing the bonding interface of the intermediate layer and the high-rigidity ceramic plate on the bonding surface of the lower electrode and the vicinity thereof in the embodiment of the present application.

[0048] Figure 7 is a cross-sectional transmission electron microscope (TEM) photograph showing the bonding interface of the intermediate layer and the first surface of the high-rigidity ceramic plate on the bonding surface of the support substrate and the vicinity thereof.

[0049] Figure 8 is a cross-sectional transmission electron microscope (TEM) photograph of the piezoelectric vibration element. DETAILED DESCRIPTION

[0050] Hereinafter, the embodiment of the present application will be described in further detail with appropriate reference to the accompanying drawings.

[0051] Figure 1 and Figure 2 relate to the invention of the first aspect.

[0052] In the preferred embodiment, as shown in Figure 1 (a), the piezoelectric body 2 has a first surface 2a and a second surface 2b. The lower electrode 3 and the intermediate layer 4 are provided on the first surface 2a of the piezoelectric body 2. Next, the bonding surface 4a of the intermediate layer 4 is irradiated with a neutral atom beam like an arrow A, thereby activating the intermediate layer 4a.

[0053] On the other hand, as shown in Figure 1 (b), the bonding surface 5a of the support substrate 5 is irradiated with a neutral atom beam like an arrow B, thereby activating the bonding surface 5a. Next, as shown in Figure 1 (c), the bonding surface 4a of the intermediate layer 4 and the bonding surface 5a of the support substrate 5 are brought into contact with each other, and direct bonding is performed, thereby obtaining a bonded body. Typically, an amorphous layer 6 is generated along the boundary of the support substrate 5 and the intermediate layer 4.

[0054] Next, as shown in Figure 2 (a), the piezoelectric body of the bonded body is processed to be thinned, thereby forming a piezoelectric layer 2A having a desired thickness. The thickness of the piezoelectric layer 2A is appropriately changed depending on the target vibration frequency. 2c is a processed surface (second surface) of the piezoelectric layer 2A. Next, as shown in Figure 2 (b), the upper electrode 1 is formed on the second surface 2c of the piezoelectric layer 2A, thereby obtaining a piezoelectric vibration element 11.

[0055] Figure 3 and Figure 4 The application relating to the second aspect.

[0056] As Figure 3 (a) shows, the high-rigidity ceramic body 7 has a first face 7a and a second face 7b. An intermediate layer 8 is provided on the first face 7a of the high-rigidity ceramic body 7. Next, as shown by an arrow C, the bonding face 8a of the intermediate layer 8 is irradiated with a neutral atom beam, thereby activating the bonding face 8a. On the other hand, as shown by Figure 3 (b), the bonding face 5a of the support substrate 5 is irradiated with a neutral atom beam as shown by an arrow B, thereby activating the bonding face 5a.

[0057] Next, as shown by Figure 3 (c), the bonding face 8a of the intermediate layer 8 and the bonding face 5a of the support substrate 5 are brought into contact with each other, and direct bonding is performed, thereby obtaining a bonded body. At this time, typically, an amorphous layer 10 is generated along the interface between the bonding face 8a and the bonding face 5a.

[0058] Next, the high-rigidity ceramic body 7 is processed to be thinned, thereby forming a high-rigidity ceramic plate 7A having a desired thickness. Next, an intermediate layer 16 is provided on the second face 7c of the high-rigidity ceramic plate 7A, and the bonding face 16a of the intermediate layer is irradiated with a neutral atom beam as shown by an arrow D, thereby performing surface activation.

[0059] On the other hand, as shown by Figure 3 (d), a lower electrode 3 and an intermediate layer 4 are provided in this order on the first face 2a of the piezoelectric body 2, and the bonding face 4a of the intermediate layer 4 is activated with a neutral atom beam E. Next, as shown by Figure 4 (a), the bonding face 4a of the intermediate layer 4 and the intermediate layer 16 on the second face 7c of the high-rigidity ceramic plate 7A are brought into contact with each other, and direct bonding is performed, thereby obtaining a bonded body. At this time, typically, an amorphous layer is generated along the interface between the intermediate layer 4 which has been directly bonded and the intermediate layer 16.

[0060] Next, as shown by Figure 4 (b), the piezoelectric body 2 of the bonded body is processed to be thinned, thereby forming a piezoelectric layer 2A having a desired thickness. The thickness of the piezoelectric layer 2A is appropriately changed depending on the target vibration frequency. 2c is a processed face (second face) of the piezoelectric layer 2A. Next, as shown by Figure 4 (c), an upper electrode 1 is formed on the second face 2c of the piezoelectric layer 2A, thereby obtaining a piezoelectric vibration element 12.

[0061] The element of the present application has a piezoelectric layer formed of a block-shaped piezoelectric material, and has a first face and a second face.

[0062] The bulk piezoelectric material refers to a piezoelectric material formed in a bulk shape by a crystal growth method or a sintering method, and not a piezoelectric material formed in a state of being deposited on a substrate. Generally, the piezoelectric material has good crystallinity and high strength.

[0063] In particular, the bulk piezoelectric material has a characteristic that, because of the high crystallinity, the piezoelectric constant d 31 (the extension in the direction along the electrode surface) is greater than that of a deposited product. In the case of a bulk product, the piezoelectric constant (d 31 : pc / N = pm / V) is, for example, 150 or more (sometimes more than 200), and even so, the piezoelectric constant of a deposited product is 150 or less, and it is often around 100 on average.

[0064] The piezoelectric material is not particularly limited, and examples include lead-based perovskite oxides (for example, lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT)). In addition, La (lanthanum), Nb (niobium), and / or Sr (strontium) can be added to the lead-based perovskite oxide (for example, PZT), and oxides such as Pb(Mg, Nb)O3, Pb(Ni, Nb)O3, PbTiO3, or combinations thereof can be used.

[0065] From the viewpoint of mechanical strength during operation, the thickness of the piezoelectric body before processing is preferably 200 μm or more. In addition, the thickness of the piezoelectric layer (vibration body) after processing depends on the target vibration frequency, and can be, for example, 0.5 μm to 50 μm.

[0066] The material of the upper electrode and the lower electrode is not particularly limited, and there is no problem as long as a voltage that controls the vibration of the piezoelectric layer can be applied, and examples include platinum, gold, Au-Cu, Al, and Al-Cu alloy. In addition, a buffer layer of Cr, Ti, or the like for improving the adhesion of each electrode can be provided between the piezoelectric layer and the upper electrode, and between the high-rigidity ceramic plate and the lower electrode.

[0067] In the case of forming a piezoelectric body such as PZT on a support substrate using a deposition method, a seed layer for growing the piezoelectric body on the support substrate is necessary. From the viewpoint of culturing the piezoelectric body, the material of the seed layer is generally Pt, and in the deposition method, the lower electrode has no other choice but Pt in practice.

[0068] On the other hand, in the present application, since the piezoelectric material in a block form is bonded to the support substrate to produce the vibration body, the lower electrode can be bonded to the piezoelectric body without being affected by the material, film thickness, and the like of the lower electrode. Therefore, the electrode material that is most suitable for the device and the process can be selected. For example, compared to Pt, Au can be easily etched, and thus the lower electrode can be miniaturized. Generally, if the lower electrode is miniaturized, the wiring resistance increases, and the degradation of the device characteristics and the degradation of the reliability due to heat generation become problematic, but since the resistivity of Au is smaller than that of Pt, even if miniaturized, the problem caused by the increase in the wiring resistance can be avoided. Therefore, the miniaturization and the high performance of the device can be achieved.

[0069] From the above viewpoint, the material of the lower electrode is particularly preferably Au, and Ag, Cu, Al, W, Mo can also be preferably used, and an alloy of Au, Ag, Cu, Al, W, Mo can also be preferably used. In addition, the adhesion can be improved by providing the aforementioned buffer layer between the lower electrode and the piezoelectric body.

[0070] In the first aspect of the application, an intermediate layer can be provided on the lower electrode, and an intermediate layer can be provided on the support substrate. In this case, the direct bonding has the following embodiments.

[0071] (1) The intermediate layer on the lower electrode and the support substrate are directly bonded.

[0072] (2) The intermediate layer on the support substrate and the lower electrode are directly bonded.

[0073] (3) The intermediate layer on the lower electrode and the intermediate layer on the support substrate are directly bonded.

[0074] In addition, in the second aspect of the application, an intermediate layer can be provided on the bonding surface of the lower electrode, and an intermediate layer can be provided on the first surface of the high-rigidity ceramic plate. In this case, the direct bonding has the following embodiments.

[0075] (1) The intermediate layer on the bonding surface of the lower electrode and the second surface of the high-rigidity ceramic plate are directly bonded.

[0076] (2) The intermediate layer on the second surface of the high-rigidity ceramic plate and the bonding surface of the lower electrode are directly bonded.

[0077] (3) The intermediate layer on the bonding surface of the lower electrode and the intermediate layer on the second surface of the high-rigidity ceramic plate are directly bonded.

[0078] In addition, in the second aspect of the application, an intermediate layer can be provided on the bonding surface of the support substrate, and an intermediate layer can be provided on the first surface of the high-rigidity ceramic body. In this case, the direct bonding has the following embodiments.

[0079] (1) Directly bonding the intermediate layer on the bonding surface of the support substrate and the first surface of the high-rigidity ceramic body.

[0080] (2) Directly bonding the intermediate layer on the first surface of the high-rigidity ceramic plate and the bonding surface of the support substrate.

[0081] (3) Directly bonding the intermediate layer on the first surface of the high-rigidity ceramic plate and the intermediate layer on the bonding surface of the support substrate.

[0082] In any of the above, an amorphous layer is sometimes generated along the interface of the direct bonding.

[0083] The above intermediate layer is preferable in improving the bonding strength between the lower electrode and the high-rigidity ceramic plate, between the high-rigidity ceramic plate and the support substrate.

[0084] The material of the intermediate layer is not limited, and examples include silicon oxide, tantalum pentoxide, titanium oxide, zirconium oxide, hafnium oxide, niobium oxide, bismuth oxide, aluminum oxide, magnesium oxide, aluminum nitride, silicon nitride, and silicon.

[0085] The thickness of the intermediate layer is not particularly limited, and is preferably 0.01 to 1 μm, and more preferably 0.01 to 0.5 μm, from the viewpoint of manufacturing cost.

[0086] The film formation method of the intermediate layer is not limited, and examples include sputtering, chemical vapor deposition (CVD), and evaporation.

[0087] The material of the support substrate is not particularly limited, and is preferably a metal oxide, aluminum nitride, silicon carbide, silicon, glass, a metal, or SOI (Silicon on Insulator). The metal oxide can be an oxide of a single metal, or a composite oxide of multiple metals. The metal oxide is preferably selected from the group consisting of silicon aluminum oxygen nitrogen ceramic, sapphire, cordierite, mullite, and alumina. The alumina is preferably a light-transmitting alumina. Examples of the metal include SUS, copper, and aluminum.

[0088] The relative density of the support substrate is preferably 95.5% or more, and can be 100%, from the viewpoint of bonding strength. The relative density is measured by the Archimedes method. The manufacturing method of the support substrate is not particularly limited, and is preferably sintering or crystal growth.

[0089] The high-rigidity ceramic constituting the high-rigidity ceramic plate has a Young's modulus (JIS R1602) of 200 GPa or more, a bending strength (JIS R1601) of 310 MPa or more, and a fracture toughness (JIS R1607) of 6 MPa m1 / 2 or more. The above materials.

[0090] As the kind of the high-rigidity ceramic, silicon-aluminum-oxynitride ceramic, transparent alumina, sapphire, and the like can be exemplified.

[0091] The silicon-aluminum-oxynitride ceramic is a ceramic obtained by sintering a mixture of silicon nitride and alumina, and has the following composition.

[0092] Si 6－z Al z O z N 8－z

[0093] That is, the silicon-aluminum-oxynitride ceramic has a composition in which alumina is mixed in silicon nitride, and z represents the mixing ratio of alumina. z is more preferably 0.5 or greater. In addition, z is more preferably 4.0 or less.

[0094] Sapphire is a single crystal having a composition of Al2O3, and alumina is a polycrystal having a composition of Al2O3.

[0095] In the case where the intermediate layer and the support substrate, the intermediate layer and the lower electrode, the intermediate layer and the high-rigidity ceramic body, the intermediate layer and the support substrate, and the intermediate layer are directly bonded to each other, the following method is preferable.

[0096] First, the bonding surfaces of the respective intermediate layers, the bonding surface of the support substrate, the bonding surface of the high-rigidity ceramic body, and the bonding surface of the lower electrode are planarized to obtain respective planar surfaces. Here, the planarization method of the respective bonding surfaces includes lap, chemical mechanical polishing processing (CMP), and the like. In addition, the arithmetic mean roughness Ra of the planar surfaces is preferably 1 nm or less, and more preferably 0.3 nm or less.

[0097] Next, the respective bonding surfaces are cleaned so as to remove the residue of the polishing agent and the processing deterioration layer. The cleaning method of the respective bonding surfaces includes wet cleaning, dry cleaning, brushing, and the like, but in order to obtain a clean surface simply and efficiently, brushing is preferable. At this time, it is particularly preferable to use Sunwash LH540 as the cleaning liquid, and then to clean using a mixed solution of acetone and IPA (isopropyl alcohol) with a brushing machine.

[0098] Next, the respective bonding surfaces are activated by irradiating neutral atomic beams thereto.

[0099] When surface activation is performed using a neutralizing beam, it is preferable to use a device as described in Patent Literature 2 to generate a neutralizing beam and perform irradiation. That is, as a beam source, a high-speed atom beam source of the saddle field type is used. Then, an inert gas is introduced into a chamber, and a high voltage is applied from a direct current power source to an electrode. Accordingly, electrons e move due to an electric field of the saddle field type generated between the electrode (anode) and the housing (cathode), and a beam of atoms and ions derived from the inert gas is generated. Of the beam that reaches the grid, the ion beam is neutralized at the grid, and thus a beam of neutral atoms is emitted from the high-speed atom beam source. The atom species that constitute the beam are preferably an inert gas (argon, nitrogen, or the like).

[0100] The voltage when activation is performed using beam irradiation is preferably 0.5 to 2.0 kV, and the current is preferably 50 to 200 mA.

[0101] Next, the activated bonding surfaces are brought into contact with each other in a vacuum atmosphere, and bonding is performed. The temperature at this time is room temperature, but specifically, it is preferably 40°C or lower, and more preferably 30°C or lower. In addition, the temperature at the time of bonding is particularly preferably 20°C or higher and 25°C or lower. The pressure at the time of bonding is preferably 100 to 20,000 N.

[0102] An amorphous layer is sometimes generated between the support substrate and the intermediate layer. The composition of this amorphous layer contains: metal atoms that constitute the intermediate layer, metal atoms that constitute the support substrate, oxygen atoms or nitrogen atoms that constitute the support substrate, and sometimes argon.

[0103] In addition, an amorphous layer is sometimes generated between the lower electrode and the intermediate layer. The composition of this amorphous layer contains: metal atoms that constitute the intermediate layer, metal atoms that constitute the lower electrode, and sometimes argon.

[0104] In addition, an amorphous layer is sometimes generated between the high-rigidity ceramic plate and the intermediate layer. The composition of this amorphous layer contains: metal atoms that constitute the intermediate layer, metal atoms that constitute the high-rigidity ceramic plate, oxygen atoms or nitrogen atoms that constitute the high-rigidity ceramic plate, and sometimes argon.

[0105] In addition, an amorphous layer is sometimes generated between the piezoelectric body and the intermediate layer. The composition of this amorphous layer contains: metal atoms that constitute the intermediate layer, metal atoms that constitute the piezoelectric body, and sometimes argon.

[0106] In the preferable embodiment, for the manufacture of the substrate of the first aspect, the lower electrode and the intermediate layer are provided on the piezoelectric body, and next, the bonding surface of the intermediate layer and the bonding surface of the support substrate are directly bonded, thereby obtaining a bonded body. In this case, an amorphous layer is typically generated along the boundary between the support substrate and the intermediate layer.

[0107] Next, the piezoelectric body of the bonded body is processed to be thinned, thereby forming a piezoelectric layer having a desired thickness, to obtain a piezoelectric vibration substrate. Next, as shown in (b), an upper electrode is formed on the second face of the piezoelectric layer, thereby obtaining a piezoelectric vibration element. Figure 2 (b), an upper electrode is formed on the second face of the piezoelectric layer, thereby obtaining a piezoelectric vibration element.

[0108] Further, for the production of the substrate of the second aspect, an intermediate layer is provided on the first face of the high-rigidity ceramic body. Next, the intermediate layer and the bonding face of the support substrate are directly bonded, to obtain a bonded body. At this time, typically, an amorphous layer is generated along the interface of the bonding face of the intermediate layer and the support substrate. Next, the high-rigidity ceramic body is processed to be thinned, thereby forming a high-rigidity ceramic plate having a desired thickness.

[0109] On the other hand, a lower electrode is provided on the first face of the piezoelectric body, and an intermediate layer is provided on the bonding face of the lower electrode.

[0110] Then, an intermediate layer is provided on the second face of the high-rigidity ceramic plate, and the intermediate layer is directly bonded to the intermediate layer on the bonding face of the lower electrode. Next, a piezoelectric layer is obtained by processing the piezoelectric body.

[0111] The piezoelectric vibration element of the present application can be preferably used for an actuator of a MEMS element or the like.

[0112] Example

[0113] (Example Al)

[0114] The piezoelectric vibration element 11 shown in (b) was trial-produced in accordance with the method explained with reference to Figure 1 and Figure 2 The piezoelectric vibration element 11 shown in (b) was trial-produced in accordance with the method explained with reference to Figure 2 (b), an upper electrode is formed on the second face of the piezoelectric layer, thereby obtaining a piezoelectric vibration element.

[0115] Here, the piezoelectric body 2 was a block of PZT having a thickness of 250 μm, and the material of the upper electrode 1 and the lower electrode 3 was Pt. An intermediate layer 4 formed of amorphous silicon was provided on the lower electrode 3 by sputtering. Further, a support substrate 5 formed of silicon was prepared. Next, the bonding face 5a of the support substrate 5 and the bonding face 4a of the intermediate layer 4 were finished by chemical mechanical polishing (CMP) so that the respective arithmetic average roughness Ra was 0.2 nm.

[0116] Next, the bonding face 5a of the support substrate 5 and the bonding face 4a of the intermediate layer 4 were cleaned to remove dirt, and were introduced into a vacuum chamber. The vacuum was drawn to 10 -6 Pa or more and less than 10 -5After the Pa, the bonding surfaces 4a, 5a are irradiated with a high-speed atomic beam (acceleration voltage 1 kV, Ar flow rate 27 seem) for 120 seconds. Next, the bonding surface 5a of the support substrate 5 and the bonding surface 4a of the intermediate layer 4 are brought into contact, and then, pressing is performed at 10,000 N for 2 minutes to effect bonding.

[0117] Next, the piezoelectric layer 2A having a thickness of 1 μm is formed by polishing and grinding the one main surface 2b of the piezoelectric body 2. Next, the upper electrode 1 is formed on the second surface 2c of the piezoelectric layer 2A by sputtering, thereby obtaining the piezoelectric vibration element 11.

[0118] The piezoelectric vibration element 11 is mounted on a package, and wire bonding is performed. In the bonding process, the piezoelectric vibration element 11 is subjected to heating (150°C), ultrasonic vibration (80 kHz), and load (500 gf). As a result, the rate of occurrence of defective products in which cracks or notches are generated in the piezoelectric vibration element 11 was 5%.

[0119] Figure 5 is a cross-sectional transmission electron microscope (TEM) photograph (magnification 2 million times) showing the bonding interface between the intermediate layer of the piezoelectric vibration element 11 and the support substrate and the periphery thereof. Figure 5 In the photograph, the bright area on the upper side is the intermediate layer (amorphous silicon), the area on the lower side is the support substrate (silicon), and the band-shaped area in the central portion is an amorphous layer generated at the time of bonding. The ratio of each atom in the support substrate, the amorphous layer, and the intermediate layer is as follows.

[0120] Table 1

[0121] Composition unit (atm %) Si O Ar Intermediate layer (a-Si film) 93.6 6.4 0.0 Bonding interface (amorphous layer) 93.3 5.0 1.7 Support substrate (Si substrate) 98.8 1.2 0.0

[0122] (Comparative Example Al)

[0123] A piezoelectric vibration element is trial-produced by forming a piezoelectric layer by a vapor deposition method.

[0124] That is, a lower electrode 3 formed of Pt, a piezoelectric layer formed of PZT having a thickness of 1 μm, and an upper electrode formed of Pt are formed on a support substrate formed of silicon by sputtering, thereby obtaining a piezoelectric vibration element.

[0125] Next, the piezoelectric vibration element is mounted on a package, and heating, ultrasonic vibration, and load are applied thereto in the same manner as in Example Al. As a result, the rate of occurrence of defective products in which cracks or notches are generated in the piezoelectric vibration element was 20%.

[0126] (Example Bl)

[0127] The piezoelectric vibrating element 11 was fabricated in the same manner as in Example A1. However, unlike Example A1, the piezoelectric body 2 and the piezoelectric layer 2A were made of PMN-PT. Otherwise, it was the same as in Example A1. The resulting piezoelectric vibrating element 11 was mounted in a package, and heat, ultrasonic vibration, and load were applied in the same manner as in Example A1. As a result, the defect rate of the piezoelectric vibrating element with cracks or gaps was 6%.

[0128] (Comparative Example B1)

[0129] A piezoelectric vibrating element 11 was fabricated in the same manner as Comparative Example A1. However, unlike Comparative Example A1, the material of the piezoelectric layer was PMN-PT. Otherwise, it was the same as Comparative Example A1. The obtained piezoelectric vibrating element was mounted in a package, and heat, ultrasonic vibration, and load were applied in the same manner as in Example A1. As a result, the defect rate of the piezoelectric vibrating element with cracks or gaps was 22%.

[0130] (Example C1)

[0131] According to reference Figure 3 and Figure 4 The method of explanation, trial production Figure 4 (c) shows the piezoelectric vibrating element 12.

[0132] Among them, such as Figure 3 As shown in (a), an intermediate layer 8 formed of amorphous silicon is provided on the first surface 7a of a high-rigidity ceramic body 7 formed of silicon-aluminum-oxygen-nitrogen ceramic with a thickness of 250 μm. Additionally, as... Figure 3 (b) shows that an intermediate layer formed of amorphous silicon is prepared on the surface of a support substrate 5 with a thickness of 500 μm formed of silicon. Next, chemical mechanical polishing (CMP) is used to finish the intermediate layer bonding surface 5a of the support substrate 5 and the bonding surface 8a of the intermediate layer 8, so that the arithmetic mean roughness Ra is 0.2 nm.

[0133] Next, the intermediate layer bonding surface 5a of the support substrate 5 and the bonding surface 8a of the intermediate layer 8 are cleaned to remove dirt, and then introduced into the vacuum chamber. The vacuum is then evacuated to 10... －6 Pa or higher and less than 10 －5 After Pa, each bonding surface 5a and 8a was irradiated with a high-speed atomic beam (accelerating voltage 1 kV, Ar flow rate 27 sccm) for 120 seconds. Next, the bonding surfaces 5a and 8a of the intermediate layer of the support substrate 5 and the intermediate layer 8 were brought into contact and bonded by applying pressure of 10000 N for 2 minutes. The resulting bond was then heated at 100°C for 20 hours.

[0134] Next, the second surface 7b of the high-rigidity ceramic body 7 is ground and polished, thereby achieving the following: Figure 3As shown in (c), a high-rigidity ceramic plate 7A with a thickness of 50 μm is formed. However, in this embodiment, an intermediate layer 16 is not provided on the second surface 7c of the high-rigidity ceramic plate 7A.

[0135] On the other hand, such as Figure 3 As shown in (d), the piezoelectric body 2 is a bulk PZT with a thickness of 250 μm. On the first surface 2a of the piezoelectric body 2, Ti (15 nm) / Pt (200 nm) film is formed as the lower electrode 3. Then, an intermediate layer 4 formed of amorphous silicon is set by sputtering.

[0136] Next, chemical mechanical polishing (CMP) was used to process the second surface 7c and the intermediate layer 4 (refer to) of the high-rigidity ceramic plate 7A. Figure 1 The mating surface 4a of (a) is finished to make the arithmetic mean roughness Ra of each surface 0.2 nm.

[0137] Next, the second surface 7c of the high-rigidity ceramic plate 7A and the joint surface 4a of the intermediate layer 4 are cleaned to remove dirt, and then introduced into the vacuum chamber. The vacuum is then evacuated to 10... －6 Pa or higher and less than 10 －5 After Pa, the second surface 7c and the bonding surface 4a are irradiated with a high-speed atomic beam (accelerating voltage 1 kV, Ar flow rate 27 sccm) for 120 seconds. Next, the second surface 7c of the high-rigidity ceramic plate 7A and the bonding surface 4a of the intermediate layer 4 are brought into contact and bonded by applying pressure of 10000 N for 2 minutes. The resulting bond is then heated at 100°C for 20 hours.

[0138] Next, the second surface 2b of the piezoelectric element 2 is ground and polished, thereby, as Figure 4 As shown in (b), a piezoelectric layer 2A with a thickness of 1 μm is formed. Next, the upper electrode 1 (Ti (15 nm) / Pt (200 nm)) is deposited by sputtering to obtain the piezoelectric resonant element 12.

[0139] The piezoelectric vibrating element 12 is mounted in the package and wire-bonded. During the bonding process, the piezoelectric vibrating element 12 is subjected to heating (150°C), ultrasonic vibration (80 kHz), and a load (500 gf). As a result, the defective product rate with cracks or notches in the piezoelectric vibrating element 11 is 5%.

[0140] Figure 6 This is a transmission electron microscope (TEM) image (2 millionx magnification) showing the interface between the intermediate layer and the high-rigidity ceramic plate on the bonding surface of the lower electrode 3 and its surrounding area. Figure 6In the figure, the bright area on the upper side is the intermediate layer (amorphous silicon), the dark area on the lower side is the high-rigidity ceramic plate (silicon aluminum oxygen nitrogen ceramic), and the band-shaped area in the central portion is the amorphous layer generated at the time of bonding. The ratio of each atom in the high-rigidity ceramic plate, the amorphous layer, and the intermediate layer is as follows.

[0141] Table 2

[0142]

[0143] Figure 7 is a cross-sectional transmission electron microscope (TEM) photograph (magnification 2 million times) showing the bonding interface of the intermediate layer on the bonding surface 5a of the support substrate 5 and the intermediate layer on the first surface of the high-rigidity ceramic plate and the periphery thereof. Figure 7 In the figure, the bright area on the upper side is the intermediate layer (amorphous silicon), the dark area on the lower side is the support substrate (silicon). Also, the band-shaped area between the two intermediate layers is the amorphous layer generated at the time of bonding. The ratio of each atom in the intermediate layer on the high-rigidity ceramic plate, the amorphous layer on the first surface, the intermediate layer on the support substrate, and the support substrate is as follows.

[0144] Table 3

[0145]

[0146] (Example D1)

[0147] A piezoelectric vibration element was trial-manufactured in the same manner as in Example Al.

[0148] However, unlike Example Al, the material of the buffer layer on the piezoelectric body was made Cr, and the materials of the lower electrode and the upper electrode were made Au. Also, no intermediate layer was provided on the lower electrode, and no intermediate layer was provided on the support substrate, and the lower electrode and the support substrate were directly bonded.

[0149] Specifically, a block of PZT having a thickness of 250 μm was used as the piezoelectric body 2, and a buffer layer and a lower electrode were formed on the piezoelectric body 2 using a sputtering method. The material of the buffer layer was made Cr, and the material of the lower electrode was made Au. Also, a support substrate 5 formed of silicon was prepared. Next, the bonding surface 5a of the support substrate 5 and the bonding surface of the lower electrode were finished using chemical mechanical polishing (CMP) so that the arithmetic average roughness Ra of each was 0.2 nm.

[0150] Next, the bonding surface 5a of the support substrate 5 and the bonding surface of the lower electrode were cleaned to remove dirt, and were introduced into a vacuum chamber. The vacuum was drawn to 10 －6 Pa or more and less than 10 －5After the bonding, the bonding surface of the piezoelectric body 2 and the bonding surface of the lower electrode were contacted and bonded by pressing at 10000 N for 2 minutes.

[0151] Next, the piezoelectric layer 2A having a thickness of 1 μm was formed by grinding and polishing one main surface 2b of the piezoelectric body 2. Next, a buffer layer formed of Cr and an upper electrode formed of Au were formed on the second surface 2c of the piezoelectric layer 2A by sputtering to obtain a piezoelectric vibration element.

[0152] The piezoelectric vibration element was mounted on a package and wire-bonded. In the bonding process, the piezoelectric vibration element was subjected to heating (150°C), ultrasonic vibration (80 kHz), and load (500 gf). As a result, the rate of defective products in which cracks or notches were generated in the piezoelectric vibration element 11 was 3%.

[0153] Figure 8 is a cross-sectional transmission electron microscope (TEM) photograph (magnification: 2 million times) of the piezoelectric vibration element. Figure 8 In the photograph, the bright area on the upper side is the piezoelectric layer, and on the first surface of the piezoelectric layer, the Cr layer and the Au layer are shown in the form of bands, respectively. Further, the lower side is the support substrate (silicon), and the band-shaped area between the support substrate and the Au layer is an amorphous layer generated at the time of bonding.

Claims

1. A piezoelectric vibration substrate, characterized by, Possessing: a piezoelectric layer formed of a block-shaped piezoelectric material and having a first surface and a second surface on the opposite side of the first surface; a lower electrode on the first surface of the piezoelectric layer; and a support substrate bonded to the lower electrode, an intermediate layer between the lower electrode and the support substrate, the intermediate layer being composed of silicon oxide, tantalum pentoxide, titanium oxide, zirconium oxide, hafnium oxide, niobium oxide, bismuth oxide, aluminum oxide, magnesium oxide, aluminum nitride, silicon nitride, or silicon, the lower electrode and the support substrate being directly bonded via the intermediate layer, an amorphous layer being present along the directly bonded interface of the lower electrode and the intermediate layer, the directly bonded interface of the support substrate and the intermediate layer, or the directly bonded interface in the intermediate layer.

2. A piezoelectric vibration element characterized by comprising: Possessing: the piezoelectric vibration substrate according to claim 1, and an upper electrode on the second surface of the piezoelectric layer.

3. A piezoelectric vibration substrate, characterized by, Possessing: a piezoelectric layer formed of a block-shaped piezoelectric material and having a first surface and a second surface on the opposite side of the first surface; a lower electrode on the first surface of the piezoelectric layer; a high-rigidity ceramic plate bonded to the lower electrode; and a support substrate bonded to the high-rigidity ceramic plate, an intermediate layer between the lower electrode and the high-rigidity ceramic plate, and an intermediate layer between the high-rigidity ceramic plate and the support substrate, an amorphous layer being present along the interface of the lower electrode and the high-rigidity ceramic plate, and an amorphous layer being present along the interface of the high-rigidity ceramic plate and the support substrate.

4. The piezoelectric vibration substrate according to claim 3, wherein the intermediate layer is composed of silicon oxide, tantalum pentoxide, titanium oxide, zirconium oxide, hafnium oxide, niobium oxide, bismuth oxide, aluminum oxide, magnesium oxide, aluminum nitride, silicon nitride, or silicon.

5. The piezoelectric vibration substrate according to claim 3 or 4, wherein an upper electrode is provided on the second surface of the piezoelectric layer.

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