Sputtering target materials and sputtering targets

Abstract

To provide a sputtering target material excellent in characteristics.SOLUTION: A sputtering target material is composed of a sintered body of an oxide including potassium, sodium, niobium, and oxygen. A ratio of a total area of cavities in a unit area of a sputter surface is equal to or less than 12.0%, and a mean diameter of cavities existing in the sputter surface is equal to or less than 0.60 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to sputtering target materials and sputtering targets. [Background technology]

[0002] As a material for depositing a piezoelectric thin film, a sputtering target material (hereinafter referred to as a KNN target material or simply as a target material) made of a sintered body of an oxide containing potassium, sodium, niobium, and oxygen may be used (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-146623 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to improve the properties of KNN target materials. [Means for solving the problem]

[0005] According to one aspect of the present disclosure, A sputtering target material comprising a sintered body of an oxide containing potassium, sodium, niobium, and oxygen, The ratio of the total area of ​​voids per unit area of ​​the sputtering surface is 12.0% or less, The average diameter of voids present on the sputtering surface is 0.60 μm or less A sputtering target material is provided.

[0006] According to another aspect of the present disclosure, The sputtering target material according to the above aspect, a backing plate bonded to the sputtering target material; A sputtering target comprising: [Effects of the Invention]

[0007] According to the present disclosure, it is possible to improve the characteristics of the KNN target material. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating one embodiment of a target material 10 according to the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating a manufacturing flow of the target material 10 of the present disclosure. [Figure 3] FIG. 3 is a schematic diagram of a sintering apparatus 100 used in the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] <One aspect of the present disclosure> Hereinafter, one embodiment of the present disclosure will be described mainly with reference to FIGS.

[0010] (1) Target material composition The target material 10 in this embodiment is mainly composed of a sintered body containing an oxide (alkali niobium oxide) containing potassium (K), sodium (Na), niobium (Nb), and oxygen (O), i.e., a KNN sintered body. The crystal grains that mainly constitute the KNN sintered body have a perovskite structure. Specifically, the KNN sintered body is composed of a sintered body having a composition formula (K 1-x Na x)It is represented by NbO3(0 < x < 1), and the coefficient x[=Na / (K + Na)] in the above compositional formula satisfies 0 < x < 1, preferably 0.4 ≤ x ≤ 0.8. The KNN sintered body constituting the target material 10 of this embodiment is a substantially oxide sintered body composed of potassium, sodium, niobium, and oxygen, or an oxide sintered body further containing a dopant element shown below. Here, "substantially" means that 99% or more of all the atoms constituting the KNN sintered body are composed of potassium, sodium, niobium, and oxygen, or when the KNN sintered body contains a dopant element, it is composed of potassium, sodium, niobium, oxygen, and the dopant element.

[0011] The composition ((K + Na) / Nb) of K, Na, and Nb in the target material 10 satisfies the relationship of 0.90 or more and 1.25 or less, more preferably 0.95 or more and 1.20 or less, and still more preferably 1.00 or more and 1.10 or less. Here, K, Na, and Nb in the formula of (K + Na) / Nb are the numbers of K atoms, Na atoms, and Nb atoms contained in the KNN sintered body, respectively. Although the composition ratio of the target material 10 can be estimated from the charged amount of the raw materials, it can also be measured by a known method. For example, it can be determined by an inductively coupled plasma atomic emission spectrometer (ICP-AES, such as SPS5000 manufactured by Seiko Instruments Inc., etc.).

[0012] At least one element (dopant) selected from the group shown below may be added to the target material 10 at a concentration of, for example, 5 at % or less. The dopants include lithium (Li), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), bismuth (Bi), antimony (Sb), vanadium (V), indium (In), tantalum (Ta), molybdenum (Mo), tungsten (W), chromium (Cr), titanium (Ti), zirconium (Zr), hafnium (Hf), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium ( Examples of the element include at least one element selected from the group consisting of Sm, europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), copper (Cu), zinc (Zn), silver (Ag), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), aluminum (Al), silicon (Si), germanium (Ge), tin (Sn), and gallium (Ga). When multiple elements are contained, the total concentration is 5 at% or less, and the amount of dopant added is usually 0.1 at% or more.

[0013] The target material 10 is molded, for example, into a disk shape and bonded (attached) to a backing plate (cooling plate) (not shown) made of Cu or the like via a bonding material such as In, Sn, or an alloy containing these metals, and is used as a sputtering target. Of the two main surfaces of the target material 10, the surface other than the surface bonded to the cooling plate is the surface exposed to plasma such as argon (Ar) during film formation processing, i.e., is used as a sputtering surface 10s that emits atoms that constitute the film.

[0014] When the target material 10 is disk-shaped, the diameter of the main surface of the target material 10, preferably the diameter of the sputtering surface 10s, is not particularly limited, but is preferably 75 mm or more, more preferably 80 mm or more, even more preferably 90 mm or more, even more preferably 100 mm or more, and particularly preferably 200 mm or more. The area of ​​the main surface of the target material 10, preferably the area of ​​the sputtering surface 10s, is preferably 4500 mm 2 More than 5000mm, preferably 2 More preferably, 6000mm 2 More than 7500mm, and even more preferably 2 More than 15,000 mm, especially preferred 2 That's all.

[0015] The target material 10 may be a plate-like material with a rectangular main surface, and the length of the long side of the main surface of the target material 10, preferably the length of the long side of the sputtering surface 10s, is preferably 80 mm or more, more preferably 100 mm or more, even more preferably 120 mm or more, still more preferably 150 mm or more, and particularly preferably 200 mm or more. The length of the short side of the main surface of the target material 10, preferably the length of the short side of the sputtering surface 10s, is preferably 50 mm or more, more preferably 80 mm or more, and even more preferably 100 mm or more. The area of ​​the main surface of the target material 10, preferably the area of ​​the sputtering surface 10s, is preferably 4500 mm. 2 More than 5000mm, preferably 2 More preferably, 6000mm 2 More than 7500mm, and even more preferably 2 More than 15,000 mm, especially preferred 2 That's all.

[0016] The thickness of the target material 10 is not particularly limited, but is preferably 3.0 mm or more, more preferably 5.0 mm or more, even more preferably 7.5 mm or more, and is preferably 25 mm or less, more preferably 20 mm or less, even more preferably 15 mm or less.

[0017] The backing plate (cooling plate) is made of a conductive material, such as a metal or an alloy thereof, for example, Cu, a Cu alloy, Al, an Al alloy, Ti, stainless steel (SUS), etc. The size of the cooling plate is not particularly limited as long as it can bond and support the target material 10 and can be attached to the sputtering apparatus, but it is preferably approximately the same size as the bonding surface of the target material 10, and is preferably larger.

[0018] As will be described in detail later, when manufacturing the target material 10, various raw material powders containing K, Na, and Nb are mixed and then calcined, pulverized, and so on to prepare a raw material powder (hereinafter referred to as KNN raw material powder). From the viewpoint of powder homogeneity, the KNN raw material powder is preferably an oxide containing K, Na, and Nb in a solid solution state. In this embodiment, a predetermined amount of KNN raw material powder is subjected to mechanical pressure to form a powder compact, and at the same time, this powder compact is heated by passing a pulse current through it to be sintered, in other words, spark plasma sintering (hereinafter simply referred to as SPS) is performed.

[0019] In this sintering process, the powder compact is first pulse-current heated to a heating temperature of 450°C or higher under relatively low mechanical pressure conditions to expel residual gases and the like from the powder compact (hereinafter, this process is also referred to as degassing or low-pressure SPS).The degassed powder compact is then pulse-current heated under relatively high mechanical pressure conditions at least as high as necessary to promote the sintering reaction, to sinter the powder compact (hereinafter, this process is also referred to as full-pressure SPS).

[0020] The target material 10 in this embodiment is sintered using a novel method of performing low-pressure SPS followed by full-pressure SPS. Therefore, it not only has a high relative density but also possesses novel features not exhibited by target materials sintered by full-pressure SPS without performing low-pressure SPS or by target materials sintered using a so-called hot press method. Specifically, the target material 10 in this embodiment possesses at least one of Features 1 and 2 described below. As a result, the target material 10 in this embodiment further possesses at least one of Features 3 to 6 relating to mechanical strength, etc. The relative density of the target material 10 in this embodiment is 80% or more, preferably 85% or more, more preferably 90% or more, even more preferably 95% or more, and particularly preferably 98% or more across the entire sputtering surface. The relative density (%) here is a value calculated by (measured density / KNN theoretical density)×100. The theoretical density of KNN is, for example, 4.52 g / cm for KNN with a (K / (Na+K)) of 0.35. 3 is.

[0021] The target material 10 in this embodiment is composed of crystal grains having a number average particle size, as observed in a cross section parallel to the sputtering surface 10s, of, for example, 0.10 μm to 20 μm, preferably 0.15 μm to 10 μm, more preferably 0.20 μm to 5.0 μm, and particularly preferably 0.25 μm to 1.5 μm. The target material 10 is also composed of crystal grains having an area average particle size, as observed in a cross section parallel to the sputtering surface 10s, of, for example, 0.10 μm to 20 μm, preferably 0.20 μm to 10 μm, more preferably 0.30 μm to 5.0 μm, and particularly preferably 0.45 μm to 2.0 μm. When the number average particle size and area average particle size of the target material 10 are within the above ranges, the mechanical strength of the target material 10 is easily increased. The number average particle size and area average particle size of the target material 10 in this embodiment can be preferably determined by analyzing an electron backscattered diffraction pattern (EBSD) image of the sputtering surface 10s of the target material 10. The crystal grain size determined by EBSD analysis is indicated by the diameter of a circle having the same area as the measured crystal grains, and the number average particle size Nd (μm) can be determined by the average particle size determined by the Number method in the EBSD measurement. In the Number method, the value obtained by dividing the total area of ​​the analyzed object by the number of crystal grains is the average area of ​​the crystal grains, and is expressed as [measurement area (μm 2The average grain size is the diameter of a circle calculated by the formula [(measurement area - area with CI value below a certain value) / number of crystals]. When using OIM, a crystal orientation analysis software developed by TSL Solutions, Inc., for the analysis, if the area being evaluated on the target material 10 contains many voids or defects, the area where the Confidence Index (CI value) defined by OIM is below a certain value can be excluded, and the average grain size can be calculated from the value of [(measurement area - area with CI value below a certain value) / number of crystals]. The area-average grain size Nv (μm) can be calculated using the area fraction method. In the area fraction method, the average grain size of the crystal grains is calculated by multiplying each area value by its proportion of the area of ​​each crystal grain to the total area. The diameter of the calculated area when the circle is calculated is the average grain size. In EBSD analysis, the number average grain size Nd (μm) and area average grain size Nv (μm) can be calculated by regarding boundaries where the crystal orientation difference is a certain value or more, for example, 15° or more, as crystal grain boundaries.

[0022] The number average particle diameter Nd (μm) and the area average particle diameter Nv (μm) may be calculated using the following formulas. i is the grain size (μm) of the observed crystal grains, and n i is the observed particle diameter d i The number of grains with a diameter of 1 / 2 μm is shown. i is the diameter of a perfect circle having an area equal to the area of ​​the observed crystal grain, that is, the circle equivalent diameter (μm).

[0023] Number average particle diameter Nd(μm)=Σ(d i ×n i ) / Σn i Area average particle diameter Nv(μm)=Σ(d i 3 ×n i ) / Σ(d i 2 ×n i )

[0024] The area-average particle diameter Nv (μm) is an average value weighted according to the size of the particle area. When some crystal grains grow larger than the other crystal grains, the area-average particle diameter Nv (μm) becomes larger than the number-average particle diameter Nd (μm). However, the difference between the area-average particle diameter Nv (μm) and the number-average particle diameter Nd (μm) of the target material 10 in this embodiment is small, with the difference (Nv - Nd) being preferably 1.1 μm or less, more preferably 1.0 μm or less, even more preferably 0.75 μm or less, and particularly preferably 0.50 μm or less. Furthermore, the value of (Nv - Nd) / Nd is small, with the value being preferably 2.1 or less, preferably 1.5 or less, more preferably 1.0 or less, even more preferably 0.80 or less, even more preferably 0.70 or less, particularly preferably 0.60 or less, and particularly preferably 0.50 or less, resulting in excellent particle diameter uniformity. The number-average particle size and area-average particle size of the target material 10 in this embodiment show equivalent values ​​both when the heat treatment in an oxygen-containing atmosphere or in the air (hereinafter, also referred to as oxidation treatment) is omitted in the manufacturing process described later and when the oxidation treatment is performed.

[0025] Various novel features that the target material 10 of this embodiment may have will be described below.

[0026] (Feature 1) One of the features that the target material 10 may have is: the ratio of the total area Sv of voids present within the observation field to the observation area S of the sputtering surface 10s, Sv / S×100[%], i.e., the ratio of Sv per unit area of ​​the sputtering surface 10s (hereinafter also referred to as porosity), is 12.0% or less; And the average diameter of the voids present on the sputtering surface 10s is 0.60 μm or less. The following are some of the reasons:

[0027] This characteristic can be realized when an oxidation treatment is carried out in the manufacturing process described below.

[0028] The voids appear on the sputtering surface 10s due to voids generated inside the target material 10, and are observed as openings of recessed spaces on the sputtering surface 10s. The total area and average diameter of the voids present on the sputtering surface 10s can be calculated by analyzing optical microscope images or scanning electron microscope (hereinafter sometimes referred to as SEM) images of the sputtering surface 10s using image analysis software. The total area of ​​the voids refers to the sum of the planar areas (cross-sectional areas) of the openings, and can be determined by calculating the total area of ​​the voids using the image analysis. The ratio of the total area of ​​the voids to the measured area can be calculated. The average diameter of the voids refers to the average value of the circle-equivalent diameters (μm) of multiple voids observed within an arbitrary observation field on the sputtering surface 10s, and this value is substantially equivalent to the average diameter of the voids present on the sputtering surface 10s. The average diameter of the voids can be determined, for example, by calculating the area of ​​each void by image analysis, and calculating the circle-equivalent diameter (50% area average diameter) from the area when the cumulative area is 50% of the total area obtained by adding up all of the void areas.

[0029] In the manufacturing process of the target material 10 of this embodiment, a novel method of performing low-pressure SPS followed by full-pressure SPS is adopted, which makes it possible to suppress the occurrence of voids in the sputtering surface 10s and to make the voids smaller than when sintering is performed by full-pressure SPS without performing low-pressure SPS or when sintering is performed using a hot press method, thereby achieving the above-mentioned characteristics. However, when sintering is performed by full-pressure SPS without performing low-pressure SPS or when sintering is performed using a hot press method, the above-mentioned characteristics regarding at least one of the porosity and the average diameter of the voids cannot be obtained.

[0030] (Feature 2) One of the features that the target material 10 may have is: The maximum diameter of voids present on the sputtering surface 10s is 1.0 μm or less. The following are some of the reasons:

[0031] This characteristic can be realized when an oxidation treatment is carried out in the manufacturing process described below.

[0032] The maximum diameter of voids refers to the circle-equivalent diameter (μm) of the largest void among multiple voids observed within an arbitrary observation field on the sputtering surface 10s, and this value is substantially equivalent to the maximum diameter of voids present on the sputtering surface 10s. In the manufacturing process of the target material 10 of this embodiment, a novel method of performing low-pressure SPS followed by full-pressure SPS is adopted. This allows for smaller voids than when full-pressure SPS is performed without low-pressure SPS or when sintering is performed using a hot press, thereby achieving the above-mentioned characteristics. Note that when full-pressure SPS is performed without low-pressure SPS or when sintering is performed using a hot press, the above-mentioned characteristics cannot be achieved.

[0033] (Feature 3) One of the features that the target material 10 may have is: Volume resistivity at 25°C is 6.0 x 10 11 less than Ω·cm, Vickers hardness is 460 or more, and flexural strength is 90 MPa or more. The following are some of the reasons:

[0034] This characteristic can be exhibited when the oxidation treatment is omitted in the manufacturing process described below. The Vickers hardness (Hv) of the target material 10 (or the KNN sintered compact) can be measured using a Vickers hardness tester in accordance with JIS R 1610:2003, and can be measured, for example, by the method described in the Examples. The flexural strength of the target material 10 (or the KNN sintered compact) can be determined by a three-point bending test in accordance with JIS R 1601:2008, and can be measured, for example, by the method described in the Examples.

[0035] In the manufacturing process of the target material 10 of this embodiment, a novel method is adopted in which low-pressure SPS is performed followed by full-pressure SPS, thereby making it possible to obtain at least one of the above-mentioned features 1 and 2. As a result, it becomes possible to increase the Vickers hardness of the target material 10 while also increasing its flexural strength. Note that when full-pressure SPS is performed without low-pressure SPS and sintering is performed, or when sintering is performed using a hot press method, the above-mentioned features 1 and 2 are not exhibited, and when oxidation treatment is omitted (volume resistivity at 25°C is 6.0 × 10 11 In the case where the hardness is less than Ω·cm, the above-mentioned characteristics regarding at least one of the Vickers hardness and the flexural strength are not obtained.

[0036] (Feature 4) One of the features that the target material 10 may have is: Volume resistivity at 25°C is 6.0 x 10 11 Ω·cm or more, Vickers hardness is 250 or more, and flexural strength is 90 MPa or more. The following are some of the reasons:

[0037] This characteristic can be realized when an oxidation treatment is carried out in the manufacturing process described below.

[0038] In the manufacturing process of the target material 10 of this embodiment, a novel method is adopted in which low-pressure SPS is performed followed by full-pressure SPS, thereby making it possible to obtain at least one of the above-mentioned features 1 and 2. As a result, it is possible to increase the Vickers hardness of the target material 10 while also increasing its flexural strength. Note that when full-pressure SPS is performed without low-pressure SPS and sintering is performed, or when sintering is performed using a hot press method, the above-mentioned features 1 and 2 are not exhibited, and when oxidation treatment is performed (volume resistivity at 25°C is 6.0 × 10 11 In the case where the hardness is Ω·cm or more, the above-mentioned characteristics regarding at least either the Vickers hardness or the flexural strength are not obtained.

[0039] (Feature 5) One of the features that the target material 10 may have is: After heat treatment in air at 900°C for 5 hours, the Vickers hardness remains at more than 50% of the Vickers hardness before the heat treatment. The following are some of the reasons:

[0040] This feature can be achieved in both cases where the oxidation treatment is omitted and where the oxidation treatment is carried out in the manufacturing process described below.

[0041] In the manufacturing process of the target material 10 of this embodiment, a novel method is adopted in which low-pressure SPS is performed followed by full-pressure SPS, thereby achieving at least one of the above-mentioned features 1 and 2, and as a result, the above-mentioned features regarding the Vickers hardness before and after heat treatment are achieved. Note that if full-pressure SPS is performed without low-pressure SPS and sintering is performed, or if sintering is performed using a hot press method, the above-mentioned features 1 and 2 are not manifested and the above-mentioned features cannot be achieved.

[0042] (Feature 6) One of the features that the target material 10 may have is: The relative density after heat treatment in air at 900°C for 5 hours remains at more than 95% of the relative density before heat treatment. The following are some of the reasons:

[0043] This feature can be achieved in both cases where the oxidation treatment is omitted and where the oxidation treatment is carried out in the manufacturing process described below.

[0044] In the manufacturing process of the target material 10 of this embodiment, a novel method is adopted in which low-pressure SPS is performed followed by full-pressure SPS, thereby achieving at least one of the above-mentioned features 1 and 2, and as a result, the above-mentioned features are achieved with respect to the relative density before and after heat treatment. Note that if full-pressure SPS is performed without low-pressure SPS or if sintering is performed using a hot press method, the above-mentioned features 1 and 2 are not achieved, and the above-mentioned features are not achieved.

[0045] (2) Target material manufacturing method A preferred embodiment of the method for producing the target material 10 in this aspect will be described in detail with reference to FIGS.

[0046] (Preparation of starting powder) First, as starting raw material powders, powder containing K, powder containing Na, and powder containing Nb, for example, potassium carbonate (K2CO3) powder, sodium carbonate (Na2CO3) powder, and niobium pentoxide (Nb2O5) powder, are prepared.

[0047] Here, "powder consisting of a K compound" refers to a powder whose main component is a K compound. It may be composed solely of a K compound powder, or it may contain powders of other compounds in addition to the powder of the K compound (the main component). Similarly, "powder consisting of a Na compound" refers to a powder whose main component is a Na compound. It may be composed solely of a Na compound powder, or it may contain powders of other compounds in addition to the powder of the Na compound (the main component). "powder consisting of a Nb compound" refers to a powder whose main component is a Nb compound. It may be composed solely of a Nb compound powder, or it may contain powders of other compounds in addition to the powder of the Nb compound (the main component). The K compound refers to at least one selected from the group consisting of K oxide, K composite oxide, and K compound that becomes an oxide upon heating, such as the carbonates listed above, as well as oxalates. The Na compound refers to at least one selected from the group consisting of Na oxide, Na composite oxide, and Na compound that becomes an oxide upon heating, such as the carbonates listed above, as well as oxalates. The Nb compound is at least one selected from the group consisting of Nb oxides, Nb composite oxides, and Nb compounds that become oxides upon heating, and examples thereof include niobium pentoxide shown above.

[0048] Furthermore, as required, a powder containing at least one dopant element selected from the group consisting of Li, Mg, Ca, Sr, Ba, Bi, Sb, V, In, Ta, Mo, W, Cr, Ti, Zr, Hf, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Zn, Ag, Mn, Fe, Co, Ni, Al, Si, Ge, Sn, and Ga is prepared as a starting raw material powder, for example, a powder of the element itself, an oxide powder containing the element, a composite oxide powder containing the element, or a powder of a compound containing the element (e.g., carbonate, oxalate) that becomes an oxide when heated.

[0049] The average particle diameter of these starting raw material powders is, for example, a median diameter D 50It is preferable that the particle size is less than 1 mm, and if necessary, it is preferable to preliminarily crush the starting raw material powder before weighing.

[0050] (weighing, mixing) Next, each of the starting raw material powders is weighed, and the mixing ratio of the starting raw material powders is adjusted so that the final target material 10 has the desired composition. Weighing may be performed in the atmosphere, but is preferably performed in a low-humidity atmosphere such as an inert gas atmosphere, a vacuum, or a dry air atmosphere, and it is also preferable to thoroughly dry each starting raw material powder before performing the weighing. Next, the weighed starting raw material powders are dry-mixed using a mixer such as a Henschel mixer, blender, ribbon mixer, super mixer, Nauta mixer, intensive mixer, or automatic mortar.

[0051] (primary firing, coarse grinding) The obtained mixed powder is subjected to primary firing in an electric furnace or the like in an oxidizing atmosphere such as air or an oxygen gas atmosphere to obtain a fired product containing K, Na, and Nb. Preferably, in the primary firing, the raw material mixed powder is subjected to a solid-phase reaction to obtain a fired product in which K, Na, and Nb are in a solid solution state. The obtained fired product is then coarsely pulverized using a grinding means such as a ball mill, bead mill, vibration mill, attritor, jet mill, atomizer, or cutter mill to obtain a fired powder (hereinafter, KNN fired powder). When K, Na, and Nb are in a solid solution state in the primary firing, a KNN fired powder in which K, Na, and Nb are in a solid solution state (hereinafter, KNN solid solution powder) can be obtained.

[0052] The heating temperature during primary firing is preferably 500°C or higher, more preferably 550°C or higher, even more preferably 600°C or higher, and preferably 750°C or lower, more preferably 700°C or lower. When the heating temperature is above the lower limit, it is easy to obtain a KNN solid solution powder in which K, Na, and Nb are in a solid solution state, and it is easy to obtain a fired powder with high homogeneity. When the heating temperature is below the upper limit, it is easy to increase the BET specific surface area of ​​the KNN fired powder and the KNN solid solution powder, and it is easy to obtain a fired powder with high sinterability.

[0053] The time for primary firing is not particularly limited, but is preferably 3 hours or more and 20 hours or less, more preferably 4 hours or more and 15 hours or less, and even more preferably 5 hours or more and 10 hours or less.

[0054] (calcination, coarse grinding) The obtained KNN calcined powder (or KNN solid solution powder) is further calcined in an oxidizing atmosphere such as air or an oxygen gas atmosphere, and then coarsely pulverized using a milling method such as a ball mill, bead mill, vibration mill, attritor, jet mill, atomizer, etc. to obtain KNN calcined powder. By performing the calcination, impurities such as moisture, carbon components, and chlorine can be removed from the KNN calcined powder, and high-purity KNN calcined powder can be obtained.

[0055] The heating temperature during calcination is preferably 500° C. or higher, more preferably 600° C. or higher, even more preferably 650° C. or higher, and particularly preferably 700° C. or higher, and is preferably 1150° C. or lower, more preferably 1100° C. or lower, and even more preferably 1000° C. or lower. When the heating temperature is above the lower limit, a high-purity KNN calcined powder is easily obtained, and when the heating temperature is below the upper limit, a KNN raw material powder with a large BET specific surface area and high sinterability is easily obtained.

[0056] The heating time during calcination is not particularly limited, but is preferably 3 hours or more and 50 hours or less, more preferably 3.5 hours or more and 30 hours or less, even more preferably 4 hours or more and 20 hours or less, and particularly preferably 5 hours or more and 12 hours or less.

[0057] In the calcination step, from the viewpoint of facilitating the removal of impurities, multi-stage heat treatment may be carried out at different heating temperatures.

[0058] (finely pulverized) The KNN calcined powder obtained by coarse pulverization is further pulverized using a pulverizing means such as a ball mill, a bead mill, a vibration mill, an attritor, an atomizer, or a jet mill, preferably a jet mill, and if necessary, dried after pulverization to obtain a KNN raw material powder having predetermined specifications (specific surface area, impurity concentration, etc.).

[0059] For example, when the calcined powder is pulverized using a jet mill, the processing speed is 1.0 kg / h to 8.0 kg / h, preferably 1.2 kg / h to 6.0 kg / h, and more preferably 1.5 kg / h to 3.0 kg / h. The introduction pressure is 0.1 MPa to 2.0 MPa, preferably 0.5 MPa to 1.8 MPa, and more preferably 1.0 MPa to 1.7 MPa, and the pulverization pressure is 0.1 MPa to 2.0 MPa, preferably 0.5 MPa to 1.8 MPa, and more preferably 1.0 MPa to 1.7 MPa. Pulverizing the calcined powder under these conditions makes it easier to obtain a raw material powder with a large BET specific surface area and high sinterability.

[0060] By going through the above steps, the KNN raw material powder used for the SPS sintering of this embodiment is obtained. The BET specific surface area of ​​the KNN raw material powder is preferably 1.0 m 2 / g or more, more preferably 2.0m 2 / g or more, more preferably 2.5m 2 / g or more, particularly preferably 3.0m 2 / g or more, preferably 10m 2 / g or less, more preferably 8.0m 2 / g or less, more preferably 7.0m 2 / g or less, particularly preferably 6.0m 2 / g or less. When the BET specific surface area of ​​the KNN raw material powder is equal to or greater than the above lower limit, sinterability is improved, and a high-density KNN sintered body is likely to be obtained. Furthermore, when the BET specific surface area of ​​the KNN raw material powder is equal to or less than the above upper limit, the amount of gas components (e.g., gas components contained in the atmosphere, carbon dioxide, carbon monoxide, methane, etc.) and moisture adsorbed to the raw material powder after production can be reduced, making it easier to obtain a KNN sintered body with few impurities and voids. The BET specific surface area of ​​the KNN raw material powder can be measured using a gas adsorption apparatus and determined by the method described in the Examples. The obtained KNN raw material powder is heated and dried, for example, at 180 to 200°C, before use, as needed.

[0061] The carbon concentration contained in the KNN raw material powder is preferably 250 ppm or less, and more preferably 200 ppm or less.

[0062] The above-mentioned processes, such as primary firing, coarse pulverization, calcination, coarse pulverization, and jet mill pulverization, can be partially or completely repeated as needed, or any of the processes can be omitted. Furthermore, after these processes are completed or between processes, a sieving process or the like can be added. The mixing and pulverization methods are not limited to the above examples, and a wide variety of other pulverization methods can be adopted. The conditions for these processes can also be selected widely depending on the purpose of achieving the above specifications.

[0063] Next, a preferred embodiment of the low-pressure SPS and full-pressure SPS processes will be described with reference to Fig. 3. Fig. 3 is a schematic diagram of a sintering apparatus 100 used in these processes. The sintering apparatus 100 includes a chamber 101, a die 102, punches 103 and 104, pressure devices 105 and 106, a vacuum pump 110, a pressure gauge 111, a pulse current device 120, etc.

[0064] (Low pressure SPS) First, a predetermined amount of KNN raw material powder having the above-mentioned specifications is filled into a cylindrical die (sintering mold) 102. Next, the die 102 filled with the KNN raw material powder is housed in a chamber 101 and placed between a pair of upper and lower punches 103 and 104. Then, while the chamber 101 is evacuated using a vacuum pump 110, the pressure inside the chamber 101 is monitored with a pressure gauge 111. The die 102 and punches 103 and 104 may be made of any conductive material, but are preferably made of a carbon material such as graphite.

[0065] When the desired pressure is reached inside the chamber 101, the pressure devices 105 and 106 are operated to apply mechanical pressure to the KNN raw material powder filled in the die 102 via the punches 103 and 104, while the pulse current application device 120 starts to apply pulse current to the KNN raw material powder to heat it. With the start of pulse current application, the temperature of the green compact formed by pressing the KNN raw material powder gradually rises from a starting temperature of about room temperature (25°C) to a predetermined degassing temperature shown below.

[0066] The degassing temperature is 450°C or higher, which can be set to a temperature similar to the sintering temperature in the conventional SPS described below, but the mechanical pressure applied (degassing pressure) is much smaller than the mechanical pressure (sintering pressure) in the conventional SPS. As a result, in low-pressure SPS, the sintering reaction of the KNN raw material powder in the compact proceeds slowly, and degassing from the compact due to the simultaneous heating occurs more easily.

[0067] The mechanical pressure in the low-pressure SPS step should be sufficient to allow stable current flow in the SPS apparatus, but from the viewpoint of facilitating the discharge of residual gas from the powder compact, it is preferably 1 MPa or more, more preferably 5 MPa or more, even more preferably 7 MPa or more, and even more preferably 8 MPa or more, and is preferably 15 MPa or less, more preferably 12 MPa or less, and even more preferably 10 MPa or less.

[0068] The degassing temperature in the low-pressure SPS step is preferably 500°C or higher, more preferably 600°C or higher, even more preferably 700°C or higher, even more preferably 800°C or higher, and particularly preferably 900°C or higher, and is preferably 1200°C or lower, more preferably 1100°C or lower. When the degassing temperature in the low-pressure SPS step is within the above range, residual gas can be easily discharged, and a sintered body with high mechanical strength can be easily obtained.

[0069] The heating time at the degassing temperature is not particularly limited, and may be such that heating is performed at the heating temperature or higher for a certain period of time by providing a sufficient temperature rise time, or the state at which the degassing temperature has been reached may be maintained for a certain period of time. When the state at which the degassing temperature has been reached is maintained, the maintenance time is preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 20 minutes or more, and is preferably 10 hours or less, more preferably 5 hours or less, even more preferably 3 hours or less, still more preferably 60 minutes or less, particularly preferably 50 minutes or less, and especially preferably 40 minutes or less.

[0070] Furthermore, low-pressure SPS uses pulsed current heating, which allows the effects of electromagnetic energy, Joule heating, and discharge plasma generated between particles to efficiently desorb residual gases (e.g., carbon monoxide, carbon dioxide, moisture, and gas molecules containing chlorine-based impurities) adsorbed on the grain surfaces and release them from the compact. Low-pressure SPS efficiently degassing the compact while suppressing excessive grain growth while inducing a sintering reaction in the KNN raw powder. This reduces voids in the compact and densifies it. In other words, it reduces the excess space around the grains in the compact, allowing the grains to be condensed at a higher density.

[0071] When gas release from the powder compact begins, the pressure inside the chamber 101 rises, but when gas release from the powder compact is completed, the pressure inside the chamber 101 drops again. Therefore, by monitoring this pressure change with the pressure gauge 111, the completion timing of the low-pressure SPS can be determined.

[0072] Other conditions for low-pressure SPS include the following: Green compact temperature (starting temperature): Room temperature (25℃) ~ 80℃ Ambient pressure (pressure inside the chamber): 10 Pa or less

[0073] (Main pressure SPS) After the gas has been released from the powder compact, the mechanical pressure applied to the powder compact is increased to a value greater than that applied in the low-pressure SPS while continuing to evacuate the chamber 101 and to heat the powder compact by applying pulse current using the pulse current applying device 120. The mechanical pressure applied at this time (sintering pressure) is set to a value greater than or equal to that required to sufficiently promote the sintering reaction of the powder compact.

[0074] The mechanical pressure in this pressurized SPS process is preferably 25 MPa or more, more preferably 30 MPa or more, even more preferably 35 MPa or more, from the viewpoint of obtaining a sintered body that is high-density and resistant to cracking, and is preferably 70 MPa or less, more preferably 60 MPa or less, even more preferably 50 MPa or less.

[0075] Furthermore, from the viewpoint of obtaining a sintered body that is high in density and resistant to cracking, the heating temperature in this pressure SPS step is preferably 700°C or higher, more preferably 750°C or higher, even more preferably 800°C or higher, even more preferably 850°C or higher, and particularly preferably 900°C or higher, and is preferably 1100°C or lower, more preferably 1000°C or lower, even more preferably 980°C or lower, and particularly preferably 960°C or lower.

[0076] The heating time at the above heating temperature is not particularly limited, and may be such that heating is performed at the above heating temperature or higher for a certain period of time by providing a sufficient temperature rise time, or the state in which the predetermined heating temperature has been reached may be maintained for a certain period of time. When the heating temperature is maintained for a certain period of time, the maintenance time is preferably 10 minutes or more, more preferably 15 minutes or more, and even more preferably 20 minutes or more, and is preferably 240 minutes or less, more preferably 180 minutes or less, and even more preferably 120 minutes or less.

[0077] This process allows the green compact to be sintered to obtain a high-density sintered body. Compared to sintering using hot pressing, sintering using SPS allows for uniform sintering to proceed at a lower sintering temperature in a shorter period of time, which suppresses the growth of crystal grains in the sintered body and also makes it possible to densify the sintered body.

[0078] Other conditions for carrying out the pressurized SPS are as follows: Ambient pressure (pressure inside the chamber): 10 Pa or less

[0079] Although one embodiment of low-pressure SPS and full-pressure SPS has been exemplified above, the SPS sintering may be carried out in an inert atmosphere, for example, in an atmosphere of an inert gas such as nitrogen, argon, helium, or hydrogen.

[0080] (oxidation treatment) Note that performing low-pressure SPS or full-pressure SPS can result in the elimination of impurities such as carbon components from the green compact, while also elimination of some oxygen from the oxide sintered body, which may result in a slight decrease in the insulating properties of the final target material 10. Therefore, if necessary, after performing full-pressure SPS, the oxide sintered body may be heat-treated in an oxygen-containing atmosphere to increase its resistance and restore its insulating properties. Furthermore, this oxidation treatment can further reduce impurities remaining during SPS sintering.

[0081] The oxidation treatment is carried out in an oxidizing atmosphere such as air or an oxygen-containing atmosphere at a heating temperature of 500° C. to 1100° C., preferably 700° C. to 1050° C., more preferably 800° C. to 1020° C., and even more preferably 850° C. to 1000° C. The heating time is 1 hour to 40 hours, preferably 2 hours to 20 hours, more preferably 3 hours to 10 hours, and even more preferably 4 hours to 7 hours.

[0082] The oxidation treatment can be omitted if necessary. When the oxidation treatment is omitted, the target material 10 finally obtained has a surface roughness of, for example, 6.0×10 at 25° C. 11 In addition, when the oxidation treatment is performed, the target material 10 finally obtained has a volume resistivity of, for example, 6.0×10 11 It will have a volume resistivity of Ω·cm or more.

[0083] (Finishing and joining to backing plate) Thereafter, if necessary, the sintered body is cut into a mold having an area of, for example, 4500 mm 2 As described above, the target material 10 in this embodiment is obtained by grinding the material into a disk shape having a thickness of 3 mm or more and adjusting the surface condition by polishing the surface. The target material 10 is bonded to a backing plate made of Cu or the like via a bonding material such as In, Sn, or an alloy containing these metals, and is used as a sputtering target.

[0084] (3) Effects According to this embodiment, one or more of the following effects can be obtained.

[0085] (a) The target material 10 in this embodiment is sintered by a novel method in which low-pressure SPS is performed followed by full-pressure SPS, and therefore has at least one of the above-mentioned features 1 and 2.

[0086] As a result, the target material 10 in this embodiment further has at least one of the above-mentioned features 3 to 6 relating to mechanical strength and the like.

[0087] The target material 10 having the properties shown in Features 3 and 4 is less likely to crack, chip, or the like during machining such as grinding when manufacturing the target material 10, and during sputtering film formation using the target material 10. Furthermore, abnormal discharge caused by cracks or chips is less likely to occur during sputtering film formation, which makes it possible to suppress composition changes and deterioration in the properties of the resulting sputtering film (piezoelectric thin film).

[0088] Furthermore, the target material 10 having the properties shown in Features 5 and 6 is unlikely to change in Vickers hardness or relative density before and after heat treatment, and therefore can be stably used in sputtering film formation processes and the like in which the target material 10 reaches high temperatures.

[0089] Note that when sintering is performed by full-pressure SPS without low-pressure SPS, or when sintering is performed using a hot press method, neither Features 1 nor 2 are exhibited, and as a result, none of Features 3 to 6 are obtained.

[0090] (b) When the oxidation treatment is performed by appropriately selecting the manufacturing conditions of the target material 10 from the above-mentioned range of conditions (volume resistivity at 25°C is 6.0 × 10 11 In the case where the resistivity is Ω·cm or more, the porosity can be set not only to 12.0% or less, but also to preferably 10.0% or less, more preferably 8.00% or less, even more preferably 6.00% or less, still more preferably 4.00% or less, particularly preferably 2.00% or less, especially more preferably 1.00% or less, and especially more preferably 0.75% or less, and the average diameter of the pores can be set not only to 0.60 μm or less, but also to preferably 0.50 μm or less, more preferably 0.40 μm or less, even more preferably 0.30 μm or less, and even more preferably 0.25 μm or less.

[0091] In addition, by appropriately selecting the manufacturing conditions of the target material 10 from the above-mentioned range of conditions, when an oxidation treatment is performed (volume resistivity at 25°C is 6.0 × 10 11 In the case where the resistivity is Ω·cm or more, the maximum diameter of the voids can be not only set to 1.0 μm or less, but also preferably set to 0.80 μm or less, more preferably 0.62 μm or less, even more preferably 0.60 μm or less, still more preferably 0.50 μm or less, and particularly preferably 0.40 μm or less.

[0092] In these cases, the mechanical strength of the target material 10 can be further improved.

[0093] Specifically, when oxidation treatment was performed (volume resistivity at 25°C was 6.0 × 10 11In the case where the hardness is Ω·cm or more, it is possible to make the Vickers hardness not only 210 or more, but also preferably 250 or more, more preferably 300 or more, even more preferably 350 or more, still more preferably 400 or more, particularly preferably 450 or more, and particularly preferably 500 or more. In addition, it is possible to make the flexural strength not only 90 MPa or more, but also preferably 100 MPa or more, more preferably 110 MPa or more, even more preferably 120 MPa or more, and still more preferably 130 MPa or more.

[0094] As a result, it is possible to further improve the stability of the Vickers hardness and relative density of the target material 10 before and after the heat treatment.

[0095] Specifically, when oxidation treatment is performed, the Vickers hardness after heat treatment in air at 900°C for 5 hours can be made not only to be more than 50% of the Vickers hardness before heat treatment, but also preferably to be more than 70%, more preferably more than 90%, more preferably more than 95%, and more preferably more than 100%.

[0096] Furthermore, the relative density after heat treatment under conditions of 900°C in air for 5 hours can be made not only to be more than 95% of the relative density before heat treatment, but also to be preferably more than 97%, more preferably more than 99%, and more preferably more than 100%.

[0097] There is no particular restriction on the lower limit of the porosity. However, when the relative density of the target material 10 exceeds 95%, it is preferable to set the porosity to 0.05% or more, preferably 0.10% or more, more preferably 0.15% or more, even more preferably 0.20% or more, and even more preferably 0.25% or more, so that stress generated by the thermal load during sputtering can be alleviated and cracking and chipping of the target material 10 during sputtering can be more reliably suppressed.

[0098] There is also no particular lower limit for the average void diameter. However, when the relative density of the target material 10 exceeds 95%, it is preferable to set the average void diameter to 0.05 μm or more, preferably 0.10 μm or more, more preferably 0.15 μm or more, even more preferably 0.20 μm or more, and even more preferably 0.22 μm or more, so that stress generated by the thermal load during sputtering can be alleviated and cracking and chipping of the target material 10 during sputtering can be more reliably suppressed.

[0099] There is also no particular restriction on the lower limit of the maximum diameter of the voids. However, when the relative density of the target material 10 exceeds 95%, it is preferable to set the maximum diameter of the voids to 0.08 μm or more, preferably 0.12 μm or more, more preferably 0.18 μm or more, even more preferably 0.20 μm or more, still more preferably 0.25 μm or more, particularly preferably 0.30 μm or more, and particularly preferably 0.35 μm or more, so that stress generated by the thermal load during sputtering can be alleviated and cracking and chipping of the target material 10 during sputtering can be more reliably suppressed.

[0100] <Other Aspects of the Present Disclosure> Although various aspects of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described aspects and can be modified in various ways without departing from the spirit and scope of the present disclosure. [Example]

[0101] The present disclosure will be described in more detail below based on examples and comparative examples, but the present disclosure is not limited to the following examples. First, the devices, conditions, methods, etc. used when measuring the target materials prepared in the examples and comparative examples will be described.

[0102] <Grain size of target material> Sample preparation: Performed by polishing method (polished with waterproof abrasive paper and then buffed until there were no large scratches that would interfere with the evaluation). Equipment: Hitachi High-Tech Corporation ultra-high resolution analytical scanning electron microscope SU-70 EBSD detector manufactured by TSL Solutions Co., Ltd. Analysis software: OIM Analysis Ver. 8 by TSL Solutions Co., Ltd. Measurement magnification: 3000x Measurement area: 30μm x 50μm Step size: 0.06 μm Grain boundary angle: 15° Crystal information of KNN: The space group and lattice constant were determined by X-ray diffraction, and the information shown in Table 1 below was used. Analysis method: Cleanup processing was performed to remove noise, and a grain boundary map was created under the condition of a grain boundary angle of 15° (boundaries with a crystal orientation difference of 15° or more were considered to be grain boundaries), and particle size was analyzed. If voids or other imperfections were present, a threshold was set for the IQ (Image Quality) value. The EBSD Number method and Area Fraction method were used to calculate the area and particle diameter (circle equivalent diameter) of each particle, and the number-average particle diameter and area-average particle diameter were determined. In addition, when calculating particle size, particles of 0.20 μm or larger were included in the calculation in order to remove areas with poor crystallinity that could not be analyzed and microcrystals as noise.

[0103] <Porosity and pore diameter of target material> Sample preparation: Performed by polishing method (polished with waterproof abrasive paper and then buffed until there were no large scratches that would interfere with the evaluation). Equipment: Hitachi High-Tech Corporation ultra-high resolution field emission scanning electron microscope SU-8000 Measurement magnification: 5000x Analysis method: For SEM images acquired using the above equipment and conditions, the voids and the matrix were binarized using the image analysis software "Adobe Photoshop (registered trademark)," and the area ratio of the voids to the measured area was calculated to calculate the porosity. Furthermore, the image calculation software "ScnImage" was used to calculate the area of ​​each void, and the diameter (circle-equivalent diameter) of each void was also calculated assuming the shape was an equivalent circle. The average diameter of the voids was determined by calculating the circle-equivalent diameter from the area when the cumulative area relative to the total area of ​​the calculated voids was 50%. The maximum diameter of the voids was determined by extracting the maximum value from the calculated void diameters.

[0104] <Vickers hardness> The Vickers hardness of the target materials of the examples and comparative examples was measured using the following apparatus, conditions and method. Equipment: Mitutoyo Corporation Micro Vickers Hardness Tester HM-114 Atmosphere: Atmospheric Temperature: Room temperature (25℃) Test force: 1.0 kgf Load application acceleration: 10μm / s Holding time: 15sec Number of measurement points: 5 points Test method: This test conforms to JIS R 1610, and uses a Vickers indenter (a pyramidal indenter with a square base and two opposing surfaces that form an angle of 136 degrees) to make an indentation on the test surface. The Vickers hardness is calculated from the test force and the indentation surface area calculated from the diagonal length of the indentation, and the average is calculated from the measurement results at five points.

[0105] <Folding strength> The bending strength of the target materials of the examples and comparative examples was measured using the following equipment, conditions and method. Equipment: Instron universal testing machine 5582 (load cell 500N) Atmosphere: Atmospheric Temperature: Room temperature (25℃) Test speed: 0.5 mm / min Distance between fulcrums: L=30mm Jig material: SiC Test method: Evaluation was performed using a three-point bending test in accordance with JIS R 1601. A test piece (size: 3mm x 4mm x 40mm) was placed on two supports spaced a fixed distance apart (30mm), and a load was applied to the center point between the supports to determine the bending strength from the maximum load at which the piece broke.

[0106] <Relative density> The relative densities of the target materials of the examples and comparative examples were measured using the following apparatus and method. Equipment: Alpha Mirage electronic hydrometer MDS300 Test method: The density of the target material cut to a predetermined size was measured using the above-mentioned device by the Archimedes method. The density was calculated based on the theoretical density of KNN (4.52 g / cm 3 ) to obtain the relative density (%) (= measured density / theoretical density × 100).

[0107] <Insulation evaluation> The insulating properties of the target materials of the examples and comparative examples were evaluated by measuring the volume resistivity using the following equipment, test, and method. Equipment: Mitani Micronics Co., Ltd. Screen printing machine MODEL MEC=2400E Resistivity measuring device manufactured by Nishiyama Manufacturing Co., Ltd. ADC Corporation Digital Ultra-High Resistance / Micro Current Meter Model 5450 Test method: DC three terminal method Measurement temperature: room temperature (25℃) Measurement atmosphere: Argon atmosphere (purity 99.9999% Ar, flow rate 300cc / min) Measurement method: Using a screen printer and a platinum paste manufactured by Tanaka Kikinzoku Kogyo K.K., main electrodes, guard electrodes were formed on the upper surface of a target material sample cut into a predetermined size, and a counter electrode was formed on the lower surface of the target material sample. Each electrode can be formed by drying the platinum paste printed on the sample at 150 °C for 12 hours and then performing a baking process (Ar atmosphere, 1000 °C) using an atmospheric tube furnace. After holding the sample with electrodes in an environment at room temperature (25 °C) for 15 minutes, a DC voltage of 100 V was applied, the current after charging for 1 minute was measured, the volume resistance of the sample was obtained, and the volume resistivity was calculated from the thickness and electrode area of the sample.

[0108] <BET specific surface area of KNN raw material powder> The BET specific surface area of the KNN raw material powder obtained in the production example was measured by the BET single-point method by nitrogen adsorption using a specific surface area measuring device (Monosorb, manufactured by Quantachrome Instruments).

[0109] [Production of KNN raw material powder 1] <Production Example 1> K2CO3 powder, Na2CO3 powder, and Nb2O5 powder were prepared as starting raw material powders. By the method described in JP-A-2018-197181, in terms of atomic conversion, sodium 32.5 mol%, potassium 17.5 mol%, niobium 50.0 mol%, the ratio of alkali metal to niobium ((Na + K) / Nb) was 1.00, and the ratio of potassium to sodium and potassium (K / (Na + K)) was 0.35. By mixing the raw material powders, firing at 650 °C for 7 hours, and pulverizing, KNN raw material powder 1 in which K, Na, and Nb were solid-dissolved was obtained. The composition of the obtained KNN raw material powder 1 was measured by a high-frequency inductively coupled plasma optical emission spectrometer after acid dissolution, and it was confirmed that it was almost the same as the charged ratio. By X-ray diffraction analysis, it was confirmed that it was a solid solution of K, Na, and Nb. Also, the BET specific surface area of KNN raw material powder 1 was 6.9 m 2 / g.

[0110] [Production of KNN raw material powder 2] <Production Example 2> The KNN raw material powder 1 obtained in Production Example 1 was fired in an electric furnace at 750°C for 5 hours and then at 1000°C for 5 hours to obtain KNN raw material powder 2. The BET specific surface area of ​​the obtained KNN raw material powder 2 was 3.3 m 2 / g.

[0111] [Production of KNN raw powder 3] <Production Example 3> The KNN raw material powder 1 obtained in Production Example 1 was fired in an electric furnace at 750°C for 5 hours and then at 900°C for 5 hours to obtain KNN raw material powder 3. The BET specific surface area of ​​the obtained KNN raw material powder 3 was 3.6 m 2 / g.

[0112] [Production of KNN raw powder 4] <Production Example 4> K2CO3 powder, Na2CO3 powder, and Nb2O5 powder were prepared as starting raw material powders and mixed so that the [K / (K+Na)] value was 0.35 and the [(Na+K) / Nb] value was 1.00. MnO powder and CuO powder were also mixed to contain predetermined concentrations of Mn and Cu. The mixture was fired at 650°C for 7 hours and then pulverized to obtain KNN raw material powder 4, which is a solid solution of K, Na, and Nb. The composition of the obtained KNN raw material powder 4 was measured using a high-frequency inductively coupled plasma atomic emission spectrometer after acid dissolution and confirmed to be approximately the same as the feed ratio. X-ray diffraction analysis confirmed that it was a solid solution of K, Na, and Nb. The BET specific surface area of ​​KNN raw material powder 4 was 6.9 m 2 / g.

[0113] Example 1 The KNN raw material powder 2 obtained in Production Example 2 was heated to 200°C and dried, and then placed in a pulse current pressure sintering machine SPS9.40MK-VII (manufactured by SPS Syntex Co., Ltd.) equipped with a graphite die measuring φ170 mm x φ101.6 mm x t100 mm and a graphite punch measuring φ101.6 mm x t65 mm. Under a vacuum atmosphere (atmospheric pressure less than 10 Pa) and pressurized at 10 MPa, heating by discharge plasma was initiated, and the temperature was raised from 25°C to 900°C at a rate of 50°C / min. During this time, desorption of gas components and an increase in atmospheric pressure were confirmed. The pressure was gradually increased to 30 MPa, and then the temperature was raised to 1020°C at 10°C / min and held at 1020°C for 75 minutes. Thereafter, the current and pressure were stopped and the material was cooled to obtain a disk-shaped target material (KNN sintered compact, a target material with low insulation properties) with a diameter of approximately 101 mm and a thickness of 5 mm.

[0114] The obtained target material was then oxidized in air at 900°C for 5 hours, and the surface was then ground to obtain a KNN target material (highly insulating target material) with a diameter of 100 mm and a thickness of 5 mm.

[0115] The number average particle size of the obtained target material was 0.60 μm, and the area average particle size was 1.05 μm.

[0116] The composition of the target material obtained was measured using a high-frequency inductively coupled plasma optical emission spectrometer after microwave decomposition, and it was confirmed that the [K / (K+Na)] value was 0.35 and the [(Na+K) / Nb] value was 1.0.

[0117] <Conditions for low pressure SPS> Mechanical pressure: 10 MPa Heating temperature: ~900℃ Ambient pressure (pressure inside the chamber): Less than 10 Pa (rising to 30 Pa)

[0118] <Conditions for this pressurized SPS> Mechanical pressure: 30 MPa (pressure starts at 900°C) Heating temperature: 1020°C (heat from 900°C at 10°C / min, hold for 75 minutes after reaching 1020°C) Ambient pressure (pressure inside the chamber): Less than 10 Pa

[0119] Example 2 A KNN target material having a diameter of 100 mm and a thickness of 5 mm was obtained in the same manner as in Example 1, except that the KNN raw material powder 3 obtained in Production Example 3 was used and the pressurized SPS was performed under the conditions shown below.

[0120] The number average particle size of the obtained target material was 0.49 μm, and the area average particle size was 0.71 μm.

[0121] <Conditions for this pressurized SPS> Mechanical pressure: 40 MPa (pressure starts at 900°C) Heating temperature: 900-1010°C (heat from 900°C to 1010°C at 2.5°C / min, no holding time) Ambient pressure (pressure inside the chamber): Less than 10 Pa

[0122] Comparative Example 1 A KNN target material having a diameter of 100 mm and a thickness of 5 mm was obtained in the same manner as in Example 1, except that the KNN raw material powder 4 obtained in Production Example 4 was used and low-pressure SPS and full-pressure SPS were performed under the conditions shown below.

[0123] <Conditions for low pressure SPS> Mechanical pressure: 10 MPa Heating temperature: 400°C (heat from 25°C to 400°C at 13°C / min, then hold for 60 minutes) Ambient pressure (pressure inside the chamber): Less than 10 Pa (rising to 20 Pa)

[0124] <Conditions for this pressurized SPS> Mechanical pressure: 40 MPa (pressure starts at 400°C) Heating temperature: up to 910°C (heat from 400°C to 800°C at 4°C / min, then heat to 910°C at 1.2°C / min and hold for 10 minutes) Ambient pressure (pressure inside the chamber): Less than 10 Pa

[0125] Comparative Example 2 Using the KNN raw material powder 1 obtained in Production Example 1, a KNN target material having a diameter of 100 mm and a thickness of 5 mm was obtained in the same manner as in Example 1, except that low-pressure SPS was not performed and main-pressure SPS was performed under the conditions shown below.

[0126] <Conditions for low pressure SPS> Not implemented

[0127] <Conditions for this pressurized SPS> Mechanical pressure: 40 MPa (pressurization starts at 25°C) Heating temperature: 800°C (heat from 25°C to 800°C at 50°C / min, then hold for 160 minutes) Ambient pressure (pressure inside the chamber): Less than 10 Pa (rising to 30 Pa)

[0128] <Evaluation of voids> The sputtering surfaces of the target materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were observed by SEM, and the porosity (%), which is the ratio of the total area of ​​voids present in the sputtering surface, the average diameter (μm) of the voids present on the sputtering surface, and the maximum diameter (μm) of the voids present on the sputtering surface were measured.

[0129] Furthermore, the Vickers hardness, relative density, and bending strength of Examples 1 and 2 and Comparative Examples 1 and 2 were measured.

[0130] The Vickers hardness and relative density were measured before oxidation treatment (volume resistivity at 25°C was 6.0 × 10 11 Ω cm), and after oxidation treatment (volume resistivity at 25°C is 6.0×10 11 The target materials obtained in the examples and comparative examples all had a volume resistivity of 6.0×10 at 25°C before oxidation treatment. 11 Ω·cm or less, and the volume resistivity at 25°C after oxidation treatment is 6.0×10 11The flexural strength was measured after the oxidation treatment. Note that the flexural strength either remains unchanged by the oxidation treatment or decreases slightly due to the removal of carbon impurities from the sintered body, so the flexural strength before the oxidation treatment is equal to or greater than the flexural strength after the oxidation treatment.

[0131] The results of these measurements are shown in Table 1.

[0132] [Table 1]

[0133] In both Examples 1 and 2, it was confirmed that the porosity was 12.0% or less, the average pore diameter was 0.60 μm or less, and the maximum pore diameter was 1.0 μm or less.

[0134] In both Examples 1 and 2, it was confirmed that the Vickers hardness was 460 or more before the oxidation treatment and 250 or more after the oxidation treatment. In addition, it was confirmed that the flexural strength was 90 MPa or more after the oxidation treatment. From this, it was inferred that the flexural strength was 90 MPa or more even before the oxidation treatment in both Examples 1 and 2. Since Examples 1 and 2 have these mechanical strength properties, it was confirmed that no cracks or chips occurred during grinding or the subsequent sputtering film formation process.

[0135] Furthermore, when the Vickers hardness of Examples 1 and 2 was compared before and after the oxidation treatment, it was confirmed that there was no significant change in these values, and that the Vickers hardness after the heat treatment (oxidation treatment) was maintained at more than 50% of the Vickers hardness before the heat treatment.

[0136] Furthermore, when the relative densities of Examples 1 and 2 were compared before and after the oxidation treatment, it was confirmed that these values ​​also did not change significantly, and that the relative density after the heat treatment (oxidation treatment) was maintained at more than 95% of the relative density before the heat treatment.

[0137] In contrast, in Comparative Examples 1 and 2, it was confirmed that the porosity was greater than 12.0%, the average pore diameter was greater than 0.60 μm, and the maximum pore diameter was also larger than those of Examples 1 and 2.

[0138] In Comparative Examples 1 and 2, it was confirmed that the Vickers hardness was less than 460 before the oxidation treatment and less than 250 after the oxidation treatment. In addition, it was confirmed that the flexural strength was less than 90 MPa after the oxidation treatment in Comparative Examples 1 and 2. From this, it was inferred that the flexural strength was less than 90 MPa even before the oxidation treatment in Comparative Examples 1 and 2. In Comparative Examples 2 and 3, it was confirmed that cracks and chips occurred during grinding and the subsequent sputtering film formation process.

[0139] Furthermore, when the Vickers hardness of Comparative Examples 1 and 2 was compared before and after the oxidation treatment, it was confirmed that these values ​​changed significantly, and that the Vickers hardness after the heat treatment (oxidation treatment) was reduced to less than 50% of the Vickers hardness before the heat treatment.

[0140] Furthermore, when the relative densities of Comparative Examples 1 and 2 were compared before and after the oxidation treatment, it was confirmed that these values ​​also changed relatively significantly, and that the relative density after the heat treatment (oxidation treatment) was reduced to 95% or less of the relative density before the heat treatment.

[0141] <Preferred aspects of the present disclosure> Preferred aspects of the present disclosure will be described below.

[0142] (Appendix 1) According to one aspect of the present disclosure, A sputtering target material comprising a sintered body of an oxide containing potassium, sodium, niobium, and oxygen, The ratio of the total area of ​​voids per unit area of ​​the sputtering surface is 12.0% or less, The average diameter of voids present on the sputtering surface is 0.60 μm or less A sputtering target material is provided.

[0143] (Appendix 2) Preferably, The maximum diameter of voids present on the sputtering surface is 1.0 μm or less.

[0144] (Appendix 3) According to another aspect of the present disclosure, A sputtering target material comprising a sintered body of an oxide containing potassium, sodium, niobium, and oxygen, Volume resistivity at 25°C is 6.0 x 10 11 less than Ω·cm, Vickers hardness is 460 or more, and bending strength is 90 MPa or more A sputtering target material is provided.

[0145] (Appendix 4) According to yet another aspect of the present disclosure, A sputtering target material comprising a sintered body of an oxide containing potassium, sodium, niobium, and oxygen, Volume resistivity at 25°C is 6.0 x 10 11 Ω·cm or more, Vickers hardness is 250 or more, and bending strength is 90 MPa or more A sputtering target material is provided.

[0146] (Appendix 5) Preferably, The Vickers hardness after heat treatment in air at 900° C. for 5 hours remains at more than 50% of the Vickers hardness before the heat treatment.

[0147] (Appendix 6) Preferably, After heat treatment in air at 900° C. for 5 hours, the relative density is maintained at more than 95% of the relative density before the heat treatment.

[0148] (Appendix 7) Preferably, The dopant contains at least one element selected from the group consisting of Li, Mg, Ca, Sr, Ba, Bi, Sb, V, In, Ta, Mo, W, Cr, Ti, Zr, Hf, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Zn, Ag, Mn, Fe, Co, Ni, Al, Si, Ge, Sn, and Ga.

[0149] (Appendix 8) Preferably, The main surface is 4500 mm 2 It has an area of ​​more than 100m2.

[0150] (Appendix 9) According to yet another aspect of the present disclosure, A sputtering target material according to any one of appendices 1 to 8, a backing plate bonded to the sputtering target material; A sputtering target comprising: [Explanation of symbols]

[0151] 10 Target material 10s sputter surface

Claims

1. A sputtering target material comprising a sintered body of an oxide represented by the composition formula (K 1-x Na x )NbO 3 (0<x<1), (K+Na) / Nb is 0.90 or more and 1.25 or less, There are voids on the sputtered surface that are observed as openings of recessed spaces, the ratio of the total area of ​​the voids to the unit area of ​​the sputtering surface is 12.0% or less; The 50% area average diameter of the voids present on the sputtering surface is 0.60 μm or less. Sputtering target material.

2. The maximum diameter of the voids present on the sputtering surface is 1.0 μm or less. The sputtering target material according to claim 1 .

3. The dopant contains at least one element selected from the group consisting of Li, Mg, Ca, Sr, Ba, Bi, Sb, V, In, Ta, Mo, W, Cr, Ti, Zr, Hf, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Zn, Ag, Mn, Fe, Co, Ni, Al, Si, Ge, Sn, and Ga. The sputtering target material according to claim 1 or 2.

4. The main surface is 4500 mm ２ With an area of ​​more than The sputtering target material according to any one of claims 1 to 3.

5. The sputtering target material according to any one of claims 1 to 4, a backing plate bonded to the sputtering target material; A sputtering target comprising:

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