Method of depositing PZT thin film laminate and PZT thin film laminate

Abstract

To provide a method of depositing a PZT thin film laminate that can improve piezoelectric property, and to provide a PZT thin film laminate.SOLUTION: A method of depositing a PZT thin film laminate includes the steps of: providing a substrate having a platinum electrode layer that is provided on the substrate; and forming a PZT film using a film deposition source that is doped with lanthanum, nickel and niobium.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for producing a PZT thin film laminate using lead zirconate titanate (PZT), and to a PZT thin film laminate. [Background technology]

[0002] Thin films made of lead zirconate titanate (Pb(Zr,Ti)O3) (hereinafter referred to as PZT), which has excellent piezoelectric and ferroelectric properties, are used in memory elements such as non-volatile memory (FeRAM), as well as MEMS (Micro Electro Mechanical Systems) technology such as inkjet heads and acceleration sensors, taking advantage of their ferroelectric properties.

[0003] In recent years, it has been known that when forming a PZT film by sputtering, the piezoelectric constant and dielectric strength can be improved by forming a buffer layer made of LaNiO3 between the platinum electrode layer and the PZT thin film as an underlayer (see, for example, Patent Document 1).

[0004] In addition, a technology has been disclosed in which a PZT thin film layer is formed on a buffer layer made of LaNiO3 by sputtering at a temperature of less than 500°C using a PZT target doped with a metal containing nickel, thereby improving the dielectric strength of the PZT thin film. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2015 / 137198 [Patent Document 2] JP 2019-52326 A Summary of the Invention [Problem to be solved by the invention]

[0006] Thus, there is a demand for improved piezoelectric properties of PZT films. Therefore, an object of the present invention is to provide a method for forming a PZT film and a PZT thin film laminate that can further improve the piezoelectric properties. [Means for solving the problem]

[0007] To achieve the above objective, a method for manufacturing a PZT thin film laminate according to one aspect of the present invention includes providing a substrate having a platinum electrode layer disposed thereon. The method includes forming a PZT film using a film source doped with lanthanum, nickel, and niobium.

[0008] A buffer layer made of LaNiO3 may be provided on the platinum electrode layer.

[0009] The buffer layer may have a thickness of 5 nm or more and 200 nm or less.

[0010] the lanthanum content is 0.5 atomic % or more and 5 atomic % or less with respect to 100 atomic % of lead zirconate titanate having a stoichiometric composition, the content of nickel is 0.5 atomic % or more and 5 atomic % or less relative to 100 atomic % of lead zirconate titanate having a stoichiometric composition; The content of the niobium may be 2 atomic % or more and 20 atomic % or less relative to 100 atomic % of the lead zirconate titanate.

[0011] the lanthanum content is 3 atomic % relative to 100 atomic % of the lead zirconate titanate; the content of said nickel is 3 atomic % relative to 100 atomic % of said lead zirconate titanate, The content of the niobium may be 6 atomic % relative to 100 atomic % of the lead zirconate titanate.

[0012] In order to achieve the above object, a PZT thin film laminate according to one embodiment of the present invention includes a platinum electrode layer provided on a substrate, and a PZT film containing predetermined amounts of lanthanum, nickel, and niobium provided on the platinum electrode layer. Effect of the Invention

[0013] According to the present invention, when forming a PZT thin film layer, a film formation source doped with a metal containing lanthanum, nickel, and niobium is used, thereby making it possible to improve the piezoelectric properties of the PZT film. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view showing an example of the configuration of a PZT thin film laminate according to an embodiment of the present invention. [Diagram 2] 13 shows the experimental results showing the relationship between the piezoelectric constant and the type of metal doped into the PZT thin film laminate and the thickness of the buffer layer. [Diagram 3] FIG. 11 is a diagram showing the relationship between the mean failure life of a PZT thin film laminate and the type of metal doped into the PZT thin film laminate. [Figure 4] 13 shows the experimental results showing the relationship between the piezoelectric constant and the film formation temperature depending on the type of metal doped into the PZT thin film laminate. [Diagram 5] 1 shows experimental results of X-ray analysis of a PZT thin film laminate, where (A) shows the experimental result of Comparative Example 2 and (B) shows the experimental result of Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] [PZT thin film laminate] FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a PZT thin film laminate 100 according to an embodiment of the present invention.

[0017] The PZT thin film laminate 100 is constructed by laminating a silicon oxide layer 2, an adhesion layer 3, a platinum layer 4, a buffer layer 5, and a PZT layer 6 in this order on a substrate 1.

[0018] The substrate 1 is typically a semiconductor substrate such as a Si substrate. Alternatively, a substrate made of other materials such as a glass substrate may be used. The thickness of the substrate 1 is not particularly limited and is, for example, 725 μm.

[0019] The silicon oxide layer 2 may be a natural oxide film (thermal oxide film) formed on the surface of the substrate 1, or may be a sputtered film or a vapor deposition film formed by a sputtering method, a CVD method, or the like on the surface of the substrate 1. The thickness of the silicon oxide layer 2 is not particularly limited and is, for example, 100 nm.

[0020] The adhesion layer 3 is intended to increase the adhesion between the silicon oxide layer 2 and the platinum layer 4, and is made of, for example, titanium oxide or titanium metal. The adhesion layer 3 is formed by, for example, a sputtering method. The thickness of the adhesion layer 3 is not particularly limited, and is, for example, 35 nm.

[0021] The platinum layer 4 is a conductive layer configured as a lower electrode, and is formed, for example, by a sputtering method on the adhesion layer 3. The thickness of the platinum layer 4 is not particularly limited, and is, for example, 100 nm.

[0022] The buffer layer 5 constitutes an underlayer for the PZT layer 6, and has a perovskite structure similar to the PZT layer 6. The buffer layer 5 is made of a material (LNO:LaNiO3) containing lanthanum (La), nickel (Ni), and oxygen (O). The buffer layer 5 is formed on the platinum layer 4 by, for example, a sputtering method. In this case, a LaNiO3 target is used as the sputtering target, and sputtering is performed by applying high-frequency power (for example, 13.56 MHz) in, for example, argon gas as a sputtering gas. The substrate temperature during sputtering is preferably set to a temperature lower than 400°C. For example, it is preferably set to a temperature between 300°C and 350°C.

[0023] The thickness of the buffer layer 5 is not particularly limited, and is, for example, 5 nm to 200 nm. By setting the thickness of the buffer layer 5 to 200 nm or less, a film having a perovskite single phase structure without a different phase such as a pyrochlore phase can be stably formed. Furthermore, by forming the buffer layer 5 to a thickness of 5 nm or more as an underlayer for the PZT layer 6, a PZT layer 6 with high crystallinity can be stably formed, and by forming the buffer layer 5 to a thickness of 10 nm or more, a PZT layer 6 with even higher crystallinity can be stably formed.

[0024] The PZT layer 6 is a PZT film having a perovskite structure. The PZT layer 6 is made of lead zirconate titanate (Pb 1.30 Zr 0.52 Ti 0.48 O3 (hereinafter also referred to as "PurePZT")) is formed by sputtering a PZT target doped with a predetermined amount of lanthanum (La), nickel (Ni), and niobium (Nb). The thickness of the PZT layer 6 is not particularly limited, and is, for example, 2 μm.

[0025] The doping amounts of the metals containing lanthanum and nickel in the PZT target are not particularly limited, but are preferably set to 0.5 atm% or more and 5 atm% or less relative to 100 atm% of PZT, and more preferably 3 atm% relative to 100 atm% of PZT.

[0026] Furthermore, the doping amount of the niobium-containing metal in the PZT target is not particularly limited, but is preferably set to 2 atm% or more and 20 atm% or less relative to 100 atm% PZT, more preferably 6 atm% or more and 20 atm% or less relative to 100 atm% PZT, and most preferably 6 atm% relative to 100 atm% PZT.

[0027] In this embodiment, PurePZT is doped with a predetermined amount of lanthanum, nickel, and niobium, but the combination is not limited to this. 2+ , Mn 3+ ) may be additionally doped.

[0028] As film formation conditions, for example, in argon gas which is a sputtering gas, high-frequency power (for example, 13.56 MHz) is applied to perform sputtering.

[0029] The substrate temperature during sputtering is preferably set to a temperature lower than 500°C. For example, it is preferably set to 425°C or higher and 485°C or lower.

[0030] Although not shown, the PZT thin film laminate 100 further has, as an upper electrode, a conductor layer formed on the PZT film 6. The upper electrode may be composed of a conductor layer similar to the lower electrode (platinum layer).

[0031] [Method for manufacturing PZT thin film laminate] Subsequently, a method for manufacturing the PZT thin film laminate 100 will be described.

[0032] [Formation of buffer layer made of LaNiO3] An evaluation substrate on which an SiO2 layer (silicon oxide layer 2), a TiO x layer (adhesion layer 3), and a platinum electrode layer (platinum layer 4) were formed in this order was used on the Si substrate.

[0033] Using this evaluation substrate, a buffer layer 5 made of a LaNiO3 layer with a film thickness of 100 nm was formed on the surface of the platinum layer 4 by the DC pulse sputtering method. In this case, a LaNiO3 target was used as the sputtering target, and argon gas was used as the sputtering gas with a pressure of 0.1 Pa. Also, the substrate temperature during sputtering was controlled to be 350°C.

[0034] [Formation of PZT thin film layer] The PZT layer 6 is formed by RF magnetron sputtering using a sputtering device (SME200E manufactured by ULVAC Co., Ltd.). As described above, the target material is a PZT target, which is a film formation source in which PurePZT is doped with a predetermined amount of lanthanum, nickel, and niobium (Nb). The PZT target is placed in a vacuum chamber (not shown). The formation of the PZT thin film layer is not limited to the sputtering method, and known film formation techniques such as vapor deposition, CVD, and sol-gel methods can also be used.

[0035] In the case of the above-mentioned deposition method, for example, in the vacuum deposition method, the PZT layer 6 can be formed by evaporating a deposition material, which is a film formation source doped with a predetermined amount of lanthanum, nickel, and niobium (Nb), onto PurePZT in a vacuum chamber.

[0036] In the case of the above-mentioned CVD method, for example, in the thermal CVD method, a film formation source in which PurePZT is doped with a predetermined amount of lanthanum, nickel, and niobium (Nb) and gasified is supplied into a chamber, and thermal energy is applied to form the PZT layer 6.

[0037] In the case of the above-mentioned sol-gel method, pure PZT is doped with a predetermined amount of lanthanum, nickel, and niobium (Nb), and the solution, which is a film formation source dissolved in a solvent, is applied to the surface of the buffer layer 5 by, for example, a spin coating method to form the PZT layer 6.

[0038] The substrate 1, on which the silicon oxide layer 2, adhesion layer 3, platinum layer 4, and buffer layer 5 are laminated in this order, is carried into a vacuum chamber maintained at a reduced pressure and placed on a stage facing the PZT target. Argon gas is introduced into the vacuum chamber, and the PZT target is sputtered under a predetermined pressure to form a PZT layer 6 on the buffer layer 5 of the substrate 1.

[0039] As the discharge method, a magnetron RF discharge method using high frequency power (for example, 13.56 MHz) is typically adopted. The deposition pressure is typically 0.5 Pa or less, and preferably 0.03 Pa or more and 0.5 Pa or less. The lower the deposition pressure, the more excellent the high temperature stability and dielectric strength voltage of the PZT film that can be formed.

[0040] The substrate temperature is preferably 500° C. or less, for example, 425° C. to 485° C. By keeping the substrate temperature at 500° C. or less, grain growth of PZT is suppressed, and the surface roughness of the PZT layer 6 can be reduced.

[0041] The stage supporting the substrate 1 in the vacuum chamber is typically connected to a floating potential. However, the stage may be configured to be capable of controlling the impedance between the stage and the ground potential. This makes it possible to arbitrarily adjust the potential of the substrate 1 during sputtering, and by controlling the reverse sputtering of the substrate surface by ions in the plasma, a PZT layer 6 with few internal defects can be formed.

[0042] The PZT layer 6 formed by sputtering a PZT target doped with 0.5 atomic % or more of lanthanum and nickel with respect to 100 atomic % pure PZT can stably form PZT crystals with a perovskite structure in which defects are suppressed because the lanthanum (La) suppresses the generation of oxygen ion vacancies and the nickel (Ni) suppresses the generation of lead ion vacancies. This can improve the dielectric strength and high temperature stability of the PZT layer 6.

[0043] Furthermore, the piezoelectric constant of the PZT layer 6 formed by sputtering a PZT target doped with niobium (Nb) can be improved compared to 100 atomic % pure PZT. If the amount of niobium (Nb) exceeds 20 atomic %, the crystal orientation may deteriorate. EXAMPLES

[0044] Examples of the present invention will now be described.

[0045] Example 1 A 35-nm-thick TiO x A layer (adhesion layer 3) and a platinum electrode layer (platinum layer 4) having a thickness of 100 nm were formed in this order.

[0046] Next, a buffer layer 5 made of a LaNiO3 layer having a thickness of 100 nm was formed on the surface of the platinum layer 4 by DC pulse sputtering. A LiNiO3 target was used as the sputtering target, and sputtering was performed in an argon gas atmosphere at 0.1 Pa. The substrate temperature at this time was set to 350°C.

[0047] Subsequently, a 2 μm-thick PZT thin film (PZT layer 6) was formed by RF magnetron sputtering on the surface of the buffer layer 5. A PZT target doped with 3 atomic % each of lanthanum and nickel and 6 atomic % of niobium (Nb) relative to 100 atomic % of pure PZT was used as the sputtering target, and the PZT target was sputtered in an argon gas atmosphere of 0.2 Pa. The substrate temperature was 485° C.

[0048] The evaluation results of the formed PZT layer 6 are shown below. FIG. 2 shows the experimental results showing the relationship between the piezoelectric constant and the type of metal doped in the PZT layer 6 and the thickness of the buffer layer 5. As shown in FIG. 2, the piezoelectric constant (-e 31 ) is 16.5C / m 2 It was.

[0049] FIG. 3 is a diagram showing the relationship between the mean time to failure of the PZT thin film laminate 100 and the type of metal doped in the PZT thin film laminate 100. As shown in FIG. 3, the high temperature stability of the PZT layer 6 formed in Example 1 was evaluated. The evaluation of high temperature stability refers to the evaluation of the time-dependent dielectric breakdown (TDDB) phenomenon in a low electric field, and the mean time to failure (MTTF) of the PZT film on which the upper electrode was formed was measured. The MTTF (unit: time (h)) was calculated using the Weibull distribution. The MTTF was defined as the time until dielectric breakdown occurred when a voltage of +40V was continuously applied to the PZT film in a high temperature environment of 85°C. Here, the dielectric breakdown of the PZT film was defined as detection of a leak current exceeding 1 μA in an upper electrode with a diameter of 500 μm. The measured values ​​were calculated from the results of more than 10 measurements using a Weibull distribution model. As a result, the MTTF of PZTA, which is the PZT thin film laminate of this example, is approximately 1 × 10 9 It was time.

[0050] Furthermore, FIG. 4 is a diagram showing the relationship between the piezoelectric constant and the film formation temperature. As shown in FIG. 4, when the film formation temperature exceeded 600° C. (particularly when it exceeded 700° C.), the piezoelectric constant decreased.

[0051] FIG. 5 shows the experimental results of X-ray analysis of the PZT thin film laminate 100, where (A) shows the experimental results of Comparative Example 2 and (B) shows the experimental results of Example 1.

[0052] As shown in FIG. 5(B), no growth of the pyrochlore phase was confirmed from the (001) / (100) orientation of PZTA, which is the PZT thin film laminate of this example.

[0053] Example 2 In this embodiment, the conditions are the same as those in the first embodiment, except that the thickness of the buffer layer 5 is 40 nm.

[0054] As shown in FIG. 2, the piezoelectric constant (-e 31) is 17.5C / m 2 It was.

[0055] Comparative Example 1 A PZT film was formed under the same conditions as in Example 1, except that pure PZT was used as the PZT target.

[0056] As shown in FIG. 2, the piezoelectric constant (-e 31 ) is 14.6C / m 2 It was.

[0057] As shown in FIG. 3, the MTTF of the PZT thin film laminate of this comparative example was approximately 2000 hours.

[0058] Comparative Example 2 A PZT film was formed under the same conditions as in Example 1, except that a target in which 100 atomic % pure PZT was doped with 3 atomic % each of lanthanum and nickel was used as the PZT target.

[0059] As shown in FIG. 2, the piezoelectric constant (-e 31 ) is 14.7C / m 2 It was.

[0060] As shown in FIG. 3, the MTTF of the PZT thin film laminate of this comparative example is approximately 2×10 6 It was time.

[0061] Furthermore, as shown in FIG. 5(A), no growth of the pyrochlore phase was confirmed from the (001) / (100) orientation of the PZT thin film laminate of this comparative example.

[0062] The compositions of the PZT targets and the evaluation results of the PZT layers 6 in Examples 1 and 2 and Comparative Examples 1 and 2 are summarized in Table 1.

[0063] [Table 1]

[0064] It was confirmed that Example 1 had a higher piezoelectric constant value than Comparative Examples 1 and 2. It was also confirmed that Example 1 had a significantly higher MTTF value in TDDB than Comparative Examples 1 and 2. This allows for a significant improvement in the piezoelectric constant value and the MTTF value (improvement in piezoelectric properties was confirmed).

[0065] According to Example 2, it was confirmed that the value of the piezoelectric constant was improved compared to Example 1. Furthermore, since the buffer layer 5 can be made thinner (production is possible with less material), productivity can be improved. Furthermore, since the buffer layer 5 can be made thinner, the entire PZT thin film laminate 100 can be made thinner, which allows for weight reduction and miniaturization.

[0066] In other words, the value of the piezoelectric constant can be improved significantly as the thickness of the buffer layer 5 is reduced. In addition, the value of the piezoelectric constant and TDDB can be improved by doping with La (lanthanum), Ni (nickel) and Nb (niobium).

[0067] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment, and various modifications can be made thereto.

[0068] For example, in the above embodiment, the doping amount of lanthanum and nickel with respect to 100 atomic % of PurePZT is set to 0.5 atomic % or more and 5 atomic % or less, but is not limited thereto, and lanthanum and nickel may be doped in an amount exceeding 5 atomic % as long as desired piezoelectric characteristics, dielectric strength voltage, and high temperature stability are obtained. Similarly, the doping amount of niobium is set to 2 atomic % or more and 20 atomic % or less, but is not limited thereto, and niobium may be doped in an amount exceeding 20 atomic % or less than 2 atomic % as long as desired piezoelectric characteristics, dielectric strength voltage, and high temperature stability are obtained. In the above embodiment, the PZT layer 6 is provided on the platinum layer 4 via the buffer layer 5, but is not limited thereto, and the PZT layer 6 may be provided on the platinum layer 4. Furthermore, in the above embodiment, the platinum layer 4 is provided on the silicon oxide layer 2 via the adhesion layer 3, but is not limited thereto, and the platinum layer 4 may be provided on the silicon oxide layer 2. [Explanation of symbols]

[0069] 1...Substrate 2. Silicon oxide layer 3...Adhesive layer 4…Platinum layer 5…Buffer layer 6…PZT layer 100...PZT thin film laminate

Claims

1. Prepare a substrate having a platinum electrode layer provided on the substrate, and form a PZT film using a film-forming source doped with lanthanum, nickel, and niobium. A method for manufacturing a PZT thin film laminate.

2. The method for manufacturing a PZT thin film laminate according to Claim 1, A buffer layer made of LaNiO provided on the platinum electrode layer ３ having A method for manufacturing a PZT thin film laminate.

3. The method for manufacturing a PZT thin film laminate according to Claim 2, wherein the thickness of the buffer layer is 5 nm or more and 200 nm or less. A method for manufacturing a PZT thin film laminate.

4. The method for manufacturing a PZT thin film laminate according to Claims 1 to 3, wherein the content of the lanthanum is 0.5 atomic % or more and 5 atomic % or less with respect to 100 atomic % of lead zirconate titanate having a stoichiometric composition, the content of the nickel is 0.5 atomic % or more and 5 atomic % or less with respect to 100 atomic % of lead zirconate titanate having a stoichiometric composition, and the content of the niobium is 2 atomic % or more and 20 atomic % or less with respect to 100 atomic % of the lead zirconate titanate. A method for manufacturing a PZT thin film laminate.

5. The method for manufacturing a PZT thin film laminate according to Claim 4, wherein the content of the lanthanum is 3 atomic % with respect to 100 atomic % of the lead zirconate titanate, the content of the nickel is 3 atomic % with respect to 100 atomic % of the lead zirconate titanate, and the content of the niobium is 6 atomic % with respect to 100 atomic % of the lead zirconate titanate. A method for manufacturing a PZT thin film laminate.

6. A PZT thin film laminate comprising a platinum electrode layer provided on a substrate and a PZT film containing a predetermined amount of lanthanum, nickel, and niobium provided on the platinum electrode layer. A PZT thin film laminate.

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