WO2020161997A1 - Nitride piezoelectric substance and mems device using same - Google Patents

Nitride piezoelectric substance and mems device using same Download PDF

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WO2020161997A1
WO2020161997A1 PCT/JP2019/046057 JP2019046057W WO2020161997A1 WO 2020161997 A1 WO2020161997 A1 WO 2020161997A1 JP 2019046057 W JP2019046057 W JP 2019046057W WO 2020161997 A1 WO2020161997 A1 WO 2020161997A1
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piezoelectric
piezoelectric body
constant
range
aluminum nitride
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French (fr)
Japanese (ja)
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浩志 山田
和也 江藤
平田 研二
雅人 上原
スリ アユ アンガライニ
秋山 守人
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国立研究開発法人産業技術総合研究所
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B81MICROSTRUCTURAL TECHNOLOGY
    • B81BMICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B3/00Devices comprising flexible or deformable elements, e.g. comprising elastic tongues or membranes
    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10NELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00Piezoelectric or electrostrictive devices
    • H10N30/20Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10NELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00Piezoelectric or electrostrictive devices
    • H10N30/30Piezoelectric or electrostrictive devices with mechanical input and electrical output, e.g. functioning as generators or sensors
    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10NELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00Piezoelectric or electrostrictive devices
    • H10N30/80Constructional details
    • H10N30/85Piezoelectric or electrostrictive active materials
    • H10N30/853Ceramic compositions

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  • the present invention relates to a zirconium-doped aluminum nitride piezoelectric body and a MEMS device using the same.
  • FBAR Biharmonic Resonator
  • the FBAR filter is a filter using a resonator that uses a thickness extensional vibration mode of a thin film exhibiting piezoelectric response, and has a characteristic that resonance in the gigahertz band is possible. Since the FBAR filter having such characteristics has low loss and can operate in a wide band, it is expected to contribute to further high frequency compatibility, downsizing and power saving of portable devices.
  • Examples of the piezoelectric material of the piezoelectric thin film used for such FBAR include scandium-added aluminum nitride (see Patent Document 1), inexpensive aluminum nitride and niobium-added aluminum nitride (see Non-Patent Document 1), and the like. Are listed.
  • aluminum nitride to which scandium is added has a high piezoelectric constant and is expected to be used in the next generation high frequency filter.
  • scandium-added aluminum nitride is expected to be used for various MEMS devices such as a pressure sensor, an acceleration sensor, a physical sensor such as a gyro sensor, and an actuator.
  • nitride piezoelectric body having a piezoelectric constant d 33 higher than that of aluminum nitride added with the same concentration (mol %) of scandium, and a MEMS device using the same. ..
  • the inventor of the present invention found that when zirconium (Zr) was added (doped) to aluminum nitride (AlN), aluminum nitride containing scandium (Sc) at the same concentration was added. It was discovered that the lattice constant ratio c/a was smaller than that of The inventor of the present invention has found that aluminum nitride added with zirconium has a higher piezoelectric constant d 33 than aluminum nitride added with the same concentration of scandium.
  • a first aspect of the present invention for solving the above-mentioned problems resides in a piezoelectric body characterized by being represented by a chemical formula Al 1-X Zr X N, where X is in a range of more than 0 and less than 0.4. ..
  • the first aspect it is possible to provide a piezoelectric body having a piezoelectric constant d 33 higher than that of aluminum nitride added with the same concentration of scandium.
  • a second aspect of the present invention is the piezoelectric body according to the first aspect, wherein X is in the range of more than 0 and not more than 0.375.
  • a third aspect of the present invention is the piezoelectric body according to the first aspect, wherein X is in the range of more than 0 and less than 0.3.
  • the mixed enthalpy of the wurtzite type crystal structure is lower than the mixed enthalpy of the rock salt type crystal structure, so that the crystal structure is more stable.
  • a piezoelectric body can be provided.
  • a fourth aspect of the present invention is the piezoelectric body according to the first aspect, characterized in that the lattice constant ratio c/a is in the range of 1.25 or more and 1.60 or less.
  • a fifth aspect of the present invention is the piezoelectric body according to the second aspect, characterized in that the lattice constant ratio c/a is in the range of 1.29 or more and 1.60 or less.
  • a sixth aspect of the present invention is the piezoelectric body according to the third aspect, characterized in that the lattice constant ratio c/a is in the range of 1.42 or more and 1.60 or less.
  • a seventh aspect of the present invention is a MEMS device using the piezoelectric body according to any one of the first to sixth aspects.
  • the “MEMS device” is not particularly limited as long as it is a microelectromechanical system, and examples thereof include physical sensors such as pressure sensors, acceleration sensors, gyro sensors, actuators, microphones, fingerprint authentication sensors, vibration power generators, and the like. Can be mentioned.
  • the seventh aspect has low loss and can operate in a wide band. Therefore, by using this piezoelectric material, it is possible to provide a MEMS device that is compatible with high frequencies, has a small size, and has reduced power consumption. In particular, when the MEMS device is a sensor, it is possible to provide a sensor that has low loss and can operate in a wide band as compared with a conventional sensor.
  • FIG. 1 is a diagram showing an example of a calculation model of Al 1-X Zr X N used in the simulation according to the first embodiment.
  • FIG. 2 is a graph showing the relationship between the concentration X of Zr and Sc and the obtained lattice constants a and c and the lattice constant ratio c/a.
  • FIG. 3 is a graph showing the relationship between the concentration X of Zr and Sc and the piezoelectric stress constant e 33 .
  • FIG. 4 is a graph showing the relationship between the concentration X of Zr and Sc and the elastic constant C 33 .
  • FIG. 5 is a graph showing the relationship between the concentration X of Zr and Sc and the obtained piezoelectric constant d 33 of each piezoelectric body.
  • FIG. 1 is a diagram showing an example of a calculation model of Al 1-X Zr X N used in the simulation according to the first embodiment.
  • FIG. 2 is a graph showing the relationship between the concentration X of Zr and Sc and the obtained lattice
  • FIG. 6 is a graph showing the relationship between the concentration X of Zr and the mixed enthalpy in the case where the crystal structure of Al 1-X Zr X N is wurtzite type and the mixed enthalpy in the case of rock salt type.
  • VASP Vehicle Ab initio Simulation Package
  • first-principles calculation is a general term for electronic state calculation methods that do not use fitting parameters and the like, and the electronic state can be calculated only by the atomic number and coordinates of each atom constituting a unit cell or molecule. It is a technique that can be done.
  • a unit cell composed of two aluminum atoms and two nitrogen atoms is quadrupled in the a-axis and b-axis directions and doubled in the c-axis direction to obtain 64 aluminum atoms and 64 aluminum atoms.
  • Non-doped AlN having a wurtzite crystal structure of a supercell composed of nitrogen atoms was used for the simulation. Then, for AlN having this wurtzite crystal structure, the atomic coordinates, the cell volume, and the cell shape were all moved simultaneously to perform the first-principles calculation, and the electronic state of non-doped AlN having a stable structure was calculated.
  • Table 1 shows the lattice constant in the a-axis direction, the lattice constant in the c-axis direction, and the lattice constant in the a-axis direction and the lattice constant in the c-axis direction calculated from the electronic state of AlN having a stable structure obtained by the first principle calculation. Ratio (c/a) (calculated value). Table 1 also shows experimental values obtained by actually forming a non-doped AlN film by a sputtering method and measuring the AlN film by an X-ray diffraction method.
  • FIG. 1 is a diagram showing an example of a calculation model of Al 1-X Zr X N used in the simulation according to the present embodiment.
  • the calculation model of this doped AlN has a wurtzite crystal structure in which 16 Al atoms are replaced with Zr atoms in a unit cell composed of 64 Al atoms and 64 N atoms.
  • the concentration X of Zr atoms used in this simulation becomes 0.25 (25 at.%).
  • the piezoelectric body of Al 1-X Zr X N can be actually manufactured by the manufacturing method described in Patent Document 1 described above.
  • the electronic state of the stable structure can be calculated by the first principle calculation, as in the case of non-doped AlN. Then, the lattice constant in the a-axis direction, the lattice constant in the c-axis direction, and the lattice constant ratio c/a can be calculated from this electronic state.
  • the position in the crystal structure of the added Zr atom was the SQS model (Special quasi-random structure model) in which the Zr atom was randomly arranged at the position of the Al atom.
  • the simulation results greatly vary depending on the arrangement of Zr atoms in the crystal structure. Therefore, by using the SQS model, artificial placement of Zr can be eliminated, so the simulation result of this embodiment is close to the actual crystal structure and highly reliable.
  • FIG. 2 shows the relationship between the concentration X of Zr and Sc, the obtained lattice constants a and c, and the obtained lattice constant ratio c/a.
  • the piezoelectric stress constant e 33 and the elastic constant C 33 of Al 1-X Zr X N can be calculated from the minute change in the total energy at that time. That is, the piezoelectric stress constant e 33 and the elastic constant C 33 of Al 1-X Zr X N can be calculated using the first principle calculation. Similarly, the piezoelectric stress constant e 33 and the elastic constant C 33 of Al 1-X Sc X N can be calculated respectively.
  • the square mark is the calculation result of AlN doped with Zr
  • the circle mark is the calculation result of AlN doped with Sc.
  • FIG. 5 shows the relationship between the concentration X of Zr and Sc and the obtained piezoelectric constant d 33 of each piezoelectric body.
  • the square mark is the calculation result of AlN doped with Zr
  • the circle mark is the calculation result of AlN doped with Sc.
  • Al 1-X Zr X N has the same concentration of Sc added aluminum nitride (Al 1-X Sc).
  • X N) has a higher piezoelectric constant d 33 , and when X becomes 0.4 or more, the piezoelectric constant d 33 sharply decreases and becomes a value lower than that of aluminum nitride to which Sc of the same concentration is added. I found out.
  • the lattice constant ratio c/a is preferably in the range of 1.25 or more and 1.60 or less.
  • the piezoelectric constant d 33 of Al 1-X Zr X N has the highest value when X is 0.375, and becomes smaller when X exceeds 0.375. Therefore, X is larger than 0 and is 0.375 or less. Is preferred. In this X range, the lattice constant ratio c/a is preferably in the range of 1.29 or more and 1.60 or less.
  • FIG. 6 shows the relationship between the concentration X of Zr and the mixing enthalpy in the case where the crystal structure of Al 1-X Zr X N is wurtzite type and the mixing enthalpy in the case of rock salt type.
  • the rhombus mark indicates the mixed enthalpy in the case of wurtzite type
  • the square mark indicates the mixed enthalpy of rock salt type.
  • the range of X is preferably larger than 0 and smaller than 0.3.
  • Al 1-X Zr X N in this range becomes a piezoelectric body having a more stable crystal structure.
  • the lattice constant ratio c/a is preferably 1.42 or more and 1.60 or less.
  • the piezoelectric material having the Zr concentration X in the above range and having a high piezoelectric constant d 33 has low loss and can operate in a wide band. Therefore, by using the piezoelectric body having the Zr concentration X in the above-described range, it is possible to provide a MEMS device that can contribute to further high frequency compatibility, size reduction, and power saving of portable equipment.
  • Zr is present in a large amount on the surface of the earth or near the surface of the earth and is widely distributed.

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  • Computer Hardware Design (AREA)
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Abstract

[Problem] The purpose of the present invention is to provide: a nitride piezoelectric substance having a piezoelectric constant d33 higher than that of aluminum nitride having added thereto scandium at the same concentration; and a MEMS device using said nitride piezoelectric substance. [Solution] This nitride piezoelectric substance is represented by chemical formula Al1-XZrXN, wherein X is in a range of more than 0 but less than 0.4.

Description

窒化物圧電体およびそれを用いたMEMSデバイスNitride piezoelectric body and MEMS device using the same
本発明は、ジルコニウムを添加した窒化アルミニウムの圧電体およびそれを用いたMEMSデバイスに関するものである。 TECHNICAL FIELD The present invention relates to a zirconium-doped aluminum nitride piezoelectric body and a MEMS device using the same.
圧電現象を利用するデバイスは、幅広い分野において用いられており、小型化および省電力化が強く求められている携帯電話機などの携帯用機器において、その使用が拡大している。その一例として、薄膜バルク音響波共振子(Film Bulk Acoustic Resonator;FBAR)を用いたFBARフィルタがある。 Devices utilizing the piezoelectric phenomenon are used in a wide range of fields, and their use is expanding in portable devices such as mobile phones, which are strongly required to be downsized and to save power. An example thereof is an FBAR filter using a thin film bulk acoustic wave resonator (Film Bulk Acoustic Resonator; FBAR).
FBARフィルタは、圧電応答性を示す薄膜の厚み縦振動モードを用いた共振子によるフィルタであり、ギガヘルツ帯域における共振が可能であるという特性を有する。このような特性を有するFBARフィルタは、低損失であり、かつ広帯域で動作可能であることから、携帯用機器のさらなる高周波対応化、小型化および省電力化に寄与することが期待されている。 The FBAR filter is a filter using a resonator that uses a thickness extensional vibration mode of a thin film exhibiting piezoelectric response, and has a characteristic that resonance in the gigahertz band is possible. Since the FBAR filter having such characteristics has low loss and can operate in a wide band, it is expected to contribute to further high frequency compatibility, downsizing and power saving of portable devices.
このようなFBARに用いられる圧電体薄膜の圧電体材料としては、例えばスカンジウムを添加した窒化アルミニウム(特許文献1参照)や、安価なマグネシウムとニオブを添加した窒化アルミニウム(非特許文献1参照)等が挙げられる。特にスカンジウムを添加した窒化アルミニウムは、高い圧電定数を有し、次世代の高周波フィルタへの利用が期待されている。また、スカンジウムを添加した窒化アルミニウムは、圧力センサや加速度センサ、ジャイロセンサなどの物理センサ、アクチュエータ等の様々なMEMSデバイスへの利用が期待されている。 Examples of the piezoelectric material of the piezoelectric thin film used for such FBAR include scandium-added aluminum nitride (see Patent Document 1), inexpensive aluminum nitride and niobium-added aluminum nitride (see Non-Patent Document 1), and the like. Are listed. In particular, aluminum nitride to which scandium is added has a high piezoelectric constant and is expected to be used in the next generation high frequency filter. In addition, scandium-added aluminum nitride is expected to be used for various MEMS devices such as a pressure sensor, an acceleration sensor, a physical sensor such as a gyro sensor, and an actuator.
特開2009-10926号公報Japanese Patent Laid-Open No. 2009-10926
しかしながら、スカンジウム(Sc)は高価な希土類元素であり、スカンジウムを添加した窒化アルミニウム(AlN)で構成された圧電体は他の物質で構成された圧電体と比較して、製造コストが高額になってしまうという問題点があった。また、添加する元素の濃度(モル%)が等しい場合において、スカンジウムを添加した窒化アルミニウムよりも高い圧電定数d33を有する圧電体が存在していなかった。 However, scandium (Sc) is an expensive rare earth element, and a piezoelectric body made of scandium-added aluminum nitride (AlN) has a higher manufacturing cost than piezoelectric bodies made of other substances. There was a problem that it would end up. In addition, when the concentrations (mol%) of the added elements were equal, there was no piezoelectric body having a piezoelectric constant d 33 higher than that of aluminum nitride to which scandium was added.
さらに、窒化アルミニウムに添加する元素の種類を増やすと、圧電体の組成制御や製造時のプロセス管理が煩雑になるという問題点があった。 Further, if the number of kinds of elements added to aluminum nitride is increased, there is a problem that composition control of the piezoelectric body and process control during manufacturing become complicated.
本発明は上述した事情に鑑み、同濃度(モル%)のスカンジウムを添加した窒化アルミニウムよりも高い圧電定数d33を有する窒化物圧電体およびそれを用いたMEMSデバイスを提供することを目的とする。 In view of the above-mentioned circumstances, it is an object of the present invention to provide a nitride piezoelectric body having a piezoelectric constant d 33 higher than that of aluminum nitride added with the same concentration (mol %) of scandium, and a MEMS device using the same. ..
本発明の発明者は、上述した問題点に関して鋭意研究を続けた結果、窒化アルミニウム(AlN)にジルコニウム(Zr)を添加する(ドープさせる)と、同濃度のスカンジウム(Sc)を添加した窒化アルミニウムと比較して、格子定数比c/aが小さくなることを発見した。そして、本発明の発明者は、ジルコニウムを添加した窒化アルミニウムは、同濃度のスカンジウムを添加した窒化アルミニウムよりも高い圧電定数d33を有することを見出し、以下のような画期的な圧電体を発明した。 The inventor of the present invention, as a result of continuing earnest research on the above-mentioned problems, found that when zirconium (Zr) was added (doped) to aluminum nitride (AlN), aluminum nitride containing scandium (Sc) at the same concentration was added. It was discovered that the lattice constant ratio c/a was smaller than that of The inventor of the present invention has found that aluminum nitride added with zirconium has a higher piezoelectric constant d 33 than aluminum nitride added with the same concentration of scandium. Invented
上記課題を解決するための本発明の第1の態様は、化学式Al1-XZrNで表され、Xは0より大きく0.4より小さい範囲にあることを特徴とする圧電体にある。 A first aspect of the present invention for solving the above-mentioned problems resides in a piezoelectric body characterized by being represented by a chemical formula Al 1-X Zr X N, where X is in a range of more than 0 and less than 0.4. ..
かかる第1の態様では、同濃度のスカンジウムを添加した窒化アルミニウムよりも高い圧電定数d33を有する圧電体を提供することができる。 In the first aspect, it is possible to provide a piezoelectric body having a piezoelectric constant d 33 higher than that of aluminum nitride added with the same concentration of scandium.
本発明の第2の態様は、Xは0より大きく0.375以下の範囲にあることを特徴とする第1の態様に記載の圧電体にある。 A second aspect of the present invention is the piezoelectric body according to the first aspect, wherein X is in the range of more than 0 and not more than 0.375.
かかる第2の態様では、同濃度のスカンジウムを添加した窒化アルミニウムよりも高い圧電定数d33を有する圧電体を提供することができる。 In the second aspect, it is possible to provide a piezoelectric body having a piezoelectric constant d 33 higher than that of aluminum nitride added with the same concentration of scandium.
本発明の第3の態様は、Xは0より大きく0.3より小さい範囲にあることを特徴とする第1の態様に記載の圧電体にある。 A third aspect of the present invention is the piezoelectric body according to the first aspect, wherein X is in the range of more than 0 and less than 0.3.
かかる第3の態様では、Xが0.3より小さい範囲では、ウルツ鉱型結晶構造の混合エンタルピーの方が、岩塩型結晶構造の混合エンタルピーよりも低い数値となるので、結晶構造がより安定した圧電体を提供することができる。 In the third aspect, in the range where X is less than 0.3, the mixed enthalpy of the wurtzite type crystal structure is lower than the mixed enthalpy of the rock salt type crystal structure, so that the crystal structure is more stable. A piezoelectric body can be provided.
本発明の第4の態様は、格子定数比c/aが1.25以上で1.60以下の範囲にあることを特徴とする第1の態様に記載の圧電体にある。 A fourth aspect of the present invention is the piezoelectric body according to the first aspect, characterized in that the lattice constant ratio c/a is in the range of 1.25 or more and 1.60 or less.
かかる第4の態様では、同濃度のスカンジウムを添加した窒化アルミニウムよりも、より高い圧電定数d33を有する圧電体を提供することができる。 In the fourth aspect, it is possible to provide a piezoelectric body having a higher piezoelectric constant d 33 than that of aluminum nitride added with scandium of the same concentration.
本発明の第5の態様は、格子定数比c/aが1.29以上で1.60以下の範囲にあることを特徴とする第2の態様に記載の圧電体にある。 A fifth aspect of the present invention is the piezoelectric body according to the second aspect, characterized in that the lattice constant ratio c/a is in the range of 1.29 or more and 1.60 or less.
かかる第5の態様では、同濃度のスカンジウムを添加した窒化アルミニウムよりも、さらに高い圧電定数d33を有する圧電体を提供することができる。 In the fifth aspect, it is possible to provide a piezoelectric body having a higher piezoelectric constant d 33 than that of aluminum nitride to which scandium having the same concentration is added.
本発明の第6の態様は、格子定数比c/aが1.42以上で1.60以下の範囲にあることを特徴とする第3の態様に記載の圧電体にある。 A sixth aspect of the present invention is the piezoelectric body according to the third aspect, characterized in that the lattice constant ratio c/a is in the range of 1.42 or more and 1.60 or less.
かかる第6の態様では、同濃度のスカンジウムを添加した窒化アルミニウムよりも、特に高い圧電定数d33を有する圧電体を提供することができる。 In the sixth aspect, it is possible to provide a piezoelectric body having a piezoelectric constant d 33 which is particularly higher than that of aluminum nitride to which scandium of the same concentration is added.
本発明の第7の態様は、第1~第6の態様の何れか1つに記載の圧電体を用いたMEMSデバイスにある。 A seventh aspect of the present invention is a MEMS device using the piezoelectric body according to any one of the first to sixth aspects.
ここで、「MEMSデバイス」とは、微小電気機械システムであれば特に限定されず、例えば、圧力センサ、加速度センサ、ジャイロセンサなどの物理センサやアクチュエータ、マイクロフォン、指紋認証センサ、振動発電機等が挙げられる。 Here, the “MEMS device” is not particularly limited as long as it is a microelectromechanical system, and examples thereof include physical sensors such as pressure sensors, acceleration sensors, gyro sensors, actuators, microphones, fingerprint authentication sensors, vibration power generators, and the like. Can be mentioned.
かかる第7の態様は、低損失であり、かつ広帯域で動作可能である。したがって、この圧電体を用いることにより、高周波対応化、小型化および省電力化されたMEMSデバイスを提供することができる。特にMEMSデバイスがセンサの場合には、従来のセンサと比較して、低損失であり、かつ広帯域で動作可能なものを提供することができる。 The seventh aspect has low loss and can operate in a wide band. Therefore, by using this piezoelectric material, it is possible to provide a MEMS device that is compatible with high frequencies, has a small size, and has reduced power consumption. In particular, when the MEMS device is a sensor, it is possible to provide a sensor that has low loss and can operate in a wide band as compared with a conventional sensor.
図1は実施形態1に係るシミュレーションに用いたAl1-XZrNの計算モデルの一例を示す図である。FIG. 1 is a diagram showing an example of a calculation model of Al 1-X Zr X N used in the simulation according to the first embodiment. 図2はZrおよびScの濃度Xと、得られた各格子定数a、cおよび各格子定数比c/aとの関係を示すグラフである。FIG. 2 is a graph showing the relationship between the concentration X of Zr and Sc and the obtained lattice constants a and c and the lattice constant ratio c/a. 図3はZrおよびScの濃度Xと、圧電応力定数e33との関係を示すグラフである。FIG. 3 is a graph showing the relationship between the concentration X of Zr and Sc and the piezoelectric stress constant e 33 . 図4はZrおよびScの濃度Xと、弾性定数C33との関係を示すグラフである。FIG. 4 is a graph showing the relationship between the concentration X of Zr and Sc and the elastic constant C 33 . 図5はZrおよびScの濃度Xと、得られた各圧電体の圧電定数d33との関係を示すグラフである。FIG. 5 is a graph showing the relationship between the concentration X of Zr and Sc and the obtained piezoelectric constant d 33 of each piezoelectric body. 図6はZrの濃度Xと、Al1-XZrNの結晶構造がウルツ鉱型の場合の混合エンタルピーおよび岩塩型の場合の混合エンタルピーとの関係を示すグラフである。FIG. 6 is a graph showing the relationship between the concentration X of Zr and the mixed enthalpy in the case where the crystal structure of Al 1-X Zr X N is wurtzite type and the mixed enthalpy in the case of rock salt type.
以下に添付図面を参照して、本発明に係る圧電体の実施形態を説明する。なお、本発明は、以下の実施形態に限定されるものではない。
(実施形態1)
Embodiments of a piezoelectric body according to the present invention will be described below with reference to the accompanying drawings. The present invention is not limited to the embodiments below.
(Embodiment 1)
まず、本発明の発明者が、アルミニウム(Al)と窒素(N)のみからなる窒化アルミニウム(ノンドープAlN)に対して行ったシミュレーションについて説明する。シミュレーションには、第1原理計算(first-principle calculation)と呼ばれる計算方法を採用しているVASP(Vienna Ab initio Simulation Package)というソフトウェアを用いた。ここで、第1原理計算とは、フィッティングパラメータ等を使用しない電子状態計算方法の総称であり、単位格子あるいは分子等を構成する各原子の原子番号と座標だけで、電子状態を計算することができる手法である。 First, a simulation performed by the inventor of the present invention on aluminum nitride (non-doped AlN) composed only of aluminum (Al) and nitrogen (N) will be described. For the simulation, software called VASP (Vienna Ab initio Simulation Package), which employs a calculation method called first-principle calculation, was used. Here, the first-principles calculation is a general term for electronic state calculation methods that do not use fitting parameters and the like, and the electronic state can be calculated only by the atomic number and coordinates of each atom constituting a unit cell or molecule. It is a technique that can be done.
本実施形態のシミュレーションでは、2個のアルミニウム原子と2個の窒素原子とからなる単位格子を、a軸、b軸方向に4倍、及びc軸方向に2倍した64個のアルミニウム原子と64個の窒素原子とからなるスーパーセルのウルツ鉱型結晶構造のノンドープAlNをシミュレーションに用いた。そして、このウルツ鉱型結晶構造のAlNに対して、原子座標、セル体積およびセル形状の全てを同時に動かして第1原理計算を行い、安定構造のノンドープAlNの電子状態を計算した。 In the simulation of this embodiment, a unit cell composed of two aluminum atoms and two nitrogen atoms is quadrupled in the a-axis and b-axis directions and doubled in the c-axis direction to obtain 64 aluminum atoms and 64 aluminum atoms. Non-doped AlN having a wurtzite crystal structure of a supercell composed of nitrogen atoms was used for the simulation. Then, for AlN having this wurtzite crystal structure, the atomic coordinates, the cell volume, and the cell shape were all moved simultaneously to perform the first-principles calculation, and the electronic state of non-doped AlN having a stable structure was calculated.
表1は、第1原理計算で求めた安定構造のAlNの電子状態から算出したa軸方向の格子定数、c軸方向の格子定数およびa軸方向の格子定数とc軸方向の格子定数との比(c/a)(計算値)である。また、実際にスパッタ法を用いてノンドープAlN膜を成膜して、このAlN膜に対してX線回折法を用いて測定した実験値についても表1に示す。 Table 1 shows the lattice constant in the a-axis direction, the lattice constant in the c-axis direction, and the lattice constant in the a-axis direction and the lattice constant in the c-axis direction calculated from the electronic state of AlN having a stable structure obtained by the first principle calculation. Ratio (c/a) (calculated value). Table 1 also shows experimental values obtained by actually forming a non-doped AlN film by a sputtering method and measuring the AlN film by an X-ray diffraction method.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
この表に示すように、各計算値は、実験値とほぼ同じ数値となり、これらの相対誤差は1%以内に収まっている。この結果より、本実施形態におけるシミュレーションは、十分に信頼できることが分かった。 As shown in this table, each calculated value is almost the same as the experimental value, and the relative error between them is within 1%. From this result, it was found that the simulation in this embodiment is sufficiently reliable.
次に、窒化アルミニウム(AlN)に、ジルコニウム(Zr)をドープ(添加)させたAl1-XZrN(1<X<0.5)に対して行ったシミュレーションについて説明する。図1は、本実施形態に係るシミュレーションに用いたAl1-XZrNの計算モデルの一例を示す図である。 Next, a simulation performed on Al 1-X Zr X N (1<X<0.5) in which aluminum nitride (AlN) is doped (added) with zirconium (Zr) will be described. FIG. 1 is a diagram showing an example of a calculation model of Al 1-X Zr X N used in the simulation according to the present embodiment.
この図に示すように、このドープAlNの計算モデルは、64個のAl原子と64個のN原子とからなる単位格子のうち、16個のAl原子をZr原子に置き換えたウルツ鉱型結晶構造となっている。ここで、Al原子数およびZr原子数の総数を1としたときの、Zr原子の個数(濃度)をXとする。すると、このシミュレーションに用いたZr原子の濃度Xは、0.25(25at.%)となる。なお、Al1-XZrNの圧電体は、上述した特許文献1に記載された製造方法で実際に作製することができる。 As shown in this figure, the calculation model of this doped AlN has a wurtzite crystal structure in which 16 Al atoms are replaced with Zr atoms in a unit cell composed of 64 Al atoms and 64 N atoms. Has become. Here, when the total number of Al atoms and Zr atoms is 1, the number (concentration) of Zr atoms is X. Then, the concentration X of Zr atoms used in this simulation becomes 0.25 (25 at.%). The piezoelectric body of Al 1-X Zr X N can be actually manufactured by the manufacturing method described in Patent Document 1 described above.
このAl1-XZrNについても、ノンドープAlNの場合と同様に、第1原理計算により安定構造の電子状態を計算することができる。そして、この電子状態からa軸方向の格子定数、c軸方向の格子定数および格子定数比c/aを算出することができる。 Also for this Al 1-X Zr X N, the electronic state of the stable structure can be calculated by the first principle calculation, as in the case of non-doped AlN. Then, the lattice constant in the a-axis direction, the lattice constant in the c-axis direction, and the lattice constant ratio c/a can be calculated from this electronic state.
なお、このシミュレーションにおいて、添加するZr原子の結晶構造中の位置は、Zr原子をAl原子の位置にランダムに配置するSQSモデル(Special quasi-random structure model)を用いた。結晶構造中のZr原子の配置により、シミュレーション結果は大きく変動する。そこで、SQSモデルを用いることによって、人為的なZrの配置を排除できるので、本実施形態のシミュレーション結果は、現実の結晶構造に近く、信頼性の高いものとなる。 In addition, in this simulation, the position in the crystal structure of the added Zr atom was the SQS model (Special quasi-random structure model) in which the Zr atom was randomly arranged at the position of the Al atom. The simulation results greatly vary depending on the arrangement of Zr atoms in the crystal structure. Therefore, by using the SQS model, artificial placement of Zr can be eliminated, so the simulation result of this embodiment is close to the actual crystal structure and highly reliable.
図2に、ZrおよびScの濃度Xと、得られた各格子定数a、cとの関係と、得られた各格子定数比c/aとの関係を示す。 FIG. 2 shows the relationship between the concentration X of Zr and Sc, the obtained lattice constants a and c, and the obtained lattice constant ratio c/a.
この図から、ZrをドープさせたAlNの格子定数比c/aは、同濃度のScをドープさせたAlNのものよりも小さくなることが分かった。したがって、ZrをドープさせたAlNは、同濃度のScをドープさせたAlNよりも高い圧電定数d33を有することが分かった。 From this figure, it was found that the lattice constant ratio c/a of AlN doped with Zr was smaller than that of AlN doped with Sc of the same concentration. Therefore, it was found that Zr-doped AlN has a higher piezoelectric constant d 33 than AlN doped with the same concentration of Sc.
次に、Al1-XZrNの結晶格子に微小な歪みを強制的に加える。すると、その際の全エネルギーの微小変化から、Al1-XZrNの圧電応力定数e33および弾性定数C33をそれぞれ計算することができる。すなわち、第1原理計算を用いて、Al1-XZrNの圧電応力定数e33および弾性定数C33をそれぞれ計算することができる。また、同様にして、Al1-XScNの圧電応力定数e33および弾性定数C33もそれぞれ計算することができる。それらの結果を図3および図4に示す。ここで、四角マークはZrをドープさせたAlNの計算結果であり、丸マークはScをドープさせたAlNの計算結果である。 Next, a minute strain is forcibly applied to the crystal lattice of Al 1-X Zr X N. Then, the piezoelectric stress constant e 33 and the elastic constant C 33 of Al 1-X Zr X N can be calculated from the minute change in the total energy at that time. That is, the piezoelectric stress constant e 33 and the elastic constant C 33 of Al 1-X Zr X N can be calculated using the first principle calculation. Similarly, the piezoelectric stress constant e 33 and the elastic constant C 33 of Al 1-X Sc X N can be calculated respectively. The results are shown in FIGS. 3 and 4. Here, the square mark is the calculation result of AlN doped with Zr, and the circle mark is the calculation result of AlN doped with Sc.
さらに、c軸方向の圧電定数d33と、圧電応力定数e33および弾性定数C33との間には、下記の数1の関係式が成立する。そこで、この関係式に、上記で算出されたAl1-XZrNの圧電応力定数e33および弾性定数C33をそれぞれ代入することによって、Al1-XZrNの圧電定数d33を算出することができる。 Furthermore, the following relational expression of Formula 1 is established between the piezoelectric constant d 33 in the c-axis direction, the piezoelectric stress constant e 33, and the elastic constant C 33 . Therefore, by substituting the piezoelectric stress constant e 33 of Al 1-X Zr X N and the elastic constant C 33 calculated above into this relational expression, the piezoelectric constant d 33 of Al 1-X Zr X N can be obtained. It can be calculated.
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
また、Scをドープさせた窒化アルミニウム(Al1-XScN(1<X<0.5))についても、同様にしてAl1-XScNの圧電定数d33を算出した。 For aluminum nitride doped with Sc (Al 1-X Sc X N (1<X<0.5)), the piezoelectric constant d 33 of Al 1-X Sc X N was calculated in the same manner.
図5に、ZrおよびScの濃度Xと、得られた各圧電体の圧電定数d33との関係を示す。ここで、四角マークはZrをドープさせたAlNの計算結果であり、丸マークはScをドープさせたAlNの計算結果である。 FIG. 5 shows the relationship between the concentration X of Zr and Sc and the obtained piezoelectric constant d 33 of each piezoelectric body. Here, the square mark is the calculation result of AlN doped with Zr, and the circle mark is the calculation result of AlN doped with Sc.
この図に示すように、Al1-XZrNは、Xが0より大きく0.4(40at.%)より小さい場合には、同濃度のScを添加した窒化アルミニウム(Al1-XScN)よりも高い圧電定数d33を有し、Xが0.4以上になると、圧電定数d33が急激に減少して同濃度のScを添加した窒化アルミニウムのものよりも低い値になることが分かった。なお、このXの範囲において、格子定数比c/aは、1.25以上で1.60以下の範囲にあることが好ましい。 As shown in this figure, when X is larger than 0 and smaller than 0.4 (40 at. %), Al 1-X Zr X N has the same concentration of Sc added aluminum nitride (Al 1-X Sc). X N) has a higher piezoelectric constant d 33 , and when X becomes 0.4 or more, the piezoelectric constant d 33 sharply decreases and becomes a value lower than that of aluminum nitride to which Sc of the same concentration is added. I found out. In this range of X, the lattice constant ratio c/a is preferably in the range of 1.25 or more and 1.60 or less.
また、Al1-XZrNの圧電定数d33は、Xが0.375の時に最も高い値を有し、0.375を超えると小さくなることから、Xは0より大きく0.375以下の範囲が好ましい。なお、このXの範囲において、格子定数比c/aは、1.29以上で1.60以下の範囲にあることが好ましい。 Further, the piezoelectric constant d 33 of Al 1-X Zr X N has the highest value when X is 0.375, and becomes smaller when X exceeds 0.375. Therefore, X is larger than 0 and is 0.375 or less. Is preferred. In this X range, the lattice constant ratio c/a is preferably in the range of 1.29 or more and 1.60 or less.
さらに、図6に、Zrの濃度Xと、Al1-XZrNの結晶構造がウルツ鉱型の場合の混合エンタルピー(Mixing Enthalpy)および岩塩型の場合の混合エンタルピーとの関係を示す。ここで、ひし形マークはウルツ鉱型の場合の混合エンタルピーを示し、四角マークは岩塩型の混合エンタルピーを示す。 Further, FIG. 6 shows the relationship between the concentration X of Zr and the mixing enthalpy in the case where the crystal structure of Al 1-X Zr X N is wurtzite type and the mixing enthalpy in the case of rock salt type. Here, the rhombus mark indicates the mixed enthalpy in the case of wurtzite type, and the square mark indicates the mixed enthalpy of rock salt type.
この図に示すように、Xが0.3(30at.%)よりも小さい場合には、結晶構造がウルツ鉱型のAl1-XZrNが安定であり、Xが0.3よりも大きい場合には岩塩型のAl1-XZrNが安定であることが分かる。ここで、ウルツ鉱型の結晶は圧電性を示すが、岩塩型の結晶は圧電性を示さないと考えられている。したがって、Xは0より大きく0.3より小さい範囲が好ましい。この範囲のAl1-XZrNは結晶構造がより安定した圧電体となる。なお、このXの範囲において、格子定数比c/aは1.42以上で1.60以下の範囲にあることが好ましい。 As shown in this figure, when X is smaller than 0.3 (30 at. %), Al 1-X Zr X N having a wurtzite crystal structure is stable, and X is smaller than 0.3. It can be seen that the rock salt type Al 1-X Zr X N is stable when it is large. Here, it is considered that wurtzite type crystals show piezoelectricity, whereas rock salt type crystals do not show piezoelectricity. Therefore, the range of X is preferably larger than 0 and smaller than 0.3. Al 1-X Zr X N in this range becomes a piezoelectric body having a more stable crystal structure. In this range of X, the lattice constant ratio c/a is preferably 1.42 or more and 1.60 or less.
加えて、Zrの濃度Xが上述した範囲にあって、高い圧電定数d33を有する圧電体は、低損失であり、かつ広帯域で動作可能である。したがって、Zrの濃度Xが上述した範囲の圧電体を用いることにより、携帯用機器のさらなる高周波対応化、小型化および省電力化に寄与することができるMEMSデバイスを提供することができる。 In addition, the piezoelectric material having the Zr concentration X in the above range and having a high piezoelectric constant d 33 has low loss and can operate in a wide band. Therefore, by using the piezoelectric body having the Zr concentration X in the above-described range, it is possible to provide a MEMS device that can contribute to further high frequency compatibility, size reduction, and power saving of portable equipment.
さらに、Zrは、地表または地表近くに多量に存在し、かつ広く分布している。その結果、本発明によれば、地政学的な影響を受けずに、高い圧電定数d33を有する圧電体およびその圧電体を用いたMEMSデバイスを提供することができる。

 
Further, Zr is present in a large amount on the surface of the earth or near the surface of the earth and is widely distributed. As a result, according to the present invention, it is possible to provide a piezoelectric body having a high piezoelectric constant d 33 and a MEMS device using the piezoelectric body without being affected by geopolitics.

Claims (7)

  1. 化学式Al1-XZrNで表され、Xは0より大きく0.4より小さい範囲にあることを特徴とする圧電体。 A piezoelectric body represented by the chemical formula Al 1-X Zr X N, wherein X is in the range of more than 0 and less than 0.4.
  2. Xは0より大きく0.375以下の範囲にあることを特徴とする請求項1に記載の圧電体。 The piezoelectric body according to claim 1, wherein X is in the range of more than 0 and not more than 0.375.
  3. Xは0より大きく0.3より小さい範囲にあることを特徴とする請求項1に記載の圧電体。 2. The piezoelectric body according to claim 1, wherein X is in a range larger than 0 and smaller than 0.3.
  4. 格子定数比c/aが1.25以上で1.60以下の範囲にあることを特徴とする請求項1に記載の圧電体。 The piezoelectric body according to claim 1, wherein the lattice constant ratio c/a is in the range of 1.25 or more and 1.60 or less.
  5. 格子定数比c/aが1.29以上で1.60以下の範囲にあることを特徴とする請求項2に記載の圧電体。 The piezoelectric body according to claim 2, wherein the lattice constant ratio c/a is in the range of 1.29 or more and 1.60 or less.
  6. 格子定数比c/aが1.42以上で1.60以下の範囲にあることを特徴とする請求項3に記載の圧電体。 4. The piezoelectric body according to claim 3, wherein the lattice constant ratio c/a is in the range of 1.42 or more and 1.60 or less.
  7. 請求項1~6の何れか1項に記載の圧電体を用いたMEMSデバイス。
     

     
    A MEMS device using the piezoelectric body according to any one of claims 1 to 6.


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