JP4102872B2 - High crystalline barium titanate ultrafine particles and method for producing the same - Google Patents
High crystalline barium titanate ultrafine particles and method for producing the same Download PDFInfo
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- 229910002113 barium titanate Inorganic materials 0.000 title claims description 50
- JRPBQTZRNDNNOP-UHFFFAOYSA-N barium titanate Chemical compound [Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-] JRPBQTZRNDNNOP-UHFFFAOYSA-N 0.000 title claims description 49
- 238000004519 manufacturing process Methods 0.000 title claims description 11
- 239000011882 ultra-fine particle Substances 0.000 title claims description 5
- 239000002245 particle Substances 0.000 claims description 27
- 239000013078 crystal Substances 0.000 claims description 20
- 239000007864 aqueous solution Substances 0.000 claims description 17
- 239000010936 titanium Substances 0.000 claims description 15
- 239000002994 raw material Substances 0.000 claims description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 12
- 239000010419 fine particle Substances 0.000 claims description 11
- 238000001027 hydrothermal synthesis Methods 0.000 claims description 11
- 238000000034 method Methods 0.000 claims description 11
- -1 titanium alkoxide Chemical class 0.000 claims description 11
- 229910052719 titanium Inorganic materials 0.000 claims description 8
- 238000002156 mixing Methods 0.000 claims description 6
- 229910010413 TiO 2 Inorganic materials 0.000 claims description 5
- 238000004220 aggregation Methods 0.000 claims description 5
- 230000002776 aggregation Effects 0.000 claims description 5
- 150000003609 titanium compounds Chemical class 0.000 claims description 5
- 238000010335 hydrothermal treatment Methods 0.000 claims description 4
- 125000002887 hydroxy group Chemical group [H]O* 0.000 claims description 4
- 159000000009 barium salts Chemical class 0.000 claims description 3
- DCKVFVYPWDKYDN-UHFFFAOYSA-L oxygen(2-);titanium(4+);sulfate Chemical compound [O-2].[Ti+4].[O-]S([O-])(=O)=O DCKVFVYPWDKYDN-UHFFFAOYSA-L 0.000 claims description 2
- 229910000348 titanium sulfate Inorganic materials 0.000 claims description 2
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 48
- 239000000047 product Substances 0.000 description 18
- 238000006243 chemical reaction Methods 0.000 description 17
- IWOUKMZUPDVPGQ-UHFFFAOYSA-N barium nitrate Chemical compound [Ba+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O IWOUKMZUPDVPGQ-UHFFFAOYSA-N 0.000 description 14
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 12
- 239000000243 solution Substances 0.000 description 12
- LLZRNZOLAXHGLL-UHFFFAOYSA-J titanic acid Chemical compound O[Ti](O)(O)O LLZRNZOLAXHGLL-UHFFFAOYSA-J 0.000 description 11
- 239000003513 alkali Substances 0.000 description 10
- 239000010408 film Substances 0.000 description 8
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 7
- 239000012071 phase Substances 0.000 description 7
- AYJRCSIUFZENHW-UHFFFAOYSA-L barium carbonate Chemical compound [Ba+2].[O-]C([O-])=O AYJRCSIUFZENHW-UHFFFAOYSA-L 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 239000002002 slurry Substances 0.000 description 6
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 6
- 238000001000 micrograph Methods 0.000 description 5
- 239000000758 substrate Substances 0.000 description 5
- 229910052788 barium Inorganic materials 0.000 description 4
- 229910001422 barium ion Inorganic materials 0.000 description 4
- 239000012153 distilled water Substances 0.000 description 4
- 239000011259 mixed solution Substances 0.000 description 4
- 235000006408 oxalic acid Nutrition 0.000 description 4
- 239000000843 powder Substances 0.000 description 4
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical group [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 3
- RQPZNWPYLFFXCP-UHFFFAOYSA-L barium dihydroxide Chemical compound [OH-].[OH-].[Ba+2] RQPZNWPYLFFXCP-UHFFFAOYSA-L 0.000 description 3
- 229910001863 barium hydroxide Inorganic materials 0.000 description 3
- 239000003990 capacitor Substances 0.000 description 3
- 239000012295 chemical reaction liquid Substances 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 238000002003 electron diffraction Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000002243 precursor Substances 0.000 description 3
- 238000003980 solgel method Methods 0.000 description 3
- 238000010532 solid phase synthesis reaction Methods 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical group [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 238000003917 TEM image Methods 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 238000007792 addition Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- WDIHJSXYQDMJHN-UHFFFAOYSA-L barium chloride Chemical compound [Cl-].[Cl-].[Ba+2] WDIHJSXYQDMJHN-UHFFFAOYSA-L 0.000 description 2
- 229910001626 barium chloride Inorganic materials 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005755 formation reaction Methods 0.000 description 2
- 238000004811 liquid chromatography Methods 0.000 description 2
- 238000000634 powder X-ray diffraction Methods 0.000 description 2
- 238000010298 pulverizing process Methods 0.000 description 2
- 230000035484 reaction time Effects 0.000 description 2
- 230000000630 rising effect Effects 0.000 description 2
- 238000001878 scanning electron micrograph Methods 0.000 description 2
- 238000007086 side reaction Methods 0.000 description 2
- 229910052814 silicon oxide Inorganic materials 0.000 description 2
- 238000003746 solid phase reaction Methods 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- XJDNKRIXUMDJCW-UHFFFAOYSA-J titanium tetrachloride Chemical compound Cl[Ti](Cl)(Cl)Cl XJDNKRIXUMDJCW-UHFFFAOYSA-J 0.000 description 2
- 229910002651 NO3 Inorganic materials 0.000 description 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 1
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 1
- XHCLAFWTIXFWPH-UHFFFAOYSA-N [O-2].[O-2].[O-2].[O-2].[O-2].[V+5].[V+5] Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[V+5].[V+5] XHCLAFWTIXFWPH-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 150000004703 alkoxides Chemical class 0.000 description 1
- 238000000889 atomisation Methods 0.000 description 1
- GXUARMXARIJAFV-UHFFFAOYSA-L barium oxalate Chemical compound [Ba+2].[O-]C(=O)C([O-])=O GXUARMXARIJAFV-UHFFFAOYSA-L 0.000 description 1
- 229940094800 barium oxalate Drugs 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- RKTYLMNFRDHKIL-UHFFFAOYSA-N copper;5,10,15,20-tetraphenylporphyrin-22,24-diide Chemical group [Cu+2].C1=CC(C(=C2C=CC([N-]2)=C(C=2C=CC=CC=2)C=2C=CC(N=2)=C(C=2C=CC=CC=2)C2=CC=C3[N-]2)C=2C=CC=CC=2)=NC1=C3C1=CC=CC=C1 RKTYLMNFRDHKIL-UHFFFAOYSA-N 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000004128 high performance liquid chromatography Methods 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 230000003301 hydrolyzing effect Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 239000013067 intermediate product Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- QKKWJYSVXDGOOJ-UHFFFAOYSA-N oxalic acid;oxotitanium Chemical compound [Ti]=O.OC(=O)C(O)=O QKKWJYSVXDGOOJ-UHFFFAOYSA-N 0.000 description 1
- 239000011164 primary particle Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000010992 reflux Methods 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000010900 secondary nucleation Methods 0.000 description 1
- 229910052711 selenium Inorganic materials 0.000 description 1
- 239000011669 selenium Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000012265 solid product Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 229910001935 vanadium oxide Inorganic materials 0.000 description 1
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids
Landscapes
- Inorganic Compounds Of Heavy Metals (AREA)
- Crystals, And After-Treatments Of Crystals (AREA)
- Ceramic Capacitors (AREA)
- Semiconductor Memories (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、電子基板材料のひとつである誘電体絶縁膜へ適用できる粒子径３０ｎｍ以下の単結晶性、高結晶化度の立方晶チタン酸バリウム（ＢａＴｉＯ３）粒子およびそれを好適に製造可能な製造方法に関する。
【０００２】
【従来の技術】
ＩＴ産業の目覚ましい発展にともない大容量高密度メモリーの開発が進められている。現在、メモリーの主流であるＤＲＡＭのセル面積を決定するキャパシタの微細化を目的として、従来のシリコン酸化膜に代わる材料として高誘電体絶縁膜が注目されており、チタン酸バリウム（ＢａＴｉＯ３）はその候補のひとつの物質である。チタン酸バリウムは、常温常圧下での安定相として２種類の結晶構造をとる。ひとつは、強誘電特性を示す正方晶ＢａＴｉＯ３と強誘電特性を示さないが高誘電体である立方晶ＢａＴｉＯ３である。立方晶チタン酸バリウムは従来用いられている絶縁膜の酸化シリコンや酸化バナジウムらと比較して比誘電率が約１００倍近くあるため、例えば、キャパシタの絶縁膜へ適用すると、その絶縁膜の厚さを数１０ｎｍ程度に抑えることが可能であり、微細かつ薄いキャパシタが実現できる。
チタン酸バリウムを用いた誘電体絶縁膜はゾルゲル法の薄膜技術を応用した手法が検討されている（Ａｐｐｌ． Ｐｈｙｓ． Ｌｅｔｔ．， ５９， ３５４７（１９９１））。しかし、基板上に成膜する場合、チタン酸バリウムのプレカーサを塗布した後、結晶化のための８００℃から１０００℃の加熱が必要であり、基板材料やトランジスタへのダメージを与えるため、用いることができる材料は制限される。そこで、高温処理が不要な高結晶性の微粒子を用いれば、基板および下部トランジスタへの影響が軽微になることが期待される。そのためには、高結晶性でかつ数１０ｎｍのチタン酸バリウム微粒子が必要とされる。
【０００３】
チタン酸バリウム微粒子は、固相反応法、シュウ酸法、ゾルゲル法、水熱合成法のいずれかによって製造される。固相反応（Ｊ． Ｍａｔｅｒ． Ｓｃｉ．， １８， ３０４１（１９８３））は、原料として酸化チタンと炭酸バリウムの固体粉末を用いて、混合後、高温で焼成して目的化合物を得る。得られる粒子の結晶性は高いが、粒子径が数１０μｍであるため、粉砕、分級操作により微粒化されるが、高々数１００ｎｍ程度である。
シュウ酸法（粉体工学会誌， ３４（１１）， ３２−３３（１９９７））は、塩化バリウム、四塩化チタンをシュウ酸溶液に溶解させたのちに加熱、分離、乾燥を経て、シュウ酸バリウムチタニルを得て、それを仮焼処理し、チタン酸バリウムを得る。シュウ酸法におけるチタン酸バリウム生成反応は、シュウ酸バリウムチタニルの分解により、酸化チタンと炭酸バリウムが生成し、それが固相法と同一の反応によって進行する。そのため、組成の均質性は固相法より優れているが、粒子径は固相法と同程度であり、微粒化のためには、粉砕、分級操作が必要となる。
ゾルゲル法は、原料にチタンアルコキシドとバリウムアルコキシドの混合溶液を還流操作により複合アルコキシドを作成した後に、徐々に塩との加水分解反応によって、アモルファスまたは部分的に結晶化したチタン酸バリウムのプレカーサを得、それを８００℃から１０００℃で熱処理することで行われる（特許公報，平３−３９０１４（１９９１））。熱処理する前の非結晶性プレカーサは数１０ｎｍの水酸基を内在する非常に結晶性が低い微粒状のＢａＴｉＯ３であり、これらは、熱処理によって、粒子成長、凝集体、多結晶体となる。
水熱合成法では、原料であるチタン水酸化物と水酸化バリウムを水熱処理することで、結晶性チタン酸バリウムを合成する（例えば、Ｐｏｗｄｅｒ Ｔｅｃｈ．， １１０， ２（２０００））。数１０ｎｍの微粒子が生成するが、低温かつ高濃度のアルカリ性の条件下での反応であるため、結晶化度はかならずしも高くなく、表面や内部に水酸化物イオンを含む場合が多い。高濃度のアルカリの添加は、チタン酸バリウムの生成反応が、酸化チタンを中間生成物として経るため（Ｊ． Ｅｕｒ． Ｃｅｒａｍ． Ｓｏｃ．， １９， ９７３（１９９９））、酸化チタンの溶解を促進するためである。さらに、酸化チタンの溶解が律速となり、チタン酸バリウムを高い収率で得るためには数時間から数日の長時間の反応時間を必要とする。
【発明が解決しようとする課題】
【０００４】
表１に各手法によって得られるチタン酸バリウム粒子の特性を整理する。本発明は上記の問題点に着目してなされたもので、高結晶かつ単結晶性で粒子径が３０ｎｍ以下の立方晶チタン酸バリウム微粒子を、比較的低温、短時間かつ効率良く製造することのできるチタン酸バリウム酸化物の製造方法を提供することを目的としている。
【０００５】
【表１】
【０００６】
本発明のチタン酸バリウム微粒子は、バリウムイオンとチタンイオンとを超臨界または亜臨界状態の水中にて水熱反応させ、一次粒子径が３０ｎｍ以下であり、その粒子は残存水酸イオンが少なく、凝集のない、結晶化度が高いチタン酸バリウム酸化物を製造することを特徴としている。これらの特徴を有するチタン酸バリウム粒子を得るには、反応により生成する核の凝集を抑制するとともに、結晶表面での２次核発生を抑制する必要がある。一般に金属酸化物の結晶化度を上げるために高温処理することが望ましいが、高温、高圧の超臨界または亜臨界状態では、水は非極性のガス状となり、非極性を有するチタン酸バリウム酸化物の生成速度が著しく大きくなるとともに溶存するイオン濃度が極めて低くなることから、２次核発生や過度の結晶成長が生じ難く、生成する粒子径も小さくなる。９０℃程度での水熱反応で合成されたチタン酸バリウムは、結晶内部や結晶表面に結晶水や水酸基を含むことが一般的であるが、これらは製品（生成物）の誘電率低下の一因となりうる。しかし、臨界点近傍の亜臨界状態や超臨界状態の水中での水熱反応により合成または処理することで、結晶水や水酸基を含まない結晶化度の高いチタン酸バリウムを得ることができる。
【０００７】
本発明に用いるチタン源には塩化チタン、硫酸チタン、チタンアルコキシドなどの適当なチタン化合物を用意する。水溶性であることが適するが、適当なＴｉ化合物を加水分解させて得られる固体生成物チタン水酸化物（ＴｉＯ２ｘＨ２Ｏ）を含むスラリーでも可能である。バリウム源には、硝酸バリウム、塩化バリウム、水酸化バリウムなどの適当なバリウム塩を用意する。水溶性であることが好適である。上記のチタンイオン、バリウムイオンの個々の溶液または混合溶液に、アルカリを加えて中性よりも高いｐＨの溶液をすることが必要である。ここでのアルカリは、ＬｉＯＨ， ＮａＯＨ， ＫＯＨ， ＮＨ４ＯＨであるが、原料であるＢａ（ＯＨ）２を用いることが好適である。チタン化合物とバリウム塩の混合溶液を用いてもよいが、チタン酸バリウムは常温下でも反応生成するため、それが結晶核となり粒子成長を妨げる意味で、超臨界または亜臨界状態に加熱する直前に混合することが好適である。
【０００８】
本発明のチタン酸バリウム酸化物の製造方法は、急速昇温水熱反応を、水酸イオンを適宜添加した条件下で行うことが好ましい。このようにすれば、前記チタン、バリウム混合水溶液に水酸イオンを適宜添加してアルカリ性にすることで、昇温過程で結晶化しやすい水酸化チタンが溶解され易くなり、従って、これら昇温過程において生成した副反応物質が反応生成物中に残留して結晶品質に悪影響を及ぼし、目的とするチタン酸バリウムの収率低下を防止することができる。本発明のチタン酸バリウムの製造方法は、水熱反応を、バリウムイオンとチタンイオンまたはチタン水酸化物の混合溶液を超臨界または亜臨界状態が得られる所定温度に急速に昇温させて実施することが好ましい。このようにすれば、前記水溶液を急速な昇温により迅速に超臨界または亜臨界状態として水熱反応を行うことにより、昇温中に生じる副反応により目的とするチタン酸バリウムの収量が低下したり、核の凝集や結晶表面での２次核発生により生成物の結晶状態が悪化したりすることを防止することができる。
本発明のチタン酸バリウムの製造方法は、チタン酸バリウム微粒子が生成した後も亜臨界または超臨界条件下で所定時間水熱処理することで、結晶微粒子を成長させずに結晶化度を向上させることが好ましい。このようにすれば、生成するチタン酸バリウムの粒径が増大することなく、その結晶化度を向上させることができる。反応温度は１００℃以上で立方晶ＢａＴｉＯ３が生成するが、超臨界条件（＞４００℃）であることが好適である。
【発明の実施の形態】
【０００９】
以下、本発明の実施の形態を、図面に基づき説明する。図１に、本実施形態に用いたチタン酸バリウムの製造装置の構成を示す。製造装置は、原料である硝酸バリウム水溶液、チタン水酸化物スラリー水溶液、水酸化ナトリウム水溶液および原料溶液昇温用の４基の液体クロマトグラフィ用高圧ポンプ、反応管および蒸留水加熱用の２基の電気炉、反応液冷却用熱交換器、および圧力調整器（背圧弁）から構成される。
ガラス製容器内のチタン水酸化物スラリー水溶液１、硝酸バリウム水溶液２および水酸化ナトリウム水溶液３を高速液体クロマトグラフィ用無脈流ポンプ５，６，７により、それぞれ流量２， ２， ４ｃｍ３／ｍｉｎで送液した。チタン水酸化物スラリー水溶液と硝酸バリウム水溶液は混合点ＭＰ１にて混合されたのち、混合点ＭＰ２にて水酸化ナトリウム水溶液と混合され、反応管方向へ送られる。一方、蒸留水４は、別の高圧ポンプ８により流量１１ｃｍ３／ｍｉｎで管型電気炉９に送液され、そこで蒸留水は原料溶液の加熱に必要な超臨界水とした。Ｔｉ−Ｂａ混合水溶液は、前記超臨界水と混合点ＭＰ３にて接触し、急速に反応温度まで昇温され、水熱反応が開始させた。反応液は、管状電気炉１１によって一定温度に保持された反応管１０を一定時間滞在後、反応管出口の２重管型の熱交換器１２により冷却後、背圧弁１３にて降圧し、回収容器１４に捕集した。
生成した粒子は、出口より反応液とともにスラリーとして回収される。回収した溶液を適当なフィルターによりろ別し、生成した粉体を回収する。これらの粒子の特性は、粉末Ｘ線回折および電子線回折像の解析により結晶構造を同定できる。また、組成はＩＣＰ法によって決定される。粒子径や凝集の程度は電子顕微鏡観察によって評価される。
【００１０】
【実施例】
次に実施例により本発明をさらに詳細に説明するが、本発明は、これらの例によってなんら限定されるものではない。
【００１１】
実施例１
流通式反応装置により、反応温度４００℃， 反応圧力３０ＭＰａ，滞在時間２．０秒としたときの得られた生成物の電子顕微鏡像を示す。このときのチタン水酸化物、硝酸バリウム、水酸化ナトリウムの原料溶液濃度は、それぞれ、０．０２Ｍ， ０．０４Ｍ， ０．１６Ｍである。図２（ａ）に生成物の電子顕微鏡像を、図２（ｂ）に電子線回折像を示す。粒子径は３０ｎｍ以下であり、粒子ひとつひとつが分離しており、凝集していないことがわかる。電子線回折像からは、これら粒子の結晶構造は立方晶チタン酸バリウムであり、回折像がリング状に現れていないことから、多結晶体ではないことがわかる。図３に高倍率の電子顕微鏡像を示す。通常の水熱合成またはゾルゲル法で得られるチタン酸バリウムの超微粒子は、結晶化度が低く、その形状も球状の場合がほとんどである。しかし、本発明によって生成するチタン酸バリウム微粒子は結晶構造を反映した立方体形であり、ひとつひとつの粒子の結晶面が観察されることから、この図からも、高結晶かつ単結晶性微粒子であることがわかる。図４に生成物のＸＲＤチャートを示す。図４に示すように、ほぼ単一相の立方晶チタン酸バリウム（ＪＣＰＤＳ ３１−１７４）が生成していることがわかる。組成分析結果からＴｉＯ２・ｘＢａＯのｘの値は、０．９８であった。
【００１２】
実施例２
この例では、原料溶液のＢａ／Ｔｉモル比および添加した水酸化ナトリウム濃度比の生成物結晶構造へ及ぼす影響を調べた。チタン水酸化物濃度を０．０２Ｍと固定し、Ｂａ（ＮＯ３）２濃度を０．０２Ｍ〜０．１Ｍ、添加する水酸化ナトリウム濃度を０．０２〜０．２０Ｍまで変化させた。反応温度は４００℃， 反応圧力は３０ＭＰａ， 反応時間は２．１秒とした。図５に生成物のＢａ／Ｔｉモル比、水酸化ナトリウム濃度依存性を示す。添加した水酸化ナトリウム濃度は、硝酸バリウム由来の硝酸イオンに対する比（アルカリモル比）によって整理した。原料溶液中のＢａ／Ｔｉモル比を２：１として、水酸化ナトリウム濃度の硝酸イオン濃度に対する比を０， １， ３， ５， ７とした場合、水酸化ナトリウムを加えない場合（アルカリモル比０）は、生成物はＴｉＯ２（アナターゼ）であった。アルカリモル比を１とした場合は単一相のＢａＴｉＯ３が得られた。さらに水酸化ナトリウム濃度を大きくし、アルカリモル比を２以上とすると、生成物はチタン酸バリウムと炭酸バリウムの混合物になった。これは、アルカリモル比が増加することで、回収溶液のｐＨも高くなり、冷却回収後の溶液に溶解した炭酸ガスと未反応のバリウムイオンが反応して生成したものである。
【００１３】
化学量論比であるＢａ：Ｔｉ＝１：１の原料を用いた場合、ＮａＯＨ濃度を０．０４Ｍ（アルカリモル比１）では、生成物は酸化チタンとチタン酸バリウムの混合物であった。しかし、ＮａＯＨ濃度を大きくして、０．０８Ｍ（アルカリモル比２）とすることで、単一相のチタン酸バリウムを得ることができた。このことから、Ｂａ／Ｔｉモル比、およびアルカリ濃度を調整することで、チタン酸バリウムを単一相で合成できる条件を設定できる。
【００１４】
実施例３
ここでは、反応プロセスの簡略化を目的として、常温のチタン水酸化物（０．０２Ｍ）と４８０℃まで加熱された水酸化バリウム水溶液（０．０４Ｍ）とを反応させた。図６に生成物の粉末Ｘ線回折像を示す。実施例１と同様に、単一相の立方晶チタン酸バリウム（ＪＣＰＤＳ ３１−１７４）が得られた。このときのｘの値は０．９１であった。図７に生成したチタン酸バリウム粒子の電子顕微鏡像（ＳＥＭ像）を示す。平均粒子径は３０ｎｍでかつ粒子サイズ分布は小さく、未凝集であることが確認できる。以上、本発明の実施形態を図面により前記各実施例にて説明してきたが、本発明はこれら各実施例に限定されるものではなく、本発明の主旨を逸脱しない範囲における変更や追加があっても本発明に含まれることは言うまでもない。
【発明の効果】
【００１５】
以上のように、請求項１〜請求項３に記載の発明によれば、例えば、チタン酸バリウム薄膜の調整の際に結晶化度向上のための加熱処理が不要となり、基板や素子にダメージを与えることなく加工が可能となる。請求項４〜７記載の発明によれば、結晶化度が高く、単結晶性の粒子径が３０ｎｍ以下の立方晶チタン酸バリウムを比較的低温でかつ、短時間に製造できる。
【００１６】
【図面の簡単な説明】
【図１】流通式水熱合成反応装置
１：チタン水酸化物スラリー槽；２：硝酸バリウム水溶液槽；３：水酸化ナトリウム水溶液槽；４：蒸留水槽；５、６，７，８：液体クロマトグラフィー用高圧ポンプ；９：電気炉；１０：反応管；１１：電気炉；１２：二重冷却管；１３：背圧弁；１４：回収容器
【図２】生成物の電子顕微鏡像 （ａ） ＴＥＭ像 （ｂ） 電子線回折像
【図３】生成物の高倍率ＴＥＭ像
【図４】生成物のＸＲＤチャート
【図５】原料のＢａ／Ｔｉ組成とＮａＯＨ濃度の生成相への影響
【図６】実施例３で合成した生成物の電子顕微鏡像（ＳＥＭ像）
【図７】実施例３で合成した生成物のＸＲＤチャート[0001]
BACKGROUND OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention is applicable to a dielectric insulating film, which is one of electronic substrate materials, and has a single crystallinity and high crystallinity cubic barium titanate (BaTiO 3 ) particles having a particle diameter of 30 nm or less and can be preferably produced. It relates to a manufacturing method.
[0002]
[Prior art]
With the remarkable development of the IT industry, development of large-capacity high-density memory is underway. At present, for the purpose of miniaturization of capacitors that determine the cell area of DRAM, which is the mainstream of memory, high dielectric insulating films are attracting attention as an alternative to conventional silicon oxide films. Barium titanate (BaTiO 3 ) One of the candidates. Barium titanate has two types of crystal structures as a stable phase at normal temperature and pressure. One is tetragonal BaTiO 3 that exhibits ferroelectric characteristics and cubic BaTiO 3 that does not exhibit ferroelectric characteristics but is a high dielectric. Cubic barium titanate has a relative dielectric constant of about 100 times that of silicon oxide and vanadium oxide, which are conventionally used insulating films. For example, when applied to an insulating film of a capacitor, the thickness of the insulating film The thickness can be suppressed to about several tens of nm, and a fine and thin capacitor can be realized.
A dielectric insulating film using barium titanate has been studied by applying a sol-gel thin film technique (Appl. Phys. Lett., 59, 3547 (1991)). However, when a film is formed on a substrate, it is necessary to apply heat from 800 ° C. to 1000 ° C. for crystallization after applying a precursor of barium titanate, which causes damage to the substrate material and the transistor. The materials that can be used are limited. Therefore, if highly crystalline fine particles that do not require high-temperature treatment are used, it is expected that the influence on the substrate and the lower transistor will be reduced. For this purpose, barium titanate fine particles having high crystallinity and several tens of nm are required.
[0003]
The barium titanate fine particles are produced by any one of a solid phase reaction method, an oxalic acid method, a sol-gel method, and a hydrothermal synthesis method. In the solid phase reaction (J. Mater. Sci., 18, 3041 (1983)), a solid powder of titanium oxide and barium carbonate is used as a raw material, and after mixing, the target compound is obtained by baking at a high temperature. Although the crystallinity of the obtained particles is high, since the particle diameter is several tens of μm, they are atomized by pulverization and classification operations, but are about several hundred nm at most.
In the oxalic acid method (Journal of Powder Engineering, 34 (11), 32-33 (1997)), barium chloride and titanium tetrachloride are dissolved in an oxalic acid solution, and then heated, separated, and dried, followed by barium oxalate. Titanyl is obtained and calcined to obtain barium titanate. In the oxalic acid method, the barium titanate production reaction produces titanium oxide and barium carbonate by the decomposition of barium titanyl oxalate, which proceeds by the same reaction as in the solid phase method. Therefore, the homogeneity of the composition is superior to that of the solid phase method, but the particle size is similar to that of the solid phase method, and pulverization and classification operations are required for atomization.
In the sol-gel method, a composite alkoxide is prepared by refluxing a mixed solution of titanium alkoxide and barium alkoxide as a raw material, and then a precursor of amorphous or partially crystallized barium titanate is obtained by a hydrolysis reaction with a salt gradually. It is performed by heat-treating it at 800 ° C. to 1000 ° C. (Patent Publication, Hei 3-39014 (1991)). The amorphous precursor before the heat treatment is BaTiO 3 having a very low crystallinity containing a hydroxyl group of several tens of nm, and these become a particle growth, an aggregate and a polycrystal by the heat treatment.
In the hydrothermal synthesis method, crystalline barium titanate is synthesized by hydrothermal treatment of raw material titanium hydroxide and barium hydroxide (for example, Powder Tech., 110, 2 (2000)). Although fine particles of several tens of nanometers are generated, the degree of crystallinity is not always high because of the reaction under low temperature and high concentration alkaline conditions, and in many cases, hydroxide ions are included on the surface or inside. Addition of a high concentration of alkali promotes dissolution of titanium oxide because the formation reaction of barium titanate passes through titanium oxide as an intermediate product (J. Eur. Ceram. Soc., 19, 973 (1999)). Because. Furthermore, dissolution of titanium oxide becomes rate limiting, and a long reaction time of several hours to several days is required to obtain barium titanate with a high yield.
[Problems to be solved by the invention]
[0004]
Table 1 summarizes the characteristics of the barium titanate particles obtained by each method. The present invention has been made by paying attention to the above-mentioned problems, and can efficiently produce cubic barium titanate fine particles having high crystallinity and single crystallinity and having a particle diameter of 30 nm or less at a relatively low temperature in a short time. It aims at providing the manufacturing method of the barium titanate oxide which can be performed.
[0005]
[Table 1]
[0006]
The barium titanate fine particles of the present invention are hydrothermally reacted in supercritical or subcritical water with barium ions and titanium ions, the primary particle diameter is 30 nm or less, the particles have few residual hydroxide ions, It is characterized by producing barium titanate oxide having high crystallinity without aggregation. In order to obtain barium titanate particles having these characteristics, it is necessary to suppress the aggregation of nuclei generated by the reaction and to suppress the generation of secondary nuclei on the crystal surface. In general, high-temperature treatment is desirable to increase the crystallinity of metal oxides. However, in high-temperature, high-pressure supercritical or subcritical state, water becomes a nonpolar gaseous state, and barium titanate oxide having nonpolarity Since the generation rate of selenium increases remarkably and the concentration of dissolved ions becomes extremely low, secondary nucleation and excessive crystal growth are unlikely to occur, and the generated particle size is also reduced. Barium titanate synthesized by a hydrothermal reaction at about 90 ° C. generally contains crystal water and hydroxyl groups inside the crystal or on the crystal surface, but these are one of the factors that lower the dielectric constant of the product (product). It can be a factor. However, barium titanate having a high degree of crystallinity that does not contain crystal water or hydroxyl groups can be obtained by synthesis or treatment by hydrothermal reaction in subcritical or supercritical water near the critical point.
[0007]
For the titanium source used in the present invention, an appropriate titanium compound such as titanium chloride, titanium sulfate, or titanium alkoxide is prepared. It is suitable to be water-soluble, but a slurry containing a solid product titanium hydroxide (TiO 2 xH 2 O) obtained by hydrolyzing an appropriate Ti compound is also possible. For the barium source, an appropriate barium salt such as barium nitrate, barium chloride, or barium hydroxide is prepared. It is preferable that it is water-soluble. It is necessary to add an alkali to each solution or mixed solution of the above titanium ions and barium ions to form a solution having a pH higher than neutrality. The alkali here is LiOH, NaOH, KOH, or NH 4 OH, but Ba (OH) 2 as the raw material is preferably used. A mixed solution of titanium compound and barium salt may be used, but since barium titanate reacts and generates even at room temperature, it becomes a crystal nucleus and prevents particle growth, so just before heating to a supercritical or subcritical state. Mixing is preferred.
[0008]
In the method for producing a barium titanate oxide according to the present invention, it is preferable to perform the rapid temperature rising hydrothermal reaction under conditions to which a hydroxide ion is appropriately added. In this way, by appropriately adding hydroxide ions to the titanium / barium mixed aqueous solution to make it alkaline, titanium hydroxide which is easily crystallized in the temperature rising process is easily dissolved. The produced side reaction substance remains in the reaction product and adversely affects the crystal quality, and the reduction in the yield of the target barium titanate can be prevented. In the method for producing barium titanate of the present invention, the hydrothermal reaction is carried out by rapidly raising the mixed solution of barium ions and titanium ions or titanium hydroxide to a predetermined temperature at which a supercritical or subcritical state is obtained. It is preferable. In this way, the yield of the target barium titanate is reduced by the side reaction that occurs during the temperature increase by performing the hydrothermal reaction in which the aqueous solution is rapidly brought into a supercritical or subcritical state by a rapid temperature increase. Or deterioration of the crystalline state of the product due to aggregation of nuclei or generation of secondary nuclei on the crystal surface.
According to the method for producing barium titanate of the present invention, the degree of crystallinity is improved without growing crystal fine particles by hydrothermal treatment for a predetermined time under subcritical or supercritical conditions even after the formation of barium titanate fine particles. Is preferred. In this way, the crystallinity can be improved without increasing the particle size of the barium titanate produced. Cubic BaTiO3 is produced at a reaction temperature of 100 ° C. or higher, but it is preferable that the reaction temperature is supercritical (> 400 ° C.).
DETAILED DESCRIPTION OF THE INVENTION
[0009]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, the structure of the manufacturing apparatus of the barium titanate used for this embodiment is shown. The production equipment consists of a barium nitrate aqueous solution, a titanium hydroxide slurry aqueous solution, a sodium hydroxide aqueous solution, and four liquid chromatography high-pressure pumps for raising the temperature of the raw material solution, a reaction tube and two electric heaters for heating distilled water. It consists of a furnace, a heat exchanger for cooling the reaction liquid, and a pressure regulator (back pressure valve).
A titanium hydroxide slurry aqueous solution 1, a barium nitrate aqueous solution 2 and a sodium hydroxide aqueous solution 3 in a glass container were fed at a flow rate of 2, 2, 4 cm 3 / min respectively by non-pulsating flow pumps 5, 6 and 7 for high performance liquid chromatography. Liquid was sent. The titanium hydroxide slurry aqueous solution and the barium nitrate aqueous solution are mixed at the mixing point MP1, and then mixed with the sodium hydroxide aqueous solution at the mixing point MP2, and sent to the reaction tube. On the other hand, the distilled
The generated particles are recovered as a slurry together with the reaction liquid from the outlet. The collected solution is filtered through an appropriate filter, and the produced powder is collected. As for the characteristics of these particles, the crystal structure can be identified by analysis of powder X-ray diffraction and electron diffraction images. The composition is determined by the ICP method. The particle diameter and the degree of aggregation are evaluated by observation with an electron microscope.
[0010]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
[0011]
Example 1
The electron microscope image of the obtained product when the reaction temperature is 400 ° C., the reaction pressure is 30 MPa, and the residence time is 2.0 seconds by a flow reactor is shown. The raw material solution concentrations of titanium hydroxide, barium nitrate, and sodium hydroxide at this time are 0.02M, 0.04M, and 0.16M, respectively. FIG. 2A shows an electron microscope image of the product, and FIG. 2B shows an electron beam diffraction image. It can be seen that the particle diameter is 30 nm or less, and the particles are separated and not aggregated. From the electron diffraction image, it can be seen that the crystal structure of these particles is cubic barium titanate, and the diffraction image does not appear in a ring shape, so that it is not a polycrystal. FIG. 3 shows a high magnification electron microscope image. The ultrafine particles of barium titanate obtained by the usual hydrothermal synthesis or sol-gel method have a low crystallinity and are almost spherical in shape. However, since the barium titanate fine particles produced by the present invention have a cubic shape reflecting the crystal structure and the crystal plane of each particle is observed, this figure also shows that the particles are highly crystalline and single crystalline fine particles. I understand. FIG. 4 shows an XRD chart of the product. As shown in FIG. 4, it can be seen that substantially single-phase cubic barium titanate (JCPDS 31-174) is produced. From the result of the composition analysis, the value of x of TiO 2 · xBaO was 0.98.
[0012]
Example 2
In this example, the influence of the Ba / Ti molar ratio of the raw material solution and the added sodium hydroxide concentration ratio on the product crystal structure was examined. The titanium hydroxide concentration was fixed at 0.02 M, the Ba (NO 3 ) 2 concentration was changed from 0.02 M to 0.1 M, and the sodium hydroxide concentration to be added was changed from 0.02 to 0.20 M. The reaction temperature was 400 ° C., the reaction pressure was 30 MPa, and the reaction time was 2.1 seconds. FIG. 5 shows the Ba / Ti molar ratio and sodium hydroxide concentration dependence of the product. The added sodium hydroxide concentration was arranged according to the ratio (alkaline molar ratio) to nitrate ions derived from barium nitrate. When the Ba / Ti molar ratio in the raw material solution is 2: 1 and the ratio of the sodium hydroxide concentration to the nitrate ion concentration is 0, 1, 3, 5, 7, no sodium hydroxide is added (alkali molar ratio) 0), the product was TiO 2 (anatase). When the alkali molar ratio was 1, single-phase BaTiO 3 was obtained. When the sodium hydroxide concentration was further increased and the alkali molar ratio was 2 or more, the product was a mixture of barium titanate and barium carbonate. This is because the pH of the recovered solution increases as the alkali molar ratio increases, and carbon dioxide dissolved in the solution after cooling and recovery reacts with unreacted barium ions.
[0013]
When a raw material having a stoichiometric ratio of Ba: Ti = 1: 1 was used, the product was a mixture of titanium oxide and barium titanate at a NaOH concentration of 0.04 M (alkali molar ratio 1). However, a single-phase barium titanate could be obtained by increasing the NaOH concentration to 0.08 M (alkali molar ratio 2). From this, the conditions under which barium titanate can be synthesized in a single phase can be set by adjusting the Ba / Ti molar ratio and the alkali concentration.
[0014]
Example 3
Here, for the purpose of simplifying the reaction process, normal temperature titanium hydroxide (0.02M) was reacted with an aqueous barium hydroxide solution (0.04M) heated to 480 ° C. FIG. 6 shows a powder X-ray diffraction image of the product. As in Example 1, single-phase cubic barium titanate (JCPDS 31-174) was obtained. The value of x at this time was 0.91. FIG. 7 shows an electron microscope image (SEM image) of the generated barium titanate particles. The average particle size is 30 nm, the particle size distribution is small, and it can be confirmed that the particles are not aggregated. The embodiments of the present invention have been described with reference to the above-described examples. However, the present invention is not limited to these examples, and there are changes and additions within the scope of the present invention. However, it goes without saying that it is included in the present invention.
【The invention's effect】
[0015]
As described above, according to the first to third aspects of the invention, for example, when adjusting the barium titanate thin film, heat treatment for improving the crystallinity is unnecessary, and the substrate and the element are damaged. Processing is possible without giving. According to the fourth to seventh aspects of the present invention, cubic barium titanate having a high degree of crystallinity and a single crystal particle size of 30 nm or less can be produced at a relatively low temperature and in a short time.
[0016]
[Brief description of the drawings]
1] Flow-type hydrothermal synthesis reactor 1: titanium hydroxide slurry tank; 2: barium nitrate aqueous solution tank; 3: sodium hydroxide aqueous solution tank; 4: distilled water tank; 5, 6, 7, 8: liquid chromatography 9: Electric furnace; 10: Reaction tube; 11: Electric furnace; 12: Double cooling tube; 13: Back pressure valve; 14: Collection vessel [Figure 2] Electron microscopic image of the product (a) TEM Image (b) Electron diffraction image [FIG. 3] High-magnification TEM image of the product [FIG. 4] XRD chart of the product [FIG. 5] Effect of raw material Ba / Ti composition and NaOH concentration on the product phase [FIG. Electron microscope image (SEM image) of the product synthesized in Example 3
7 is an XRD chart of the product synthesized in Example 3. FIG.
Claims (4)
ＴｉＯ２・ｘＢａＯ
（式中のｘは０．９〜１．２の数である）で表される高結晶性チタン酸バリウム超微粒子であって、チタン酸バリウムの結晶構造が立方晶であること、粒子径が３０ｎｍ以下の単結晶であること、凝集がなく、結晶水や水酸基を含まないこと、を特徴とする高結晶性チタン酸バリウム微粒子。The basic structure is the general formula TiO 2 xBaO
(Wherein x is a number from 0.9 to 1.2), and the crystal structure of the barium titanate ultrafine particles is cubic, and the particle diameter is Highly crystalline barium titanate fine particles characterized by being a single crystal of 30 nm or less, having no aggregation, and containing no crystal water or a hydroxyl group .
ＴｉＯ２・ｘＢａＯ
（式中のｘは０．９〜１．２の数である）で表される高結晶性チタン酸バリウム超微粒子の製造方法。After mixing the titanium compound aqueous solution and the barium salt aqueous solution and adding the alkaline aqueous solution, the basic structure is represented by the general formula TiO 2 · xBaO by performing the hydrothermal reaction under the condition that the hydrothermal treatment time is within 20 seconds.
(Wherein x is a number from 0.9 to 1.2).
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| JP5637389B2 (en) * | 2011-03-14 | 2014-12-10 | 独立行政法人産業技術総合研究所 | Method for producing barium titanate nanocrystals |
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