JP4368004B2 - Optical waveguide device and method for manufacturing optical waveguide device - Google Patents

Description

【００６３】
【実施例】
（実施例１）
サファイアＡｌ₂Ｏ₃（１１０２）単結晶基板１２上へ固相エピタキシャル成長によって膜厚１０ｎｍのエピタキシャルＰＬＴ（２８／１００）からなるバッファ層としての第１強誘電体層１４を成長させ、さらに膜厚９０ｎｍのエピタキシャルＰＬＺＴ（９／６５／３５）薄膜からなる光導波路としての第２強誘電体層１６を成長させることによって、図１に示す構造の光導波路素子を作製した。
【００６４】
以下に、製造方法を詳細に説明する。
（１）第１強誘電体層１４（バッファ層）の形成
無水酢酸鉛（Ｐｂ（ＣＨ₃ＣＯＯ）₂）、ランタンイソプロポキシド（Ｌａ（Ｏ−ｉ−Ｃ₃Ｈ₇）₃）、及びチタンイソプロポキシド（Ｔｉ（Ｏ−ｉ−Ｃ₃Ｈ₇）₄）を出発原料として用い、Ｐｂが他の元素に対して化学量論組成であるＰｂ：Ｌａ：Ｚｒ：Ｔｉ＝７２：２８：１００の割合となるように２−メトキシエタノールに溶解し、６時間の蒸留を行った後、さらに１８時間の還流を行い、最終的にＴｉ濃度で０．６ＭのＰＬＴ（２８／１００）用前駆体溶液を得た。得られた前駆体溶液を、０．２μｍのフィルターを通してサファイア基板へスピンコーティングにより塗布し塗布膜を得た。サファイア基板は、溶剤洗浄、ＨＣｌによるエッチング、脱イオン水によるリンスを行い、最後にＮ₂中にてエタノールのスピンコーティングによって乾燥した後使用した。なお、以上の工程は総てＮ₂雰囲気中にて行った。
【００６５】
次に、塗布膜を形成した基板を加湿した酸素雰囲気中に置き、１０℃／ｓｅｃにて昇温して３００℃にて２分間保持の後、１０℃／ｓｅｃにて昇温して６５０℃に３０分間保持し、最後に電気炉の電源を切り冷却し、膜厚１０ｎｍのＰＬＴ（２８／１００）バッファ層を固相エピタキシャル成長した。得られたバッファ層の表面を高分解能走査型電子顕微鏡（ＳＥＭ）によって観察すると、図７に示すように島状構造の形態になっていた。
（２）第２強誘電体層１６（薄膜光導波路）の形成
バッファ層形成の場合と同様に、無水酢酸鉛（Ｐｂ（ＣＨ₃ＣＯＯ）₂）、ランタンイソプロポキシド（Ｌａ（Ｏ−ｉ−Ｃ₃Ｈ₇）₃）、ジルコニウムイソプロポキシド（Ｚｒ（Ｏ−ｉ−Ｃ₃Ｈ₇）₄）、及びチタンイソプロポキシド（Ｔｉ（Ｏ−ｉ−Ｃ₃Ｈ₇）₄）を出発原料として用い、Ｐｂが他の元素に対して化学量論組成であるＰｂ：Ｌａ：Ｚｒ：Ｔｉ＝９１：９：６５：３５の割合となるように２−メトキシエタノールに溶解し、６時間の蒸留を行った後、さらに１８時間の還流を行い、最終的にＺｒ＋Ｔｉ濃度で０．６ ＭのＰＬＺＴ（９／６５／３５）用前駆体溶液を得た。得られた前駆体溶液を０．２μｍのフィルターを通して、ＰＬＴ（２８／１００）バッファ層を設けたＡｌ₂Ｏ₃基板へスピンコーティングにより塗布した。以上の操作はすべてＮ₂雰囲気中にて行った。
【００６６】
次に、塗布膜を形成した基板を加湿した酸素雰囲気中に置き、１０℃／ｓｅｃにて昇温して３００℃にて２分間保持の後、１０℃／ｓｅｃにて昇温して６５０℃に３０分間保持し、最後に電気炉の電源を切り冷却し、膜厚９０ｎｍのＰＬＺＴ（９／６５／３５）薄膜を固相エピタキシャル成長し、光導波路素子を得た。
【００６７】
図８にこの光導波路素子のＸ線回折θ−２θパターンを示す。図８から、２θ＝３１．０°付近ＰＬＺＴ（１１０）の回折強度は１２８ｋｃｐｓと強く、ペロブスカイト単一相が形成されていることがわかる。また、各層の結晶学的関係は、単一配向のＰＬＺＴ（１１０）／／ＰＬＴ（１１０）／／Ａｌ₂Ｏ₃（１１０２）であった。また、ＰＬＺＴ（１１０）面によるロッキングカーブ半値幅は０．９１３°と良好であった。
【００６８】
また、本実施例のエピタキシャルＰＬＺＴ薄膜の表面は光学顕微鏡の観察では均一なために何も見えなかった。さらに、このＰＬＺＴ（９／６５／３５）薄膜表面を高分解能ＳＥＭによって観察した結果を図９に示すが、図９に示すように、表面は極めて均一かつ平滑であり、粒界や細孔の全くみられない、コントラストの得られないほど鏡面状の表面であった。
【００６９】
（比較例１）
実施例１と同様に、サファイアＡｌ₂Ｏ₃（１１０２）単結晶基板上へ、固相エピタキシャル成長によってエピタキシャルＰＬＺＴ（９／６５／３５）薄膜を直接成長させることによって光導波路素子を作製した。
【００７０】
Ｐｂが他の元素に対して化学量論組成であるＰＬＺＴ（９／６５／３５）用前駆体溶液をサファイア基板へスピンコーティングにより塗布した。この塗布膜を形成した基板を加湿した酸素雰囲気中に置き、１０℃／ｓｅｃにて昇温して３５０℃にて２分間保持した後、１０℃／ｓｅｃにて昇温して６５０℃に３０分間保持した。最後に電気炉の電源を切り冷却し、膜厚９０ｎｍのＰＬＺＴ（９／６５／３５）薄膜が形成された光導波路素子を得た。
【００７１】
図１０にこの光導波路素子のＸ線回折θ−２θパターンを示す。図１０から各層の結晶学的関係がほぼ単一配向のＰＬＺＴ（１１０）／／Ａｌ₂Ｏ₃（１１０２）の構造の光導波路素子が得られていることが分かる。しかしながら、２θ＝３１．０°付近ＰＬＺＴ（１１０）の回折強度は２ｋｃｐｓと極めて弱く、２θ＝２９．２°付近にはパイロクロア相を示すピークが１ｋｃｐｓ程度の強度でみられた。 また、本比較例のエピタキシャルＰＬＺＴ薄膜表面を光学顕微鏡によって観察したところ、図１１に示すようにロゼット構造と一般的に呼ばれる薔薇状のぺロブスカイト相をパイロクロア相が囲んだような不均一な濃淡のみられる表面であった。
【００７２】
（実施例２）
サファイアＡｌ₂Ｏ₃（１１０２）単結晶基板１２上へ固相エピタキシャル成長によって膜厚１０ｎｍ、屈折率２．５０のエピタキシャルＰＬＴ（２８／１００）からなるバッファ層としての第１強誘電体層１４を成長させ、さらに膜厚５４０ｎｍ、屈折率２．５０のエピタキシャルＰＬＺＴ（９／６５／３５）からなる薄膜光導波路としての第２強誘電体層１６を成長させることによって、実施例１の場合と同様に、図１に示す構造の光導波路素子を作製した。
【００７３】
まず、ＰＬＴ（２８／１００）用前駆体溶液をサファイア基板へスピンコーティングにより塗布した。この塗布膜を形成した基板を加湿した酸素雰囲気中に置き、１０℃／ｓｅｃにて昇温して３００℃にて２分間保持の後、１０℃／ｓｅｃにて昇温して６５０℃に３０分間保持した。最後に電気炉の電源を切り冷却し、膜厚１０ｎｍのＰＬＴ（２８／１００）バッファ層を固相エピタキシャル成長した。このバッファ層の表面を原子間力顕微鏡（ＡＦＭ）によって観察すると、図１２に示すように、やはり島状構造の形態になっていた。
【００７４】
次に、Ｐｂが他の元素に対して化学量論組成より１５％過剰であるＰＬＺＴ（９／６５／３５）用前駆体溶液を、ＰＬＴ（２８／１００）バッファ層を設けたサファイア基板へスピンコーティングにより塗布した。この塗布膜を形成した基板を加湿した酸素雰囲気中に置き、１０℃／ｓｅｃにて昇温して３００℃にて２分間保持の後、８０℃／ｓｅｃにて昇温して７５０℃に２分間保持した。最後に電気炉の電源を切り冷却し、膜厚９０ｎｍの第一層目のＰＬＺＴ（９／６５／３５）薄膜を固相エピタキシャル成長した。これをさらに５回繰り返すことにより総膜厚５４０ｎｍのエピタキシャルＰＬＺＴ（９／６５／３５）薄膜が形成された光導波路素子を得た。なお、最後の層を結晶化した後、１℃／秒の冷却速度で冷却を行った。
【００７５】
この光導波路素子のＸ線回折θ−２θパターンを調べたところ、ペロブスカイト単一相であり、各層の結晶学的関係は単一配向のＰＬＺＴ（１１０）／／ＰＬＴ（１１０）／／Ａｌ₂Ｏ₃（１１０２）であった。また、このエピタキシャルＰＬＺＴ（９／６５／３５）薄膜表面を高分解能ＳＥＭによって観察したところ、表面は極めて均一かつ平滑であり、粒界や細孔の全くみられない、コントラストの得られないほど鏡面状の表面であった。さらに、図１３に示すＡＦＭ解析の結果から、本実施例のエピタキシャルＰＬＺＴ（９／６５／３５）薄膜表面のＲａ表面粗さを同定すると、粗さはわずか１．２ｎｍであった。
【００７６】
次に、光導波路特性の評価を行った。プリズムカップリングによってレーザ光を本実施例のエピタキシャルＰＬＺＴ薄膜に導入し、光伝搬方向のＴＥ₀モードの散乱光強度分布を光ファイバーによって測定した。散乱光強度の対数と光伝搬距離の関係の傾きより、光伝搬損失を求めたところ６３３ｎｍの波長で７ｄＢ／ｃｍと優れた特性を示した。
【００７７】
また、ＴＥ₀モード及びＴＥ₁モードより屈折率を求めると、６３３ｎｍの波長で２．４９７とバルクと同等の屈折率を示し、高密度でペロブスカイト単一相であることが分かった。さらに、サファイア基板裏面にダイアモンドカッターで傷をつけ、へき開を行うことによって容易にレーザ光の入出射端面を形成することができた。
【００７８】
このように、本実施例によるエピタキシャルＰＬＺＴ薄膜は、極めて単結晶に近く、均一性に優れた光導波路として使用可能な薄膜であるとともに、光導波路素子としての加工も容易であった。
【００７９】
（実施例３）
サファイアＡｌ₂Ｏ₃（１１０２）単結晶基板上へ固相エピタキシャル成長によって膜厚１０ｎｍ、屈折率２．５７のエピタキシャルＰＬＴ（２０／１００）バッファ層を成長させ、さらに屈折率２．５６のエピタキシャルＰＺＴ（５２／４８）薄膜光導波路を成長させることによって、実施例１の場合と同様に、図１に示す構造の光導波路素子を作製した。
【００８０】
得られた光導波路素子の表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相であり、各層の結晶学的関係は単一配向のＰＬＺＴ（１１０）／／ＰＬＴ（１１０）／／Ａｌ₂Ｏ₃（１１０２）であった。
【００８１】
（実施例４）
サファイアＡｌ₂Ｏ₃（１１０２）単結晶基板上へ固相エピタキシャル成長によって膜厚１０ｎｍ、屈折率２．６３のエピタキシャルＰＺＴ（２０／８０）バッファ層を成長させ、さらに屈折率２．６２のエピタキシャルＰＺＴ（２５／７５）薄膜光導波路を成長させることによって、実施例１の場合と同様に、図１に示す構造の光導波路素子を作製した。
【００８２】
得られた光導波路素子の表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相であり、各層の結晶学的関係は単一配向のＰＬＺＴ（１１０）／／ＰＬＴ（１１０）／／Ａｌ₂Ｏ₃（１１０２）であった。
【００８３】
（実施例５）
サファイアＡｌ₂Ｏ₃（０００１）単結晶基板上へ固相エピタキシャル成長によって膜厚５ｎｍ、屈折率２．５０のエピタキシャルＰＬＴ（２８／１００）バッファ層を成長させ、さらに屈折率２．５０のエピタキシャルＰＬＺＴ（８／６５／３５）薄膜光導波路を成長させることによって、実施例１の場合と同様に、図１に示す構造の光導波路素子を作製した。
【００８４】
得られた光導波路素子の表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相であり、各層の結晶学的関係は単一配向のＰＬＺＴ（１１１）／／ＰＬＴ（１１１）／／Ａｌ₂Ｏ₃（０００１）であった。
【００８５】
（実施例６）
サファイアＡｌ₂Ｏ₃（０００１）単結晶基板上へＲｆマグネトロンスパッタリングによって膜厚１０ｎｍ、屈折率２．５０のエピタキシャルＰＬＴ（２８／１００）バッファ層を成長させ、さらに同じくＲｆマグネトロンスパッタリングによって屈折率２．５０のエピタキシャルＰＬＺＴ（８／６５／３５）薄膜光導波路を成長させることによって、実施例１の場合と同様に、図１に示す構造の光導波路素子を作製した。
【００８６】
得られた光導波路素子の表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相であり、各層の結晶学的関係は単一配向のＰＬＺＴ（１１１）／／ＰＬＴ（１１１）／／Ａｌ₂Ｏ₃（０００１）であった。
【００８７】
（実施例７）
ＭｇＯ（１００）単結晶基板上へ実施例１と同様に固相エピタキシャル成長によって膜厚１０ｎｍ、屈折率２．５０のエピタキシャルＰＬＴ（２８／１００）バッファ層を成長させ、さらに、屈折率２．５０のエピタキシャルＰＬＺＴ（８／６５／３５）薄膜光導波路を成長させることによって、実施例１の場合と同様に、図１に示す構造の光導波路素子を作製した。
【００８８】
得られた光導波路素子の表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相であり、各層の結晶学的関係は単一配向のＰＬＺＴ（００１）／／ＰＬＴ（００１）／／ＭｇＯ（１００）であった。
【００８９】
（実施例８）
ＭｇＯバッファ層をエピタキシャル成長したＧａＡｓ（１００）単結晶基板上へ、膜厚１０ｎｍ、屈折率２．５０のエピタキシャルＰＬＴ（２８／１００）バッファ層と屈折率２．５０のエピタキシャルＰＬＺＴ（８／６５／３５）薄膜光導波路を成長させることによって、実施例１の場合と同様に、図１に示す構造の光導波路素子を作製した。
【００９０】
ＧａＡｓ（１００）基板へのエピタキシャルＭｇＯバッファ層は、金属Ｍｇターゲット表面をＵＶレーザーパルスにより瞬間的に加熱し蒸着を行うエキシマレーザーデポジション法を用い、酸素雰囲気での反応性成膜によって３５０℃の基板温度で成長した。
【００９１】
次に、ＭｇＯバッファ層上へＰＬＴバッファ層をレーザーデポジション法によってその場エピタキシャル成長した後、実施例１と同様に固相エピタキシャル成長させてエピタキシャルＰＬＺＴ（８／６５／３５）薄膜光導波路を成長させた。
【００９２】
得られた光導波路素子の表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相であり、各層の結晶学的関係は単一配向のＰＬＺＴ（００１）／／ＰＬＴ（００１）／／ ＭｇＯ（１００）／／ＧａＡｓ（１００）であった。
【００９３】
（実施例９）
実施例８と同様の方法で、エピタキシャルＭｇＯバッファ層をＳｉ（１００）単結晶基板上へ設け、さらに膜厚１０ｎｍ、屈折率２．５７のエピタキシャルＰＬＴ（２０／１００）バッファ層と屈折率２．５６のエピタキシャルＰＺＴ（５２／４８）薄膜光導波路を成長させることによって、実施例１の場合と同様に、図１に示す構造の光導波路素子を作製した。
【００９４】
得られた光導波路素子の表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相であり、各層の結晶学的関係は単一配向のＰＺＴ（００１）／／ＰＬＴ（００１）／／ＭｇＯ（１００）／／Ｓｉ（１００）であった。
【００９５】
（実施例１０）
ＳｒＴｉＯ₃（１００）単結晶基板上へ、実施例１と同様に固相エピタキシャル成長によって膜厚１０ｎｍ、屈折率２．５０のエピタキシャルＰＬＴ（２８／１００）バッファ層を成長させ、さらに屈折率２．５０のエピタキシャルＰＬＺＴ（９／６５／３５）薄膜光導波路を成長させることによって、実施例１の場合と同様に、図１に示す構造の光導波路素子を作製した。
【００９６】
得られた光導波路素子の表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相であり、各層の結晶学的関係は単一配向のＰＬＺＴ（００１）／／ＰＬＴ（００１）／／ＳｒＴｉＯ₃（０００１）であった。
【００９７】
（実施例１１）
本実施例においては、サファイアＡｌ₂Ｏ₃（１１０２）単結晶基板１２上へ固相エピタキシによって屈折率２．５０、膜厚１０ｎｍのエピタキシャルＰＬＴ（２８／１００）からなる第１バッファ層としての第１強誘電体層１４を成長させ、次に屈折率２．５０、膜厚５００ｎｍのエピタキシャルＰＬＺＴ（９／６５／３５）からなる第２バッファ層としての第２強誘電体層１６を成長させ、さらに屈折率２．５６、膜厚８００ｎｍのエピタキシャルＰＺＴ（５２／４８）からなる薄膜光導波路としての第３強誘電体層１８を成長させることによって、図５に示す光導波路素子を作製した。
【００９８】
まず、無水酢酸鉛（Ｐｂ（ＣＨ₃ＣＯＯ）₂）、ランタンイソプロポキシド（Ｌａ（Ｏ−ｉ−Ｃ₃Ｈ₇）₃）、およびチタンイソプロポキシド（Ｔｉ（Ｏ−ｉ−Ｃ₃Ｈ₇）₄）を出発原料として用い、Ｐｂが他の元素に対して化学量論組成であるＰｂ：Ｌａ：Ｔｉ＝７２：２８：１００の割合となるように２−メトキシエタノールに溶解し、６時間の蒸留を行ったのち１８時間の還流を行い、最終的にＴｉ濃度で０．６ＭのＰＬＺＴ（２８／０／１００）用前駆体溶液を得た。さらに、この前駆体溶液を０．２μｍのフィルターを通してＡｌ₂Ｏ₃基板へスピンコーティングを行った。以上の操作はすべてＮ₂雰囲気中にて行った。
【００９９】
スピンコーティングの前に、基板は溶剤洗浄、ＨＣｌによるエッチング、脱イオン水によるリンスを行い、最後にＮ₂中にてエタノールのスピンコーティングによって乾燥した。次に、加湿Ｏ₂雰囲気中で１０℃／ｓｅｃにて昇温して３００℃にて２分間保持の後、１０℃／ｓｅｃにて昇温して６５０℃に３０分間保持し、最後に電気炉の電源を切り冷却した。
【０１００】
これにより膜厚１０ｎｍのＰＬＴ（２８／１００）第１バッファ層を固相エピタキシャル成長した。同様に形成したＰＬＴ（２８／０／１００）バッファ層の表面を高分解能走査型電子顕微鏡（ＳＥＭ）によって観察すると、図７に示すような島状構造の形態になっていた。
【０１０１】
次に、同様に無水酢酸鉛（Ｐｂ（ＣＨ₃ＣＯＯ）₂）、ランタンイソプロポキシド（Ｌａ（Ｏ−ｉ−Ｃ₃Ｈ₇）₃）、ジルコニウムイソプロポキシド（Ｚｒ（Ｏ−ｉ−Ｃ₃Ｈ₇）₄）、およびチタンイソプロポキシド（Ｔｉ（Ｏ−ｉ−Ｃ₃Ｈ₇）₄を出発原料として用い、Ｐｂが他の元素に対して化学量論組成であるＰｂ：Ｌａ：Ｚｒ：Ｔｉ＝９１：９：６５：３５の割合となるように２−メトキシエタノールに溶解し、６時間の蒸留を行ったのち１８時間の還流を行い、最終的にＺｒ＋Ｔｉ濃度で０．６ＭのＰＬＺＴ（９／６５／３５）用前駆体溶液を得た。
【０１０２】
さらに、この前駆体溶液を０．２μｍのフィルターを通してＰＬＴ（２８／１００）第１バッファ層を設けたＡｌ₂Ｏ₃基板へスピンコーティングを行った。以上の操作はすべてＮ₂雰囲気中にて行った。次に、加湿Ｏ₂雰囲気中で１０℃／ｓｅｃにて昇温して３５０℃にて２分間保持の後、１０℃／ｓｅｃにて昇温して６５０℃に２分間保持し、最後に電気炉の電源を切り冷却した。これにより膜厚１００ ｎｍのＰＬＺＴ（９／６５／３５）薄膜を固相エピタキシャル成長した。これをさらに４回繰り返すことにより総膜厚５００ｎｍのエピタキシャルＰＬＺＴ（９／６５／３５）第２バッファ層が得られた。
【０１０３】
次に、同様に無水酢酸鉛（Ｐｂ（ＣＨ₃ＣＯＯ）₂）、ジルコニウムイソプロポキシド（Ｚｒ（Ｏ−ｉ−Ｃ₃Ｈ₇）₄）、およびチタンイソプロポキシド（Ｔｉ（Ｏ−ｉ−Ｃ₃Ｈ₇）₄）を出発原料として用い、Ｐｂが他の元素に対して化学量論組成であるＰｂ：Ｚｒ：Ｔｉ＝１００：５２：４８の割合となるように２−メトキシエタノールに溶解し、６時間の蒸留を行ったのち１８時間の還流を行い、最終的にＺｒ＋Ｔｉ濃度で０．６ＭのＰＺＴ（５２／４８）用前駆体溶液を得た。さらに、この前駆体溶液を０．２μｍのフィルターを通してＰＬＺＴ（９／６５／３５）第２バッファ層を設けたＡｌ₂Ｏ₃基板へスピンコーティングを行った。以上の操作はすべてＮ₂雰囲気中にて行った。
【０１０４】
次に、加湿Ｏ₂雰囲気中で１０℃／ｓｅｃにて昇温して３５０℃にて２分間保持の後、１０℃／ｓｅｃにて昇温して６５０℃に２分間保持し、最後に電気炉の電源を切り冷却した。これにより膜厚１００ｎｍのＰＬＺＴ（９／６５／３５）薄膜を固相エピタキシャル成長した。これをさらに７回繰り返すことにより総膜厚８００ｎｍのエピタキシャルＰＺＴ（５２／４８）薄膜光導波路層が得られた。なお、最後の結晶化は６５０℃に３０分間保持することによって行い、最後に１℃／ｓｅｃの速度で冷却した。
【０１０５】
Ｘ線回折θ−２θパターンによると、結晶学的関係は単一配向のＰＺＴ（１１０）／／ＰＬＺＴ（１１０）／／ＰＬＴ（１１０）／／Ａｌ₂Ｏ₃（１１０２）の構造が得られた。本実施例のエピタキシャルＰＬＺＴ薄膜の表面は光学顕微鏡の観察では均一なために何も見えず、さらに高分解能ＳＥＭによって観察した結果も極めて均一かつ平滑であり、粒界や細孔の全くみられない、コントラストの得られないほど鏡面状の表面であった。
【０１０６】
光導波路特性の評価を行なうため、プリズムカップリングによって波長６３３ｎｍのレーザ光を本実施例のエピタキシャルＰＺＴ薄膜導波路に導入し、光伝搬方向の散乱光強度分布を光ファイバーによって測定した。散乱光強度の対数と光伝搬距離の関係の傾きより、光伝搬損失を求めたところ優れた特性を示した。
【０１０７】
なお、本実施例では波長６３３ｎｍ用の構造としたが、波長１３１０ｎｍや１５５０ｎｍなどの長波長用の構造も、本発明に従って波長６３３ｎｍ用の構造と比較して第２バッファ層と薄膜光導波路層を厚くすれば同様に構成できることはいうまでもない。
【０１０８】
さらに、サファイア基板裏面にダイアモンド・カッターで傷をつけ、へき開を行うことによって容易にレーザ光の入出射端面を形成することができた。このように、本実施例によるエピタキシャルＰＬＺＴ薄膜は、極めて単結晶に近く、均一性に優れた光導波路として使用可能な薄膜であるとともに、光導波路素子としての加工も容易であった。
【０１０９】
（実施例１２）
本実施例においては、実施例１１と同様に固相エピタキシによってサファイアＡｌ₂Ｏ₃（１１０２）単結晶基板１２上へ屈折率２．５０、膜厚１０ ｎｍのエピタキシャルＰＬＴ（２８／１００）からなる第１バッファ層としての第１強誘電体層１４を成長させ、次に屈折率２．４８、膜厚６００ｎｍのエピタキシャルＰＬＺＴ（９／８０／２０）からなる第２バッファ層としての第２強誘電体層１６を成長させ、さらに屈折率２．５０、膜厚１４００ｎｍのエピタキシャルＰＬＺＴ（９／６５／３５）からなる薄膜光導波路としての第３強誘電体層１８を成長させることによって、図５に示す構造の光導波路素子を作製した。
【０１１０】
まず、ＰＬＴ（２８／１００）用前駆体溶液をＡｌ₂Ｏ₃基板へスピンコーティングを行い、加湿Ｏ₂雰囲気中で１０℃／ｓｅｃにて昇温して３００℃にて２分間保持の後、１０℃／ｓｅｃにて昇温して６５０℃に３０分間保持し、最後に電気炉の電源を切り冷却した。これにより膜厚１０ｎｍのＰＬＴ（２８／１００）第１バッファ層を固相エピタキシャル成長した。
【０１１１】
次に、Ｐｂが他の元素に対して化学量論組成より１５％過剰であるＰＬＺＴ（９／８０／２０）用前駆体溶液をＰＬＴ（２８／１００）第１バッファ層を設けたＡｌ₂Ｏ₃基板へスピンコーティングを行い、加湿Ｏ₂雰囲気中で１０℃／ｓｅｃにて昇温して３００℃にて２分間保持の後、８０℃／ｓｅｃにて昇温して７５０℃に２分間保持し、最後に電気炉の電源を切り冷却した。これにより膜厚１００ ｎｍの第一層目のＰＬＺＴ（９／８０／２０）薄膜を固相エピタキシャル成長した。これをさらに５回繰り返すことにより総膜厚６００ ｎｍのエピタキシャルＰＬＺＴ（９／８０／２０）第２バッファ層が得られた。
【０１１２】
次に、Ｐｂが他の元素に対して化学量論組成より１５％過剰であるＰＬＺＴ（９／６５／３５）用前駆体溶液をＰＬＺＴ（９／８０／２０）第２バッファ層を設けたＡｌ₂Ｏ₃基板へスピンコーティングを行い、加湿Ｏ₂雰囲気中で１０℃／ｓｅｃにて昇温して３００℃にて２分間保持の後、８０℃／ｓｅｃにて昇温して７５０℃に２分間保持し、最後に電気炉の電源を切り冷却した。これにより膜厚１００ｎｍの第一層目のＰＬＺＴ（９／６５／３５）薄膜を固相エピタキシャル成長した。これをさらに１３回繰り返すことにより総膜厚１４００ｎｍのエピタキシャルＰＬＺＴ（９／６５／３５）薄膜光導波路層が得られた。最後の層の結晶化の後、１℃／秒の冷却速度で冷却を行った。
【０１１３】
Ｘ線回折θ−２θパターンによると、結晶学的関係は単一配向のＰＬＺＴ（１１０）／／ＰＬＺＴ（１１０）／／ＰＬＴ（１１０）／／Ａｌ₂Ｏ₃（１１０２）の構造が得られた。本実施例のエピタキシャルＰＬＺＴ薄膜の表面を高分解能ＳＥＭによって観察した所、表面は極めて均一かつ平滑であり、粒界や細孔の全くみられない、コントラストの得られないほど鏡面状の表面であった。
【０１１４】
光導波路特性の評価を行なうため、プリズムカップリングによって波長６３３ｎｍのレーザ光を本実施例のエピタキシャルＰＬＺＴ薄膜に導入し、光伝搬方向の散乱光強度分布を光ファイバーによって測定した。散乱光強度の対数と光伝搬距離の関係の傾きより、光伝搬損失を求めたところ優れた特性を示した。さらに、サファイア基板裏面にダイアモンドカッターで傷をつけ、へき開を行うことによって容易にレーザ光の入出射端面を形成することができた。このように、本実施例によるエピタキシャルＰＬＺＴ薄膜は、極めて単結晶に近く、均一性に優れた光導波路として使用可能な薄膜であるとともに、光導波路素子としての加工も容易であった。
（実施例１３）
本実施例においては、実施例１１とほぼ同様にして、サファイアＡｌ₂Ｏ₃（１１０２）単結晶基板１２上へ固相エピタキシによって屈折率２．７１、膜厚４０ｎｍのエピタキシャルＰｂＴｉＯ₃からなる第１バッファ層としての第１強誘電体層１４を成長させ、次に屈折率２．４９、膜厚６００ｎｍのエピタキシャルＰＺＴ（８５／１５）からなる第２バッファ層としての第２強誘電体層１６を成長させ、さらに、屈折率２．５６、膜厚７００ｎｍのエピタキシャルＰＺＴ（５２／４８）からなる薄膜光導波路としての第３強誘電体層１８を成長させることによって、図５に示す構造の光導波路素子を作製した。表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相で結晶学的関係は単一配向のＰＺＴ（１１０）／／ＰＺＴ（１１０）／／ＰＺＴ（１１０）／／Ａｌ₂Ｏ₃（１１０２）であった。
【０１１５】
（実施例１４）
本実施例においては、実施例１１とほぼ同様にして、サファイアＡｌ₂Ｏ₃（１１０２）単結晶基板１２上へ固相エピタキシによって屈折率２．６３、膜厚５ｎｍのエピタキシャルＰＺＴ（２０／８０）からなる第１バッファ層としての第１強誘電体層１４を成長させ、次に屈折率２．４９、膜厚５００ｎｍののエピタキシャルＰＺＴ（８５／１５）からなる第２バッファ層としての第２強誘電体層１６を成長させ、さらに屈折率２．５６、膜厚７００ｎｍののエピタキシャルＰＺＴ（５２／４８）からなる薄膜光導波路としての第３強誘電体層１８を成長させることによって、図５に示す構造の光導波路素子を作製した。表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相で結晶学的関係は単一配向のＰＺＴ（１１０）／／ＰＺＴ（１１０）／／ＰＺＴ（１１０）／／Ａｌ₂Ｏ₃（１１０２）であった。
【０１１６】
（実施例１５）
本実施例においては、サファイアＡｌ₂Ｏ₃（０００１）単結晶基板１２上へＲｆマグネトロンスパッタリングによって屈折率２．５０、膜厚１０ｎｍのエピタキシャルＰＬＴ（２８／１００）からなる第１バッファ層としての第１強誘電体層１４を６５０℃で成長させ、次に屈折率２．４８、膜厚６００ｎｍのエピタキシャルＰＬＺＴ（９／８０／２０）からなる第２バッファ層としての第２強誘電体層１６を成長させ、さらに屈折率２．５０、膜厚１４００ｎｍのエピタキシャルＰＬＺＴ（９／６５／３５）からなる薄膜光導波路としての第３強誘電体層１８を成長させることによって、図５に示す構造の光導波路素子を作製した。Ｘ線回折θ−２θパターンによると、結晶学的関係は単一配向のＰＬＺＴ（１１１）／／ＰＬＺＴ（１１１）／／ＰＬＴ（１１１）／／Ａｌ₂Ｏ₃（０００１）の構造が得られた。
【０１１７】
（実施例１６）
本実施例においては、実施例１１と同様に、ＭｇＯ（１００）単結晶基板上１２へ固相エピタキシによって屈折率２．５０、膜厚１０ｎｍのエピタキシャルＰＬＴ（２８／１００）からなる第１バッファ層としての第１強誘電体層１４を成長させ、次に屈折率２．４８、膜厚６００ｎｍのエピタキシャルＰＬＺＴ（９／８０／２０）からなる第２バッファ層としての第２強誘電体層１６を成長させ、さらに屈折率２．５０、膜厚１４００ｎｍのエピタキシャルＰＬＺＴ（９／６５／３５）からなる薄膜光導波路としての第３強誘電体層１８を成長させることによって、図５に示す構造の光導波路素子を作製した。Ｘ線回折θ−２θパターンによると、結晶学的関係は単一配向のＰＬＺＴ（１１１）／／ＰＬＺＴ（００１）／／ＰＬＴ（００１）／／ＭｇＯ（１００）の構造が得られた。
【０１１８】
（実施例１７）
本実施例においては、ＭｇＯバッファ層をエピタキシャル成長したＧａＡｓ（１００）単結晶基板１２上へ、屈折率２．５０、膜厚１０ｎｍのエピタキシャルＰＬＴ（２８／１００）からなる第１バッファ層としての第１強誘電体層１４と、屈折率２．４８、膜厚６００ｎｍのエピタキシャルＰＬＺＴ（８／８０／２０）からなる第２バッファ層としての第２強誘電体層１６と、屈折率２．５０、膜厚１４００ｎｍのエピタキシャルＰＬＺＴ（８／６５／３５）からなる薄膜光導波路としての第３強誘電体層１８を成長させることによって光導波路素子を作製した。
【０１１９】
ＧａＡｓ（１００）基板へのエピタキシャルＭｇＯバッファ層は、金属Ｍｇターゲット表面をＵＶレーザーパルスにより瞬間的に加熱し蒸着を行うエキシマレーザーデポジション法を用い、Ｏ₂雰囲気での反応性成膜によって３５０℃の基板温度で成長した。さらに、ＭｇＯバッファー層上へＰＬＴ第１バッファ層、ＰＬＺＴ第２バッファ層、およびＰＬＺＴ光導波路層をレーザーデポジション法によってその場エピタキシャル成長させた。表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相で結晶学的関係は単一配向のＰＬＺＴ（００１）／／ＰＬＺＴ（００１）／／ＰＬＴ（００１）／／ＭｇＯ（１００）／／ＧａＡｓ（１００）の構造が得られた。
【０１２０】
（実施例１８）
本実施例においては、実施例１７と同様の方法で、エピタキシャルＭｇＯバッファ層をＳｉ（１００）単結晶基板１２上へ設け、さらに屈折率２．５７、膜厚１０ｎｍのエピタキシャルＰＬＴ（２０／１００）からなる第１バッファ層としての第１強誘電体層１４と、屈折率２．５０、膜厚５００ｎｍのエピタキシャルＰＬＺＴ（８／６５／３５）からなる第２バッファ層としての第２強誘電体層１６と、屈折率２．５６、膜厚８００ｎｍのエピタキシャルＰＺＴ（５２／４８）からなる薄膜光導波路としての第３強誘電体層１８を成長させることによって光導波路素子を作製した。表面は極めて均一かつ平滑であり、Ｘ線回折θ−２θパターンによると、ペロブスカイト単一相で結晶学的関係は単一配向のＰＺＴ（００１）／／ＰＬＺＴ（００１）／／ＰＬＴ（００１）／／ＭｇＯ（１００）／／Ｓｉ（１００）の構造が得られた。
【０１２１】
（実施例１９）
本実施例においては、実施例１１と同様に、ＳｒＴｉＯ₃（１００）単結晶基板１２上へ固相エピタキシによって屈折率２．５０、膜厚１０ｎｍのエピタキシャルＰＬＺＴ（２８／０／１００）からなる第１バッファ層としての第１強誘電体層１４を成長させ、次に屈折率２．４８、膜厚６００ｎｍのエピタキシャルＰＬＺＴ（９／８０／２０）からなる第２バッファ層としての第２強誘電体層１６を成長させ、さらに屈折率２．５０、膜厚１４００ｎｍのエピタキシャルＰＬＺＴ（９／６５／３５）からなる薄膜光導波路としての第３強誘電体層１８を成長させることによって作製した。Ｘ線回折θ−２θパターンによると、結晶学的関係は単一配向のＰＬＺＴ（００１）／／ＰＬＺＴ（００１）／／ＰＬＴ（００１）／／ＳｒＴｉＯ₃（０００１）の構造が得られた。
【０１２２】
【発明の効果】
本発明によれば、組成が均一であり、表面が光学的に平滑であり、かつ、単結晶状のエピタキシャルＰＬＺＴ強誘電体薄膜を備えた光導波路素子が提供される。また、組成を安定に制御しつつ、表面が光学的に平滑であり、かつ、単結晶状のエピタキシャルＰＬＺＴ強誘電体薄膜を形成することができる光導波路素子の製造方法が提供される。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態に係る光導波路素子の層構成を示す概略断面図である。
【図２】Ｐｂ_1-x Ｌａ_x（Ｚｒ_yＴｉ_1-y）_1-x/4Ｏ₃の相図である。
【図３】本発明の光導波路素子の作製工程（第１強誘電体層作製工程）を示す模式断面図である。
【図４】基板上にバッファ層を深く形成した場合の模式断面図である。
【図５】本発明の第２の実施の形態に係る光導波路素子の層構成を示す概略断面図である。
【図６】過剰Ｐｂ量と昇温速度の関係を示すグラフである。
【図７】実施例１のサファイア基板上に設けられたＰＬＴバッファ層表面のＳＥＭ写真である。
【図８】実施例１の光導波路素子のＸ線回折パターンを示す図である。
【図９】実施例１の光導波路素子表面のＳＥＭ写真である。
【図１０】比較例１の光導波路素子のＸ線回折パターンを示す図である。
【図１１】比較例１の光導波路素子の光学顕微鏡写真である。
【図１２】実施例２のサファイア基板上に設けられたＰＬＴバッファ層表面のＡＦＭ写真である。
【図１３】実施例２の光導波路素子表面のＡＦＭ写真である。
【図１４】基板上に形成された多結晶薄膜の模式断面図である。
【図１５】基板上に形成された細孔を含むエピタキシャル薄膜の模式断面図である。
【図１６】基板上に形成されたパイロクロア相が残留する不均一なエピタキシャル薄膜の模式断面図である。
【符号の説明】
１２ 単結晶基板
１４ 第１強誘電体層
１６ 第２強誘電体層
１８ 第３強誘電体層
１００ 基板
１０２ 強誘電体薄膜（ペレブスカイト相）
１０４ パイロクロア相[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical waveguide device and a method for manufacturing the optical waveguide device, and more specifically, a PLZT-based optical waveguide device that can be used as an optical device such as an optical switch, a light modulation device, a light deflection device, a second harmonic device, and the like. It relates to the manufacturing method.
[0002]
[Prior art]
Optical waveguide elements that use oxide ferroelectrics for thin film optical waveguides have many characteristics such as second harmonic elements, optical switches, and light modulation elements due to the excellent nonlinear optical effect and electro-optical effect of ferroelectrics. Application to this field is being studied. Conventionally, these elements using oxide ferroelectrics are LiNbO. _Three Or LiTaO _Three The optical waveguide structure fabricated by thermal diffusion of Ti and ion exchange of protons has been used for single crystal wafers, but higher efficiency of the second harmonic element and lower drive voltage of the optical switch, light modulation element, etc. In addition, for the reason that an optical integrated device can be manufactured, a thin film optical waveguide structure in which a ferroelectric thin film is heteroepitaxially grown on a single crystal substrate made of different materials has been studied. However, in order to apply thin-film optical waveguides fabricated by heteroepitaxial growth to second harmonic elements, optical switches, optical modulation elements, etc. It is indispensable to produce a thin ferroelectric thin film.
[0003]
LiNbO by the vapor phase growth method such as RF-magnetron sputtering method, ion beam sputtering method, laser ablation method, MOCVD method (metal organic vapor phase growth method). _Three LiTaO _Three , KNbO _Three Etc., BaTiO _Three , PbTiO _Three , Pb _1-x La _x (Zr _1-y Ti _y ) _{1-x / 4} O _Three (PLZT), Bi _Four Ti _Three O ₁₂ A number of such epitaxial ferroelectric thin films are formed on an oxide single crystal substrate. However, all the vapor phase growth methods have problems that the apparatus to be used is very expensive, the composition control is difficult and the composition is not uniform, and the surface property of the obtained thin film is poor. Therefore, a practical single crystal ferroelectric thin film cannot be obtained.
[0004]
Japanese Examined Patent Publication No. 62-27482 discloses a thin film forming method called a sol-gel method, in which a ferroelectric thin film is obtained by applying an organometallic compound to a substrate and then heating it. A ferroelectric thin film having a thickness of 200 nm can be obtained. By using this sol-gel method, it is possible to precisely control the chemical composition, lower the temperature of the process, make the thin film uniform, and reduce the equipment cost. However, even if baking is performed at a high temperature, the ferroelectric thin film 102 formed on the substrate 100 by the sol-gel method is a polycrystalline thin film as shown in FIG. Scattering is too large to be used as an optical waveguide. Polycrystalline thin films cannot fully utilize the physical properties of ferroelectrics based on polarization. Even if they are composed of ferroelectric thin films formed by sol-gel methods for nonvolatile memory and FET optical waveguides Device characteristics cannot be obtained.
[0005]
The inventor conducted an improvement study on a method for producing a ferroelectric thin film by a sol-gel method, and as shown in K. Nashimoto and MJ Cima, Mater. Lett. 10, 7, 8 (1991) 348. Lithium and Nb ethoxides (LiOC), which are organometallic compounds ₂ H _Five And Nb (OC ₂ H _Five ) _Five ) Is applied to a sapphire single crystal substrate, and then heated to form a ferroelectric thin film LiNbO on the sapphire single crystal substrate. _Three Was found to grow epitaxially.
[0006]
In the process of this epitaxial growth, Li [Nb (OC ₂ H _Five ) ₆ When water is added to the precursor solution, after firing, LiNbO _Three The thin film changed from an oriented film to a polycrystalline film, but when the moisture content was zero and firing with a precursor that did not hydrolyze, the LiNbO film became a temperature of only 400 ° C. _Three The thin film could be epitaxially grown, and a thin film having a single crystal shape and a smooth surface could be obtained. However, epitaxial LiNbO fired at a temperature of 400 ° C. _Three When the ferroelectric thin film was observed with a TEM (transmission electron microscope), the cross section of the thin film contained pores with a diameter of several nanometers, the density was not sufficiently high, and the refractive index was not comparable to that of a single crystal.
[0007]
Next, when this method is used for firing at a high temperature close to 700 ° C., the polycrystalline film and the orientation film are greatly reduced in density by crystal grain growth and pore diameter growth, but epitaxial LiNbO _Three Even after crystal grain growth, the thin film has extremely large sub-grains (a crystal grain structure but a structure in which the orientation of each crystal grain is substantially or completely aligned) compared to a polycrystalline film and an oriented film. It was density. The polycrystalline film and the orientation film became opaque after high-temperature firing, whereas the epitaxial film showed a higher refractive index than the polycrystalline film and the orientation film and was substantially transparent. As described above, the ferroelectric thin film fired at a temperature of 700 ° C. is a single crystal, has a very large sub-grain compared to a polycrystalline film and an oriented film, has a high density, and a refractive index. However, when the cross section of the thin film was observed with a TEM, the LiNbO formed on the substrate 100 as shown in FIG. _Three The ferroelectric thin film 102 contained some pores, the surface was not optically smooth, and the transparency of the film was not sufficient.
[0008]
On the other hand, Pb _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three The (PLZT) -based material has a very large electro-optic coefficient among ferroelectric materials, and LiNbO has a composition exhibiting a primary electro-optic coefficient. _Three It is known that the composition showing the second-order electro-optic coefficient has a maximum level value among the ferroelectric materials, and the application is most expected for the ferroelectric. One of the materials (GH Haertling and CE Land, J. Amer. Ceram. Soc. Vol. 54. p.1 (1971)).
[0009]
For this reason, many attempts have been made to reduce the thickness of PLZT by vapor deposition such as sputtering. _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three (PLZT) 0 <x <20, 20 <y <100, particularly Pb which is one of the compositions exhibiting the best electro-optical properties _0.91 La _0.09 (Zr _0.65 Ti _0.35 ) _0.98 O _Three It is difficult to reduce the thickness of (PLZT (9/65/35)) without impairing its electro-optical characteristics, and there has been no example of using PLZT in this range for a thin-film optical waveguide. In PLZT having the above composition range, the pyrochlore phase which is a non-ferroelectric phase is stable, and the pyrochlore phase tends to remain at the time of crystallization. Only a non-uniform epitaxial thin film having a structure surrounded by the phase 104 can be obtained. For this reason, it is considered that the electro-optical characteristics are deteriorated. The pyrochlore phase 104 remains in the same ABO as PLZT. _Three SrTiO having a perovskite structure and good lattice matching _Three This was also observed when PLZT (9/65/35) was grown on the substrate, and it was impossible to avoid deterioration of the film properties.
[0010]
Temporarily SrTiO _Three Even if it is possible to epitaxially grow a PLZT thin film having a uniform perovskite phase on a substrate, SrTiO _Three In this case, only a substrate having a size of about 1 inch can be manufactured, and since there is no cleavage, SrTiO _Three Even if a PLZT thin film is provided on the substrate, the end face must be mechanically polished in order to use it as an optical waveguide device, and the process is complicated and a lot of production time is required.
[0011]
On the other hand, for sapphire and MgO, it is possible to obtain a substrate having a size of several inches. Further, since a sapphire substrate, MgO substrate, or a GaAs substrate or Si substrate using MgO as a buffer layer has a cleavage property, an end face can be easily formed by cleavage, and a significant cost reduction can be expected. Furthermore, if a PLZT thin film can be provided on these substrates, monolithic integration with semiconductor devices becomes possible. Therefore, in order to enable a wider range of applications, it is necessary to epitaxially grow a PLZT thin film having a perovskite phase on a substrate such as sapphire or MgO.
[0012]
However, when a substrate having a non-perovskite structure such as sapphire is used, extremely significant pyrochlore phase remains. That is, ABO such as sapphire and MgO _Three It is extremely difficult to epitaxially grow a PLZT thin film having a uniform perovskite phase on a surface having no type perovskite structure.
[0013]
As described above, heteroepitaxial growth of a single crystal ferroelectric thin film having a uniform composition is generally difficult, and an optical waveguide device having an epitaxial PLZT thin film optical waveguide having a uniform perovskite phase has not yet been put into practical use.
[0014]
[Problems to be solved by the invention]
The present invention has been made in view of the above situation in the prior art, and an object of the present invention is a single crystal epitaxial PLZT ferroelectric thin film having a uniform composition, an optically smooth surface, and the like. It is providing the optical waveguide element provided with. Another object of the present invention is to produce an optical waveguide device capable of forming a monocrystalline epitaxial PLZT ferroelectric thin film having a surface that is optically smooth while stably controlling the composition. It is to provide a method.
[0015]
[Means for Solving the Problems]
The present inventors have intensively studied to improve the crystal phase uniformity of the PLZT ferroelectric thin film, and have completed the present invention.
[0016]
An optical waveguide device of the present invention is provided on a single crystal substrate and the single crystal substrate. The Pb with 0 <x <0.30 and 0 <y <0.20 _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase A first ferroelectric layer and a direct lamination on the first ferroelectric layer; 0 Pb in the range of <x <0.20, 0.20 <y <1.0 _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase And a second ferroelectric layer.
[0017]
When the second ferroelectric layer is used as an optical waveguide, it is preferable that a difference in refractive index between the first ferroelectric layer and the second ferroelectric layer is 0.05 or less.
[0018]
An optical waveguide device of the present invention is provided on a single crystal substrate and the single crystal substrate. The Pb in the range of 0 <x <0.30 and 0 <y <0.20 _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase A first ferroelectric layer and a direct lamination on the first ferroelectric layer; The Pb in the range of 0 <x <0.20, 0.20 <y <1.0 _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase A second ferroelectric layer and a refractive index greater than that of the second ferroelectric layer provided on the second ferroelectric layer; No Pb in the range of 0 <x <0.20, 0.20 <y <1.0 _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase And a third ferroelectric layer.
[0019]
When a third ferroelectric layer is further provided on the second ferroelectric layer, and the third ferroelectric layer is used as an optical waveguide, the second ferroelectric layer, the third ferroelectric layer, The refractive index difference is preferably 0.01 or more.
[0020]
The film thickness of the first ferroelectric layer is preferably 1 nm to 40 nm. Further, as the single crystal substrate, sapphire (Al ₂ O _Three ), Magnesium oxide (MgO), a semiconductor having a magnesium oxide (MgO) layer on its surface, and SrTiO _Three Any of these can be used.
[0021]
The method for manufacturing an optical waveguide device of the present invention includes a Pb in a range of 0 <x <0.30 and 0 <y <0.20 on a single crystal substrate. _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase First ferroelectric layer The A first ferroelectric layer forming step to be formed, and a Pb in a range of 0 <x <0.20 and 0.20 <y <1.0 are directly laminated on the first ferroelectric layer. _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase Second ferroelectric layer The And a second ferroelectric layer forming step to be formed.
[0022]
Further, Pb in the range of 0 <x <0.20, 0.20 <y <1.0, which has a refractive index larger than that of the second ferroelectric layer, on the second ferroelectric layer. _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase Third ferroelectric layer The A third ferroelectric layer forming step to be formed is added to the above two steps.
[0023]
In this manufacturing method, the first ferroelectric layer, the second ferroelectric layer, and the third ferroelectric layer are coated with a ferroelectric precursor made of an organometallic compound to form a thin film, It may be formed by repeatedly performing a pyrolysis step of thermally decomposing the thin film and a crystallization step of raising the temperature of the thin film after pyrolysis to a crystal growth temperature and solid-phase epitaxial growth one or more times. preferable.
[0024]
The organometallic compound as the coating material is Pb. _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three It is preferable to contain Pb in excess of the stoichiometric composition, and the organometallic compound is preferably obtained by mixing or reacting two or more compounds selected from metal alkoxides and metal salts.
[0025]
Further, in the crystallization step, when the temperature is raised to the crystal growth temperature, it is preferable to raise the temperature range of at least 350 to 450 ° C. at a rate of temperature increase of 10 to 500 ° C./second, Is preferably 600 to 800 ° C.
[0026]
Furthermore, it is preferable that the thermal decomposition step and / or the crystallization step be performed in an atmosphere containing oxygen.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail based on specific embodiments.
(First embodiment)
As shown in FIG. 1, the optical waveguide device according to the first embodiment of the present invention is easy to form a perovskite single-phase epitaxial film on a single crystal substrate 12 where a pyrochlore phase is difficult to form. Pb in the range of x <0.30, 0 <y <0.20 _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase After the first ferroelectric layer 14 is provided as a buffer layer, the electro-optical characteristics are excellent on the first ferroelectric layer 14. The In the range of 0 <x <0.20, 0.20 <y <1.0 P b _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase The second ferroelectric layer 16 is formed as an optical waveguide layer.
[0029]
FIG. 2 shows a phase diagram of PLZT. A range of 0 <x <0.30 and 0 <y <0.20 is indicated by a horizontal line, and a range of 0 <x <0.20 and 0.20 <y <1.0 is indicated by a vertical line.
[0030]
In the first embodiment, before forming the second ferroelectric layer 16 having excellent electro-optical characteristics, epitaxial Pb having a composition range of 0 <x <0.30 and 0 <y <0.20 is formed. _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three A first ferroelectric layer 14 made of (PLZT) is epitaxially grown in advance on the surface of the single crystal substrate 12. In PLZT having this composition range, it is difficult to form a pyrochlore layer and epitaxial growth of a perovskite single phase can be easily performed.
[0031]
As shown in FIG. 3, the film thickness of the first ferroelectric layer is preferably 1 nm to 40 nm so that the crystal grains are separated into islands. If the film thickness of the first ferroelectric layer 14 is too thick, a deep groove is formed in the crystal grain boundary as shown in FIG. 4, and it becomes difficult to fill the groove.
[0032]
Next, Pb in the range of 0 <x <0.20 and 0.20 <y <1.0 is formed on the first ferroelectric layer 14. _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three (PLZT) Perovskite single phase When the second ferroelectric layer 16 is epitaxially grown, even if the crystal grains of the first ferroelectric layer 14 are separated into islands, it is possible to fill the gap without creating a gap between the islands. The surface of the second ferroelectric layer 16 is smooth.
[0033]
Further, Pb in the range of 0 <x <0.20 and 0.20 <y <1.0 used for the second ferroelectric layer 16 is used. _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three (PLZT) usually has a composition in which it is difficult to grow a perovskite single phase, but the second ferroelectric layer 16 grows on the first ferroelectric layer 14 having the same crystal structure and composition. Thus, epitaxial growth as a single perovskite phase is possible without the formation of a pyrochlore layer.
[0034]
The film thickness of the second ferroelectric layer 16 is preferably from 100 nm to 10000 nm in terms of being thicker than the cut-off film thickness of the optical waveguide mode and having a single mode or an appropriate number of modes.
[0035]
The refractive index of the second ferroelectric layer 16 which is also an optical waveguide is required to prevent light scattering at the interface between the first ferroelectric layer 14 and the second ferroelectric layer 16, so that the first ferroelectric layer The refractive index of the layer 14 is preferably the same or substantially the same, and the difference in refractive index between the first ferroelectric layer 14 and the second ferroelectric layer 16 is preferably 0.05 or less, and 0.01 or less. It is more preferable.
[0036]
Pb _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three In (PLZT), the refractive index increases as y decreases, while the refractive index decreases as x increases. For this reason, the refractive index can be adjusted by setting the amounts of x and y to appropriate values.
(Second Embodiment)
In the optical waveguide device according to the second embodiment of the present invention, as shown in FIG. 5, it is difficult to form a pyrochlore phase on the single crystal substrate 12, and a perovskite single phase epitaxial film can be easily obtained. Ru Pb in the range of 0 <x <0.30 and 0 <y <0.20 _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase After providing the first ferroelectric layer 14 as the first buffer layer , Pb in the range of 0 <x <0.20, 0.20 <y <1.0 _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase A second ferroelectric layer 16 is provided as a second buffer layer. On the second ferroelectric layer 16, it has excellent electro-optic characteristics and has a refractive index higher than that of the second ferroelectric layer 16. But big No Pb in the range of 0 <x <0.20, 0.20 <y <1.0 _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three Consist of Perovskite single phase The third ferroelectric layer 18 is formed as an optical waveguide layer.
[0037]
Also in the second embodiment, before forming the second ferroelectric layer 16, the first ferroelectric layer made of PLZT having a composition range in which the pyrochlore layer is difficult to form and the perovskite single phase epitaxial growth is easy. 14 is epitaxially grown on the surface of the single crystal substrate 12 in the same manner as in the first embodiment, and the second ferroelectric layer 16 having a smooth surface is formed as a perovskite single phase without generating a pyrochlore layer. Epitaxial growth is possible.
[0038]
In the second embodiment, the second ferroelectric layer 16 provided between the first ferroelectric layer 14 and the third ferroelectric layer 18 which is an optical waveguide is a third optical waveguide. It is provided as a second buffer layer that isolates light propagating through the ferroelectric layer 18 from the first ferroelectric layer 14.
[0039]
As in the first embodiment, the film thickness of the first ferroelectric layer 14 is preferably 1 nm to 40 nm so that the crystal grains are separated into islands. The film thickness of the second ferroelectric layer 16 is appropriately determined according to the film thickness of the first ferroelectric layer 14, but the first ferroelectric layer 14 and the third ferroelectric layer 18 are optically coupled. In order to separate, it is preferable to set it as 100 nm to 10000 nm. The film thickness of the third ferroelectric layer 18 is preferably 100 nm to 10000 nm from the viewpoint of being thicker than the cut-off film thickness of the optical waveguide mode and having a single mode or an appropriate number of modes.
[0040]
The refractive index of the third ferroelectric layer 18 that is also an optical waveguide is used to eliminate the influence of light scattering due to the refractive index distribution between the first ferroelectric layer 14 and the second ferroelectric layer 16 having an island structure. In addition, the refractive index of the second ferroelectric layer 16 needs to be larger than the refractive index of the second ferroelectric layer 16, and the refractive index difference between the second ferroelectric layer 16 and the third ferroelectric layer 18 is 0.001 or more. Preferably, 0.01 or more is more preferable.
[0041]
In the first and second embodiments, the optical waveguide element is constituted by the single crystal substrate, the buffer layer, and the optical waveguide. However, in order to reduce light scattering and light absorption by the upper electrode, the optical waveguide element is used. Another ferroelectric layer may be provided as a cladding layer on the road. Moreover, you may provide two or more optical waveguide layers as needed.
[0042]
As a material of the single crystal substrate 12 of the present invention, ZrO ₂ , Y ₂ O _Three 8% -ZrO ₂ , MgO, MgAl ₂ O _Four , Al ₂ O _Three ZnO, Al-doped ZnO, In ₂ O _Three , RuO ₂ ZnGa ₂ O _Four , CdGa ₂ O _Four , CdGa ₂ O _Four , Mg ₂ TiO _Four MgTi ₂ O _Four , SrTiO _Three Nb-doped SrTiO _Three La-doped SrTiO _Three , BaTiO _Three , BaZrO _Three LaAlO _Three LiNbO _Three LiTaO _Three , BaPbO _Three , SrRuO _Three , YBa ₂ Cu _Three O _7-x , SrVO _Three LaNiO _Three , La _0.5 Sr _0.5 CoO _Three Oxides, etc., and single semiconductors such as Si, Ge, and diamond provided on the surface thereof, AlAs, AlSb, AlP, GaAs, GaSb, InP, InAs, InSb, AlGaP, AlLnP, AlGaAs, Examples include III-V compound semiconductors such as AlInAs, AlAsSb, GaInAs, GaInSb, GaAsSb, and InAsSb, and II-VI compound semiconductors such as ZnS, ZnSe, ZnTe, CaSe, CdTe, HgSe, HgTe, and CdS. . SrTiO from the point of thin film quality _Three Nb-doped SrTiO _Three La-doped SrTiO _Three In addition, from the viewpoint of large area and cleavage, Al ₂ O _Three MgO, MgO layer / Si, MgO layer / GaAs are more preferable.
[0043]
The first ferroelectric layer 14, the second ferroelectric layer 16, and the third ferroelectric layer 18 of the present invention are suitable for the formation of a film having a smooth surface. It is preferable to form by the used solid phase epitaxial growth. Specifically, a coating process in which a ferroelectric precursor made of an organometallic compound is applied to form a thin film, a thermal decomposition process in which the thin film is pyrolyzed, and a temperature of the pyrolyzed thin film is raised to a crystal growth temperature. The crystallization step for solid phase epitaxial growth is preferably carried out by repeating the process one or more times.
[0044]
First, a ferroelectric precursor made of an organometallic compound is applied to form a thin film (application process).
[0045]
The metal organic compound is selected from a metal alkoxide or a metal salt which is a reaction product of a metal of Pb, La, Zr, and Ti and an organic compound, preferably an organic compound having a boiling point of 80 ° C. or higher at normal pressure. .
[0046]
As a ratio of Pb, La, Zr, and Ti, Pb is different from other elements in terms of Pb. _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three It is effective to add in excess of the stoichiometric composition, and it is desirable to add 5 at% (5 mol%) or more. By adding excessive Pb in this way, it is possible to suppress the pyrochlore phase, which is a Pb deficient tendency and a non-ferroelectric phase, and it becomes easier to finally obtain a uniform epitaxial ferroelectric thin film. It is also effective to add a small amount of various organometallic compounds containing metal elements other than Pb, La, Zr, and Ti as necessary.
[0047]
As an organic ligand of a metal alkoxide compound, R ₁ O- or R ₂ OR _Three Selected from O- (wherein R ₁ And R ₂ Represents an aliphatic hydrocarbon group, R _Three Represents a divalent aliphatic hydrocarbon group which may have an ether bond). The metal alkoxide compound is R ₁ OH or R ₂ OR _Three It can be synthesized by distillation or reflux in an organic solvent represented by OH, and R ₁ And R ₂ As the aliphatic hydrocarbon group, an alkyl group having 1 to 4 carbon atoms is preferable, and R _Three Are preferably an alkylene group having 2 to 4 carbon atoms and a divalent group having 4 to 8 carbon atoms in which an alkylene group having 2 to 4 carbon atoms is bonded by an ether bond.
[0048]
Although it is possible to apply the metal organic compound after hydrolysis, it is desirable not to hydrolyze it in order to obtain an epitaxial ferroelectric thin film.
[0049]
The coating solution is prepared by reacting the metal organic compound with a dehydrated solvent or dissolving it in a solvent to obtain a solution having a predetermined concentration. As the solvent, a solvent selected from alcohols, diketones, ketone acids, alkyl esters, oxyacids, oxyketones, and acetic acid having a boiling point of 80 ° C. or higher at normal pressure can be used. Specifically, as the solvent having a boiling point of 80 ° C. or more, for example, (CH _Three ) ₂ CHOH (boiling point 82.3 ° C.), CH _Three (C ₂ H _Five ) CHOH (boiling point 99.5 ° C.), (CH _Three ) ₂ CHCH ₂ OH (boiling point 108 ° C.), C _Four H ₉ OH (boiling point 117.7 ° C.), (CH _Three ) ₂ CHC ₂ H _Four OH (boiling point 130.5 ° C.), CH _Three OCH ₂ CH ₂ OH (boiling point 124.5 ° C.), C ₂ H _Five OCH ₂ CH ₂ OH (boiling point 135 ° C.), C _Four H ₉ OCH ₂ CH ₂ Alcohols such as OH (boiling point 171 ° C.) are most desirable, but are not limited to these. ₂ H _Five OH (boiling point: 78.3 ° C.) can also be used.
[0050]
The coating is performed by a method selected from a spin coating method, a dipping method, a spray method, a screen printing method, and an ink jet method. The single crystal substrate is preferably previously washed with a solvent, etched, rinsed, and dried. Moreover, it is desirable to perform the process from preparation of a coating solution to application | coating in dry nitrogen or argon atmosphere from the point of the quality of the thin film obtained.
[0051]
Next, the obtained thin film is thermally decomposed in an atmosphere containing oxygen to form an amorphous thin film (thermal decomposition step).
[0052]
Pyrolysis is preferably performed in a temperature range of 100 to 500 ° C., desirably 200 to 400 ° C., where crystallization does not occur, and a temperature increase rate of 0.1 to 1000 ° C./second, desirably 1 to 100 ° C./second. It is preferable to heat the substrate to this temperature range at a rate of temperature increase of.
[0053]
Next, the pyrolyzed thin film is heated to the crystal growth temperature, and the ferroelectric thin film is grown from the substrate surface in a solid phase epitaxial manner in an atmosphere containing oxygen (crystallization step).
[0054]
Crystal growth is preferably performed by heating at a temperature of 600 ° C. or higher, preferably 600 to 1200 ° C., more preferably 600 to 800 ° C. for 1 second to 24 hours, preferably 10 seconds to 12 hours. In order to suppress the nucleation of the pyrochlore phase, the temperature rise to the crystal growth temperature is within a temperature range where the nuclei of the pyrochlore phase are generated, specifically, a temperature range of 350 to 450 ° C. It is preferable that the temperature is increased at a high rate, more preferably at a rate of 20 to 100 ° C./second. It is preferable from the viewpoint of productivity that the temperature raising rate is applied not only in the nucleation temperature range of the pyrochlore phase but also throughout the temperature raising process.
[0055]
Further, the nucleation of the pyrochlore phase can also be suppressed by increasing the excess amount of Pb from 0% or by increasing the temperature rising rate to 10 ° C./second or more. More preferably, the excess amount of Pb is more than 0% and the heating rate is 10 ° C./second or more. As shown in the range A in FIG. 6, the Pb amount is 5% or more and the heating rate is More preferably, it is 20 ° C./second or more.
[0056]
Crystallization is preferably performed in an oxygen-containing atmosphere, preferably in oxygen, from the viewpoint of the quality of the thin film, and it is more preferable to use oxygen that has been dried for at least a predetermined time. It is also possible to humidify as necessary. After crystal growth, it is desirable to hold at a temperature lower than the growth temperature, preferably 100 to 600 ° C., and then lower the temperature. The cooling is preferably performed at a cooling rate of 0.01 to 100 ° C./second.
[0057]
By repeating the coating process to the crystallization process several times, a ferroelectric thin film having a predetermined film thickness can be formed. In forming the thin film once, it is preferable to form a film of 10 nm to 1000 nm, and it is more preferable to form a film of 50 nm to 200 nm.
[0058]
The first ferroelectric layer 14, the second ferroelectric layer 16, and the third ferroelectric layer 18 of the present invention are formed by electron beam evaporation, flash evaporation, ion plating, Rf-magnetron sputtering, ion Other epitaxial growth methods selected from vapor phase epitaxial growth methods such as beam sputtering, laser ablation, MBE, CVD, plasma CVD, and MOCVD, and solid phase epitaxial growth methods using wet processes such as sol-gel method and MOD method. It can also be produced by a film method.
[0059]
As described above, in the present invention, the first ferroelectric layer made of PLZT having a composition range in which the pyrochlore layer is hard to be formed and the perovskite single phase can be easily epitaxially grown is first formed on the surface of the single crystal substrate. Then, on the first ferroelectric layer or the second ferroelectric layer formed on the first ferroelectric layer, an optical waveguide layer made of PLZT having a composition range excellent in electro-optical characteristics is formed. An optical waveguide layer having a density and refractive index comparable to that of a single crystal and having an optically smooth surface can be formed on single crystal substrates of different materials.
[0060]
In particular, a second ferroelectric layer having a predetermined thickness is formed as a second buffer layer on the first ferroelectric layer, and a third ferroelectric layer that is an optical waveguide is formed on the second ferroelectric layer. By doing so, the light propagating through the optical waveguide can be isolated from the first ferroelectric layer, and the light is generated by the refractive index distribution between the first ferroelectric layer and the second ferroelectric layer having an island-like structure. It can be made less susceptible to scattering.
[0061]
Table 1 shows a comparison between the manufacturing method of the optical waveguide element of the present invention and other manufacturing methods. The production method of the present invention is superior to the conventional vapor phase epitaxial growth method, the solid phase epitaxial growth method using the conventional vapor phase growth film, and the conventional sol-gel method. It is a manufacturing method that excels in most aspects such as film thickness uniformity and equipment cost.
[0062]
[Table 1]

[0063]
【Example】
(Example 1)
Sapphire Al ₂ O _Three (1 1 02) A first ferroelectric layer 14 as a buffer layer made of epitaxial PLT (28/100) having a film thickness of 10 nm is grown on the single crystal substrate 12 by solid phase epitaxial growth, and further epitaxial PLZT (9/90 nm) having a film thickness of 90 nm. 65/35) By growing the second ferroelectric layer 16 as an optical waveguide made of a thin film, an optical waveguide device having the structure shown in FIG. 1 was produced.
[0064]
Below, a manufacturing method is demonstrated in detail.
(1) Formation of the first ferroelectric layer 14 (buffer layer)
Anhydrous lead acetate (Pb (CH _Three COO) ₂ ), Lanthanum isopropoxide (La (O-i-C _Three H ₇ ) _Three ), And titanium isopropoxide (Ti (O-i-C _Three H ₇ ) _Four ) As a starting material, and Pb is dissolved in 2-methoxyethanol so that it has a ratio of Pb: La: Zr: Ti = 72: 28: 100, which is a stoichiometric composition with respect to other elements, for 6 hours. Then, the mixture was further refluxed for 18 hours to finally obtain a precursor solution for PLT (28/100) having a Ti concentration of 0.6M. The obtained precursor solution was applied by spin coating to a sapphire substrate through a 0.2 μm filter to obtain a coating film. The sapphire substrate is cleaned with solvent, etched with HCl, rinsed with deionized water, and finally N ₂ Used after drying in ethanol by spin coating. All the above processes are N ₂ I went in the atmosphere.
[0065]
Next, the substrate on which the coating film is formed is placed in a humidified oxygen atmosphere, heated at 10 ° C./sec and held at 300 ° C. for 2 minutes, and then heated at 10 ° C./sec and 650 ° C. And finally, the electric furnace was turned off and cooled, and a PLT (28/100) buffer layer having a thickness of 10 nm was grown by solid phase epitaxial growth. When the surface of the obtained buffer layer was observed with a high-resolution scanning electron microscope (SEM), it was in the form of an island structure as shown in FIG.
(2) Formation of second ferroelectric layer 16 (thin film optical waveguide)
Similar to the buffer layer formation, anhydrous lead acetate (Pb (CH _Three COO) ₂ ), Lanthanum isopropoxide (La (O-i-C _Three H ₇ ) _Three ), Zirconium isopropoxide (Zr (Oi-C _Three H ₇ ) _Four ), And titanium isopropoxide (Ti (O-i-C _Three H ₇ ) _Four ) As a starting material, and dissolved in 2-methoxyethanol so that Pb has a stoichiometric composition of Pb: La: Zr: Ti = 91: 9: 65: 35 with respect to other elements, After 6 hours of distillation, the mixture was further refluxed for 18 hours to finally obtain a precursor solution for PLZT (9/65/35) having a Zr + Ti concentration of 0.6 M. The obtained precursor solution was passed through a 0.2 μm filter and Al provided with a PLT (28/100) buffer layer. ₂ O _Three The substrate was applied by spin coating. All the above operations are N ₂ I went in the atmosphere.
[0066]
Next, the substrate on which the coating film is formed is placed in a humidified oxygen atmosphere, heated at 10 ° C./sec and held at 300 ° C. for 2 minutes, and then heated at 10 ° C./sec and 650 ° C. And finally, the electric furnace was turned off and cooled, and a PLZT (9/65/35) thin film having a film thickness of 90 nm was solid-phase epitaxially grown to obtain an optical waveguide device.
[0067]
FIG. 8 shows an X-ray diffraction θ-2θ pattern of this optical waveguide element. FIG. 8 indicates that the diffraction intensity of PLZT (110) near 2θ = 31.0 ° is as strong as 128 kcps, and a perovskite single phase is formed. The crystallographic relationship of each layer is as follows: PLZT (110) // PLT (110) // Al of single orientation ₂ O _Three (1 1 02). Further, the rocking curve half-width by the PLZT (110) plane was 0.913 °, which was good.
[0068]
Further, the surface of the epitaxial PLZT thin film of this example was not visible because it was uniform by observation with an optical microscope. Furthermore, the result of observing the surface of this PLZT (9/65/35) thin film with a high resolution SEM is shown in FIG. 9. As shown in FIG. 9, the surface is extremely uniform and smooth, and the grain boundaries and pores are It was a mirror-like surface that could not be seen at all, and a contrast could not be obtained.
[0069]
(Comparative Example 1)
Similar to Example 1, sapphire Al ₂ O _Three (1 1 02) An optical waveguide device was fabricated by directly growing an epitaxial PLZT (9/65/35) thin film on a single crystal substrate by solid phase epitaxial growth.
[0070]
A precursor solution for PLZT (9/65/35) in which Pb has a stoichiometric composition with respect to other elements was applied to a sapphire substrate by spin coating. The substrate on which the coating film is formed is placed in a humidified oxygen atmosphere, heated at 10 ° C./sec and held at 350 ° C. for 2 minutes, and then heated at 10 ° C./sec to 650 ° C. for 30 minutes. Hold for a minute. Finally, the electric furnace was turned off and cooled to obtain an optical waveguide device on which a 90 nm thick PLZT (9/65/35) thin film was formed.
[0071]
FIG. 10 shows an X-ray diffraction θ-2θ pattern of this optical waveguide element. From FIG. 10, the crystallographic relationship of each layer is PLZT (110) // Al with almost single orientation. ₂ O _Three (1 1 It can be seen that an optical waveguide device having the structure (02) is obtained. However, the diffraction intensity of PLZT (110) near 2θ = 31.0 ° was extremely weak at 2 kcps, and a peak indicating a pyrochlore phase was observed at an intensity of about 1 kcps near 2θ = 29.2 °. In addition, when the surface of the epitaxial PLZT thin film of this comparative example was observed with an optical microscope, only a non-uniform shading in which a pyrochlore phase surrounded a rose-shaped perovskite phase generally called a rosette structure as shown in FIG. Surface.
[0072]
(Example 2)
Sapphire Al ₂ O _Three (1 1 02) A first ferroelectric layer 14 as a buffer layer made of epitaxial PLT (28/100) having a film thickness of 10 nm and a refractive index of 2.50 is grown on the single crystal substrate 12 by solid phase epitaxial growth, and further a film thickness of 540 nm. The second ferroelectric layer 16 as a thin film optical waveguide made of epitaxial PLZT (9/65/35) having a refractive index of 2.50 is grown to form the structure shown in FIG. An optical waveguide device was manufactured.
[0073]
First, a precursor solution for PLT (28/100) was applied to a sapphire substrate by spin coating. The substrate on which this coating film was formed was placed in a humidified oxygen atmosphere, heated at 10 ° C./sec and held at 300 ° C. for 2 minutes, then heated at 10 ° C./sec and heated to 650 ° C. for 30 minutes. Hold for a minute. Finally, the electric furnace was turned off and cooled, and a 10 nm thick PLT (28/100) buffer layer was grown by solid phase epitaxial growth. When the surface of this buffer layer was observed with an atomic force microscope (AFM), it was still in the form of an island structure as shown in FIG.
[0074]
Next, a precursor solution for PLZT (9/65/35) in which Pb is 15% in excess of the stoichiometric composition with respect to other elements is spun onto a sapphire substrate provided with a PLT (28/100) buffer layer. Applied by coating. The substrate on which this coating film was formed was placed in a humidified oxygen atmosphere, heated at 10 ° C./sec and held at 300 ° C. for 2 minutes, then heated at 80 ° C./sec and increased to 2 at 750 ° C. Hold for a minute. Finally, the electric furnace was turned off and cooled to solid-phase epitaxially grow a first PLZT (9/65/35) thin film having a thickness of 90 nm. This was further repeated 5 times to obtain an optical waveguide device in which an epitaxial PLZT (9/65/35) thin film having a total film thickness of 540 nm was formed. In addition, after crystallizing the last layer, it cooled at the cooling rate of 1 degree-C / sec.
[0075]
When the X-ray diffraction θ-2θ pattern of this optical waveguide element was examined, it was a perovskite single phase, and the crystallographic relationship of each layer was PLZT (110) // PLT (110) // Al of single orientation. ₂ O _Three (1 1 02). Further, when the surface of this epitaxial PLZT (9/65/35) thin film was observed with a high-resolution SEM, the surface was extremely uniform and smooth, with no grain boundaries or pores at all, and a mirror surface that could not provide contrast. Surface. Furthermore, when the Ra surface roughness of the surface of the epitaxial PLZT (9/65/35) thin film of this example was identified from the results of the AFM analysis shown in FIG. 13, the roughness was only 1.2 nm.
[0076]
Next, the optical waveguide characteristics were evaluated. Laser light is introduced into the epitaxial PLZT thin film of this embodiment by prism coupling, and TE in the light propagation direction is introduced. ₀ The scattered light intensity distribution of the mode was measured with an optical fiber. The light propagation loss was determined from the slope of the relationship between the logarithm of the scattered light intensity and the light propagation distance, and it showed an excellent characteristic of 7 dB / cm at a wavelength of 633 nm.
[0077]
TE ₀ Mode and TE ₁ When the refractive index was obtained from the mode, it was found that the refractive index was 2.497 at a wavelength of 633 nm, which was the same as that of the bulk, and it was a high-density perovskite single phase. Furthermore, the laser light incident / exit end face could be easily formed by scratching the rear surface of the sapphire substrate with a diamond cutter and cleaving it.
[0078]
As described above, the epitaxial PLZT thin film according to this example is a thin film that is very close to a single crystal and can be used as an optical waveguide having excellent uniformity, and can be easily processed as an optical waveguide element.
[0079]
(Example 3)
Sapphire Al ₂ O _Three (1 1 02) An epitaxial PLT (20/100) buffer layer having a film thickness of 10 nm and a refractive index of 2.57 is grown on a single crystal substrate by solid phase epitaxial growth, and further an epitaxial PZT (52/48) thin film light having a refractive index of 2.56. By growing the waveguide, an optical waveguide device having the structure shown in FIG. 1 was produced in the same manner as in Example 1.
[0080]
The surface of the obtained optical waveguide device is extremely uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, it is a perovskite single phase, and the crystallographic relationship of each layer is unidirectional PLZT (110) /// PLT (110) // Al ₂ O _Three (1 1 02).
[0081]
(Example 4)
Sapphire Al ₂ O _Three (1 1 02) An epitaxial PZT (20/80) buffer layer having a film thickness of 10 nm and a refractive index of 2.63 is grown on a single crystal substrate by solid phase epitaxial growth, and an epitaxial PZT (25/75) thin film light having a refractive index of 2.62 is further grown. By growing the waveguide, an optical waveguide device having the structure shown in FIG. 1 was produced in the same manner as in Example 1.
[0082]
The surface of the obtained optical waveguide device is extremely uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, it is a perovskite single phase, and the crystallographic relationship of each layer is unidirectional PLZT (110) /// PLT (110) // Al ₂ O _Three (1 1 02).
[0083]
(Example 5)
Sapphire Al ₂ O _Three An epitaxial PLT (28/100) buffer layer having a film thickness of 5 nm and a refractive index of 2.50 is grown on a (0001) single crystal substrate by solid phase epitaxial growth, and an epitaxial PLZT (8/65/35) having a refractive index of 2.50 is further grown. 1) As in the case of Example 1, an optical waveguide device having the structure shown in FIG.
[0084]
The surface of the obtained optical waveguide device is extremely uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, it is a perovskite single phase, and the crystallographic relationship of each layer is unidirectional PLZT (111) /// PLT (111) // Al ₂ O _Three (0001).
[0085]
(Example 6)
Sapphire Al ₂ O _Three An epitaxial PLT (28/100) buffer layer having a thickness of 10 nm and a refractive index of 2.50 is grown on a (0001) single crystal substrate by Rf magnetron sputtering, and also epitaxial PLZT (refractive index of 2.50 by Rf magnetron sputtering). 8/65/35) By growing a thin-film optical waveguide, an optical waveguide device having the structure shown in FIG.
[0086]
The surface of the obtained optical waveguide device is extremely uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, it is a perovskite single phase, and the crystallographic relationship of each layer is unidirectional PLZT (111) /// PLT (111) // Al ₂ O _Three (0001).
[0087]
(Example 7)
An epitaxial PLT (28/100) buffer layer having a film thickness of 10 nm and a refractive index of 2.50 is grown on a MgO (100) single crystal substrate by solid phase epitaxial growth in the same manner as in Example 1, and further a refractive index of 2.50. By growing an epitaxial PLZT (8/65/35) thin-film optical waveguide, an optical waveguide device having the structure shown in FIG.
[0088]
The surface of the obtained optical waveguide device is extremely uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, it is a perovskite single phase, and the crystallographic relationship of each layer is a single orientation PLZT (001) /// PLT (001) // MgO (100).
[0089]
(Example 8)
An epitaxial PLT (28/100) buffer layer having a thickness of 10 nm and a refractive index of 2.50 and an epitaxial PLZT having a refractive index of 2.50 (8/65/35) are formed on a GaAs (100) single crystal substrate on which an MgO buffer layer is epitaxially grown. 1) As in the case of Example 1, an optical waveguide device having the structure shown in FIG.
[0090]
The epitaxial MgO buffer layer on the GaAs (100) substrate is formed at 350 ° C. by reactive film formation in an oxygen atmosphere using an excimer laser deposition method in which the surface of the metal Mg target is instantaneously heated by UV laser pulses to perform deposition. Grown at substrate temperature.
[0091]
Next, after in situ epitaxial growth of a PLT buffer layer on the MgO buffer layer by a laser deposition method, solid phase epitaxial growth was performed in the same manner as in Example 1 to grow an epitaxial PLZT (8/65/35) thin film optical waveguide. .
[0092]
The surface of the obtained optical waveguide device is very uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, it is a perovskite single phase, and the crystallographic relationship of each layer is unidirectional PLZT (001) /// PLT (001) // MgO (100) // GaAs (100).
[0093]
Example 9
In the same manner as in Example 8, an epitaxial MgO buffer layer is provided on a Si (100) single crystal substrate, an epitaxial PLT (20/100) buffer layer having a thickness of 10 nm and a refractive index of 2.57, and a refractive index of 2. By growing 56 epitaxial PZT (52/48) thin-film optical waveguides, an optical waveguide device having the structure shown in FIG.
[0094]
The surface of the obtained optical waveguide device is extremely uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, it is a perovskite single phase, and the crystallographic relationship of each layer is PZT (001) /// PLT (001) // MgO (100) // Si (100).
[0095]
(Example 10)
SrTiO _Three An epitaxial PLT (28/100) buffer layer having a film thickness of 10 nm and a refractive index of 2.50 is grown on a (100) single crystal substrate by solid phase epitaxial growth in the same manner as in Example 1, and further an epitaxial having a refractive index of 2.50. By growing a PLZT (9/65/35) thin film optical waveguide, an optical waveguide device having the structure shown in FIG.
[0096]
The surface of the obtained optical waveguide device is very uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, it is a perovskite single phase, and the crystallographic relationship of each layer is unidirectional PLZT (001) /// PLT (001) // SrTiO _Three (0001).
[0097]
Example 11
In this example, sapphire Al ₂ O _Three (1 1 02) A first ferroelectric layer 14 as a first buffer layer made of epitaxial PLT (28/100) having a refractive index of 2.50 and a film thickness of 10 nm is grown on the single crystal substrate 12 by solid phase epitaxy, A second ferroelectric layer 16 as a second buffer layer made of epitaxial PLZT (9/65/35) having a refractive index of 2.50 and a thickness of 500 nm is grown, and further epitaxial having a refractive index of 2.56 and a thickness of 800 nm. The third ferroelectric layer 18 as a thin film optical waveguide made of PZT (52/48) was grown to produce the optical waveguide device shown in FIG.
[0098]
First, anhydrous lead acetate (Pb (CH _Three COO) ₂ ), Lanthanum isopropoxide (La (O-i-C _Three H ₇ ) _Three ), And titanium isopropoxide (Ti (O-i-C _Three H ₇ ) _Four ) As a starting material, Pb is dissolved in 2-methoxyethanol so that it has a stoichiometric composition of Pb: La: Ti = 72: 28: 100 with respect to other elements, and distilled for 6 hours. Then, reflux was performed for 18 hours to finally obtain a precursor solution for PLZT (28/0/100) having a Ti concentration of 0.6M. Further, this precursor solution was passed through a 0.2 μm filter to make Al. ₂ O _Three The substrate was spin coated. All the above operations are N ₂ I went in the atmosphere.
[0099]
Prior to spin coating, the substrate is solvent cleaned, etched with HCl, rinsed with deionized water, and finally N ₂ Dry in by spin coating with ethanol. Next, humidification O ₂ Temperature was raised at 10 ° C / sec in an atmosphere and held at 300 ° C for 2 minutes, then heated at 10 ° C / sec and held at 650 ° C for 30 minutes. Finally, the electric furnace was turned off and cooled. did.
[0100]
As a result, a 10 nm thick PLT (28/100) first buffer layer was grown by solid phase epitaxial growth. When the surface of the similarly formed PLT (28/0/100) buffer layer was observed with a high-resolution scanning electron microscope (SEM), it was in the form of an island structure as shown in FIG.
[0101]
Next, in the same way, anhydrous lead acetate (Pb (CH _Three COO) ₂ ), Lanthanum isopropoxide (La (O-i-C _Three H ₇ ) _Three ), Zirconium isopropoxide (Zr (Oi-C _Three H ₇ ) _Four ), And titanium isopropoxide (Ti (O-i-C _Three H ₇ ) _Four Is dissolved in 2-methoxyethanol so that Pb has a stoichiometric composition of Pb: La: Zr: Ti = 91: 9: 65: 35 with respect to other elements. After performing distillation for a period of time, the mixture was refluxed for 18 hours to finally obtain a precursor solution for PLZT (9/65/35) having a Zr + Ti concentration of 0.6 M.
[0102]
Furthermore, this precursor solution was passed through a 0.2 μm filter and Al was provided with a PLT (28/100) first buffer layer. ₂ O _Three The substrate was spin coated. All the above operations are N ₂ I went in the atmosphere. Next, humidification O ₂ Raise the temperature at 10 ° C / sec and hold at 350 ° C for 2 minutes in the atmosphere, then raise the temperature at 10 ° C / sec and hold at 650 ° C for 2 minutes. did. Thereby, a PLZT (9/65/35) thin film having a thickness of 100 nm was grown by solid phase epitaxial growth. By repeating this four more times, an epitaxial PLZT (9/65/35) second buffer layer having a total film thickness of 500 nm was obtained.
[0103]
Next, in the same way, anhydrous lead acetate (Pb (CH _Three COO) ₂ ), Zirconium isopropoxide (Zr (Oi-C _Three H ₇ ) _Four ), And titanium isopropoxide (Ti (O-i-C _Three H ₇ ) _Four ) As a starting material, Pb is dissolved in 2-methoxyethanol so that the proportion of Pb: Zr: Ti = 100: 52: 48, which is a stoichiometric composition with respect to other elements, is distilled for 6 hours. Then, refluxing was performed for 18 hours to finally obtain a precursor solution for PZT (52/48) having a Zr + Ti concentration of 0.6M. Further, this precursor solution was passed through a 0.2 μm filter and an Al provided with a PLZT (9/65/35) second buffer layer. ₂ O _Three The substrate was spin coated. All the above operations are N ₂ I went in the atmosphere.
[0104]
Next, humidification O ₂ Raise the temperature at 10 ° C / sec and hold at 350 ° C for 2 minutes in the atmosphere, then raise the temperature at 10 ° C / sec and hold at 650 ° C for 2 minutes. did. As a result, a 100 nm thick PLZT (9/65/35) thin film was grown by solid phase epitaxial growth. By repeating this seven more times, an epitaxial PZT (52/48) thin film optical waveguide layer having a total film thickness of 800 nm was obtained. The final crystallization was performed by holding at 650 ° C. for 30 minutes, and finally cooling was performed at a rate of 1 ° C./sec.
[0105]
According to the X-ray diffraction θ-2θ pattern, the crystallographic relationship is unidirectional PZT (110) // PLZT (110) // PLT (110) // Al ₂ O _Three (1 1 02) structure was obtained. Since the surface of the epitaxial PLZT thin film of this example is uniform when observed with an optical microscope, nothing can be seen. Furthermore, the result of observation with a high-resolution SEM is extremely uniform and smooth, and no grain boundaries or pores are observed. The surface was so specular that contrast could not be obtained.
[0106]
In order to evaluate the optical waveguide characteristics, laser light having a wavelength of 633 nm was introduced into the epitaxial PZT thin film waveguide of this example by prism coupling, and the scattered light intensity distribution in the light propagation direction was measured with an optical fiber. The light propagation loss was calculated from the slope of the relationship between the logarithm of the scattered light intensity and the light propagation distance.
[0107]
In this embodiment, the structure for the wavelength of 633 nm is used, but the structure for a long wavelength such as the wavelength of 1310 nm or 1550 nm is also different from the structure for the wavelength of 633 nm according to the present invention in that the second buffer layer and the thin film optical waveguide layer are formed. Needless to say, if the thickness is increased, the same configuration can be obtained.
[0108]
Furthermore, the laser light incident / exit end face could be easily formed by scratching the rear surface of the sapphire substrate with a diamond cutter and cleaving it. As described above, the epitaxial PLZT thin film according to this example is a thin film that is very close to a single crystal and can be used as an optical waveguide having excellent uniformity, and can be easily processed as an optical waveguide element.
[0109]
Example 12
In this example, as in Example 11, sapphire Al was obtained by solid phase epitaxy. ₂ O _Three (1 1 02) A first ferroelectric layer 14 as a first buffer layer made of epitaxial PLT (28/100) having a refractive index of 2.50 and a thickness of 10 nm is grown on the single crystal substrate 12, and then a refractive index of 2 A second ferroelectric layer 16 as a second buffer layer made of epitaxial PLZT (9/80/20) having a thickness of .48 and 600 nm is grown, and further epitaxial PLZT (9 having a refractive index of 2.50 and a thickness of 1400 nm) is formed. An optical waveguide device having a structure shown in FIG. 5 was produced by growing the third ferroelectric layer 18 as a thin film optical waveguide composed of / 65/35).
[0110]
First, a precursor solution for PLT (28/100) is made of Al. ₂ O _Three Apply spin coating to substrate and humidify ₂ Temperature was raised at 10 ° C / sec in an atmosphere and held at 300 ° C for 2 minutes, then heated at 10 ° C / sec and held at 650 ° C for 30 minutes. Finally, the electric furnace was turned off and cooled. did. As a result, a 10 nm thick PLT (28/100) first buffer layer was grown by solid phase epitaxial growth.
[0111]
Next, a precursor solution for PLZT (9/80/20) in which Pb is 15% in excess of the stoichiometric composition with respect to other elements is used as an Al provided with a PLT (28/100) first buffer layer. ₂ O _Three Apply spin coating to substrate and humidify ₂ After raising the temperature at 10 ° C / sec in an atmosphere and holding at 300 ° C for 2 minutes, the temperature was raised at 80 ° C / sec and held at 750 ° C for 2 minutes. Finally, the electric furnace was turned off and cooled. did. Thus, a first layer PLZT (9/80/20) thin film having a thickness of 100 nm was grown by solid phase epitaxial growth. By repeating this further 5 times, an epitaxial PLZT (9/80/20) second buffer layer having a total film thickness of 600 nm was obtained.
[0112]
Next, a precursor solution for PLZT (9/65/35) in which Pb is 15% in excess of the stoichiometric composition with respect to other elements is used as Al provided with a second buffer layer of PLZT (9/80/20). ₂ O _Three Apply spin coating to substrate and humidify ₂ After raising the temperature at 10 ° C / sec in an atmosphere and holding at 300 ° C for 2 minutes, the temperature was raised at 80 ° C / sec and held at 750 ° C for 2 minutes. Finally, the electric furnace was turned off and cooled. did. As a result, a first layer PLZT (9/65/35) thin film having a thickness of 100 nm was grown by solid phase epitaxial growth. By repeating this 13 times, an epitaxial PLZT (9/65/35) thin film optical waveguide layer having a total film thickness of 1400 nm was obtained. After crystallization of the last layer, cooling was performed at a cooling rate of 1 ° C./second.
[0113]
According to the X-ray diffraction θ-2θ pattern, the crystallographic relationship is unidirectional PLZT (110) // PLZT (110) // PLT (110) // Al ₂ O _Three (1 1 02) structure was obtained. When the surface of the epitaxial PLZT thin film of this example was observed with a high-resolution SEM, the surface was extremely uniform and smooth, with no grain boundaries or pores, and a mirror-like surface with no contrast. It was.
[0114]
In order to evaluate the optical waveguide characteristics, laser light having a wavelength of 633 nm was introduced into the epitaxial PLZT thin film of this example by prism coupling, and the scattered light intensity distribution in the light propagation direction was measured with an optical fiber. The light propagation loss was found from the slope of the relationship between the logarithm of the scattered light intensity and the light propagation distance. Furthermore, the laser light incident / exit end face could be easily formed by scratching the rear surface of the sapphire substrate with a diamond cutter and cleaving it. As described above, the epitaxial PLZT thin film according to this example is a thin film that is very close to a single crystal and can be used as an optical waveguide having excellent uniformity, and can be easily processed as an optical waveguide element.
(Example 13)
In this example, sapphire Al was used in substantially the same manner as in Example 11. ₂ O _Three (1 1 02) Epitaxial PbTiO having a refractive index of 2.71 and a film thickness of 40 nm by solid phase epitaxy onto the single crystal substrate 12 _Three The first ferroelectric layer 14 is grown as a first buffer layer, and then the second ferroelectric layer as a second buffer layer made of epitaxial PZT (85/15) having a refractive index of 2.49 and a thickness of 600 nm. The body layer 16 is grown, and the third ferroelectric layer 18 as a thin film optical waveguide made of epitaxial PZT (52/48) having a refractive index of 2.56 and a thickness of 700 nm is grown, as shown in FIG. An optical waveguide device having a structure was produced. The surface is extremely uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, the perovskite single phase and the crystallographic relationship is PZT (110) // PZT (110) // PZT (110) / / Al ₂ O _Three (1 1 02).
[0115]
(Example 14)
In this example, sapphire Al was used in substantially the same manner as in Example 11. ₂ O _Three (1 1 02) A first ferroelectric layer 14 as a first buffer layer made of epitaxial PZT (20/80) having a refractive index of 2.63 and a film thickness of 5 nm is grown on the single crystal substrate 12 by solid phase epitaxy, A second ferroelectric layer 16 as a second buffer layer made of epitaxial PZT (85/15) having a refractive index of 2.49 and a thickness of 500 nm is grown, and further epitaxial having a refractive index of 2.56 and a thickness of 700 nm. By growing the third ferroelectric layer 18 as a thin film optical waveguide made of PZT (52/48), an optical waveguide device having the structure shown in FIG. 5 was produced. The surface is extremely uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, the perovskite single phase and the crystallographic relationship is PZT (110) // PZT (110) // PZT (110) / / Al ₂ O _Three (1 1 02).
[0116]
(Example 15)
In this example, sapphire Al ₂ O _Three A first ferroelectric layer 14 as a first buffer layer made of epitaxial PLT (28/100) having a refractive index of 2.50 and a film thickness of 10 nm is grown on a (0001) single crystal substrate 12 at 650 ° C. by Rf magnetron sputtering. Next, a second ferroelectric layer 16 as a second buffer layer made of epitaxial PLZT (9/80/20) having a refractive index of 2.48 and a thickness of 600 nm is grown, and further a refractive index of 2.50 and a film By growing the third ferroelectric layer 18 as a thin film optical waveguide made of epitaxial PLZT (9/65/35) having a thickness of 1400 nm, an optical waveguide device having the structure shown in FIG. 5 was produced. According to the X-ray diffraction θ-2θ pattern, the crystallographic relationship is unidirectional PLZT (111) // PLZT (111) // PLT (111) // Al ₂ O _Three A structure of (0001) was obtained.
[0117]
(Example 16)
In this example, as in Example 11, the first buffer layer made of epitaxial PLT (28/100) having a refractive index of 2.50 and a film thickness of 10 nm was formed on the MgO (100) single crystal substrate 12 by solid phase epitaxy. The first ferroelectric layer 14 as a second buffer layer made of epitaxial PLZT (9/80/20) having a refractive index of 2.48 and a film thickness of 600 nm is then grown. The third ferroelectric layer 18 is grown as a thin film optical waveguide made of epitaxial PLZT (9/65/35) having a refractive index of 2.50 and a film thickness of 1400 nm. A waveguide element was produced. According to the X-ray diffraction θ-2θ pattern, a crystallographic relationship was obtained with a structure of PLZT (111) // PLZT (001) // PLT (001) // MgO (100) with a single orientation.
[0118]
(Example 17)
In this embodiment, a first buffer layer made of epitaxial PLT (28/100) having a refractive index of 2.50 and a thickness of 10 nm is formed on a GaAs (100) single crystal substrate 12 on which an MgO buffer layer has been epitaxially grown. A ferroelectric layer 14, a second ferroelectric layer 16 as a second buffer layer made of epitaxial PLZT (8/80/20) having a refractive index of 2.48 and a thickness of 600 nm, a refractive index of 2.50, a film An optical waveguide device was manufactured by growing the third ferroelectric layer 18 as a thin film optical waveguide made of epitaxial PLZT (8/65/35) having a thickness of 1400 nm.
[0119]
An epitaxial MgO buffer layer on a GaAs (100) substrate is formed by using an excimer laser deposition method in which a metal Mg target surface is instantaneously heated by a UV laser pulse to perform deposition. ₂ The substrate was grown at a substrate temperature of 350 ° C. by reactive film formation in an atmosphere. Furthermore, a PLT first buffer layer, a PLZT second buffer layer, and a PLZT optical waveguide layer were epitaxially grown in situ on the MgO buffer layer by a laser deposition method. The surface is very uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, the perovskite single phase and the crystallographic relationship is PLZT (001) // PLZT (001) // PLT (001) / A structure of / MgO (100) // GaAs (100) was obtained.
[0120]
(Example 18)
In this example, an epitaxial MgO buffer layer is provided on the Si (100) single crystal substrate 12 by the same method as in Example 17, and further an epitaxial PLT (20/100) having a refractive index of 2.57 and a film thickness of 10 nm. A first ferroelectric layer 14 as a first buffer layer, and a second ferroelectric layer as a second buffer layer made of epitaxial PLZT (8/65/35) having a refractive index of 2.50 and a thickness of 500 nm. 16 and a third ferroelectric layer 18 as a thin film optical waveguide made of epitaxial PZT (52/48) having a refractive index of 2.56 and a film thickness of 800 nm was grown to produce an optical waveguide device. The surface is very uniform and smooth, and according to the X-ray diffraction θ-2θ pattern, the perovskite single phase and the crystallographic relationship is PZT (001) // PLZT (001) // PLT (001) / A structure of / MgO (100) // Si (100) was obtained.
[0121]
Example 19
In this example, as in Example 11, SrTiO _Three A first ferroelectric layer 14 as a first buffer layer made of epitaxial PLZT (28/0/100) having a refractive index of 2.50 and a thickness of 10 nm is grown on a (100) single crystal substrate 12 by solid phase epitaxy. Next, a second ferroelectric layer 16 as a second buffer layer made of epitaxial PLZT (9/80/20) having a refractive index of 2.48 and a film thickness of 600 nm is grown, and further a refractive index of 2.50 and a film thickness. The third ferroelectric layer 18 as a thin film optical waveguide made of 1400 nm epitaxial PLZT (9/65/35) was grown. According to the X-ray diffraction θ-2θ pattern, the crystallographic relationship is unidirectional PLZT (001) // PLZT (001) // PLT (001) // SrTiO _Three A structure of (0001) was obtained.
[0122]
【The invention's effect】
According to the present invention, there is provided an optical waveguide device having a uniform composition, an optically smooth surface, and a single crystal epitaxial PLZT ferroelectric thin film. Also provided is a method of manufacturing an optical waveguide device capable of forming a single crystal epitaxial PLZT ferroelectric thin film having a surface that is optically smooth while stably controlling the composition.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a layer structure of an optical waveguide device according to a first embodiment of the present invention.
FIG. 2 Pb _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O _Three FIG.
FIG. 3 is a schematic cross-sectional view showing a manufacturing process (first ferroelectric layer manufacturing process) of the optical waveguide device of the present invention.
FIG. 4 is a schematic cross-sectional view when a buffer layer is formed deeply on a substrate.
FIG. 5 is a schematic cross-sectional view showing a layer structure of an optical waveguide device according to a second embodiment of the present invention.
FIG. 6 is a graph showing the relationship between the amount of excess Pb and the rate of temperature increase.
7 is a SEM photograph of the surface of a PLT buffer layer provided on the sapphire substrate of Example 1. FIG.
8 is a diagram showing an X-ray diffraction pattern of the optical waveguide device of Example 1. FIG.
9 is a SEM photograph of the surface of the optical waveguide device of Example 1. FIG.
10 is a diagram showing an X-ray diffraction pattern of the optical waveguide device of Comparative Example 1. FIG.
11 is an optical micrograph of the optical waveguide device of Comparative Example 1. FIG.
12 is an AFM photograph of the surface of a PLT buffer layer provided on the sapphire substrate of Example 2. FIG.
13 is an AFM photograph of the surface of the optical waveguide device of Example 2. FIG.
FIG. 14 is a schematic cross-sectional view of a polycrystalline thin film formed on a substrate.
FIG. 15 is a schematic cross-sectional view of an epitaxial thin film including pores formed on a substrate.
FIG. 16 is a schematic cross-sectional view of a non-uniform epitaxial thin film in which a pyrochlore phase remains formed on a substrate.
[Explanation of symbols]
12 Single crystal substrate
14 First ferroelectric layer
16 Second ferroelectric layer
18 Third ferroelectric layer
100 substrates
102 Ferroelectric thin film (perebskite phase)
104 Pyrochlore phase

Claims (16)

A single crystal substrate;
Provided on a single crystal substrate 0 <x <0.30,0 <y < 0.20 for _{Pb 1-x La x (Zr} y Ti 1-y) perovskite single consisting _{1-x /} 4 O ₃ A first ferroelectric layer of phase;
0 provided directly laminated on the first ferroelectric layer <x <0.20,0.20 <ranging _{y <1.0 Pb 1-x La} x (Zr y Ti 1-y) _A second ferroelectric layer of _{1-x / 4} O ₃ perovskite single phase;
An optical waveguide device having:   The optical waveguide device according to claim 1, wherein a difference in refractive index between the first ferroelectric layer and the second ferroelectric layer is 0.05 or less. A single crystal substrate;
0 provided on a single crystal substrate _{<x <0.30,0 <Pb 1-} x La x (Zr y Ti 1-y) in the range of y <0.20 perovskite consisting _{1-x /} 4 O ₃ A single-phase first ferroelectric layer;
0 provided directly laminated on the first ferroelectric layer <x <0.20,0.20 <ranging _{y <1.0 Pb 1-x La} x (Zr y Ti 1-y) _A second ferroelectric layer of _{1-x / 4} O ₃ perovskite single phase;
Pb _1-x La _x provided on the second ferroelectric layer and having a refractive index greater than that of the second ferroelectric layer in the range of 0 <x <0.20 and 0.20 <y <1.0. a third ferroelectric layer having a perovskite single phase consisting of _{(Zr y Ti 1-y)} 1-x / 4 O 3,
An optical waveguide device having:   The optical waveguide element according to claim 3, wherein a difference in refractive index between the second ferroelectric layer and the third ferroelectric layer is 0.01 or more.   The optical waveguide element according to any one of claims 1 to 4, wherein the first ferroelectric layer has a thickness of 1 nm to 40 nm. The optical waveguide device according to any one of claims 1 to 5, wherein the single crystal substrate is sapphire (Al ₂ O ₃ ).     The optical waveguide device according to any one of claims 1 to 5, wherein the single crystal substrate is magnesium oxide (MgO).     The optical waveguide device according to any one of claims 1 to 5, wherein the single crystal substrate is a semiconductor having a magnesium oxide (MgO) layer on a surface thereof. The optical waveguide device according to any one of claims 1 to 5, wherein the single crystal substrate is made of a material containing at least SrTiO ₃ . On a single crystal substrate, 0 <x <0.30,0 <Pb 1-x La x (Zr y Ti 1-y) in the range of y <0.20 perovskite single consisting _{1-x /} 4 O ₃ A first ferroelectric layer forming step of forming a first ferroelectric layer of a phase;
Directly laminated on the first ferroelectric layer, 0 <x <0.20,0.20 <y <1.0 in the range of _{Pb 1-x La x (Zr} y Ti 1-y) 1- a second ferroelectric layer forming step of forming a perovskite single phase second ferroelectric layer made of _{x / 4} O ₃ ;
Have a, the first ferroelectric layer, and the second ferroelectric layer coating step of forming a thin film by coating the ferroelectric precursor consisting of an organometallic compound, thermally decomposed thermally the thin film A method for manufacturing an optical waveguide device, wherein a decomposition step and a crystallization step in which a thin film after the thermal decomposition is heated to a crystal growth temperature and subjected to solid phase epitaxial growth are repeated one or more times . On a single crystal substrate, 0 <x <0.30,0 <Pb 1-x La x (Zr y Ti 1-y) in the range of y <0.20 perovskite single consisting _{1-x /} 4 O ₃ A first ferroelectric layer forming step of forming a first ferroelectric layer of a phase;
Directly laminated on the first ferroelectric layer, 0 <x <0.20,0.20 <y <1.0 in the range of _{Pb 1-x La x (Zr} y Ti 1-y) 1- a second ferroelectric layer forming step of forming a perovskite single phase second ferroelectric layer made of _{x / 4} O ₃ ;
Pb _1-x La _x provided on the second ferroelectric layer and having a refractive index greater than that of the second ferroelectric layer in the range of 0 <x <0.20 and 0.20 <y <1.0. and _{(Zr y Ti 1-y)} 1-x / 4 O a _three third ferroelectric layer forming step of forming a third ferroelectric layer having a perovskite single phase,
The first ferroelectric layer, the second ferroelectric layer, and the third ferroelectric layer are coated with a ferroelectric precursor made of an organometallic compound to form a thin film. An optical light formed by repeating a thermal decomposition step of thermally decomposing the thin film, and a crystallization step of raising the temperature of the thin film after pyrolysis to a crystal growth temperature and performing solid phase epitaxial growth one or more times. A method for manufacturing a waveguide element. The organometallic compound, method of manufacturing the optical waveguide device according to _{Pb 1-x La x (Zr} y Ti 1-y) according to claim 11 comprising _{1-x / 4} O ₃ excess Pb stoichiometric composition .   The method of manufacturing an optical waveguide element according to claim 11 or 12, wherein the organometallic compound is obtained by mixing or reacting two or more compounds selected from metal alkoxides and metal salts.   In the crystallization step, when the temperature is raised to the crystal growth temperature, the temperature is raised in a temperature range of at least 350 to 450 ° C at a rate of temperature rise of 10 to 500 ° C / second. 2. A method for manufacturing an optical waveguide device according to item 1.   The method for manufacturing an optical waveguide device according to any one of claims 11 to 14, wherein the crystal growth temperature is 600 to 800 ° C.   The method for manufacturing an optical waveguide element according to claim 11, wherein the pyrolysis step and / or the crystallization step are performed in an atmosphere containing oxygen.

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