JP3726134B2 - Electroluminescent light emitting layer thin film, inorganic thin film electroluminescent element, and method for producing light emitting layer thin film - Google Patents
Electroluminescent light emitting layer thin film, inorganic thin film electroluminescent element, and method for producing light emitting layer thin film Download PDFInfo
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- JP3726134B2 JP3726134B2 JP2002273461A JP2002273461A JP3726134B2 JP 3726134 B2 JP3726134 B2 JP 3726134B2 JP 2002273461 A JP2002273461 A JP 2002273461A JP 2002273461 A JP2002273461 A JP 2002273461A JP 3726134 B2 JP3726134 B2 JP 3726134B2
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- 239000010409 thin film Substances 0.000 title claims description 41
- 238000004519 manufacturing process Methods 0.000 title claims description 13
- 150000001875 compounds Chemical class 0.000 claims description 12
- 239000000843 powder Substances 0.000 claims description 12
- 239000008188 pellet Substances 0.000 claims description 9
- 238000010438 heat treatment Methods 0.000 claims description 7
- 229910052701 rubidium Inorganic materials 0.000 claims description 6
- 229910052717 sulfur Inorganic materials 0.000 claims description 6
- 239000011261 inert gas Substances 0.000 claims description 4
- 229910052684 Cerium Inorganic materials 0.000 claims description 3
- 238000001704 evaporation Methods 0.000 claims description 3
- 238000010894 electron beam technology Methods 0.000 claims description 2
- 230000008020 evaporation Effects 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims description 2
- 238000007740 vapor deposition Methods 0.000 claims description 2
- ZMIGMASIKSOYAM-UHFFFAOYSA-N cerium Chemical compound [Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce] ZMIGMASIKSOYAM-UHFFFAOYSA-N 0.000 claims 2
- IGLNJRXAVVLDKE-UHFFFAOYSA-N rubidium atom Chemical compound [Rb] IGLNJRXAVVLDKE-UHFFFAOYSA-N 0.000 claims 1
- ZEGFMFQPWDMMEP-UHFFFAOYSA-N strontium;sulfide Chemical compound [S-2].[Sr+2] ZEGFMFQPWDMMEP-UHFFFAOYSA-N 0.000 claims 1
- 239000000758 substrate Substances 0.000 description 10
- 229910052783 alkali metal Inorganic materials 0.000 description 9
- 150000001340 alkali metals Chemical class 0.000 description 9
- 239000011572 manganese Substances 0.000 description 9
- 239000011734 sodium Substances 0.000 description 9
- 230000007547 defect Effects 0.000 description 8
- 239000011521 glass Substances 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 238000000034 method Methods 0.000 description 7
- CNRZQDQNVUKEJG-UHFFFAOYSA-N oxo-bis(oxoalumanyloxy)titanium Chemical compound O=[Al]O[Ti](=O)O[Al]=O CNRZQDQNVUKEJG-UHFFFAOYSA-N 0.000 description 7
- 229910052700 potassium Inorganic materials 0.000 description 7
- 229910052984 zinc sulfide Inorganic materials 0.000 description 7
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 229910052708 sodium Inorganic materials 0.000 description 6
- 238000000137 annealing Methods 0.000 description 5
- 238000000295 emission spectrum Methods 0.000 description 5
- 239000010408 film Substances 0.000 description 5
- 230000006866 deterioration Effects 0.000 description 4
- 238000005401 electroluminescence Methods 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000010304 firing Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 2
- 230000004913 activation Effects 0.000 description 2
- 150000001768 cations Chemical class 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000005090 crystal field Methods 0.000 description 2
- 238000005566 electron beam evaporation Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 238000005424 photoluminescence Methods 0.000 description 2
- 229910052712 strontium Inorganic materials 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- 239000011593 sulfur Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 239000011701 zinc Substances 0.000 description 2
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000010549 co-Evaporation Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000005137 deposition process Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- AMGQUBHHOARCQH-UHFFFAOYSA-N indium;oxotin Chemical compound [In].[Sn]=O AMGQUBHHOARCQH-UHFFFAOYSA-N 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 230000001678 irradiating effect Effects 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- -1 manganese-activated zinc sulfide Chemical class 0.000 description 1
- 239000011812 mixed powder Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 229910001419 rubidium ion Inorganic materials 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
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- Electroluminescent Light Sources (AREA)
- Luminescent Compositions (AREA)
- Physical Vapour Deposition (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、電子ディスプレイの一つである無機薄膜エレクトロルミネッセンスに関し、特に青緑色材料であるＳｒＳ：Ｃｅ薄膜の改良に係るエレクトロルミネッセンス（以下、ＥＬと略記する）発光層薄膜、同薄膜を発光層とするＥＬ素子及びＥＬ発光層薄膜の製造方法に関する。
【０００２】
【従来の技術】
ＳｒＳ：Ｃｅは青色ＥＬ材料として、長年、研究・開発が行われており、すでにＥＬディスプレイ・パネルとして実用化されているＺｎＳ：Ｍｎ（マンガンで付活した硫化亜鉛）に次ぐ輝度と発光効率を示す事から、実用に近いＥＬ材料として期待されてきた。ＳｒＳ：Ｃｅの優れた点は、ＳｒＳ：ＣｅとＺｎＳ：Ｍｎとを組み合わせる事により、容易に白色発光が得られる事である。ＺｎＳ：Ｍｎとの組み合わせでバランスのよい白色を再現するためには、ＳｒＳ：Ｃｅの発光色をＣＩＥ（Ｃommission Ｉnternationale de ｌ'Ｅcairag）色度座標値で（０．１８、０．３７）以下にする必要がある。しかし製造方法や条件によっては、ＳｒＳ：Ｃｅ本来の発光色に比べ緑色成分が強くなり、それがＳｒＳ：Ｃｅの実用化を妨げている原因のひとつになっている。
【０００３】
ＳｒＳ：Ｃｅの発光色の緑色化は、以下のような物理的要因により起こると考えられる。ＳｅＳ：Ｃｅの発光は３価の陽イオンとしてＳｒＳ格子中に取り込まれたＣe3+イオンから発せられる。Ce3+の発光色が変わるのは、発光に関与するＣｅ3+の５ｄ電子のエネルギー値が、結晶場（ＳｅＳ結晶内におけるＣｅ3+の周りの電場の強さや空間対称性）の影響により変化しやすいためである。結晶場が変化する要因として、ＳrＳ格子内に形成されるＳｒ（ストロンチウム）やＳ（硫黄）空孔や不純物などが考えられる。またＳrＳ母体自身も化学的に不安定であるため、格子欠陥を作りやすい。さらにＣｅ3+の置換位置のＳｒが２価の陽イオンであり、Ｃｅ3+と価数が異なるため、価数の違いを補償するような欠陥が生成され易い。
【０００４】
以上のように、ＳｒＳ：Ｃｅ発光の緑色化は材料固有の問題ではあるが、焼成温度に制約のないＳｒＳ：Ｃｅ蛍光体粉末においては、１０００℃以上の高温における焼成により、ＳｒＳの十分な結晶化とＣｅ発光中心の付活化が可能である。更に［１］ＳｒとＳの組成比を制御することにより（例えば、特許文献１参照。）、［２］アルカリ金属Ｌｉ，Ｎａ，Ｋ，Ｒｂの添加などにより（例えば、非特許文献１参照。）、本来の青緑色発光を保ち、しかも高い発光効率を有する蛍光体粉末が作製されている。
【０００５】
それに対しＥＬ素子の発光層用としてＳｒＳ：Ｃｅ薄膜を作製する場合、ＥＬ素子に使用する基板や絶縁層材料などの耐熱性により成膜時の温度が制限される。一般にガラス基板を用いた場合で６５０℃、セラミック基板を用いた場合でも７００〜８００℃あたりが上限とされている。したがって、粉末蛍光体と違い、十分なＳｒＳの結晶化、Ｃｅ発光中心の付活化が難しく、本来の青緑色発光で高発光効率を有するＳｒＳ：Ｃｅ薄膜は得られていない。このような低温度域で高品質なＳｒＳ：Ｃｅを作製するために、［３］Ｓｒ2+とＣｅ3+の価数の違いを補償するための電荷補償剤として１価の元素Ｎａ（ナトリウム），Ｋ（カリウム），Ａｇ（銀）、または5価の元素Ｎ（窒素）やＰ（燐）などを添加する（例えば、非特許文献２参照。）、［４］Ｓr欠陥を埋め合わせるねらいから遷移金属元素Ｚｎ（亜鉛）やＭｎ（マンガン）を添加する（例えば、非特許文献３参照。）、［５］薄膜の作製後に、別途、熱処理を施す（例えば、非特許文献4参照。）などの検討が行われている。これらの取り組みにもかかわらず、依然としてＣｅ3+ の発光色は十分に制御しきれておらず、ＳｒＳ：Ｃｅ薄膜を発光層に用いたＥＬディスプレイ・パネルの量産には至っていない。
【０００６】
【特許文献１】
特開2000−129254号公報（明細書段落［０００５］、［００１１］）
【０００７】
【非特許文献１】
H．Fukada他，Improved Luminescent Properties of SrS：Ce Powder Phosphors through Co-Doping with Alkali Metals，Proc．10th Int．Workshop on Inorganic and Organic Electroluminescence，(2000)pp．113-116.
【０００８】
【非特許文献２】
K．O．Velthaus他，New Deposition Process for Very Blue and Bright SrS：Ce TFEL Devices，Digest of 1997 SID International Symposium，(1997)pp．411-414．
【０００９】
【非特許文献３】
Ｒ．H．Mauch他，Improved SrS：Ce，Cl TFEL Devices by ZnS Co-Evaporation，Digest of 1995 SID International Symposium，(1995)pp．720-723．
【００１０】
【非特許文献４】
K．Ohmi他，Improvement of Crystallographic and Electroluminescent Characteristics of SrS：Ce Thin Film Devices by Post-deposition Annealing in Ar-S Atmosphere，J．Appl．Phys．，Vol．78(1995)pp．428-434．
【００１１】
【発明が解決しようとする課題】
ＳｒＳ：Ｃｅよりなる発光層薄膜は、いずれの従来例もＳｒＳ：Ｃｅの本来の発光色である青緑色を安定に再現させるには問題があった。本発明はその問題を解決する新たな添加材料を提供するとともに、その発光層薄膜の製造方法を提供する。
【００１２】
【課題を解決するための手段】
本発明は、ＳｒＳ：ＣｅにＲｂを添加したエレクトロルミネッセンス発光層薄膜、望ましくはＣｅ濃度が０．０１〜１ｍｏｌ％、Ｒｂ濃度が０．０１〜５ｍｏｌ％であるＳｒＳ：ＣｅにＲｂを添加したエレクトロルミネッセンス発光層薄膜を提供する。本書ではＳｒＳ：ＣｅにＲｂを添加した物質をＳｒＳ：Ｃｅ，Ｒｂと略記することがある。
【００１３】
又、本発明は、ＳｒＳ：ＣｅにＲｂを添加した薄膜を発光層とした無機薄膜エレクトロルミネッセンス素子、望ましくはＣｅ濃度が０．０１〜１ｍｏｌ％、Ｒｂ濃度が０．０１〜５ｍｏｌ％であるＳｒＳ：ＣｅにＲｂを添加した薄膜を発光層とした無機薄膜エレクトロルミネッセンス素子を提供する。
【００１４】
ここで、Ｃｅ濃度が０．０１ｍｏｌ％未満だとＣｅによる付活効果がほとんど認められず、１ｍｏｌ％をこえるとＳｒＳ内に欠陥を生じさせてしまい、発光効率が低下する。又、Ｒｂ濃度が０．０１ｍｏｌ％未満だとＲｂ添加の効果がほとんどなく、５ｍｏｌ％をこえるとＳｒＳ内に欠陥を生じさせてしまい、発光効率が低下する。尚、ＲｂがＣｅの電荷を補償するという作用に限るなら、Ｒｂの量はＣｅと同量が最適と考えられるが、実際は母体であるＳｒＳ内にＳｒ欠陥が存在し、Ｒｂはその欠陥も補償すると考えられＲｂの上限値はＣｅの上限値よりも高くなっている。
【００１５】
更に又、ＳｒＳとＣｅ化合物とＲｂ化合物とを混合した粉末からなるペレットに電子線を照射し、蒸発によって得られたＳｒＳ：Ｃｅ，Ｒｂ薄膜を不活性ガス雰囲気中にて４００〜８００℃の温度範囲にて熱処理を行う発光層薄膜の製造方法を提供する。又、この場合Ｃｅ化合物としてはＣｅ2Ｓ3，ＣｅＣｌ3，ＣｅＦ3のいずれか一つ以上を、Ｒｂ化合物としてはＲｂ2Ｓ，Ｒｂ2ＳＯ4，ＲｂＮＯ3のいずれか一つ以上を用いるのが好適である。
【００１６】
熱処理の温度は、結晶性改善という目的でＳｒＳ：Ｃｅ，Ｒｂ薄膜の成膜温度よりも高いことが条件で４００℃以上となり、成膜の下地となる基板が熱劣化を起さない温度という条件で８００℃以下が選ばれる。
【００１７】
又、本発明は、発光層薄膜の製造に際し用いるペレットとしてＳｒＳとＣｅ化合物とＲｂ化合物とを混合した粉末からなる小塊を用いるが、Ｒｂ濃度を０．１〜１０ｍｏｌ％とする。ここで、Ｒｂ濃度が０．１ｍｏｌ％未満だとＲｂ濃度添加の効果がほとんどなく、又１０ｍｏｌ％をこえると、ＳｒＳ母体内に欠陥を生じさせる要因となるほか、焼成炉の劣化も生じさせる欠点がある。又、Ｒｂ濃度の上限値が成膜物の上限値より高いのは、蒸気圧の高いＲｂの工程中の蒸発が考慮されたためである。
【００１８】
【発明の実施の形態】
本発明は、基本的にＳｒＳ：ＣｅにＲｂを添加したＥＬ発光層薄膜である。ここで、Ｒｂはアルカリ金属の一つであるため、上記従来の技術で説明したように、粉末蛍光体の製造における電荷補償剤としての効果が指摘されてはいたが、薄膜蛍光体においてその有効性を明示した例はない。Ｒｂ+イオンの置換先であるＳｒ2+のイオン半径が、Ｎａ+ やＫ+に近いため、電荷補償剤としてはＲｂ+よりもむしろＮａやＫの方が適していると考えられていた。
【００１９】
本発明では、Ｒｂを添加したＳｒＳ:Ｃｅ薄膜を発光層に用いたＥＬ素子が、本来の青緑色を示し、６００℃以上における熱処理に対しても安定である事を見い出した。それは、ひとたびＳｒの格子位置に添加されたＲｂ+ は、イオン半径が大きいためにＮａやＫに比べて熱拡散を起こしにくく、ＳｒＳ格子中に安定に存在できるためと考えられる。
【００２０】
図１は、本発明の一実施例における無機薄膜ＥＬ素子の構造を示す図である。図１に示すように、ガラス基板６上にＩＴＯ(Indium Tin Oxide)透明電極５、ＡＴＯ(Aluminium Titanium Oxide)第一絶縁層４、ＳｒＳ：Ｃｅ，Ｒｂ発光層３、ＡＴＯ第二絶縁層２、Ａｌ（アルミニウム）背面電極１を順に成膜することによりＥＬ素子を作製した。ＥＬ発光はガラス基板６を透して取り出す。各層の膜厚は、ＡＴＯ第一絶縁層４とＡＴＯ第二絶縁層２がともに２８０ｎｍ、ＳｒＳ：Ｃｅ，Ｒｂ発光層薄膜が１．２μｍである。
【００２１】
ＳｒＳ：Ｃｅ，Ｒｂ発光層は、電子線蒸着法により作製した。蒸着中、ガラス基板は４７０℃に保持した。成膜に要した時間は５〜１０分である。また、硫黄の不足を補うため、蒸着中に硫化水素を５sccm（標準条件下における毎分の量ｃｃ）供給した。
【００２２】
電子線蒸着に用いたＳｒＳ：Ｃｅ，Ｒｂペレットは、以下の方法により作製した。まずＳｒＳ粉末、Ｃｅ2Ｓ3粉末、Ｒｂ2Ｓ粉末を不活性ガス中で混合した。ＳｒＳに対するＣｅ2Ｓ3とＲｂ2Ｓの添加濃度は、それぞれ０．１ｍｏｌ％、４ｍｏｌ％である。それらを一軸性加圧成型法によりペレットの形に成型し、更に冷間等方向圧加圧法により３００ＭＰａ（メガパスカル）にて成型した。成型後のペレットは、不活性ガス（アルゴン：Ａｒ）雰囲気中にて９００℃、１時間、焼成した。同様な方法により、Ｒｂ2Ｓの代わりにＮａ2Ｓ，Ｋ2Ｓを添加したものも作製した。
【００２３】
図２は、上記の方法により作製したＳｒＳ：Ｃｅ薄膜ＥＬ素子（埋積したそのまま、即ちアニールなし）の１ＫＨｚ駆動の発光スペクトルである。横軸に波長（Wavelength）（ナノメートル）、縦軸に強度（Intensity）（任意単位）をとっている。試料の素子は、Ｎａ，Ｋ，Ｒｂを添加したものと、アルカリ金属を何も添加していないもの（Ｎｉｌ）の４つである。また同図には、緑色化していない本来のＳｒＳ：Ｃｅ発光の例として、ＳｒＳ：Ｃｅ粉末のフォトルミネッセンス（ＰＬ）スペクトルも示す。アルカリ金属を何も添加していない素子に比べ、添加した素子の発光スペクトルは、粉末試料のスペクトルに近い事が分かる。その中でもＲｂを添加した素子のスペクトルは、粉末試料のものと殆ど同じであり、Ｒｂが最も効果的である事が分かる。Ｒｂを添加した素子のＣＩＥ色度座標値は（０．１８，０．３４）である。これは、ＺｎＳ：Ｍｎとの組み合わせによる白色光の再現が可能な数値である。
【００２４】
図３は、輝度改善のために、６５０℃、１時間の熱処理を施したＥＬ素子の発光スペクトルを示す。横軸に波長（Wavelength）（ナノメートル）、縦軸に強度（Intensity）（任意単位）をとっている。Ｎａ，Ｋを添加した素子では、熱処理により、発光スペクトルが緑色側にシフトし、何も添加していない素子のものに近づく。それに対し、Ｒｂを添加した素子のスペクトルは、熱処理を施しても殆ど変化していない。つまり、Ｒｂを添加した素子の発光スペクトルは、熱的にも安定である事が分かる。
【００２５】
図４に、図２で示した素子の輝度（Luminance）（カンデラ／ｍ２）−印加電圧（Applied Voltage）（ボルト）特性を示す。アルカリ金属を何も添加していない素子に対し、Ｒｂを添加したものは輝度が１割ほど減少している。
【００２６】
図５は、同素子の移動電荷量（Transferred Charge）（マイクロクーロン／ｃｍ2）−印加電圧（Applied Voltage）（ボルト）特性である。アルカリ金属を何も添加していない素子に対し、アルカリ金属、特にＫやＲｂを添加した素子は、移動電荷量が３割ほど減少する。移動電荷量が減少すると、消費電力の低減がなされるＲｂを添加した素子は、図４、５を見比べると、移動電荷量の減少に対し輝度の減少割合が少ない。つまりＲｂ添加により、発光効率の向上がなされる。
【００２７】
図６に素子劣化試験の結果を示す。横軸に駆動時間（Aging Time）、縦軸に輝度（Luminance）（任意単位）と効率（Efficiency）（任意単位）をとっている。評価には、アルカリ金属を何も添加していない素子（Nil）と、Ｒｂを添加した素子を用いた。劣化試験は、ＥＬ素子を周波数１kHzのパルス電圧により駆動し、発光開始しきい電圧から４０Ｖ高い電圧にて行った。初期値に対する相対輝度、相対効率は、共にＲｂの添加により減少割合が低減されており、素子の劣化が改善されている事が分かる。
【００２８】
【発明の効果】
以上の説明からわかるように、本発明はＳｒＳ：Ｃｅの本来の発光色である青緑色を安定に再現されることが出来る。更に、上記の発光色の安定な再現性が、ガラス基板が耐えうる６５０℃以下の比較的低温域での熱処理によって得られる。従って、すでにＺｎＳ：Ｍｎで実績のある従来どおりのガラス基板を用いた青色薄膜ＥＬ素子の量産を可能とし、ＺｎＳ：Ｍｎと組合わせて白色ＥＬパネルの量産も可能となる。
【図面の簡単な説明】
【図１】本発明の一実施例における無機薄膜ＥＬ素子の構造を示す図。
【図２】本発明のＥＬ素子を含むアニール前の各試料素子の波長に対する発光強度特性図。
【図３】本発明のＥＬ素子を含むアニール後の各試料素子の波長に対する発光強度特性図。
【図４】本発明のＥＬ素子を含むアニール前の各試料素子の印加電圧に対する輝度特性図。
【図５】本発明のＥＬ素子を含む各試料素子の印加電圧に対する移動電荷量特性図。
【図６】本発明のＥＬ素子の駆動時間に対する輝度及び効率の関係を示す図。
【符号の説明】
１ Ａｌ背面電極
２ ＡＴＯ第二絶縁層
３ ＳｒＳ：Ｃｅ，Ｒｂ発光層
４ ＡＴＯ第一絶縁層
５ ＩＴＯ透明電極
６ ガラス基板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inorganic thin film electroluminescence which is one of electronic displays, and in particular, an electroluminescence (hereinafter abbreviated as EL) light emitting layer thin film related to an improvement of a SrS: Ce thin film which is a blue-green material. The present invention relates to an EL element and a method for producing an EL light emitting layer thin film.
[0002]
[Prior art]
SrS: Ce is a blue EL material that has been researched and developed for many years and has the brightness and luminous efficiency next to ZnS: Mn (manganese-activated zinc sulfide) that has already been put to practical use as an EL display panel. As shown, it has been expected as an EL material close to practical use. The excellent point of SrS: Ce is that white light emission can be easily obtained by combining SrS: Ce and ZnS: Mn. In order to reproduce a balanced white color in combination with ZnS: Mn, the emission color of SrS: Ce is set to (0.18, 0.37) or less in terms of CIE (Commission Internationale de l'Ecairag) chromaticity coordinate values. There is a need to. However, depending on the manufacturing method and conditions, the green component becomes stronger than the original emission color of SrS: Ce, which is one of the causes that hinder the practical application of SrS: Ce.
[0003]
The greening of the emission color of SrS: Ce is considered to occur due to the following physical factors. The light emission of SeS: Ce is emitted from Ce 3+ ions incorporated into the SrS lattice as trivalent cations. The Ce 3+ emission color changes because the energy value of the Ce 3+ 5d electrons involved in the emission is influenced by the crystal field (electric field strength and spatial symmetry around Ce 3+ in the SeS crystal). It is because it is easy to change. Possible causes of the crystal field change include Sr (strontium), S (sulfur) vacancies and impurities formed in the SrS lattice. Also, since the SrS matrix itself is chemically unstable, it is easy to make lattice defects. Furthermore, since Sr at the substitution position of Ce 3+ is a divalent cation and has a valence different from that of Ce 3+ , defects that compensate for the difference in valence are likely to be generated.
[0004]
As described above, greening of SrS: Ce emission is a problem inherent to the material, but in the case of SrS: Ce phosphor powder with no restriction on the firing temperature, sufficient SrS crystals are obtained by firing at a high temperature of 1000 ° C. or higher. And activation of the Ce emission center is possible. Further, [1] By controlling the composition ratio of Sr and S (see, for example, Patent Document 1), [2] By adding alkali metals Li, Na, K, Rb, etc. (for example, see Non-Patent Document 1). ), Phosphor powders that maintain the original blue-green emission and have high luminous efficiency have been produced.
[0005]
On the other hand, when an SrS: Ce thin film is manufactured for a light emitting layer of an EL element, the temperature at the time of film formation is limited by the heat resistance of a substrate or an insulating layer material used for the EL element. Generally, when a glass substrate is used, the upper limit is about 650 ° C., and even when a ceramic substrate is used, the upper limit is about 700 to 800 ° C. Therefore, unlike a powder phosphor, it is difficult to sufficiently crystallize SrS and activate the Ce emission center, and an SrS: Ce thin film having high emission efficiency with original blue-green emission has not been obtained. In order to produce high-quality SrS: Ce in such a low temperature range, [3] a monovalent element Na (sodium as a charge compensator for compensating for the difference in valence between Sr 2+ and Ce 3+ ), K (potassium), Ag (silver), or pentavalent elements N (nitrogen), P (phosphorus), etc. (see, for example, Non-Patent Document 2), [4] To make up for Sr defects A transition metal element Zn (zinc) or Mn (manganese) is added (for example, see Non-Patent Document 3), [5] After the thin film is formed, heat treatment is separately performed (for example, see Non-Patent Document 4), and the like. Is being studied. Despite these efforts, the emission color of Ce 3+ has not been fully controlled, and mass production of EL display panels using an SrS: Ce thin film as a light emitting layer has not been achieved.
[0006]
[Patent Document 1]
JP 2000-129254 A (paragraphs [0005] and [0011] in the specification)
[0007]
[Non-Patent Document 1]
H. Fukada et al., Improved Luminescent Properties of SrS: Ce Powder Phosphors through Co-Doping with Alkali Metals, Proc. 10th Int. Workshop on Inorganic and Organic Electroluminescence, (2000) pp. 113-116.
[0008]
[Non-Patent Document 2]
K. O. Velthaus et al., New Deposition Process for Very Blue and Bright Srs: Ce TFEL Devices, Digest of 1997 SID International Symposium, (1997) pp. 411-414.
[0009]
[Non-Patent Document 3]
R. H. Mauch et al., Improved SrS: Ce, Cl TFEL Devices by ZnS Co-Evaporation, Digest of 1995 SID International Symposium, (1995) pp. 720-723.
[0010]
[Non-Patent Document 4]
K. Ohmi et al., Improvement of Crystallographic and Electroluminescent Characteristics of SrS: Ce Thin Film Devices by Post-deposition Annealing in Ar-S Atmosphere, J. Appl. Phys. , Vol. 78 (1995) pp. 428-434.
[0011]
[Problems to be solved by the invention]
The light emitting layer thin film made of SrS: Ce has a problem in stably reproducing the blue-green color, which is the original emission color of SrS: Ce, in any of the conventional examples. The present invention provides a new additive material that solves the problem and a method for producing the light emitting layer thin film.
[0012]
[Means for Solving the Problems]
The present invention relates to an electroluminescent light-emitting layer thin film in which Rb is added to SrS: Ce, preferably an electroluminescent layer in which Rb is added to SrS: Ce having a Ce concentration of 0.01 to 1 mol% and an Rb concentration of 0.01 to 5 mol%. A luminescent light emitting layer thin film is provided. In this document, a substance obtained by adding Rb to SrS: Ce is sometimes abbreviated as SrS: Ce, Rb.
[0013]
The present invention also relates to an inorganic thin film electroluminescent device having a light emitting layer made of a thin film obtained by adding Rb to SrS: Ce, preferably SrS having a Ce concentration of 0.01 to 1 mol% and an Rb concentration of 0.01 to 5 mol%. The present invention provides an inorganic thin film electroluminescence device having a light emitting layer made of a thin film obtained by adding Rb to Ce.
[0014]
Here, when the Ce concentration is less than 0.01 mol%, the activation effect by Ce is hardly recognized, and when it exceeds 1 mol%, defects are generated in SrS, and the light emission efficiency is lowered. Further, if the Rb concentration is less than 0.01 mol%, there is almost no effect of adding Rb, and if it exceeds 5 mol%, defects are generated in SrS, and the luminous efficiency is lowered. Note that if Rb is limited to the effect of compensating the charge of Ce, the amount of Rb is considered to be the same as that of Ce. However, in reality, Sr defects exist in the host SrS, and Rb also compensates for the defects. It is considered that the upper limit value of Rb is higher than the upper limit value of Ce.
[0015]
Furthermore, the SrS: Ce, Rb thin film obtained by irradiating an electron beam to a pellet made of a mixed powder of SrS, Ce compound and Rb compound and evaporating the pellet is heated at a temperature of 400 to 800 ° C. in an inert gas atmosphere. Provided is a method for producing a light-emitting layer thin film that is heat-treated in a range. In this case, one or more of Ce 2 S 3 , CeCl 3 and CeF 3 is used as the Ce compound, and one or more of Rb 2 S, Rb 2 SO 4 and RbNO 3 is used as the Rb compound. Is preferred.
[0016]
The temperature of the heat treatment is 400 ° C. or higher under the condition that it is higher than the film formation temperature of the SrS: Ce, Rb thin film for the purpose of improving the crystallinity, and the temperature is such that the substrate as the base of the film does not undergo thermal degradation 800 ° C. or lower is selected.
[0017]
In the present invention, a small lump made of powder obtained by mixing SrS, Ce compound, and Rb compound is used as a pellet used in the production of the light emitting layer thin film, and the Rb concentration is set to 0.1 to 10 mol%. Here, if the Rb concentration is less than 0.1 mol%, there is almost no effect of adding the Rb concentration, and if it exceeds 10 mol%, it becomes a factor causing defects in the SrS matrix, and also causes the deterioration of the firing furnace. There is. Moreover, the reason why the upper limit value of the Rb concentration is higher than the upper limit value of the film is that evaporation during the process of Rb having a high vapor pressure is taken into consideration.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is basically an EL light-emitting layer thin film in which Rb is added to SrS: Ce. Here, since Rb is one of the alkali metals, the effect as a charge compensator in the production of the powder phosphor has been pointed out as described in the above prior art, but it is effective in the thin film phosphor. There are no examples of sex. Since the ionic radius of Sr 2+ , which is the substitution destination of Rb + ions, is close to Na + or K + , Na or K was considered more suitable as a charge compensator than Rb + .
[0019]
In the present invention, it has been found that an EL element using a SrS: Ce thin film to which Rb is added as a light emitting layer exhibits an original blue-green color and is stable to heat treatment at 600 ° C. or higher. This is presumably because Rb + once added to the lattice position of Sr is less likely to cause thermal diffusion than Na or K because of its large ionic radius and can exist stably in the SrS lattice.
[0020]
FIG. 1 is a diagram showing the structure of an inorganic thin film EL element in one embodiment of the present invention. As shown in FIG. 1, an ITO (Indium Tin Oxide)
[0021]
The SrS: Ce, Rb light emitting layer was produced by an electron beam evaporation method. During the vapor deposition, the glass substrate was kept at 470 ° C. The time required for film formation is 5 to 10 minutes. In order to make up for the shortage of sulfur, 5 sccm of hydrogen sulfide was supplied during deposition (amount cc per minute under standard conditions).
[0022]
The SrS: Ce, Rb pellet used for electron beam evaporation was produced by the following method. First, SrS powder, Ce 2 S 3 powder, and Rb 2 S powder were mixed in an inert gas. The addition concentrations of Ce 2 S 3 and Rb 2 S with respect to SrS are 0.1 mol% and 4 mol%, respectively. They were molded into pellets by a uniaxial pressure molding method, and further molded at 300 MPa (megapascal) by a cold isostatic pressure method. The molded pellets were fired at 900 ° C. for 1 hour in an inert gas (argon: Ar) atmosphere. By the same method, a material in which Na 2 S, K 2 S was added instead of Rb 2 S was also produced.
[0023]
FIG. 2 is an emission spectrum of 1 KHz drive of the SrS: Ce thin film EL element (as it is embedded, that is, without annealing) manufactured by the above method. The horizontal axis represents wavelength (nanometer) and the vertical axis represents intensity (arbitrary unit). There are four sample elements, one with Na, K, and Rb added and one with no alkali metal added (Nil). The figure also shows a photoluminescence (PL) spectrum of SrS: Ce powder as an example of the original SrS: Ce emission that is not green. It can be seen that the emission spectrum of the added element is close to the spectrum of the powder sample compared to the element to which no alkali metal was added. Among them, the spectrum of the element to which Rb is added is almost the same as that of the powder sample, and it can be seen that Rb is the most effective. The CIE chromaticity coordinate value of the element to which Rb is added is (0.18, 0.34). This is a numerical value capable of reproducing white light by a combination with ZnS: Mn.
[0024]
FIG. 3 shows an emission spectrum of an EL element that has been heat-treated at 650 ° C. for 1 hour in order to improve luminance. The horizontal axis represents wavelength (nanometer) and the vertical axis represents intensity (arbitrary unit). In the element to which Na and K are added, the emission spectrum shifts to the green side by heat treatment, and approaches that of the element to which nothing is added. On the other hand, the spectrum of the element to which Rb was added hardly changed even after heat treatment. That is, it can be seen that the emission spectrum of the element to which Rb is added is thermally stable.
[0025]
FIG. 4 shows luminance (Luminance) (candela / m 2 ) -applied voltage (volt) characteristics of the element shown in FIG. In contrast to the device to which no alkali metal is added, the luminance of the device to which Rb is added is reduced by about 10%.
[0026]
FIG. 5 shows the transfer charge (microcoulomb / cm 2 ) -applied voltage (volt) characteristics of the element. Compared to the device to which no alkali metal is added, the amount of mobile charge is reduced by about 30% in the device to which alkali metal, particularly K or Rb is added. In comparison with FIGS. 4 and 5, the element to which Rb is added, whose power consumption is reduced when the amount of mobile charge is reduced, has a lower luminance reduction rate than the amount of mobile charge. That is, the luminous efficiency is improved by adding Rb.
[0027]
FIG. 6 shows the result of the element deterioration test. The horizontal axis represents drive time (Aging Time), and the vertical axis represents luminance (arbitrary unit) and efficiency (arbitrary unit). For the evaluation, an element to which no alkali metal was added (Nil) and an element to which Rb was added were used. The deterioration test was performed by driving the EL element with a pulse voltage having a frequency of 1 kHz and a voltage 40V higher than the threshold voltage for starting light emission. Both the relative luminance and the relative efficiency with respect to the initial value are reduced by the addition of Rb, and it can be seen that the deterioration of the element is improved.
[0028]
【The invention's effect】
As can be seen from the above description, the present invention can stably reproduce blue-green, which is the original emission color of SrS: Ce. Furthermore, the above-described stable reproducibility of the luminescent color can be obtained by a heat treatment in a relatively low temperature range of 650 ° C. or lower that the glass substrate can withstand. Therefore, mass production of a blue thin film EL element using a conventional glass substrate already proven in ZnS: Mn is possible, and mass production of a white EL panel is also possible in combination with ZnS: Mn.
[Brief description of the drawings]
FIG. 1 is a diagram showing a structure of an inorganic thin film EL element in one embodiment of the present invention.
FIG. 2 is a light emission intensity characteristic diagram with respect to wavelength of each sample element before annealing including the EL element of the present invention.
FIG. 3 is an emission intensity characteristic diagram with respect to wavelength of each sample element after annealing including the EL element of the present invention.
FIG. 4 is a luminance characteristic diagram with respect to applied voltage of each sample element before annealing including the EL element of the present invention.
FIG. 5 is a characteristic diagram of mobile charge amount with respect to applied voltage of each sample element including the EL element of the present invention.
FIG. 6 is a graph showing a relationship between luminance and efficiency with respect to driving time of an EL element of the present invention.
[Explanation of symbols]
DESCRIPTION OF
Claims (7)
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