TWI402874B - Laminated ceramic capacitors - Google Patents

Laminated ceramic capacitors Download PDF

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TWI402874B
TWI402874B TW096130889A TW96130889A TWI402874B TW I402874 B TWI402874 B TW I402874B TW 096130889 A TW096130889 A TW 096130889A TW 96130889 A TW96130889 A TW 96130889A TW I402874 B TWI402874 B TW I402874B
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dielectric
ceramic
ceramic capacitor
laminated
laminated ceramic
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TW200830339A (en
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Shinsuke Takeoka
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Taiyo Yuden Kk
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Description

層疊陶瓷電容器
本發明係與內部電極包含卑金屬之層疊陶瓷電容器有關,且係與將Cu使用於內部電極之層疊陶瓷電容器有關。
在使用於攜帶型機器、通信機器等電子機器之層疊陶瓷電容器方面,小型化及高容量化之需求與日俱增。又,有關可靠度之需求亦增大,因此,介電率之溫度特性(TC)平坦且高溫加速壽命特性(以下稱為壽命特性)良好之層疊陶瓷電容器成為一大市場需求。
就作為如此之小型大容量的層疊陶瓷電容器之製得機構而言,譬如有如日本特開平5-9066號公報所示般使用非還原性介電體瓷器組成物之方法。然而,為了使之具有耐還原性,此種介電體瓷器組成物係添加了許多添加物。基於此因,為了將此介電體瓷器組成物進行燒結,則需要1100℃以上之燒結溫度。又,內部電極亦必須使用融點高之Ni。
另一方面,從能量效率之面,已有人提出可以1000℃程度之低溫燒結的材料所構成的層疊陶瓷電容器。譬如,有方法使用了非還原性介電體瓷器組成物,而其係可與日本特開平5-217426號公報所示Cu等內部電極材料同時燒結者。然而,在如此之介電體瓷器組成物方面,雖溫度特性平坦,但介電率低,故難以製得小型大容量之層疊陶瓷電容器。
又,在製得溫度特性平坦且介電率高(ε≧2000)之層疊陶瓷電容器方面,譬如有方法使用包含燒結體粒子(晶粒)之介電體瓷器,而其係具有日本特開平10-308321號公報所示般之核殼結構者。如此之核殼結構有必要使Mg等添加物擴散至結晶粒子。然而,為了使添加物擴散至結晶粒子,則需要1100℃以上之燒結溫度。
[專利文獻1]日本特開平5-9066號公報[專利文獻2]日本特開平5-217426號公報[專利文獻3]日本特開平10-308321號公報
本發明之目的為獲得一種層疊陶瓷電容器,其係在還原氣體環境下可在1080℃以下燒結,介電率為2000以上,且溫度特性符合X7R特性或X8R特性者。
本發明提出一種層疊陶瓷電容器作為第1解決方法,其包含:陶瓷層疊體,其係呈略長方體形狀者;內部電極,其係在該陶瓷層疊體中,形成為經由介電陶瓷對向且被往交互不同之端面拉出者;及外部電極,其係形成於前述陶瓷層疊體之兩端面,電性連接於被拉出至該端面的前述內部電極之各個者;其特徵為:前述內部電極包含Cu或Cu合金;前述介電陶瓷係以BaTiO3 (BT)為主體之鈣鈦礦型介電體材料的燒結體,而其係包含以剖面觀察時直徑的平均值為400 nm以下之晶粒與粒界者;前述晶粒係包含具有晶域圖案之介電體及形成於該介電體表面之殼者。
根據上述第1解決方法,可獲得溫度特性符合X7R特性或X8R特性之層疊陶瓷電容器。又,藉由在1080℃以下之較低溫還原氣體環境下之燒結,而可獲得介電率2000以上之介電陶瓷,故可獲得小型且大容量之層疊陶瓷電容器。
又,提出一種層疊陶瓷電容器作為第2解決方法,其係設以剖面觀察時前述晶粒直徑的平均值為D、前述殼厚度的平均值為t時,t/D為2%~10%者。根據前述第2解決方法,可獲得一種層疊陶瓷電容器,其係溫度特性符合X7R特性或X8R特性,且具有在150℃-20 V/μm之環境下24小時以上不劣化之壽命特性者。
又,本發明提出一種層疊陶瓷電容器作為第3解決方法,其係在被前述內部電極所夾住之前述介電陶瓷中分佈著Cu者。根據上述第3解決方法,藉由Cu分佈於介電陶瓷,而殼及粒界之電位障壁變高,因此,即使於1080℃以下之較低溫還原氣體環境下燒結後之介電陶瓷,亦可獲得充分之絕緣性,高溫加速壽命特性提高。
根據本發明,可獲得一種層疊陶瓷電容器,其係在還原氣體環境下可在1080℃以下燒結,介電率為2000以上,且溫度特性符合X7R特性或X8R特性者。
針對與本發明有關之層疊陶瓷電容器之實施型態作說明。如圖1所示,本實施形態之層疊陶瓷電容器1具備陶瓷層疊體2,其包含:介電陶瓷3,其係作層狀重疊而成者;及內部電極4,其係經由該介電陶瓷而對向形成者。在陶瓷層疊體2之兩端面上以與內部電極電性連接之方式形成外部電極5,在其上方依照需要而形成第1電鍍層6、第2電鍍層7。
如圖2所示般,介電陶瓷3包含晶粒8與粒界12。前述晶粒8係如圖3所示般,包含介電體9、及形成於該介電體9之表面的殼10。介電體9具有條狀之晶域圖案11。此晶域圖案係以TEM(穿透式電子顯微鏡)觀察介電陶瓷之剖面時所見之模樣,且係藉由結晶粒子之自發分極所顯現者。介電體9與殼10由於光學特性不同,因此其交界處可作較明確之觀察。
殼10係在燒結過程中,譬如稀土類之化合物、Mn之化合物等添加物及介電體9之一部分融解於已成液相之燒結助劑中而產生固熔體,並再度析出於介電體9之表面而形成者。此殼10係絕緣電阻比介電體9為高,厚度越大則壽命特性越提高。再者,就稀土類之化合物而言,係從La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu及Y所選出之至少1種之氧化物。又,就Mn之化合物而言,譬如有MnO、MnCO3 、Mn3 O4 等氧化物。又,粒界12係位於晶粒與晶粒間之部分,存在著已成為液相之燒結助劑、添加物。
另一方面,在溫度特性方面,係依照晶粒之大小、介電體與殼之平衡而決定。欲製得X7R特性或X8R特性之層疊陶瓷電容器,係使用前述晶粒之徑的平均值為400 nm以下之介電陶瓷。如晶粒之徑的平均值為400 nm以下,相較於超過400 nm以上者,晶粒本身之介電率變低,因此介電率之溫度變化變小,可在更廣之溫度範圍獲得平坦之溫度特性。又,為了兼具良好之壽命特性與X7R特性或X8R特性般之溫度特性,係使用如下條件之介電陶瓷:該條件係如前述晶粒之徑的平均值為D、前述殼之厚度的平均值為t時,則t/D成為2%~10%。再者,X7R特性係指,以25℃時之介電率為基準,在-55℃~125℃之溫度範圍內,介電率之變化率為±15%之情形。又,X8R特性係指,以25℃時之介電率為基準,在-55℃~150℃之溫度範圍內,介電率之變化率為±15%之情形。
在此,根據圖4,說明晶粒之徑的平均值D及殼之厚度的平均值t的算出方法。首先,以TEM將介電陶瓷層之剖面作擴大觀察,針對一個晶粒8進行如次之測定。以圍繞晶粒8之方式,畫出圓×0,然後,以將此圓×0分成8等分之方式,畫出4條線分×1、×2、×3及×4。接著,針對線分×1,將跨於晶粒8之長度L進行測定。接著,進行測定從介電體9與殼10之交界處至粒界為止之寬度W1及W2,並算出(W1+W2)/2=W之值。針對線分×2、×3及×4亦進行L與W之算出,並算出晶粒1個之L與W的平均值。接著,將此針對100個晶粒進行,從L之平均值求出晶粒之徑的平均值D,從W之平均值求出t。
又,如介電陶瓷3係以將BaTiO3 設為主體之鈣鈦礦型介電體材料之燒結體所構成的情形,可製得介電率2000以上之介電陶瓷。就將BaTiO3 設為主體之鈣鈦礦型介電體材料而言,除BaTiO3 之外,還有將Ba之一部分以Ca或Sr進行置換者、將Ti之一部分以Zr或Hf進行置換者等。
再者,將BaTiO3 設為主體之鈣鈦礦型介電體係通常以1100℃以上之溫度所燒結者為多,在使用燒結助劑等於1080℃以下或1000℃以下之還原氣體環境使之緻密化的情形,絕緣電阻係變低、壽命特性降低。然而,將內部電極4以Cu或Cu合金形成之情形,內部電極4之Cu之一部分係擴散至介電陶瓷3(尤其擴散至夾於內部電極4之介電陶瓷3)中。藉由此擴散分佈後之Cu而使殼10及粒界12之電位障壁變高,而可獲得充分之絕緣性,使高溫加速特性得以提昇。就Cu合金而言,譬如有Cu-Ni合金、Cu-Ag合金等。
再者,內部電極4係藉由把導電膠以網板印刷等方法印刷於陶瓷軟性薄片而形成。又,欲從內部電極4將Cu之一部分擴散於介電陶瓷3中時,可藉由如下方式進行:在燒結後(含燒結步驟中之降溫時),於氮等氣體環境中以700℃程度之溫度進行加熱處理。
外部電極5係以Cu、Ni、Ag、Cu-Ni合金、Cu-Ag合金所構成,以下列方式形成:將導電膠塗佈於已燒結之陶瓷層疊體2後進行烘烤,或將導電膠塗佈於未燒結之陶瓷層疊體2後與陶瓷層疊體2之燒結同時進行烘烤。在外部電極5之上,係藉由電解電鍍等而形成電鍍層6、7。第1電鍍層6具有保護外部電極5之功能,係由Ni、Cu等所構成。第2電鍍層7具有加強銲錫濡濕性之功能,係由Sn或Sn合金等所構成。
在此,根據具體實施例,針對本發明之效果作說明。首先,如表1所示般,準備了M1~M14之出發原料。
在此,關於添加物及燒結助劑,係以對主成分100mol之mol數表示。又,關於BT粒子之大小,係以SEM(掃描電此顯微鏡)將主成分之原料粉末作擴大觀察,針對300個粒子進行粒子徑測定,作為其平均值。
(實施例1)
準備表1之出發原料M3,將之以球磨機進行15小時之濕式混合,乾燥後於400℃在大氣環境中作2小時之預燒,進行乾式粉碎而獲得介電體材料粉末。接著,在此粉末加入聚乙烯醇縮丁醛、有機溶劑、可塑劑並作混合,而形成陶瓷漿。將此陶瓷漿以滾筒塗佈機予以薄片化,而製得厚度5 μm之陶瓷軟性薄片。在此陶瓷軟性薄片上以網版印刷進行塗佈Cu內部電極膠(試料1-1)或Ni內部電極膠(試料1-2),而形成內部電極圖案。把已形成內部電極圖案之陶瓷軟性薄片,進行堆疊20片並壓合,將之作切斷分割為4.0×2.0mm大小,而形成粗製晶片。將此粗製晶片在氮氣體環境中進行脫膠,機著在還原氣體環境中以表2所示溫度進行燒結。燒結模式係設為如下模式:以表所示溫度保持2小時,其後使溫度下降,在約700℃將氣體環境變換為氮氣體環境,在保持2小時後,下降至室溫。燒結後將Cu外部電極膠塗佈於內部電極露出面,在惰性氣體中進行烘烤。
針對藉由此方式所製得之3.2×1.6 mm大小且內部電極間之介電陶瓷厚度為4 μm的層疊陶瓷電容器,將晶粒徑之平均值、t/D、介電率、溫度特性、高溫加速壽命進行測定,並整理為表2。再者,介電率係在25℃將靜電電容以LCR計進行測定,從試料之層疊陶瓷電容器的交叉面積、介電陶瓷厚度及層數進行計算而求出。又,溫度特性係以25℃之靜電電容為基準,把在-55℃~125℃(X7R)或-55℃~150℃(X8R)之靜電電容的變化為±15%之範圍者設為合格。又,高溫加速壽命係以150℃、20 V/μm之負荷,施行各試料各15個,將絕緣電阻值成為1 MΩ以下之時間為24小時以上的情形設為○。
從上述結果可知,內部電極為Cu者,可製得介電率為2000以上、溫度特性符合X7R特性或X8R特性、且高溫加速壽命特性良好之層疊陶瓷電容器。另一方面,內部電極為Ni者,在1000℃之燒結方面,高溫加速壽命特性並無法符合所期望之水準。
(實施例2)
準備表1之出發原料M4,除以表3所示條件施行濕式混合之攪拌時間與燒結溫度之外,並以與實施例1同樣方式,形成層疊陶瓷電容器,進行測定晶粒徑之平均值、t/D、介電率、溫度特性、高溫加速壽命,並整理為表3。
從上述結果可知,內部電極為Cu、晶粒徑之平均值為400 nm以下、t/D為2~10%者,可製得介電率為2000以上、溫度特性符合X7R特性或X8R特性、且高溫加速壽命特性良好之層疊陶瓷電容器。另一方面,如t/D小於2%,則壽命特性降低,如大於10%,則溫度特性不符合X7R特性或X8R特性。再者,從表3可知,t/D係可藉由調整燒結溫度、攪拌時間而進行控制。
(實施例3)
準備表1之出發原料M1及M2,以與實施例1同樣方式形成層疊陶瓷電容器,進行測定晶粒徑之平均值、t/D、介電率、溫度特性、高溫加速壽命,並整理為表4。在此,針對添加物之效果進行驗證。
從上述結果可知,關於添加物,如為僅含有Mn氧化物與稀土類氧化物的任一方之情形,則壽命特性降低。
(實施例4)
準備表1之出發原料M5及M6,以與實施例1同樣方式形成層疊陶瓷電容器,進行測定晶粒徑之平均值、t/D、介電率、溫度特性、高溫加速壽命,並整理為表5。
從上述結果可知,內部電極為Cu、晶粒徑之平均值為0.40 μm(亦即400nm)者,可製得溫度特性符合X7R特性之層疊陶瓷電容器。另一方面,晶粒徑之平均值為0.45 μm者,溫度特性並不符合X7R特性或X8R特性。
(實施例5)
準備表1之出發原料M7~M14,以與實施例1同樣方式形成層疊陶瓷電容器,進行測定晶粒徑之平均值、t/D、介電率、溫度特性、高溫加速壽命,並整理為表6。在此,係針對改變稀土類之種類之情形及改變主成分鈣鈦礦介電體之情形進行驗證。
從上述結果可知,即使將稀土類之種類改變為Dy以外者,或將主成分鈣鈦礦介電體作改變,內部電極為Cu、晶粒徑之平均值為400 nm且t/D為2~10%者,亦可製得溫度特性符合X7R特性或X8R特性且高溫加速壽命良好之層疊陶瓷電容器。
從上述結果可知,如為本發明範圍之層疊陶瓷電容器的話,於還原氣體環境下可進行在1080℃以下之燒結,可製得介電率為2000以上、溫度特性符合X7R特性或X8R特性之層疊陶瓷電容器。
1...層疊陶瓷電容器
2...陶瓷層疊體
3...介電陶瓷
4...內部電極
5...外部電極
6...第1電鍍層
7...第2電鍍層
8...晶粒
9...介電體
10...殼
11...晶域圖案
12...粒界
圖1係顯示本發明之層疊陶瓷電容器之模式剖面圖。
圖2係圖1之A的部分擴大圖。
圖3係顯示晶粒之微細結構之模式圖。
圖4係顯示晶粒徑之平均值與殼之厚度之平均值的測定方法之圖。
8...晶粒
9...介電體
10...殼
11...晶域圖案

Claims (7)

  1. 一種層疊陶瓷電容器,包含:陶瓷層疊體,其係呈略長方體形狀者;內部電極,其係在該陶瓷層疊體中,形成為經由介電陶瓷對向且被往交互不同之端面拉出者;及外部電極,其係形成於前述陶瓷層疊體之兩端面,電性連接於被拉出至該端面的前述內部電極之各個者;前述內部電極包含Cu或Cu合金;前述介電陶瓷係以BaTiO3 為主體之鈣鈦礦型介電體材料的燒結體,而其係包含以剖面觀察時直徑的平均值為400 nm以下之晶粒與粒界者;前述晶粒係包含具有晶域圖案之介電體及形成於該介電體表面之殼者;Cu係分佈在置於前述內部電極間之前述介電陶瓷中;設以剖面觀察時前述晶粒直徑之平均值為D、前述殼厚度之平均值為t時,t/D為2%~10%。
  2. 一種層疊陶瓷電容器,其包含:陶瓷層疊體,其係呈略長方體形狀,且包含層積於厚度方向上之複數個介電陶瓷層,該複數介電陶瓷層末端形成彼此相對之端面;內部電極,其係形成於彼此層疊之各介電陶瓷層之間,且該內部電極由各別之二末端面交互延伸;及外部電極,其係形成於前述內部電極之兩端面,且電性連接於被拉出至該端面的前述內部電極之各個者;前述內部電極各包含Cu或Cu合金;前述介電陶瓷層各為主要包含BaTiO3 之鈣鈦礦型介電體材料的燒結體,而其係包含以剖面觀察時直徑的平均 值為400 nm以下之晶粒與粒界者;前述晶粒係包含具有晶域圖案之介電體及形成於該介電體表面之殼者;Cu係由與介電陶瓷層接觸之內部電極擴散且分佈於介電陶瓷層中;設以剖面觀察時前述晶粒直徑之平均值為D、前述殼厚度之平均值為t時,t/D為2%~10%。
  3. 如請求項2之層疊陶瓷電容器,其介電率為2000以上,且滿足X7R特性或X8R特性。
  4. 如請求項2之層疊陶瓷電容器,其中,各介電陶瓷層之厚度為1 μm至10 μm。
  5. 如請求項2之層疊陶瓷電容器,其中,各介電陶瓷層進而包含稀土類之化合物及Mn之氧化物。
  6. 如請求項5之層疊陶瓷電容器,其中,稀土類之化合物至少包含La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu及Y所選出之至少1種之氧化物。
  7. 如請求項2之層疊陶瓷電容器,其中,於形成燒結體時,該殼係沉澱物。
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