BaTiO_3基多层片式热敏陶瓷材料研究
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摘要
近几年来，随着微电子技术和表面贴装技术的快速发展，电子元器件的集成化、微型化、片式化已经成为当今微电子技术发展的趋势，而正温度系数热敏电阻（PTCR）陶瓷器件也朝着微型化、片式化和低阻化方向发展。由于传统的单层式BaTiO_3基PTCR陶瓷材料的固有电阻率很高，无法进一步地降低其室温电阻，而多层片式BaTiO_3基PTCR陶瓷材料不仅具有较低的室温电阻和较高的升阻比，而且还具有尺寸小、稳定性好、耐大电流冲击能力好等优点，常用作过载电流保护元件，是一个具有巨大的市场前景和实用价值的研究课题。
采用流延的制作方法和还原再氧化的烧结工艺来制备多层片式BaTiO_3基PTCR陶瓷材料，通过系统地研究Ba/Ti比、A位施主掺杂、B位施主掺杂、烧结温度、降温方式、再氧化热处理工艺等对该多层片式PTCR陶瓷材料的影响，成功地制备出室温电阻为0.3和升阻比（Lg(Rmax/Rmin)）为3.3的多层片式Ba(Ti_(1-x)Nb_x)O_3基陶瓷以及室温电阻为0.13和升阻比为3.2的多层片式Ba_(1.001)(Ti_(1-x)Nb_x)O_3基陶瓷。其具体的研究如下：
采用流延法来制备片式BaTiO_3基PTCR陶瓷，研究了Ba/Ti比对其电性能、微结构以及PTCR效应的影响，结果表明了Ti过量样品的平均晶粒尺寸大小变化不大，它的室温电阻率很小，受再氧化时间和Ba/Ti比的影响也较小；与之相反，Ba过量的样品晶粒大且颗粒大小分布不均，它的室温电阻率较大，受再氧化时间和Ba/Ti比的影响也较大。实验研究表明Ba/Ti为1.006的(Ba_(m-0.007)Sm_(0.007))TiO_3基陶瓷的室温电阻率和升阻比分别为80.8·cm和3，高Ba/Ti比（m=1.026）的(Ba_(m-0.007)Sm_(0.007))TiO_3基陶瓷的室温电阻率和升阻比分别为108.5·cm和3.8。
对于高Ba/Ti比片式Ba_(1.022-x)Sm_xTiO_3基陶瓷来说，采用同样的共烧法研究了烧结温度和冷却方式对该样品的微观结构、电性能和PTCR特性等的影响，结果表明了高施主掺杂浓度可以抑制样品晶粒的生长，样品的室温电阻率和升阻比都随着烧结温度的升高而减小，较高温度烧结的样品的室温电阻率变化很小，低温烧结可以获得较高的耐压值。此外，样品的冷却速率越慢，气孔就越少，该陶瓷样品的室温电阻率随着冷却速率的增加而增加，并且适当地延长冷却时间可以降低样品的室温电阻率。样品的临界施主掺杂浓度随着冷却速率的增加而逐渐地向着低浓度方向移动，冷却速率为4℃/min的样品具有较好的PTCR效应，它的室温电阻率、升阻比、受主态密度（NS）和肖特基势垒高度（）分别为157.4·cm、3.16、6.911013cm–2和0.59eV。高冷却速率可以导致样品晶界内比晶粒内更易于失氧，而低冷却速率比高冷却速率更容易使晶粒和晶界失氧。
采用还原再氧化的烧结方法，研究了施主掺杂量、烧结温度和再氧化温度对多层片式Ba(Ti_(1-x)Nb_x)O_3基陶瓷的电性能和PTCR特性的影响，成功地制备出了尺寸为3.6mm×1.8mm×1.4mm、室温电阻为0.3和升阻比为3.3的多层片式PTCR陶瓷器件。样品在还原气氛中1100℃~1220℃下烧结2h且在空气中600℃再氧化1h后它的受主态密度NS是介于2.47×10~(13)~7.19×10~(130cm~(–2)范围内。
最后研究了施主掺杂0.35mol%Nb~(5+)的多层片式Ba(Ti_(1-x)Nb_x)O_3基陶瓷在还原气氛中1160℃烧结2h且在空气中600℃再氧化0~8h，实验结果表明样品在600℃低温下再氧化也可以得到很低的室温电阻和较好的PTCR效应，700℃是晶粒获得再氧化的临界温度，理想的再氧化温度和时间应分别控制在850℃和6h以内。另外，还推断出在Ni Ba(Ti_(1-x)Nb_x)O_3界面层内Nb~(5+)替代Ti~(4+)位起施主作用和Ni~(2+)替代Ti~(4+)位起受主作用是相互补偿的，这是B位施主掺杂的优势。成功地制备出了尺寸为3.6mm×1.8mm×1.4mm、室温电阻为0.38和升阻比为3.5的多层片式Ba(Ti_(1-x)Nb_x)O_3基陶瓷器件，并且还成功地制备出尺寸为3.6mm×1.8mm×1.4mm、室温电阻为0.13、升阻比为3.2和温度系数约为6%/℃的多层片式Ba_(1.001)(Ti_(1-x)Nb_x)O_3基陶瓷器件。
In recent years, with the rapid development of microelectronics and surface-mountingtechnique (SMT), integration, miniaturization and chip type of electronic component havebecome the trend of today’s microelectronics technology. Accordingly micromation, chiptype and low room-temperature resistance are the developmental trend of the positivetemperature coefficient of resistivity (PTCR) ceramics. It is difficult to further reduce theinherent resistance of the BaTiO_3-based PTCR ceramics by the traditional method. However,the multilayer chip type PTCR ceramics not only have the lower room-temperatureresistance and the higher resistivity jump, but also have small size, well stability, goodenduring large current rushing, which are used to the protection component of the overloadcurrent in integrated circuit, therefore become a research subject with large market prospectand practical value.
The multilayer chip BaTiO_3-based PTCR ceramics are prepared by tape casting andreduction reoxidation method. The influence of Ba/Ti rate, donor dopants of A site, donordopants of B site, sintering temperature and reoxidation heat treatment on the electricalproperties of the multilayer chip Ba(Ti_(1-x)Nb_x)O_3ceramics has been studied. The ceramicswith the room-temperature resistance of0.3and a resistance jump (Lg(Rmax/Rmin)) of3.3were successfully prepared. moreover, the multilayer chip Ba1.001(Ti1-xNbx)O3ceramics withroom-temperature resistance of0.13and a resistance jump of3.2. The detailed research isas follows:
The chip type BaTiO_3-based ceramics are prepared by reduction reoxidation method.The effect of Ba/Ti rate on the electrical properties, microstructure, and PTCR effect of thesamples is studied. The results indicated that the mean grain size of the excess-Ti sampleshas a little change; its room-temperature resistivity is very small and rarely affected by thereoxidation time and Ba/Ti rate, while the characteristics of the excess-Ba samples is justcontrary to the excess-Ti samples. The room-temperature resistivity and the resistivity jumpof the (Ba_(m-0.007)Sm_(0.007))TiO_3ceramics with Ba/Ti rate (m) of1.006and1.026are80.8·cm,3and108.5·cm,3.8, respectively.
The effect of the sintering temperature and the cooling mode on microstructure, electrical properties and PTCR characteristics of the chip type Ba_(1.022-x)Sm_xTiO_3ceramicswith high Ba/Ti rate has been investigated. The results indicated that the grain growth isinhibited by the high donor-doped concentration, the room-temperature resistivity and theresistivity jump of the samples decrease with an increase of the sintering temperature. Thelow room-temperature resistivity of the samples can be obtained by the higher sinteringtemperature. The higher breakdown voltage of the samples is obtained based on the lowersintering temperature. In addition, it is indicated that the lower cooling rate, the porosity isless. The room-temperature resistivity of the samples increases with increase in the coolingrate, and lower room-temperature resistivity is obtained by prolonging the cooling duration;moreover, the corresponding dopant concentration of the minimum resistivity is shifted tolower values with increasing cooling rate. In addition, samples that have been cooled at acooling rate of4°C/min after sintering in a reducing atmosphere show pronounced PTCRcharacteristics, with a resistance-jumping ratio greater by3.16orders of magnitude, inaddition to achieving a low room-temperature resisitivity of157.4·cm. Furthermore, theacceptor-state density (Ns) and height of the potential barrier () for these samples are6.9110~(13)cm~(–2)and0.59eV, respectively. A higher cooling rate leads to a larger number ofoxygen losses in the grain-boundary region.
On the basis of the reduction reoxidation method, the influence of the donor-dopedconcentration, the sintering temperature and reoxidation temperature on the electricalproperties and PTCR characteristics of the multilayer chip type Ba(Ti_(1-x)Nb_x)O_3ceramicshave been investigated. The ceramics with a size of3.6mm×1.8mm×1.4mm obtained ata low reoxidized temperature of600°C after sintering at1160°C show a remarkable PTCReffect, with a resistance jump larger by3.3orders of magnitude, along with a low RTresistance of0.3. Furthermore, the acceptor-state density of the samples sintered at thesintering temperature of1100–1220°C is in the range from2.47×1013to7.19×1013cm–2.Finally, the influence of the annealing treatment on the electrical properties and PTCRbehavior of mutilayer Ba(Ti_(1-x)Nb_x)O_3-based ceramics with Ni internal electrode has beeninvestigated. The results indicate that the room-temperature resistance and grain-boundaryresistance of the ceramics both increase with the increasing reoxidation temperature or time.In addition, the0.35mol%Nb~(5+)-doped Ba(Ti_(1-x)Nb_x)O_3ceramics with a size of3.6mm×1.8mm×1.4mm reoxidized under a low temperature of600°C for6h after sintering1160°C for2h showed a remarkable PTCR behavior, with a resistance jump of3.5orders ofmagnitude, along with a low RT resistance of0.38. Meanwhile, the multilayer chip typeBa_(1.001)(Ti_(1-x)Nb_x)O_3-based ceramics with a size of3.6mm×1.8mm×1.4mm, a resistanceof0.13, a resistance jump of3.2, and a temperature coefficient of6%/C was successfullyprepared. In addition,700C for the grains is the critical reoxidation temperature. Theperfect reoxidation temperature should be controlled as not longer than850C, moreover,the suitable reoxidation time should be controlled within6h. In particularly, it is consideredthat Ti site in BaTiO_3should be replaced by Nb~(5+)in order to compensate the acceptor actionsof Ni diffused from inner electrodes for the interface layer of Ni Ba_(1.001)(Ti_(1-x)Nb_x)O_3, this isthe advantages of the B-site donor dopant to the multilayer chip type BaTiO_3-based PTCRceramics.
采用流延的制作方法和还原再氧化的烧结工艺来制备多层片式BaTiO_3基PTCR陶瓷材料，通过系统地研究Ba/Ti比、A位施主掺杂、B位施主掺杂、烧结温度、降温方式、再氧化热处理工艺等对该多层片式PTCR陶瓷材料的影响，成功地制备出室温电阻为0.3和升阻比（Lg(Rmax/Rmin)）为3.3的多层片式Ba(Ti_(1-x)Nb_x)O_3基陶瓷以及室温电阻为0.13和升阻比为3.2的多层片式Ba_(1.001)(Ti_(1-x)Nb_x)O_3基陶瓷。其具体的研究如下：
采用流延法来制备片式BaTiO_3基PTCR陶瓷，研究了Ba/Ti比对其电性能、微结构以及PTCR效应的影响，结果表明了Ti过量样品的平均晶粒尺寸大小变化不大，它的室温电阻率很小，受再氧化时间和Ba/Ti比的影响也较小；与之相反，Ba过量的样品晶粒大且颗粒大小分布不均，它的室温电阻率较大，受再氧化时间和Ba/Ti比的影响也较大。实验研究表明Ba/Ti为1.006的(Ba_(m-0.007)Sm_(0.007))TiO_3基陶瓷的室温电阻率和升阻比分别为80.8·cm和3，高Ba/Ti比（m=1.026）的(Ba_(m-0.007)Sm_(0.007))TiO_3基陶瓷的室温电阻率和升阻比分别为108.5·cm和3.8。
对于高Ba/Ti比片式Ba_(1.022-x)Sm_xTiO_3基陶瓷来说，采用同样的共烧法研究了烧结温度和冷却方式对该样品的微观结构、电性能和PTCR特性等的影响，结果表明了高施主掺杂浓度可以抑制样品晶粒的生长，样品的室温电阻率和升阻比都随着烧结温度的升高而减小，较高温度烧结的样品的室温电阻率变化很小，低温烧结可以获得较高的耐压值。此外，样品的冷却速率越慢，气孔就越少，该陶瓷样品的室温电阻率随着冷却速率的增加而增加，并且适当地延长冷却时间可以降低样品的室温电阻率。样品的临界施主掺杂浓度随着冷却速率的增加而逐渐地向着低浓度方向移动，冷却速率为4℃/min的样品具有较好的PTCR效应，它的室温电阻率、升阻比、受主态密度（NS）和肖特基势垒高度（）分别为157.4·cm、3.16、6.911013cm–2和0.59eV。高冷却速率可以导致样品晶界内比晶粒内更易于失氧，而低冷却速率比高冷却速率更容易使晶粒和晶界失氧。
采用还原再氧化的烧结方法，研究了施主掺杂量、烧结温度和再氧化温度对多层片式Ba(Ti_(1-x)Nb_x)O_3基陶瓷的电性能和PTCR特性的影响，成功地制备出了尺寸为3.6mm×1.8mm×1.4mm、室温电阻为0.3和升阻比为3.3的多层片式PTCR陶瓷器件。样品在还原气氛中1100℃~1220℃下烧结2h且在空气中600℃再氧化1h后它的受主态密度NS是介于2.47×10~(13)~7.19×10~(130cm~(–2)范围内。
最后研究了施主掺杂0.35mol%Nb~(5+)的多层片式Ba(Ti_(1-x)Nb_x)O_3基陶瓷在还原气氛中1160℃烧结2h且在空气中600℃再氧化0~8h，实验结果表明样品在600℃低温下再氧化也可以得到很低的室温电阻和较好的PTCR效应，700℃是晶粒获得再氧化的临界温度，理想的再氧化温度和时间应分别控制在850℃和6h以内。另外，还推断出在Ni Ba(Ti_(1-x)Nb_x)O_3界面层内Nb~(5+)替代Ti~(4+)位起施主作用和Ni~(2+)替代Ti~(4+)位起受主作用是相互补偿的，这是B位施主掺杂的优势。成功地制备出了尺寸为3.6mm×1.8mm×1.4mm、室温电阻为0.38和升阻比为3.5的多层片式Ba(Ti_(1-x)Nb_x)O_3基陶瓷器件，并且还成功地制备出尺寸为3.6mm×1.8mm×1.4mm、室温电阻为0.13、升阻比为3.2和温度系数约为6%/℃的多层片式Ba_(1.001)(Ti_(1-x)Nb_x)O_3基陶瓷器件。
In recent years, with the rapid development of microelectronics and surface-mountingtechnique (SMT), integration, miniaturization and chip type of electronic component havebecome the trend of today’s microelectronics technology. Accordingly micromation, chiptype and low room-temperature resistance are the developmental trend of the positivetemperature coefficient of resistivity (PTCR) ceramics. It is difficult to further reduce theinherent resistance of the BaTiO_3-based PTCR ceramics by the traditional method. However,the multilayer chip type PTCR ceramics not only have the lower room-temperatureresistance and the higher resistivity jump, but also have small size, well stability, goodenduring large current rushing, which are used to the protection component of the overloadcurrent in integrated circuit, therefore become a research subject with large market prospectand practical value.
The multilayer chip BaTiO_3-based PTCR ceramics are prepared by tape casting andreduction reoxidation method. The influence of Ba/Ti rate, donor dopants of A site, donordopants of B site, sintering temperature and reoxidation heat treatment on the electricalproperties of the multilayer chip Ba(Ti_(1-x)Nb_x)O_3ceramics has been studied. The ceramicswith the room-temperature resistance of0.3and a resistance jump (Lg(Rmax/Rmin)) of3.3were successfully prepared. moreover, the multilayer chip Ba1.001(Ti1-xNbx)O3ceramics withroom-temperature resistance of0.13and a resistance jump of3.2. The detailed research isas follows:
The chip type BaTiO_3-based ceramics are prepared by reduction reoxidation method.The effect of Ba/Ti rate on the electrical properties, microstructure, and PTCR effect of thesamples is studied. The results indicated that the mean grain size of the excess-Ti sampleshas a little change; its room-temperature resistivity is very small and rarely affected by thereoxidation time and Ba/Ti rate, while the characteristics of the excess-Ba samples is justcontrary to the excess-Ti samples. The room-temperature resistivity and the resistivity jumpof the (Ba_(m-0.007)Sm_(0.007))TiO_3ceramics with Ba/Ti rate (m) of1.006and1.026are80.8·cm,3and108.5·cm,3.8, respectively.
The effect of the sintering temperature and the cooling mode on microstructure, electrical properties and PTCR characteristics of the chip type Ba_(1.022-x)Sm_xTiO_3ceramicswith high Ba/Ti rate has been investigated. The results indicated that the grain growth isinhibited by the high donor-doped concentration, the room-temperature resistivity and theresistivity jump of the samples decrease with an increase of the sintering temperature. Thelow room-temperature resistivity of the samples can be obtained by the higher sinteringtemperature. The higher breakdown voltage of the samples is obtained based on the lowersintering temperature. In addition, it is indicated that the lower cooling rate, the porosity isless. The room-temperature resistivity of the samples increases with increase in the coolingrate, and lower room-temperature resistivity is obtained by prolonging the cooling duration;moreover, the corresponding dopant concentration of the minimum resistivity is shifted tolower values with increasing cooling rate. In addition, samples that have been cooled at acooling rate of4°C/min after sintering in a reducing atmosphere show pronounced PTCRcharacteristics, with a resistance-jumping ratio greater by3.16orders of magnitude, inaddition to achieving a low room-temperature resisitivity of157.4·cm. Furthermore, theacceptor-state density (Ns) and height of the potential barrier () for these samples are6.9110~(13)cm~(–2)and0.59eV, respectively. A higher cooling rate leads to a larger number ofoxygen losses in the grain-boundary region.
On the basis of the reduction reoxidation method, the influence of the donor-dopedconcentration, the sintering temperature and reoxidation temperature on the electricalproperties and PTCR characteristics of the multilayer chip type Ba(Ti_(1-x)Nb_x)O_3ceramicshave been investigated. The ceramics with a size of3.6mm×1.8mm×1.4mm obtained ata low reoxidized temperature of600°C after sintering at1160°C show a remarkable PTCReffect, with a resistance jump larger by3.3orders of magnitude, along with a low RTresistance of0.3. Furthermore, the acceptor-state density of the samples sintered at thesintering temperature of1100–1220°C is in the range from2.47×1013to7.19×1013cm–2.Finally, the influence of the annealing treatment on the electrical properties and PTCRbehavior of mutilayer Ba(Ti_(1-x)Nb_x)O_3-based ceramics with Ni internal electrode has beeninvestigated. The results indicate that the room-temperature resistance and grain-boundaryresistance of the ceramics both increase with the increasing reoxidation temperature or time.In addition, the0.35mol%Nb~(5+)-doped Ba(Ti_(1-x)Nb_x)O_3ceramics with a size of3.6mm×1.8mm×1.4mm reoxidized under a low temperature of600°C for6h after sintering1160°C for2h showed a remarkable PTCR behavior, with a resistance jump of3.5orders ofmagnitude, along with a low RT resistance of0.38. Meanwhile, the multilayer chip typeBa_(1.001)(Ti_(1-x)Nb_x)O_3-based ceramics with a size of3.6mm×1.8mm×1.4mm, a resistanceof0.13, a resistance jump of3.2, and a temperature coefficient of6%/C was successfullyprepared. In addition,700C for the grains is the critical reoxidation temperature. Theperfect reoxidation temperature should be controlled as not longer than850C, moreover,the suitable reoxidation time should be controlled within6h. In particularly, it is consideredthat Ti site in BaTiO_3should be replaced by Nb~(5+)in order to compensate the acceptor actionsof Ni diffused from inner electrodes for the interface layer of Ni Ba_(1.001)(Ti_(1-x)Nb_x)O_3, this isthe advantages of the B-site donor dopant to the multilayer chip type BaTiO_3-based PTCRceramics.
引文
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