Ba_xSr_（1-x）TiO_3铁电薄膜的制备及漏电流机理分析
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摘要
钛酸锶钡(BaxSr1-xTiO3,简记为BST)薄膜具有介电常数大、介电损耗低、非线性强、漏电流小、居里温度可调、热释电性高等特点,因此在超高密度集成的随机存储器(DRAM)、介质移相器、压控滤波器和非制冷红外探测等方面有着广泛的应用前景。在器件中,BST薄膜工作在外加直流电压下,过大的漏电流将严重影响薄膜器件的工作稳定性和使用寿命。本文围绕如何通过镁掺杂和制作钛酸锶钡与偏氟乙烯-三氟乙烯共聚物(P(VDF-TrFE))的复合膜来减小漏电流,以及低电场下漏电流机制的问题,通过实验制备和理论计算的方法来研究BST薄膜的漏电流相关特性。
首先,采用溶胶凝胶法(Sol-Gel)在Pt(111)/Ti/SiO2/Si(100)基片上制备了Mg掺杂的钛酸锶钡薄膜Ba0.4Sr0.6MgyTiO3(BSMT),研究了不同掺杂Mg含量和不同退火温度对BSMT薄膜漏电流特性的影响。用X射线衍射、扫描电子显微镜确定薄膜样品的成分和微观结构,并对BSMT薄膜的电流-电压特性(I-V)进行了测量。研究表明,随着Mg的加入,BSMT薄膜漏电流随之减小。当薄膜在700°C退火时有最小的漏电流,这可以用在XRD观察的薄膜在700°C下退火时结晶度最差来解释。
接着,分析了BSMT在低电场区(小于115kV/cm)的漏电流机制。用实验数据对比了两个模型------肖特基模型(Schottky current model)和肖特基限制电流模型(Schottky-limited current model),其中前者只适用于当绝缘体中的电子平均自由程大于或等于绝缘体厚度的情况,而后者则适用于相反的情况,实验结果对两种模型都符合得较好。文中提出了区分两种模型的方法,通过进一步比较从两种模型下所提取的光频介电常数? r,结论表明肖特基限制电流模型更加符合实验结果。在较高电场下,薄膜的漏电流机理为空间电荷限制电流(SCLC)。
最后,在Pt(111)/Ti/SiO2/Si(100)基片上制备了Ba0.4Sr0.6TiO3/P(VDF-TrFE)双层复合膜,其中Ba0.4Sr0.6TiO3薄膜层采用磁控溅射法,P(VDF-TrFE)薄膜层采用溶胶凝胶法(Sol-Gel)制作。考察了不同厚度P(VDF-TrFE)薄膜层对复合膜漏电流和电容值的影响。对复合薄膜的电流-电压特性(I-V)、电容-电压特性(C-V)一一进行了测量。实验结果表明随着P(VDF-TrFE)有机薄膜层的增加,复合薄膜的介电常数和漏电流有所降低。5V电压下,当所加P(VDF-TrFE)有机层厚度为150nm时,BST薄膜漏电流从10-8A下降到2×10-9A。
Barium strontium titanate(BaxSr1-xTiO3, short for BST)thin films were widelyapplied in ultra-high density integrated DRAM, dielectric phase filters, tunable filtersand uncooled infrared detector, due to its high dielectric permittivity, low dielectricloss, high dielectric nonlinearity, low leakage current, variable Curie temperature, andgood pyroelectric properties. In devices, BST thin film was directly applied DCvoltage, large leakage current can impact seriously on the stability and life time ofdevices. In present work, Mg-doped BST thin films and BST/Poly(Vinylidenefluoride—trifluoroethylene)(P(VDF-TrFE)) bilayer composites ferroelectric thin filmswere investigated, we study the properties of BST thin film by experimental andtheoretical calculation approach.
First, thin films of Mg-doped Barium strontium titanate (Ba0.4Sr0.6MgyTiO3,BSMT) thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by sol-geltechnique. The effects of Mg content and annealing temperature on the leakagecurrent properties were studied, respectively. The crystallized phase andmicrostructure were investigated using X-ray diffraction (XRD) and scanning electronmicroscope (SEM). Then leakage current-voltage (I-V) of the BSMT thin films weremeasured. The measured results showed that, as the Mg content in BST increased, theleakage current of BSMT thin films decreased. Meanwhile, the films annealed at700°C possessed the lowest leakage, which maybe explained byits worst crystallinityin the XRD spectra.
Second, the electrical conduction leakage mechanism in the low-field region,below 115 kV/cm, was investigated. Our experimental data fit both the Schottkycurrent model and the Schottky-limited current model well. The former is applicableto insulators onlyif the electronic mean-free path in the insulator is equal to or greaterthan the thickness of the insulator, but the latter is applicable when the situation is theopposite. Amethod to distinguish them was proposed in this work. By comparing theextracted values of optical dielectric constantε, the Schottky-limited current modelprovides a better fit to the experiment results. At higher field region the conductionmechanism is a space-charge-limited conduction (SCLC) current.
Finally, the Ba0.4Sr0.6TiO3/P(VDF-TrFE) bilayer composites ferroelectric thinfilms were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates, Ba0.4Sr0.6TiO3 and P(VDF-TrFE) thin films were prepared by RF Magnetron Sputtering and sol-gelmethods, respectively. The effects of different thickness of P(VDF-TrFE) thin filmson leakage current and dielectric permittivity were studied. Leakage current-voltage(I-V) and capacitance-voltage loops(C-V) of the Ba0.4Sr0.6TiO3/P(VDF-TrFE) thin filmwere measured. As the P(VDF-TrFE) thin films thickness increased, leakage currentand dielectric permittivity were reduced. When the thickness of P(VDF-TrFE) layerincreased to 150nm, the leakage of BST thin film decreased to 2×10-9Afrom 10-8Aat5V.
首先,采用溶胶凝胶法(Sol-Gel)在Pt(111)/Ti/SiO2/Si(100)基片上制备了Mg掺杂的钛酸锶钡薄膜Ba0.4Sr0.6MgyTiO3(BSMT),研究了不同掺杂Mg含量和不同退火温度对BSMT薄膜漏电流特性的影响。用X射线衍射、扫描电子显微镜确定薄膜样品的成分和微观结构,并对BSMT薄膜的电流-电压特性(I-V)进行了测量。研究表明,随着Mg的加入,BSMT薄膜漏电流随之减小。当薄膜在700°C退火时有最小的漏电流,这可以用在XRD观察的薄膜在700°C下退火时结晶度最差来解释。
接着,分析了BSMT在低电场区(小于115kV/cm)的漏电流机制。用实验数据对比了两个模型------肖特基模型(Schottky current model)和肖特基限制电流模型(Schottky-limited current model),其中前者只适用于当绝缘体中的电子平均自由程大于或等于绝缘体厚度的情况,而后者则适用于相反的情况,实验结果对两种模型都符合得较好。文中提出了区分两种模型的方法,通过进一步比较从两种模型下所提取的光频介电常数? r,结论表明肖特基限制电流模型更加符合实验结果。在较高电场下,薄膜的漏电流机理为空间电荷限制电流(SCLC)。
最后,在Pt(111)/Ti/SiO2/Si(100)基片上制备了Ba0.4Sr0.6TiO3/P(VDF-TrFE)双层复合膜,其中Ba0.4Sr0.6TiO3薄膜层采用磁控溅射法,P(VDF-TrFE)薄膜层采用溶胶凝胶法(Sol-Gel)制作。考察了不同厚度P(VDF-TrFE)薄膜层对复合膜漏电流和电容值的影响。对复合薄膜的电流-电压特性(I-V)、电容-电压特性(C-V)一一进行了测量。实验结果表明随着P(VDF-TrFE)有机薄膜层的增加,复合薄膜的介电常数和漏电流有所降低。5V电压下,当所加P(VDF-TrFE)有机层厚度为150nm时,BST薄膜漏电流从10-8A下降到2×10-9A。
Barium strontium titanate(BaxSr1-xTiO3, short for BST)thin films were widelyapplied in ultra-high density integrated DRAM, dielectric phase filters, tunable filtersand uncooled infrared detector, due to its high dielectric permittivity, low dielectricloss, high dielectric nonlinearity, low leakage current, variable Curie temperature, andgood pyroelectric properties. In devices, BST thin film was directly applied DCvoltage, large leakage current can impact seriously on the stability and life time ofdevices. In present work, Mg-doped BST thin films and BST/Poly(Vinylidenefluoride—trifluoroethylene)(P(VDF-TrFE)) bilayer composites ferroelectric thin filmswere investigated, we study the properties of BST thin film by experimental andtheoretical calculation approach.
First, thin films of Mg-doped Barium strontium titanate (Ba0.4Sr0.6MgyTiO3,BSMT) thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by sol-geltechnique. The effects of Mg content and annealing temperature on the leakagecurrent properties were studied, respectively. The crystallized phase andmicrostructure were investigated using X-ray diffraction (XRD) and scanning electronmicroscope (SEM). Then leakage current-voltage (I-V) of the BSMT thin films weremeasured. The measured results showed that, as the Mg content in BST increased, theleakage current of BSMT thin films decreased. Meanwhile, the films annealed at700°C possessed the lowest leakage, which maybe explained byits worst crystallinityin the XRD spectra.
Second, the electrical conduction leakage mechanism in the low-field region,below 115 kV/cm, was investigated. Our experimental data fit both the Schottkycurrent model and the Schottky-limited current model well. The former is applicableto insulators onlyif the electronic mean-free path in the insulator is equal to or greaterthan the thickness of the insulator, but the latter is applicable when the situation is theopposite. Amethod to distinguish them was proposed in this work. By comparing theextracted values of optical dielectric constantε, the Schottky-limited current modelprovides a better fit to the experiment results. At higher field region the conductionmechanism is a space-charge-limited conduction (SCLC) current.
Finally, the Ba0.4Sr0.6TiO3/P(VDF-TrFE) bilayer composites ferroelectric thinfilms were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates, Ba0.4Sr0.6TiO3 and P(VDF-TrFE) thin films were prepared by RF Magnetron Sputtering and sol-gelmethods, respectively. The effects of different thickness of P(VDF-TrFE) thin filmson leakage current and dielectric permittivity were studied. Leakage current-voltage(I-V) and capacitance-voltage loops(C-V) of the Ba0.4Sr0.6TiO3/P(VDF-TrFE) thin filmwere measured. As the P(VDF-TrFE) thin films thickness increased, leakage currentand dielectric permittivity were reduced. When the thickness of P(VDF-TrFE) layerincreased to 150nm, the leakage of BST thin film decreased to 2×10-9Afrom 10-8Aat5V.
引文
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