硅片上集成高介电调谐率的柱状纳米晶BaTiO3铁电薄膜

钛酸钡(BaTiO₃)具有优异的介电、铁电、压电和热释电等性能, 在微电子机械系统和集成电路领域具有广泛的应用。降低BaTiO₃薄膜的制备温度使其与现有的CMOS-Si工艺兼容, 已成为应用研究和技术开发中亟需解决的问题。本研究引入与BaTiO₃晶格常数相匹配的LaNiO₃作为缓冲层, 以调控其薄膜结晶取向, 在单晶Si(100)基底上450 ℃溅射制备了结构致密的柱状纳米晶BaTiO₃薄膜。研究表明：450 ℃溅射温度在保持连续柱状晶结构和(001)择优取向的前提下, 能获得相对较大的柱状晶粒(平均晶粒直径27 nm), 一定残余应变也有助于其获得了较好的铁电和介电性能。剩余极化强度和最大极化强度分别达到了7和43 μC·cm^-2。该薄膜具有良好的绝缘性, 在 0.8 MV·cm^-1电场下, 漏电流密度仅为10^-5 A·cm^-2。其相对介电常数ε_r展现了优异的频率稳定性：在1 kHz时ε_r为155, 当测试频率升至1 MHz, ε_r仅轻微降低至145。薄膜的介电损耗较小, 约为0.01~0.03 (1 kHz ~ 1 MHz)。通过电容-电压测试, 该薄膜材料展示出高达51%的介电调谐率, 品质因子亦达到17(@1 MHz)。本研究所获得的BaTiO₃薄膜在介电调谐器件中有着良好的应用前景。

Columnar Nanograined BaTiO3 Ferroelectric Thin Films Integrated on Si with a Sizable Dielectric Tunability

BaTiO₃ has a wide range of applications in microelectromechanical systems and integrated circuits due to its excellent dielectric, ferroelectric, piezoelectric, and pyroelectric properties. For the applied research and device applications of BaTiO₃ films, reducing its deposition temperature to be compatible with the CMOS-Si technology is an important Challenge. Here, with the help of a LaNiO₃ buffer layer which has a closely-matched lattice with BaTiO₃, (001)-textured BaTiO₃ films were sputter-deposited at 450 ℃ on single crystalline Si(100) substrates, which consisting of well-cryotallized, evenly-distributed columnar nanograins with an average grain size of 27 nm. Our result showed that this deposition temperature can maintain the columnar nanograin structure with a relatively large grain size, leading to a good ferroelectric performance. In addition, a small residual strain on Si was also helpful to improve its ferroelectric and dielectric properties. The remnant polarization and saturated polarization of these BaTiO₃ films reached 7 and 43 μC·cm^-2, respectively, while leakage current densities were as low as 10^-5 A·cm^-2 at an applied electric field of 0.8 MV·cm^-1. These BaTiO₃ films also displayed excellent frequency stability with a low dielectric loss in which relative dielectric constant measured to be ~155 at 1 kHz, slightly being reduced to ~145 after increasing the frequency to 1 MHz. Meanwhile, the dielectric loss slightly increased from 0.01 at 1 kHz to 0.03 at 1 MHz. Lastly, through capacitance-voltage (C-V) tests, these films exhibited a large dielectric tunability of~51% and a figure of merit (FOM) of ~17 (@1 MHz). These films have a good potential for applications in tunable dielectrics.