Dielectric spectroscopy of perovskite-type artificial superlattice in micro to millimeter wave region

由原子级薄膜技术制成的人工超晶格，由于其人造结构，有可能显示出优异的新性质。在这项研究中，我们发展了一种测量钙钛矿型人工超晶格介电性能的技术，从kHz到几GHz，以便发现这种超晶格在微米和毫米波区域的独特性质。首先，研制了一套介电性能测量系统，测量了BaTiO_3/SrTiO_3超晶格的介电性能，测量频率可达110 MHz。超晶格的介电常数是通过对薄膜上的叉指电极获得的导纳数据的电磁场分析确定的。结果表明，具有10个晶胞周期的超晶格在110 MHz范围内具有很高的介电常数，可达33,000。测量了超晶格的介电性能，发现尽管材料具有顺电/顺电结合，但具有10个晶胞周期的超晶格仍表现出铁电性。此外，还提出了一种新的微波介电性能测量方法。在该方法中，使用细平面电极来测量样品的导纳。在100 MHz以下，超晶格的介电常数在8,000以上，而在3 GHz时，介电常数下降了4,000左右。

Artificial superlattices made by a thin film technology of atomic level have potential to show excellent and new properties due to the man made structures. In this study, we have developed a technology to measure dielectric properties of the perovskite type artificial superlattices from kHz to few GHz in order to find unique properties of the superlattices in micro and millimeter wave regions. At first, a system which enables us to measure dielectric properties up to 110MHz was developed and the properties of BaTiO_3/SrTiO_3 superlattices were measured. The dielectric permittivity of the superlattices was determined using electromagnetic field analysis of admittance data obtained using interdigital electrodes on the films. It was found that the superlattice with the period of 10 unit cells showed high permittivity of 33,000 up to 110 MHz. The dielectric properties of SrZrO_3/SrTiO_3 superlattices were also measured and it was found that the superlattice with the period of 10 unit cells showed ferroelectricity in spite of the paraelectric/paraelectric combination of the materials. Furthermore, a new measuring method of dielectric properties in micro wave region was proposed. In this method, fine planer electrodes were employed to measure admittance of the specimen. The dielectric permittivity of [(SrZrO_3)_<10>/(SrTiO_3)_<10>]_4 superlattice was above 8,000 below 100 MHz and it decreased around 4,000 at 3 GHz.