Yttrium iron garnet (YIG) is a promising material for various terahertz applications due to its special optical properties. At present, a high-quality YIG wafer is the desire of terahertz communities and it is still challenging to prepare substrate-free YIG single crystal films. In this work, we prepared wafer-level substrate-free La:YIG single crystal films, for the first time, to our knowledge. Terahertz optical and magneto-optical properties of La:YIG films were characterized by terahertz time domain spectroscopy (THz-TDS). Results show that the as-prepared La:YIG film has an insertion loss of less than 3 dB and a low absorption coefficient of less than 10 cm−1$10{\mathrm{cm}}^{-1}$ below 1.6 THz. Benefitting from the thickness of the substrate-free YIG films and low insertion loss, their terahertz properties could be further manipulated by simply using a wafer-stacking technique. When four La:YIG films were stacked, there was an insertion loss of less than 10 dB in the range of 0.1−1.2 THz$0.1-1.2\mathrm{THz}$. The Faraday rotation angle of the four-layer-stacked La:YIG films reached 19°, and the isolation could reach 17 dB. By further increasing the stacking number to eight pieces, a remarkable Faraday rotation angle of 45° was achieved with an isolation of 23 dB, which is important for practical application in the THz band. This material may provide a milestone opportunity to make various non-reciprocal devices, such as isolators and phase shifters.

中文翻译：

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用于宽带可调谐太赫兹隔离器的晶圆级无衬底 YIG 单晶薄膜

钇铁石榴石（YIG）由于其特殊的光学特性，是一种用于各种太赫兹应用的有前途的材料。目前，高质量的YIG晶圆是太赫兹界的共同愿望，而制备无衬底的YIG单晶薄膜仍然具有挑战性。据我们所知，在这项工作中，我们首次制备了晶圆级无衬底的 La:YIG 单晶薄膜。La:YIG 薄膜的太赫兹光学和磁光特性通过太赫兹时域光谱 (THz-TDS) 进行表征。结果表明，所制备的La:YIG薄膜在1.6 THz以下具有小于3 dB的插入损耗和小于10 cm - 1 $10{\mathrm{cm}}^{-1}$的低吸收系数。受益于无基板 YIG 薄膜的厚度和低插入损耗，它们的太赫兹特性可以通过简单地使用晶圆堆叠技术来进一步控制。当四片 La:YIG 薄膜堆叠时，在0.1 – 1.2 THz $0.1-1.2\mathrm{THz}$范围内的插入损耗小于 10 dB 。四层堆叠的La:YIG薄膜的法拉第旋转角达到19°，隔离度可达17 dB。通过进一步将堆叠数量增加到八片，实现了 45° 的法拉第旋转角和 23 dB 的隔离度，这对于太赫兹频段的实际应用非常重要。这种材料可能为制造各种不可逆器件（例如隔离器和移相器）提供里程碑式的机会。