Dielectric Constant and Loss Tangent of Silicon at 700–900 GHz at Cryogenic Temperatures

Quasi-optical superconducting hot-electron bolometer (HEB) mixers have shown a competitive sensitivity at a frequency slightly lower than 1 THz when compared to superconducting SIS mixers. The advantage of low LO power requirement makes superconducting HEB mixers, especially suitable for array application. The far-field beam pattern, as well as coupling efficiency of quasi-optical superconducting HEB mixers, depends strongly upon the lens shape and the dielectric constant of the lens material. Therefore, in this letter we precisely measured the dielectric constant and loss tangent of high resistivity silicon at 4, 77, and 300 K in the frequency range of 700-900 GHz where many important molecular lines located. The measurements are performed by employing a quasi-optical vector network analyzer with a dynamic range as high as 110 dB to ensure high precision measurement. In addition, the dielectric constant of high-density polyethylene (HDPE) and polymethylpentene (TPX/PMP) are also measured since they are widely used in terahertz quasi-optical system.