Wideband dielectric properties of silicon and glass substrates for terahertz integrated circuits and microsystems

Abstract

This paper presents a comprehensive study of the optical and electrical dielectric material properties of six commonly-used silicon and glass substrates at terahertz (THz) frequencies, including refractive index, absorption coefficient, dielectric constant and loss factor. The material characterization techniques used in this paper feature THz time-domain transmission and reflection spectroscopy with the measurement frequencies from 0.5 THz up to a maximum of 6.5 THz. Of the six selected dielectric and semiconductor substrates, two are silicon wafers with resistivities ranging from 0.001 to 0.02 Ω-cm. From the measurement results, loss tangents of the selected silicon wafers range from 0.680 to 5.455 and the dielectric constants are from 1.079 to 17.735. The four other wafers are all glass-based substrates: D263 glass, Borofloat 33 glass, fused silica and Sapphire. From the measurements, it is found that the THz dielectric properties vary considerably between the substrate samples e.g. dielectric constants range from 1.925 to 3.207 while loss tangents are from 0.042 × 10−3 to 0.127. Most of the selected silicon and glass-based substrates are quite useful for many THz applications, e.g., THz integrated circuits (THz ICs), THz microsystem technologies (THz MSTs) and THz system-on-a-chip (THz SoC) and system-on-substrate (SiP).

Performance Analysis of Millimeter-Wave Optic Modulators in Thin-Film Lithium Niobate

“…At these frequencies there also exist resonance-like features likely due to reflections at the two ends of the transmission lines. The extracted αd gives rise to an effective dielectric loss tangent of 0.025 for this transmission line mode, which is consistent with the loss tangents of the dielectrics involved here, i.e., 0.025 for silicon [29], 0.008 for lithium niobate [30], and 0.000042 for SiO2 [31].…”

RF Glass Technology Is Going Mainstream: Review and Future Applications

“…Specifically regarding the mm-wave spectrum, different fused silica substrates have recently been characterized in [31] up to 110 GHz by means of a loaded disc resonator showing very constant permittivity and loss tangent values of r =3.8±0.1 and tanδ=1.5-5 × 10 −4 , respectively. Among other inorganic substrates for sub-THz and THz components, similar electric properties for fused silica have been reported in [32] across the frequency range from 0.5 THz to 6.5 THz using THz time-domain spectroscopy. Moreover, fused silica -like many other glass materials -features of high chemical and thermal resistance [33], [21], but the downside is its relatively low CTE for using in heterogeneous integration technologies.…”

Integrated Lithium Niobate Intensity Modulator on a Silicon Handle With Slow-Wave Electrodes

“…There is a rapid drop-off in S(2,1) from DC to roughly 1 GHz from a low-frequency impedance mismatch. On the Si handle, with its high-microwave absorption tangent (tanδ Si = .025 dB/cm −1 ) compared to LiNbO 3 (tanδ LN = .008 dB/cm −1 ) and SiO 2 (tanδ SiO2 = .000042 dB/cm −1 ), dielectric loss dominates above roughly 50 GHz [16]. Furthermore, considering ϵ Si = 11.7, W STEM must be relatively wide to properly match n RF and n og which does not significantly reduce current bunching in the interaction region when compared to a standard CPW design [7].…”