Terra tool - IEEE Circuits and Devices Magazine

hin film characterization is important for the semiconductor industry as it pushes for smaller and faster circuits and devices. Materials with a high dielectric constant are required for improved insulation and reduction of tunneling between layers, and low dielectric materials are needed for interconnects with reduced capacitance [1]. As feature sizes of circuits and devices approach 100 nm and chip frequencies climb into the upper gigahertz to terahertz range, it becomes increasingly important to have a convenient method of characterizing properties of thin dielectric films in the gigahertz to terahertz frequency range [2]. Thin-film dielectric materials are being explored for many applications. Interest in plastic-based electronics is spurring the development of organic-inorganic hybrid materials and organic transistors on plastic [3], [4]. Single crystal optoelectronic devices are being developed for thin-film transistors and microelectromechanical systems (MOEMS) [5]. In certain materials, the optical and dielectric properties of thin films are assumed to be different from those of bulk materials since the structures of the thin films are altered due to the presence of fine grains, mechanical stresses, formation of interfacial layers, or rough interfaces during the thin-film deposition process [6]. One way of measuring dielectric and optical properties of materials at terahertz frequency during the past decade has been terahertz time-domain spectroscopy [7]. This method extracts both real and imaginary parts of the dielectric property of materials by measuring the temporal electric field transmitted through materials. The Fourier-transformed spectrum from the measured terahertz waveform in the time-domain gives information on both amplitude and phase, so that it can extract real and imaginary parts of dielectric properties in the frequency domain. This method was successfully demonstrated with several materials such as semiconductors, liquids, gases, biological materials, and superconductors to obtain dielectric properties of materials [8]-[11]. However, if the thickness of the material is comparable to or thinner than the wavelength of the terahertz wave, the phase and amplitude changes by dielectric materials tends to be difficult to measure with time-domain spectroscopy because of the very small interaction length. To overcome this difficulty, terahertz