High Terahertz Absorbing Nanoscale Metal Films for Fabrication of Micromechanical Bi-material THz Sensors

摘要

The terahertz (THz) region of the electromagnetic spectrum covers frequencies ranging from approximately 100 GHz to 10 THz. This region of the spectrum has not been fully utilized due to the lack of compact and efficient sources as well as detectors. The aim of the present research is to explore the use of thin metal films as high THz absorbing materials and determine their THz absorbing characteristics analytically as well as experimentally. The films are to be used in bi-material based suspended structure, which sense minute changes in temperature due to THz absorption via difference in thermal expansion coefficients. The amount of deformation can be measured by reflecting a light beam from the pixel structure to determine the THz power incident on it. During the initial phase, design and fabrication of efficient THz absorbing multi- layer stack was carried out. The stack consists of a dielectric Bragg reflector and a metal film. The Bragg reflector serves to maximize reflection in the visible spectral range (required by the readout scheme), while the metal serves to provide strong absorption of THz radiation. The absorption characteristics of the stack were simulated using COMSOL finite element modeling and theoretical analysis performed using Fresnel's equations and then compared with the corresponding experimental results. The measured absorption characteristics of the stack agree well with the analysis. In addition, the thickness of the metal film was optimized for maximizing the THz absorption of the stack.