Silicon-based passives fro integrated microwave and infrared applications

An investigation of Si-based passive components in microwave and infrared frequencies has been undertaken. Coplanar wavegudies (CPWs) with electrodes in direct contact with moderately doped Si substrates were characterized at microwave frequencies. A new nonlinear circuit model applicable for CPW lines on both direct metal-semiconductor contacts and SiO2/Si MOS-like substrates has been developed and verified experimentally using bias-dependent s-parameter measurements from 100 MHz to 10 GHz. In contrast to conventional R-L-C-G models, the proposed model replicates dispersive effects due to finite substrate resistivity by including nonlinear frequency-independent junction capacitances and conductances. The modeled junction capacitances and conductances show excellent scalability with line geometry and substrate doping concentration. Capacitance-voltage and current-voltage measurements have been performed to investigate the model's substrate doping type dependence (both n- and p-type). Analysis of the model indicates that a full back-to-back metal-semiconductor junction contact model is required for CPWs on n-type substrates, while the higher Schottky barrier height of typical metal contacts to p-type Si permits a simpler one-sided junction model for CPWs on p-type substrates.

For infrared detector applications, dipole antennas backed by a dielectric-filled cavity were also explored to increase air-side directive gain for antenna-coupled diode detectors. The proposed antenna schemes are designed to be compatible with conventional IC fabrication processes. A parametric study of antenna design reveals that a 10 dB boresight gain can be achieved when the cavity dimensions are properly chosen to excite predominantly TE10 mode aperture fields. The dipole resonant frequency is found to decrease with increasing dipole length and its input impedance is sensitive to the dipole position within the cavity.

K-band scale models of the antenna were fabricated and measured at 28.3 GHz to conclusively evaluate the performance of the antenna designs. The antennas demonstrated 10 dB directivity and –25 dB cross-polarization at boresight. The cross-polarization was limited by the dipole feed and misalignment. Measured antenna radiation efficiency was better than 70% throughout the interested frequency range. The power loss was attributed to filling dielectric and metallic sidewall loss. The measured s-parameters and radiation pattern showed good match to 3-dimensional electromagnetic simulations using HFSS.