Millimeter-Wave Permittivity Variations of an HR Silicon Substrate from the Photoconductive Effect

Abstract

The photoinduced microwave complex permittivity of a highly resistive single-crystal silicon wafer was extracted from a bistatic free-space characterization test bench operating in the 26.5–40 GHz frequency band under CW optical illumination at wavelengths of 806 and 971 nm. Significant variations in the real and imaginary parts of the substrate’s permittivity induced by direct photoconductivity are reported, with an optical power density dependence, in agreement with the theoretical predictions. These experimental results open the route to ultrafast system reconfiguration of microwave devices in integrated technology by an external EMI-protected and contactless control with unprecedented performance.

Optically Controlled Gain Modulation for Microwave Metasurface Antennas

“…These variations are due to the change in permittivity caused by the different light penetration depths at different optical wavelengths. This was also found in [ 48 ].…”

“…The photoinduced microwave complex permittivity of a highly resistive single-crystal silicon wafer can be extracted by the use of these formulas from a bistatic free-space characterization test bench operating in the Ka-band under CW optical illumination at wavelengths of 806 and 971 nm. The characterization test bench is illustrated in [ 48 ]…”

“…The numerical results of normalized radiation patterns are shown in Figure 4 . Complex dielectric constants, shown in this figure, are retrieved by the formulas described in Section 2 and the measurements presented in [ 48 ], based on the optical power density (OPD) and optical wavelength specified in the next section.…”