Optical Characterizations of Polarization-Sensitive Millimeter-Wave Silicon Bolometers

International audienceIn this paper, we investigate two bolometer detectors with a pixel size of 500 µm and 1200 µm to address, respectively, the 0.6 mm and 1.5 mm wavelengths in order to study the temperature and polarization of cosmic microwave background (CMB). The pixels are polarization sensitive using Ti/TiN superconducting absorbers. They are deposited on suspended doped Silicon thermometers operating at low temperature, typically in the range 50–100 mK. A quarter-wavelength optical cavity formed between absorbers and metal reflector of these pixels is adapted for an absorption around 100 µm. In order to address the millimeter band, we have used a dielectric (Silicon) superstrate placed above the absorbers to shift the absorption band to larger wavelengths. In this paper, we have conducted finite-element (FEM) electromagnetic simulations to optimize the pixel design. The optical absorption measurements of the pixels were performed at room temperature using a terahertz time-domain spectrometer (THz-TDS) and at 300 mK with a Fourier-transform spectrometer (FTS). Finally, an estimation of pixels performances is discussed showing, an expected high responsivity of around 10$^{11}$ V/W and a low noise equivalent power (NEP) of 10$^{–18}$ W/Hz$^{1/2}$