Search

In 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 1011 V/W and a low noise equivalent power (NEP) of 10–18 W/Hz1/2. [ABSTRACT FROM AUTHOR]

Polarization-sensitive detectors at 120-500 GHz are required for the observation of the cosmic microwave background radiation. In this paper, superconducting thin films based on Ti/TiN bilayers are developed to be integrated as electromagnetic wave absorbers in suspended cooled silicon bolometers. The critical temperature (Tc) is tuned in the range of 600-800 mK through the superconductivity proximity effect between Ti and TiN to optimize the absorption of the incident power while minimizing the heat capacity of the system at low temperature. Ti/TiN bilayer samples are fabricated on silicon with two different thicknesses (100/5 and 300/5 nm). Electrical characterizations at low temperature have been performed and revealed the effect of thermal annealing (20-250 °C) on residual stress, Tc, critical magnetic field (Hc) and resistance above Tc. A physical characterization by X-ray photoelectron spectroscopy provides evidences of oxidized states which may explain these effects. [ABSTRACT FROM AUTHOR]