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We report on the implementation of a vacuum parallel-plate capacitor manufactured using a straightforward process that allows to accurately set nanoscale vacuum gaps in order to reach fairly large capacitances with small footprints. Vacuum gaps between 150 and 300 nm have been achieved. To prevent native oxides and therefore two-level systems, both electrodes are made of TiN-based layers. We implemented the vacuum parallel-plate capacitors into lumped-element kinetic inductance detectors and compared their performances to standard interdigitated capacitor-based detectors. The vacuum capacitor detectors achieved higher quality factors (up to 1.1 × 106) and lower frequency noise (2.8 ± 0.5 Hz2/Hz at 10 Hz). Furthermore, we demonstrate that the noise generated within the meander of the lumped-element kinetic inductance detector can be as important as the one generated in the capacitance. [ABSTRACT FROM AUTHOR]

YBa2Cu3O6+x (YBCO) cuprates are semiconductive when oxygen depleted (x < 0.5). They can be used for uncooled thermal detection in the near-infrared: (i) low temperature deposition on silicon substrates, leading to an amorphous phase (a-YBCO); (ii) pyroelectric properties exploited in thermal detectors offering both low noise and fast response above 1 MHz. However, a-YBCO films exhibit a small direct current (DC) electrical conductivity, with strong non-linearity of current–voltage plots. Calcium doping is well known for improving the transport properties of oxygen-rich YBCO films (x > 0.7). In this paper, we consider the performances of pyroelectric detectors made from calcium-doped (10 at. %) and undoped a-YBCO films. First, the surface microstructure, composition, and DC electrical properties of a-Y0.9Ca0.1Ba2Cu3O6+x films were investigated; then devices were tested at 850 nm wavelength and results were analyzed with an analytical model. A lower DC conductivity was measured for the calcium-doped material, which exhibited a slightly rougher surface, with copper-rich precipitates. The calcium-doped device exhibited a higher specific detectivity ( D * = 7.5 × 10 7   c m · H z / W at 100 kHz) than the undoped device. Moreover, a shorter thermal time constant (<8 ns) was inferred as compared to the undoped device and commercially available pyroelectric sensors, thus paving the way to significant improvements for fast infrared imaging applications. [ABSTRACT FROM AUTHOR]

To improve the optical coupling in microwave kinetic inductance detectors (MKIDs), we investigate the use of a reflective plate beneath the meandered absorber. We designed, fabricated and characterized high-Q factors TiN-based MKIDs on sapphire operating at optical wavelengths with a Au/Nb reflective thin bilayer below the meander. The reflector is set at a quarter-wave distance from the meander using a transparent Al2O3 dielectric layer to reach the peak photon absorption. We expect the plate to recover undetected photons by reflecting them back onto the absorber. [ABSTRACT FROM AUTHOR]

Following optical pulses (λ = 405 nm) on titanium nitride microwave kinetic inductance detectors cooled down at temperatures T ≤ T c / 20 ( T c ≃ 4.6 K), we observe a large phase-response highlighting two different modes simultaneously that are nevertheless related. The first corresponds to the well-known transition of cooper-pair breaking into quasi-particles, which produces a known phase response. This is immediately followed by a large inverse response lasting several hundreds of microseconds to several milliseconds depending on the temperature. We propose to model this inverse pulse as the thermal perturbation of the superconductor and interaction with a two-level system (TLS) that reduces the dielectric constant, which in turn modifies the capacitance and, therefore, the resonance frequency. The ratio of the TLS responding to the illumination is on the order of that of the area of the inductor to the whole resonator. [ABSTRACT FROM AUTHOR]

We present an antenna-coupled Kinetic Inductance Detector for millimeter wave astronomy. Next-generation telescopes for observing the cosmic microwave background are demanding in terms of number of detectors and focal plane area filling efficiency. Moreover, foreground reduction in B-Mode polarimetry requires sky observation with multiple frequency bands. In this context, KIDs are a promising technology because of their large multiplexing rate, while antenna coupling can provide multi-band and dual-polarization solutions in compact design. We have developed polarization-sensitive dual-band pixel at 140 and 160 GHz with a bandwidth of almost 8% for each sub-band. The design involves a microstrip-excited slot antenna and two open-stub band-pass filters to direct the signal toward two resonators. These are lumped elements capacitively coupled to the antenna and include an aluminum strip as absorber. The architecture proposed is particularly simple to fabricate, via-less and only involves two metallization levels. The transition does not require any dielectric deposition above the resonator, thus preventing limitations from any source of noise due to a non-monocrystalline substrate. Furthermore, the same coupling technique can be applied to many types of microstrip-excited antennas, which allow to accommodate band-pass filters. [ABSTRACT FROM AUTHOR]