Superconducting circuit elements used in millimeter-submillimeter (mm-submm) astronomy would greatly benefit from deposited dielectrics with small dielectric loss and noise. This will enable the use of multilayer circuit elements and thereby increase the efficiency of mm-submm filters and allow for a miniaturization of microwave kinetic inductance detectors (MKIDs). Amorphous dielectrics introduce excess loss and noise compared with their crystalline counterparts, due to two-level system defects of unknown microscopic origin. We deposited hydrogenated amorphous silicon films using plasma-enhanced chemical vapor deposition, at substrate temperatures of 100°C, 250°C, and 350°C. The measured void volume fraction, hydrogen content, microstructure parameter, and bond-Angle disorder are negatively correlated with the substrate temperature. All three films have a loss tangent below 10-5 for a resonator energy of 105 photons, at 120 mK and 4 to 7 GHz. This makes these films promising for MKIDs and on-chip mm-submm filters.

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Photo-conductive lens antennas (PCAs) exploit the ultra-short photoconductivity phenomenon of specific semiconductors in order to generate pulsed radiation in the THz regime. State of the art PCAs suffer from high dispersion and low radiation efficiency over the large generated bandwidth due to the poor coupling between the antenna and the dielectric lens. In this work, a leaky lens PCA is proposed to overcome these issues. The presented structure, indeed, aims at a 1:15 bandwidth (0.1 THz – 1.5 THz). The design, assembly and manufacture of a LT-GaAs membrane-based leaky lens PCA are shown and discussed together with the measurement of the radiated power.@en

We present the design, fabrication, and characterization of a broadband leaky lens antenna for broadband, spectroscopic imaging applications. The antenna is designed for operation in the 300-900 GHz band. We integrate the antenna directly into an Al-NbTiN hybrid microwave kinetic inductance detector (MKID) to measure the beam pattern and absolute coupling efficiency at three frequency bands centered around 350, 650, and 850 GHz, covering the full antenna band. We find an aperture efficiency \eta _{ap} \approx 0.4 over the whole frequency band, limited by lens reflections. We find a good match with simulations for both the patterns and efficiency, demonstrating a 1:3 bandwidth in the submillimeter wavelength range for future on-chip spectrometers.

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With increasing array size, it is increasingly important to control stray radiation inside the detector chips themselves. We demonstrate this effect with focal plane arrays of absorber coupled Lumped Element microwave Kinetic Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the response from a point source at the pixel position is at a similar level to the stray response integrated over the entire chip area. For the antenna coupled arrays, we show that this effect can be suppressed by incorporating an on-chip stray light absorber. A similar method should be possible with the LEKID array, especially when they are lens coupled.

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Optically pumped pulsed THz emitters exploit the transient motion of photo-generated charge carriers in semiconductors, to produce, coupled to micro-antenna, radiated power over a wide bandwidth up to the THz frequencies. The radiation performance of the antenna greatly affects dispersion of the energy spectrum generated by the photoconductive source and if not properly designed it causes low radiated power. This work presents the design, the fabrication process, the electromagnetic and the thermal analyses of a pulsed photoconductive micro-antenna based on the leaky lens antenna concept. This device shows high radiation efficiency over a band ranging from 0.1 to 1.5 THz, thus being a suitable emitter for THz time-domain sensing system.

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