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Lumped-element kinetic inductance detectors (LEKIDs) have recently shown considerable promise as direct-absorption mm-wavelength detectors for astronomical applications. One major research thrust within the Néel Iram Kids Array (NIKA) collaboration has been to investigate the suitability of these detectors for deployment at the 30-meter IRAM telescope located on Pico Veleta in Spain. Compared to microwave kinetic inductance detectors (MKID), using quarter wavelength resonators, the resonant circuit of a LEKID consists of a discrete inductance and capacitance coupled to a feedline. A high and constant current density distribution in the inductive part of these resonators makes them very sensitive. Due to only one metal layer on a silicon substrate, the fabrication is relatively easy. In order to optimize the LEKIDs for this application, we have recently probed a wide variety of individual resonator and array parameters through simulation and physical testing. This included determining the optimal feed-line coupling, pixel geometry, resonator distribution within an array (in order to minimize pixel cross-talk), and resonator frequency spacing. Based on these results, a 32-pixel Aluminum array was fabricated and tested in a dilution fridge with optical access, yielding an average optical NEP of ∼7.2 x 10-16 W/Hz 1/2. In October 2009 a first prototype of LEKIDs has been tested at the IRAM 30 m telescope and first astronomical results have been achieved. © 2010 SPIE

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We report the realization of very small area resonant tunneling diodes (RTD's) for integrated microwave applications. Diodes with areas down to 3×3 μm2 were fabricated with the necessary coplanar lines for microwave wafer probing. Peak to valley ratios up to 3.5 with peak current densities ranging from 0.6 A/cm2 to 1.5 kA/cm2 have been achieved for Al0.4Ga0.6 As/GaAS double barrier heterostructures grown by MBE on Semi-Insulating substractes. Reflection gain versus frequency measurements in the 1.5-26.5 GHz range, at room temperature, were performed. The smaller devices exhibit a maximum cut off frequency for the negative differential resistance of 18 GHz. For high current versions, we expect significant increase in frequency limit