Remarks on the method of comparison equations (generalized WKB method) and the generalized Ermakov-Pinney equation

The connection between the method of comparison equations (generalized WKB method) and the Ermakov-Pinney equation is established. A perturbative scheme of solution of the generalized Ermakov-Pinney equation is developed and is applied to the construction of perturbative series for second-order differential equations with and without turning points.Comment: The collective of the authors is enlarged and the calculations in Sec. 3 are correcte

Submillimeter superconducting integrated receivers: Fabrication and yield

Fabrication procedure and yield analysis of superconducting integrated receivers is reported. These chip receivers, apart from the quasi-optical SIS mixers, contain internal local oscillators and associated rf and de interfaces. Due to both complexity and design requirements of the integrated circuit, certain restrictions are applied to the standard Nb/Al/AlxOy/Nb SNEAP process. To obtain accurate area for micron-size SIS junctions and thickness for multi-layer SiO2 insulation, a few solutions and modifications were developed. The possibility of transfering this fabrication process worldwide has been proven experimentally

Niobium tunnel junctions with multi-layered electrodes

The current-voltage characteristics of the niobium - aluminum oxide - niobium tunnel junctions have been studied systematically and are compared with numerical simulations based on the microscopic theory of the proximity effect. The thickness of the base niobium layer is varied from 35 to 500 mn while the thickness of the aluminum layer is kept constant (about 9 mm). In a separate series of experiments the aluminum thickness is varied from 2 to 30 mn for two fixed thickness of the base electrode: 50 and 200 mn. The appropriate conditions for a full suppression of the so called "knee" structure at the gap voltage in the current-voltage characteristic are experimentally determined and theoretically interpreted in the framework of the microscopic theory. The influence of the additional aluminum layer in a composite base electrode on the properties of the tunnel junction have been studied in dependence on the aluminum thickness and distance of this layer from the barrier. The obtained results demonstrate that the current-voltage characteristics of tunnel junction can be engineering by an appropriate layer thickness of compound base electrode

Superconducting chip receivers for imaging application

Experimental details of a unique superconducting imaging array receiver are discussed. Each pixel contains an internally pumped receiver chip mounted on the back of the elliptical microwave lens. Each chip comprises a quasi-optical SIS mixer integrated with a superconducting flux-flow oscillator (FFO) both fabricated from the same Nb/AlOx/Nb trilayer on a silicon substrate. Properties of the integrated lens antenna were studied using an externally pumped reference SIS mixer which showed antenna sidelobes below -17 dB and a receiver double side band noise temperature, T-RX(DSB), below 100 K within the frequency range 460 - 500 GHz that is close to the quantum noise. For the imaging array T-RX(DSB) = 150 K has been measured at 500 GHz using the internal flux-flow oscillator as a local oscillator (LO). A balanced SIS mixer was tested showing T-RX(DSB) <100 K within the range of 480 - 510 GHz using the internal LO. A computer system was developed to control simultaneously the de bias of the SIS mixer and the frequency and power provided by FFO. The system also performs automatic optimization of the receiver noise temperature

Integrated submm wave receiver with superconductive local oscillator

A fully superconductive integrated receiver is very promising for submm space astronomy where low weight, low power consumption, and limited volume are required. The new versions of the integrated quasioptical submm wave receiver have been designed, fabricated and tested in the frequency range of 450-700 GHz. The integrated receiver chip comprises a planar double dipole antenna, SIS-mixer and on-chip superconductive Flux-Flow Oscillator (FFO) with matching circuits. The receiver noise temperature (DSB) as low as 140 K at 500 GHz has been obtained. A light-weight and low power consuming submm imaging array is under development. Each of 9 pixels of the array is realized by an all-Nb single-chip superconductive receiver, mounted on an elliptical silicon lens with anti-reflection coating. The experimental test results of one pixel receiver are presented. A computer based system is developed to control the operation of the integrated receiver