A superconducting 4 bit instantaneous frequency meter at 10 GHz with integrated resistors and air-bridges
Introduction
A 4 bit instantaneous frequency measurement (IFM) subsystem for a bandwidth of 1 GHz at a center frequency of 10 GHz has already been implemented with Y1Ba2Cu3O7−δ coplanar delay lines on a single 2″-LaAlO3 substrate[1]. Wilkinson power dividers with hybrid resistors and ultrasonically bonded air bridges were used. To improve the transmission characteristics and the reproducibility a new device with integrated resistors and bridges on a single 2″-MgO substrate has been developed.
In this paper a fully integrated 4 bit IFM with integrated power dividers and a special coplanar delay line design with integrated bridges is presented. It can be easily fabricated with a superconducting film in only one plane, is mechanically stable (no problems during temperature cycles), and has a small volume and weight.
To use these advantages a careful design and simulation of coplanar structures and an optimisation of the deposition and structuring of different films are required since detection and correction of artifacts in analog complex microwave integrated circuits is not an easy task.
Section snippets
Basic design considerations
A 4 bit Instantaneous Frequency Measurement system for a frequency range between 9.5 and 10.5 GHz requires four interferometers with delay differences of 475, 1000, 2000 and 4000 ps[2]. The 4 way power divider and the 4 interferometers are integrated with coplanar waveguides on a 30×40 mm2 substrate of a 2″-MgO wafer (Fig. 1).
Detectors, amplifiers and 1 bit A/D-converters are implemented with semiconductors on separate substrates.
Test vehicle with Niobium delay lines
The feasibility of the integrated IFM concept is first tested with Nb delay lines on a 500 μm MgO substrate. The implemented coplanar delay lines with 90° bend sections are shown in Fig. 3.
The IFM comprises 11 integrated power dividers with integrated resistors. The delay of each interferometer is adjusted by the number of 90° bend line sections. 1280 sections are used for the LSB delay line, 640 for bit 3, 320 for bit 2 and 152 for the MSB. A total number of 2656 bridges is integrated on this
Prototype with YBCO delay lines
An integrated IFM with YBCO delay lines has been fabricated with the same coplanar delay line structure in Fig. 3. A micrograph of the 4 bit IFM on a 500 μm thick and 30×40 mm2 MgO substrate is shown in Fig. 6.
A 300 nm thick YBCO film with a CeO buffer layer has been deposited on a 2″-wafer by thermal coevaporation[7]. The films are etched with an Ar-ion beam through a resist mask on a stage cooled down to about 77 K[8]. The dielectric bricks are made of thermally evaporated SiO.
The interferometer
Acknowledgements
This work was supported in part by the German BMBF under Grant No. 13 N 6324 2.
References (8)
- et al.
Laser reflection measurements for end point detection and analysis in Nb/Al2O3–Al/Nb Josephson circuit fabrication
Physica C
(1993) - et al.
RHEED studies of epitaxial growth of YBCO films prepared by thermal coevaporation
J. Less Common Methods
(1990) - et al.
Step edge junctions on NdGaO3 substrates at 77 K
Cryogenics
(1993) - M. Biehl et al., A 4 bit instantaneous frequency meter at 10GHz with coplanar YBCO delay lines, IEEE Trans. on Appl....
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