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Superconducting Microwave Filters

Sormeh Setoodeh

Published Feb 22, 2011• 3 citations
OpenAlex

Abstract

Superconducting microelectronics (SME) technology has the potential of realizing very high speed digital receivers capable of performing direct digitization of radio frequency signals with very low power consumption. The SME receiver is implemented on a single chip using Niobium based low temperature superconductive (LTS) Josephson Junction (JJ) technology by HYPRES. Analogue RF filters are still required at the receiver front end and are key components of the overall superconductor digital receiver. SME receivers usually require two types of RF filters; a wideband bandpass filter and a bandstop filter (a notch filter). The notch filter is required to eliminate interference and unwanted signals in the passband. In this thesis, design of highly miniaturized lumped element wideband and bandstop filters is investigated and some challenges are addressed. The filters are fabricated by the HYPRES process and therefore can be integrated with the SME receiver on the same chip. \nIn a wideband filter, the coupling between the adjacent resonators is high. Achieving such a strong coupling is one of the challenges of designing wideband filters. The wideband filters realized with distributed elements usually suffer from very low spurious frequency. As the bandwidth of the filter becomes wider, the spurious peak of the second harmonic gets closer to the passband of the filter. In the first part of this work, the possibility of realizing lumped element superconducting bandpass filters (BPF) with a relative bandwidth of 80% is investigated. \nIn the second part of the thesis, design and realization of lumped element superconducting bandstop filters (BSF) is discussed. The challenge for designing a bandstop filter is providing a good match over a wide frequency range. So narrowband inverters cannot be used. Instead, usually λ/4 matched transmission lines provide 90° phase shift between the resonators of a notch filter. The possibility of replacing the long transmission line with other means or eliminating the inverters and using both shunt and series resonators are investigated. Having both series and shunt resonators introduces some new challenges that are addressed in the thesis and discussed thoroughly. \nA tunable notch resonator is presented. The tunability is provided by a superconducting MEMS varactor that is realized in our group by doing some post processing on the device fabricated by HYPRES. The tunability range of the device at cryogenic temperatures is investigated. A 3-pole tunable BSF is also designed that uses the same tunable resonators. The tunability of the filter is investigated through simulation.

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Superconducting microelectronics (SME) technology has the potential of realizing very high speed digital receivers capable of performing direct digitization of radio frequency signals with very low power consumption. The SME receiver is implemented on a single chip using Niobium based low temperature superconductive (LTS) Josephson Junction (JJ) technology by HYPRES. Analogue RF filters are still required at the receiver front end and are key components of the overall superconductor digital receiver. SME receivers usually require two types of RF filters; a wideband bandpass filter and a bandstop filter (a notch filter). The notch filter is required to eliminate interference and unwanted signals in the passband. In this thesis, design of highly miniaturized lumped element wideband and bandstop filters is investigated and some challenges are addressed. The filters are fabricated by the HYPRES process and therefore can be integrated with the SME receiver on the same chip. \nIn a wideband filter, the coupling between the adjacent resonators is high. Achieving such a strong coupling is one of the challenges of designing wideband filters. The wideband filters realized with distributed elements usually suffer from very low spurious frequency. As the bandwidth of the filter becomes wider, the spurious peak of the second harmonic gets closer to the passband of the filter. In the first part of this work, the possibility of realizing lumped element superconducting bandpass filters (BPF) with a relative bandwidth of 80% is investigated. \nIn the second part of the thesis, design and realization of lumped element superconducting bandstop filters (BSF) is discussed. The challenge for designing a bandstop filter is providing a good match over a wide frequency range. So narrowband inverters cannot be used. Instead, usually λ/4 matched transmission lines provide 90° phase shift between the resonators of a notch filter. The possibility of replacing the long transmission line with other means or eliminating the inverters and using both shunt and series resonators are investigated. Having both series and shunt resonators introduces some new challenges that are addressed in the thesis and discussed thoroughly. \nA tunable notch resonator is presented. The tunability is provided by a superconducting MEMS varactor that is realized in our group by doing some post processing on the device fabricated by HYPRES. The tunability range of the device at cryogenic temperatures is investigated. A 3-pole tunable BSF is also designed that uses the same tunable resonators. The tunability of the filter is investigated through simulation.
Abstract This paper presents a new class of sharp-selectivity low-temperature superconducting filter that incorporates lumped element resonant couplings. Dependent on a novel synthesis approach, the proposed filter exhibits great advantages such as: (1) a very simple in-line topology (without any cross coupling), (2) extremely compact size based on lumped inductor-capacitor (LC) elements, and (3) multiple transmission zeros (TZs) independently generated and controlled (via each resonant coupling). To facilitate the physical implementation, a group of lumped element circuit models are detailed, where series LC units are adopted for both the resonators and the resonant couplings. Considering an in-line topology here, the entire filter layout is then designed by cascading the lumped models one after another. For verification, a 5th-order bandpass filter centered at 5 GHz, with 500 MHz bandwidth and 3 TZs, is designed, simulated, and tested at cryogenic temperature (4.2 K). Moreover, preliminary simulations of the presented filter in series with an on-chip rapid single-flux-quantum microwave pulse generator are discussed for superconducting quantum applications.
Superconducting micro-electronics (SME) technology is capable of realizing extremely high speed digital receivers performing direct digitization of microwave signals with very low power consumption. SME technology uses integrated circuits based on Josephson junctions and rapid single-flux quantum (RSFQ) logic operating at 4°K. The analogue-to-digital converter (ADC) is a basic building block of such receivers. Quantization and sampling are two fundamental parts of ADCs. Flash ADCs are the fastest converters and consist of comparators and a resistor network. \nThis thesis investigates the use of a multi-layer niobium-based low-temperature superconducting process to implement a resistor network. Several configurations for resistors are investigated both electrically and thermally. The resistors are designed to maintain their values from DC to 50GHz. Floating metal structures are added and optimized to minimize the inductance of the structure in order to obtain frequency-independent resistors over a frequency range of 50GHz. Several resistors and R-2R ladder networks are fabricated in the same process and measured in an RF cryogenic probe station at the Centre for Integrated RF Engineering (CIRFE) Lab at the University of Waterloo. Theoretical thermal analysis, is also carried out for these resistors to investigate temperature variations through the structures when operating at different power levels. The investigation is important for making sure that the resistors’ dissipated heat does not raise the local temperature above the transition temperature of niobium.
We propose a mechanically tunable superconducting microwave filter based on lumped elements composed of planar meander-line inductors (L) and inter-digital capacitors (C). As the first step, we have designed and evaluated a 3-pole Chebyshev bandpass filters with lumped elements using a circuit simulator. It is found that the center frequency, bandwidth and skirt rejection of the filter can be controlled by changing only the capacitance. The L and C elements values are estimated using an electromagnetic simulator. Furthermore, we have fabricated the inter-digital capacitor designed with the above procedure. We have evaluated change of the C values using mechanical tuning as a step toward a tunable superconducting microwave filter.
With increasing applications of quantum systems operating at high frequencies, the role of integrated microwave components for quantum circuits becomes more and more important. In this article, we present low-temperature superconducting bandpass-bandstop diplexers for a new generation of quantum AC-voltage standards operating at 1 GHz. Based on stringent requirements, the diplexers are designed to provide low passband loss, good stopband rejection, and otherwise a broad ideally matched spectrum with excellent spurious-free performance. A second-order 1 GHz superconducting bandpass-bandstop diplexer is fabricated and characterized for verification. To this end, a cryogenic setup and on-chip calibration standards are implemented for S-parameter measurements. The experimental results exhibit low insertion loss as low as 0.03 dB in the passband section and high rejection in the bandstop branch exceeding 43 dB. Furthermore, the diplexer features wide spurious-free response extending to more than14⋅f014 \cdot \mathrm{f}_{0}14⋅f0​and occupies a very compact area of only1.8mm×1.2mm1.8 \text{mm} \times 1.2 \text{mm}1.8mm×1.2mm.
We present techniques to miniaturize superconducting ultra narrowband filters for on-chip applications. The filters are designed for 2 GHz, 5 GHz and 10 GHz operating frequencies. The expected bandwidths of the designed filters are 2-20 MHz. The designs are of 7 stages Chebyshev filters having maximum passband ripples of 0.5 dB. On-chip filters are particularly interesting as they are applicable for monolithic design with the RSFQ circuit aiming qubit applications. One of the designs is a quasi-lumped filter where the effective wave propagation constant has been increased by the addition of lumped components to the superconducting microstrip line (SMSL). Additionally, this design provides the optimum width of an SMSL without violating design rules. The other design consists of distributed and lumped components. The area of the filter is in the range of 1-2 square mm. We present the filter topologies and corresponding experimental results for the frequency response of these on-chip filters designed for Hypres 4.5 kA/cm2 fabrication process.
Superconductor-based microwave and millimeter-wave components play a crucial role in various applications, particularly in superconductor-based digital receivers and superconductor-based quantum computing systems. This article aims to provide an overview of recent advancements in superconductor microwave and millimeter-wave devices implemented in a multilayer nio­bium fabrication process. These devices cover a broad frequency range, from 300 MHz to 100 GHz, and include bandpass/band-reject filters, wideband cou­plers, niobium-based microelectromechanical sys­tems switches, phase shifters, filters-based power protection circuits, phase shifter-based power limiters, tunable attenuators, and supercon­ductor-based magnet-less circulators.