arXiv subjects

Leif Grönberg

Publications and source records attributed to Leif Grönberg.

25 records · Page 2Linked to original sources

arXiv2018

Two SQUID amplifiers intended to alleviate the summing node inductance problem in multiplexed arrays of Transition Edge Sensors

Frequency Domain Multiplexed detector arrays constructed of superconducting Transition Edge Sensors in the current-summing configuration suffer from the finite impedance of the summing node which should ideally be zero. We suggest two circuits to alleviate the effect. The first circuit uses a capacitive resonant transformer to increase the voltages and decrease the currents of TES signals to overcome the parasitic inductance of the interconnections. On the SQUID chip impedance transform to the opposite direction takes place. The second circuit implements a power combiner having a better branch-to-branch isolation than a simple T-junction. Two SQUID devices have been designed and fabricated for a proof-of-principle demonstration of the circuits.

astro-ph.IM↗

arXiv2018

Efficient thermionic operation and phonon isolation by a semiconductor-superconductor junction

Control of heat flux at small length scales is crucial for numerous solid-state devices and systems. In addition to the thermal management of information and communication devices the mastering of heat transfer channels down to the nanoscale also enable, e.g., new memory concepts, high sensitivity detectors and sensors, energy harvesters and compact solid-state refrigerators. Electronic coolers and thermal detectors for electromagnetic radiation, especially, rely on the maximization of electro-thermal response and blockade of phonon transport. In this work, we propose and demonstrate that efficient electro-thermal operation and phonon transfer blocking can be achieved in a single solid-state thermionic junction. Our experimental demonstration relies on suspended semiconductor-superconductor junctions where the electro-thermal response arises from the superconducting energy gap, and the phonon blocking naturally results from the transmission bottleneck at the junction. We suspend different size degenerately doped silicon chips (up to macroscopic scale) directly from the junctions and cool these by biasing the junctions. The electronic cooling operation characteristics are accompanied by measurement and analysis of the thermal resistance components in the structures indicating the operation principle of phonon blocking in the junctions.

cond-mat.mes-hall↗

arXiv2018

Flux-driven Josephson parametric amplifier for sub-GHz frequencies fabricated with side-wall passivated spacer junction technology

We present experimental results on a Josephson parametric amplifier tailored for readout of ultra-sensitive thermal microwave detectors. In particular, we discuss the impact of fabrication details on the performance. We show that the small volume of deposited dielectric materials enabled by the side-wall passivated spacer niobium junction technology leads to robust operation across a wide range of operating temperatures up to 1.5 K. The flux-pumped amplifier has gain in excess of 20 dB in three-wave mixing and its center frequency is tunable between 540 MHz and 640 MHz. At 600 MHz, the amplifier adds 105 mK $\pm$ 9 mK of noise, as determined with the hot/cold source method. Phase-sensitive amplification is demonstrated with the device.

cond-mat.supr-con↗

arXiv2018

Side-wall spacer passivated sub-um Josephson junction fabrication process

We present a structure and a fabrication method for superconducting tunnel junctions down to the dimensions of 200 nm using i-line UV lithography. The key element is a side-wall-passivating spacer structure (SWAPS) which is shaped for smooth crossline contacting and low parasitic capacitance. The SWAPS structure enables formation of junctions with dimensions at or below the lithography-limited linewidth. An additional benefit is avoiding the excessive use of amorphous dielectric materials which is favorable in sub-Kelvin microwave applications often plagued by nonlinear and lossy dielectrics. We apply the structure to niobium trilayer junctions, and provide characterization results yielding evidence on wafer-scale scalability, and critical current density tuning in the range of 0.1 -- 3.0 kA/cm$^2$. We discuss the applicability of the junction process in the context of different applications, such as, SQUID magnetometers and Josephson parametric amplifiers.

cond-mat.supr-con↗

arXiv2017

Flux-tunable heat sink for quantum electric circuits

Superconducting microwave circuits show great potential for practical quantum technological applications such as quantum information processing. However, fast and on-demand initialization of the quantum degrees of freedom in these devices remains a challenge. Here, we experimentally implement a tunable heat sink that is potentially suitable for the initialization of superconducting qubits. Our device consists of two coupled resonators. The first resonator has a high quality factor and a fixed frequency whereas the second resonator is designed to have a low quality factor and a tunable resonance frequency. We engineer the low quality factor using an on-chip resistor and the frequency tunability using a superconducting quantum interference device. When the two resonators are in resonance, the photons in the high-quality resonator can be efficiently dissipated. We show that the corresponding loaded quality factor can be tuned from above $10^5$ down to a few thousand at 10 GHz in good quantitative agreement with our theoretical model.

cond-mat.mes-hall↗

arXiv2016

Conformal Titanium Nitride in a Porous Silicon Matrix: a Nanomaterial for In-Chip Supercapacitors

Today's supercapacitor energy storages are typically discrete devices aimed for printed boards and power applications. The development of autonomous sensor networks and wearable electronics and the miniaturisation of mobile devices would benefit substantially from solutions in which the energy storage is integrated with the active device. Nanostructures based on porous silicon (PS) provide a route towards integration due to the very high inherent surface area to volume ratio and compatibility with microelectronics fabrication processes. Unfortunately, pristine PS has limited wettability and poor chemical stability in electrolytes and the high resistance of the PS matrix severely limits the power efficiency. In this work, we demonstrate that excellent wettability and electro-chemical properties in aqueous and organic electrolytes can be obtained by coating the PS matrix with an ultra-thin layer of titanium nitride by atomic layer deposition. Our approach leads to very high specific capacitance (15 F/cm$^3$), energy density (1.3 mWh/cm$^3$), power density (up to 214 W/cm$^3$) and excellent stability (more than 13,000 cycles). Furthermore, we show that the PS-TiN nanomaterial can be integrated inside a silicon chip monolithically by combining MEMS and nanofabrication techniques. This leads to realisation of in-chip supercapacitor, i.e., it opens a new way to exploit the otherwise inactive volume of a silicon chip to store energy.

cond-mat.mtrl-sci↗

arXiv2014

Kinetic Inductance Magnetometer

Ultrasensitive magnetic field detection is utilized in the fields of science, medicine and industry. We report on a novel magnetometer relying on the kinetic inductance of superconducting material. The kinetic inductance exhibits a non-linear response with respect to DC current, a fact that is exploited by applying magnetic flux through a superconducting loop to generate a shielding current and a change in the inductance of the loop. The magnetometer is arranged into a resonator, allowing readout through a transmission measurement that makes the device compatible with radio frequency multiplexing techniques. The device is fabricated using a single thin-film layer of NbN, simplifying the fabrication process compared to existing magnetometer technologies considerably. Our experimental data, supported by theory, demonstrates a magnetometer having potential to replace established technology in applications requiring ultra-high sensitivity.

physics.ins-det↗