Quasiparticle Diffusion in Al Films Coupled to Tungsten Transition Edge Sensors

We report recent results obtained from several W/Al test devices on Si wafers fabricated specifically to better understand energy collection in phonon sensors used for the Cryogenic Dark Matter Search (CDMS) experiment. The devices under study consist of three different lengths of 250 \(\upmu \) m-wide by 300 nm-thick Al absorber films, coupled to 250 \(\upmu \) m x 250 \(\upmu \) m (40 nm thick) W-TESs at each end of the Al film. An \(^{55}\) Fe source was used to excite a NaCl reflector producing 2.6 keV Cl X-rays that were absorbed in our test device after passing through a collimator. The impinging X-rays broke Cooper pairs in the Al film, producing quasiparticles that we detected after they propagated into the W-TESs. We studied the diffusion of these quasiparticles in the Al, trapping effects in the Al film, and energy transmission at the Al/W interfaces.     

Weak-Link Phenomena in AC-Biased Transition Edge Sensors

It has been recently demonstrated that superconducting transition edge-sensors behave as weak-links due to longitudinally induced superconductivity from the leads with higher \(T_c\) . In this work we study the implication of this behaviour for transition-edge sensors (TES)-based bolometers and microcalorimeter under ac bias. The TESs are read-out at frequencies between 1 and \(5 \,\mathrm {MHz}\) by a frequency domain multiplexer based on a linearised two-stage SQUID amplifier and high- \(Q\) lithographically made superconducting \(LC\) resonators. In particular, we focus on SRON TiAu TES bolometers with a measured dark noise equivalent power of \(3.2\times 10^{-19}\,{\mathrm{W}/\sqrt{\mathrm{Hz}}}\) developed for the short wavelength band for the instrument SAFARI on the SPICA telescope.     

Towards Ultra-Low-Noise MoAu Transition Edge Sensors

We report initial measurements on our first MoAu transition edge sensors (TESs). The TESs formed from a bilayer of 40?nm of Mo and 106?nm of Au showed transition temperatures of about 320?mK, higher than identical TESs with a MoCu bilayer which is consistent with a reduced electron transmission coefficient between the bilayer films. We report measurements of thermal conductance in the 200?nm thick silicon nitride SiN _x support structures at this temperature, TES dynamic behaviour and current noise measurements.     

Alternative Readout Electronics for Superconducting Transition Edge Sensors

A simple idea of using transformers as impedance adapters between TES and conventional JFET amplifiers, allowing to built an electronic readout system that does not degenerate the signal, will be presented. The theoretical modelling and systematic experimental results of such devices, indicate that there is a frequency range were the amplifier noise is negligible with respect to the TES noise.     

Accurate Thermal Conductance and Impedance Measurements of Transition Edge Sensors

Past measurements of the thermal coupling of superconducting transition edge sensor (TES) calorimeters suspended on SiN membranes produced wide-ranging values for the exponent of the thermal coupling through the membranes. We present a measurement technique that is less susceptible to current dependence of the phase transition than the previous measurements. An initial measurement produced the expected exponent for a 2-D phonon gas: thermal conductance is proportional to T ². In doing these measurements, we employ a modification to Lindeman’s equivalent circuit technique for measuring TES complex impedance.      

Design of an Optical Absorption Cavity for Titanium Transition Edge Sensors

We have developed a TES optical photon detector with a titanium superconducting film showing a very fast response with rise time and fall times of 30 ns and 313 ns, respectively. The fast response is promising for many quantum measurement applications. Increasing the quantum efficiency of this device from the current value of ∼20% makes the detector even more suitable for these applications. Here we report on simulation and experimental results of a cavity designed to improve optical photon absorption of titanium.     

Quasiparticle Edge Losses in Double STJs Strip X-Rays Detectors

The 2D diffusion model of the strip X-ray detector was developed. The detector consists of a long superconducting strip, which is ended by the trapping layers and superconducting tunnel junctions at each end. The model takes into account the diffusion of the excess quasiparticles, quasiparticle trapping at the tunnel junctions and quasiparticle losses in the volume of the strip and at the strip boundaries. The analytical solution was obtained. It has been shown that quasiparticle losses at the strip boundaries caused the dependence of the signals on the photon absorption site in transverse direction. The latter worsens the energy resolution and transforms the spectral line of the detector to nongaussian shape.      

Selective Sensors of Nitrogen Dioxide Based on Thin Tungsten Oxide Films under Optical Irradiation

Technical Physics Letters - It is shown that NO2 present in air, beginning at a concentration of 1 ppm, can be selectively detected by sensors based on Au/WO3:Au thin films activated by laser diode...     

TES用超导薄膜制备及特性研究

超导转变边沿传感器(TES)是光强单位坎[德拉]量子化所需的单光子探测器,金属超导薄膜物理特性的研究是TES研究的基础.采用不同电源功率磁控溅射制备高纯Al、Ti超导纳米薄膜,分析其薄膜生长速率随气压和功率的变化.利用表面应力仪及电学测量仪,分析薄膜表面应力及电学特征.最后将薄膜放入商用稀释制冷机中,进行超低温测试,获...     

氧化钨基半导体气体传感器的研究进展

近年来,氧化钨(WO_3)基半导体气体传感器由于可用来检测低浓度二氧化氮、二氧化硫、臭氧和氨气等气体而受到广泛关注。将WO_3基材料分为4类:纯WO_3材料、氧化物-WO_3复合材料、贵金属-WO_3复合材料和有机物-WO_3复合材料,总结近年来中外文献中WO_3基材料对不同气体的响应性能,展现近年来国内外WO_3基半导体气体传感器的研究进展。最后根据已有的工作进展,提出合成新型纳米材料、降低工作温度、提高传感器选择性应成为WO_3基半导体气体传感器下一阶段的研究重点。     

A Fabrication Process for Microstrip-Coupled Superconducting Transition Edge Sensors Giving Highly Reproducible Device Characteristics

Astronomical instruments for measuring Cosmic Microwave Background polarisation, such as CLOVER, require large arrays of Superconducting Transition Edge Sensors (TESs). We report recent results from a processing route development aimed at high yield fabrication of microstrip-coupled TESs. The incoming signal is delivered onto a silicon nitride membrane by means of a superconducting microstrip transmission line. This transmission line is then terminated with a thin-film load resistor. The wafer-based fabrication route of the Mo/Cu TESs gives highly reproducible device characteristics in terms of superconducting transition temperature, electrical and thermal characteristics. An overall device yield of 65% has been achieved for a multi-wafer processing run.      

Enhancement of Josephson Quasiparticle Current in Coupled Superconducting Single-electron Transistors

The Josephson quasiparticle (JQP) cycle in a voltage-biasedsuperconducting single-electron transistor (SSET) combinescoherent Cooper pair tunneling with incoherent quasiparticledecay. We have measured a striking modification of the JQPprocess in a system of two SSET's having a large mutualcapacitance. We find, among other effects, that the JQPcurrent in one SSET may be enhanced by the presence of aquasiparticle current through the other SSET. A simplified model of the coupled-SSET system is presented which reproducesthe enhancement effect.     

A Comparison of Fundamental Noise in Kinetic Inductance Detectors and Transition Edge Sensors for Millimeter-Wave Applications

Kinetic inductance detectors (KIDs) show promise as a competitive technology for astronomical observations over a wide range of wavelengths. We are interested in comparing the fundamental limitations to the sensitivity of KIDs with that of transition edge sensors (TESs) at millimeter wavelengths, specifically over the wavelengths required for studies of the Cosmic Microwave Background (CMB). We calculate the total fundamental noise arising from optical and thermal excitations in TESs and KIDs for a variety of bath temperatures and optical loading scenarios for applications at millimeter wavelengths. Special consideration is given to the case of ground-based observations of 100 GHz radiation with a 100 mK bath temperature, conditions consistent with the planned second module of the QUBIC telescope, a CMB instrument Battistelli (Astropart Phys 34:705, 2011). Under these conditions, a titanium nitride KID with optimized critical temperature pays a few percent noise penalty compared to a typical optimized TES.     

Mo/Au Bilayers Deposited by Sputtering at Room Temperature for Transition Edge Sensors Fabrication

We report on the fabrication and characterisation of Mo/Au bilayers which are intended to be used as high resolution cryogenic imaging spectrometers for next generation of X-ray Astrophysical observatories in space. Mo/Au bilayers have been deposited by sputtering at room temperature on Si₃N₄ bulk and membranes. The composition of the bilayers as well as their interfaces have been characterised by Rutherford Backscattering Spectroscopy (RBS). Results indicate absence of interdiffusion. Further structural characterization has been performed by X-ray diffraction and Atomic Force Microscopy. The transition temperature T _c of the Mo/Au bilayers has been tuned by changing the Au layer thickness. Very sharp superconducting transitions have been observed with transition widths as small as 0.3 mK. These films look therefore extremely promising for the intended detectors, as well as for other applications in materials science and nanotechnology.      

Energy Collection Efficiency of Tungsten Transition-Edge Sensors in the Near-Infrared

Single-photon detectors operating at visible and near-infrared wavelengths with high detection efficiency and low noise are a requirement for many quantum-information applications. Detection of visible and near-infrared light at the single-photon level and discrimination between one- and two-photon absorption events place stringent requirements on TES design in terms of heat capacity, thermometry, and optical detection efficiency. Energy loss in the conversion of the photon energy in tungsten TESs to heat degrades the performance of these devices. By fabricating TESs on surface-micromachined Si₃N₄ membranes we improved the energy collection efficiency by a factor of two, to ∼80% energy efficiency.      

Proximity Coupled Interdigitated Sensors to Detect Insulation Damage in Power System Cables

Proximity coupled interdigitated sensors are introduced to detect insulation damage in power system cables. A new empirical model for interdigitated sensors with conducting backplane is developed. The validity of this newly proposed model is verified by comparing the results obtained from the new model with simulation and experimental results. It is shown that while the existing models fail to correspond to the simulation and experimental results due to the presence of the conducting backplane, the new model can fairly approximate the effect of the backplane on the sensor performance. A meander and a quarter-circular sensor are designed for insulation damage detection. Measurement results on planar dielectric materials, as well as practical power line cables are presented to demonstrate the usefulness of these sensors. Such sensors placed on microrobots crawling along power cables could lead to the potential autonomous monitoring of an electric power system.     

A Fabrication Route for Arrays of Ultra-low-Noise MoAu Transition Edge Sensors on Thin Silicon Nitride for Space Applications

We describe a process route to fabricate arrays of Ultra-low-Noise MoAu Transition Edge Sensors (TESs). The low thermal conductance required for space applications is achieved using 200?nm-thick Silicon Nitride (SiN _x ) patterned to form long-thin legs with widths of 2.1?μm. Using bilayers formed on SiN _x islands from films with 40 nm-thick Mo and Au thicknesses in the range 30 to 280 nm deposited by dc-sputtering in ultra-high vacuum we can obtain tunable transition temperatures in the range 700 to 70?mK. The sensors use large-area absorbers fabricated from high resistivity, thin-film β-phase Ta to provide impedance-matching to incident radiation. The absorbers are patterned to reduce the heat capacity associated with the nitride support structure and include Au thermalizing features to assist the heat flow into the TES. Arrays of 400 detectors at the pixel spacing required for the long-wavelength band of the far-infrared instrument SAFARI are now being fabricated. Device yields approaching 99% are achieved.