A Transition-Edge Sensor with Two Excess Noise Mechanisms

We present noise data measured from a Ti/Au transition-edge sensor that is coupled via a dot matrix to a Cu/Bi absorber. The observed noise properties can be explained by a combination of excess white noise and internal thermal fluctuations. Quite unexpectedly, the excess white noise level goes down if one biases the sensor deep enough in the transition.      

Suppression of excess noise in Transition-Edge Sensors using magnetic field and geometry

We report recent progress at NIST on Mo/Cu Transition-Edge Sensors (TESs). While the signal-band noise of our sensors agrees with theory, we observe excess high-frequency noise. We describe this noise and demonstrate that it can be strongly suppressed by a magnetic field perpendicular to the plane of the sensor. Both the excess noise and =(T/R)(dR/dT) depend strongly on field so our results show that accurate comparisons between devices are only possible when the field is well known or constant. We also present results showing the noise performance of TES designs incorporating parallel and perpendicular normal metal bars, an array of normal metal islands, and in wedge-shaped devices. We demonstrate significant reduction of high-frequency noise with the perpendicular bar devices at the cost of reduced . Both the bars and the magnetic field are useful noise reduction techniques for bolometers.     

Characterization of a High-Performance Ti/Au TES Microcalorimeter with a Central Cu Absorber

We are developing X-ray microcalorimeters based on Ti/Au transition-edge sensors (TES). Among sensors we have fabricated, one with a Cu absorber at the center of the TES shows a particularly good X-ray energy resolution: 1.56 eV at 250 eV and 2.5 eV at 5.9 keV. In this paper, a detailed study of its impedance and noise is presented. The noise is not explained by a sum of known sources. The magnitude of unexplained noise is largest when the sensitivity of the TES on temperature (α) and on current (β) are the highest. The observed relation between the noise level and sensitivity suggests a source of thermal fluctuations inside the TES or between the TES and the absorber. We also found that β is linearly correlated to the product of α and current, which limits the effective sensitivity that is expressed as α/(1+β).      

Comparative Study of TiAu-Based TES Microcalorimeters with Different Geometries

Seven microcalorimeters with different geometries have been tested and their performance is compared. The study, for TiAu TESs with a Cu absorber, indicates the presence of so-called constant voltage noise and internal thermal fluctuation noise. The constant voltage noise is not changed by a normal metal pattern on the TES, or by a magnetic field. The energy resolution of the detectors, having different heat capacities, is 2.5 and 5.0 eV (at 5.9 keV).      

Superconducting Detectors and the Casimir Effect

Many types of superconducting detectors naturally form Casimir cavities (Superconducting Tunnel Junctions, some Transition Edge Sensor geometries). We show that by influencing the energy balance of the superconducting-to-normal (S–N) transition of the cavity boundaries the Casimir effect can have an effect on the microscopic parameters of the detector, such as the superconducting energy gap and critical field. In order to determine whether these effects are practically important a rigorous mathematical discussion of the energy balance of the detector’s transition is required. We discuss the basis for such a rigorous analysis as well as the type of electromagnetism required and the inadequacy of existing Casimir effect solutions when applied to the superconducting system.      

The non-equilibrium response of a high-resolution Ti/Au X-ray microcalorimeter

We have studied the response of a high resolution Ti/Au transition edge sensor (TES) microcalorimeter with an energy resolution of 6.2±0.7 eV at 1.5 keV and 7.8±0.9 eV at 6.4 keV. We find that the sensitivity ≡R/T dR/dT of the TES varies significantly along the superconducting-to-normal transition that the bias point traverses during a pulse. Furthermore, is reduced significantly during a pulse compared to its equilibrium value calculated from the DC characteristics. This leads to an overestimate of the expected energy resolution when basing the prediction on the equilibrium sensitivity.     

Analysis of Nuclear Material by Alpha Spectroscopy with a Transition-Edge Microcalorimeter

We present measurements from a cryogenic microcalorimeter designed to detect alpha particles. The enhanced resolution of microcalorimeter alpha detectors will provide new capabilities for actinide analysis. We demonstrate a spectral resolution of 2.4 keV full width at half maximum (FWHM) for 5.3 MeV alpha particles from a ²¹⁰Po source. In addition, we present an alpha spectrum from ²⁰⁹Po showing the first direct measurement of decay into the ²⁰⁵Pb ground state. Finally, measurements of 100 keV gamma-rays from a Gd source show an ultimate alpha particle resolution of 159 eV to be achievable which may provide an avenue for investigating ion energy loss mechanisms in bulk materials.      

Characterization and reduction of noise in Mo/Au transition edge sensors

We measured noise in a variety of Mo/Au transition-edge sensor (TES) X-ray calorimeters. We investigated the relationship between the noise, bias, and the superconducting phase transition in the TESs. Our square TES calorimeters have achieved very good energy resolutions (2.4 eV at 1.5 keV) but their resolutions have been limited by broadband white excess noise generated by the TES when it is biased in the phase transition. We have recently fabricated Mo/Cu TESs with interdigitated normal metal bars deposited on top of the bilayer. The new TES calorimeters have demonstrated little or no excess noise in the phase transition. These results point the way to development of TES calorimeters with higher energy resolution.     

Effect of Thin Ballistic Membranes on Transition-Edge Sensor Performance

We calculate the energy resolution and time constant of a transition edge sensor, designed for 10 keV operation, and mounted on a thin ballistic dielectric membrane. Our treatment uses the correct phonon modes from elasticity theory (Lamb-modes), and spans the transition from 3D to 2D behavior. Several optimization schemes are discussed, and Johnson-noise like excess noise is taken into account. Thinning the membrane improves the energy resolution slightly. More importantly and somewhat counterintuitively, the effective time constant can be reduced significantly by decreasing the membrane thickness in the 2D limit.      

Characterization of Mo/Au Transition-Edge Sensors with Different Geometric Configurations

Mo/Au transition-edge sensors exhibit weak-link behavior in the measured temperature, \(T\) and field, \(B\) dependence of the critical current \(I_\mathrm{{C}}(T,B)\) . This is a consequence of the longitudinal proximitization between the Nb electrical bias contacts and the bilayer. Understanding how weak-link superconductivity impacts the resistive transition and the detector energy resolution is of great interest. In this contribution we present studies of \(I_\mathrm{{C}}(T,B)\) for three devices that have different geometries of metallic depositions on top of the sensor used for noise mitigation and X-ray absorption. Results show that these features change the measured \(I_\mathrm{{C}}(T,B)\) compared to the previously seen measurements on devices without additional deposition layers. Measurements of the small signal transition parameters \(\alpha \) and \(\beta \) also reveal differences between designs that impact the measured response to X-rays and energy resolution.     

Simulations of Noise in Phase-Separated Transition-Edge Sensors for SuperCDMS

We briefly review a simple model of superconducting-normal phase-separation in transition-edge sensors (TESs) in the SuperCDMS experiment. After discussing some design considerations relevant to the TESs in the experiment, we study noise sources in both the phase-separated and phase-uniform cases. Such simulations will be valuable for optimizing the critical temperature and TES length of future SuperCDMS detectors.     

CMOS图像传感器的消噪技术

目的　介绍 CMOS图像传感器的消噪技术 .方法　比较了 CMOS图像传感器与CCD图像传感器的优缺点 ,分析了 CMOS图像传感器消噪技术的方法 ,介绍了其研制现状及发展趋势 .结果　目前采用的消噪技术有效地降低了噪声 ,提高了信噪比 .结论　预见了CMOS图像传感器消噪技术的发展趋势 .     

Parameter comparison for low-noise Mo/Au TES bolometers

We describe a comparative investigation of the parameters of MoAu-bilayer TES bolometers designed for infrared detectors. A set of devices with variations in geometry were fabricated at the NASA/GSFC detector development facility. These detectors have different bilayer aspect ratios (providing differing normal state resistances and current densities), and have varieties of normal metal regions to study the effects of geometry on noise. These normal metal regions are oriented either parallel to or transverse to the direction of current flow, or both. The lowest noise detectors are found to have normal metal regions oriented transversely. For about a dozen different devices, we have measured a large set of parameters by means of a suite of tests. These include complex impedance measurements to derive time constants; IV curves to determine resistance and power; thermal conductance measurements; noise measurements as a function of device resistance; and direct resistance vs. temperature measurements.     

Intrinsic noise sources in superconductors near the transition temperature

The performance of Transition Edge Sensors (TES) is limited by excess noise that is not predicted by the current theory of microcalorimeters and bolometers. The nature of this noise is currently unknown, but is likely to be dominated by fundamental physics of supeconductors. The University of Miami has recently started a joint effort between the microcalorimeter group and the superconductivity group to study and characterize the noise in TES. In particular, we plan to investigate the effect of flux motion due to self-field and external field and the effect of fluctuating order parameter by measuring the para-conductivity due to fluctuations in the number of Cooper pairs near the transition. We also plan to characterize the fundamental physical parameters of the TES to better predict their properties. In this paper we report our preliminary qualitative assessment of the problem, based on the literature, and we illustrate the experimental techniques that we plan to use for the investigation.     

The Noise and Energy Resolution of the Ti/Au Bilayer X-ray TES Calorimeter with an Au Absorber

We fabricated the TES microcalorimeter with TES(Ti/Au) and gold absorber, and obtained FWHM energy resolution of 4.8±0.3 eV at 5.9 keV. The baseline resolution, i.e. the resolution determined by noise, was 4.1±0.1 eV. From the noise spectra we found that the square of the baseline resolution could be approximately decomposed into contributions of three noise components. They are estimated to be (2.5 eV)² (the intrinsic noise), (1.5 eV)² (the readout noise), and (3.0 eV)² (so-called excess noise). There is additional broadening of (2.5 eV)² from the baseline resolution. The excess noise is the largest limiting factor of the energy resolution of the device.      

虚拟传声器的有源噪声控制

研究虚拟传声器的有源噪声控制问题。该技术适用于控制区域不适合放置误差传声器的场合。将误差传声器置于控制区域之外,得到测量误差。采用前向差分预测算法预测控制区域内的残余误差信号,然后利用自适应LMS算法,得到最优的噪声控制滤波器。为了尽量消除预测中存在的误差,采用自适应变权值预测算法。仿真结果表明该方法能有效地抑制噪声,使控制区域内的噪声信号得到明显衰减。     

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.      

自由声场自适应有源噪声控制中误差传感器的布放

合理地布放误差传感器可以减小自适应有源噪声控制系统的复杂性，提高降噪量。本文研究了自由声场条件下误差传感器布放与ＡＡＮＣ系统降噪效果的关系，从理论和实验两个方面总结了自由场误差传感器布放规律。     

Analyses on the operating point dependence of the energy resolution with a Ti/Au TES microcalorimeter

We examined the performance of a single pixel Ti/Au transition-edge sensor (TES) calorimeter for incident X-ray energies of Al-K, Cr-K, and Fe-K, as a function of the TES resistance. We find that the energy resolution does not always degrade with increasing energy. The best energy resolution of 5.7±0.9 eV at 6.4 keV is obtained, which is possibly even better than the baseline width of 6.5±0.2 eV. Assuming that the noise level is determined by the noise spectrum NS(f;RR+dR(E)) considering the resistance change of dR(E), instead of NS(f;R) at the operating point, these results may be explained by the fact that the noise decreases at the higher TES resistance. The pulse variation appears to have a minimum at a certain resistance of R+dR(E)48 mΩ, and the best energy resolution for each line is obtained at such an operating point, respectively. The pulse variation could be enhanced when the fluctuation of the TES sensitivity is large at R+dR(E).     

Large Bolometer Arrays with Superconducting NbSi Sensors for Future Space Experiments

New techniques in microelectronics allow to build large arrays of bolometers filling the focal plane of submillimeter and millimeter telescopes. The expected sensitivity increase is the key for the next generation of space experiments in this wavelength range. Superconducting bolometers offer currently the best prospects in terms of sensitivity and multiplexed readout. We present here the developments led in France based on NbSi alloy thermometers. The manufacturing process of a 23 pixel array and the test setup are described.