Phonon Noise Research Articles

Influence of Different Substrates on the Detectivity of Pyroelectric Sensors

Nanosized lead titanate doped with calcium and lanthanum (PCLT) powder obtained by the sol-gel method was homogeneously mixed with vinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] to form nanocomposites. Several pyroelectric sensors were prepared on porous silicon dioxide, on poly(ethylene terephthalate) (PET) film and on bulk silicon substrates, respectively. The nanocomposite PCLT/P(VDF-TrFE) sensing film was deposited by spin-coating and Ni-Cr film was deposited as the top electrode and absorption layer. Experimental results showed that the substrate of the pyroelectric sensor could significantly affect the specific detectivity. The porous silicon dioxide and PET plastic film substrates could effectively decrease the thermal conductivity and the thermal fluctuation noise of the pyroelectric element, increase the voltage responsivity and the specific detectivity. The results indicated that the specific detectivity of PCLT/P(VDF-TrFE) pyroelectric sensors based on porous silicon dioxide and PET plastic film substrates reached 4.2E6 and 3.4E7 cmHz 1/2 W m 1 respectively, which is about 1-2 orders of magnitude higher than that of the sensors formed under the same condition on the bulk silicon substrate.

2‐cm GPS altimetry over Crater Lake

Differences in electromagnetic path delay, between direct Global Positioning System (GPS) signals and those reflected from the surface of Crater Lake, have led to lake surface height estimates with 2‐cm precision in 1 second. This is the first high‐precision altimetric demonstration with GPS from sufficient altitude (≈ 480 m) to probe fundamental experimental errors, which bear on future air‐and spaceborne passive GPS altimetry. It also serves as the first demonstration of a new approach to altimetric remote sensing in the coastal region, an area that is poorly measured by conventional radar altimetry. Time‐series analyses suggest that tropospheric and thermal noise fluctuations dominate the altimetric error in this experiment. Estimating the differential delay from several simultaneously visible satellites may enable tropospheric error estimation and correction. Thermal noise on the reflected signal will be reduced with fully polarimetric observations and larger antenna apertures.

Silicon nitride micromesh bolometer array for submillimeter astrophysics

We present the design and performance of a feedhorn-coupled bolometer array intended for a sensitive 350-mum photometer camera. Silicon nitride micromesh absorbers minimize the suspended mass and heat capacity of the bolometers. The temperature transducers, neutron-transmutation-doped Ge thermistors, are attached to the absorber with In bump bonds. Vapor-deposited electrical leads address the thermistors and determine the thermal conductance of the bolometers. The bolometer array demonstrates a dark noise-equivalent power of 2.9 x 10(-17) W/ radicalHz and a mean heat capacity of 1.3 pJ/K at 390 mK. We measure the optical efficiency of the bolometer and feedhorn to be 0.45-0.65 by comparing the response to blackbody calibration sources. The bolometer array demonstrates theoretical noise performance arising from the photon and the phonon and Johnson noise, with photon noise dominant under the design background conditions. We measure the ratio of total noise to photon noise to be 1.21 under an absorbed optical power of 2.4 pW. Excess noise is negligible for audio frequencies as low as 30 mHz. We summarize the trade-offs between bare and feedhorn-coupled detectors and discuss the estimated performance limits of micromesh bolometers. The bolometer array demonstrates the sensitivity required for photon noise-limited performance from a spaceborne, passively cooled telescope.

Noise and energy resolution of X-ray microcalorimeters

Two type of sensor geometries of voltage-biased X-ray microcalorimeters with a phase-transition thermometer have been built and tested. Both devices show, in addition to the well-known noise sources of thermal fluctuation noise or phonon noise from the heatlink to the bath and Johnson noise from the thermometer resistance, also thermal fluctuation noise from the thermometer itself. In both cases however the measured energy resolution is limited by other sources. The energy resolution of the asymmetric lateral type of sensor, 12 to 15 eV @ 5.9 keV, is limited by a position dependent heatleak of the absorber to the bath. The energy resolution of the symmetric lateral sensor, 6.8+/-0.3 eV FWHM @ 5.9 keV, is limited by excess noise at frequencies below 1000 Hz. The origin of this noise component is unknown so far.

Thermal fluctuation noise in a voltage biased superconducting transition edge thermometer

The current noise at the output of a microcalorimeter with a voltage biased superconducting transition edge thermometer is studied in detail. In addition to the two well-known noise sources: thermal fluctuation noise from the heat link to the bath and Johnson noise from the resistive thermometer, a third noise source strongly correlated with the steepness of the thermometer is required to fit the measured noise spectra. Thermal fluctuation noise, originating in the thermometer itself, fully explains the additional noise. A simple model provides quantitative agreement between the observed and calculated noise spectra for all bias points in the superconducting transition.

Excess noise in YBa2Cu3O7 epitaxial films and antenna-type microbolometers based on them

Monte Carlo modelled anneals of YBa2Cu3O7 epitaxial films have been carried out, and the excess flicker noise in the operating frequency and temperature ranges were shown to be dominated by oxygen migration near small-angle block boundaries. Optimization of film and planar-microstructure fabrication permitted reaching a record-low Hooge noise parameter (1.8×10−4 at 93 K) for test structures, which can be used to prepare high-performance antenna-type strip microbolometers. Calculations show that the reduction of the microstrip size to 1×0.7 µm2 and of the flicker noise made possible detection of radiation within the spectral range from 3 mm to 300 µm (100–1000 GHz) at 90 K, with a nanosecond response and a noise-equivalent power of 1.5×10−12 W/Hz1/2 at frequencies from 30 to 107 Hz, which is close to the limitations imposed by phonon noise.

Multi-pixel readout of transition-edge sensors using a multi-input SQUID

We propose a new method to read out signals from a TES (superconducting Transition-Edge Sensor) calorimeter array with a single or a small number of SQUIDs. Since phonon noise and Johnson noise of a calorimeter can be made very small in these calorimeters, an increase in noise, thus a degradation of energy resolution by adding signals from plural pixels together at some stage of signal processing may be acceptable for some applications of TES calorimeters. We propose to use a SQUID with multi-input coils which will sense signals from different pixels. The input coils of a SQUID are electrically well-isolated from each other. The pixel that generates a signal can be identified by utilizing additional information, such as the pulse shape. We studied the feasibility of this method with analysis and simulations, and show for example, that a 16×16 pixel array can be read out with 16 SQUIDs.

On the concept of a normal metal hot-electron microbolometer for space applications

We present a theoretical analysis and experimental evaluation of a hot-electron microbolometer with normal metal absorber for ultrasensitive detecting infrared and submillimeter waves. The basic version of the antenna coupled microbolometer makes use of a hot-electron effect in the thin film resistive strip and Andreev reflection of hot electrons at SN interface between the strip and superconducting antenna. A value of NEP=5/spl middot/10/sup -18/ W/Hz/sup 1/2/ for the thermal fluctuation noise and the thermal time constant t=0.2 /spl mu/s at 300 mK have been estimated for one of the realized devices with thermal conductance G/spl ap/6/spl middot/10/sup -12/ W/K. At 100 mK, the thermal conductance has been decreased to G/spl ap/7/spl middot/10/sup -14/ W/K, that gives estimations for the thermal NEP=2/spl middot/10/sup -19/ W/Hz/sup 1/2/ and the time constant t=5 /spl mu/s. An advanced version of the microbolometer includes also additional SIN junctions connected to the resistive strip for electronic cooling the absorber. Such microbolometer is intended as a detector of millimeter and submillimeter wave radiation for space applications.

Yoctocalorimetry: phonon counting in nanostructures

It appears feasible with nanostructures to perform calorimetry at the level of individual thermal phonons. Here I outline an approach employing monocrystalline mesoscopic insulators, which can now be patterned from semiconductor heterostructures into complex geometries with full, three-dimensional relief. Successive application of these techniques also enables definition of integrated nanoscale thermal transducers; coupling these to a dc SQUID readout yields the requisite energy sensitivity and temporal resolution with minimal back action. The prospect of phonon counting opens intriguing experimental possibilities with analogies in quantum optics. These include fluctuation-based phonon spectroscopy, phonon shot noise in the energy relaxation of nanoscale systems, and quantum statistical phenomena such as phonon bunching and anticorrelated electron–phonon exchange.

Magnetic hysteresis dynamics of thin Co films on Cu(001)

Hysteresis properties of ultrathin (2--4 monolayers) epitaxial Co films grown on Cu(001) surfaces are studied as a function of film thickness, temperature and the strength ${(H}_{0}),$ in-plane direction, and frequency (\ensuremath{\Omega}) of applied sinusoidal magnetic field. Scaling of the hysteresis loop area (power loss) of the form ${A=A}_{0}{+H}_{0}^{\ensuremath{\alpha}}{\ensuremath{\Omega}}^{\ensuremath{\beta}}\ensuremath{\zeta}(H,\ensuremath{\Omega})$ where \ensuremath{\zeta} is a scaling function is explored. All films exhibit a threshold field ${(H}_{t})$ where switching between equivalent magnetized states is initiated. Hysteresis loop areas measured over five decades in frequency exhibit very weak power-law dependence $(\ensuremath{\beta}\ensuremath{\sim}0.02).$ No evidence of a dynamic phase transition is observed and no indication of a low-frequency $({\ensuremath{\Omega}}_{0}\ensuremath{\sim}{10}^{2}\mathrm{Hz})$ characteristic resonance is apparent over the drive frequency range covered. The observed weak power-law scaling does not support results of prior experiments that have been interpreted as corroborating the mean-field Ising model $(\ensuremath{\alpha}=\ensuremath{\beta}=\frac{2}{3})$ and continuum spin models of thin-film hysteresis energy-loss scaling. The measured frequency and applied field-dependent scaling of the dynamic coercive force ${(H}_{c}^{*})$ also appears to be inconsistent with recent phenomenological models of hysteresis behavior based on domain-wall motion that predict that ${H}_{c}^{*}$ scales as $\mathrm{ln}\mathrm{H\ifmmode \dot{}\else \.{}\fi{}}.$ The results of this study of Co on Cu(001) and a corresponding study of Fe on W(110) suggest that the dynamics of magnetization reversal in real ultrathin film systems do not exhibit universal behavior in the low-field low-frequency limit. Recent theoretical results based on a more realistic model that accounts for thermal noise and spatial fluctuations in the dynamics yield logarithmic scaling at low \ensuremath{\Omega} and effective exponents \ensuremath{\beta} that are compatible with the experiments. A simple physical picture of low drive-frequency energy-loss scaling is described that accounts for the experimental observations.

Effect of sodium perturbations on rat chemoreceptor spike generation: implications for a Poisson model.

1. The sensitivity of arterial chemoreceptor spike generation to reductions in excitability was examined using rat chemoreceptors in vitro. Axonal excitability was reduced by reducing extracellular sodium concentration ([Na+]o) by 10-40% or by applying low doses of tetrodotoxin (TTX). 2. In normoxia and in hypoxia, an isosmotic reduction in [Na+]o caused a proportional decrease in single-fibre, spiking nerve activity. For a 20% reduction in [Na+]o, nerve activity decreased to 54 +/- 7% of control in normoxia and 41 +/- 5% in hypoxia. 3. Low doses of TTX (25-50 nM) caused a similar decrease in spiking frequency, but this response was variable amongst fibres, with some fibres unaffected by TTX. 4. A reduction in [Na+]o by 20% caused a slowing of conduction velocity, measured using an electrical stimulus delivered to an electrode placed in the carotid body. Threshold current for spike generation was increased by about 2.7 +/- 1.4%. Threshold current increased by 6.5 +/- 3.7% following a 40% reduction in [Na+]o. 5. The spike generation process was modelled as a Poisson process in which depolarizing events summate and give rise to an action potential. The experimental data were best fitted to a high order process characterized by a large number of events and high event threshold. 6. This result is not consistent with depolarization events caused by episodic transmitter release, but suggests that afferent spike generation is an endogenous process in the afferent nerve fibres, perhaps linked to random channel activity or to thermal noise fluctuations.

Noise of high-Tc superconducting films and bolometers

The results of the noise investigations of high-T c superconducting films (HTS) and bolometers are reported. HTS films produced by the magnetron and laser depositions on various substrates were studied. Structural, excess noise and critical current properties were investigated Noise measurements of antenna YBa 2 Cu 3 O 7-x microbolometer on NdGaO 3 substrate and GdBa 2 Cu 3 O 7-x bolometer on Si-membrane showed that the noise parameters of bolometers were limited by only the phonon noise at operating frequency.

Scaling limit of digital circuits due to thermal noise

The error probability at a node of a digital circuit exposed to thermal noise agitation is investigated and the minimal dissipation–reliability relation for practical electronic circuits is derived. The digital circuit is modeled by an inverter chain with ideal transfer characteristics, and the error probability due to spurious data transfer caused by the thermal noise fluctuation is evaluated as a function of the node switching energy. The maximal error probability at each node allowed by the reliability requirement of the total system leads us to the minimal node energy dissipated per logical switching, which amounts to around 12 eV in the future 1010 gate system operated at a 10 GHz clock rate with a 104 FIT level reliability. In view of the device size-scaling trend of large-scale integrated circuits, the minimal node energy is expected to be reached at a feature size of 10–20 nm.

Spectrum of thermal fluctuation noise in diffusion and phonon cooled hot-electron mixers

A systematic study of the intermediate frequency noise bandwidth of Nb thin-film superconducting hot-electron bolometers is presented. We have measured the spectrum of the output noise as well as the conversion efficiency over a very broad intermediate frequency range (from 0.1 to 7.5 GHz) for devices varying in length from 0.08 μm to 3 μm. Local oscillator and rf signals from 8 to 40 GHz were used. For a device of a given length, the spectrum of the output noise and the conversion efficiency behave similarly for intermediate frequencies less than the gain bandwidth, in accordance with a simple thermal model for both the mixing and thermal fluctuation noise. For higher intermediate frequencies the conversion efficiency decreases; in contrast, the noise decreases but has a second contribution which dominates at higher frequency. The noise bandwidth is larger than the gain bandwidth, and the mixer noise is low, between 120 and 530 K (double side band).

A high-T/sub c/ superconductor bolometer on a silicon nitride membrane

In this paper, we describe the design, fabrication, and performance of a high-T/sub c/ GdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// superconductor bolometer positioned on a 2/spl times/ 2-mm/sup 2/ 1-/spl mu/m-thick silicon nitride membrane. The bolometer structure has an effective area of 0.64 mm/sup 2/ and was grown on a specially developed silicon-on-nitride (SON) layer. This layer was made by direct bonding of silicon nitride to silicon after chemical mechanical polishing. The operation temperature of the bolometer is 85 K. A thermal conductance G=3.3/spl middot/10/sup -5/ W/K with a time constant of 27 ms has been achieved. The electrical noise equivalent power (NEP) at 5 Hz is 3.7/spl middot/10/sup -2/ WHz/sup -1/2/, which is very close to the theoretical phonon noise limit of 3.6/spl middot/10/sup -12/ WHz/sup -1/2/, meaning that the excess noise of the superconducting film is very low. This bolometer is comparable to other bolometers with respect to high electrical performance. Our investigations are now aimed at decreasing the NEP for 84-/spl mu/m radiation by further reduction of G and adding an absorption layer to the detector. This bolometer is intended to be used as a detector in a Fabry-Perot (FP)-based satellite instrument designed for remote sensing of atmospheric hydroxyl.

Optimum duration of measurement for reducing thermal noise limitations in torsion pendulum experiments

Statistical estimates of thermal noise fluctuation of a linear harmonic oscillator used to detect weak forces are reexamined with special reference to gravitational experiments. Thermal noise limitation on the measurement of displacement of an oscillator is studied. It is found that the signal response of an oscillator reaches the maximum value while the thermal noise response reaches the minimum value at the same time during the transient state of the oscillator, and the precision of the experiments in the transient state could increase about two orders higher than that in the equilibrium state for typical experiments. It is also found that there is an optimum duration of measurement in which the uncertainty due to thermal noise in this period is the least.

Evolution of phonon noise and phonon state preparation in a model for generation of hypersonic phonons by laser

The evolution of phonon noise and the quantum correlation between phonon and photon in a model of the generation of hypersonic phonons by laser have been analyzed according to the quantum theory. The cases of perfect phase matching, phase mismatch, and losses have been discussed, respectively. It is shown that the phonon state preparation can be performed by measuring a quadrature component of the idle light field under certain conditions.

Induced gate noise in MOSFETs revisited: The submicron case

At high frequencies the gate admittance of the MOSFET contains a conductive component because of the capacitive coupling of the gate electrode to the channel. The thermal noise fluctuations, originating in the channel, induce a gate current outwards from the gate electrode. Based on a proved two-region model for the drain current noise of a sub-micron MOSFET, it is shown that the calculated gate-noise current increases significantly, compared to that predicted by a classical model, valid for long channel devices.

Low noise high-Tc superconducting bolometers on silicon nitride membranes for far-infrared detection

High-Tc GdBa2Cu3O7−δ superconductor bolometers with operation temperatures near 89 K, large receiving areas of 0.95 mm2 and very high detectivity have been made. The bolometers are supported by 0.62 μm thick silicon nitride membranes. A specially developed silicon-on-nitride layer was used to enable the epitaxial growth of the high-Tc superconductor. Using a gold black absorption layer an absorption efficiency for wavelengths between 70 and 200 μm of about 83% has been established. The noise of the best devices is fully dominated by the intrinsic phonon noise of the thermal conductance G, and not by the 1/f noise of the superconducting film. The temperature dependence of the noise and the resulting optimum bias temperature have been investigated. In the analysis the often neglected effect of electrothermal feedback has been taken into account. The minimum electrical noise equivalent power (NEP) of a bolometer with a time constant τ of 95 ms is 2.9 pW/Hz1/2 which corresponds with an electrical detectivity D* of 3.4×1010 cm Hz1/2/W. Similar bolometers with τ=27 ms and NEP=3.8 pW/Hz1/2 were also made. No degradation of the bolometers could be observed after vibration tests, thermal cycling and half a year storage. Measurements of the noise of a Pr doped YBa2Cu3O7−δ film with Tc=40 K show that with such films the performance of air bridge type high-Tc bolometers could be improved.

Evolution of phonon noise and quantum nondemolition measurements in the model for detection of hypersonic phonons by squeezed light

The evolution of phonon quadrature component fluctuations has been analyzed in the model for detection of hypersonic phonon by squeezed light. According to quantum theory, it is shown that the quantum nondemolition measurement of the amplitude quadrature of the hypersonic phonons can be performed by detecting the phase quadrature of the squeezed light.