Tunneling two-level systems and 1/ f -noise: A century of nuisance

Noise in Solid State Devices

A survey is given of the most important noise problems in solid-state devices. Section II discusses shot noise in metal-semiconductor diodes, p-n junctions, and transistors at low injection; noise due to recombination and generation in the junction space-charge region; high-level injection effects; noise in photodiodes, avalanche diodes, and diode particle detectors, and shot noise in the leakage currents in field-effect transistors (FETs). Section III discusses thermal noise and induced gate noise in FETs; generation-recombination noise in FETs and transistors at low temperatures; noise due to recombination centers in the space-charge region(s) of FETs, and noise in space-charge-limited solid-state diodes. Section IV attempts to give a unified account of 1/f noise in solid-state devices in terms of the fluctuating occupancy of traps in the surface oxide; discusses the kinetics of these traps; applies this to flicker noise in junction diodes, transistors, and FETs, and briefly discusses flicker noise in Gunn diodes and burst noise in junction diodes and transistors. Section V discusses shot noise in the light emission of luminescent diodes and lasers, and noise in optical heterodyning. Section VI discusses circuit applications. It deals with the noise figure of negative conductance amplifiers (tunnel diodes and parametric amplifiers), and of FET, transistor, and mixer circuits. In the latter discussion capacitive up-converters, and diode, FET, and transistor mixers are dealt with.

Parasitic two-level tunneling systems (TLS) emerge in amorphous dielectrics and constitute a serious nuisance for various microfabricated devices, where they act as a source of noise and decoherence. Here, we demonstrate a new test bed for the study of TLS in various materials which provides access to properties of individual TLS as well as their ensemble response. We terminate a superconducting transmission-line resonator with a capacitor that hosts TLS in its dielectric. By tuning TLS via applied mechanical strain, we observe the signatures of individual TLS strongly coupled to the resonator in its transmission characteristics and extract the coupling components of their dipole moments and energy relaxation rates. The strong and well-defined coupling to the TLS bath results in pronounced resonator frequency fluctuations and excess phase noise, through which we can study TLS ensemble effects such as spectral diffusion, and probe theoretical models of TLS interactions.

Contrarily to current theories based on hypothetical traps where charge carriers can translocate to, this paper gives an explanation for 1/f electrical noise in solid-state devices based on well known electrical effects taking place in these devices. A parasitic capacitor and the backgating effect of its thermal noise, both overlooked in the course of the years, are the basis of the above explanation. The above effect produces a resistance noise with a Lorentzian spectrum in any unbiased resistor. As soon as the resistor is biased, this spectrum is scattered into a continuous set of Lorentzian noise terms that synthesize 1/f noise over a frequency band that is an exponential function of the bias voltage V_DS expressed in thermal units V_T. This is due to the exponential dependence of the dynamical resistance in most semiconductor junctions. A V_DS=180mV is thus enough to give 1/f noise over three decades at room temperature. This unexpected and non-linear feature, where the spectrum of this noise results from the own bias used to measure it, has kept 1/f noise as a puzzling and enigmatic noise for more than eighty years. The above theory, born in the solid-state field, can also be generalized to other devices where two orthogonal forces or energy gradients appear while electrical noise is being measured.

Noise within solid-state systems at low temperatures can typically be traced back to material defects. In amorphous materials, these defects are broadly described by the tunneling two-level systems (TLSs) model. TLS have recently taken on further relevance in quantum computing because they dominate the coherence limit of superconducting quantum circuits. Efforts to mitigate TLS impacts have thus far focused on circuit design, material selection, and surface treatments. Our work takes an approach that directly modifies TLS properties. This is achieved by creating an acoustic bandgap that suppresses all microwave-frequency phonons around the operating frequency of a transmon qubit. For embedded TLS strongly coupled to the transmon qubit, we measure a pronounced increase in relaxation time by two orders of magnitude, with the longest T1 time exceeding 5 milliseconds. Our work opens avenues for studying the physics of highly coherent TLS and methods for mitigating noise within solid-state quantum devices.

Tunneling two-level systems (TLSs) are believed to be the source of phenomena such as the universal low temperature properties in disordered and amorphous solids, and 1/f noise. The existence of these phenomena in a large variety of dissimilar physical systems testifies for the universal nature of the TLSs, which however, is not yet known. Following a recent suggestion that attributes the low temperature TLSs to inversion pairs [M. Schechter and P. C. E. Stamp, arXiv:0910.1283.] we calculate explicitly the TLS-phonon coupling of inversion symmetric and asymmetric TLSs in a given disordered crystal. Our work (a)estimates parameters that support the theory in M. Schechter and P. C. E. Stamp, arXiv:0910.1283, in its general form, and (b)positively identifies, for the first time, the relevant TLSs in a given system.

International audience

Limiting noise sources in various solid state devices are discussed. This involves shot noise in p-n diodes, shot noise in p-n-p transistors, both at low and at very high injection, thermal noise in JFETs and MOSFETs, including hot electron effects and high-frequency effects, noise due to donors in n-channel JFETs noise.

Amorphous solids, as well as many disordered lattices, display remarkable universality in their low temperature acoustic properties. This universality is attributed to the attenuation of phonons by tunneling two-level systems (TLSs), facilitated by the interaction of the TLSs with the phonon field. TLS-phonon interaction also mediates effective TLS–TLS interactions, which dictates the existence of a glassy phase and its low energy properties. Here we consider KBr:CN, the archetypal disordered lattice showing universality. We calculate numerically, using conjugate gradients method, the effective TLS–TLS interactions for inversion symmetric (CN flips) and asymmetric (CN rotations) TLSs, in the absence and presence of disorder, in two and three dimensions. The observed dependence of the magnitude and spatial power law of the interaction on TLS symmetry, and its change with disorder, characterizes TLS–TLS interactions in disordered lattices in both extreme and moderate dilutions. Our results are in good agreement with the two-TLS model, recently introduced to explain long-standing questions regarding the quantitative universality of phonon attenuation and the energy scale of ≈1–3 K below which universality is observed.

Fourth international conference on “physical aspects of noise in solid state devices”: 9–11 September 1975

Introduction to noise in solid state devices

formula omitted] Fourth international conference on “physical aspects of noise in solid state devices”

Fourth International Conference on “Physical Aspects of Noise in Solid State Devices” 9–11 September 1975

Fourth international conference on “Physical Aspect of Noise in Solid State Devices” : 9–11 September 1975

Noise in solid state devices and systems (Panel Discussion)