Low Flicker Noise Research Articles

Valence-band tunneling induced low frequency noise in ultrathin oxide (15Å) n-type metal-oxide-semiconductor field effect transistors

Low frequency flicker noise in n-type metal-oxide-semiconductor field effect transistors (n-MOSFETs) with 15Å gate oxide is investigated. A noise generation mechanism resulting from valence band tunneling is proposed. In strong inversion condition, valence-band electron tunneling takes place and results in the splitting of electron and hole quasi-Fermi levels in the channel. The excess low frequency noise is attributed to electron and hole recombination at interface traps between the two quasi-Fermi levels. Random telegraph signal in a small area device is characterized to support our model.

A micropower CMOS, direct-conversion, VLF receiver chip for magnetic-field wireless applications

A micropower CMOS, direct-conversion very low frequency (VLF) receiver is described for receiving low-level magnetic fields from resonant sensors. The single-chip, phase locked loop (PLL)-synthesized receiver covers a frequency range of 10-82 kHz and provides both analog and 9-b digital baseband I and Q outputs. Digital I and Q outputs are accumulated in a companion digital chip which provides baseband signal processing. Emphasis is plated on the receiver micropower RF preamplifier which uses a lateral bipolar input device because of the significant increase in flicker noise illustrated for PMOS devices in weak inversion. Lateral bipolar transistors are also utilized in the mixer and IF stages for low flicker noise and low dc offsets. Special attention is given to isolating the internal local oscillator signals from the low-level RF input (0.3 /spl mu/V noise floor in 300 Hz BW), and local oscillator feedthrough is indiscernible in the RF preamplifier output noise spectrum. The 100% duty-cycle receiver, intended for miniature, battery-operated wireless applications, operates approximately four months at 80 /spl mu/A from a 6-V, 220-mA-hr battery.

Resistance flicker noise and current percolation in c-oriented YBa 2Cu 3O 7− x films in the vicinity of Tc

Noise properties of c-oriented YBa 2Cu 3O 7− x fioms near T c have been investigated both experimentally and theoretically. The films studied are divided into two groups. The resistance noise and transport properties for the films (1) are controlled by the grain boundary junctions. The films (2) are of high structural perfection and have very low flicker noise levels. Their S R( T)-characteristics near T c are quantitatively described by a novel percolation model. The model takes into account static T c-inhomogeneities of the film and the presence of defects that modulate the local T c. Distribution functions of T c were obtained and defect density of states as well as a scale of T c-relief were estimated. The spatial current distribution is studied by low-temperature SEM. The method is originally used for T c-mapping of the films. A special algorithm for the LTSEM data treatment for inhomogeneous films using the effective medium approach and allowing us to derive local transition curves is proposed.

Enantiometric purity determination to 1 % level using a laser-based polarimetric HPLC detector

The development of laser-based polarimetric detectors for high-performance liquid chromatography (HPLC) (Yeung et al . 1980; Bobbitt & Yeung 1986) with noise levels in the range of 0.1-10 p° has provided a significant advance in the quantitation of chiral molecules. We have designed an instrument based on an 820 nm diode laser which has the advantages of low source flicker noise and compact design (Lloyd et al . 1989). Detection limits were found to be in the range 0.1-2 pg, dependent on the specific rotation of the chiral molecule and the chromatographic peak width (Goodall et al. 1990).

Application of laser-excited atomic fluorescence spectrometry to the determination of iron

A frequency-doubled, flashlamp-pumped tunable dye laser is used to excite the Stokes direct-line atomic fluorescence transition of iron (296.7 nm/373.5 nm). Limits of detection are determined with single (0.6 ng/ml) and multipass (0.2 ng/ml) and with a l s time constant (a 0.06 ng/ml limit detection is obtained with an 8 s time constant). Noise sources limiting precision at both low (background flame emission shot and flicker noise) and high concentrations (laser pulse to pulse variability) concentrations are investigated and the technique is used for the determination of iron in simulated fresh water NBS SRM-1643), unalloyed copper (NBS SRM-394) and fly ash (NBS SRM-1633).

Low-noise integrated silicon-gate FET amplifier

A high-gain silicon-gate FET amplifier having low noise is described, and results of gain and noise measurements are presented. To obtain low flicker and thermal noise, the input FET was designed as a large-area device (0.336 mm/SUP 2/) with large channel width-to-length ratio (130:1).

Flicker Noise in Oxide Cathodes Arising from Diffusion and Drift of Ionized Donors

A theory is presented which investigates the emission fluctuations arising from random arrival of barium at the surface of the grains followed by donor migration through the effective emitting part of the grains. The basic causes for the noise are diffusion of donor centers and electrolysis in the coating, processes which are known to be vital in cathode operation. The computed spectra are characterized by a diffusion relaxation time, a diffusion-conduction time constant, and a parameter involving the electric field in the coating surface layer. Three different types of spectra result from this. Experimental data are reported, mainly on 2×2 diodes which support various aspects of the theory. The dependence of the turnover frequencies on temperature, activation, and current is in good agreement with the predicted results. The magnitude of the noise is close to Poissonian, contrary to previous claims. Recommendations for attaining low flicker noise are given.

Recent developments in silicon radar crystals

Crystal valves have undergone considerable development in recent years, and much improved silicon detectors and mixers are now available. The improvements stem partly from a fuller understanding of semiconductor phenomena, partly from more rigorous design techniques, but largely from advances in materials technology, particularly with regard to the production of silicon tailored to meet specific requirements.With detectors, operation with maximum sensitivity over greater bandwidths has been the principal requirement. Progress in design is illustrated by reference to a range of experimental broadband crystals intended to cover frequencies from the lower end of the microwave spectrum up to 40Gc/s. These experimental types are being superseded by a new range of high-sensitivity detectors which operate with a small positive d.c. bias and give better stability and resistance to burnout and, moreover, are far easier to manufacture. Performance data are presented in some detail.Mixers have been improved in overall noise factor, particularly at Xband, and tighter control of their r.f. properties has been achieved. Compared with other semiconductors, silicon-type mixers are relatively insensitive to variations in local-oscillator drive power and resistance of the d.c. circuit or to temperature changes. The use of silicon proves particularly advantageous for low-flicker noise mixers, which are required in c.w. radars.Significant improvements in the conversion loss of mixers and in the sensitivity of detectors are becoming possible through the reduction of series-spreading resistance with crystals which use silicon films deposited epitaxially on to more highly conducting substrates.