L.K.J. Vandamme

Experimental studies on 1/f noise

Experimental studies on 1/f noise are reviewed with emphasis on experiments that may be decisive in finding the correct theoretical model for this type of noise. The experimental results are confronted with two theories: McWhorters (1959) surface state theory and Clarke and Vosss (1974) theory of local temperature fluctuations. The applicability of either theory turns out to be very limited. The validity of an empirical relation is investigated. Its application to electronic devices proves successful. Experiments show that 1/f noise obeying the empirical relation ( alpha noise) is a fluctuation in the part of the mobility that is due to lattice scattering.

Noise as a diagnostic tool for quality and reliability of electronic devices

Experimental facts about noise are presented which help us to understand the correlation between noise in a device and its reliability. The main advantages of noise measurements are that the tests are less destructive, faster and more sensitive than DC measurements after accelerated life tests. The following topics are addressed: 1) the kind of noise spectra in view of reliability diagnostics such as thermal noise, shot noise, the typical poor-device indicators like burst noise and generation-recombination noise and the 1/f/sup 2/ and 1/f noise; 2) why conduction noise is a quality indicator; 3) the quality of electrical contacts and vias; 4) electromigration damage; 5) the reliability in diode type devices like solar cells, laser diodes, and bipolar transistors; and 6) the series resistance in modern short channel MESFET, MODFET, and MOST devices. >

1/f noise in MOS devices, mobility or number fluctuations?

Recent experimental studies on 1/f noise in MOS transistors are reviewed. Arguments are given for the two schools of thought on the origin of 1/f noise. The consequences of models based on carrier-number /spl Delta/N or mobility fluctuations /spl Delta//spl mu/ on the device geometry and on the bias dependence of the 1/f noise are discussed. Circuit-simulation-oriented equations for the 1/f noise are discussed. The effects of scaling down on the 1/f noise is studied in the ohmic region as well as in saturation. In the ohmic region the contribution of the series resistance often can be ignored. However, in saturation the noise of the gate-voltage-dependent series resistance on the drain side plays a role in lightly doped drain LDD mini-MOSTs. Surface and bulk p-channel devices are compared and the differences between n-and p-MOSTs often observed is discussed. The relation between degradation effects by hot carriers or by /spl gamma/-irradiation on the one hand and the 1/f noise on the other is considered in terms of a /spl Delta/N or /spl Delta//spl mu/. Experimental results suggest that 1/f noise in n-MOSTs is dominated by /spl Delta/N while in p-MOSTs the noise is due to /spl Delta//spl mu/. >

General relation between refractive index and energy gap in semiconductors

Abstract A review is given of existing relations and rules of thumb between refractive index and energy gap in semiconductors. An error deviation was calculated on more than one hundred materials. With only one set of fitting parameters, our model n2 = 1 + [A/(Eg + B)]2, based on the classical oscillator theory, gives good fit except for IV–VI materials like PbS, PbSe, PbTe. The constant A was found to have the same value as the hydrogen ionization energy i.e. 13.6 eV and B = 3.4 eV.

What Do We Certainly Know About

1/f noise is a fluctuation in the conductance of semiconductors and metals. This noise could be a fluctuation in the number of free electrons or in their mobility. Many experimental studies have proved that the 1/f noise in homogeneous samples is a fluctuation in the mobility. There is a reliable empirical relation for the power density of the mobility noise. Theoretical models for mobility noise have not had much influence in the discussions. The theoretical position for number fluctuations is quite the opposite. The generally accepted McWhorter model is simple; however, very few experimental studies definitely prove number fluctuations and exclude uncorrelated mobility fluctuations. There is an extensive literature on noise in MOSTs. Submicrometer MOSTs are notorious for their high low-frequency noise. Almost all studies start from the McWhorter generation-recombination (GR) model. The discussion is confused by the many complications of the MOSTs, such as mobility degradation, surface and contacts effects, size of the samples, etc. An additional problem is that the real 1/f noise is often mixed up with other types of low-frequency noise, such as burst and GR noises. A critical discussion is given for the Kirton and Uren model. Analytical expressions are presented for the results of their computer simulations. This explains their surprising discovery that the density of McWhorter states may be ldquosubstantiallyrdquo different from the usual 1/ tau distribution.

\hbox{1}/f

Recently, unified noise models, like BSIM3, have been proposed in literature to describe the 1/f noise of n- and p-type MOSFETs in all operating regimes. These models combine carrier number fluctuations and correlated mobility fluctuations. The latter are induced by the Coulomb scattering of free carriers at trapped interface charge. The unified 1/f noise models assume implicitly that the mobility, limited by Coulomb scattering, does not depend on the inversion carrier density. However, this assumption is not correct in view of theoretical calculations and recent experimental results. In this paper, we show that the correlated mobility fluctuations are negligible, if the correct dependence on inversion carrier density is taken into account for the Coulomb scattering limited mobility. Consequently, the unified 1/f noise models cannot predict the 1/f noise observed experimentally in p-type MOSFETs, except if nonphysical fitting parameters are used. This paper serves as a critical discussion on the unified 1/f noise models for MOSFETs. Here it is not our intention to propose a new 1/f noise model.

Noise in MOSTs?

The 1/f noise in normally-on MODFETs biased at low drain voltages is investigated. The experimentally observed relative noise in the drain current S/sub I//I/sup 2/ versus the effective gate voltage V/sub G/=V/sub GS/-V/sub off/ shows three regions which are explained. The observed dependencies are S/sub I//I/sup 2/ varies as V/sub G//sup m/ with the exponents m=-1, -3, 0 with increasing values of V/sub G/. The model explains m=-1 as the region where the resistance and the 1/f noise stem from the 2-D electron gas under the gate electrode; the region with m=0 at large V/sub G/ or V/sub GS/ equivalent to 0 is due to the dominant contribution of the series resistance. In the region at intermediate V/sub G/, m=-3, the 1/f noise stems from the channel under the gate electrode, and the drain-source resistance is already dominated by the series resistance. >

Critical discussion on unified 1/f noise models for MOSFETs

Values of the temperature coefficient of the refractive index were obtained from the derivation of a simple relation between energy band‐gap and refractive index in semiconductors. These values, (dn/dT)/n, were compared to the experimental data found in literature. Our model, with only one fitting parameter dB/dT=2.5×10−5 K−1 for all semiconductors, results in the best agreement with experimental data.

1/f noise in MODFETs at low drain bias

The conductivity fluctuations in 1‐MeV, boron‐implanted layers in silicon have been investigated at room temperature with the anneal temperature as a parameter. The 1/ f  noise parameter α has been calculated from conductance, Hall voltage, and noise experiments. Annealing of the implants causes, in addition to an increase in the number of electrically active impurities, a decrease in the 1/ f  noise parameter α by a factor of at least 50. The α value is proportional to eΔE/kTan, with an annealing activation energy ΔE=1.1 eV in a temperature range of 722 K <Tan<1022 K. The annealing affects the quality of the crystal, the scattering mechanism, the temperature dependence of the mobility, and the value of α. The better the crystal, the lower the 1/ f  noise parameter α.

Empirical temperature dependence of the refractive index of semiconductors

A measurement system comprised of an ultra-low-distortion function generator, lock-in amplifier, and semiconductor parameter analyzer is used for sensitive extraction of the small-signal thermal impedance network of bipolar devices and circuits. The extraction procedure is demonstrated through measurements on several silicon-on-glass NPN test structures. Behavioral modeling of the mutual thermal coupling obtained by fitting a multipole rational complex function to measured data is presented.