A new and accurate approach to charge-pumping measurements for the determination of the Si-SiO 2 interface state density directly on MOS transistors is presented. By a careful analysis of the different processes of emission of electrons towards the conduction band and of holes towards the valence band, depending on the charge state of the interface, all the previously ill-understood phenomena can be explained and the deviations from the simple charge-pumping theory can be accounted for. The presence of a geometric component in some transistor configurations is illustrated and the influence of trapping time constants is discussed. Furthermore, based on this insight, a new technique is developed for the determination of the energy distribution of interface states in small-area transistors, without requiring the knowledge of the surface potential dependence on gate voltage.

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A reliable approach to charge-pumping measurements in MOS transistors

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: McWhorter's (1959) surface state theory and Clarke and Voss's (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.

http://iopscience.iop.org/article/10.1088/0034-4885/44/5/001/pdf

Experimental studies on 1/f noise

A simple model describing the DC behavior of MOS transistors operating in weak inversion is derived on the basis of previous publications. This model includes only two parameters and is suitable for circuit design. It is verified experimentally for both p- and n-channel test transistors of a Si-gate low-voltage CMOS technology. Various circuit configurations taking advantage of weak inversion operation are described and analyzed: two different current references based on known bipolar circuits, an amplitude detector scheme which is then applied to a quartz oscillator with the result of a very low-power consumption (<0.1 /spl mu/W at 32 kHz), and a low-frequency bandpass amplifier. All these circuits are insensitive to threshold and mobility variations, and compatible with a CMOS technology dedicated to digital low-power circuits.

CMOS analog integrated circuits based on weak inversion operations

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. >

/pdf/noise-as-a-diagnostic-tool-for-quality-and-reliability-of-3vrnkdk5vf.pdf

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

A characteristic interface trap was observed in a hole trapping experiment when electrons were captured by trapped holes injected by an avalanche in the silicon. The observations could be explained by the generation of new electronic states through relaxation of strained bonds which were proposed to be the origin of hole traps. The result is either a weak bond in the network or two dangling bonds with no net charge. The weak bond or dangling bonds give rise to neutral traps in the bulk and interface traps at the interface of the oxide. The presence of interface traps for such defects at the interface is predicted by theoretical calculations.

Interface trap generation in silicon dioxide when electrons are captured by trapped holes

By a careful process SiSiO2-interfaces can be made with a low oxide charge Qox and with a low surface states density Nss. For dry oxides on (100) Nss-values as low as a few 109 cm−2 eV−1 are found on samples with an oxide charge density of 3·0 × 1010 cm−2. Only the Nicollian-Goetzberger conductance method is proved to give reasonable results on these structures. The quasi-static low frequency C-V-technique is in good agreement with the conductance technique for samples with Nss-values higher than 1·0 × 1010 cm−2 eV−1. The spatial fluctuation of surface potential, mainly caused by oxide charge fluctuations, is an important parameter when studying the high or low frequency C-V-characteristics. Some irregularities in the experimental Nss-φs-curves are explained.

Measurement of low densities of surface states at the SiSiO2-interface

The most important characteristics of the MOS transistor operating in weak inversion are discussed. When the drain voltage is greater than a few kT/q it is demonstrated that the drain current can be written as the product of the geometrical factor W/L , the minority carrier diffusion constant, and the inversion charge at the source. In the classical theory, the slope of the In I D versus V G curve is only influenced by the capture of minority carriers by surface states. It is demonstrated that the N ss values obtained from these current measurements are in disagreement with the values found by independent surface states measuring techniques.

Inadequacy of the classical theory of the MOS transistor operating in weak inversion

The drain current I D versus gate voltage V G of a MOST operating in weak inversion, and the influence of surface potential fluctuations on this characteristic have been studied before [1] The purpose of this paper is to derive an expression of the drain current I D versus the drain voltage V D for long channel devices. It is demonstrated that the surface potential fluctuations don't affect the slope of the I D -V D curve whereas the density N SS of surface states strongly influences the slope for small drain voltages. This yields a simple and useful technique to determine N SS on M.O.S. transistors.

Theory of the M. O. S. transistor in weak inversion - new method to determine the number of surface states

The classical theory of the MOS transistor operating in weak inversion, attributes the slope of the In I D versus V G curve to the capture of minority carriers by surface states. The discrepancy between the N ss values given by this theory and by independentt surface states measuring techniques is explained by the influence of surface potential fluctuations. These fluctuations are caused by the statistical distribution of the oxide charge.

The influence of surface potential fluctuations on the operation of the MOS transistor in weak inversion

Experimental values of the standard deviation σs of fluctuations of surface potential are discussed. A comparison is made between the experiments and the theory of Nicollian and Goetzberger recently generalized by the mathematical model of Brews. We conclude that Brews's model adequately represents most of the data, provided both positive and negative fixed charges are assumed to be present simultaneously in our devices.

G. Broux

Papers

Measurement of low densities of surface states at the SiSiO2-interface

Inadequacy of the classical theory of the MOS transistor operating in weak inversion

Theory of the M. O. S. transistor in weak inversion - new method to determine the number of surface states

The influence of surface potential fluctuations on the operation of the MOS transistor in weak inversion

Discussion of the surface‐potential fluctuations caused by oxide‐charge fluctuations