C. Ciofi

Comparative study of drain and gate low-frequency noise in nMOSFETs with hafnium-based gate dielectrics

In this paper, complementary measurements of the drain and the gate low-frequency noise are used as a powerful probe for sensing the hafnium-related defects in nMOSFETs with high-k gate stacks and polysilicon gate electrode. Drain noise measurements indicate that for low hafnium content (23%) and thin high-k thickness (2nm), the defect density at the substrate/dielectrics interface is similar to the case of conventional SiO/sub 2/. Gate-noise measurements suggest that the defect density in the bulk of the high-k gate stacks and at the gate/dielectrics interface is strongly degraded by the hafnium content.

Noise and fluctuations in submicrometric Al-Si interconnect lines

Low-frequency noise (LFN) in excess has been observed in the past in metal lines subjected to high current densities. Different types of noise and fluctuations have been identified and are briefly summarized in the first part of this paper. Then, some new experimental results, obtained with Al/Si submicrometric lines, are presented. In particular, it has been possible to identify and separate the contribution of three different sources of noise and, from the analysis of the noise component directly related to electromigration, an activation energy of about 1.4 eV has been obtained. This value clearly indicates that in these samples bulk electromigration is the main cause of the noise generation. Moreover, the consistency between the measured level of noise and the value of some physical quantities, contained in a model previously proposed, has been verified. In the final section of the paper, old and new results are utilized in an attempt to provide a satisfactory answer to some of the most important unsolved questions in this field.

Electrical Characterization and Hydrogen Peroxide Sensing Properties of Gold/Nafion:Polypyrrole/MWCNTs Electrochemical Devices

Electrochemical devices using as substrates copier grade transparency sheets are developed by using ion conducting Nafion: polypyrrole mixtures, deposited between gold bottom electrodes and upper electrodes based on Multi Walled Carbon Nanotubes (MWCNTs). The electrical properties of the Nafion:polypyrrole blends and of the gold/Nafion:polypyrrole/MWCNTs devices are investigated under dry conditions and in deionized water by means of frequency dependent impedance measurements and time domain electrical characterization. According to current-voltage measurements carried out in deionized water, the steady state current forms cycles characterized by redox peaks, the intensity and position of which reversibly change in response to H2O2, with a lower detection limit in the micromolar range. The sensitivity that is obtained is comparable with that of other electrochemical sensors that however, unlike our devices, require supporting electrolytes.

Low-frequency (1/f) noise behavior of locally stressed HfO/sub 2//TiN gate-stack pMOSFETs

The low-frequency noise behavior of locally strained pMOSFETs with a 7HfO/sub 2//TiN gate stack is reported. Different ways of compressive-strain engineering have been compared: a Si/sub 3/N/sub 4/ cap layer, SiGe source/drain (S/D) regions, or the combination of both. It is shown that the use of a cap layer does not degrade the 1/f noise magnitude, while an increase of this parameter is found for SiGe S/D devices. This increase is ascribed to the creation of additional traps in the high-k oxide by the SiGe S/D processing. The effect appears to be independent of the germanium content in the range studied (15%-25%). Another conclusion is that no direct correlation has been observed here between the applied stress and the noise magnitude.

Ultra low noise, PC-based measurement system for the characterization of the metallizations of integrated circuits

Low frequency noise measurements have been successfully used in research laboratories for the characterization of electromigration in interconnection lines of integrated circuits. In this paper an ultra-low noise system capable of performing such measurements contemporaneously on a statistically significant number of samples is described. The system, designed with the aim to make advantageous the utilization of the technique also in industrial environment, is controlled by a personal computer and makes available up to 255 independent input channels for noise measurements. A purposely designed ultra-low noise preamplifier and the use of an optical link between the PC and the low noise section, has allowed to obtain a total background noise which is some orders of magnitude lower than that of preexistent instrumentation.

GALS Networks on Chip: A New Solution for Asynchronous Delay-Insensitive Links

In this paper a cost effective solution for asynchronous delay-insensitive on-chip communication is proposed. Our solution is based on the Berger coding scheme and allows to obtain a very low wire overhead. For instance, the results of our evaluation show that a 64-bit link can be built paying a wire overhead of 10% and 30 equivalent two-input gates per wire. As a general rule, when the number of bits to be transmitted increases, the wire overhead decreases and the gate overhead remains almost the same

How to enlarge the bandwidth without increasing the noise in OP-AMP-based transimpedance amplifier

Increasing the bandwidth without degrading the noise performance represents the main challenge in the design of transimpedance amplifiers. This paper presents a novel circuit topology for a transimpedance amplifier that allows obtaining an improved tradeoff between equivalent input noise and bandwidth with respect to the conventional approach. The effectiveness of the new topology has been demonstrated by designing and testing a prototype of a transimpedance amplifier based on the proposed topology

An ultralow noise preamplifier for low frequency noise measurements

Low frequency noise measurements are among the most sensitive tools for the investigation of the quality and of the reliability of semiconductor devices. The sensitivity that can be obtained depends on the background noise of the low noise preamplifier coupled to the device under test (DUT) that, at very low frequencies, is dominated by flicker noise. The low frequency noise produced by the DUT, on the other end, is very often the most interesting signal to be detected and analyzed. In this work we propose a very simple topology for the realization of a general purpose low noise preamplifier whose noise performances, at very low frequencies (below 10 Hz), are significantly better than those that can be obtained by the most popular commercial instrumentation. Indeed, a gain of 80 dB with a pass band extending from a few tens of mHz up to a few kHz with an equivalent input voltage noise as low as 14 nV/square root(Hz) (100 mHz), 1.4 nV/square root(Hz) (1 Hz), 1.0 nV/square root(Hz) (10 Hz), and 0.8 nV/square root(Hz) (1 kHz) are consistently obtained by using quite standard electronic components and with no need for trimming and/or calibration steps. Moreover, the junction field-effect transistor input stage of the amplifier is characterized by an equivalent input current noise below 4 fA/square root(Hz) in the entire bandwidth, resulting in negligible background noise degradation for DUT impedances in excess of 100 kohms.

DEDICATED INSTRUMENTATION FOR HIGH SENSITIVITY, LOW FREQUENCY NOISE MEASUREMENT SYSTEMS

Low Frequency Noise Measurements (LFNM) can be used as very sensitive tool for the characterization o f the quality and the reliability of electron devices. However, especially in those cases in which the frequency range of interest extends below 1 Hz, instrumentation with an acceptable low level of background noise is not e asily found on the market. In fact, at very low frequencies, the flicker noise introduced by the electronic components which make up the instrumentation becomes predominant and several interesting phenomena which could be detected by means of LFNM may result completely hidden in the background noise. This consideration is not limited to the case of input preamplifiers but does extend to any piece of instrumentation that contributes to the LFNM systems, and in particular to the power supplies used for biasing the Device Under Test. During the last few years, our research groups have been strongly involved in the design of very low noise instrumentation for application in the field of LFNM. In this work we report the main results which we have ob tained together w ith a discussion of the d esign guidelines that have a llowed us, in a few cases, to reach noise levels not to be equalled by any instrumentation available on the market.

A new method for high-sensitivity noise measurements

A new method for high-sensitivity noise measurement, based on the elaboration in the time domain of the signals coming from two identical amplifiers, is presented in this paper. The most important advantage of this method, which in most cases allows obtaining an equivalent background noise 30 dB below that of the amplifiers which are used in the measurement chain, lies in its simplicity and in the fact that it does not depend on the method used for the estimation of the noise spectra.