Carrier Number Fluctuation Model Research Articles

Low-frequency noise analysis of Si/SiGe channel pMOSFETs

Low-frequency noise characteristics of 0.1 μm Si 1− x Ge x channel pMOSFETs were studied by numerical simulations in the framework of the carrier number fluctuation model as well as the correlated fluctuation in the mobility model. Simulation results predict that Si 1− x Ge x channel pMOSFETs could offer improved low-frequency noise performance as compared to the conventional bulk Si devices. This improvement in Si 1− x Ge x channel pMOSFETs could be attributed to less effective oxide trap density for noise generation due to the increasing separation of quasi-Fermi level and valence band edge at Si–SiO 2 interface by Ge-induced band offset.

Origin of low-frequency noise in polycrystalline silicon thin-film transistors

Low-frequency drain current fluctuation noise was measured in a series of polycrystalline silicon thin-film transistors (polysilicon TFTs), characterized by an average grain size Lg and in-grain defect density Din. In one type of polysilicon TFT, Din is low (about 5×108 cm−2) and Lg varies from about 67 to 145 nm. In another type of polysilicon TFT, Lg remains constant (about 2.5 μm) and Din varies from about 5×1012 to 5×1010 cm−2. It is demonstrated that the noise originates from fluctuations of carriers due to carrier capture/release processes: (a) in traps located near the polysilicon/SiO2 interface and (b) in traps located at the grain boundaries. The polysilicon/SiO2 interface is distinguished from that of the crystalline silicon/SiO2 by comprising the in-grain traps, in addition to the oxide traps. The proposed carrier number fluctuation model, sufficient to explain noise in polysilicon TFTs, is closely related to the structural parameters Lg and Din of the polysilicon layer.

Flicker noise in gate overlapped polycrystalline silicon thin-film transistors

A study of the noise performance of gate overlapped polycrystalline silicon thin-film transistors (TFTs) is presented. Low-frequency noise measurements were carried out on n- and p-type samples fabricated by excimer laser crystallization. It is shown that the carrier number fluctuation model applies not only to n-type but also to p-type devices. The density of oxide traps was extracted from the noise measurements and was of the order of 10/sup 18/-10/sup 19/ eV/sup -1/ cm/sup -3/.

Avalanche-induced excess noise in polycrystalline silicon thin-film transistors

The low-frequency noise behavior of polycrystalline silicon thin-film transistors, operated in the avalanche multiplication region of the output characteristics, is investigated. The avalanche-induced current noise, originating from generation-recombination processes in the depletion region of the drain junction, can be described by the carrier number fluctuation model. Using a model for the excess noise in silicon-on-insulator metal-oxide-semiconductor field-effect transistors operated in the kink regime, an analytical expression for the avalanche-induced current noise is derived taking into account an exponential distribution of the gap states. Comparison of the experimental noise data with the theoretical model indicates that, in addition to the avalanche multiplication, hot-carrier effects contribute significantly to the current increase in the avalanche regime.

Low frequency noise and random telegraph signals in 0.35 μm silicon CMOS devices

A detailed study of the low frequency noise in Si MOS devices from a 0.35 μm CMOS technology is presented. The normalized drain current noise WLS I d/I d 2 has been systematically investigated at a fixed frequency and constant normalized drain current. In large area devices (>5–7 μm 2), the noise is typically 1/f-like, whereas, in small area devices (≤1 μm 2), the noise stems from the contribution of one or several RTS components. In large area devices, the 1/f noise can easily be interpreted by a classical carrier number fluctuation model. A multi-RTS component scheme has to be employed in the case of small area devices.

Improved Analysis of Low Frequency Noise in Field-Effect MOS Transistors

An improved analysis of low frequency trapping noise in a MOS device is proposed. This analysis takes into account the supplementary fluctuations of the mobility induced by those of the interface charge. It enables an adequate description of the gate voltage dependence of the input equivalent gate voltage noise to be obtained in various actual situations. The outputs given by the Hooge mobility fluctuation model are also presented and discussed with respect to those obtained by the carrier number fluctuation model. In particular, the impact of the channel length or channel width, and the model type on the input gate voltage and drain current noise characteristics is studied and compared to typical experimental data. Finally, a procedure for the diagnosis of the low frequency noise sources in a MOS transistor is proposed. Une analyse appronfodie du bruit basse fréquence dans le transistor MOS est proposée. Cette analyse permet d'obtenir une description adéquate de la dépendance en tension de grille de la densité spectrale en entrée valable pour differentes situations. Les résultats que procure le modèle de fluctuation de mobilité de Hooge sont également présentés et discutés par rapport à ceux du modèle de fluctuation du nombre de porteur. L'influence de la longueur ou de la largeur de canal, et du type de modèle sur les caractéristiques de bruit en entrée et en courant est étudiée et comparée à des résultats expérimentaux typiques. Enfin, une procédure de diagnostic des sources de bruit basse fréquence d'un transistor MOS est proposée.

A study of flicker noise in MOS transistors operated at room and liquid helium temperatures

A study of flicker noise in MOS transistors operated in the linear and non linear regions at room and liquid helium temperatures is proposed. Besides, a theoretical analysis of the drain current noise characteristics is developed in the framework of the mobility fluctuation model as well as of the carrier number fluctuation model. It is shown experimentally that a close correlation between the drain current spectral density and the transconductance squared dependencies with gate voltage (or drain current) and drain voltage is observed in our devices both at room and liquid helium temperatures. Therefore, it is concluded that the carrier number fluctuation model is not only applicable to MOS devices operated at room temperature but also at liquid helium temperature in ohmic and non ohmic regimes. In addition, peculiarities of the drain current noise related to the appearance of a kink effect at liquid helium temperature in the saturation current characteristics are also discussed.

Flicker noise in MOS transistors operated at room and liquid helium temperatures

Flicker noise in MOS transistors operated in the linear and non linear regions is studied at room and liquid helium temperatures. A theoretical analysis of the drain current noise is conducted within the mobility and carrier number fluctuation models. A close correlation between the drain current noise and the transconductance squared dependencies with gate and drain voltages is found experimentally both at room and liquid helium temperatures. It is concluded that the carrier number fluctuation model is suitable for the interpretation of our data at room and liquid helium temperatures in ohmic and non ohmic regimes. Peculiarities of the drain current noise in the kink effect region are also discussed.

1/f noise interpretation of the effect of gate oxide nitridation and reoxidation in dielectric traps

Nitrided gate oxides and reoxidized nitrided gate oxides exhibit increased reliability under electrical and radiation stress and improved dopant barrier properties. However, the process of nitridation introduces oxide charges and traps. In this paper, 1/f noise measurements in MOSFETs and the carrier number fluctuation (McWhorter) model are used to extract the dielectric trap density in space and energy near the conduction and valence band edges of silicon. It is found that reoxidation can be used to reduce nitridation induced interface traps to levels found in oxides.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Flicker noise in metal-oxide-semiconductor transistors from liquid helium to room temperature

A study of the normalized drain current spectral density SId/I2d as a function of drain current has been carried out on n channel metal-oxide-semiconductor transistors at very low (4 K), low (77 K), and room temperatures. It is demonstrated experimentally that the drain current dependence of SId/I2d is strongly correlated to that of the transconductance-current ratio squared (gm/Id)2. This result clearly shows that the carrier-number fluctuation model is applicable not only at room temperature but also at low and very low temperatures. Therefore, it is proved that the mobility fluctuation model is inadequate for the interpretation of our flicker noise data.

A 1/f noise technique to extract the oxide trap density near the conduction band edge of silicon

The use of 1/f noise measurements in n-channel MOSFETs to extract the oxide trap density in space and energy near and above the conduction band edge of silicon is investigated. The conventional carrier number fluctuation model of 1/f noise that attributes 1/f noise to the trapping and detrapping of inversion layer carriers by oxide traps is reviewed. It is shown that oxide band bending in devices with a nonuniform oxide trap distribution leads to a gate voltage dependence in the magnitude and exponent gamma (V/sub gs/) of the 1/f/sup gamma / noise spectrum. An extension of the 1/f noise number fluctuation model that includes both carrier number fluctuations and correlated mobility fluctuations is then studied. Correlated mobility fluctuations are attributed to the coulombic scattering of inversion layer carriers by the fluctuating trapped charge. It is shown that the correlated fluctuation model predicts a gate voltage dependence in the magnitude and exponent gamma of the 1/f/sup gamma / noise spectrum even for a uniform oxide trap distribution. By analyzing the 1/f noise magnitude and exponent data in n-channel MOSFETs having various oxide thicknesses, both models are used to extract the oxide trap density over a wide range of space and energy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Carrier number fluctuation model of 1/f noise in a semiconductor device

From Suh's total carrier number fluctuation model of 1/f noise generation mechanism, a model that seems to be able to describe the behavior of 1/f noise in various semiconductor devices is presented. The model is formulated in a simple logical procedure without any ambiguous or obscure assumptions and expresses the voltage fluctuation spectral density and the current fluctuation spectral density in terms of the short-circuited channel current fluctuation spectral density. The obtained expressions seem to fit in various experimental results.