Normalized Drain Current Spectral Density Research Articles

Analysis of low-frequency noise in the amorphous indium zinc oxide thin film transistors

Properties of low-frequency noise in the amorphous InZnO thin film transistors have been investigated in this paper. Due to the emission and trapping processes of carriers between trapping states located in the interface between the IZO layer and gate insulator, the drain current spectral density shows a 1/fγ(γ =0.75) low-frequency noise behavior. In addition, the normalized drain current spectral density is decreased linearly with the increase of gate length and width. This property confirms that the low-frequency noise in the IZO TFTs is due to the flicker noise in the channel, the contribution of source/drain contact and parasitic resistances can be ignored. Finally, based on the number fluctuation theory and the mobility fluctuation theory, the γ and average Hooge's parameters have been extracted to estimate the quality of devices and materials.

Determination of interface state distribution in polysilicon thin film transistors from low-frequency noise measurements: Application to analysis of electrical properties

Low-frequency noise is studied in n-channel furnace solid phase crystallized and in laser solid phase crystallized (LSPC) polysilicon TFTs biased from weak to strong inversion. Noise analysis is supported by theoretical results of the additivity of generation-recombination spectra to explain trapping/detrapping processes following the tunneling theory of carriers into the gate oxide. In the weak inversion region the normalized drain current spectral density is inversely proportional to the number of trapped carriers. The corresponding distribution of the trap states [density of states (DOS)] in the polysilicon band gap at the interface is determined. In the strong inversion region the normalized drain current spectral density is proportional to the effective oxide trap number/(freecarriernumber)2 ratio. For LSPC devices the DOS is one decade lower and the corresponding effective oxide trap number is one decade higher. The results are attributed to the effects of the laser annealing on the active layer crystal quality. Quantitative dependence of DOS with static conduction parameters in relation with interface quality is then analyzed.

ANALYSIS OF LOW FREQUENCY DRAIN CURRENT NOISE IN AlGaN/GaN HEMTS ON Si SUBSTRATE

This paper deals with the analysis of the low frequency drain current noise in gallium nitride FET on silicon substrate. The drain current noise is compared for devices with gate length of 1.5μm and 3.5μm. We discuss two types of noise mechanisms both used as a diagnostic tool: generation-recombination noise and 1/f noise. Measurements in saturation regime have revealed a g-r noise mechanism correlated with the activation of discrete traps. The analysis of the normalized drain current spectral density vs. the normalized gate voltage Vgn=(Vg-Vt)/|Vt| has been studied. In particular, we have pointed out that the evolution of the 1/f noise level strongly depends on the evolution of the gate leakage current. On the basis of the 1/f normalized noise, i.e. the αH/N parameter, GaN HEMT on silicon have demonstrated as low LF noise as GaAs based transistors.

Impact of the high vertical electric field on low-frequency noise in thin-gate oxide MOSFETs

In this paper, quantum effects induced by the high vertical electric field, i.e., inversion layer quantization and gate current tunneling, are taken into account to model the low-frequency noise behavior of 0.13 /spl mu/m technology node thin gate oxide MOSFETs. First, we show that the modifications induced by inversion layer quantization in the band structure and spatial distribution of the inversion layer carriers must be taken into account when extracting an effective density of traps from 1/f noise measurements. The ultrathin gate oxide and the high substrate doping of scaled MOSFETs create a strong electrical field in the inversion layer, which causes the surface conduction (n-) or valence (p-MOSFET) band to split into discrete energy levels. The first allowed state resides then above (below) the conduction (valence) band level in the bulk, giving rise to a band gap widening and in addition the spatially localized charge centroid is at a finite distance from the SiO/sub 2//Si interface. The impact on both dc and noise parameters of these quantum effects have been numerically calculated and compared to experimental results. The main conclusions coming out of this study is that if the inversion layer quantization is neglected, inaccurate oxide trap densities will be derived from the input-referred voltage noise spectral density S/sub VC/:. A similar conclusion will hold for the extraction of the scattering coefficient derived in the frame of a correlated number fluctuations model or for the effective Hooge parameter, derived from the normalized drain current spectral density S/sub ID//I/sub D//sup 2/. Finally, a particular gate tunneling mechanism namely Electron Valence Band (EVB) tunneling is shown to modify the noise behavior of thin gate oxide devices in terms of a self-biasing body effect.

Hot-carrier-induced modifications to the noise performance of polycrystalline silicon thin-film transistors

Modifications of noise performances induced by hot-carrier degradation in polycrystalline silicon thin-film transistors, made by excimer laser crystallization, are presented. In particular, the normalized drain current spectral density of these devices shows an evident 1/f behavior, and as the device characteristics are degraded by prolonged bias stressing, the noise performances worsen. Hot-carrier degradation results in the formation of both interface states, that have been evaluated through the analysis of the sheet conductance, as well as of oxide traps near the insulator/semiconductor interface, as evidenced by the 1/f noise measurements. A strong correlation between interface state and oxide trap densities has been found, suggesting a common origin for the generation mechanism of the two types of defects.

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.