A. Luque Rodríguez

Effects of Gate Oxide and Junction Nonuniformity on the DC and Low-Frequency Noise Performance of Four-Gate Transistors

The effects of imperfections on the electrical performance of four-gate field-effect transistors (G4-FETs) have been studied. Variations in the oxide trap distribution and in the metallurgical boundary of the junction gates impact the low-frequency noise and the static (dc) performance of the G4-FET. By modeling, iterative characterization of published experimental data, and extensive simulations, it is shown that these effects originate from trap distributions in the gate oxides and in the depleted regions of the semiconductor channel. The proposed models are based on established models, such as the unified flicker noise model, with modifications and improvements that extend to trap distributions with gradients, variable frequency slope α of 1/fα noise spectra, and are applicable for gate stacks with high-k dielectrics, such as HfO2 and HfSiON. The characterization procedures allowed for identifying optimum profiles of the metallurgical boundary of junction gates, which simultaneously improve the dc and noise performances of the G4-FET, such as subthreshold swing and low noise. The results indicate the importance of the precise control of depletion and conduction in the channels of multiple-gate FETs.

High Doping Density/High Electric Field, Stress and Heterojunction Effects on the Characteristics of CMOS Compatible p-n Junctions

This paper critically reviews the different mechanisms impacting the current-voltage and capacitance voltage characteristics of complementary metal oxide semiconductor (CMOS) compatible p-n junctions. Special attention is given to the influence of high doping density/high electric fields, mechanical stress and the presence of a hetero-junction either at the junction or in the depletion region. The basic mechanisms reported in the literature are checked for their validity for state-of-the-art structures and processing techniques. Critical issues are pointed out and illustrated for advanced CMOS compatible hetero-junctions, where high-field effects, like trap-assisted tunneling (TAT) and band-to-band-tunneling (BTBT) play a prominent role. The presence of an isotype hetero-junction gives rise to frequency dispersion in the depletion layer capacitance, which becomes more pronounced in combination with grown-in or processing-induced defects at the hetero-interface. Finally, the challenges and opportunities for future devices are addressed.

Insights in low frequency noise of advanced and high-mobility channel transistors

An overview is given on the impact of the implementation of high-mobility channel materials and novel device architectures on the low-frequency (LF) noise behavior of 22 nm and below CMOS transistors. It will be shown that a similar 1/f noise power spectral density (PSD) can be achieved for SiGe-channel planar and bulk FinFET devices, whereby mobility fluctuations are dominant. At the same time, it is demonstrated that processing-induced Generation-Recombination (GR) noise can yield a strong device-to-device variability in the PSD. This is illustrated for both bulk FinFETs and thin-film ultra-thin buried oxide (UTBOX) Silicon-On-Insulator (SOI) MOSFETs. A model is presented for the LF noise in narrow, fully-depleted (FD) device structures, allowing the extraction of the oxide trap density profiles and silicon film GR center parameters. This model explains the occurrence of Lorentzian GR noise with gate voltage dependent parameters in planar or vertical FD devices and at the same time points out a new source of noise variability, which becomes important for future bulk FinFET technology nodes.

Study of 1/f and generation-recombination noise in four gate transistors

In this work, we study different noise sources that are present in four-gate field-effect-transistors (G4-FET). We present a model for the generation-recombination (g-r) noise due to traps located in the depletion regions and in the bulk, and for the 1/f noise due to traps in the top and bottom oxides. One of the main advantages of this structure is that the position and size of the conduction channel can be controlled by the application of adequate voltages to its gates (front and back MOS gates and two lateral JFET gates). However, the channel is also prone to be affected by the noise sources distributed throughout the device. Thus, the current noise power spectral density is a combination of all these noise sources. Experimental data showing such a combination are interpreted with our model.

Modeling impact of electric field and strain on the leakage of embedded SiGe source/drain junctions

A study of the leakage current in strained p+n Si1−xGex/Si hetero-junctions is presented. The reduction in the band gap, induced by stress forces, and the doping level at the hetero-interface, due to the use of halo implantations, are varied by changing the recess depth. A comparison between simulation results and experimental data is presented to analyze the validity of the models used in this work.

Effect of traps in the performance of Four Gate Transistors

In this work, a study of traps located in the bulk and the Si-SiO2 interfaces of four gate transistors (G4-FETs), and their effect in the performance of these transistors, is presented. Different kinds of low frequency noise spectra measured at different voltages applied to the gates show that traps in the bulk and traps at the interfaces are the origin of such different spectra. We propose a model to evaluate low frequency noise produced in the bulk and surfaces of the device. This model is incorporated in a 2D simulator that confirms the experimental trends. It also allows us to separate the contribution of both sources and study the effects of different kinds of bulk traps on the low frequency noise.

Photon absorption in regimented quantum dot arrays

A study of the intraband absorption coefficient in cuboid InAs quantum dot periodic nanostructures embedded in GaAs is presented. The miniband structure of electron states in the conduction band is related to the shape of the quantum dots. The effect of strain is also taken into account in the simulations through a previous 8×8 k·p calculation. We analyze the influence on the absorption coefficient on the miniband structure of the systems.

DC and low-frequency noise optimization of four-gate transistors

The effects of different parameters on the DC and low-frequency noise performance of four gate field effect transistors (G4-FET) are studied. Experimental data of the drain current and the current noise power spectral density (PSD) are compared with simulation results. The comparisons show that the drain current and its associated noise are very sensitive to the doping profile of the pn junctions that constitute the lateral gates of the device. The presence of recombination centers also modifies the performance of the device. These centers can degrade the excellent subthreshold slope that the G4-FET transistor exhibits. At the same time, the generation-recombination (g-r) noise produced by deep traps in the depletion regions of the device can be reduced by the presence of these recombination centers. In this work, we propose a procedure to determine an optimal dopant profile of the lateral pn junctions of the device that minimizes the subthreshold slope and the low frequency noise and maximizes the transconductance.

Ge content and recess depth dependence of the band-to-band tunneling current in Si 1-x Ge x /Si hetero-junctions

In this paper, a study of the leakage current through strained p+ n Si1-xGex/Si hetero-junctions is presented. The reduction in the band gap, induced by stress forces, and the doping level at the hetero-interface, due to the use of halo implantations, are varied by changing the Ge content and the recess depth. A comparison between simulation results and experimental data is presented to analyze the suitability of the models used in this work. An optimization study to decrease the band-to-band tunneling component in the leakage current as a function of these two technological parameters is presented.

Optoelectronic properties in InAs/GaAs quantum dots arrays systems

A study of the physics of electronic states in cubic InAs quantum dot periodic nanostructures embedded in GaAs is presented. The miniband structure of electron states in the conduction band is related to the size and density of the quantum dots. The effect of strain is also taken into account in the simulations. The photon-electron absorption coefficient is obtained for different quantum dot configurations and different light polarization as well.