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International audience; Silicon On Insulator-based devices seem to be the best candidates for the ultimate integration of Integrated Circuits on silicon. An overview of the main SOI materials and advantages of SOI for the Nanoelectronics of the next decades is presented. Nanoscale CMOS, emerging and beyond-CMOS nanodevices, based on innovative concepts, technologies and device architectures, are addressed. The flexibility of the SOI structure and the possibility to realize new architectures allow to obtain optimum electrical properties for both low power and high performance circuits. These transistors are also very interesting for high frequency and memory applications. The performance and physical mechanisms are investigated in single- and multi-gate/multi-channel inversion- or accumulation-mode thin film MOSFETs, realized on various semiconductors (Si, Ge, III-V, CNT), down to sub-10 nm gate length. The impact of strains in the channel and of high k materials is discussed. The interest of advanced emerging and beyond-CMOS nanodevices on SOI for long term applications, based on nanowires or small slope switch structures is also highlighted. The influence of key device parameters on electrical and thermal floating body effects, short channel and quantum effects, noise, variability, as well as on hot carrier effects, versus temperature, is shown for various device architectures.

Excess current, induced by impact ionization (kink effect) has been investigated in short-channel polysilicon thin-film transistors (TFTs). We have shown, both experimentally and by using two-dimensional (2-D) numerical simulations, that the output characteristics are substantially degraded by the kink effect as the channel length is reduced. In particular, we have shown that the excess current, triggered by the impact ionization and enhanced by the parasitic bipolar transistor action, scales nearly as L-2, thus making very difficult the downscaling of polysilicon TFTs. Such L dependence has been clarified through a detailed analysis of the current components obtained from 2-D numerical simulations. The analysis demonstrates that there are fundamental issues with the output characteristics, and it appears that the introduction of appropriate drain field relief structures will be necessary for the fabrication of short-channel polysilicon TFTs with high output impedance.

Kink effect can spoil the otherwise excellent low-noise performance of InAs/AlSb HEMTs. It has its origin in the pile up of holes (generated by impact ionization) taking place mainly at the drain side of the buffer, which leads to a reduction of the gate-induced channel depletion and results in a drain current enhancement. Our results indicate that the generation of holes by impact ionization and their further recombination lead to fluctuations in the charge of the hole pile up, which provoke an important increase of the drain-current noise, even when the kink effect is hardly perceptible in the output characteristics., ROOTHz (FP7-243845)

This paper presents a method of eliminating corner effects in triple-gate bulk FinFETs. The parasitic device in FinFET's corners can be turned off by increasing body doping in corner regions by corner implantation. Corner implantation described in this work does not require additional masks, rotation or tilt. This method is investigated in idealized (with rectangular cross-section of the fin) and realistic (with rounded top corners of the fin) triple-gate bulk FinFETs and has shown considerable improvements: kink effect in transfer characteristics is completely eliminated, threshold voltage increased by up to 0.43 V, subthreshold swing and drain-induced barrier-lowering decreased to values under 95 mV/dec and 16 mV/V, respectively. Optimization is performed on the realistic rounded-corner FinFET structure to find the proper body doping and corner implantation peak values for acceptable threshold voltage and on-state current.

A semiclassical 2D ensemble Monte Carlo simulator is used to perform a physical microscopic analysis of kink effect in InAs/AlSb High Electron Mobility Transistors (HEMTs). Due to the small bandgap of InAs, these devices are very susceptible to suffer impact ionization processes, with the subsequent hole transport through the structure, both implicated in the kink effect. The results indicate that, for high enough VDS, holes generated by impact ionization tend to pile up in the buffer (at the gate-drain side) due to the valence-band energy barrier between the buffer and the channel. Due to this accumulation of positive charge the channel is further opened and ID increases, leading to the kink effect in the I-V characteristics and even to the device breakdown. The microscopic understanding of this phenomenon provides useful information for a design optimization of kink-effect-free InAs HEMTs., ROOTHz (FP7-243845)

This paper presents a method of suppressing kink effects which originate in the corners of triple-gate bulk FinFETs. We propose corner implantation to turn off the parasitic corner device which has lower threshold voltage than the bulk device. This method is investigated in triple-gate bulk FinFETs by 3D numerical simulations. Threshold voltage shift of 0.434 V with a decrease in on-state current of only 23% is achieved, while the kink effect in devices' current-voltage characteristics is completely eliminated. Corner implantation improves devices' immunity to short-channel effects.

Here, a new approach for calculating the triggering drain bias at the onset of the kink effect, kink voltage, V kink , for PD SOI NMOS devices utilizing electron drift properties in the channel is given. This approach directly relates electron mobility in the channel to the kink effect and enables one to determine kink voltage knowing the device technology. It also gives the possibility for calculating mobility from the kink voltage. Theory is compared to the previously published experimental results and based on this match, the behavior of the kink voltage for PD SOI NMOS components for various technology parameters is predicted. Explanation for the appearance of the kink in the volt regime below the band gap of silicon is also given. From this consideration, design rules for PD SOI NMOS devices are derived in order to soothe the kink effect.

Recently, we proposed asymmetric fingered polysilicon thin film transistors, where the transistor channel region is split into two zones with different lengths separated by a floating n+ region, which allows an effective reduction of the kink effect. In this work, we analysed the experimental electrical characteristics by using numerical simulations for a specific channel configuration and then we studied the effects of prolonged bias stress on these devices and conventional non self-aligned thin film transistors. We found that asymmetric fingered transistors are characterized by a substantial reduction of the transconductance degradation induced by hot carrier effect, if compared to conventional thin film transistors. By modeling the device with two transistor in series, we could explain the reduced effects of hot carrier-induced degradation.

Short channel effects have been investigated in n-channel polysilicon thin film transistors. Transconductance degradation has been observed when reducing the channel length L and this effect has been explained with the presence of a parasitic resistance related to residual implant damage. Threshold voltage slighlty decreases for channel length around L=1 Am and simulations confirm that the roll-off of the threshold voltage is expected for Lb1 Am. In the output characteristics a stronger kink effect has been observed at short L which, from a comprehensive analysis of the current components, can be attributed to an enhanced parasitic bipolar transistor action.

The physical origin of the kink and its dynamics are investigated in AlGaAs/GaAs doped-channel heterostructure field-effect transistors (HFETs) both through measurements and two-dimensional (2D) device simulations. The kink is shown to arise from the interaction of surface deep acceptors with impact-ionization-generated holes, the latter partially discharging the deep levels and therefore leading to conductive-channel widening and to drain-current increase. Under pulsed operation, kink dynamics is governed by hole emission and capture phenomena, prevailing at low and high drain-source voltages, respectively.

Experimental results obtained in depletion AlGaAs/GaAs HEMTs showing the presence of a remarkable increase of transconductance with frequency associated with a kink effect in the current-voltage curves is reported. Transconductance increase occurs at high frequencies with increasing drain source voltage. All these effects are ascribed to field enhanced electron emission from deep levels present in the AlGaAs layer.

The channel noise current spectral density of n-type enhancement SOS-MOS transistors versus the drain-source voltage VDs exhibits a peak not only for a floating bulk electrode but also when it is grounded. In the latter case, this peak appears at higher values of VDs. This suggests the kink effect which is now masked on the D.C. characteristics I D- V DS by a stronger multiplication. Theoretically we characterize this effect by means of an equivalent circuitry (electrical and noise) where the bulk electrode and the multiplication current generator associated with the drain space charge region are taken into account.

We perform a physical analysis of the kink effect in InAs/AlSb high electron mobility transistors by means of a semiclassical 2D ensemble Monte Carlo simulator. Due to the small bandgap of InAs, InAs/AlSb high electron mobility transistors are very susceptible to suffer from impact ionization processes, with the subsequent hole transport through the structure, both implicated in the kink effect. When the drain-to-source voltage VDS is high enough for the onset of impact ionization, holes generated tend to pile up at the gate-drain side of the buffer. This occurs due to the valence-band energy barrier between the buffer and the channel. Because of this accumulation of positive charge, the channel is further opened and the drain current ID increases, leading to the kink effect in the I–V characteristics., ROOTHz (FP7-243845)