Thierry Ouisse

Ultimately thin double-gate SOI MOSFETs

The operation of 1-3 nm thick SOI MOSFETs, in double-gate (DG) mode and single-gate (SG) mode (for either front or back channel), is systematically analyzed. Strong interface coupling and threshold voltage variation, a large influence of substrate depletion underneath the buried oxide, the absence of drain current transients, and degradation in electron mobility are typical effects in these ultra-thin MOSFETs. The comparison of SG and DG configurations demonstrates the superiority of DG-MOSFETs: ideal subthreshold swing and remarkably improved transconductance (consistently higher than twice the value in SG-MOSFETs). The experimental data and the difference between SG and DG modes is explained by combining classical models with quantum calculations. The key effect in ultimately thin DG-MOSFETs is volume inversion, which primarily leads to an improvement in mobility, whereas the total inversion charge is only marginally modified.

Adaptation of the charge pumping technique to gated p-i-n diodes fabricated on silicon on insulator

The charge pumping technique was applied to MOS p-i-n diodes and used to characterize silicon-on-insulator films synthesized by oxygen implantation. The flatband and threshold voltages, effective channel length, capture cross sections, and densities of traps at the front and back interfaces were extracted. The parameters of the charge pumping phenomenon were systematically studied, and the ranges of validity are discussed. A parasitic component, due to an excess recombination of mobile carriers, occurs for very short transients during both the rise and fall of the gate pulse. It is demonstrated that the carrier reservoirs situated at the back interface play a significant role. Other specific features related to the dual-gate operation and interface coupling in silicon-on-insulator films are presented. An improved model is developed for the interpretation of the interface state profile in the energy gap. >

Influence of series resistances and interface coupling on the transconductance of fully-depleted silicon-on-insulator MOSFETs

Abstract A model is proposed to describe the variation of the transaconductance in fully-depleted silicon on insulator MOSFETs as a function of the front/back gate biases, channel length and series resistances. The influence of series resistances on the static characteristics of short-channel transistors depends on the region of operation, via the front and back gate voltages, and is a maximum when both interfaces are inverted. Simple analytical expressions explain the gradual deformation of the transconductance curve and the lowering of the transconductance peak with increasing series resistances. The model is experimentally verified by associating external resistors to the transistor. It is shown that a major consequence of X-ray irradiations in short-channel SIMOX MOSFETs is the trapping of positive charges in the buried oxide, which causes activation of interface coupling effects and enhanced influence of series resistances.

Large area quasi-free standing monolayer graphene on 3C-SiC(111)

Large scale, homogeneous quasi-free standing monolayer graphene is obtained on cubic silicon carbide, i.e., the 3C-SiC(111) surface, which represents an appealing and cost effective platform for graphene growth. The quasi-free monolayer is produced by intercalation of hydrogen under the interfacial, (6 root 3 x 6 root 3)R30 degrees-reconstructed carbon layer. After intercalation, angle resolved photoemission spectroscopy reveals sharp linear pi-bands. The decoupling of graphene from the substrate is identified by x-ray photoemission spectroscopy and low energy electron diffraction. Atomic force microscopy and low energy electron microscopy demonstrate that homogeneous monolayer domains extend over areas of hundreds of square-micrometers

Hot-carrier-induced degradation of the back interface in short-channel silicon-on-insulator MOSFETS

The tolerance of silicon-on-insulator MOSFETs to hot-carrier injection into the buried oxide is investigated. It is shown that stressing of the back channel results in reversible electron trapping and formation of localized defects at the buried interface. This damage is responsible for the transconductance overshoot, large threshold voltage shift, and attenuated kink effect. It is also noticed that even in moderately thin films the back oxide damage does not affect the front-channel operation and, conversely, stressing the front channel does not generate defects at the buried interface. These findings indicate that the hot-carrier degradation of the buried oxide might be chosen as a sensitive criterion for optimizing SIMOX (separation by implantation of oxygen) structures.<<ETX>>

Low-frequency noise characterization of n- and p-MOSFET's with ultrathin oxynitride gate films

MOSFETs with ultrathin (5 to 8.5 nm) silicon oxynitride gate film prepared by low-pressure rapid thermal chemical vapor deposition (RTCVD) using SiH/sub 4/, N/sub 2/O and NH/sub 3/ gases, are studied by low-frequency noise measurements (1 Hz up to 5 kHz). The analysis takes into account the correlated mobility fluctuations induced by those of the interfacial oxide charge. The nitrogen concentration, determined from SIMS analysis, varies from 0 to 11% atomic percentage. A comparison of the electrical properties between thermal and silicon oxynitride films is presented. The increasing LF noise signal with nitrogen atomic percentage indicates the presence of a higher density of slow interface traps with increasing nitrogen incorporation. Besides, a higher Coulomb scattering rate due to the nitridation induced interface charge explains reasonably well the degradation of the low field mobility after nitridation.

Electron trapping in irradiated SIMOX buried oxides

Presented are new results of X-ray exposure of silicon-on-insulator devices fabricated on SIMOX (separation by implantation of oxygen) substrates. It is shown that the presence of numerous electron traps in the buried oxide may dominate the back-gate threshold voltage shift of strongly irradiated SIMOX transistors. A rebound effect occurs under a negative oxide field, due to the trapping of negative charges rather than to interface states generation. Irradiated transistors also show an increased sensitivity to hot-carrier effects.<<ETX>>

Revealing the electronic band structure of trilayer graphene on SiC: An angle-resolved photoemission study

In recent times, trilayer graphene has attracted wide attention owing to its stacking and electric-field-dependent electronic properties. However, a direct and well-resolved experimental visualization of its band structure has not yet been reported. In this paper, we present angle-resolved photoemission spectroscopy data which show with high resolution the electronic band structure of trilayer graphene obtained on alpha-SiC(0001) and beta-SiC(111) via hydrogen intercalation. Electronic bands obtained from tight-binding calculations are fitted to the experimental data to extract the interatomic hopping parameters for Bernal and rhombohedral stacked trilayers. Low-energy electron microscopy measurements demonstrate that the trilayer domains extend over areas of tens of square micrometers, suggesting the feasibility of exploiting this material in electronic and photonic devices. Furthermore, our results suggest that, on SiC substrates, the occurrence of a rhombohedral stacked trilayer is significantly higher than in natural bulk graphite. (Less)

Self-heating effects in silicon carbide MESFETs

Silicon carbide materials offer specific advantages to MESFET applications. However, to put them to good use requires to apply higher drain voltages than in GaAs devices. Therefore, in spite of the high thermal conductivity of the SiC substrates, this leads to a large power dissipation and a substantial increase in the local temperature. Depending on the device configuration, this self-heating can induce a negative differential conductance at very low frequency near dc regime. A simple analytical model is proposed, which yields a reasonable fit of the MESFET static characteristics. Further experimental evidence for such effects is also given, which corroborates the predictions of the model.

Imaging electron wave functions inside open quantum rings

Combining scanning gate microscopy (SGM) experiments and simulations, we demonstrate low temperature imaging of the electron probability density |Psi|(2)(x,y) in embedded mesoscopic quantum rings. The tip-induced conductance modulations share the same temperature dependence as the Aharonov-Bohm effect, indicating that they originate from electron wave function interferences. Simulations of both |Psi|(2)(x,y) and SGM conductance maps reproduce the main experimental observations and link fringes in SGM images to |Psi|(2)(x,y).