Area of work
3D Monte Carlo simulator development - Hole Transport
The investigation of alternate channel materials such as Germanium and III-V alloys as alternative channel materials and potential technology boosters has experienced a revived impetus, with Germanium proving especially promising for p-channel MOSFETs where higher carrier mobility and drive current compared to conventional CMOS devices have already been successfully demonstrated. The already superior hole mobility of Germanium as compared to Silicon can be improved further by employing strain and exploiting different substrate and channel orientations. The choice of device architecture is also of importance in this respect, with a suitable design required to properly take advantage of the benefits of the material, hence structures such as double or single gate SOI, FinFET and IFQW are all gaining interest.
The simulation of hole transport in CMOS devices is complicated by the warped bandstructure, rendering the conventional analytical approaches used for electron transport inappropriate. On this basis, the Glasgow 3D Monte Carlo simulator employs a 6-band k•p full band structure to study hole transport in bulk material as well as devices. This methodology allows for the inclusion of strain and simulation of arbritary substrate and channel orientations.
Scattering from acoustic, optical and SO phonons, ionized impurities and surface roughness are included via a combination of conventional scattering rates and fluctuations of carriers real space trajectories captured via the denisty gradient quantum corrections applied to the classical potential.
Recent grants worked on
|2008 - Present
Germanium, in at the birth of the electronics revolution, is experiencing a renaissance as a semiconductor material - possibly even rivalling silicon, and is attracting huge interest as the silicon end-game hots up. It is perceived, audaciously but by many, as a potential candidate to maintain silicon-like technology and associated devices well beyond the envisaged end of silicon development (around 2020) and also take the technology into exciting new areas and performance regimes. This project sets out to explore some of the intriguing aspects and consequences of the fundamental electronic structure of Ge not previously examined. There are good theoretical arguments to suggest that some critical performance parameters can be dramatically enhanced if carriers travel in non-conventional crystallographic directions and when the germanium is under strain. Hence, this work will investigate how these new environments affect the velocity/mobility and "effective" mass of the carriers (electrons and holes) and the processes that impede their motion (scattering).
|2007 - 2008||
IRC in Bio-Nanotechnology
As CMOS devices shrink towards the scale of biological macro-molecules a direct connection can be made between them and the proteins which govern the majority of biological functions. Brownian dynamics (BD) simulation methods have proved to be both computationally efficient and accurate in the study of ion conduction through nano-pores such as Ion Channel proteins, which can provide greater understanding of their structure-function relationship. Since mesoscopic simulation methods such as BD can be applied on time scales which allow the direct comparison of simulation currents with experiment. The ability to simulate Current-Voltage characteristics is currently beyond the scope of Molecular dynamics (MD) simulations due to the extremely fine time discretisation required for MD, and continuum simulations (drift-diffusion, PNP), while easily comparable to experimental measurements, fail to account for the discrete nature of ions and their interactions.
|2003 - 2007||
Simulation of UTB SOI devices (Fujistu Studentship)
Scaling of conventional MOSFETs to decananometer dimensions requires heavy channel doping and extremely thin gate oxides in order to suppress short-channel effects (SCEs). However, the former degrades mobility and drive current and increases junction leakage due to band-to-band tunnelling, and the latter introduces gate leakage current. Alternative architectures such as ultrathin body (UTB) silicon-on-insulator (SOI) and multiple-gate MOSFETS offer superior electrostatic integrity and resistance to SCE and can tolerate very low channel doping so are inherently more resistant to random-dopant induced parameter fluctuations. However, scaling of UTB MOSFETs to channel lengths below 10 nm requires a sub-5 nm silicon body thickness , where several factors start to affect transport and device performance. Surface roughness, confined acoustic phonon and Coulomb scattering degrade the mobility in competition with band splitting and volume inversion, which enhance mobility and performance. In addition, roughness at both silicon/oxide interfaces, on the scale of one to two interatomic layers, results in body thickness variations (BTVs) along the channel. The corresponding fluctuation in subband energy levels along the channel introduces additional scattering and, thus, mobility degradation for silicon thicknesses below 5 nm, which is a phenomena that was initially observed and studied in quantum wells.
To study this phenomena, a 3D Monte Carlo simulation methodology was developed that includes complex quantum confinement effects resulting from BTV captured through the introduction of robust and efficient density gradient quantum corrections, which captures scattering from these fluctuations through the real space trajectories of the particles driven by the quantum corrected effective quantum potential. This allows the study of the enhanced current variability due to the corresponding transport variations.
- S.-Y. Liao, E. Towie, D. Balaz, C. Riddet, B. Cheng and A. Asenov, "Impact of the statistical variability on 15nm IIIV and Ge MOSFET based SRAM design," 14th Ultimate Integration on Silicon (ULIS): Coventry, UK, Mar. 19-21, 2013.
- E. Towie, C. Riddet and A. Asenov, "Monte Carlo Simulation of the Effect of Interface Roughness in Implant-Free Quantum-Well MOSFETs," 14th Ultimate Integration on Silicon (ULIS): Coventry, UK, Mar. 19-21, 2013.
- K. H. Chan, C. Riddet, J. R. Watling and A. Asenov, "Monte Carlo Simulations of Ge Implant Free Quantum Well FETs - The Role of Substrate and Channel Orientation," 2012 International Silicon-Germanium Technology and Device Meeting (ISTDM): June 4-6, 2012.
- C. Riddet, J. R. Watling, K. Chan, E. H. C. Parker, T. E. Whall, D. R. Leadley and A. Asenov, "Hole Mobility in Germanium as a Function of Substrate and Channel Orientation, Strain, Doping, and Temperature," IEEE Transactions on Electron Devices, Vol. 59, No. 7, pp. 1878–1884, July 2012.
- E. Towie, S.-Y. Liao, C. Riddet and A. Asenov, "InGaAs Implant-Free Quantum-Well MOSFETs - Performance Evaluation Using 3D Monte Carlo Simulation," Intel European Research and Innovation Conference: Dublin, Ireland, Oct. 3-4, 2012.
- J. R. Watling, C. Riddet and A. Asenov, "Accurate and efficient modelling of inelastic hole-acoustic phonon scattering in Monte Carlo simulations," 15th International Workshop on Computational Electronics (IWCE): May 22-25, 2012.
- B. Benbakhti, K. Chan, E. Towie, K. Kalna, C. Riddet, X. Wang, G. Eneman, G. Hellings, K. De Meyer, M. Meuris and A. Asenov, "Numerical analysis of the new Implant-Free Quantum-Well CMOS: DualLogic approach," Solid-State Electronics, Vol. 63, No. 1, pp. 14–18, Sept. 2011.
- K. Chan, C. Riddet, J. R. Watling and A. Asenov, "Monte Carlo Simulation of a 20nm Gate Length Implant Free Quantum Well Ge p-MOSFET with different Lateral Spacer Width," 12th Ultimate Integration on Silicon: Cork, Ireland, Mar. 14-16, 2011.
- C. Riddet, C. L. Alexander, A. R. Brown, S. Roy and A. Asenov, "Simulation of "Ab Initio" Quantum Confinement Scattering in UTB MOSFETs Using Three-Dimensional Ensemble Monte Carlo," IEEE Transactions on Electron Devices, Vol. 58, No. 3, pp. 600–608, Mar. 2011.
- C. Riddet, K. Chan and A. Asenov, "Monte Carlo study of the impact of strain and orientation on hole transport in germanium and silicon," UK Semiconductors: July 6-7, 2011.
- C. Riddet, K. Chan and A. Asenov, "Full-band Monte Carlo Simulations of Hole Transport in Germanium: from bulk material to devices," 17th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures: Aug. 7-12, 2011.
- E. Towie, K. Chan, B. Benbakhti, C. Riddet and A. Asenov, "Statistical Variability in Implant-Free Quantum-Well MOSFETs with InGaAs and Ge: A comparative 3D simulation study," Intel European Research and Innovation Conference: Oct. 12-14, 2011.
- E. Towie, K. Chan, C. Riddet and A. Asenov, "High Mobility Channel MOSFETs for CMOS: A Comparative Implant-Free Quantum-Well 3D Statistical Variability Study," European Workshop on Heterostructure Technology: Nov. 7-9, 2011.
- J. R. Watling, C. Riddet, KH. Chan and A. Asenov, "Simulation of hole-mobility in doped relaxed and strained Ge," Microelectronic Engineering, Vol. 88, No. 4, pp. 462–464, Apr. 2011.
- A. R. Brown, J. R. Watling, G. Roy, C. Riddet, C. L. Alexander, U. Kovac, A. Martinez and A. Asenov, "Use of density gradient quantum corrections in the simulation of statistical variability in MOSFETs," Journal of Computational Electronics, Vol. 9, No. 3-4, pp. 187–196, 2010.
- K. Chan, B. Benbakhti, C. Riddet, J. R. Watling and A. Asenov, "Simulation study of the 20 nm gate-length Ge implant-free quantum well p-MOSFET," Microelectronic Engineering, Vol. 88, No. 4, pp. 362–365, Oct. 2010.
- K. Chan, B. Benbakhti, C. Riddet, J. R. Watling and A. Asenov, "Simulation study of the 20 nm gate-length Ge implant-free quantum well p-MOSFET," European Materials Research Society: Strabourg, France, June 7-11, 2010.
- U. Kovac, C. L. Alexander, G. Roy, C. Riddet, B. Cheng and A. Asenov, "Hierarchical Simulation of Statistical Variability: From 3-D MC with ‘ab initio’ Ionized Impurity Scattering to Statistical Compact Models," IEEE Transactions on Electron Devices, 2010.
- C. Riddet, J. R. Watling, K. Chan and A. Asenov, "Monte Carlo simulation study of the impact of strain and substrate orientation on hole mobility in Germanium," in Proc. 2nd Workshop on Theory, Modelling and Computational Methods for Semiconductor Materials and Nanostructures, York, UK, Jan. 13-15, 2010, p. 17.
- C. Riddet, J. R. Watling, K. Chan and A. Asenov, "Monte Carlo simulation study of the impact of strain and substrate orientation on hole mobility in Germanium," Journal of Physics Conferences Series, Vol. 242, p. 012017, 2010.
- C. Riddet, J. R. Watling, K. Chan, A. Asenov, B. De Jaeger, J. Mitard and M. Meuris, "Monte Carlo Simulation Study of Hole Mobility in Germanium MOS Inversion Layers," in Proc. 14th International Workshop on Computational Electronics (IWCE), Oct. 27-29, 2010, pp. 239–242.
- J. R. Watling, C. Riddet, KH. Chan and A. Asenov, "Simulation of hole-mobility in doped relaxed and strained Ge layers," Journal of Applied Physics, Vol. 108, p. 093715, 2010.
- A. Asenov, A. R. Brown, G. Roy, B. Cheng, C. L. Alexander, C. Riddet, U. Kovac, A. Martinez, N. Seoane and S. Roy, "Simulation of statistical variability in nano-CMOS transistors using drift-diffusion, Monte Carlo and non-equilibrium Green’s function techniques," Journal of Computational Electronics, Vol. 8, No. 3-4, pp. 349–373, 2009.
- P. Palestri, C. L. Alexander, A. Asenov, V. Aubry-Fortuna, G. Baccarani, A. Bournel, M. Braccioli, B. Cheng, P. Dolfus, A. Esposito, D. Esseni, C. Fenouillet-Beranger, C. Fiegna, G. Fiori, A. Ghetti, G. Iannaccone, A. Martinez, B. Majkusiak, S. Monfray, V. Peikert, S. Reggiani, C. Riddet, J. Saint-Martin, E. Sangiorgi, A. Schenk, L. Selmi, L. Silvestri, P. Toniutti and J. Walczak, "A comparison of advanced transport models for the computation of the drain current in nanoscale nMOSFETs," Solid-State Electronics, Vol. 53, No. 12, pp. 1293–1302, Dec. 2009.
- A. Asenov, S. Roy, A. R. Brown, G. Roy, C. L. Alexander, C. Riddet, C. Millar, B. Cheng, A. Martinez, N. Seoane, D. Reid, M. Faiz. Bukhori, X. Wang and U. Kovac, "Advanced simulation of statistical variability and reliability in nano CMOS transistors," in Proc. IEDM, USA, Dec. 2008, p. 421.
- C. Riddet, A. R. Brown, S. Roy and A. Asenov, "Boundary Conditions for Density Gradient Corrections in 3D Monte Carlo Simulations," Journal of Computational Electronics, Vol. 7, No. 3, pp. 231–235, 2008.
- C. Riddet and A. Asenov, "Convergence Properties of Density Gradient Quantum Corrections in 3D Ensemble Monte Carlo Simulations," in Proc. Simulation of Semiconductor Processes and Devices 2008, Hakone, Japan, pp. 261–264.
- C. Riddet, A. R. Brown, C. L. Alexander, J. R. Watling, S. Roy and A. Asenov, "3-D Monte Carlo simulation of the impact of quantum confinement scattering on the magnitude of current fluctuations in double gate MOSFETs," IEEE Transactions on Nanotechnology, Vol. 6, No. 1, pp. 48–55, 2007.
- C. Riddet, A. R. Brown, S. Roy and A. Asenov, "Boundary conditions for density gradient corrections in 3D Monte Carlo simulations," 12th International Workshop on Computational Electronics: Oct. 8-10, 2007.
- C. Riddet, A. R. Brown, C. L. Alexander, S. Roy and A. Asenov, "Efficient density gradient quantum corrections for 3D Monte Carlo simulations," ser. International Conference on Simulation of Semiconductor Processes and Devices, SISPAD 2006, California,USA,
- C. Riddet, A. R. Brown, C. L. Alexander, J. R. Watling, S. Roy and A. Asenov, "Impact of quantum confinement scattering on the magnitude of current fluctuations in double gate MOSFETs," ser. Silicon Nanoelectronics Workshop 2005,
- C. Riddet, A. R. Brown, C. L. Alexander, J. R. Watling, S. Roy and A. Asenov, "Scattering from body thickness fluctuations in double gate MOSFETs. An ab initio Monte Carlo simulation study," ser. International workshop on Computational Electronics, IWCE-10, West Lafayette, USA, pp. 194–195.
- C. Riddet, A. R. Brown, C. L. Alexander, J. R. Watling, S. Roy and A. Asenov, "Scattering From Body Thickness Fluctuations in Double Gate MOSFETs. An ab initio Monte Carlo Study." J. Comp. Elec, Vol. 3, pp. 341–345, 2004.