Christoph Jungemann

Bio: Christoph Jungemann is an academic researcher from RWTH Aachen University. The author has contributed to research in topics: Boltzmann equation & Monte Carlo method. The author has an hindex of 27, co-authored 264 publications receiving 3060 citations. Previous affiliations of Christoph Jungemann include Braunschweig University of Technology & National Experimental University of the Armed Forces.

Impact ionization MOS (I-MOS)-Part II: experimental results

Abstract: Part I of this paper dealt with the fundamental understanding of device physics and circuit design in a novel transistor, based on the field-effect control of impact-ionization (I-MOS). This paper focuses on experimental results obtained on various silicon-based prototypes of the I-MOS. The fabricated p-channel I-MOS devices showed extremely abrupt transitions from the OFF state to the ON state with a subthreshold slope of less than 10 mV/dec at 300 K. These first experimental prototypes of the I-MOS also showed significant hot carrier effects resulting in threshold voltage shifts and degradation of subthreshold slope with repeated measurements. Hot carrier damage was seen to be much worse in nMOS devices than in pMOS devices. Monte Carlo simulations revealed that the hot carrier damage was caused by holes (electrons) underneath the gate in pMOS (nMOS) devices and, thus, consequently explained the difference in hot carrier effects in p-channel versus n-channel I-MOS transistors. Recessed channel devices were also explored to understand the effects of surfaces on the enhancement in the breakdown voltage in I-MOS devices. In order to reduce the breakdown voltage needed for device operation, simple p-i-n devices were fabricated in germanium. These devices showed much lower values of breakdown voltage and excellent matches to MEDICI simulations.

Hierarchical Device Simulation: The Monte-Carlo Perspective

Abstract: Introduction References Semiclassical Transport Theory The Boltzmann Transport Equation * Balance Equations * The Microscopic Relaxation Time * Fluctuations in the Steady-State * References The Monte-Carlo Method Basic Monte-Carlo Methods * The Monte-Carlo Solver of the Boltzmann Equation * Velocity Autocorrelation Function * Basic Statistics * Convergence Estimation * References Scattering Mechanisms Phonon Scattering * Alloy Scattering * Impurity Scattering * Impact Ionization by Electrons * Surface Roughness Scattering * References Full-Band Structure Basic Properties of the Band Structure of Relaxed Silicon * Basic Properties of the Band Structure of Strained SiGe * k-Space Grid * Calculation of the Density of States * Mass Tensor Evaluation * Particle Motion in Phase-Space * Selection of a Final State in k-Space * References Device Simulation Device Discretization * Band Edges * Poisson Equation * Self-Consistent Device Simulation * Nonlinear Poisson Equation * Nonself-Consistent Device Simulation * Statistical Enhancement * Terminal Current Estimation * Contact Resistance * Normalization of Physical Quantities * References Momentum-Based Transport Models The Hydrodynamic Model * Small-Signal Analysis * Noise Analysis * The Drift-Diffusion Model * Transport and Noise Parameter Simulation * References Stochastic Properties of Monte-Carlo Device Simulations Stochastic Error * In-Advance CPU Time Estimation * References Results N+ NN+ and P+ PP+ Structures * MOSFETs * SiGe HBTs Subject Index

High-mobility low band-to-band-tunneling strained-Germanium double-gate heterostructure FETs: Simulations

Abstract: Large band-to-band tunneling (BTBT) leakage currents can ultimately limit the scalability of high-mobility (small-bandgap) materials. This paper presents a novel heterostructure double-gate FET (DGFET) that can significantly reduce BTBT leakage currents while retaining its high mobility, making it suitable for scaling into the sub-20-nm regime. In particular, through one-dimensional Poisson-Schrodinger, full-band Monte Carlo, and detailed BTBT simulations, the tradeoffs between carrier transport, electrostatics, and BTBT leakage in high-mobility sub-20-nm Si-strained SiGe-Si (high germanium concentration) heterostructure PMOS DGFETs are thoroughly analyzed. The results show a dramatic (>100/spl times/) reduction in BTBT and an excellent electrostatic control of the channel while maintaining very high drive currents and switching frequencies in these nanoscale transistors.

Stable discretization of the Boltzmann equation based on spherical harmonics, box integration, and a maximum entropy dissipation principle

Abstract: The Boltzmann equation for transport in semiconductors is projected onto spherical harmonics in such a way that the resultant balance equations for the coefficients of the distribution function times the generalized density of states can be discretized over energy and real spaces by box integration. This ensures exact current continuity for the discrete equations. Spurious oscillations of the distribution function are suppressed by stabilization based on a maximum entropy dissipation principle avoiding the H transformation. The derived formulation can be used on arbitrary grids as long as box integration is possible. The approach works not only with analytical bands but also with full band structures in the case of holes. Results are presented for holes in bulk silicon based on a full band structure and electrons in a Si NPN bipolar junction transistor. The convergence of the spherical harmonics expansion is shown for a device, and it is found that the quasiballistic transport in nanoscale devices requires an expansion of considerably higher order than the usual first one. The stability of the discretization is demonstrated for a range of grid spacings in the real space and bias points which produce huge gradients in the electron density and electric field. It is shown that the resultant large linear system of equations can be solved in a memory efficient way by the numerically robust package ILUPACK.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Considerations for Ultimate CMOS Scaling

Abstract: This review paper explores considerations for ultimate CMOS transistor scaling Transistor architectures such as extremely thin silicon-on-insulator and FinFET (and related architectures such as TriGate, Omega-FET, Pi-Gate), as well as nanowire device architectures, are compared and contrasted Key technology challenges (such as advanced gate stacks, mobility, resistance, and capacitance) shared by all of the architectures will be discussed in relation to recent research results

Essential physics of carrier transport in nanoscale MOSFETs

Abstract: The device physics of nanoscale MOSFETs is explored by numerical simulations of a model transistor. The physics of charge control, source velocity saturation due to thermal injection, and scattering in ultrasmall devices are examined. The results show that the essential physics of nanoscale MOSFETs can be understood in terms of a conceptually simple scattering model.

Scalable energy-efficient magnetoelectric spin-orbit logic.

Abstract: Since the early 1980s, most electronics have relied on the use of complementary metal–oxide–semiconductor (CMOS) transistors. However, the principles of CMOS operation, involving a switchable semiconductor conductance controlled by an insulating gate, have remained largely unchanged, even as transistors are miniaturized to sizes of 10 nanometres. We investigated what dimensionally scalable logic technology beyond CMOS could provide improvements in efficiency and performance for von Neumann architectures and enable growth in emerging computing such as artifical intelligence. Such a computing technology needs to allow progressive miniaturization, reduce switching energy, improve device interconnection and provide a complete logic and memory family. Here we propose a scalable spintronic logic device that operates via spin–orbit transduction (the coupling of an electron’s angular momentum with its linear momentum) combined with magnetoelectric switching. The device uses advanced quantum materials, especially correlated oxides and topological states of matter, for collective switching and detection. We describe progress in magnetoelectric switching and spin–orbit detection of state, and show that in comparison with CMOS technology our device has superior switching energy (by a factor of 10 to 30), lower switching voltage (by a factor of 5) and enhanced logic density (by a factor of 5). In addition, its non-volatility enables ultralow standby power, which is critical to modern computing. The properties of our device indicate that the proposed technology could enable the development of multi-generational computing. A scalable spintronic device operating via spin–orbit transduction and magnetoelectric switching and using advanced quantum materials shows non-volatility and improved performance and energy efficiency compared with CMOS devices.