Island growth and step instabilities on flat and vicinal surfaces

Surface physics aims at understanding the basic atomistic processes and mechanisms responsible for the variety of observed structures during surface growth. In addition, surface growth has important consequences in modern technological applications. Molecular beam epitaxy (MBE) is an established method to grow surface structures, admitting also modeling surface growth through simple microscopic processes such as diffusion and deposition of atoms. The rather limited parameter range in MBE where smooth layer-by-layer growth is realized can be extended, e.g., with ion assisted deposition techniques. Thus new microscopic processes are added to traditional MBE growth. Customarily island growth and step-flow are treated as separate growth modes. Consequently, there does not exist a growth model which includes all relevant aspects of surface growth in a realistic way. The aim of this thesis is to bridge the gap between these traditional approaches. Including other microscopic processes in addition to deposition and surface diffusion introduces new scaling relations and length scales. In addition, not only the scaling of the growth structures but also their stability is of importance. Moreover, unstable growth often possesses a dynamically selected length scale. It is of interest to understand the behavior of these new time and length scales and their scaling properties when constructing more realistic growth models. To this end, we consider various aspects of surface growth. First, we simulate island growth with aggregation, fragmentation, and deposition on flat surfaces. The generalized rate equations are introduced, and the scaling forms for the island size distributions and the mean island size are proposed and compared with simulation results. Next, stability of circular islands is studied by generalizing the rectangular case to radial geometry. A stability criterion for the island radius is derived in the long wavelength limit. Then, stability of step edges on vicinal surfaces is considered. The simulation results demonstrate the dynamical wavelength selection with a quantitative prediction for the selected wavelength as well as the mechanism behind the instability. The average shape of the unstable step patterns is found to have an invariant form, insensitive to the parameters of the model. Finally, the simulations extended to include both island growth and step edge instability reveal that these growth modes are coupled with a new length scale, and are inpendent only in the submonolayer regime.reviewe

Kinetic Monte Carlo simulations of oscillatory shape evolution for electromigration-driven islands

The shape evolution of two-dimensional islands under electromigration-driven periphery diffusion is studied by kinetic Monte Carlo (KMC) simulations and continuum theory. The energetics of the KMC model is adapted to the Cu(100) surface, and the continuum model is matched to the KMC model by a suitably parametrized choice of the orientation-dependent step stiffness and step atom mobility. At 700 K shape oscillations predicted by continuum theory are quantitatively verified by the KMC simulations, while at 500 K qualitative differences between the two modeling approaches are found.Comment: 7 pages, 6 figure

A low-power push-push D-band VCO with 11.6% FTR utilizing back-gate control in 22nm FDSOI

Abstract This paper proposes a D-band push-push voltage controlled oscillator implemented using 22nm FDSOI CMOS technology. The back-gate controls are employed to achieve a wide frequency tuning range (FTR) and low power consumption. Inductive coupling with the dummy fill blocks are optimized to improve the resonator quality factor. The measured results demonstrate a wide tuning range of 11.6% from 138‐155.1 GHz with a supply voltage of 0.9 V. The output power of the VCO is -16 dBm at a center frequency of 146.6 GHz with a phase noise of -90.1 dBc/Hz at 10 MHz offset. The VCO consumes a low power of 12.2 mW with a compact area of 259x249 µ m² • The corresponding FOMT is -163.9 dBc/Hz

108 and 124 GHz fundamental VCOs with 21% and 7% DC-to-RF efficiency in 22nm CMOS FDSOI

This paper presents the design of two high efficiency fundamental voltage controlled oscillators (VCO) for sub-THz applications. The design optimizes the transistor for voltage gain, swing and PAE at the operating frequency to achieve 21% and 7% DC-to-RF efficiencies. The varactor and back-gate voltages are utilized for tuning control. The back-gate controls improves the relative tuning range of the VCOs by ∼ 50%. Layout techniques are employed in the transistor and inductor to improve the VCO frequency. The two VCOs are implemented in 22nm CMOS FDSOI, oscillate at 108.7 GHz and 124 GHz having an output power of 3.41 and −1.45 dBm with a tuning range of 3.4% and 3.7%, respectively. The chip operates at a supply voltage of 0.7V and an IBIAS of 1.4mA with a core power consumption of 10.2mW and 9.9mW, respectively. The active area is 0.095x0.087 mm²