Post-Silicon Group IV Materials: Selected Applications of Quantum Mechanics to Device Simulation

Quantum mechanics is applied to the study and simulation of two features of group IV semiconductor devices: metal/n-type 4H-SiC interfaces for SiC-based Schottky diodes and GeO2 gate dielectrics for Ge-based Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs). SiC is well suited for power electronics due to its relatively wide bandgap and high breakdown field. In Schottky power diodes, one consideration in device performance is reverse saturation leakage. For metal/4H-SiC interfaces, reverse saturation leakage current is modeled with quantum transmission calculated by the Symmetrized Transfer Matrix Method (STMM). The classical thermionic emission model and quantum model are compared for multiple donor concentrations. The quantum model is then compared to experimental results for Ti/4H-SiC measurements, and the effect of Fermi pinning is included to account for the correct barrier height. Multiple donor concentrations are again modeled to best fit the bias dependence of the measured curves to find an effective doping level to reflect possible barrier thinning. Ge is considered as a possible replacement for Si in MOSFET design as device lengths continue to scale down to match Moore's Law and Si MOSFETs become increasingly difficult to fabricate. Ge is considered due to its relatively high electron and hole mobilities, and its ability to grow a native oxide like Si. However, GeO2 and the Ge/GeO2 interface suffer from high defect densities, with one such defect being the oxygen vacancy defect. For GeO2, the oxygen vacancy defect, and corresponding fluorine passivation, are modeled using Density Functional Theory (DFT) to calculate the atomic configurations and energies. Incorporation of fluorine atoms in the vicinity of the defect is modeled, as well as the incorporation of fluorine atoms within the oxide network. Hydrogen passivation is also modeled and found to not be as energetically favorable. Finally, fluorine diffusion through the oxide network is investigated by calculating the reaction pathway between fluorine incorporation sites in the network

Magnetic Microdevices for MRI-Based Detection of SARS-CoV-2 Viruses

Goal: To develop a micron-scale device that can operate as an MRI-based reporter for the presence of SARS-CoV-2 virus. Methods: Iron rod microdevices were constructed via template-guided synthesis and suspended in phosphate buffered saline (PBS). Heat-inactivated SARS-CoV-2 viruses were added to the samples and imaged with low-field MRI. Results: MRI of microdevices and viruses showed decreased signal intensity at low concentrations of viruses that recovered at higher concentrations. Electron micrographs suggest that reduced MRI intensity may be due to concentration-dependent shielding of water protons from local magnetic inhomogeneities caused by the iron microdevices. Conclusions: The preliminary results presented in this letter provide justification for further studies exploring the potential diagnostic role of magnetic microdevices in assessing the presence and concentration of SARS-CoV-2 viruses

Opening the Blood Brain Barrier with an Electropermanent Magnet System

Opening the blood brain barrier (BBB) under imaging guidance may be useful for the treatment of many brain disorders. Rapidly applied magnetic fields have the potential to generate electric fields in brain tissue that, if properly timed, may enable safe and effective BBB opening. By tuning magnetic pulses generated by a novel electropermanent magnet (EPM) array, we demonstrate the opening of tight junctions in a BBB model culture in vitro, and show that induced monophasic electrical pulses are more effective than biphasic ones. We confirmed, with in vivo contrast-enhanced MRI, that the BBB can be opened with monophasic pulses. As electropermanent magnets have demonstrated efficacy at tuning B0 fields for magnetic resonance imaging studies, our results suggest the possibility of implementing an EPM-based hybrid theragnostic device that could both image the brain and enhance drug transport across the BBB in a single sitting