Custom Cell Placement Automation for Asynchronous VLSI

Asynchronous Very-Large-Scale-Integration (VLSI) integrated circuits have demonstrated many advantages over their synchronous counterparts, including low power consumption, elastic pipelining, robustness against manufacturing and temperature variations, etc. However, the lack of dedicated electronic design automation (EDA) tools, especially physical layout automation tools, largely limits the adoption of asynchronous circuits. Existing commercial placement tools are optimized for synchronous circuits, and require a standard cell library provided by semiconductor foundries to complete the physical design. The physical layouts of cells in this library have the same height to simplify the placement problem and the power distribution network. Although the standard cell methodology also works for asynchronous designs, the performance is inferior compared with counterparts designed using the full-custom design methodology. To tackle this challenge, we propose a gridded cell layout methodology for asynchronous circuits, in which the cell height and cell width can be any integer multiple of two grid values. The gridded cell approach combines the shape regularity of standard cells with the size flexibility of full-custom layouts. Therefore, this approach can achieve a better space utilization ratio and lower wire length for asynchronous designs. Experiments have shown that the gridded cell placement approach reduces area without impacting the routability. We have also used this placer to tape out a chip in a 65nm process technology, demonstrating that our placer generates design-rule clean results

Theoretical and experimental study of magnetic proximity effect

Magnetic proximity effect in a heterostructure, which consists of a semiconductor thin film or a 2D material sheet and a ferromagnetic insulator film, has a great potential in spintronics applications. However, a complete study of magnetic proximity effect has been highly challenging. We theoretically and experimentally investigate the proximity-induced exchange splitting in a semiconductor thin film or a 2D material sheet adjacent to a ferromagnetic insulator layer. Theoretical calculations indicate that proximity-induced exchange splitting can largely enhance the performance of spintronic applications. Photoluminescence experiment shows that the spin splitting in the semiconductor thin film induced by the proximity effect can be directly controlled by the magnetization of the ferromagnetic insulator layers. Such a sandwich structure not only serves as a platform to clarify the magnetic proximity effect at ferromagnetic insulator/semiconductor interfaces but also provides insights into designing spin-filter superlattices which can generate fully spin-polarized currents. The unit cell of the ferromagnetic superlattice is a ferromagnetic insulator/semiconductor bilayer. These ferromagnetic insulator layers create periodically arranged spin-dependent barriers, with semiconductor layers as quantum wells. In Chapter 2, we will cover the band structure of the ferromagnetic superlattice, and we will use standard approaches to study the electron transport together with spin transport in this superlattice. We will show that the translational symmetry along the superlattice growth direction ensures the wavevector a good quantum number, and the weak coupling between adjacent quantum wells leads to the formation of minibands (meV), which is far narrower than the bandwidth of conventional semiconductors (eV). The thickness of the bilayer unit cell determines the widths of minibands, and the spin dependent barriers lead to spin splitting minibands. In our study, we find that by carefully choosing the thickness of ferromagnetic insulator layers and semiconductor layers, the lowest spin degenerate miniband can split into two spin-resolved minibands. This half-metallic band structure makes possible the current through this superlattice 100\% spin-polarized. We will prove that in the so-called miniband conduction regime, the current in a superlattice with high crystal quality is indeed perfectly polarized under a small voltage bias. Because of the spin-dependent barriers in the superlattice, the induced half-metallic miniband paves a way to create a perfectly polarized spin current without an exponential increase of the device resistance, which can hardly be realized using a single spin-filter barrier. 2-dimensional (2D) materials are promising candidates to realize next generation devices for spintronic applications with low-power consumption and quantum operation capability. Magnetic proximity effect can induce an interface exchange field into 2D materials from the adjacent ferromagnetic insulator, which enables efficient spin modulation in 2D devices. In particular, Chapter 3 shows the graphene nanoribbon with armchair boundaries has the so-called Dirac cone and metallic band structure. Relativistic quasi-particles and weak spin-orbit coupling in graphene ensure a relatively long spin lifetime and also a long spin diffusion/relaxation length. A strong magnetic exchange field arises due to the interfacial coupling, which can be determined from Zeeman spin-Hall effect. Based on these properties of graphene, we propose a new type of spin field effect transistor (SpinFET) using a graphene nanoribbon with armchair boundaries as the conduction channel. By making use of the interfacial exchange field which derives from the direct coupling with ferromagnetic insulator gate and the quantum confinement effect, the control and manipulation of magnetization of the ferromagnetic insulator layer can modulate the Hamiltonian of the relativistic quasi-particles in the graphene nanoribbon, which controls the time evolution of electron spin and thus make efficient spin modulation feasible. Our numerical calculation shows that the spin lifetime and diffusion length are both long enough so that a phase difference of $\pi$ can be introduced within a time far below the spin lifetime. Thermal noise makes no influence on the current modulation due to the Dirac-like dispersion relation and the negligible spin-orbit coupling, which is crucial to realize large ON-OFF ratios

Flexible Electrodes for Smart Bandages: Feasibility Exploration

Flexible electrodes are revolutionizing the field of wearable health-monitoring and therapeutic devices by enabling the production of large, lightweight, and thin gadgets. These electrodes are incredibly beneficial for collecting bioelectric signals from the human body. They offer stable, high-quality signals while ensuring breathability and skin-friendly contact. Products for which flexible electrodes are actively being developed include innovative wearable devices, portable medical equipment, and brain-computer interfaces. Wearable medical devices necessitate the integration of electrodes, power sources, and microcontroller chips. Flexible electrodes offer several advantages, namely, flexibility, comfort, biocompatibility, and superior signal quality. Flexible electrodes made using conductive ink and a polyurethane film with an adhesive layer are capable of long-term monitoring while maintaining high signal quality. The primary objective of this study is to refine the design of flexible electrodes used in wearable health-monitoring and therapeutic devices. By fabricating micro-perforated structures with various aperture sizes and spacings and applying silver ink on Z-conductive electrodes, the aim is to identify the optimal combination of aperture size and spacing. To this end, a measuring and fitting process is employed. We discovered that Z-conductive electrodes with a hole spacing of 0.28 mm exhibited the lowest impedance values in the low-frequency range of 5 kHz-50 kHz. Comparatively, holes with a spacing of 0.4 mm had the lowest impedance in the high-frequency range of 100-500 kHz. These findings may facilitate future mass production efforts for our industrial partner, Ti2 Pty Ltd. This research contributes to innovation in wearable medical technologies by enhancing the performance of flexible electrodes, thereby improving the quality of biometric signal collection and the comfortability of wearable devices

Robusni algoritam praćenja mjerenjem smjera pomoću strukturiranog potpunog Kalmanovog filtra zasnovanog na metodi najmanjih kvadrata

A nonlinear approach called the robust structured total least squares kalman filter (RSTLS-KF) algorithm is proposed for solving tracking inaccuracy caused by outliers in bearings-only multi-station passive tracking. In that regard, the robust extremal function is introduced to the weighted structured total least squares (WSTLS) location criterion, and then the improved Danish equivalent weight function is built on the basis, which can identify outliers automatically and reduce the weight of the polluted data. Finally, the observation equation is linearized according to the RSTLS location result with the structured total least norm (STLN) solution. Hence location and velocity of the target can be given by the Kalman filter. Simulation results show that tracking performance of the RSTLS-KF is comparable or better than that of conventional algorithms. Furthermore, when outliers appear, the RSTLS-KF is accurate and robust, whereas the conventional algorithms become distort seriously.U ovome radu predložen je nelinearni pristup za rješavanje netočnosti uzrokovanih netipčnim vrijednostima kod praćenja mjerenjem smjera pasivnim senzorima s više stanica. Pristup je zasnovan na robusnom strukturiranom potpunom Kalmanovom filtru zasnovanom na metodi najmanjih kvadrata. Pomoću predložene metode moguće je estimirati položaj i brzinu praćenog objekta. Simulacijski rezultati pokazuju da je učinkovitost predloženog algoritma jednaka ili bolja od konvencionalnih algoritama. Nadalje, u prisustvu netipčnih vrijednosti mjerenja, predloženi algoritam zadržava točnost i robusnost, dok konvencionalni algoritmi pokazuju pogreške u estimaciji