Advanced Applications of Nanoelectromechanical Systems

Nanoelectromechanical systems (NEMS) have advanced the technologies in a wide spectrum of fields, including nonlinear dynamics, sensors for force detection, mass spectrometry, inertial imaging, calorimetry, and charge sensing. Due to their low power consumption, fast response time, large dynamic range, high quality factor, and low mass, NEMS have achieved unprecedented measurement sensitivity. For optimized system functionalization and design, precise characterization of material properties at the nanoscale is essential. In this thesis, we will discuss three applications of NEMS: mechanical switches, using anharmonic nonlinearity to measure device and material properties, and mass spectrometry and inertial imaging. The first application of NEMS we discuss is NEMS switches, switches with physical moving parts. Conventional electronics, based largely on silicon transistors, is reaching a physical limit in both size and power consumption. Mechanical switches provide a promising solution to surpass this limit by forcing a jump between the on and off states. Graphene, which is a single sheet of carbon atoms arranged in a hexagonal structure, has high mechanical strength and strong planar bonding, making it an ideal candidate for nanoelectromechanical switches. In addition, graphene is conductive, which decreases resistive heating at the contact area, therefore reducing bonding issues and subsequently reducing degradation. We demonstrate using exfoliated graphene to fabricate suspended graphene NEMS switches with successful switching. The second application of NEMS we discuss in this thesis is the use of mechanical nonlinearity to measure device and material properties. While the nonlinear dynamics of NEMS have been used previously to investigate the longitudinal speed of sound of materials at nano- and micro-scales, we correct a previously attempted method that employs the anharmonicity of NEMS arising from deflection-dependent stress to interrogate the transport of RF acoustic phonons at nanometer scales. In contrast to existing approaches, this decouples intrinsic material properties, such as longitudinal speed of sound, from properties associated with linear dynamics, such as tension, of the structure. We demonstrate this approach through measurements of the longitudinal speed of sound in several NEMS devices composed of single crystal silicon along different crystal orientations. Good agreement with literature values is reported. The third application of NEMS we discuss is mass spectrometry and inertial imaging. Currently, only doubly clamped beams and cantilevers have been experimentally demonstrated for mass spectrometry. We extend the one-dimension model for mass spectrometry to a novel method for inertial imaging. We further extend the theory of mass spectrometry and inertial imaging to two dimensions by using a plate geometry. We show that the mode shape is critical in performing NEMS mass spectrometry and inertial imaging, and that the mode shapes in plates deviate from the ideal scenario with isotropic stress. We experiment with various non-ideal conditions to match non-ideal mode shape observed.</p

DEVELOPMENT OF NANO/MICROELECTROMECHANICAL SYSTEM (N/MEMS) SWITCHES

Ph.DDOCTOR OF PHILOSOPH

Non-invasive power gating techniques for bursty computation workloads using micro-electro-mechanical relays

PhD ThesisElectrostatically-actuated Micro-Electro-Mechanical/Nano-Electro- Mechanical (MEM/NEM) relays are promising devices overcoming the energy-efficiency limitations of CMOS transistors. Many exploratory research projects are currently under way investigating the mechanical, electrical and logical characteristics of MEM/NEM relays. One particular issue that this work addresses is the need for a scalable and accurate physical model of the MEM/NEM switches that can be plugged into the standard EDA software. The existing models are accurate and detailed but they suffer from the convergence problem. This problem requires finding ad-hoc workarounds and significantly impacts the designer’s productivity. In this thesis we propose a new simplified Verilog-AMS model. To test scalability of the proposed model we cross-checked it against our analysis of a range of benchmark circuits. Results show that, compared to standard models, the proposed model is sufficiently accurate with an average of 6% error and can handle larger designs without divergence. This thesis also investigates the modelling, designing and optimization of various MEM/NEM switches using 3D Finite Element Analysis (FEA) performed by the COMSOL multiphysics simulation tool. An extensive parametric sweep simulation is performed to study the energy-latency trade-offs of MEM/NEM relays. To accurately simulate MEMS/NEMS-based digital circuits, a Verilog-AMS model is proposed based on the evaluated parameters obtained from the multiphysics simulation tool. This allows an accurate calibration of the MEM/NEM relays with a significant reduction in simulation speed compared to that of 3D FEA exercised on COMSOL tool. The effectiveness of two power gating approaches in asynchronous micropipelines is also investigated using MEM/NEM switches and sleep transistors in reducing idle power dissipation with a particular target throughput. Sleep transistors are traditionally used to power gate idle circuits, however, these transistors have fundamental limitations in their effectiveness. Alternatively, MEM/NEM relays with zero leakage current can achieve greater energy savings under a certain data rate and design architecture. An asynchronous FIR filter 4 phase bundled data handshake protocol is presented. Implementation is accomplished in 90nm technology node and simulation exercised at various data rates and design complexities. It was demonstrated that our proposed approach offers 69% energy improvements at a data rate 1KHz compared to 39% of the previous work. The current trends for greater heterogeneity in future Systems-on- Chip (SoC) do not only concern their functionality but also their timing and power aspects. The increasing diversity of timing and power supply conditions, and associated concurrently operating modes, within an SoC calls for more efficient power delivery networks (PDN) for battery operated devices. This is especially important for systems with mixed duty cycling, where some parts are required to work regularly with low-throughput while other parts are activated spontaneously, i.e. in bursts. To improve their reaction time vs energy efficiency, this work proposes to incorporate a power-switching network based on MEM relays to switch the SoC power-performance state (PPS) into an active mode while eliminating the leakage current when it is idle. Results show that even with today0s large and high pull-in voltages, a MEM-relay-based power switching network (PSN) can achieve a 1000x savings in energy compared to its CMOS counterpart for low duty cycle. A simple case of optimising an on-chip charge pump required to switch-on the relay has been investigated and its energy-latency overhead has been evaluated. Heterogeneous many-core systems are increasingly being employed in modern embedded platforms for high throughput at low energy cost considerations. These applications typically exhibit bursty workloads that provide opportunities to minimize system energy. CMOS-based power gating circuitry, typically consisting of sleep transistors, is used as an effective technique for idle energy reduction in such applications. However, these transistors contribute high leakage current when driving large capacitive loads, making effective energy minimization challenging. This thesis proposes a novel MEMS-based idle energy control approach. Core to this approach is an integrated sleep mode management based on the performance-energy states and bursty workloads indicated by the performance counters. A number of PARSEC benchmark applications are used as case studies of bursty workloads, including CPU- and memory- intensive ones. These applications are exercised on an Exynos 5422 heterogeneous many-core platform, engineered with a performance counter facilities, showing 55.5% energy savings compared with an on-demand governor. Furthermore, an extensive trade-off analysis demonstrates the comparative advantages of the MEMS-based controller, including zero-leakage current and non-invasive implementations suitable for commercial off-the-shelf systems.Higher committee of education development in Iraq (HCED

DEVELOPMENT OF NEMS RELAYS IN LOGIC COMPUTATION AND RUGGED ELECTRONICS

Ph.DDOCTOR OF PHILOSOPH