Radiation-tolerant ferroelectric materials for multifunctional devices

Ferroelectric materials have switchable, spontaneous polarization in addition to strong dielectric, pyroelectric and piezoelectric response. In thin films form, these materials are leveraged for numerous microelectronic devices, including mechanical logic elements, optical sensors and transducers, precision positioners, energy harvesting units, nonvolatile memory storage, and microelectromechanical systems (MEMS) sensors and actuators. Ferroelectric materials have also become attractive for use in devices for radiation-hostile environments (e.g. aerospace, medical physics, x-ray/high energy source measurement tools, nuclear monitoring systems) due to their relatively high radiation tolerance. An increased understanding of material properties responsible for radiation tolerance will allow for development of materials for the next generation of radiation-tolerant, multifunctional devices. Lead zirconate titanate (PZT), one of the most commonly used ferroelectric materials for microscale applications, is widely known for its high polarization and piezoelectric response. However, increasing demand for smaller device footprint has pushed research efforts on PZT thin films towards their limitations, creating a need for new material systems to exceed the current standards. In this thesis, two material systems are explored as radiation tolerant ferroelectric alternatives to PZT: 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) and Hf0.5Zr0.5O2 (HZO). PMN-PT films exhibit strong piezoelectric response, exceeding that of PZT, making them a strong candidate for next generation piezoelectric MEMS devices. Additionally, the large amount of chemical, polar, and structural heterogeneities in this material imply a large degree of entropy, which could result in accommodation of radiation-induced defects and enhanced radiation tolerance. HZO thin films exhibit strong polarization properties at only a few nanometers in thickness. Combined with its CMOS compatibility and the potential to fabricate complex 3D structures using atomic layer deposition, HZO has become an attractive material for (ferroelectric) non-volatile memory applications. Total ionization dose (TID) studies, using gamma-radiation doses up to 10 Mrad(Si), were performed to understand the radiation tolerance of PMN-PT and HZO thin films. Processing-structure-property relations were explored to identify the material characteristics responsible for both high functional response and high radiation tolerance. PMN-PT thin films were confirmed to exhibit equivalent or superior radiation tolerance in dielectric, polarization, and piezoelectric response than PZT thin films, largely unaffected by microstructural differences. Although the HZO thin films suffered significantly from aging, the films fabricated via plasma-enhanced atomic layer deposition exhibited superior radiation tolerance in polarization response than PZT thin films. The studies illustrate different pathways for concomitant enhanced functionality and higher radiation tolerance in ferroelectric thin films.Ph.D

Doctor of Philosophy

dissertationThis dissertation describes the design, fabrication, testing, reliability, and harsh environment performance of single-device Micro-electro-mechanical-system (MEMS)- based digital logic gates, such as XOR and AND, for applications in ultra-low-power computation in unforgiving settings such as high ionizing radiation and high temperatures. Within the scope of this dissertation are several significant contributions. First, this work was the first ever to report the evolution in logic design architecture from a CMOS-paradigm to a MEMS architecture utilizing a single functional device per logic, as opposed to multiple relays per logic. This novel approach reduces the number of devices needed to implement a logic function by approximately 10X, leading to better reliability, yield, speed, and overall better characteristics (subthreshold characteristics, smaller turn-on/off voltage variations, etc.) and it simplifies implementation of MEMSbased circuits. The logic gates illustrate ~1.5V turn-on voltage at 5MHz with >109 cycles of reliable operations and low operational power consumption (leakage current and power <10-9A, <1^W). Second, this work is the first ever to report an intensive study on the cycle-bycycle evolution of contact resistance (Rc) up to 100,000 cycles, on materials such as, Ir, Pt, W, Ni, Cr, Ti, Cu, Al, and graphite, which are materials commonly used in MEMS switches. Adhesion forces between contacts were also studied using a contact-modeAFM, force vs. displacement, experiment. Results show that materials with high Young's modulus, high melting temperatures, and high density show low initial contact resistances and low adhesion forces (such as Ir, Pt, and W). Third, the devices were interrogated separately in harsh environments where they were exposed to high doses of ionizing radiation (90kW) in a nuclear reactor for a prolonged time (120 min) and, separately, at high temperatures (409K). Here, results show that solid-state devices begin to deteriorate almost immediately to a point where their gate can no longer control the drain-to-source current, whereas MEMS switches survive such ionizing radiation and temperatures portraying clear ON and OFF states for far longer. In terms of the applications empowered and the breadth of topics covered to accomplish these results, the work presented here demonstrates significant contributions to an important and developing branch of engineering

The Fifth NASA Symposium on VLSI Design

The fifth annual NASA Symposium on VLSI Design had 13 sessions including Radiation Effects, Architectures, Mixed Signal, Design Techniques, Fault Testing, Synthesis, Signal Processing, and other Featured Presentations. The symposium provides insights into developments in VLSI and digital systems which can be used to increase data systems performance. The presentations share insights into next generation advances that will serve as a basis for future VLSI design

Vertical Heterostructure III-V MOSFETs for CMOS, RF and Memory Applications

This thesis focuses mainly on the co-integration of vertical nanowiren-type InAs and p-type GaSb MOSFETs on Si (Paper I & II), whereMOVPE grown vertical InAs-GaSb heterostructure nanowires areused for realizing monolithically integrated and co-processed all-III-V CMOS.Utilizing a bottom-up approach based on MOVPE grown nanowires enablesdesign flexibilities, such as in-situ doping and heterostructure formation,which serves to reduce the amount of mask steps during fabrication. By refiningthe fabrication techniques, using a self-aligned gate-last process, scaled10-20 nm diameters are achieved for balanced drive currents at Ion ∼ 100μA/μm, considering Ioff at 100 nA/μm (VDD = 0.5 V). This is enabledby greatly improved p-type MOSFET performance reaching a maximumtransconductance of 260 μA/μm at VDS = 0.5 V. Lowered power dissipationfor CMOS circuits requires good threshold voltage VT matching of the n- andp-type device, which is also demonstrated for basic inverter circuits. Thevarious effects contributing to VT-shifts are also studied in detail focusing onthe InAs channel devices (with highest transconductance of 2.6 mA/μm), byusing Electron Holography and a novel gate position variation method (PaperV).The advancements in all-III-V CMOS integration spawned individual studiesinto the strengths of the n- and p-type III-V devices, respectively. Traditionallymaterials such as InAs and InGaAs provide excellent electrontransport properties, therefore they are frequently used in devices for highfrequency RF applications. In contrast, the III-V p-type alternatives have beenlacking performance mostly due to the difficult oxidation properties of Sb-based materials. Therefore, a study of the GaSb properties, in a MOSFETchannel, was designed and enabled by new manufacturing techniques, whichallowed gate-length scaling from 40 to 140 nm for p-type Sb-based MOSFETs(Paper III). The new fabrication method allowed for integration of deviceswith symmetrical contacts as compared to previous work which relied on atunnel-contact at the source-side. By modelling based on measured data fieldeffecthole mobility of 70 cm2/Vs was calculated, well in line with previouslyreported studies on GaSb nanowires. The oxidation properties of the GaSbgate-stack was further characterized by XPS, where high intensities of xraysare achieved using a synchrotron source allowed for characterization ofnanowires (Paper VI). Here, in-situ H2-plasma treatment, in parallel with XPSmeasurements, enabled a study of the time-dependence during full removalof GaSb native oxides.The last focus of the thesis was building on the existing strengths of verticalheterostructure III-V n-type (InAs-InGaAs graded channel) devices. Typically,these devices demonstrate high-current densities (gm >3 mS/μm) and excellentmodulation properties (off-state current down to 1 nA/μm). However,minimizing the parasitic capacitances, due to various overlaps originatingfrom a low access-resistance design, has proven difficult. Therefore, newmethods for spacers in both the vertical and planar directions was developedand studied in detail. The new fabrication methods including sidewall spacersachieved gate-drain capacitance CGD levels close to 0.2 fF/μm, which isthe established limit by optimized high-speed devices. The vertical spacertechnology, using SiO2 on the nanowire sidewalls, is further improved inthis thesis which enables new co-integration schemes for memory arrays.Namely, the refined sidewall spacer method is used to realize selective recessetching of the channel and reduced capacitance for large array memoryselector devices (InAs channel) vertically integrated with Resistive RandomAccess Memory (RRAM) memristors. (Paper IV) The fabricated 1-transistor-1-memristor (1T1R) demonstrator cell shows excellent endurance and retentionfor the RRAM by maintaining constant ratio of the high and low resistive state(HRS/LRS) after 106 switching cycles

Selected topics in robotics for space exploration

Papers and abstracts included represent both formal presentations and experimental demonstrations at the Workshop on Selected Topics in Robotics for Space Exploration which took place at NASA Langley Research Center, 17-18 March 1993. The workshop was cosponsored by the Guidance, Navigation, and Control Technical Committee of the NASA Langley Research Center and the Center for Intelligent Robotic Systems for Space Exploration (CIRSSE) at RPI, Troy, NY. Participation was from industry, government, and other universities with close ties to either Langley Research Center or to CIRSSE. The presentations were very broad in scope with attention given to space assembly, space exploration, flexible structure control, and telerobotics

Development and Analysis of Non-Delay-Line Constant-Fraction Discriminator Timing Circuits, Including a Fully-Monolithic CMOS Implementation

A constant-fraction discriminator (CFD) is a time pick-off circuit providing time derivation that is insensitive to input-signal amplitude and, in some cases, input-signal rise time. CFD time pick-off circuits are useful in Positron Emission Tomography (PET) systems where Bismuth Germanate (BGO)/photomultiplier scintillation detectors detect coincident, 511-keV annihilation gamma rays. Time walk and noise-induced timing jitter in time pick-off circuits are discussed along with optimal and sub-optimal timing filters designed to minimize timing jitter. Additionally, the effects of scintillation-detector statistics on timing performance are discussed, and Monte Carlo analysis is developed to provide estimated timing and energy spectra for selected detector and time pick-off circuit configurations. The traditional delay-line CFD is then described with a discussion of deterministic (non statistical) performance and statistical Monte Carlo timing performance. A new class of non-delay-line CFD circuits utilizing lowpass- and/or allpass-filter delay-line approximations is then presented. The timing performance of these non-delay-line CFD circuits is shown to be comparable to traditional delay-line CFD circuits. Following the development and analysis of non-delay-line CFD circuits, a fully-monolithic, non-delay-line CFD circuit is presented which was fabricated in a standard digital, 2-μ, double-meta], double-poly, n-well CMOS process. The CMOS circuits developed include a low time walk comparator having a time walk of approximately 175 ps for input signals with amplitudes between 10-mV to 2000-mV and a rise time (10 - 90%) of 10 ns. Additionally, a fifth-order, continuous-time filter having a bandwidth of over 100 MHz was developed to provide CFD signal shaping without a delay line. The measured timing resolution (3.26 ns FWITh1, 6.50 ns FWTM) of the fully-monolithic, CMOS CFD is comparable to measured resolution (3.30 ns FWHM, 6.40 ns FWTM) of a commercial, discrete, bipolar CFD containing an external delay line. Each CFD was tested with a PET EGO/photomultiplier scintillation detector and a preamplifier having a 10-ns (10 - 90%) rise-time. The development of a fully-monolithic, CMOS CFD circuit, believed to be the first such reported development, is significant for PET and other systems that employ many front-end CFD time pick-off circuits

Fault-based Analysis of Industrial Cyber-Physical Systems

The fourth industrial revolution called Industry 4.0 tries to bridge the gap between traditional Electronic Design Automation (EDA) technologies and the necessity of innovating in many indus- trial fields, e.g., automotive, avionic, and manufacturing. This complex digitalization process in- volves every industrial facility and comprises the transformation of methodologies, techniques, and tools to improve the efficiency of every industrial process. The enhancement of functional safety in Industry 4.0 applications needs to exploit the studies related to model-based and data-driven anal- yses of the deployed Industrial Cyber-Physical System (ICPS). Modeling an ICPS is possible at different abstraction levels, relying on the physical details included in the model and necessary to describe specific system behaviors. However, it is extremely complicated because an ICPS is com- posed of heterogeneous components related to different physical domains, e.g., digital, electrical, and mechanical. In addition, it is also necessary to consider not only nominal behaviors but even faulty behaviors to perform more specific analyses, e.g., predictive maintenance of specific assets. Nevertheless, these faulty data are usually not present or not available directly from the industrial machinery. To overcome these limitations, constructing a virtual model of an ICPS extended with different classes of faults enables the characterization of faulty behaviors of the system influenced by different faults. In literature, these topics are addressed with non-uniformly approaches and with the absence of standardized and automatic methodologies for describing and simulating faults in the different domains composing an ICPS. This thesis attempts to overcome these state-of-the-art gaps by proposing novel methodologies, techniques, and tools to: model and simulate analog and multi-domain systems; abstract low-level models to higher-level behavioral models; and monitor industrial systems based on the Industrial Internet of Things (IIOT) paradigm. Specifically, the proposed contributions involve the exten- sion of state-of-the-art fault injection practices to improve the ICPSs safety, the development of frameworks for safety operations automatization, and the definition of a monitoring framework for ICPSs. Overall, fault injection in analog and digital models is the state of the practice to en- sure functional safety, as mentioned in the ISO 26262 standard specific for the automotive field. Starting from state-of-the-art defects defined for analog descriptions, new defects are proposed to enhance the IEEE P2427 draft standard for analog defect modeling and coverage. Moreover, dif- ferent techniques to abstract a transistor-level model to a behavioral model are proposed to speed up the simulation of faulty circuits. Therefore, unlike the electrical domain, there is no extensive use of fault injection techniques in the mechanical one. Thus, extending the fault injection to the mechanical and thermal fields allows for supporting the definition and evaluation of more reliable safety mechanisms. Hence, a taxonomy of mechanical faults is derived from the electrical domain by exploiting the physical analogies. Furthermore, specific tools are built for automatically instru- menting different descriptions with multi-domain faults. The entire work is proposed as a basis for supporting the creation of increasingly resilient and secure ICPS that need to preserve functional safety in any operating context

Strategies of development and maintenance in supervision, control, synchronization, data acquisition and processing in light sources

Programa Oficial de Doutoramento en Tecnoloxías da Información e as Comunicacións. 5032V01[Resumo] Os aceleradores de partículas e fontes de luz sincrotrón, evolucionan constantemente para estar na vangarda da tecnoloxía, levando os límites cada vez mais lonxe para explorar novos dominios e universos. Os sistemas de control son unha parte crucial desas instalacións científicas e buscan logra-la flexibilidade de manobra para poder facer experimentos moi variados, con configuracións diferentes que engloban moitos tipos de detectores, procedementos, mostras a estudar e contornas. As propostas de experimento son cada vez máis ambiciosas e van sempre un paso por diante do establecido. Precísanse detectores cada volta máis rápidos e eficientes, con máis ancho de banda e con máis resolución. Tamén é importante a operación simultánea de varios detectores tanto escalares como mono ou bidimensionáis, con mecanismos de sincronización de precisión que integren as singularidades de cada un. Este traballo estuda as solucións existentes no campo dos sistemas de control e adquisición de datos nos aceleradores de partículas e fontes de luz e raios X, ó tempo que explora novos requisitos e retos no que respecta á sincronización e velocidade de adquisición de datos para novos experimentos, a optimización do deseño, soporte, xestión de servizos e custos de operación. Tamén se estudan diferentes solucións adaptadas a cada contorna.[Resumen] Los aceleradores de partículas y fuentes de luz sincrotrón, evolucionan constantemente para estar en la vanguardia de la tecnología, y poder explorar nuevos dominios. Los sistemas de control son una parte fundamental de esas instalaciones científicas y buscan lograr la máxima flexibilidad para poder llevar a cabo experimentos más variados, con configuraciones diferentes que engloban varios tipos de detectores, procedimientos, muestras a estudiar y entornos. Los experimentos se proponen cada vez más ambiciosos y en ocasiones más allá de los límites establecidos. Se necesitan detectores cada vez más rápidos y eficientes, con más resolución y ancho de banda, que puedan sincronizarse simultáneamente con otros detectores tanto escalares como mono y bidimensionales, integrando las singularidades de cada uno y homogeneizando la adquisición de datos. Este trabajo estudia los sistemas de control y adquisición de datos de aceleradores de partículas y fuentes de luz y rayos X, y explora nuevos requisitos y retos en lo que respecta a la sincronización y velocidad de adquisición de datos, optimización y costo-eficiencia en el diseño, operación soporte, mantenimiento y gestión de servicios. También se estudian diferentes soluciones adaptadas a cada entorno.[Abstract] Particle accelerators and photon sources are constantly evolving, attaining the cutting-edge technologies to push the limits forward and explore new domains. The control systems are a crucial part of these installations and are required to provide flexible solutions to the new challenging experiments, with different kinds of detectors, setups, sample environments and procedures. Experiment proposals are more and more ambitious at each call and go often a step beyond the capabilities of the instrumentation. Detectors shall be faster, with higher efficiency, more resolution, more bandwidth and able to synchronize with other detectors of all kinds; scalars, one or two-dimensional, taking into account their singularities and homogenizing the data acquisition. This work examines the control and data acquisition systems for particle accelerators and X- ray / light sources and explores new requirements and challenges regarding synchronization and data acquisition bandwidth, optimization and cost-efficiency in the design / operation / support. It also studies different solutions depending on the environment

Digital design techniques for dependable High-Performance Computing

L'abstract è presente nell'allegato / the abstract is in the attachmen