Multi-Cycle at Speed Test

In this research, we focus on the development of an algorithm that is used to generate a minimal number of patterns for path delay test of integrated circuits using the multi-cycle at-speed test. We test the circuits in functional mode, where multiple functional cycles follow after the test pattern scan-in operation. This approach increases the delay correlation between the scan and functional test, due to more functionally realistic power supply noise. We use multiple at-speed cycles to compact K-longest paths per gate tests, which reduces the number of scan patterns. After a path is generated, we try to place each path in the first pattern in the pattern pool. If the path does not fit due to conflicts, we attempt to place it in later functional cycles. This compaction approach retains the greedy nature of the original dynamic compaction algorithm where it will stop if the path fits into a pattern. If the path is not able to compact in any of the functional cycles of patterns in the pool, we generate a new pattern. In this method, each path delay test is compared to at-speed patterns in the pool. The challenge is that the at-speed delay test in a given at-speed cycle must have its necessary value assignments set up in previous (preamble) cycles, and have the captured results propagated to a scan cell in the later (coda) cycles. For instance, if we consider three at-speed (capture) cycles after the scan-in operation, and if we need to place a fault in the first capture cycle, then we must generate it with two propagation cycles. In this case, we consider these propagation cycles as coda cycles, so the algorithm attempts to select the most observable path through them. Likewise, if we are placing the path test in the second capture cycle, then we need one preamble cycle and one coda cycle, and if we are placing the path test in the third capture cycle, we require two preamble cycles with no coda cycles

Study of Single Event Transient Error Mitigation

Single Event Transient (SET) errors in ground-level electronic devices are a growing concern in the radiation hardening field. However, effective SET mitigation technologies which satisfy ground-level demands such as generic, flexible, efficient, and fast, are limited. The classic Triple Modular Redundancy (TMR) method is the most well-known and popular technique in space and nuclear environment. But it leads to more than 200% area and power overheads, which is too costly to implement in ground-level applications. Meanwhile, the coding technique is extensively utilized to inhibit upset errors in storage cells, but the irregularity of combinatorial logics limits its use in SET mitigation. Therefore, SET mitigation techniques suitable for ground-level applications need to be addressed. Aware of the demands for SET mitigation techniques in ground-level applications, this thesis proposes two novel approaches based on the redundant wire and approximate logic techniques. The Redundant Wire is a SET mitigation technique. By selectively adding redundant wire connections, the technique can prohibit targeted transient faults from propagating on the fly. This thesis proposes a set of signature-based evaluation equations to efficiently estimate the protecting effect provided by each redundant wire candidates. Based on the estimated results, a greedy algorithm is used to insert the best candidate repeatedly. Simulation results substantiate that the evaluation equations can achieve up to 98% accuracy on average. Regarding protecting effects, the technique can mask 18.4% of the faults with a 4.3% area, 4.4% power, and 5.4% delay overhead on average. Overall, the quality of protecting results obtained are 2.8 times better than the previous work. Additionally, the impact of synthesis constraints and signature length are discussed. Approximate Logic is a partial TMR technique offering a trade-off between fault coverage and area overheads. The approximate logic consists of an under-approximate logic and an over-approximate logic. The under-approximate logic is a subset of the original min-terms and the over-approximate logic is a subset of the original max-terms. This thesis proposes a new algorithm for generating the two approximate logics. Through the generating process, the algorithm considers the intrinsic failure probabilities of each gate and utilizes a confidence interval estimate equation to minimize required computations. The technique is applied to two fault models, Stuck-at and SET, and the separate results are compared and discussed. The results show that the technique can reduce the error 75% with an area penalty of 46% on some circuits. The delay overheads of this technique are always two additional layers of logic. The two proposed SET mitigation techniques are both applicable to generic combinatorial logics and with high flexibility. The simulation shows promising SET mitigation ability. The proposed mitigation techniques provide designers more choices in developing reliable combinatorial logic in ground-level applications

Embracing Low-Power Systems with Improvement in Security and Energy-Efficiency

As the economies around the world are aligning more towards usage of computing systems, the global energy demand for computing is increasing rapidly. Additionally, the boom in AI based applications and services has already invited the pervasion of specialized computing hardware architectures for AI (accelerators). A big chunk of research in the industry and academia is being focused on providing energy efficiency to all kinds of power hungry computing architectures. This dissertation adds to these efforts. Aggressive voltage underscaling of chips is one the effective low power paradigms of providing energy efficiency. This dissertation identifies and deals with the reliability and performance problems associated with this paradigm and innovates novel energy efficient approaches. Specifically, the properties of a low power security primitive have been improved and, higher performance has been unlocked in an AI accelerator (Google TPU) in an aggressively voltage underscaled environment. And, novel power saving opportunities have been unlocked by characterizing the usage pattern of a baseline TPU with rigorous mathematical analysis

Upconverting luminescent materials for solar energy conversion

As attractive energy converters, solar cells are considered to play a vital role in covering the constantly increasing energy demands in the future. Despite the strong success in the field, a variety of solar cells including the commercially available ones are utilizing mainly the visible region of the solar spectrum, and thus are lacking the capacity to exploit effectively the infrared region. This issue gives a possibility to improve the solar cell efficiencies by using the unutilized energy of the infrared radiation. One solution to overcome this issue is to use upconverting luminescent materials which are capable of converting infrared radiation to visible by stacking photons. However, despite the potential, the rather weak conversion efficiency still limits the use of these materials. On the other hand, even small portions of this converted radiation would have significant effect on the solar cell efficiency which is why the development of these materials is desirable. The main aims of this thesis work were to investigate and develop different fabrication methods and properties of the upconverting materials that could be used in solar cells. These methods included the co-precipitation method to prepare crystalline inorganic upconverting fluoride materials, the atomic and the molecular layer deposition techniques to fabricate upconverting oxide and hybrid thin films, and the direct particles doping method for preparation of upconverting luminescent glasses. In addition, another goal was to study the possibilities to enhance the upconversion luminescence which was done by adding transition metal ions (Cr3+ or Mnn+) into the Yb3+ and Er3+ doped fluoride material. Improvement in the upconversion luminescence intensity was obtained by using Cr3+ ions. Another enhancement possibility is to use efficient NIR absorbers together with a strong upconverting lanthanide ion. The combined ALD/MLD technique was shown to enable the combination of NIR harvesting organic moiety and upconverting lanthanide ions to form a hybrid thin film. The ALD and the combined ALD/MLD techniques were demonstrated to be well suitable for upconverting thin film fabrication. Moreover, the direct particles doping method was shown to offer a promising way to introduce a variety of crystalline luminescent materials into different glass matrices.Käänteisviritteiset luminoivat materiaalit aurinkoenergian hyödyntämisessä Aurinkoenergian tarjoamia mahdollisuuksia pidetään yhtenä lupaavimmista vaihtoehdoista kasvavien energiatarpeiden täyttämisessä tulevaisuudessa. Aurinkokennot ovat kehittyneet paljon viime aikoina, mutta silti suurin osa tutkituista ja kaupallisesti saatavilla olevista aurinkokennoista pystyy hyödyntämään auringon spektristä vain näkyvän valon alueen jättäen infrapuna-alueen lähes kokonaan hyödyntämättä. Tämä ongelma tarjoaa mahdollisuuden parantaa aurinkokennojen tehokkuutta. Yksi tapa hyödyntää infrapunasäteilyn energiaa on käyttää käänteisviritteisiä luminoivia materiaaleja, jotka pystyvät muuntamaan infrapunasäteilyä näkyväksi valoksi pinoamalla fotoneja. Tämän prosessin heikko teho rajoittaa toistaiseksi materiaalien käyttöä. Toisaalta, jopa pienellä IR-säteilyn muuntomäärällä on mahdollisuus vaikuttaa merkittävästi aurinkokennon tehokkuuteen, minkä vuoksi materiaalien kehittäminen on herättänyt kiinnostusta. Väitöskirjatyön tavoitteena oli tutkia ja kehittää aurinkokennoissa mahdollisesti käytettävien käänteisviritteisten materiaalien ominaisuuksia ja valmistusmenetelmiä. Menetelmiin kuului kerasaostusmenetelmä, jolla valmistettiin kiteisiä fluoridimateriaaleja; atomi- ja molekyylikerroskasvatusmenetelmät, joilla valmistettiin kiteisiä oksidi ja amorfisia hybridiohutkalvoja; sekä seostusmetelemä luminoivien lasien valmistukseen. Lisäksi tavoitteena oli tutkia mahdollisuuksia parantaa käänteisviritteistä luminesenssia käyttämällä siirtymämetalli-ioneja (Cr3+ ja Mnn+). Käänteisviritteisen luminesenssin intensiteettiä kasvatettiin lisäämällä Cr3+ - ioneja fluoridimateriaaliin, joka oli seostettu Yb3+ ja Er3+ -ioneilla. Käänteisviritteisen luminesenssin tehostamisessa voidaan hyödyntää myös tehokkaasti NIR-säteilyä absorboivan orgaanisen osan yhdistämistä käänteisviritteisesti luminoivaan lantanidi-ioniin. Näiden osien yhdistäminen todettiin olevan mahdollista yhdistetyllä ALD/MLD -tekniikalla, jolla valmistettiin hybridikalvoja. Tämän yhdistetyn tekniikan ja ALD-tekniikan osoitettiin olevan hyvin käyttökelpoisia käänteisviritteisten kalvojen valmistuksessa. Lasimateriaaleilla tutkitun seostusmenetelmän osoitettiin olevan lupaava menetelmä erilaisten luminoivien kiteisten materiaalien lisäämisessä lasiin

Behavioral synthesis from VHDL using structured modeling

This dissertation describes work in behavioral synthesis involving the development of a VHDL Synthesis System VSS which accepts a VHDL behavioral input specification and performs technology independent synthesis to generate a circuit netlist of generic components. The VHDL language is used for input and output descriptions. An intermediate representation which incorporates signal typing and component attributes simplifies compilation and facilitates design optimization.A Structured Modeling methodology has been developed to suggest standard VHDL modeling practices for synthesis. Structured modeling provides recommendations for the use of available VHDL description styles so that optimal designs will be synthesized.A design composed of generic components is synthesized from the input description through a process of Graph Compilation, Graph Criticism, and Design Compilation. Experiments were performed to demonstrate the effects of different modeling styles on the quality of the design produced by VSS. Several alternative VHDL models were examined for each benchmark, illustrating the improvements in design quality achieved when Structured Modeling guidelines were followed

Determination of charge transfer dynamics and efficiency in solar cells sensitized with carbazole, indoline and triphenylamine dyes

Wydział FizykiNiniejsza praca została poświęcona badaniom dynamiki procesów transferu ładunku zachodzących w ogniwach słonecznych sensybilizowanych barwnikiem (ang. Dye Sensitized Solar Cells – DSSC), zawierających wysoko wydajne barwniki karbazolowe, indolinowe i trifenylaminowe. W opublikowanych artykułach, wchodzących w skład cyklu stanowiącego przedmiot tej rozprawy, opisaliśmy, jak różnorodne modyfikacje, stosowane w celu poprawienia funkcjonowania ogniw, wpływają na ultraszybkie i szybkie procesy transferu ładunku oraz jak dynamika poszczególnych procesów związana jest z całościowym funkcjonowaniem ogniw. W celu uzyskania informacji o dynamice procesów transferu ładunku, ich wydajności oraz o powiązaniu tych cech z parametrami fotowoltaicznymi ogniw, wykorzystano szeroki zakres technik eksperymentalnych, obejmujący podstawową charakterystykę fotowoltaiczną i różnorodne metody stacjonarnej i czasowo rozdzielczej spektroskopii optycznej. Część wstępna (rozdziały 1 – 4) zawiera wprowadzenie opisujące stan wiedzy na temat układów DSSC. Praca zawiera również dokładne objaśnienie metodyki wytwarzania ogniw DSSC jak również opis najważniejszych technik wykorzystanych do ich badań. Publikacje naukowe, wchodzące w skład niniejszej pracy, podsumowane zostały w rozdziale piątym i zamieszczone za rozdziałem nr 6, gdzie podsumowano konkluzje pracy.The main concern of this thesis is the dynamics of charge transfer processes occurring in Dye Sensitized Solar Cells (DSSC) comprising a top efficient carbazole, indoline and triphenylamine dyes. This dissertation is based on a series of papers reporting the effects of different modifications applied to improve DSSCs on ultrafast and fast charge transfer processes and relation between the dynamics of particular charge transfer phenomena and the overall DSSC performance. In order to gain the information on the dynamics of charge transfer processes, their efficiency and relationship with the overall photovoltaic performance of studied devices, a broad range of experimental techniques was applied, including basic photovoltaic characterization methods, electrochemical impedance spectroscopy, and a variety of stationary and time resolved optical spectroscopy methods. The opening part of the dissertation (chapters 1 – 4) provides an introduction to the current state of knowledge on DSSC. Subsequently, main experimental methods including fabrication and key characterization techniques used for purposes of this thesis are thoroughly described. The scientific papers making the basis of this thesis are described in chapter 5 and attached after chapter 6 presenting the conclusions.I kindly acknowledge the financial support from the Polish National Science Centre under project 2015/18/E/ST4/00196

Design of Hardware with Quantifiable Security against Reverse Engineering

Semiconductors are a 412 billion dollar industry and integrated circuits take on important roles in human life, from everyday use in smart-devices to critical applications like healthcare and aviation. Saving today\u27s hardware systems from attackers can be a huge concern considering the budget spent on designing these chips and the sensitive information they may contain. In particular, after fabrication, the chip can be subject to a malicious reverse engineer that tries to invasively figure out the function of the chip or other sensitive data. Subsequent to an attack, a system can be subject to cloning, counterfeiting, or IP theft. This dissertation addresses some issues concerning the security of hardware systems in such scenarios. First, the issue of privacy risks from approximate computing is investigated in Chapter 2. Simulation experiments show that the erroneous outputs produced on each chip instance can reveal the identity of the chip that performed the computation, which jeopardizes user privacy. The next two chapters deal with camouflaging, which is a technique to prevent reverse engineering from extracting circuit information from the layout. Chapter 3 provides a design automation method to protect camouflaged circuits against an adversary with prior knowledge about the circuit\u27s viable functions. Chapter 4 provides a method to reverse engineer camouflaged circuits. The proposed reverse engineering formulation uses Boolean Satisfiability (SAT) solving in a way that incorporates laser fault injection and laser voltage probing capabilities to figure out the function of an aggressively camouflaged circuit with unknown gate functions and connections. Chapter 5 addresses the challenge of secure key storage in hardware by proposing a new key storage method that applies threshold-defined behavior of memory cells to store secret information in a way that achieves a high degree of protection against invasive reverse engineering. This approach requires foundry support to encode the secrets as threshold voltage offsets in transistors. In Chapter 6, a secret key storage approach is introduced that does not rely on a trusted foundry. This approach only relies on the foundry to fabricate the hardware infrastructure for key generation but not to encode the secret key. The key is programmed by the IP integrator or the user after fabrication via directed accelerated aging of transistors. Additionally, this chapter presents the design of a working hardware prototype on PCB that demonstrates this scheme. Finally, chapter 7 concludes the dissertation and summarizes possible future research

Graph theory applied to neuroimaging data reveals key functional connectivity alterations in brain of behavioral variant Frontotemporal Dementia subjects

Brain functional architecture and anatomical structure have been intensively studied to generate efficient models of its complex mechanisms. Functional alterations and cognitive impairments are the most investigated aspects in the recent clinical research as distinctive traits of neurodegeneration. Although specific behaviours are clearly associated to neurodegeneration, information flow breakdown within the brain functional network, responsible to deeply affect cognitive skills, remains not completely understood. Behavioural variant Frontotemporal Dementia (bvFTD) is the most common type of Frontotemporal degeneration, marked by behavioural disturbances, social instabilities and impairment of executive functions. Mathematical modelling offers effective tools to inspect deviations from physiological cognitive functions and connectivity alterations. As a popular recent methodology, graph theoretical approaches applied to imaging data expanded our knowledge of neurodegenerative disorders, although the need for unbiased metrics is still an open issue. In this thesis, we propose an integrated analysis of functional features among brain areas in bvFTD patients, to assess global connectivity and topological network alterations respect to the healthy condition, using a minimum spanning tree (MST) based-model to resting state functional MRI (rs-fMRI) data. Contrary to several graph theoretical approaches, dependent to arbitrary criteria (e.g., correlation thresholds, network density or a priori distribution), MST represents an unambiguous modelling solution, ensuring full reproducibility and robustness in different conditions. Our MSTs were obtained from wavelet correlation matrices derived from mean time series intensities, extracted from 116 regions of interest (ROIs) of 41 bvFTD patients and 39 healthy controls (HC), which underwent rs-fMRI. The resulting graphs were tested for global connectivity and topological differences between the two groups, by applying a Wilcoxon rank sum test with a significance level at 0.05 (nonparametric median difference estimates with 95% confidence interval). The same test was applied for methodological comparison between MST and other common graph theory methods. After methodological comparisons, our MST model achieved the best bvFTD/HC separation performances, without a priori assumptions. Direct MST comparison between bvFTD and healty controls revealed key brain functional architecture differences. Diseased subjects showed a linear-shape network configuration tendency, with high distance between nodes, low centrality parameter values, and a low exchange information capacity (i.e., low network integration) in MST parameters. Moreover, edge-level and node-level features (i.e., superhighways, and node degree and betweenness centrality) indicated a more complex scenario, showing some of the key bvFTD dysfunctions observed in large scale resting-state functional networks (default-mode (DMN), salience (SN), and executive (EN) networks), suggesting an underlying involvement of the limbic system in the observed functional deterioration. Functional isolation has been observed as a generalized process affecting the entire bvFTD network, showing brain macro-regions isolation, with homogeneous functional distribution of brain areas, longer distances between hubs, and longer within-lobe superhighways. Conversely, the HC network showed marked functional integration, where superhighways serve as shortcuts to connect areas from different brain macro-regions. The combination of this theoretical model with rs-fMRI data constitutes an effective method to generate a clear picture of the functional divergence between bvFTD and HCs, providing possible insights on the effects of frontotemporal neurodegeneration and compensatory mechanisms underlying characteristic bvFTD cognitive, social, and executive impairments

FUNDAMENTAL STUDIES OF SURFACTANT TEMPLATED METAL OXIDE MATERIALS SYNTHESIS AND TRANSFORMATION FOR ADSORPTION AND ENERGY APPLICATIONS

This work addresses fundamental aspects of designing templates and curing conditions for the synthesis of mesoporous metal oxide thin films. The first section addresses selection of cationic-carbohydrate surfactant mixtures to synthesize templated silica thin films for selective adsorption of simple carbohydrates based on molecular imprinting. Nuclear magnetic resonance and fluorescence spectroscopy results suggest a novel structure for mixtures of alkyl glucopyranosides or xylopyranosides with cationic (trimethylammonium) surfactants. Despite thermodynamically favorable mixing, the carbohydrate headgroups in the mixed micelle adopt an inverted configuration with their headgroups in the micelle core, and therefore are inaccessible for molecular imprinting. This orientation occurs even when the alkyl tail length of the carbohydrate surfactant is greater than that of the cationic surfactant, but this limitation can be overcome by introducing a triazole linker to the carbohydrate surfactant. The next section addresses the effects of aging conditions on the structural and chemical evolution of surfactant templated silica thin films. The third section describes the synthesis of carbohydrate/cationic surfactant imprinted silica thin films with orthogonally oriented cylindrical pores by modifying the glass surface with a random copolymer. The last part of the dissertation addresses the effect of pore orientation on the transformation mechanism of block copolymer templated titania thin films during high temperature curing. Mesoporous titania thin films can be used for photochemical and solar cell applications, but doing so requires addressing the tradeoff between loss of mesostructural order and growth of crystallinity during thermal treatment. By using advanced x-ray scattering techniques it has been shown that the titania films with vertically oriented pores can better withstand the anisotropic stress that develops during thermal treatment compare to titania films with mixed pore orientation. For instance, films with parallel or mixed pores can only be heated at 400 °C for a brief time (~10 min) without loss of order, while orthogonally oriented films can be heated at 550 °C or greater for extended time periods (on the order of hours) without significant loss of long-range mesopore structure. Detailed kinetic modeling was applied to enable the comparison of activation energy for mesostructure loss in films as a function of pore orientation and thickness