Metal oxide semiconductor nanomembrane-based soft unnoticeable multifunctional electronics for wearable human-machine interfaces

Wearable human-machine interfaces (HMIs) are an important class of devices that enable human and machine interaction and teaming. Recent advances in electronics, materials, and mechanical designs have offered avenues toward wearable HMI devices. However, existing wearable HMI devices are uncomfortable to use and restrict the human body's motion, show slow response times, or are challenging to realize with multiple functions. Here, we report sol-gel-on-polymer-processed indium zinc oxide semiconductor nanomembrane-based ultrathin stretchable electronics with advantages of multifunctionality, simple manufacturing, imperceptible wearing, and robust interfacing. Multifunctional wearable HMI devices range from resistive random-access memory for data storage to field-effect transistors for interfacing and switching circuits, to various sensors for health and body motion sensing, and to microheaters for temperature delivery. The HMI devices can be not only seamlessly worn by humans but also implemented as prosthetic skin for robotics, which offer intelligent feedback, resulting in a closed-loop HMI system

SiOx-based resistive switching memory integrated in nanopillar structure fabricated by nanosphere lithography

textA highly compact, one diode-one resistor (1D-1R) SiOx-based resistive switching memory device with nano-pillar architecture has been achieved for the first time using nano-sphere lithography. The average nano-pillar height and diameter are 1.3 μm and 130 nm, respectively. Low-voltage electroforming using DC bias and AC pulse response in the 50ns regime demonstrate good potential for high-speed, low-energy nonvolatile memory. Nano-sphere deposition, oxygen-plasma isolation, and nano-pillar formation by deep-Si-etching are studied and optimized for the 1D-1R configurations. Excellent electrical performance, data retention and the potential for wafer-scale integration are promising for future non-volatile memory applications.Materials Science and Engineerin

Processos de condução eletrónica em células de memória ReRAM do tipo VCM com óxidos metálicos

New applications, such as neuromorphic computing, and the limitations of current semiconductor technologies demand a revolution in electronic devices. As one of the key enablers of a new electronics paradigm, redox-based resistive switching random access memory (ReRAM) has been the focus of much research and development. Among the ReRAM research community, Ta2O5 has emerged as one of the most popular materials, for enabling high endurance and high switching speed. Ta2O5-based ReRAM rely on the nonvolatile change of the resistance via the modulation of the oxygen content in conductive filaments, as it is described in the valence change mechanism. However, the filaments’ structure and exact composition are currently under intense debate, which hinders the development of better device design rules. The two current models in the literature consider filaments composed of oxygen vacancies and those containing metallic Ta. This work attempts to solve this dispute by reporting a detailed study of the electrical transport through the conductive filaments inside Ta2O5-based ReRAM. In parallel, the electrical transport and structure of substoichiometric TaOx thin films, grown to try and match the material of the filaments, was studied in detail. A strong correlation between the transport mechanisms in the conductive filaments inside the Ta2O5 ReRAM and in the TaOx thin films with x 1 was found. This clearly links the physical properties of the materials composing the filaments and the substoichiometric TaOx thin films. Structural analysis performed on the TaOx films reveals the presence of Ta clusters inside the films. Moreover, the electrical transport of metallic Ta films shows the same transport mechanism as TaOx with x 1, for most of the measured temperature range, from 2 K to 300 K. Beyond the transport mechanisms, both cases share a carrier concentration on the order of 1022 cm−3 and a positive magnetoresistance associated with weak antilocalization at T < 30 K. Therefore, it is concluded that the transport in the TaOx films with x 1 is dominated by a percolation chain of Ta clusters embedded in an insulating Ta2O5 matrix. These clusters exhibit disordered metal-like behaviour, where quantum corrections to the Boltzmann transport dominate the conduction. In conclusion, the electrical transport in the conductive filaments inside Ta2O5-based ReRAM devices is determined by percolation through Ta clusters, which is in line with independent observations of metallic Ta in the filaments. This work strongly supports the metallic Ta filament model.Novas aplicações, tais como computação neuromórfica, e as limitações da tecnologia de semicondutores atual exigem uma revolução nos dispositivos eletrónicos. Sendo uma peça chave para um novo paradigma da eletrónica, a memória ReRAM (redox-based resistive switching random access memory) tem sido alvo de muita investigação e desenvolvimento. O Ta2O5 é um dos materiais mais populares para usar em dispositivos ReRAM, permitindo alta durabilidade e velocidades de comutação elevadas. As ReRAM com Ta2O5 baseiam-se na mudança não volátil da resistência elétrica através da modulação da quantidade de oxigénio em filamentos condutores, como é descrito no mecanismo de alteração de valência (valence change mechanism). No entanto, a estrutura dos filamentos e a sua composição química exata, são ainda alvo de intenso debate, limitando o desenvolvimento de melhores receitas de fabricação de dispositivos. Os dois modelos atuais na literatura consideram filamentos compostos por lacunas de oxigénio e filamentos com Ta metálico. Este trabalho procura resolver esta disputa ao reportar um estudo detalhado do transporte elétrico através de filamentos condutores em dispositivos ReRAM de Ta2O5. Paralelamente, foi estudado em detalhe o transporte elétrico e a estrutura de filmes finos de TaOx subestequiométrico, depositados de forma a emular o material dos filamentos. Foi encontrada uma forte correlação entre os mecanismos de transporte nos filamentos condutores dentro dos dispositivos ReRAM de Ta2O5 e nos filmes finos de TaOx com x 1. Isto estabelece uma ligação clara entre as propriedades físicas dos materiais que compõem tanto os filamentos como os filmes finos de TaOx. A análise estrutural efetuada nos filmes de TaOx revela a presença de aglomerados de Ta. Por outro lado, o transporte elétrico em filmes finos de Ta é dominado pelos mesmos mecanismos de condução observados nos filmes de TaOx com x 1, para a maior parte da gama de temperatura de 2 K a 300 K. Ambos os casos partilham ainda uma concentração de portadores da ordem de 1022 cm−3 e uma magnetoresistência positiva associada a anti-localização fraca para T < 30 K. Portanto, é concluído que o transporte em filmes de TaOx com x 1 é dominado por uma cadeia de percolação de aglomerados de Ta embutidos numa matriz isoladora de Ta2O5. Estes aglomerados exibem um comportamento típico de metais desordenados, para os quais a condução é dominada por correções quânticas ao transporte de Boltzmann. Em conclusão, o transporte elétrico em filamentos condutores dentro de dispositivos ReRAM baseados em Ta2O5 é dominado pela percolação de aglomerados de Ta, o que corrobora observações independentes de Ta metálico nos filamentos. Assim, este trabalho suporta o modelo baseado no filamento metálico de Ta.Programa Doutoral em Engenharia Físic

Fabrication and Pseudo-Analog Characteristics of Ta2O5 -Based ReRAM Cell

Memristori on yksi elektroniikan peruskomponenteista vastuksen, kondensaattorin ja kelan lisäksi. Se on passiivinen komponentti, jonka teorian kehitti Leon Chua vuonna 1971. Kesti kuitenkin yli kolmekymmentä vuotta ennen kuin teoria pystyttiin yhdistämään kokeellisiin tuloksiin. Vuonna 2008 Hewlett Packard julkaisi artikkelin, jossa he väittivät valmistaneensa ensimmäisen toimivan memristorin. Memristori eli muistivastus on resistiivinen komponentti, jonka vastusarvoa pystytään muuttamaan. Nimens mukaisesti memristori kykenee myös säilyttämään vastusarvonsa ilman jatkuvaa virtaa ja jännitettä. Tyypillisesti memristorilla on vähintään kaksi vastusarvoa, joista kumpikin pystytään valitsemaan syöttämällä komponentille jännitettä tai virtaa. Tämän vuoksi memristoreita kutsutaankin usein resistiivisiksi kytkimiksi. Resistiivisiä kytkimiä tutkitaan nykyään paljon erityisesti niiden mahdollistaman muistiteknologian takia. Resistiivisistä kytkimistä rakennettua muistia kutsutaan ReRAM-muistiksi (lyhenne sanoista resistive random access memory). ReRAM-muisti on Flash-muistin tapaan haihtumaton muisti, jota voidaan sähköisesti ohjelmoida tai tyhjentää. Flash-muistia käytetään tällä hetkellä esimerkiksi muistitikuissa. ReRAM-muisti mahdollistaa kuitenkin nopeamman ja vähävirtaiseman toiminnan Flashiin verrattuna, joten se on tulevaisuudessa varteenotettava kilpailija markkinoilla. ReRAM-muisti mahdollistaa myös useammin bitin tallentamisen yhteen muistisoluun binäärisen (”0” tai ”1”) toiminnan sijaan. Tyypillisesti ReRAM-muistisolulla on kaksi rajoittavaa vastusarvoa, mutta näiden kahden tilan välille pystytään mahdollisesti ohjelmoimaan useampia tiloja. Muistisoluja voidaan kutsua analogisiksi, jos tilojen määrää ei ole rajoitettu. Analogisilla muistisoluilla olisi mahdollista rakentaa tehokkaasti esimerkiksi neuroverkkoja. Neuroverkoilla pyritään mallintamaan aivojen toimintaa ja suorittamaan tehtäviä, jotka ovat tyypillisesti vaikeita perinteisille tietokoneohjelmille. Neuroverkkoja käytetään esimerkiksi puheentunnistuksessa tai tekoälytoteutuksissa. Tässä diplomityössä tarkastellaan Ta2O5 -perustuvan ReRAM-muistisolun analogista toimintaa pitäen mielessä soveltuvuus neuroverkkoihin. ReRAM-muistisolun valmistus ja mittaustulokset käydään läpi. Muistisolun toiminta on harvoin täysin analogista, koska kahden rajoittavan vastusarvon välillä on usein rajattu määrä tiloja. Tämän vuoksi toimintaa kutsutaan pseudoanalogiseksi. Mittaustulokset osoittavat, että yksittäinen ReRAM-muistisolu kykenee binääriseen toimintaan hyvin. Joiltain osin yksittäinen solu kykenee tallentamaan useampia tiloja, mutta vastusarvoissa on peräkkäisten ohjelmointisyklien välillä suurta vaihtelevuutta, joka hankaloittaa tulkintaa. Valmistettu ReRAM-muistisolu ei sellaisenaan kykene toimimaan pseudoanalogisena muistina, vaan se vaati rinnalleen virtaa rajoittavan komponentin. Myös valmistusprosessin kehittäminen vähentäisi yksittäisen solun toiminnassa esiintyvää varianssia, jolloin sen toiminta muistuttaisi enemmän pseudoanalogista muistia.The memristor is one of the fundamental circuit elements in addition to a resistor, capacitor and an inductor. It is a passive component whose theory was postulated by Leon Chua in 1971. It took over 30 years before any known physical examples were discovered. In 2008 Hewlett Packard published an article where they manufactured a device which they claimed to be the first memristor found. The memristor, which is a concatenation of memory resistor, is a resistive component that has an ability to change its resistance. It can also remember its resistance value without continuous current or voltage. Typically, a memristor has at least two resistance states that can be altered. This is the reason why memristors are also called resistive switches. Resistive switches can be used in memory technologies. A memory array that has been built using resistive switches is called ReRAM (resistive random access memory). ReRAM, like Flash memory, is a non-volatile memory that can be programmed or erased electrically. Flash memories are currently used e.g. in memory sticks. However, compared to Flash, ReRAM has faster operating speed and lower power consumption, for instance. It could potentially replace current memory standards in future. A ReRAM memory cell can also store multiple bits instead of binary operation (”0” or ”1”). Typically there exists multiple intermediate resistance states between ReRAM’s limiting resistances that could be utilized. Such memory could be called analog, if the amount of intermediate states is not limited to discrete levels. Analog memories make it possible to build artificial neural networks (ANN) efficiently, for instance. ANNs try to model the behaviour of brain and to perform tasks that are difficult for traditional computer programs such as speech recognition or artificial intelligence. This thesis studies the analog behaviour of Ta 2 O 5 -based ReRAM cell. Manufacturing process and measurement results are presented. The operation of ReRAM cell is rarely fully analog as there exists limited amount of intermediate resistance states. This is the reason why operation is called pseudo-analog. Measurement results show that a single ReRAM cell is suitable for binary operation. In some cases, a single cell can store multiple resistance values but there exists significant variance in resistance states between subsequent programming cycles. The proposed ReRAM cell cannot operate as pseudo-analog ReRAM cell in itself as it needs an external current limiting component. Improving the manufacturing process should reduce the variability such that the operation would be more like a pseudo-analog memory.Siirretty Doriast

Resistive Switching in Silicon-rich Silicon Oxide

Over the recent decade, many different concepts of new emerging memories have been proposed. Examples of such include ferroelectric random access memories (FeRAMs), phase-change RAMs (PRAMs), resistive RAMs (RRAMs), magnetic RAMs (MRAMs), nano-crystal floating-gate flash memories, among others. The ultimate goal for any of these memories is to overcome the limitations of dynamic random access memories (DRAM) and flash memories. Non-volatile memories exploiting resistive switching – resistive RAM (RRAM) devices – offer the possibility of low programming energy per bit, rapid switching, and very high levels of integration – potentially in 3D. Resistive switching in a silicon-based material offers a compelling alternative to existing metal oxide-based devices, both in terms of ease of fabrication, but also in enhanced device performance. In this thesis I demonstrate a redox-based resistive switch exploiting the formation of conductive filaments in a bulk silicon-rich silicon oxide. My devices exhibit multi-level switching and analogue modulation of resistance as well as standard two-level switching. I demonstrate different operational modes (bipolar and unipolar switching modes) that make it possible to dynamically adjust device properties, in particular two highly desirable properties: non-linearity and self-rectification. Scanning tunnelling microscopy (STM), atomic force microscopy (AFM), and conductive atomic force microscopy (C-AFM) measurements provide a more detailed insight into both the location and the dimensions of the conductive filaments. I discuss aspects of conduction and switching mechanisms and we propose a physical model of resistive switching. I demonstrate room temperature quantisation of conductance in silicon oxide resistive switches, implying ballistic transport of electrons through a quantum constriction, associated with an individual silicon filament in the SiOx bulk. I develop a stochastic method to simulate microscopic formation and rupture of conductive filaments inside an oxide matrix. I use the model to discuss switching properties – endurance and switching uniformity

Resistive switching devices with improved control of oxygen vacancies dynamics

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

Growth and Oxidation of Graphene and Two-Dimensional Materials for Flexible Electronic Applications

The non-volatile storage of information is becoming increasingly important in our data-driven society. Limitations in conventional devices are driving the research and development of incorporating new materials into conventional device architectures to improve performance, as well as developing an array of emerging memory technologies based on entirely new physical processes. The discovery of graphene allowed for developing new approaches to these problems, both itself and as part of the larger, and ever-expanding family of 2D materials. In this thesis the growth and oxidation of these materials is investigated for implementing into such devices, exploiting some of the unique properties of 2D materials including atomic thinness, mechanical flexibility and tune-ability through chemical modification - to meet some challenges facing the community. This begins with the growth of graphene by chemical vapour deposition for a high quality flexible electrode material, followed by oxidation of graphene for use in resistive memory devices. The theme of oxidation is then extended to another 2D material, HfS2, which is selectively oxidised for use as high-k dielectric in Van der Waals heterostructures for FETs and resistive memory devices. Lastly, a technique for fabrication of graphene-based devices directly on the copper growth substrate is demonstrated for use in flexible devices for sensing touch and humidity

Advancements Towards Single Site Information Storage and Processing Using HfO2 Resistive Random Access Memory (ReRAM)

Resistive Random Access Memory (ReRAM) has attracted much attention among researchers due to its fast switching speeds, lower switching voltages, and feasible integration into industry compatible CMOS processing. These characteristics make ReRAM a viable candidate for next-generation Non- Volatile Memory. Transition-Metal-Oxides have been proven to be excellent materials for ReRAM applications. This work investigates the effect of various, post-deposition anneals (PDA) on the switching parameters of Ni/Cu/HfO2/TiN Resistive Memory Devices (RMD). Results are presented in the form of a Small Business Innovation Research (SBIR) grant proposal. The use of the SBIR format emphasizes understanding of the experimental design, commercial viability, and broader impacts of ReRAM technology