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Solution-based Metal Oxide Semiconductor Memristor
Publication . Martins, Raquel Azevedo; Kiazadeh, Asal; Carlos, Emanuel
Solution-based memristors have shown a great potential to fulfill several requirements of the Internet of Things (IoT) such as, high density and ultra-low power devices by using low-cost and simple fabrication methods. In this work, solution-processed indium-gallium-zinc oxide (IGZO) thin films are produced using a combustion synthesis process. To improve their performance in memristor devices different parameters are studied: the variation of molar proportion, number of deposited layers and annealing temperature. Memristors with higher number of layers and annealing temperatures show low operating voltage, good endurance, great yield, and retention up to 105 s in air environment conditions. The best condition reached was IGZO (1:3:1) memristor with 7 deposited layers annealed at 300 ºC. These devices can be programmed in a multi-level cell operation mode, up to 8 different resistive states. Furthermore, the same devices show promising features for neuromorphic computing applications since they can emulate the plasticity of a synaptic junction by replicating potentiation and depression. The results achieved are quite promising and even in some cases surpass the current state of the art.
Recent progress in optoelectronic memristors for neuromorphic and in-memory computation
Publication . Pereira, Maria Elias; Martins, Rodrigo; Fortunato, Elvira; Barquinha, Pedro; Kiazadeh, Asal; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; Institute of Physics
Neuromorphic computing has been gaining momentum for the past decades and has been appointed as the replacer of the outworn technology in conventional computing systems. Artificial neural networks (ANNs) can be composed by memristor crossbars in hardware and perform in-memory computing and storage, in a power, cost and area efficient way. In optoelectronic memristors (OEMs), resistive switching (RS) can be controlled by both optical and electronic signals. Using light as synaptic weigh modulator provides a high-speed non-destructive method, not dependent on electrical wires, that solves crosstalk issues. In particular, in artificial visual systems, OEMs can act as the artificial retina and combine optical sensing and high-level image processing. Therefore, several efforts have been made by the scientific community into developing OEMs that can meet the demands of each specific application. In this review, the recent advances in inorganic OEMs are summarized and discussed. The engineering of the device structure provides the means to manipulate RS performance and, thus, a comprehensive analysis is performed regarding the already proposed memristor materials structure and their specific characteristics. Moreover, their potential applications in logic gates, ANNs and, in more detail, on artificial visual systems are also assessed, taking into account the figures of merit described so far.
Nanoscale Memristor: Great potential for memory and synapse emulator for computing applications
Publication . Luís, Joana Cristina Marques; Deuermeier, Jonas; Kiazadeh, Asal
This work reports the fabrication and electrical characterization of Metal-Insulator-Metal (MIM) devices for neuromorphic applications using zinc-tin-oxide (ZTO) and indium-gallium-zinc-oxide (IGZO) as the switching layers and molybdenum (Mo) for the devices ‘contacts. A lithographic mask was used along with physical vapor deposition (PVD) processes for the production of the different samples’ layers. Using ZTO as a switching layer in order to replace other elements that are becoming scarce such as indium or gallium is of relevant importance, therefore it was first attempted a ZTO based MIM device.
Upon electrical characterization the ZTO devices show an analog behavior without the need of current compliance (being therefore self-limited), good multilevel storage property, reliability and a stable state retention for long periods of time. It is suspected a 2D type of switching mechanism, based on the tunneling through a Schottky barrier at the interface, however the details of the exact mechanism aren’t yet clear. Furthermore, the device is highly prone to interact with humidity present in the atmosphere and some fabrication steps, which is a possible explanation for the anticlockwise RESET.
A second batch of ZTO devices was fabricated in order to remediate the RESET process, using a passivation step, however the RESET direction wasn’t affected although the rectification properties of the devices were enhanced.
Since upon pulse testing the ZTO devices behaved erratically, this switching layer was discarded and IGZO used instead. With this alternative amorphous oxide semiconductor material, the symmetry and linearity of the conductance change was evaluated and transition from STP (Short-Term Potentiation) to LTP (Long-Term Potentiation) successfully demonstrated upon pulse repetition, showing similar decay fashion to human memory, following a Kohlrausch-Williams-Watts function (commonly called “stretched-exponential function”).
Low-temperature amorphous oxide semiconductors for thin-film transistors and memristors: physical insights and applications
Publication . Martins, Jorge de Souto; Barquinha, Pedro; Kiazadeh, Asal; Goes, João
While amorphous oxides semiconductors (AOS), namely InGaZnO (IGZO), have found market application in the display industry, their disruptive properties permit to envisage for more advanced concepts such as System-on-Panel (SoP) in which AOS devices could be used for addressing (and readout) of sensors and displays, for communication, and even for memory as oxide memristors are candidates for the next-generation memories. This work concerns the application of AOS for these applications considering the low thermal budgets (< 180 °C) required for flexible, low cost and alternative substrates. For maintaining low driving voltages, a sputtered multicomponent/multi-layered high-κ dielectric (Ta2O5+SiO2) was developed for low temperature IGZO TFTs which permitted high performance without sacrificing reliability and stability. Devices’ performance under temperature was investigated and the bias and temperature dependent mobility was modelled and included in TCAD simulation. Even for IGZO compositions yielding very high thermal activation, circuit topologies for counteracting both this and the bias stress effect were suggested. Channel length scaling of the devices was investigated, showing that operation for radio frequency identification (RFID) can be achieved without significant performance deterioration from short channel effects, which are attenuated by the high-κ dielectric, as is shown in TCAD simulation. The applicability of these devices in SoP is then exemplified by suggesting a large area flexible radiation sensing system with on-chip clock-generation, sensor matrix addressing and signal read-out, performed by the IGZO TFTs. Application for paper electronics was also shown, in which TCAD simulation was used to investigate on the unconventional floating gate structure. AOS memristors are also presented, with two distinct operation modes that could be envisaged for data storage or for synaptic applications. Employing typical TFT methodologies and materials, these are ease to integrate in oxide SoP architectures.
Characterization and modeling of resistive switching phenomena in IGZO devices
Publication . Carvalho, G.; Pereira, M. E.; Silva, C.; Deuermeier, J.; Kiazadeh, A.; Tavares, V.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; AIP - American Institute of Physics
This study explores the resistive switching phenomena present in 4 μm2 amorphous Indium-Gallium-Zinc Oxide (IGZO) memristors. Despite being extensively reported in the literature, not many studies detail the mechanisms that dominate conduction on the different states of IGZO-based devices. In this article, we demonstrate that resistive switching occurs due to the modulation of the Schottky barrier present at the bottom interface of the device. Furthermore, thermionic field emission and field emission regimes are identified as the dominant conduction mechanisms at the high resistive state of the device, while the bulk-limited ohmic conduction is found at the low resistive state. Due to the high complexity associated with creating compact models of resistive switching, a data-driven model is drafted taking systematic steps.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
3599-PPCDT
Número da atribuição
PTDC/NAN-MAT/30812/2017