Salvador Dueñas

• PhD
• Professor (Full) at University of Valladolid

Reliable data storage technologies able to operate at cryogenic temperatures are critical to implement scalable quantum computers and develop deep-space exploration systems, among other applications. Their scarce availability is pushing towards the development of emerging memories that can perform such storage in a non-volatile fashion. Resistive R...

Over the past decades, the demand for semiconductor memory devices has been steadily increasing, and is currently experiencing an unprecedented boost due to the development and expansion of artificial intelligence. Among emerging high-density non-volatile memories, resistive random-access memory (RRAM) is one of the best recourses for all kind of a...

The effort made in recent years in the development of new memories has led to a significant advance in emerging technologies, which have proven their usefulness not only in the field of memories, but also to obtain devices that perform an artificial synapse and thus emulate biological neurons. Among the novel concepts, resistive-switching random ac...

In this study, the resistive switching phenomena in TiN/Ti/HfO2/Ti metal–insulator–metal stacks is investigated, mainly focusing on the analysis of set and reset transitions. The electrical measurements in a wide temperature range reveal that the switching transitions require less voltage (and thus, less energy) as temperature rises, with the reset...

Memristive devices have shown a great potential for non-volatile memory circuits and neuromorphic computing. For both applications it is essential to know the physical mechanisms behind resistive switching; in particular, the time response to external voltage signals. To shed light in these issues we have studied the role played by the applied volt...

TiN/Ti/HfO 2 /Pt resistive switching devices have been fabricated, measured, and modeled. After programming the devices in the low resistance state, the current–voltage characteristic below the reset switching voltage was measured at different temperatures (from 90 to 350 K). A weak but complex temperature dependence was obtained for several voltag...

A new model to account for variability in resistive memories is presented. It is included in a previous general current model that considers the main physical mechanisms involved in the conductive filament formation and disruption processes that lead to different resistive states. The validity of the model has been proved for different technologies...

HfO2 and Fe2O3 thin films and laminated stacks were grown by atomic layer deposition at 350 °C from hafnium tetrachloride, ferrocene, and ozone. Nonlinear, saturating, and hysteretic magnetization was recorded in the films. Magnetization was expectedly dominated by increasing the content of Fe2O3. However, coercive force could also be enhanced by t...

An in-depth simulation and experimental study has been performed to analyze thermal effects on the variability of resistive memories. Kinetic Monte Carlo (kMC) simulations, that reproduce well the nonlinearity and stochasticity of resistive switching devices, have been employed to explain the experimental results. The series resistance and the tran...

Memristors were proposed in the early 1970s by Leon Chua as a new electrical element linking charge to flux. Since that first introduction, these devices have positioned themselves to be considered as possible fundamental ones for the generations of electronic devices to come. In this paper, we propose a new way to investigate the effects of the el...

In this work, we have studied the control of set and the reset transitions in TiN/Ti/HfO2/W resistive switching devices using a new approach based on the injection of a limited amount of charge through the use of a capacitor discharge. Instead of applying conventional voltage or current signals, the capacitor discharge through the devices is able t...

Memristors were proposed in the early ’70s of the XXth century by Leon Chua as a new electrical element linking the charge and the flux. Since that first introduction, these devices have positioned themselves to be considered as possibly fundamental for the new generations of electronic devices. It has to be mentioned that actual memristors have on...

In recent years, several materials and metal-insulator-metal devices are being intensively studied as prospective non-volatile memories due to their resistive switching effect. In this work, thickness-dependent resistive switching polarity was observed in TiN/Ti/HfO2/Pt structures as the sign of the voltages at which SET and RESET occur depended on...

Crystal structure and electrical properties of hafnium-praseodymium oxide thin films grown by atomic layer deposition on ruthenium substrate electrodes were characterized and compared with those of undoped HfO2 films. The HfO2 reference films crystallized in the stable monoclinic phase of HfO2. Mixing HfO2 and PrOx resulted in the growth of nanocry...

In the attempt to understand the behavior of HfO2-based resistive switching devices at low temperatures, TiN/Ti/HfO2/W metal–insulator–metal devices were fabricated; the atomic layer deposition technique was used to grow the high-k layer. After performing an electroforming process at room temperature, the device was cooled in a cryostat to carry ou...

Resistive switching (RS) devices are emerging electronic components that could have applications in multiple types of integrated circuits, including electronic memories, true random number generators, radiofrequency switches, neuromorphic vision sensors, and artificial neural networks. The main factor hindering the massive employment of RS devices...

The use of thin layers of amorphous hafnium oxide has been shown to be suitable for the manufacture of Resistive Random-Access memories (RRAM). These memories are of great interest because of their simple structure and non-volatile character. They are particularly appealing as they are good candidates for substituting flash memories. In this work,...

Resistive switching random access memories are being thoroughly studied as prospective non-volatile memories. In this paper, we report electrical characterization of HfO2:Al2O3based metal-insulator-metal structures devised using atomic layer deposition. Dependences of electrical behavior on HfO2:Al2O3 cycle ratio is studied. An explanation for the...

In this work, we have studied the set and the reset transitions in hafnium oxide-based metal-insulator-metal ReRAM devices using a capacitor discharge. Instead of applying a conventional voltage or current signal, we have discharged a capacitor through the devices to perform both transitions. In this way, both transitions are shown to be controllab...

Since two decades ago, research on resistive memories has continuosly grown, gathering relevance through the variety of different technologies that fit into the non-volatile memories’ area. In this study, we discuss the performance and electrical characteristics of RRAM cells constituted by MIM stacks with dielectric formed by Nb2O5-doped SiO2. We...

The use of thin layers of amorphous hafnium oxide has been shown to be suitable for the manufacture of Resistive Random Access memories (RRAM). These memories are of great interest because of their simple structure and non-volatile character. In this work, it was studied the performance of the MIM structure that takes part of a 4 kbit memory array...

In the search of materials with high charge storage densities to be used in the memory field, metal oxide perovskites such as lead zirconate titanate (PZT) result of particular interest due to its low leakage currents. Besides, ferroelectric PZT shows high remanent polarization. These properties make this material promising for high-speed and low-v...

Atomic layer deposition method was used to grow thin films consisting of ZrO2and MnO x layers. Magnetic and electric properties were studied of films deposited at 300 °C. Some deposition characteristics of the manganese(III)acetylacetonate and ozone process were investigated, such as the dependence of growth rate on the deposition temperature and f...

Thin HfO2 films were grown by atomic layer deposition on chemical vapor-deposited large-area graphene. The graphene was transferred, prior to the deposition of the HfO2 overlayer, to the HfO2 bottom dielectric layer pregrown on the Si/TiN substrate. Either HfCl4 or Hf[N(CH3)(C2H5)]4 was used as the metal precursor for the bottom layer. The O2 plasm...

The use of thin layers of amorphous hafnium oxide has been shown to be suitable for the manufacture of Resistive Random-Access memories (RRAM). These memories are of great interest because of their simple structure and non-volatile character. They are particularly appealing as they are good candidates for substituting flash memories. In this work,...

This work deals with the thermoelectric characterization of commercial lead zirconate titanate (PZT) based piezoelectric diaphragms. An in-depth analysis of the piezo- and ferroelectric behavior of the samples was carried out by measuring current voltage curves and polarization hysteresis cycles in a wide temperature range. We demonstrate that, as...

SiO2-Fe2O3 mixture films and nanolaminates were grown by atomic layer deposition from iron trichloride, hexakis(ethylamino)disilane, and ozone at 300 °C. Orthorhombic ɛ-Fe2O3 was identified in Fe2O3 reference films and in Fe2O3 layers grown to certain thicknesses between amorphous SiO2 layers. SiO2-Fe2O3 films could be magnetized in external fields...

Two-component crystalline thin film structures consisting of continuous ε-Fe2O3 bottom layers followed by top layers of BiOCl nanoflakes were grown using atomic layer deposition from FeCl3 and BiCl3 at 375 °C. Si(100) planar wafer, three-dimensional Si structures and conductive TiN/Si were exploited as substrates. Electrical measurements revealed t...

A crucial step in order to achieve fast and low-energy switching operations in resistive random access memory (RRAM) memories is the reduction of the programming pulse width. In this study, the incremental step pulse with verify algorithm (ISPVA) was implemented by using different pulse widths between 10 μs and 50 ns and assessed on Al-doped HfO2 4...

A new method to characterize the properties of leaky ferroelectric films is proposed. Double swing quiescent-current technique allows to obtain coercive field and remanent polarization in those cases in which high leakage, trap generation current and displacement current mask the ferroelectric terms themselves. Double swing quiescent-current techni...

The control of the intermediate conductance levels in HfO 2 -based MIM capacitors for neuromorphic applications is presented in this work. Using voltage or current control signals shows significant differences. The potentiation levels can be controlled in a linear way using current as control signal. These levels are achieved in very short times an...

Ferroelectric materials are very attractive for many technological applications. In the scenario of conventional CMOS technology, they are very suitable to fabricate nonvolatile memories (FeRAM) or as the gate stack of a transistor to realize a FeFET. Conventional ferroelectric materials, like PZT or SBT, exhibit very high permittivity and low coer...

Nowadays, there is an increasing interest in the fabrication of neuristors in which memristors are used to create a neuron-like behavior (1). Memristors based on resistive switching memories (RRAM) are promising candidates to implement artificial synaptic devices for their use in neuromorphic systems, due to their high number or reachable conductan...

Due to the high number of reachable conductance levels in resistive switching devices, they are good candidates to implement artificial synaptic devices. In this work, we have studied the control of the intermediate conductance levels in HfO2-based MIM capacitors using current pulses. The set transition can be controlled in a linear way using this...

Amorphous SiO2-Nb2O5 nanolaminates and mixture films were grown by atomic layer deposition. The films were grown at 300 oC from Nb(OC2H5)5, Si2(NHC2H5)6, and O3 to thicknesses ranging from 13 to 130 nm. The niobium to silicon atomic ratio was varied in the range of 0.11-7.20. After optimizing the composition, resistive switching properties could be...

In the attempt to control the polarity of the set and reset voltages in bipolar resistive switching capacitors, we have studied the switching properties of structures consisting of either two anti-series or two anti-parallel metal-insulator-metal capacitors. The capacitors were based on hafnium oxide, and W and TiN/Ti were used as bottom and top el...

In this work, we have characterized hafnium oxide based bipolar resistive switching memories (RRAM) by measuring the small-signal conductance. The samples under study exhibit a continuum of intermediate states which can be accurately controlled by means of adequate sequence of the applied stimulus. The experimental results are analyzed to obtain in...

RRAM devices are promising candidates to implement artificial synaptic devices for their use in neuromorphic systems, due to their high number or reachable conductance levels. The capacitors used in this work (TiN/Ti/ HfO 2 /W) show resistive switching behavior and reachable intermediate conductance states. We can control the conductance states by...

Nanolaminates of ZrO2 and Co3O4 were atomic layer deposited on silicon and titanium nitride at 300 °C. Films were confirmed to be polycrystalline in the as-deposited state, with the cubic phase dominating in both oxides. All films exhibited resistive switching characteristics and charge polarization and ferromagnetic behavior. Also, the relative pe...

A thorough study of the admittance of TiN/Ti/HfO2/W bipolar resistive memories [resistance random access memory (RRAM)] was carried out under different bias conditions and in a wide range of ac signal frequencies. We demonstrate that a continuum of intermediate states can be obtained by applying appropriate dc bias waveforms. Cumulative writing and...

Nanocrystalline HfO2:Al2O3 mixture films and nanolaminates were grown by atomic layer deposition at 350◦C from metal chloride precursors and water. Formation of metastable HfO2 polymorphs versus monoclinic phase was affected by the relative amount and thickness of constituent oxide layers. The films exhibited saturative magnetization and charge pol...

Atomic layer deposition method was employed to deposit thin films consisting of ZrO2 and HfO2. Zirconia films were doped with hafnia and vice versa, and also nanolaminates were formed. All depositions were carried out at 300◦C. Most films were crystalline in their as-deposited state. Zirconia exhibited the metastable cubic and tetragonal phases by...

Five-layer crystalline thin film structures were formed, consisting of ZrO2 and Co3O4 alternately grown on Si(100) substrates by atomic layer deposition at 300◦C using ZrCl4 and Co(acac)3 as the metal precursors and ozone as the oxygen precursor. The performance of the laminate films was dependent on the relative content of constituent oxide layers...

Thin mixed and nanolaminate films of ZrO2 and Al2O3 were grown by atomic layer deposition from the corresponding metal chlorides and water. The films were grown at 350◦C in order to ensure ZrO2 crystallization in the as-deposited state. The relative thicknesses of layers in the structure of the nanolaminates were controlled in order to maximize the...

Nowadays both the volatile and non-volatile memories are under a high development pressure in the current industrial context. Besides the dominant solid-state memory technologies, such as DRAM and FLASH, non-volatile resistive memories (RRAM) are considered adequate candidates to complement the memory landscape [1, 2]. In spite of the interest, no...

According to the 2014 International Technology Roadmap for Semiconductors (ITRS), resistive switching memories (RRAM) are well candidate for next generation nonvolatile memory. Their main properties are fast switching speed, good reliability, low power consumption and CMOS technology compatibility [1, 2], as well as potential scalability beyond NAN...

The γ-radiation effects on the electrical characteristics of metal–insulator-semiconductor capacitors based on HfO2, and on the resistive switching characteristics of the structures have been studied. The HfO2 was grown directly on silicon substrates by atomic layer deposition. Some of the capacitors were submitted to a γ ray irradiation using thre...

Intermediate-band semiconductors have attracted much attention for use in silicon-based solar cells and infrared detectors. In this work, n-Si substrates have been implanted with very high doses (10¹³ cm⁻² and 10¹⁴ cm⁻²) of vanadium, which gives rise to a supersaturated layer inside the semiconductor. However, the Mott limit was not exceeded. The e...

We describe the role of defects in the resistive switching behavior of metal–insulator–metal devices based on alternating Ta2O5 and TiO2 stacks. Ruthenium oxide (RuOx ) and platinum (Pt) were used as bottom and top electrodes, respectively. Insulator stacks with thickness of 5 nm were fabricated by atomic layer deposition of alternating Ta2O5 and T...

Thin solid films consisting of ZrO2 and Fe2O3 were grown by atomic layer deposition (ALD) at 400 °C. Metastable phases of ZrO2 were stabilized by Fe2O3 doping. The number of alternating ZrO2 and Fe2O3 deposition cycles were varied in order to achieve films with different cation ratios. The influence of annealing on the composition and structure of...

ZrO2 thin films were grown by atomic layer deposition using alternate surface reactions of ZrI4 and O3 precursors in the temperature range of 250–400°C to the thickness in the range of 5–100 nm. The films were dense, continuous, and consisted of mixed monoclinic and metastable polymorphs with significant contribution from cubic ZrO2. The ZrO2 films...

CoFe2O4 nanoparticles with 3–30 nm in diameter were synthesized by sol-gel method. The particles were spread as a solid discontinuous layer over planar silicon and TiN substrates by spin coating and covered by 15 nm thick ZrO2 films by atomic layer deposition. Crystal structures distinctively characteristic of CoFe2O4 and ZrO2 constituents were pre...

Mixed films of a high-permittivity oxide, Er2O3, and a magnetic material, Fe2O3, were grown by atomic layer deposition on silicon and titanium nitride at 375 °C using erbium diketonate, ferrocene, and ozone as precursors. Crystalline phases of erbium and iron oxides were formed. Growth into three-dimensional trenched structures was demonstrated. A...

Negative susceptance is experimentally measured in the low resistance state of TiN/Ti/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /W resistive RAM memories. A meminductive-like behavior appears along with the memristive effects. A detailed study of small-signal parameters measured at 0...

A new model to account for variability in resistive memories is presented. It is included in a previous general current model that considers the main physical mechanisms involved in the conductive filament formation and destruction processes that lead to different resistive states. The validity of the model has been proved for different technologie...

Similarly to the current, the admittance of TiN/Ti/HfO2/W-based resistive memories shows well-defined minor switching loops associated with partial transitions between the ON and OFF states. Excellent control of the intermediate states is achieved in these samples by means of a proper sequence of input signals and current compliances. It is shown t...

A new model to account for variability in resistive memories is presented. It is included in a previous general current model that considers the main physical mechanisms involved in the conductive filament formation and disruption processes that lead to different resistive states. The validity of the model has been proved for different technologies...

A model for filamentary conduction in RRAMs based on Metal-Insulator-Metal (MIM) structures has been developed. The model describes RRAM resistive switching processes by calculating the formation and rupture of conductive filaments (CFs) in the dielectric. The resistance of the electrodes, of the CF and the hopping current in the gap between the CF...

The electrical properties of Al 2 O 3 -based metal-insulator-semiconductor capacitors have been investigated. Three different metal gate electrodes were used: two mid-gap metals (TiN and tungsten) and aluminum, a metal with a work function close to the silicon electron affinity. Aluminum oxide films were grown on p-type silicon substrates by atomic...

A complete electrical characterization of hydrogenated amorphous silicon layers (a-Si:H) deposited on crystalline silicon (c-Si) substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD) was carried out. These structures are of interest for photovoltaic applications. Different growth temperatures between 30 and 200 °C were used...

High permittivity (high-k) dielectric films are of considerable interest as gate oxide materials in advanced complementary metal-oxide-semiconductor (CMOS), in metal-insulator-metal capacitors (MIM), and in dynamic and resistive random access memory devices as well. These materials need to be characterized and qualified prior to their inclusion on...

Ni/HfO2/Si ReRAM devices were extensively characterized. In the pristine state, they show adequate performance with low leakage currents and moderate interfacial state density. Leakage current is dominated by Poole-Frenkel mechanism. Activation energies of conduction processes and soft-optical phonons in the insulator bulk are 80 and 50 meV, respec...

Resistive switching conduction in Ni/HfO₂/Si capacitors is studied at temperatures ranging from 77 to 473 K. A model for the low-resistance state (LRS) consistent with the experimental data is proposed. The LRS current-voltage (I-V) curves show a maximum resistance, R₀, at zero bias and a minimum value, R_∞, at volta...

High permittivity (high-k) dielectric films are of considerable interest as gate oxide materials in advanced complementary metal-oxide-semiconductor (CMOS) [1] as well as in dynamic and resistive random access memory devices (DRAM and ReRAM) [2]. While high-k materials can help to solve gate leakage problems with leading-edge processes, there still...

Resistive random access memory (ReRAM) devices based on HfO 2 , in which a conducting filament (CF) that acts as a circuit breaker/switch between the electrodes, are studied intensively because of its high compatibility with CMOS process beyond the 22 nm node [1]. The breaking and forming of a CF occurs over a nanometer-scale region in a timespan o...

The energy levels created in supersaturated n-type silicon substrates with titaniumimplantation in the attempt to create an intermediate band in their band-gap are studied in detail. Two titaniumion implantation doses (1013 cm-2 and 1014 cm-2) are studied in this work by conductance transient technique and admittance spectroscopy. Conductance trans...

Dysprosium-doped zirconium oxide thin films grown by atomic layer deposition (ALD) were studied in order to assess its suitability as dielectric in metal–insulator–metal (MIM) electronic devices. The films show high stability and linearity. The film quality clearly improves after annealing at 700 °C in O2 during 30 min. All films crystallize in as-...

Holmium titanium oxide (HoTiOx) thin films of variable chemical composition grown by atomic layer deposition are studied in order to assess their suitability as dielectric materials in metal-insulator-metal electronic devices. The correlation between thermal and electrical stabilities as well as the potential usefulness of HoTiOx as a resistive swi...

Dy2O3 doped ZrO2 films are grown on silicon substrates using atomic layer deposition at 300 °C. Dy(thd)3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) and ZrCl4 are used as metal precursors and H2O as the oxygen precursor. Despite the low growth rate of Dy2O3 in a beta-diketonate/water process, the process allows deposition of thin films with the...

The effects of 2 MeV electron irradiation on the electrical properties of high-k dielectric based metal–insulator–semiconductor capacitors have been studied. Samples consist of 5.9 nm-thick films of aluminum oxide and hafnium oxide deposited by atomic layer deposition on silicon substrates. Deep-level transient spectroscopy (DLTS) and admittance me...

MIS capacitors based on Dy2O3-doped ZrO2 oxide dielectrics were studied. The oxide films were grown by ALD. Defect concentrations at the oxide/semiconductor interface and inside the oxide depended on the film annealing that reduced the interface quality and increased defect densities inside the oxide. The leakage current density decreased at modera...

In this work, we analyze the scavenging effect of titanium gates on metal-insulator-semiconductor capacitors composed of gadolinium oxide as dielectric material deposited on Si and InP substrates. The Gd2O3 film was grown by high pressure sputtering from a metallic target followed by an in situ plasma oxidation. The thickness of the Ti film was var...

Defects on mono-like (ml-Si), quasi-mono (qm-Si) and multicrystalline silicon solar cell substrates are studied in depth. Using the thermal admittance spectroscopy technique we found a single deep level with an activation energy between 213 and 224 meV and a capture cross section in the order of 10⁻¹⁵−10⁻¹⁴ cm², in the case of ml-Si samples. The 27...