Igor Stolichnov

Related publications (94)

Ferroelectric Junctionless Double-Gate Silicon-On-Insulator FET as a Tripartite Synapse

Matteo Cavalieri, Carlotta Gastaldi, Mihai Adrian Ionescu, Sadegh Kamaei Bahmaei, Ali Saeidi, Igor Stolichnov

In this work, we report the concept and experimentally demonstrate the first tunable ferroelectric (Fe) junctionless (JL) transistor (Fe-JLFET), capable of emulating the functionality of biological tri-partite synapses, which is an artificial three-terminal synapse with unique back gate high tuning of the post-synaptic current (PSC). Our device consists of a double-gate 11nm-thin film Fe-JLFET with 10nm Si-doped HfO2 ferroelectric, mimicking the functionality of a tripartite synapse. The gradual ferroelectric switching is exploited to fully reproduce the synaptic plasticity. The back-gate voltage emulates the function of an astrocyte, being used to tune the synaptic weight by more than 400x. Compared to other implementations, the newly proposed tripartite Fe-JLFET synapse device shows simplicity in fabrication, extended programmability, and robustness. We report plasticity until 2000 cycles of operation. Overall, this device concept is promising for CMOS-compatible energy-efficient implementation of future neuromorphic ICs.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2023

Giant switchable non thermally-activated conduction in 180 degrees domain walls in tetragonal Pb(Zr,Ti)O-3

Mihai Adrian Ionescu, Felix Risch, Igor Stolichnov

Conductive domain walls in ferroelectrics offer a promising concept of nanoelectronic circuits with 2D domain-wall channels playing roles of memristors or synoptic interconnections. However, domain wall conduction remains challenging to control and pA-range currents typically measured on individual walls are too low for single-channel devices. Charged domain walls show higher conductivity, but are generally unstable and difficult to create. Here, we show highly conductive and stable channels on ubiquitous 180 degrees domain walls in the archetypical ferroelectric, tetragonal Pb(Zr,Ti)O-3. These electrically erasable/rewritable channels show currents of tens of nanoamperes (200 to 400 nA/mu m) at voltages

NATURE PORTFOLIO2022

Negative Capacitance in HfO2 Gate Stack Structures With and Without Metal Interlayer

Francesco Bellando, Matteo Cavalieri, Carlotta Gastaldi, Mihai Adrian Ionescu, Ali Saeidi, Igor Stolichnov

In this work, we experimentally explore and compare FET gate stacks with and without an inner metal plane between a linear dielectric (SiO2) and a ferroelectric layer (Si-doped HfO2) operating in the negative capacitance (NC) regime. The use of nanosecond-range pulses enables us to observe hysteresis-free NC and reconstruct the S-shaped polarization-voltage curves. The devices with the inner metal plate show a higher equivalent NC value, which offers the potential for a higher differential amplification in a NC-FET. However, such a NC region is observed over a smaller range of electric field and polarization, which leads to hysteresis. Moreover, the presence of a metal layer in between the ferroelectric and the insulator favors domain formation resulting in destabilization of the NC effect. For the gate structure where the ferroelectric and the insulator are in contact, the S-shaped polarization-voltage curve shows a better agreement with Landau-Ginzburg-Devonshire formalism for the monodomain state. The uniform polarization closely mimicking the monodomain state is possible due to the polarization imprint occurring due to the structural asymmetry. By nanometer resolution polarization mapping via off-resonance piezoelectric force microscopy (PFM), we corroborate the presence of imprint, which can intrinsically stabilize one ferroelectric state. Overall, the article provides an experimental demonstration that the absence of the inner metal plane in the gate structures stabilizes the NC regime favorable for hysteresis-free NC-FET.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2022

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HfO2-based ferroelectrics are considered a promising class of materials for logic and memory applications due to their CMOS compatibility and ferroelectric figures of merit. A steep-slope field-effect-transistor (FET) switch is a device for logic applications in which a ferroelectric gate stack exploits a stabilized negative capacitance regime capable to differentially amplify the surface potential in a metal-oxide-semiconductor FET structure, resulting in the improvement of the subthreshold swing and overdrive. In a number of relevant studies of negative capacitance, intrinsic (thermodynamic) switching is assumed, since alternative switching scenarios predict undesirable hysteretic responses in logic devices. However, there is little support from the experimental data showing that the polarization reversal in HfO2-based ferroelectrics is really driven by the intrinsic switching mechanism. In this work, polarization hysteresis loops are measured over wide temperature ranges on polycrystalline Si-doped HfO2 (Si:HfO2) capacitors. The analysis herein, which is based on the classic Landau-Ginzburg-Devonshire theory, yields the temperature-dependent dielectric susceptibility values, which fit the Curie-Weiss law. The extrapolated Curie temperature value is in line with the data obtained for other HfO2-based ferroelectrics using different techniques. The work also illustrates a method to evaluate the ferroelectric equivalent negative capacitance value and range of voltages, aiming at study and optimization of a stabilized negative capacitance FET. This study indicates that the intrinsic switching provides an adequate description of the polarization hysteresis in Si:HfO2 films. This confirms the usability of hafnia-based ferroelectrics for negative capacitance logic devices, and the important role that the intrinsic mechanism plays in the dielectric response of these materials.

AMER INST PHYSICS2021

Corrections to “Experimental Details of a Steep-Slope Ferroelectric InGaAs Tunnel-FET With High-Quality PZT and Modeling Insights in the Transient Polarization”

Mihai Adrian Ionescu, Hiroshi Iwai, Ali Saeidi, Igor Stolichnov

This correspondence highlights that the Gibbs free energy description of a ferroelectric capacitor in series with a paraelectric capacitor, depends on the initial charge on the plates of the ferroelectric capacitor. An incomplete Gibbs free energy description, as in the original manuscript, leads to an incorrect simulation result. Therefore, a fully comprehensive analytical description and a corrected conclusion concerning the particular point of an increase in apparent coercive voltage in the steep-slope ferroelectric tunnel-FET, are presented.

2020

Experimental Investigation of Pulsed Laser Deposition of Ferroelectric Gd:HfO2 in a CMOS BEOL Compatible Process

Matteo Cavalieri, Carlotta Gastaldi, Mihai Adrian Ionescu, Igor Stolichnov

In this work, we report an experimental investigation of pulsed laser deposition (PLD) of thin Gd:HfO2 layers at 330 degrees C, which show ferroelectric behavior after annealing at 450 degrees C, compatible with complementary metal-oxide-semiconductor back-end-of-line processing. The material's ferroelectricity is confirmed by microstructural and electrical analysis, corroborated by hysteretic electromechanical response measured via piezoresponse force microscopy. The effect of postdeposition annealing ambient is also studied, where N-2 annealing results in higher remanent polarization, while O-2 annealing yields greater endurance properties. Furthermore, ferroelectricity is demonstrated for PLD thin films formed on a conventional TiN/Si structure, demonstrating the strong potential of this PLD material for cointegration in relevant memory and logic applications.

AMER CHEMICAL SOC2020

Intrinsic or nucleation-driven switching: An insight from nanoscopic analysis of negative capacitance Hf1-xZrxO2-based structures

Matteo Cavalieri, Carlotta Gastaldi, Mihai Adrian Ionescu, Igor Stolichnov

HfO2-based ferroelectrics have dramatically changed the application perspectives of polarization-switching materials for information processing and storage. Their CMOS compatibility and preservation of high reversible polarization down to a few nanometer thickness make them attractive for various device concepts including non-volatile memories and negative-capacitance-enhanced steep-slope transistors. In the context of these applications, the long-standing discussion of intrinsic (thermodynamic) or extrinsic nuclei-limited switching (NLS) in ferroelectrics has recently gained importance. In particular, the negative capacitance effect that is formally described by the Landau-Ginzburg-Devonshire formalism implies the intrinsic polarization switching driven by the thermodynamic coercive field. On the other hand, recent studies reported the nucleation-limited extrinsic switching, which does not result in the hysteresis-free negative capacitance effect. Here, we analyze the polarization response in the nanometer scale on the ferroelectric/dielectric bilayer where the negative capacitance has been previously demonstrated. Our analysis of the two limiting cases of quasi-static switching and the earlier reported ultra-fast polarization response supports the intrinsic polarization reversal scenario. The compatibility of this mechanism with the previously reported NLS region-by-region switching with remarkably low domain wall velocity is addressed. Our results confirm the usability of CMOS-compatible polycrystalline HZO ferroelectric films for gates operating in the negative-capacitance regime. Furthermore, they point towards possible solutions for optimizing their switching properties for applications including memories.

AMER INST PHYSICS2020

Nanowire Tunnel FET with Simultaneously Reduced Subthermionic Subthreshold Swing and Off-Current due to Negative Capacitance and Voltage Pinning Effects

Matteo Cavalieri, Mihai Adrian Ionescu, Teodor Rosca, Ali Saeidi, Igor Stolichnov

Nanowire tunnel field-effect transistors (TFETs) have been proposed as the most advanced one-dimensional (1D) devices that break the thermionic 60 mV/decade of the subthreshold swing (SS) of metal oxide semiconductor field-effect transistors (MOSFETs) by using quantum mechanical band-to-band tunneling and excellent electrostatic control. Meanwhile, negative capacitance (NC) of ferroelectrics has been proposed as a promising performance booster of MOSFETs to bypass the aforementioned fundamental limit by exploiting the differential amplification of the gate voltage under certain conditions. We combine these two principles into a single structure, a negative capacitance heterostructure TFET, and experimentally demonstrate a double beneficial effect: (i) a super-steep SS value down to 10 mV/decade and an extended low slope region that is due to the NC effect and, (ii) a remarkable off-current reduction that is experimentally observed and explained for the first time by the effect of the ferroelectric dipoles, which set the surface potential in a slightly negative value and further blocks the source tunneling current in the off-state. State-of-the-art InAs/InGaAsSb/GaSb nanowire TFETs are employed as the baseline transistor and PZT and silicon-doped HfO2 as ferroelectric materials.

AMER CHEMICAL SOC2020

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This work investigates and reports on the radio-frequency (RF) behavior in the frequency range of 5 – 35 GHz of germanium-doped (Ge-doped VO2) vanadium dioxide thin films, deposited on silicon substrates via sputtering and pulsed laser deposition (PLD) with estimated Ge concentrations of 5 % and 5.5 %. Both films exhibit critical transition temperatures (Tc) of 76.2 and 72 °C, respectively, which are higher compared to that of the undoped VO2 which undergoes reversible insulator-to-metal phase transition at 68°C. Both types of Ge-doped films show low hysteresis (< 5 °C) in their conductivity versus temperature characteristics and preserve an high off-state DC-conductivities (corresponding to the insulating state of the phase change material) of 13 S/m, for the sputtered, and, 55 S/m, for the PLD deposited film, respectively. The DC on-state (corresponding to the conductive state of the phase change material) conductivity reaches 145,000 S/m in the case of the PLD film, which represents a significant increase compared to the state-of-the art values measured for undoped VO2 thin films deposited on identical substrates. In order to further understand the off-state dissimilarities and RF behavior of the deposited Ge-doped VO2 films, we propose an original methodology for the experimental extraction of the dielectric constant (ɛr) in the GHz range of the films below 60 °C. This is achieved by exploiting the frequency shift of resonant filters. For this purpose we have fabricated coplanar waveguide (CPW) structures incorporating ultra-compact Peano space filling curves, each resonating at a different frequency between 5 and 35 GHz on two types of substrates, one with the Ge-doped VO2 thin films and another one using only SiO2 to serve as reference. The reported results and analysis contribute to the advancement of the field of metal-insulator-transition material technology with high Tc for RF industrial applications.

2020

Experimental Details of a Steep-Slope Ferroelectric InGaAs Tunnel-FET With High-Quality PZT and Modeling Insights in the Transient Polarization

Mihai Adrian Ionescu, Hiroshi Iwai, Ali Saeidi, Igor Stolichnov

The steep-slope ferroelectric tunnel-FET (SS-FeTFET), consisting of an InGaAs TFET with a sub-60 mV/dec subthreshold swing (SS) at room temperature and an externally connected high-quality single-crystalline PZT capacitor, displays improved SS compared to the standalone TFET. In this article, we describe the measurement procedure and measurement results of this SS-FeTFET in great detail. To quantitatively extract the ferroelectric (FE) polarization during voltage sweeps, device simulations of the TFET are combined with the SS-FeTFET measurement results. Finally, qualitative insight in some peculiarities of the experimental observations is given, such as the apparent coercive voltage that is larger in the SS-FeTFET than in the standalone FE, the shape of the polarization during voltage sweeps, and the small polarization hysteresis loop at voltages close to the apparent coercive voltage.

2019