HfO2 Research Articles

Synergistic Effect of Ferroelectric and HfO2/SiO2 Hetero dielectrics in Junctionless FET for Analog and RF Applications

AbstractThe synergistic effect of ferroelectric and HfO2/SiO2 (Hafnium dioxide/ Silicon dioxide) hetero dielectrics in double gate Junctionless Field Effect Transistor is investigated using TCAD Tool. The study encompasses a wide range of parameters, allowing for a detailed examination of the impact of hysteresis on the overall functionality of the double gate Junctionless FET. One crucial aspect of the investigation involves examining the analog and RF performance of the device. The high transconductance (gm) of 5.42 mS, a gain of 95 dB (decibel), a cut‐off frequency of 553.9 GHz (gigahertz), a gain transconductance frequency product (GTFP) of 50.9 THz (terahertz), and a gain bandwidth product (GBW) of 188 GHz shows its great potential for analog and RF signal processing applications as well as for other high data rate wireless applications such as Machine Learning (ML), Artificial Intelligence (AI) and Internet‐of‐Thing (IoT). The low transit time of 17 ns (nano second), with high ION/IOFF ratio range of 107 shows that the device has good switching behavior also. This aspect of the research aims to unveil the device's viability for analog and high‐frequency applications, contributing valuable insights to the emerging electronic technologies field.

Analysis and EOT Scaling on Top‐ and Double‐Gate 2D CVD‐Grown Monolayer MoS2 FETs

Abstract2D layered semiconductors have attracted considerable attention for beyond‐Si complementary metal‐oxide‐semiconductor (CMOS) technologies. They can be prepared into ultrathin channel materials toward ultrascaled device architectures, including double‐gate field‐effect‐transistors (DGFETs). This work presents an experimental analysis of DGFETs constructed from chemical vapor deposition (CVD)‐grown monolayer (1L) molybdenum disulfide (MoS2) with atomic layer deposition (ALD) of hafnium oxide (HfO2) high‐k gate dielectrics (top and bottom). This extends beyond previous studies of DGFETs based mostly on exfoliated (few‐nm thick) MoS2 flakes, and advances toward large‐area wafer‐scale processing. Here, significant improvements in performance are obtained with DGFETs (i.e., improvements in ON/OFF ratio, ON‐state current, sub‐threshold swing, etc.) compared to single top‐gate FETs. In addition to multi‐gate device architectures (e.g., DGFETs), the scaling of the equivalent oxide thickness (EOT) is crucial toward improved electrostatics required for next‐generation transistors. However, the impact of EOT scaling on the characteristics of CVD‐grown MoS2 DGFETs remains largely unexplored. Thus, this work studies the impact of EOT scaling on subthreshold swing (SS) and gate hysteresis using current–voltage (I–V) measurements with varying sweep rates. The experimental analysis and results elucidate the basic mechanisms responsible for improvements in CVD‐grown 1L‐MoS2 DGFETs compared to standard top‐gate FETs.

Induction of Synaptic Plasticity in Flexible Organic Synaptic Transistors with Cross‐Linked Polymer Dielectric

AbstractControlled cross‐linking of polymer dielectric poly (4‐vinylphenol) (PVP) is demonstrated as an effective tool in enhancing the performance of flexible organic synaptic transistors (OSTs). Investigation of variation of concentration of the cross‐linking agent methylated poly (melamine‐co‐formaldehyde) (PMCF) in PVP in bilayer combination with high‐k hafnium oxide (HfO2) as gate dielectric in devices shows that the lower concentration of cross‐linking agent results in better memory performance. OSTs with 26% PMCF concentration in PVP (by mass) exhibit excellent memory performance with memory window > 4 V for VGS sweep of ±5 V, static retention of ≈104 s, dynamic retention for 500 cycles, and ≈125 continuous program/erase cycles. Pulse paired facilitation with relaxation time constants of 370 and 4670 ms respectively for slow and rapid phases with regulating modulation amplitude of ≈1 resemble a biological synapse. Through excitatory post synaptic current characteristics, spike timing dependant plasticity and spike voltage dependant plasticity are clearly observed, with low energy consumption per spike on the order of 10 pJ. Further, by leveraging the intricate interconnected data transfer and computation phenomenon, “AND” logic is effectively implemented using these OSTs. These exciting results may open up new directions toward the development of hardware for neuromorphic computing.

Luminescence of oxygen vacancies in hafnium oxide, characteristics of emission bands and use for diagnostics of technological processes

Oxygen vacancies play an important role in the formation of the electrical and optical properties of hafnium oxide. Both conductivity and emission bands are determined by this intrinsic defect. The work studies the luminescence of oxygen vacancies. The spectral and temperature dependences of luminescence show the leading role of electron-phonon interaction. The work proposes an algorithm for determining the parameters of this interaction and constructs configuration-coordinate diagrams of emission centers that are associated with different charge states of oxygen vacancies in hafnium oxide.

Processing of hafnium oxide thin films by 2 MeV Kr ion beam for opto-electronic applications

The ion irradiation on 100 nm and 200 nm HfO2 films was performed using a 2 MeV Kr8+ beam at three different fluences viz. 1.5 × 1015 ions/cm2, 2 × 1015 ions/cm2 and 2.5 × 1015 ions/cm2 and various characterization techniques were employed to analyze the as-deposited and irradiated films. The AFM analysis showed that contrary to 200 nm films, the surface roughness of 100 nm films increases with increasing the ion fluence as also validated by FE-SEM. For 100 nm films, the phase analysis done by XRD indicated that the pristine films co-exist in dual phases of cubic and monoclinic; which also prevailed with post-irradiation. However, the pristine 200 nm films coexisted in dual monoclinic and orthorhombic phases and changed to sole orthorhombic phase with increasing ion fluences. The pristine 200 nm film showed more conductivity, which decreases with increasing ion fluences. Interestingly, the optical reflectivity of as-deposited 200 nm film was higher than that of 100 nm film and upon ion irradiation, both films showed inverse trend of reflectivity change; in 100 nm thin films, it decreases with increasing ion fluences. Thus, the ion irradiation seems to be a fascinating tool to tailor HfO2 thin films for their device applications.

Performance improvement of bilayer memristor based on hafnium oxide by Ti/W synergy and its synaptic behavior

Bilayer and multi-layer structures can effectively improve the performance of memristors, but the oxide/metal interface during the resistance switching process affects its reliability and stability. In this work, the Pt/HfO2/HfOx/W and Pt/HfO2/HfOx/Ti/W memristors with a homogeneous bilayer structure are compared to systematically investigate the effect of interface engineering on bilayer hafnium oxide devices by inserting Ti buffer layer to construct Ti/W composite electrode. Compared with the stimulated oxidation of the W electrode, the device under the synergy of Ti/W composite electrode showed better switching uniformity (The resistance of the high-resistance state and reset voltage variation coefficient decreased from 83.1 % to 31.9 % and from 9.5 % to 5.6 %, respectively.) and robust endurance (>104 cycles). Meanwhile, some essential synaptic behaviors such as nonlinear transmission characteristics, paired-pulse facilitation, and spike-timing-dependent plasticity were mimicked by using different pulse stimuli. Subsequently, the resistance switching mechanism of the device under the Ti/W synergy was explored by combining the results of I–V curve fitting and material analysis. These results provided important experimental guidance and a theoretical basis for further optimization of electrode interfacial effect in the future.

Highly sensitive and selective detection of dopamine using atomic layer deposited HfO2 ultra-thin films

The development of non-enzymatic and binder-free biosensors plays a vital role, and it possesses main benefits for effective biomolecule recognition with high sensitivity and preferred selectivity. Herein, an atomic layer deposition (ALD) was employed to develop the hafnium oxide (HfO2) nanofilm on silicon (Si) for fabricating binder-free selective and sensitive determination of the non-enzymatic electrochemical dopamine sensor. The prepared HfO2 nanofilm selectively acted as a local dopamine binding site because of the hydrophobic-hydrophobic interaction between fabricated film and dopamine, electrostatic attraction between negatively charged hydroxyl group on film surfaces, and positively charged amino group of dopamine. The developed insufficient oxygen vacancies on the HfO2 could have behaved as a charge-trapping site for better sensing properties. The developed sensor demonstrated excellent realization in sensing dopamine with a very low detection limit (0.4 pM) and swift response time of 3s which is quite precise compared with various reported literature. The fabricated HfO2/Si electrode sensor has exhibited high sensitivity, stability, and repeatability. The selectivity of dopamine sensors was at least three orders greater than other interfering biomolecules. This work proposes the essential track for the practical realization of dopamine detection in human serum and biomedical applications.

First‐Principles Calculation of Basic Properties of Rhombohedral Hafnium Oxide with Space Group R3

First‐Principles Calculation of Basic Properties of Rhombohedral Hafnium Oxide with Space Group R3

A design methodology for highly reliable operation for 2T0C dynamic random access memory application based on IGZO channel-all-around ferroelectric field-effect transistors

In this paper, the memory characteristics of In-Ga-Zn-O (IGZO)-channel ferroelectric FETs (FeFETs) with stackable vertical channel-all-around structure are investigated by technology computer-aided design (TCAD) simulation. The simulated drain current–gate voltage (I DS–V GS) curves of the IGZO FeFET show an on–off ratio of up to 107 and a memory window of 1.76 V, proving that ferroelectric hafnium oxide (FE-HfO2) is suitable for a 2T0C transistor. To solve the potential current-sharing problem of the 2T0C dynamic random access memory (DRAM) array, an advanced operation design methodology is proposed, which utilizes the bipolar polarization characteristics of FE-HfO2. This solution shows a remarkable current ratio between data “1” and data “0”, not only demonstrating the feasibility of the IGZO-based FeFET on 2T0C DRAM memory cells, but also providing an array design guideline for highly reliable 2T0C memory applications.

Early signs of efficacy in patients with anti-PD-1 naïve and anti-PD-1 resistant HNSCC treated with NBTXR3/SBRT in combination with nivolumab or pembrolizumab in the phase I trial Study 1100.

6035 Background: Overcoming resistance to immune checkpoint inhibitors (ICIs) is a major clinical challenge. NBTXR3, a novel radioenhancer composed of functionalized hafnium oxide nanoparticles administered by a single intratumoral injection, locally amplifies radiotherapy (RT) dose without adding toxicity to surrounding healthy tissue. NBTXR3/RT enhances tumor cell death, tumor antigen release, and effectively expands T-cell repertoire in preclinical models, thus potentially triggering local and systemic immune responses to help improve ICI treatment. NBTXR3 has demonstrated favorable local control in pts with LA-HNSCC. Here we report early outcomes from the ongoing Study 1100 trial in pts with locoregionally recurrent (LRR) or metastatic (M+) head & neck squamous cell carcinoma (HNSCC) who were either naïve to or who continued anti-PD-1 therapy combined with NBTRX3/RT after primary or secondary resistance to anti-PD-1 alone. Methods: A phase I dose escalation/expansion trial [NCT03589339] evaluating NBTXR3/Stereotactic Body RT (SBRT) followed by nivolumab or pembrolizumab in 3 cohorts of pts with advanced solid tumors. Pts have H&N lesions either resistant to prior ICI or naïve, or lung, liver, or soft tissue metastases from ICI-resistant advanced solid tumors. SBRT doses were: HN 35 Gy/ 5 fxns; lung 45 Gy/ 5 fxns; liver 45 Gy/ 3 fxns; soft tissue as per investigator. Primary objective is safety of NBTXR3/RT/anti-PD-1 combination and its RP2D. Secondary objectives include efficacy. Results: The RP2D was 33%. There were 55 pts with HNSCC treated in the dose escalation/expansion parts. NBTXR3 injection was feasible and safe. There were 11pts (20%) who experienced G≥3 treatment related AEs, of which 3 pts experienced G≥3 AEs (5.5%) related to NBTXR3. Preliminary results of 33 pts, who were evaluable for efficacy: are reported. 6 pts with LRR disease: (2 ICI resistant, 4 naïve);. 27 pts with M+ disease (18 ICI resistant, 9 naïve). In ICI-resistant pts, objective tumor responses were observed in 25% (5/20), and the disease control rate (DCR) was 75% (15/20). In the ICI-naïve population, objective tumor responses were observed in 54% (7/13) of pts and DCR was 77% (10/13). There were observed improvements in injected lesions as well as in some noninjected target lesions. Updated efficacy data including OS in resistant and naïve pts will be presented. Conclusions: NBTXR3/RT/anti-PD-1 combination was feasible and well tolerated. Early data suggest the addition of NBTXR3/RT to ICI showed evidence of efficacy, including in patients who failed prior ICI, opening up an opportunity to further explore the ability of NBTXR3/RT to mitigate primary or secondary resistance to ICI. Clinical trial information: NCT03589339 .

Nanoscale ferroelectric domain switching and thickness scaling impact in undoped hafnium-oxide ferroelectric devices

In this work, we investigated the polarization characteristics of nanoscale undoped hafnium oxide (HfO2) ferroelectric film. The nanoscale domain switching behavior of undoped HfO2 is mainly dominated by mixed ferroelectric/nonferroelectric crystalline phases and interface domain pinning by oxygen vacancies or defect traps. Our experimental results confirm that these issues can be improved by film thickness scaling and well-controlled mechanical stress. We demonstrated a 4-nm-thick undoped HfO2 negative capacitance thin film transistor (NCFET) with an energy-efficient switch characteristic of a low overdrive voltage of -0.6 V, a steep subthreshold swing of sub-60 mV/dec and a uniform hysteresis distribution of sub-60 mV.

High pH stability and detection of α-synuclein using an EGFET biosensor with an HfO2 gate deposited by high-power pulsed magnetron sputtering

In this research, hafnium oxide (HfO2) was first fabricated in an in-house-developed high-power pulsed magnetron sputtering system (HiPIMS) functionalized for application as a high-performance extended gate field-effect transistor (EGFET) for the detection of pH and proteins associated with Parkinson's disease (PD). PD is the second most common neurodegenerative disease in elderly people after Alzheimer's disease. The α-synuclein protein in patients’ blood may be a potential biomarker in the early stage of PD. Detection of α-synuclein with high sensitivity and nonspecific binding through HfO2-EGFET biosensors has the advantages of low cost and simple fabrication from disposable EGs. Among the duty cycle conditions tested, HfO2 deposited at a 25% duty cycle in HiPIMS exhibited superior pH sensitivity and linearity, with values of 56.4 mV/pH and 99.7%, respectively. The hysteresis width and drift coefficient are −3 mV and 0.3 mV/h, respectively. To overcome the Debye length limitation, 100-fold diluted phosphate buffer solution and the PMOS configuration were used to determine the α-synuclein for which the isoelectric point was 4.67. The negative gate bias in the PMOS configuration successfully causes α-synuclein to approach the surface of HfO2 EG to achieve a sensitivity of 12.1 mV/dec and a linearity of 99.5% in the range of 0.1–1000 pg/mL. The limit of detection is 0.198 pg/mL, and the immobilized surface ultimately binds specifically, resulting in low interference signals from other related biomarkers. This promising study shows that detecting various proteins involved in different diseases and performing clinical tests can be accomplished in the future.

Overlapping top gate electrodes based on low temperature atomic layer deposition for nanoscale ambipolar lateral junctions

We present overlapping top gate electrodes for the formation of gate defined lateral junctions in semiconducting layers as an alternative to the back gate/top gate combination and to the split gate configuration. The optical lithography microfabrication of the overlapping top gates is based on multiple layers of low-temperature atomic layer deposited hafnium oxide, which acts as a gate dielectric and as a robust insulating layer between two overlapping gate electrodes exhibiting a large dielectric breakdown field of >1×109V m−1 . The advantage of overlapping gates over the split gate approach is confirmed in model calculations of the electrostatics of the gate stack. The overlapping gate process is applied to Hall bar devices of mercury telluride in order to study the interaction of different quantum Hall states in the nn′, np, pn and pp′ regime.

Domain Switching Characteristics in Ga-Doped HfO2 Ferroelectric Thin Films with Low Coercive Field.

The gallium-doped hafnium oxide (Ga-HfO2) films with different Ga doping concentrations were prepared by adjusting the HfO2/Ga2O3 atomic layer deposition cycle ratio for high-speed and low-voltage operation in HfO2-based ferroelectric memory. The Ga-HfO2 ferroelectric films reveal a finely modulated coercive field (Ec) from 1.1 (HfO2/Ga2O3 = 32:1) to an exceptionally low 0.6 MV/cm (HfO2/Ga2O3 = 11:1). This modulation arises from the competition between domain nucleation and propagation speed during polarization switching, influenced by the intrinsic domain density and phase dispersion in the film with specific Ga doping concentrations. Higher Ec samples exhibit a nucleation-dominant switching mechanism, while lower Ec samples undergo a transition from a nucleation-dominant to a propagation-dominant reversal mechanism as the electric field increases. This work introduces Ga as a viable dopant for low Ec and offers insights into material design strategies for HfO2-based ferroelectric memory applications.

Electric-field-induced crystallization of Hf0.5Zr0.5O2 thin film based on phase-field modeling

Ferroelectricity in crystalline hafnium oxide has attracted considerable attention because of its potential application for memory devices. A recent breakthrough involves electric-field-induced crystallization, allowing HfO2-based materials to avoid high-temperature crystallization, which is unexpected in the back-end-of-line process. However, due to the lack of clarity in understanding the mechanisms during the crystallization process, we aim to employ theoretical methods for simulation, to guide experimental endeavors. In this work, we extended our phase-field model by coupling the crystallization model and time-dependent Ginzburg-Landau equation to analyze the crystalline properties and the polarization evolution of Hf0.5Zr0.5O2 thin film under applying an electric field periodic pulse. Through this approach, we found a wake-up effect during the process of crystallization and a transformation from orthorhombic nano-domains to the stripe domain. Furthermore, we have proposed an innovative artificial neural synapse concept based on the continuous polarization variation under applied electric field pulses. Our research lays the theoretical groundwork for the advancement of electric-field-induced crystallization in the hafnium oxide system.

Highly reproducible and CMOS-compatible VO2-based oscillators for brain-inspired computing.

With remarkable electrical and optical switching properties induced at low power and near room temperature (68°C), vanadium dioxide (VO2) has sparked rising interest in unconventional computing among the phase-change materials research community. The scalability and the potential to compute beyond the von Neumann model make VO2 especially appealing for implementation in oscillating neural networks for artificial intelligence applications, to solve constraint satisfaction problems, and for pattern recognition. Its integration into large networks of oscillators on a Silicon platform still poses challenges associated with the stabilization in the correct oxidation state and the ability to fabricate a structure with predictable electrical behavior showing very low variability. In this work, the role played by the different annealing parameters applied by three methods (slow thermal annealing, flash annealing, and rapid thermal annealing), following the vanadium oxide atomic layer deposition, on the formation of VO2 grains is studied and an optimal substrate stack configuration that minimizes variability between devices is proposed. Material and electrical characterizations are performed on the different films and a step-by-step recipe to build reproducible VO2-based oscillators is presented, which is argued to be made possible thanks to the introduction of a hafnium oxide (HfO2) layer between the silicon substrate and the vanadium oxide layer. Up to seven nearly identical VO2-based devices are contacted simultaneously to create a network of oscillators, paving the way for large-scale implementation of VO2 oscillating neural networks.

Molecular synthesis strategies for binary MO2 (M = V, Sn, Ti, Zr, Hf) high-entropy oxides as superior catalysts for enhanced oxygen evolution

Entropy stabilized multi-cation oxides are of significant interest in heterogeneous catalysis due to higher number of active sites, when compared to simple binary oxides, which reduces the overpotential for catalytic transformations. To control the enthalpy of mixing and suppress potential phase segregation, the use of molecular metal alkoxides for chemical cross-linking of different metal centers shows promise in creating homogenous high entropy chemical preceramic networks. Herein, we report on a high-entropy MO2 phase (M = V, Sn, Ti, Zr, Hf), synthesized by cross-linking partially hydrolyzed metal iso-propoxides [M(OH)n(OiPr)4-n]x. The amorphous xerogels calcined at 700 °C, 900 °C and 1250 °C revealed the formation of a single crystalline phase [(V, Sn, Ti, Zr, Hf)O2] that was verified by powder X-ray diffraction analysis, whereas the chemical composition was investigated by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The HEO exhibited superior catalytic activity in oxygen evolution reaction with an overpotential of 312.7 mV and an electrochemically active surface area of 0.625 F cm−2. Furthermore, the chronopotentiometry measurements confirmed a high stability (> 90 h) for the HEO samples.

Substrate temperature effects on PEALD HfAlO dielectric films for IGZO-TFT applications

Aluminum incorporated hafnium oxide (HfAlO) has garnered significant attention due to its high dielectric constant. The present study employs supercycle plasma-enhanced atomic layer deposition (PEALD) to prepare HfAlO films, switching between HfO2 and Al2O3 deposition. The effects of substate temperature on the HfAlO films are systematically investigated. The experimental results indicate that increased substrate temperatures favor Al2O3 growth on HfO2, but excessively high temperatures result in deviated PEALD growth and deteriorated film properties. The PEALD window can be reached at substrate temperatures of 300 to 350 °C. The Al content is substantially affected by the substrate temperature, despite a constant Al2O3 PEALD cycle ratio used. The film deposited at 350 °C exhibits the highest Al content, density, and (111) crystalline orientation ratio, leading to a high breakdown field of 6 MV/cm and a considerable dielectric constant of 27. The HfAlO films are applied to indium gallium zinc oxide transistor as the dielectric layer, and the 350 °C-deposited HfAlO leads to the best device performance with a remarkably high on/off current ratio of 3.5 × 109, low threshold voltage of −0.1 V, saturated mobility of 6.1 cm2 V−1 s−1, and a low subthreshold swing of 76 mV/dec.

The poly (arylene ether urea) double interface layer formed in PEEU@HfO2/PEI nanocomposites enables enhanced dielectric and energy storage performance

Polyetherimide (PEI) has great potential as a dielectric because of its high-temperature resistance, but its low energy storage density limits practical applications. Incorporating hafnium dioxide (HfO2) with a moderate dielectric constant (k) and wide bandgap can simultaneously enhance the polarization intensity of PEI and potential barriers for charge injection. Nevertheless, the poor compatibility between HfO2 and PEI inevitably introduces defects, thereby weakening the inhibitory effect on dielectric loss. To tackle this issue, an organic double interface layer is introduced to enhance dielectric performance, where the polar poly(arylene ether urea) (PEEU) containing hydrogen bonds can ensure the layer's compactness. Notably, its non-bonding urea groups serve as deep traps to capture migrating carriers, and the gradient k values of HfO2, PEEU, and PEI help mitigate electric field distortions at the interface, therefore enhancing the suppression of conduction loss. The polarity of PEEU and the introduction of multiple interfaces significantly contribute to an increased k (maximum 9.7, at 1 kHz). At 300 kV mm−1, 5 vol% PEEU@HfO2/PEI achieves a discharged energy density of 3.3 J cm−3 and a high charge-discharge efficiency of 83 %, surpassing 5 vol% HfO2/PEI by 1.95 and 2.44 times, respectively. The further COMSOL simulation verifies and proves this work as a novel design strategy for nanocomposite dielectrics.

Radiotherapy-sensitized cancer immunotherapy via cGAS-STING immune pathway by activatable nanocascade reaction

Radiotherapy-induced immune activation holds great promise for optimizing cancer treatment efficacy. Here, we describe a clinically used radiosensitizer hafnium oxide (HfO2) that was core coated with a MnO2 shell followed by a glucose oxidase (GOx) doping nanoplatform (HfO2@MnO2@GOx, HMG) to trigger ferroptosis adjuvant effects by glutathione depletion and reactive oxygen species production. This ferroptosis cascade potentiation further sensitized radiotherapy by enhancing DNA damage in 4T1 breast cancer tumor cells. The combination of HMG nanoparticles and radiotherapy effectively activated the damaged DNA and Mn2+-mediated cGAS-STING immune pathway in vitro and in vivo. This process had significant inhibitory effects on cancer progression and initiating an anticancer systemic immune response to prevent distant tumor recurrence and achieve long-lasting tumor suppression of both primary and distant tumors. Furthermore, the as-prepared HMG nanoparticles “turned on” spectral computed tomography (CT)/magnetic resonance dual-modality imaging signals, and demonstrated favorable contrast enhancement capabilities activated by under the GSH tumor microenvironment. This result highlighted the potential of nanoparticles as a theranostic nanoplatform for achieving molecular imaging guided tumor radiotherapy sensitization induced by synergistic immunotherapy.