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Pioneering flexible micro-supercapacitors, designed for exceptional energy and power density, transcend conventional storage limitations. Interdigitated electrodes (IDEs) based on laser-induced graphene (LIG), augmented with metal-oxide modifiers, harness synergies with layered graphene to achieve superior capacitance. This study presents a novel one-step process for sputtered plasma deposition of HfO 2 , resulting in enhanced supercapacitance performance. Introducing LIG-HfO 2 micro-supercapacitor (MSC) devices with varied oxygen flow rates further boosts supercapacitance performance by introducing oxygen functional groups. FESEM investigations demonstrate uniform coating of HfO 2 on LIG fibers through sputtering. Specific capacitance measurements reveal 6.4 mF/cm 2 at 5 mV/s and 4.5 mF/cm 2 at a current density of 0.04 mA/cm 2 . The LIG-HfO 2 devices exhibit outstanding supercapacitor performance, boasting at least a fourfold increase over pristine LIG. Moreover, stability testing indicates a high retention rate of 97% over 5000 cycles, ensuring practical real-time applications.

HfO2 shows promise for emerging ferroelectric and resistive switching (RS) memory devices owing to its excellent electrical properties and compatibility with complementary metal oxide semiconductor technology based on mature fabrication processes such as atomic layer deposition. Oxygen vacancy (Vo), which is the most frequently observed intrinsic defect in HfO2-based films, determines the physical/electrical properties and device performance. Vo influences the polymorphism and the resulting ferroelectric properties of HfO2. Moreover, the switching speed and endurance of ferroelectric memories are strongly correlated to the Vo concentration and redistribution. They also strongly influence the device-to-device and cycle-to-cycle variability of integrated circuits based on ferroelectric memories. The concentration, migration, and agglomeration of Vo form the main mechanism behind the RS behavior observed in HfO2, suggesting that the device performance and reliability in terms of the operating voltage, switching speed, on/off ratio, analog conductance modulation, endurance, and retention are sensitive to Vo. Therefore, the mechanism of Vo formation and its effects on the chemical, physical, and electrical properties in ferroelectric and RS HfO2 should be understood. This study comprehensively reviews the literature on Vo in HfO2 from the formation and influencing mechanism to material properties and device performance. This review contributes to the synergetic advances of current knowledge and technology in emerging HfO2-based semiconductor devices.

Atomic layer deposited (ALD) HfO2/Al2O3/HfO2 tri-layer resistive random access memory (RRAM) structure has been studied with a transparent indium tin oxide (ITO) transparent electrode. Highly stable and reliable multilevel conductance can be controlled by the set current compliance and reset stop voltage in bipolar resistive switching. Improved gradual resistive switching was achieved because of the interdiffusion in the HfO2/Al2O3 interface where tri-valent Al incorporates with HfO2 and produces HfAlO. The uniformity in bipolar resistive switching with Ion/Ioff ratio (>10) and excellent endurance up to >103 cycles was achieved. Multilevel conductance levels in potentiation/depression were realized with constant amplitude pulse train and increasing pulse amplitude. Thus, tri-layer structure-based RRAM can be a potential candidate for the synaptic device in neuromorphic computing.

Hafnium oxide (HfO2) thin films have been made by atomic vapor deposition (AVD) onto Si substrates under different growth temperature and oxygen flow. The effect of different growth conditions on the structure and optical characteristics of deposited HfO2 film has been studied using X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GIXRD) and variable angle spectroscopic ellipsometry (VASE). The XPS measurements and analyses revealed the insufficient chemical reaction at the lower oxygen flow rate and the film quality improved at higher oxygen flow rate. Via GIXRD, it was found that the HfO2 films on Si were amorphous in nature, as deposited at lower deposition temperature, while being polycrystalline at higher deposition temperature. The structural phase changes from interface to surface were demonstrated. The values of optical constants and bandgaps and their variations with the growth conditions were determined accurately from VASE and XPS. All analyses indicate that appropriate substrate temperature and oxygen flow are essential to achieve high quality of the AVD-grown HfO2 films.

HighlightsA stable laminated Al2O3/HfO2 insulator is developed by atomic layer deposition at a relatively lower temperature of 150 °C.The flexible thin-film transistors (TFTs) with bottom-gate top-contacted configuration are fabricated on a flexible substrate with the Al2O3/HfO2 insulator.The flexible TFTs present the carrier mobilities of 9.7 cm2 V−1 s−1, ON/OFF ratio of ~ 1.3 × 106, subthreshold voltage of 0.1 V, saturated current up to 0.83 mA, and subthreshold swing of 0.256 V dec−1.Flexible thin-film transistors (TFTs) have attracted wide interest in the development of flexible and wearable displays or sensors. However, the conventional high processing temperatures hinder the preparation of stable and reliable dielectric materials on flexible substrates. Here, we develop a stable laminated Al2O3/HfO2 insulator by atomic layer deposition at a relatively lower temperature of 150 °C. A sputtered amorphous indium-gallium-zinc oxide (IGZO) with the stoichiometry of In0.37Ga0.20Zn0.18O0.25 is used as the active channel material. The flexible TFTs with bottom-gate top-contacted configuration are further fabricated on a flexible polyimide substrate with the Al2O3/HfO2 nanolaminates. Benefited from the unique structural and compositional configuration in the nanolaminates consisting of amorphous Al2O3, crystallized HfO2, and the aluminate Al–Hf–O phase, the as-prepared TFTs present the carrier mobilities of 9.7 cm2 V−1 s−1, ON/OFF ratio of ~ 1.3 × 106, subthreshold voltage of 0.1 V, saturated current up to 0.83 mA, and subthreshold swing of 0.256 V dec−1, signifying a high-performance flexible TFT, which simultaneously able to withstand the bending radius of 40 mm. The TFTs with nanolaminate insulator possess satisfactory humidity stability and hysteresis behavior in a relative humidity of 60–70%, a temperature of 25–30 °C environment. The yield of IGZO-based TFTs with the nanolaminate insulator reaches 95%.

For neuromorphic computing and high-density data storage memory, memristive devices have recently gained a lot of interest. So far, memristive devices have suffered from switching parameter instability, such as distortions in resistance values of low- and high-resistance states (LRSs and HRSs), dispersion in working voltage (set and reset voltages), and a small ratio of high and low resistance, among other issues. In this context, interface engineering is a critical technique for addressing the variation issues that obstruct the use of memristive devices. Herein, we engineered a high band gap, low Gibbs free energy Al2O3 interlayer between the HfO2 switching layer and the tantalum oxy-nitride electrode (TaN) bottom electrode to operate as an oxygen reservoir, increasing the resistance ratio between HRS and LRS and enabling multilayer data storage. The Pt/HfO2/Al2O3/TaN memristive device demonstrates analog bipolar resistive switching behavior with a potential ratio of HRS and LRS of > 105 and the ability to store multi-level data with consistent retention and uniformity. On set and reset voltages, statistical analysis is used; the mean values (µ) of set and reset voltages are determined to be − 2.7 V and + 1.9 V, respectively. There is a repeatable durability over DC 1000 cycles, 105 AC cycles, and a retention time of 104 s at room temperature. Quantum conductance was obtained by increasing the reset voltage with step of 0.005 V with delay time of 0.1 s. Memristive device has also displayed synaptic properties like as potentiation/depression and paired-pulse facilitation (PPF). Results show that engineering of interlayer is an effective approach to improve the uniformity, ratio of high and low resistance, and multiple conductance quantization states and paves the way for research into neuromorphic synapses.

Non-volatile memory (NVM) will play a very important role in the next-generation digital technologies, including the Internet of things. The metal-oxide memristors, especially based on HfO 2 , have been favored by lots of researchers because of its simple structure, high integration, fast operation speed, low power consumption, and high compatibility with advanced (complementary metal oxide silicon) CMOS technologies. In this paper, a 20-level stable resistance states Al-doped HfO 2 -based memristor is presented. Its cycles endurance, data retention time, and resistance ratio are larger than 10 3 , > 10 4 s, and > 10, respectively.

We report the growth of nanoscale hafnium dioxide (HfO2) and zirconium dioxide (ZrO2) thin films using remote plasma-enhanced atomic layer deposition (PE-ALD), and the fabrication of complementary metal-oxide semiconductor (CMOS) integrated circuits using the HfO2 and ZrO2 thin films as the gate oxide. Tetrakis (dimethylamino) hafnium (Hf[N(CH3)2]4) and tetrakis (dimethylamino) zirconium (IV) (Zr[N(CH3)2]4) were used as the precursors, while O2 gas was used as the reactive gas. The PE-ALD-grown HfO2 and ZrO2 thin films were analyzed using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The XPS measurements show that the ZrO2 film has the atomic concentrations of 34% Zr, 2% C, and 64% O while the HfO2 film has the atomic concentrations of 29% Hf, 11% C, and 60% O. The HRTEM and XRD measurements show both HfO2 and ZrO2 films have polycrystalline structures. n-channel and p-channel metal-oxide semiconductor field-effect transistors (nFETs and pFETs), CMOS inverters, and CMOS ring oscillators were fabricated to test the quality of the HfO2 and ZrO2 thin films as the gate oxide. Current-voltage (IV) curves, transfer characteristics, and oscillation waveforms were measured from the fabricated transistors, inverters, and oscillators, respectively. The experimental results measured from the HfO2 and ZrO2 thin films were compared.

Resistive random-access memory (RRAM) is a promising candidate for next-generation non-volatile memory. However, due to the random formation and rupture of conductive filaments, RRMS still has disadvantages, such as small storage windows and poor stability. Therefore, the performance of RRAM can be improved by optimizing the formation and rupture of conductive filaments. In this study, a hafnium oxide-/aluminum-doped zinc oxide/hafnium oxide (HfO2/Al-ZnO/HfO2) tri-layer structure device was prepared using the sol–gel method. The oxygen-rich vacancy Al-ZnO layer was inserted into the HfO2 layers. The device had excellent RS properties, such as an excellent switch ratio of 104, retention of 104 s, and multi-level storage capability of six resistance states (one low-resistance state and five high-resistance states) and four resistance states (three low-resistance states and one high-resistance state) which were obtained by controlling stop voltage and compliance current, respectively. Mechanism analysis revealed that the device is dominated by ohmic conduction and space-charge-limited current (SCLC). We believe that the oxygen-rich vacancy concentration of the Al-ZnO insertion layer can improve the formation and rupture behaviors of conductive filaments, thereby enhancing the resistive switching (RS) performance of the device.