Low Leakage Current Density Research Articles

Self-Aligned Top-Gate Amorphous InGaZnO TFTs With Plasma Enhanced Chemical Vapor Deposited Sub-10 nm SiO2 Gate Dielectric for Low-Voltage Applications

In this letter, self-aligned top-gate (SATG) amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) with an 8.62-nm SiO2 gate dielectric grown by conventional plasma enhanced chemical vapor deposition (PECVD) at 300 °C are fabricated. The results show that the ultrathin PECVD SiO2 film has excellent dielectric properties, such as a low leakage current density of 10−8 A/cm2 at 2 MV/cm, a high breakdown electric field of 9.3 MV/cm, and an almost independent capacitance of bias frequency. The fabricated SATG a-IGZO TFTs with the ultrathin SiO2 gate dielectric exhibit high electrical performances, with major parameters, including a low gate leakage current of 10−13 A, a small subthreshold swing value of 124 mV/decade, a decent field-effect mobility of 10.13 cm2/ $\text{V}\cdot \text{s}$ , and a high ON/OFF current ratio up to 108. Furthermore, the TFTs also show a good electrical stability under positive and negative gate bias stresses.

Effect of annealing atmosphere on structural and multiferroic properties of BiFeO3 thin film prepared by RF magnetron sputtering

BFO thin films were deposited on Pt substrate by RF magnetron sputtering technology. The effects of annealing atmosphere on the phase evolution, microstructure, surface element chemical state, leakage current density, dielectric, ferroelectric and magnetic properties of BFO thin films were systematically investigated. The XRD analyses reveal that O2 annealing atmosphere benefits to prepare single phase BFO thin film compared with air. AFM images demonstrate that BFO thin film annealed in O2 shows smaller grain size and better surface roughness than that annealed in air. The XPS analyses clarify that Fe2+ and Fe3+ ions are co-existed in both obtained BFO thin films, while BFO thin film annealed in O2 shows lower Fe2+ and oxygen vacancy concentration. Comparing with BFO thin film annealed in air, BFO thin film annealed in O2 shows a lower leakage current density of 4.4 × 10−6 A/cm2 with enhanced dielectric, ferroelectric and magnetic properties. Our results provide useful reference for practical application of BFO thin film prepared by RF magnetron sputtering.

Dielectric property and energy-storage performance of (100)-preferred (1-x)PbTiO3-xBi(Mg0.5Ti0.5)O3 relaxor ferroelectric thin films

In this work, relaxor ferroelectric thin films (1-x)PbTiO3-xBi(Mg0.5Ti0.5)O3 [(1-x)PT-xBMT, x = 0.4, 0.5 and 0.6] were prepared on LaNiO3/Si(100) (LNO/Si) substrates by sol-gel method. All films exhibit a single perovskite structure and possess high compactness. As the BMT content increases, the diffusion coefficient γ increases from 1.84 to 1.92, indicating the gradually enhanced relaxor behavior. The thin film with x = 0.5 has a lower leakage current density than those of other components, which leads to a high breakdown strength. As a result, an ultrahigh recoverable energy-storage density of 51.0 J/cm3 under 2900 kV/cm was achieved in the thin film with x = 0.5. In addition, the 0.5PT-0.5BMT thin film also exhibited excellent frequency stability and temperature stability, and the both changes rate were less than 2.8%. The outstanding energy-storage performance is attributed to its excellent electric-field endurance and relaxor behavior. This work indicates the 0.5PT-0.5BMT thin films is a potential energy-storage material.

Polarization-Graded AlGaN Solar-Blind p-i-n Detector With 92% Zero-Bias External Quantum Efficiency

We report on record high zero-bias external quantum efficiency (EQE) of 92% for back-illuminated Al0.40Ga0.60N p-i-n ultra-violet (UV) photodetectors on sapphire. The zero-bias responsivity measured 211 mA/W at 289 nm, which is the highest value reported for solar-blind, p-i-n detectors realized over any epitaxial wide band-gap semiconductor. This is also the first report for a p-i-n detector, where a polarization-graded Mg-doped AlGaN layer is utilized as the p-contact layer. The devices exhibited a ten-orders of magnitude rectification, a low reverse leakage current density of 1 nA/cm2 at 10 V, a high $\text{R}_{{0}}\text{A}$ product of $1.3\times 10^{{11}} \Omega $ .cm2 and supported fields exceeding 5 MV/cm. The light-to-dark current ratio and the UV-to-visible rejection ratio for the detectors exceeded six-orders of magnitude and the thermal noise limited detectivity (D*) measured $6.1\times 10^{{14}}$ cmHz1/2W−1. The state-of-the-art performance parameters can be attributed to a high crystalline quality absorbing AlGaN epi-layer resulting from the use of an AlN/AlGaN superlattice buffer and an improved p-contact via polarization grading.

Spontaneous Generation of a Molecular Thin Hydrophobic Skin Layer on a Sub-20 nm, High-k Polymer Dielectric for Extremely Stable Organic Thin-Film Transistor Operation.

Polymer dielectric materials with hydroxyl functionalities such as poly(4-vinylphenol) and poly(vinyl alcohol) have been utilized widely in organic thin-film transistors (OTFTs) because of their excellent insulating performance gained by hydroxyl-mediated cross-linking. However, the polar hydroxyl functionality also deleteriously affects the performance of OTFTs and significantly impairs the device stability. In this study, a sub-20 nm, high-k copolymer dielectric with hydroxyl functionality, poly(2-hydroxyethyl acrylate-co-di(ethylene glycol) divinyl ether), was synthesized in the vapor phase via initiated chemical vapor deposition. The inherently dry environment offered by the vapor-phase polymer synthesis prompted the snuggling of polar hydroxyl functionalities into the bulk polymer film to form a molecular thin hydrophobic skin layer at its surface, verified by near-edge X-ray absorption fine structure analysis. The chemical composition of the copolymer dielectric was optimized systematically to achieve high dielectric constant (k ≈ 6.2) as well as extremely low leakage current densities (less than 3 × 10-8 A/cm2 in the range of ±2 MV/cm) even with sub-20 nm thickness, leading to one of the highest capacitance (higher than 300 nF/cm2) achieved by a single polymer dielectric to date. Exploiting the structural advantage of the cross-linked high-k polymer dielectric, high-performance OTFTs were obtained. Notably, the spontaneously formed molecular thin, hydrophobic skin layer in the copolymer film substantially suppressed the hysteresis in the transistor operation. The trap analysis also suggested the formation of bulk trap with a high energy barrier and sufficiently low trap densities at the semiconductor/dielectric interface, owing to the surface skin layer. Furthermore, the OTFTs with the -OH-containing copolymer dielectric showed an unprecedentedly excellent operational stability. No apparent OTFT degradation was observed up to 50 000 s of high constant voltage stress (corresponding to the applied electric field of 1.4 MV/cm) because of the markedly suppressed interfacial trap density by the hydrophobic skin layer, together with the current compensation by the bulk hydroxyl functionalities. We believe that the surface modification-free, one-step polymer dielectric synthetic strategy will provide a new insight into the design of polymer dielectric materials for high-performance, low-power soft electronic devices with high operational stability.

Effects of deposition temperature on the properties of sputtered yttrium-doped hafnium oxide thin films

Yttrium-doped HfO2 (Y:HfO2) thin films with different deposition temperature were deposited on p-type (100) silicon substrates. The composition and chemical states of each element in the films were investigated by x-ray photoelectron spectroscopy (XPS). The grazing angle incidence x-ray diffraction (GIXRD) patterns suggested the phase transformation of Y:HfO2 thin films as the increase of deposition temperature. The thickness and density of the thin films were calculated by fitting x-ray reflectivity (XRR) data. Root mean square (RMS) roughness was obtained from atomic force microscopy (AFM) images. As the deposition temperature increased, a transition from linear dielectric to ferroelectric behavior happened. Lower leakage current density was obtained by increasing the deposition temperature.

Characterization of Al Incorporation into HfO2 Dielectric by Atomic Layer Deposition.

This study presents the characteristics of HfAlO films for a series of Al incorporation ratios into a HfO2 dielectric by atomic layer deposition on a Si substrate. A small amount of Al doping into the HfO2 film can stabilize the tetragonal phase of the HfO2, which helps to achieve a higher dielectric constant (k) and lower leakage current density, as well as a higher breakdown voltage than HfO2 film on its own. Moreover, assimilation of Al2O3 into HfO2 can reduce the hysteresis width and frequency dispersion. These are indications of border trap reduction, which was also verified by the border trap extraction mechanism. X-ray photoelectron spectroscopy (XPS) analysis also verified the HfAlO microstructural properties for various Al compositions. In addition, higher amounts of Al2O3 in HfAlO resulted in better interface and dielectric behavior through trap minimization, although the equivalent-oxide-thickness (EOT) values show the opposite trend.

Low-Temperature Deposition of Inorganic–Organic HfO2–PMMA Hybrid Gate Dielectric Layers for High-Mobility ZnO Thin-Film Transistors

Low-temperature solution-processed inorganic–organic hybrid gate dielectrics are considered as emerging candidates for future low-cost flexible electronic devices, which are alternatives to high-temperature inorganic-based gate dielectric materials. In the present work, we developed a novel inorganic–organic HfO2–PMMA hybrid dielectric material by an efficient eco-friendly sol–gel method, deposited by spin-coating technique and converted into dielectric thin films at a very low thermal annealing temperature of 185 °C. The HfO2–PMMA hybrid thin-film formation was systematically investigated by FTIR and XPS techniques. Subsequently, a very low surface roughness of 0.8 nm and high uniformity of hybrid thin films were observed by tapping-mode AFM. Also, the thin films showed a hydrophilic nature with a high surface energy of 59.9 mJ/m2 as observed by the contact angle technique. The insulating properties of this hybrid film, studied by C–V and I–V measurements, showed very low leakage current density under 1 ...

Ta-doped modified Gd2O3 film for a novel high k gate dielectric

Gadolinium oxide (Gd2O3) film has potential as a candidate gate dielectric to replace HfO2. In this work, we provide a simple method by trace Ta (∼1%) doping to significantly improve the dielectric properties of Gd2O3 film. And effects of annealing temperatures of Ta-doped Gd2O3 (GTO) films are investigated in detail. Results show that GTO film annealed at 500 °C exhibits excellent performance as a novel gate dielectric material for integrated circuit, showing a small surface roughness of 0.199 nm, a large band gap of 5.45 eV, a high dielectric constant (k) of 21.2 and a low leakage current density (Jg) of 2.10 × 10−3 A/cm2. All properties of GTO films are superior to pure Gd2O3 films and these GTO films meet the requirements for next-generation gate dielectrics. In addition, impedance spectrum is first used to analyze the equivalent circuit of GTO based metal-oxide-semiconductor (MOS) capacitors, which represents a new insight to understand observed electrical behaviors.

Aqueous solution-processed, self-flattening AlOx:Y dielectrics for fully-transparent thin-film transistors

Abstract Dielectrics fabrication on rough substrates, always leading to microstructural defects and detrimental dielectric properties eventually, is a great challenge for academic endeavors in this field. We report here on self-flattening AlOx:Y dielectric thin films processed by a facile aqueous solution method. The obtained AlOx:Y dielectrics are dense, large-area uniform, and amenable to accurate control of film thickness by repeating the deposition cycles. In particular, an atomically smooth surface with a RMS of 0.10 nm was realized for the AlOx:Y film with a thickness of 14.5 nm on Si wafer, yielding a low leakage current density of 7.9 × 10-8 A cm-2@2 MV/cm, a dielectric constant of 8.8 @100 Hz, and an attenuated dielectric dispersion property. The interactions between pre-baked YOx underlayer and later-dropped AlOx precursor were comprehensively investigated, in order to understand the film growth mechanism and the origin of self-flattening effect. Fortunately, this self-flattening effect is also applicable to other substrates. A RMS of 0.81 nm was achieved on ITO glasses, and the height distribution profile of the film surface was found to follow symmetric Gaussian distribution. This preparation routine was also examined by device verification in the fully-transparent thin-film transistors. The combination of ease of preparation and attractive physical properties would provide a green-route solution platform for dielectric synthesis, for interface engineering, and for well-performed devices on rough substrates.

Tailoring optical and electrical properties of thin-film coatings based on mixed Hf and Ti oxides for optoelectronic application

In this work multi-magnetron sputtering stand was used for the deposition of the mixed oxides thin films based on HfO2 and TiO2. In order to obtain various material composition the power released to each magnetron (containing metallic hafnium and titanium targets) was precisely selected. Structural, surface, optical, electrical and mechanical properties of as-deposited coatings were analyzed. Depending on the hafnium content in the deposited thin films various types of the microstructure was obtained, i.e. HfO2-monoclinic, amorphous and TiO2-rutile. Increase of Ti content above 28at. % in the as-prepared mixed oxides coatings caused their amorphization. It was found that with an increase of Ti content in prepared coatings their surface roughness and simultaneously water contact angle decreased. Performed measurements of electrical properties revealed that the lowest leakage current density in the range of 10−7–10−8A/cm2 was obtained for amorphous coatings. Moreover, the tailoring of the dielectric constant was possible by a proper selection of material composition and microstructure of the deposited thin films. Average transparency in the visible wavelength region was in the range of ca. 79–86%. The influence of material composition and structure on shifting of the fundamental absorption edge and optical band gap energy was also observed. The refractive index increased with an increase of Ti content, while extinction coefficient was the lowest for amorphous coatings. Additionally, hardness values were dependent on the material composition and optical packing density and were in the range from 7.6GPa to 10.1GPa.

Improvement in bias-stress and long-term stabilities for in-Ga-Zn-O thin-film transistors using solution-process-compatible polymeric gate insulator

Abstract We fabricated the indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) employing a new coatable polymeric insulator, Zeocoat™ (produced by ZEON Corp., Japan) as gate insulators. Zeocoat film thickness was modulated by controlling the dilution ratio and spin-speed. The film showed low leakage current density (10−7 A/cm2 at 1 MV/cm for 215-nm-thick film) and no significant differences in dielectric constants depending on the film thicknesses or the measurement frequencies. Typical device parameters of the IGZO TFTs fabricated with optimum conditions exhibited the carrier mobility at saturation region of 2.4 cm2/V·s and subthreshold swing of 0.25 V/dec. While there were no marked instabilities in the negative-bias stress tests, the threshold voltage shift under the positive-bias stress was reduced as small as 1.5 V by increasing the deposition temperature of the Al2O3 protection layer from 150 °C to 200 °C. The device stability for long shelf-time was also improved through 100-nm-thick Al2O3 passivation layer deposited on top of the TFT.

Comparative study on hydrothermally synthesized undoped and Vanadium doped Zinc Oxide nanorods for nanoelectromechanical systems low-frequency accelerometer application

Lead-free undoped and Vanadium (V) doped Zinc Oxide (ZnO) nanorods were grown on rigid Fluorine-doped Tin Oxide substrates using a simple hydrothermal method. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate was coated on the grown nanorods to form a p-n junction. The optical, crystalline and morphological analysis were done using X-ray diffraction, Ultraviolet-Visible spectroscopy, Field Emission Scanning Electron Microscope and Spectrofluorescence. The decrease in bandgap from 3.1 eV (undoped) to 3 eV (V doped) showed increased conductivity. Current-Voltage analysis depicted an improvement in the electrical properties of V doped device in terms of a low turn-on voltage, rectification ratio and reverse leakage current density. The RC time constant was analyzed using Impedance analysis. A decrease in RC time constant value and internal resistance of 0.06 msec and 1.61 kΩ respectively for V doped ZnO device compared with undoped one showed an improved piezoelectric property. The maximum output voltages of 1.6 V and 1.9 V for 9 Hz and 1 g input respectively were observed in the V doped device. The sensitivity of undoped and V doped device was 1.71 V/g and 1.93 V/g respectively. It is evident that ~12.9% of improved sensitivity is obtained when V is doped into ZnO nanorods.

Investigation of band alignment between InAlAs and atomic-layer-deposited HfO2/Al2O3 by X-ray photoelectron spectroscopy

Band alignments between atomic layer deposition (ALD) HfO2/Al2O3 double layers and InAlAs were investigated by angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The relationship of As and Hf 4f peaks reducing with the decreasing take-off angle θ indicated upward band bending on the InAlAs surface and a potential gradient in the HfO2/Al2O3 layer. AR-XPS measurements were combined with numerical calculations. The valence band and conduction band discontinuity between HfO2/Al2O3 and InAlAs were 2.49 ± 0.2 eV and 1.86 ± 0.2 eV, respectively. A low leakage current density of 7.01 × 10−7 A cm−2 at 1 V and oxide trapped charge densities of 9.925 × 1011 cm−2 were obtained.

Low-Voltage-Operating Transistors and Logic Circuits Based on a Water-Driven ZrGdOx Dielectric with Low-Cost ZnSnO

In current work, the nontoxic, ecofriendly, water-induced (WI) gadolinium doped zirconium oxide (ZrGdOx) gate dielectrics have been integrated with low-cost spin-coating-driven ZnSnO films for thin film transistors (TFTs) and logic circuits with superior performance for the first time. High transmittance over 90% and the formation of the metastable cubic phase of Zr2O have qualified its potential application in transparent electronics. ZnSnO films annealed at 430 °C integrated with ZrGdOx films demonstrate remarkable electrical properties and low-voltage operation (2 V), including a high current on/off ratio of ∼1.1 × 106, large saturation carrier mobility of ∼3.1 cm2 V–1 S–1, extreme low leakage current density of 6 × 10–10 A cm–2, and a slight shift in threshold voltage of 0.26 V for bias stability, respectively. To verify the practicability in logic circuits, the resistor-loaded inverters are built by using ZrGdOx/ZnSnO TFTs. This work first put forward and verified that WI gate dielectrics can be favo...

Lead-free Ba2Bi4Ti5O18 thin film capacitors for energy storage applications

Abstract Lead-free Ba2Bi4Ti5O18 thin film belongs to Aurivillius phase are fabricated on Pt/Ti/SiO2/Si substrates by chemical solution deposition and the ferroelectric, leakage and dielectric are investigated. The derived film shows dielectric constant of 260 at 1 MHz and low leakage current density of 9.4 × 10−6 A/cm2 at 500 kV/cm, respectively. Interestingly, benefit from the large spontaneous and high breakdown electric field, the obtained slim electric field-polarization curve endows large energy storage density (22.6 J/cm3) and high storage efficiency (71.3%) in the Ba2Bi4Ti5O18 capacitors. Additionally, the insignificant decrease of energy storage density (3.5%) and efficiency (2.4%) is obtained after 9.8 × 109 charging-discharging cycling, which indicate senior fatigue endurance property of the film capacitor. Those results not only suggest that Ba2Bi4Ti5O18 thin film have good potential applications as the dielectric energy storage capacitors, but also provide an important clue to further explore isostructural materials in the Aurivillius family compounds.

Tailoring the multiferroic properties of BiFeO3 by co‐doping Er at Bi site with aliovalent Nb, Mn and Mo at Fe site

AbstractSingle phase multiferroic undoped BiFeO3 notoriously suffers due to the poor spin–charge coupling resulting in limitations to device applications. The present work focuses on the tailoring of its multiferroic and magnetoelectric coupling properties by synthesizing multiferroic Bi0.95Er0.05Fe0.98TM0.02O3 (TM = Nb, Mn and Mo) ceramics. The ferroelectric, magnetic, current leakage measurements and magnetoelectric effect were investigated. XRD along with the Reitveld refinement results confirms that all the samples possess perovskite based rhombohedral structure and reveals that doping of (Er, Nb), (Er, Mn) and (Er, Mo) induced the crystallographic distortion in the BFO lattice and hence induced a variation in the bond lengths and bond angle. Dual doping significantly enhanced the electrical, magnetic properties and magnetoelectric coupling as compared to BiFeO3. Doping has lowered the leakage current by three to four orders compared to BFO. The lattice distortion, reduced leakage current and destruction of spin–cycloidal structure could be the origin for these improved features. The (Er, Nb) doped BiFeO3 yields enhanced ferroelectric character with the maximum polarization value of 0.46 µC/cm2, maximum ME coupling of 0.22 mV/cm at a magnetic field of 130 G, an improved magnetization with a remanance value of 0.0903 emu/g and the lowest leakage current density.

Development of High-k Polymer Materials for Use as a Dielectric Layer in the Organic Thin-Film Transistors

In this article, we developed a series of novel high dielectric polymers based on 5-TPM-co-HEMA-co-GMA (TP) and 5-CTPM-co-HEMA-co-GMA (TP–CN) containing alkylated terphenyl and alkylated terphenyl with a cyano group, respectively. These organic insulating materials provide smooth surface topographies, lower leakage current densities (<6 × 10–7 A/cm2 at 2 MV/m), and small dielectric loss (<0.02, 103 to 105 Hz), which display excellent insulating properties. Simultaneously, two kinds of polymer films have higher dielectric constants of 6.8 and 8.6 than other dielectric constants reported in some literatures and most commercial organic dielectric materials. To investigate the potential of TP and TP–CN as gate dielectrics, we successfully prepared bottom-gate top-contact organic thin-film transistors, with para-hexaphenyl (p-6P) as the buffer layer and vanadyl phthalocyanine (VOPc) as the active layer, which yields a higher charge carrier mobility of 0.52 cm2 V–1 s–1 and on/off ratio > 104.

Ternary Gd[sbnd]Y[sbnd]O high k oxide films for next-generation gate dielectrics and their annealing temperature effects

As the feature size of integrated circuits continues to shrink, the key challenge is to find suitable gate dielectric materials to replace SiO2 and HfO2 to reduce leakage current density. In this work, ternary GdYO (GYO) high k films are prepared by radio frequency (RF) sputtering method and are compared with binary Gd2O3 and Y2O3 for their performance as gate dielectrics. The behaviors of these three samples are comprehensively investigated by x-ray diffraction, atomic force microscopy, UV-Visible spectroscopy, electrical measurements and X-ray photoelectron spectroscopy. Result shows that GYO films exhibits excellent performance as gate dielectrics for metal-oxide-semiconductor (MOS) capacitors, showing high dielectric constant (high k) of 20.94 and low leakage current density of 1.5×10−2 A/cm2. In addition, we show the effects of various annealing temperature from 400 to 700 °C on microstructure, band gap and electrical properties of GYO thin films. The results suggest GYO thin films annealing at 500, 600 and 700 °C can act as next-generation gate dielectrics, featuring for large band gaps of 5.31, 5.37 and 5.55 eV, high k values of 20.94, 18.69 and 17.67 as well as low leakage current density of 1.5×10−2, 1.54×10−3 and 9.98×10−4 A/cm2. Finally, the leakage current density transport mechanisms of all samples have been discussed in detail.

Improved performance and stability of In-Sn-Zn-O thin film transistor by introducing a meso-crystalline ZrO2 high-k gate insulator

Electrical characteristics and reliability of an In-Sn-Zn-O (ITZO) thin film transistor (TFT) using ZrO2 as a high-k gate insulator were investigated. Varying the atomic layer deposition process temperature caused differences in the ZrO2 thin film chemical state and microstructure. Corresponding changes in the electrical properties of the thin film were evaluated. While the ZrO2 thin film deposited at 300 °C exhibited an excellent thin film property, the best TFT performance as measured by subthreshold swing, effective mobility, and on/off ratio was achieved with deposition at 250 °C. The formation of meso-crystalline structure and subsequent low leakage current density enhanced the TFT performance along with the suppression of Coulombic scattering and interface defect formation. Moreover, the reliability of the TFT was demonstrated using both positive and negative bias temperature stress measurements.