Ultra-low Leakage Current Density Research Articles

Superionic fluoride gate dielectrics with low diffusion barrier for two-dimensional electronics.

Exploration of new dielectrics with a large capacitive coupling is an essential topic in modern electronics when conventional dielectrics suffer from the leakage issue near the breakdown limit. Here, to address this looming challenge, we demonstrate that rare-earth metal fluorides with extremely low ion migration barriers can generally exhibit an excellent capacitive coupling over 20 μF cm-2 (with an equivalent oxide thickness of ~0.15 nm and a large effective dielectric constant near 30) and great compatibility with scalable device manufacturing processes. Such a static dielectric capability of superionic fluorides is exemplified by MoS2 transistors exhibiting high on/off current ratios over 108, ultralow subthreshold swing of 65 mV dec-1 and ultralow leakage current density of ~10-6 A cm-2. Therefore, the fluoride-gated logic inverters can achieve notably higher static voltage gain values (surpassing ~167) compared with a conventional dielectric. Furthermore, the application of fluoride gating enables the demonstration of NAND, NOR, AND and OR logic circuits with low static energy consumption. In particular, the superconductor-insulator transition at the clean-limit Bi2Sr2CaCu2O8+δ can also be realized through fluoride gating. Our findings highlight fluoride dielectrics as a pioneering platform for advanced electronic applications and for tailoring emergent electronic states in condensed matter.

Low Leakage in High‐k Perovskite Gate Oxide SrHfO3

AbstractReducing the leakage current through the gate oxide is becoming increasingly important for power consumption reduction as well as reliability in integrated circuits as the semiconducting devices continue to scale down. Here, this work reports on the high‐k dielectric SrHfO3 (SHO) based devices with ultralow leakage current density via pulsed laser deposition (PLD). The ultralow current density is achieved by optimizing the growth conditions and the associated structural properties. In the optimized conditions, the dielectric properties of the 50‐nm‐thick SHO capacitors are measured: high dielectric constant (κ = 32), low leakage current density (<10−8 A cm−2 at 2 MV cm−1), and large breakdown field (EBD > 4 MV cm−1). The surprisingly low leakage current density of SHO is ascribed to the large bandgap (≈6 eV), the large conduction band offset (CB offset > 3 eV) with respect to the semiconductor, and the low density of defect states inside the bandgap. The optimized SHO dielectric with high dielectric constant and ultralow leakage current density is proposed for future low‐power consumption devices based on Si as well as perovskite oxide semiconductors.

Integrating GeSn photodiode on a 200 mm Ge-on-insulator photonics platform with Ge CMOS devices for advanced OEIC operating at 2 μm band.

High-performance GeSn multiple-quantum-well (MQW) photodiode is demonstrated on a 200 mm Ge-on-insulator (GeOI) photonics platform for the first time. Both GeSn MQW active layer stack and Ge layer (top Ge layer of GeOI after bonding) were grown using a single epitaxy step on a standard (001)-oriented Si substrate (donor wafer) using a reduced pressure chemical vapor deposition (RPCVD). Direct wafer bonding and layer transfer technique were then employed to transfer the GeSn MQW device layers and Ge layer to a 200 mm SiO2-terminated Si handle substrate. The surface illuminated GeSn MQW photodiode realized on this platform exhibits an ultra-low leakage current density of 25 mA/cm2 at room temperature and an enhanced photo sensitivity at 2 μm of 30 mA/W as compared to a GeSn MQW photodiode on Si at 2 μm. The underlying GeOI platform enables monolithic integration of a complete suite of photonics devices operating at 2 μm band, including GeOI strip waveguides, grating couplers, micro-ring modulators, Mach-Zehnder interferometer modulators, etc. In addition, Ge CMOS circuits can also be realized on this common platform using a "photonic-first and electronic-last" processing approach. In this work, as prototype demonstration, both Ge p- and n-channel fin field-effect transistors (FinFETs) were realized on GeOI simultaneously with decent static electrical characteristics. Subthreshold swings of 150 and 99 mV/decade at |VD| = 0.1 V and drive currents of 91 and 10.3 μA/μm at |VG-VTH| = 1 V and |VD| = 0.75 V were achieved for p- and n-FinFETs, respectively. This works illustrates the potential of integrating GeSn (as photo detection material) on GeOI platform for Ge-based optoelectronics integrated circuits (OEICs) targeting communication applications at 2 μm band.

1230 V β-Ga2O3 trench Schottky barrier diodes with an ultra-low leakage current of <1 μA/cm2

β-Ga2O3 vertical trench Schottky barrier diodes (SBDs) are realized, demonstrating superior reverse blocking characteristics than the co-fabricated regular SBDs. Taking advantage of the reduced surface field effect offered by the trench metal-insulator-semiconductor structure, the reverse leakage current in the trench SBDs is significantly suppressed. The devices have a higher breakdown voltage of 1232 V without optimized field management techniques, while having a specific on-resistance (Ron,sp) of 15 mΩ cm2. An ultra-low leakage current density of <1 μA/cm2 is achieved before breakdown, the lowest among all reported Ga2O3 Schottky barrier diodes. Fast electron trapping and slow de-trapping near the Al2O3/Ga2O3 interface are observed by repeated C-V measurements, which show an interface state ledge and positive shifts of flat-band voltages with increasing voltage stress. By comparison between pulsed and DC measurements, the device self-heating effect and the trapping effect are uncoupled. It is found that the trapping effect at the trench sidewall affects the on-resistance of the trench SBDs, even under pulsed conditions. With reduced trapping effect and better field management technique, the trench SBDs could further harvest the promising material properties of β-Ga2O3.

Self-Suspended Nanomesh Scaffold for Ultrafast Flexible Photodetectors Based on Organic Semiconducting Crystals.

Self-standing nanostructures are of fundamental interest in materials science and nanoscience and are widely used in (opto-)electronic and photonic devices as well as in micro-electromechanical systems. To date, large-area and self-standing nanoelectrode arrays assembled on flexible substrates have not been reported. Here the fabrication of a hollow nanomesh scaffold on glass and plastic substrates with a large surface area over 1 mm2 and ultralow leakage current density (≈1-10 pA mm-2 @ 2 V) across the empty scaffold is demonstrated. Thanks to the continuous sub-micrometer space formed in between the nanomesh and the bottom electrode, highly crystalline and dendritic domains of 6,13-bis(triisopropylsilylethinyl)pentacene growing within the hollow cavity can be observed. The high degree of order at the supramolecular level leads to efficient charge and exciton transport; the photovoltaic detector supported on flexible polyethylene terephthalate substrates exhibits an ultrafast photoresponse time as short as 8 ns and a signal-to-noise ratio approaching 105 . Such a hollow scaffold holds great potential as a novel device architecture toward flexible (opto-)electronic applications based on self-assembled micro/nanocrystals.

Leakage Current Mechanism of InN-Based Metal-Insulator-Semiconductor Structures with Al2O3 as Dielectric Layers.

InN-based metal-insulator-semiconductor (MIS) structures were prepared with Al2O3 as the gate oxides. Surface morphologies of InN films are improved with increasing Mg doping concentrations. At high frequencies, the measured capacitance densities deviate from the real ones with turning frequencies inversely proportional to series resistances. An ultralow leakage current density of 1.35 × 10−9 A/cm2 at 1 V is obtained. Fowler-Nordheim tunneling is the main mechanism of the leakage current at high fields, while Schottky emission dominates at low fields. Capacitance densities shift with different biases, indicating that the InN-based MIS structures can serve as potential candidates for MIS field-effect transistors.

Transparent capacitors based on nanolaminate Al2O3/TiO2/Al2O3 with H2O and O3 as oxidizers

Transparent capacitors with nanolaminate Al2O3/TiO2/Al2O3 (ATA) hybrid dielectrics have been prepared on quartz glass by atomic layer deposition. The maximal capacitance density of 14 fF/μm2 at 1 kHz was obtained. Moreover, an ultralow leakage current density of 2.1 × 10−9 A/cm2 at 1 V was realized by using O3 as the oxidizer. Fowler-Nordheim tunneling is the main mechanism of the leakage current at high fields, while several conduction mechanisms coexist at low fields. The AlZnO/ATA/AlZnO transparent capacitors exhibit an average optical transmittance of more than 80% in the visible range, which serve as good candidates for integration in transparent circuits.

Towards understanding epitaxial growth of alternative high-K dielectrics on Si(001): Application to praseodymium oxide

First investigations demonstrate that crystalline Pr2O3 on Si(001) is a promising candidate for highly scaled gate insulators, displaying a sufficiently high-K value of around 30, ultralow leakage current density, good reliability, and high electrical breakdown voltage. Here, we report on molecular beam epitaxial growth of crystalline praseodymium oxide (as Pr2O3 in the bixbyite or manganese oxide structure) on Si(001) substrates. The Pr2O3 was found to grow as (110)-single-crystalline domains, with two orthogonal in-plane orientations. Investigations of the initial growth phase indicate that the occurrence of these domains is due to the nucleation on neighboring terraces with Si dimer rows (2×1 reconstruction) perpendicular to each other. We postulate the formation of a layer consisting of very small Pr2O3 islands on top of the Si dimers in the initial stage of growth. This interface layer acts as a coincidence lattice on which further growth in the (110) orientation can occur. X-ray photoelectron spectroscopy investigations indicate that the formation of the interface layer is accompanied by oxygen accumulation in the interface.

Epitaxial praseodymium oxide: a new high- K dielectric

We show results for molecular beam epitaxial growth of praseodymium oxide on Si. On Si(1 0 0) oriented surfaces, crystalline Pr 2O 3 grows as (1 1 0)-domains, with two orthogonal in-plane orientations. Epitaxial overgrowth with Si could not been realized so far. We obtain perfect epitaxial growth of hexagonal Pr 2O 3 on Si(1 1 1). These layers can also be overgrown epitaxially with Si leading to novel tunnel structures. Crystalline Pr 2O 3 on Si(0 0 1) is a promising candidate for highly scaled gate insulators, displaying sufficiently high- K value of around 30, ultra-low leakage current density, good reliability, and high electrical breakdown voltage. The Pr 2O 3/Si(0 0 1) interface exhibits the symmetric band alignment, desired for applying such material in both n- and p-type devices. The valence band as well as the conduction band offset to Si is above 1 eV. The electron masses can be assumed to be very heavy in the oxide. This effect together with the suitable band offsets leads to the unusually low leakage currents found experimentally. Finally, the integration of crystalline Pr 2O 3 high- K gate dielectrics into a conventional CMOS process will be demonstrated.

A Silicon-Based Ferroelectric Capacitor for Memory Devices

We study a silicon-based PbTiO3/Pb(Zr0.53Ti0.47)O3/PbTiO3 capacitor,prepared by an improved sol-gel method. The ferroelectriccapacitor has a high remanent polarization of 15 µC/cm2 at a coercive fieldof about 30 kV/cm, an ultra-low leakage current density of 0.1 nA/cm2, and almostfatigue free properties. It can be used as a promising candidate forferroelectric memory devices.

Epitaxial Praseodymium Oxide: A New High-K Dielectric

ABSTRACTWe show results for molecular beam epitaxial (MBE) growth of praseodymium oxide on Si. On Si(100) oriented surfaces, crystalline Pr2O3 grows as (110)-domains, with two orthogonal in-plane orientations. Epitaxial overgrowth with Si could not been realized so far. We obtain perfect epitaxial growth of hexagonal Pr2O3 on Si(111). These layers can also be overgrown epitaxially with Si leading to novel tunnel structures. Crystalline Pr2O3 on Si(OOl) is a promising candidate for highly scaled gate insulators, displaying sufficiently high-K value of around 30, ultra-low leakage current density, good reliability, and high electrical breakdown voltage. The Pr2O3/Si(001) interface exhibits the symmetric band alignment, desired for applying such material in both n- and p-type devices. The valence band as well as the conduction band offset to Si is above 1 eV. The electron masses can be assumed to be very heavy in the oxide. This effect together with the suitable band offsets leads to the unusually low leakage currents found experimentally. Finally, the integration of crystalline Pr2O3 high-K gate dielectrics into a conventional CMOS process will be demonstrated.

High Quality Ferroelectric Capacitor for FeRAM Applications

Lead zirconate titanate (PZT) based ferroelectric capacitor using lead titanate (PT) as seeding layers has been prepared on silicon wafer by an improved sol-gel method. The novel ferroelectric capacitor has high dielectric constant of about 1200, ultralow leakage current density of 0.1nA/cm 2 , high remanent polarization of 20 w C/cm 2 at coercive field of about 30kV/cm, and almost fatigue free properties. The capacitor structure can be valuable for FeRAM applications.