Ding Shi-Jin

Characterization of Al2O3 Thin Films on GaAs Substrate Grown by Atomic Layer Deposition

Al2O3 thin films are grown by atomic layer deposition on GaAs substrates at 300°C. The structural properties of the Al2O3 thin film and the Al2O3/GaAs interface are characterized using x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and x-ray photoelectron spectroscopy (XPS). The XRD results show that the as-deposited Al2O3 film is amorphous. For 30 atomic layer deposition growth cycles, the thicknesses of the Al2O3 thin film and the interface layer from the HRTEM are 3.3 nm and 0.5 nm, respectively. XPS analyses reveal that the Al2O3/GaAs interface is almost free from As2O3.

FTIR Characterization of Fluorine Doped Silicon Dioxide Thin Films Deposited by Plasma Enhanced Chemical Vapor Deposition

Fluorine doped silicon dioxide (SiOF) thin films have been prepared by plasma enhanced chemical vapor deposition. The Fourier transform infrared spectrometry (FTIR) spectra of SiOF films are deliberated to reveal the structure change of SiO2 and the mechanism of dielectric constant reduction after doping fluorine. When F is doped in SiO2 films, the Si-O stretching absorption peak will have a blue-shift due to increase of the partial charge of the O atom. The FTIR spectra indicate that some Si-OH components in the thin film can be removed after doping fluorine. These changes reduce the ionic and orientational polarization, and result in the reduction in dielectric constant of the film. According to Gaussian fitting, it is found that the Si-F2 bonds will appear in the SiOF film with increase of the fluorine content. The Si-F2 structures are liable to react with water, and cause the same increase of absorbed moisture in the film.

Effect of Trimethyl Aluminium Surface Pretreatment on Atomic Layer Deposition Al2O3 Ultra-Thin Film on Si Substrate

Ultra-thin Al2O3 dielectric films have been deposited on Si substrates by using trimethyl aluminium (TMA) and water as precursors in an atomic layer deposition (ALD) system. Growth of the interfacial layer between ultra-thin Al2O3 and the Si substrate is effectively suppressed by a long-time TMA surface pretreatment of the Si substrate prior to Al2O3 atomic layer deposition. High resolution transmission electron microscopy (TEM) images show that the thickness of the interfacial layer is reduced to be 0.5 nm for the sample with TMA pretreatment lasting 3600 s. The x-ray photoelectron spectroscopy results indicate that the Al2O3 film deposited on the TMA-pretreated Si surface exhibits very good thermal stability. However, a hysteresis of about 50 mV is observed in the C–V curve of the samples with the TMA pretreatment.

Atomic Layer Deposition of Al2O3 on H-Passivated GeSi: Initial Surface Reaction Pathways with H/GeSi(100)-2 × 1

The reaction mechanisms of Al(CH3)3 (TMA) adsorption on H-passivated GeSi(100)-2 ? 1 surface are investigated with density functional theory. The Si?Ge and Ge?Ge one-dimer cluster models are employed to represent the GeSi(100)-2 ? 1 surface with different Ge compositions. For a Si-Ge dimer of a H-passivated SiGe surface, TMA adsorption on both Si?H* and Ge?H* sites is considered. The activation barrier of TMA with the Si?H* site (1.2eV) is higher than that of TMA with the Ge-H* site (0.91 eV), which indicates that the reaction proceeds more slowly on the Si-H* site than on the Ge-H* site. In addition, adsorption of TMA is more energetically favorable on the Ge?Ge dimer than on the Si?Ge dimer of H-passivated SiGe.

Band Structures of Metal-Oxide Capped Graphene: A First Principles Study

We perform a first-principles calculation based on density functional theory to investigate the interface between single layer graphene and metal oxides. Our study reveals that the monolayer graphene becomes semiconducting by single crystal SiO2 and Al2O3 contact, with energy gaps to ~ 0.9 and ~ 1.8eV, respectively. We find the gap originates from the breakage of π bond integrity, whose extent is related to the interface atom configuration. We believe that our results highlight a promising direction for the feasibility to apply large scale graphene layers as building blocks in future electronics devices.

Improvement of Atomic-Layer-Deposited Al2O3/GaAs Interface Property by Sulfuration and NH3 Thermal Nitridation

Fermi level pinning at the interface between high-κ gate dielectric and GaAs induced by unstable native oxides is a major obstacle for high performance GaAs-based metal-oxide-semiconductor (MOS) devices. We demonstrate the improved Al2O3/GaAs interfacial characteristics by (NH4)2S immersion and NH3 thermal pretreatment prior to Al2 O3 deposition. X-ray photoelectron spectroscopy (XPS) analysis confirms that sulfuration of GaAs surface by (NH4)2S solution can effectively reduce As-O bonds while Ga-O bonds and elemental As still exist at Al2 O3/GaAs interface. However, it is found that N incorporation during the further thermal nitridation on sulfurated GaAs can effectively suppress the native oxides and elemental As in the sequent deposition of Al2O3. Atomic force microscopy (AFM) shows that the further thermal nitridation on sulfurated GaAs surface can also improve the surface roughness.

Electrical Characterization of Metal–Insulator–Metal Capacitors with Atomic-Layer-Deposited HfO2 Dielectrics for Radio Frequency Integrated Circuit Application

Metal–insulator–metal (MIM) capacitors with atomic-layer-deposited HfO2 dielectric and TaN electrodes are investigated for rf integrated circuit applications. For 12 nm HfO2, the fabricated capacitor exhibits a high capacitance density of 15.5 fF/μm2 at 100 kHz, a small leakage current density of 6.4×10−9 A/cm2 at 1.8 V and 125°C, a breakdown electric field of 2.6 MV/cm as well as voltage coefficients of capacitance (VCCs) of 2110 ppm/V2 and -824 ppm/V at 100 kHz. Further, it is deduced that the conduction mechanism in the high field range is dominated by the Poole–Frenkel emission, and the conduction mechanism in the low field range is possibly related to trap-assisted tunnelling. Finally, comparison of various HfO2 MIM capacitors is present, suggesting that the present MIM capacitor is a promising candidate for future rf integrated circuit application.

Determining the influence of ferroelectric polarization on electrical characteristics in organic ferroelectric field-effect transistors

Organic ferroelectric field-effect transistors (OFeFETs) are regarded as a promising technology for low-cost flexible memories. However, the electrical instability is still a critical obstacle, which limits the commercialization process. Based on already established models for polarization in ferroelectrics and charge transport in OFeFETs, simulation work is performed to determine the influence of polarization fatigue and ferroelectric switching transient on electrical characteristics in OFeFETs. The polarization fatigue results in the decrease of the on-state drain current and the memory window width and thus degrades the memory performance. The output measurements during the ferroelectric switching process show a hysteresis due to the instable polarization. In the on/off measurements, a large writing/erasing pulse frequency weakens the polarization modulation and thus results in a small separation between on- and off-state drain currents. According to the electrical properties of the ferroelectric layer, suggestions are given to obtain optimal electrical characterization for OFeFETs.

Preparation of Ultra Low-κ Porous SiOCH Films from Ring-Type Siloxane with Unsaturated Hydrocarbon Side Chains by Spin-On Deposition

An ultra-low-dielectric-constant (ultra low-k, or ULK) porous SiOCH film is prepared using a single ring-type siloxane precursor of the 2,4,6,8-tetravinyl-2,4,6,8-tetramethylcyclotetrasiloxane by means of spin-on deposition, followed by crosslinking reactions between the precursor monomers under UV irradiation. The as-prepared film has an ultra low k of 2.41 at 1 MHz due to incorporation of pores and hydrocarbon crosslinkages, a leakage current density of 9.86 × 10−7 A/cm2 at 1 MV/cm, as well as a breakdown field strength of ~1.5 MV/cm. Further, annealing at 300°C results in lower k (i.e., 1.94 at 1 MHz), smaller leakage current density (2.96 × 10−7 A/cm2 at 1 MV/cm) and higher breakdown field strength (about 3.5 MV/cm), which are likely caused by the short-ranged structural rearrangement and reduction of defects in the film. Finally, the mechanical properties and surface morphology of films are also evaluated after different temperature annealing.

High density Al2O3/TaN-based metal–insulator–metal capacitors in application to radio frequency integrated circuits

Metal–insulator–metal (MIM) capacitors with atomic-layer-deposited Al2O3 dielectric and reactively sputtered TaN electrodes in application to radio frequency integrated circuits have been characterized electrically. The capacitors exhibit a high density of about 6.05 fF/μm2, a small leakage current of 4.8×10−8 A/cm2 at 3V, a high breakdown electric field of 8.61MV/cm as well as acceptable voltage coefficients of capacitance (VCCs) of 795 ppm/V2 and 268ppm/V at 1 MHz. The observed properties should be attributed to high-quality Al2O3 film and chemically stable TaN electrodes. Further, a logarithmically linear relationship between quadratic VCC and frequency is observed due to the change of relaxation time with carrier mobility in the dielectric. The conduction mechanism in the high field ranges is dominated by the Poole–Frenkel emission, and the leakage current in the low field ranges is likely to be associated with trap-assisted tunnelling. Meanwhile, the Al2O3 dielectric presents charge trapping under low voltage stresses, and defect generation under high voltage stresses, and it has a hard-breakdown performance.