Xinhong Cheng

Improvement of Al2O3 Films on Graphene Grown by Atomic Layer Deposition with Pre-H2O Treatment

We improve the surface of graphene by atomic layer deposition (ALD) without the assistance of a transition layer or surface functionalization. By controlling gas-solid physical adsorption between water molecules and graphene through the optimization of pre-H2O treatment and two-step temperature growth, we directly grew uniform and compact Al2O3 films onto graphene by ALD. Al2O3 films, deposited with 4-cycle pre-H2O treatment and 100-200 °C two-step growing process, presented a relative permittivity of 7.2 and a breakdown critical electrical field of 9 MV/cm. Moreover, the deposition of Al2O3 did not introduce any detective defects or disorders in graphene.

Property transformation of graphene with Al2O3 films deposited directly by atomic layer deposition

Al2O3 films are deposited directly onto graphene by H2O-based atomic layer deposition (ALD), and the films are pinhole-free and continuously cover the graphene surface. The growth process of Al2O3 films does not introduce any detective defects in graphene, suppresses the hysteresis effect and tunes the graphene doping to n-type. The self-cleaning of ALD growth process, together with the physically absorbed H2O and oxygen-deficient ALD environment consumes OH− bonds, suppresses the p-doping of graphene, shifts Dirac point to negative gate bias and enhances the electron mobility.

Direct growth of high-quality Al2O3 dielectric on graphene layers by low-temperature H2O-based ALD

A thin Al2O3 dielectric film was directly grown onto graphene layers without any surface treatment prior to H2O-based atomic layer deposition for the first time. The growth mechanism of Al2O3 dielectric film has been studied by changing the growth temperature and purge time. We found that the film morphology was influenced by the amount and distribution of physically adsorbed precursor molecules on the graphene, especially by physically adsorbed H2O molecules. Within an optimal temperature window, conformal and uniform Al2O3 thin films were obtained as confirmed by atomic force microscopy and transmission electron microscopy results. Raman spectroscopy revealed that no extra defects are generated in the graphene layers. Furthermore, the low leakage current and interface traps in dual-gated graphene field-effect transistors demonstrate the high-quality dielectric/graphene stack.

Improvement of SOI Trench LDMOS Performance With Double Vertical Metal Field Plate

In this paper, a novel high-voltage trench lateral double-diffused metal-oxide-semiconductor field effect transistor (TLDMOS) based on silicon-on-insulator technology is proposed. The new structure is characterized by a double vertical metal field plate (DVFP) in the oxide trench, which is surrounded by heavily doped N/P pillars [superjuction (SJ)]. The DVFP introduces five new electric field peaks in the bulk of drift region compared with the conventional TLDMOS, leading to the breakdown voltage (BV) increase. Furthermore, the DVFP and SJ provide an electrons accumulation layer at the interface of the N pillar and oxide trench under the ON-state, reducing the specific ON-resistance (RON). With the 2-D device simulation, a BV of 840 V and a RON of 60.2 mQ · cm2 are realized on a 25-μm-thick SOI layer and 0.5 μm buried oxide layer, and the Baligas figure of merit [(FOM), FOM = BV2/RON] of 11.4 MW/cm2 is achieved, breaking through the silicon limit.

Effects of rapid thermal annealing on the properties of AlN films deposited by PEALD on AlGaN/GaN heterostructures

Aluminum nitride (AlN) films have been deposited on AlGaN/GaN heterostructure substrates by plasma enhanced atomic layer deposition (PEALD). Different annealing treatments were adopted to change film structure and improve performance. Chemical composition, crystallinity, and electrical properties were studied for AlN films. The results show that some crystal grains appear in the films after annealing at a temperature of over 800 °C. The film crystalline quality increases as the annealing temperature rises. The N–O–Al bond decomposes during the high temperature annealing in N2, and some new N–Al bonds are formed in the AlN films. Annealing promotes the elemental interdiffusion between the films and the substrates. High-temperature annealing at 1000 °C in a nitrogen atmosphere can effectively promote complete nitridation of the AlN film, reduce the nitrogen vacancies, and cause the AlN film to form a semiconductor-like structure.

Interfacial structures and electrical properties of HfAl2O5 gate dielectric film annealed with a Ti capping layer

HfAl2O5 gate dielectric film with an O-gettering Ti capping layer treated with rapid thermal annealing process and its interfacial structure and electrical properties were reported. X-ray reflectivity measurements and x-ray photoelectron spectroscopy suggested that the interfacial layers were composed of a 0.5nm HfAlSiO layer and a 1.5nm Six(SiO2)1−x (x<1) layer for the as-deposited film. However, for the annealed film, HfAlSiO layer was not found and the 1.5nm Six(SiO2)1−x transformed to a 1nm SiO2. The electrical measurements indicated that the equivalent oxide thickness decreased to 2.9nm, and the leakage current was only 70μA∕cm2 at the gate bias of 10MV∕cm for the annealed film.

Al2O3/NbAlO/Al2O3 sandwich gate dielectric film on InP

Al2O3/NbAlO/Al2O3 sandwich dielectric films were grown on InP substrate and annealed. X-ray reflectivity measurements suggested that 1.0 nm interfacial layer existed at InP interface, x-ray diffraction and high resolution transmission electron microscopy indicated the films were crystallized. X-ray photoelectron spectra indicated the oxidization of InP substrate, and the valence-band offset between the dielectric film and InP interface was calculated to be 3.1 eV. The electrical measurements indicated that the leakage current density was 40 mA/cm2 at gate bias of 1 V, and the equivalent oxide thickness and the dielectric constant were 1.7 and 20 nm, respectively.

HfO2 dielectric film growth directly on graphene by H2O-based atomic layer deposition

Due to its exceptionally high carrier mobility, International Technology Roadmap for Semiconductors considers graphene to be among the candidate materials for postsilicon electronics. In order to realize graphene-based devices, thin and uniform-coverage high-κ dielectrics without any pinholes on top of graphene is required. There are no dangling bonds on defect-free graphene surface; it is difficult to grow uniform-coverage high-κ dielectrics on graphene directly by atom layer deposition. Meanwhile, degradation of defects in graphene/high-κ structure is necessary for the optimization of high-κ dielectrics fabrication technology. Here the authors report on a H2O-based atom layer deposition method used for HfO2 growth, where physically adsorbed H2O molecules on graphene surface act as oxidant, and self-limit react with metal precursors to form HfO2 film onto graphene directly. Raman spectra reveal H2O-based atom layer deposition method will not introduce defects into graphene. The surface root mean square o...

Competitive Si and La effect in HfO2 phase stabilization in multi-layer (La2O3)0.08(HfO2) films

The effect of Si diffusion in HfO2 and the presence of La on phase transformation were investigated. Tetragonal HfO2 structures exhibited high permittivity, and the addition of exotic atoms to HfO2 facilitated tetragonal phase transformation. In multi-layer (La2O3)0.08(HfO2) films, the top HfO2 layer was transformed into a perfect tetragonal structure, and the bottom HfO2 layer near the interfacial layer was of a cubic structure, after annealing at 800 °C. The permittivity reached 50–60. Si diffusion into the HfO2 film stabilized the tetragonal structure, and La incorporation into HfO2 facilitated the transition of the cubic structure.

Direct growth of Sb2Te3 on graphene by atomic layer deposition

The direct growth of Sb2Te3 on graphene is achieved by atomic layer deposition (ALD) with pre-(Me3Si)2Te treatment. The results of atomic force microscopy (AFM) indicate Volmer–Weber island growth is the dominant growth mode for ALD Sb2Te3 growth on graphene. High resolution transmission electron microscopy (HRTEM) analysis reveals perfect crystal structures of Sb2Te3 on graphene and no interface layer generation. The characterization of X-ray photoelectron spectroscopy (XPS) implies the impermeability of graphene can maintain Sb2Te3 intact and isolate the adverse effects of substrates. Our study provides a step forward to grow high quality Sb2Te3 at low temperature and expand the potential applications of graphene in ALD techniques.