Antonio T. Lucero

Atomic layer deposition of a high-k dielectric on MoS2 using trimethylaluminum and ozone.

We present an Al2O3 dielectric layer on molybdenum disulfide (MoS2), deposited using atomic layer deposition (ALD) with ozone/trimethylaluminum (TMA) and water/TMA as precursors. The results of atomic force microscopy and low-energy ion scattering spectroscopy show that using TMA and ozone as precursors leads to the formation of uniform Al2O3 layers, in contrast to the incomplete coverage we observe when using TMA/H2O as precursors. Our Raman and X-ray photoelectron spectroscopy measurements indicate minimal variations in the MoS2 structure after ozone treatment at 200 °C, suggesting its excellent chemical resistance to ozone.

Partially Fluorinated Graphene: Structural and Electrical Characterization

Despite the number of existing studies that showcase the promising application of fluorinated graphene in nanoelectronics, the impact of the fluorine bonding nature on the relevant electrical behaviors of graphene devices, especially at low fluorine content, remains to be experimentally explored. Using CF4 as the fluorinating agent, we studied the gradual structural evolution of chemical vapor deposition graphene fluorinated by CF4 plasma at a working pressure of 700 mTorr using Raman and X-ray photoelectron spectroscopy (XPS). After 10 s of fluorination, our XPS analysis revealed a co-presence of covalently and ionically bonded fluorine components; the latter has been determined being a dominant contribution to the observation of two Dirac points in the relevant electrical measurement using graphene field effect transistor devices. Additionally, this ionic C-F component (ionic bonding characteristic charge sharing) is found to be present only at low fluorine content; continuous fluorination led to a complete transition to a covalently bonded C-F structure and a dramatic increase of graphene sheet resistance. Owing to the formation of these various C-F bonding components, our temperature-dependent Raman mapping studies show an inhomogeneous defluorination from annealing temperatures starting at ∼150 °C for low fluorine coverage, whereas fully fluorinated graphene is thermally stable up to ∼300 °C.

In situ x-ray photoelectron spectroscopy and capacitance voltage characterization of plasma treatments for Al2O3/AlGaN/GaN stacks

We investigate the Al2O3/AlGaN/GaN metal-oxide-semiconductor structure pretreated by O2 anneals, N2 remote plasma, and forming gas remote plasma prior to atomic layer deposition of Al2O3 using in situ X-ray photoelectron spectroscopy, low energy electron diffraction, and capacitance- voltage measurements. Plasma pretreatments reduce the Ga-oxide/oxynitride formation and the interface state density, while inducing a threshold voltage instability.

Atomic Layer Deposition of Silicon Nitride Thin Films: A Review of Recent Progress, Challenges, and Outlooks

With the continued miniaturization of devices in the semiconductor industry, atomic layer deposition (ALD) of silicon nitride thin films (SiNx) has attracted great interest due to the inherent benefits of this process compared to other silicon nitride thin film deposition techniques. These benefits include not only high conformality and atomic-scale thickness control, but also low deposition temperatures. Over the past 20 years, recognition of the remarkable features of SiNx ALD, reinforced by experimental and theoretical investigations of the underlying surface reaction mechanism, has contributed to the development and widespread use of ALD SiNx thin films in both laboratory studies and industrial applications. Such recognition has spurred ever-increasing opportunities for the applications of the SiNx ALD technique in various arenas. Nevertheless, this technique still faces a number of challenges, which should be addressed through a collaborative effort between academia and industry. It is expected that the SiNx ALD will be further perceived as an indispensable technique for scaling next-generation ultra-large-scale integration (ULSI) technology. In this review, the authors examine the current research progress, challenges and future prospects of the SiNx ALD technique.

Low temperature synthesis of graphite on Ni films using inductively coupled plasma enhanced CVD

Controlled synthesis of graphite at low temperatures is a desirable process for a number of applications. Here, we present a study on the growth of thin graphite films on polycrystalline Ni films at low temperatures, about 380 °C, using inductively coupled plasma enhanced chemical vapor deposition. Raman analysis shows that the grown graphite films are of good quality as determined by a low ID/IG ratio, ∼0.43, for thicknesses ranging from a few layers of graphene to several nanometer thick graphitic films. The growth of graphite films was also studied as a function of time, precursor gas pressure, hydrogen concentration, substrate temperature and plasma power. We found that graphitic films can be synthesized on polycrystalline thin Ni films on SiO2/Si substrates after only 10 seconds at a substrate temperature as low as 200 °C. The amount of hydrogen radicals, adjusted by changing the hydrogen to methane gas ratio and pressure, was found to dramatically affect the quality of graphite films due to their dual role as a catalyst and an etchant. We also find that a plasma power of about 50 W is preferred in order to minimize plasma induced graphite degradation.

Large ferroelectric polarization of TiN/Hf0.5Zr0.5O2/TiN capacitors due to stress-induced crystallization at low thermal budget

We report on atomic layer deposited Hf0.5Zr0.5O2 (HZO)-based capacitors which exhibit excellent ferroelectric (FE) characteristics featuring a large switching polarization (45 μC/cm2) and a low FE saturation voltage (∼1.5 V) as extracted from pulse write/read measurements. The large FE polarization in HZO is achieved by the formation of a non-centrosymmetric orthorhombic phase, which is enabled by the TiN top electrode (TE) having a thickness of at least 90 nm. The TiN films are deposited at room temperature and annealed at 400 °C in an inert environment for at least 1 min in a rapid thermal annealing system. The room-temperature deposited TiN TE acts as a tensile stressor on the HZO film during the annealing process. The stress-inducing TiN TE is shown to inhibit the formation of the monoclinic phase during HZO crystallization, forming an orthorhombic phase that generates a large FE polarization, even at low process temperatures.

Hydroquinone-ZnO nano-laminate deposited by molecular-atomic layer deposition

In this study, we have deposited organic-inorganic hybrid semiconducting hydroquinone (HQ)/zinc oxide (ZnO) superlattices using molecular-atomic layer deposition, which enables accurate control of film thickness, excellent uniformity, and sharp interfaces at a low deposition temperature (150 °C). Self-limiting growth of organic layers is observed for the HQ precursor on ZnO surface. Nano-laminates were prepared by varying the number of HQ to ZnO cycles in order to investigate the physical and electrical effects of different HQ to ZnO ratios. It is indicated that the addition of HQ layer results in enhanced mobility and reduced carrier concentration. The highest Hall mobility of approximately 2.3 cm2/V·s and the lowest n-type carrier concentration of approximately 1.0 × 1018/cm3 were achieved with the organic-inorganic superlattice deposited with a ratio of 10 ZnO cycles to 1 HQ cycle. This study offers an approach to tune the electrical transport characteristics of ALD ZnO matrix thin films using an organ...

One-dimensional Nanomaterials for Field Effect Transistor (FET) Type Biosensor Applications

One-dimensional, nanomaterial field effect transistors (FET) are promising sensors for bio-molecule detection applications. In this paper, we review fabrication and characteristics of 1-D nanomaterial FET type biosensors. Materials such as single wall carbon nanotubes, Si nanowires, metal oxide nanowires and nanotubes, and conducting polymer nanowires have been widely investigated for biosensors, because of their high sensitivity to bio-substances, with some capable of detecting a single biomolecule. In particular, we focus on three important aspects of biosensors: alignment of nanomaterials for biosensors, surface modification of the nanostructures, and electrical detection mechanism of the 1-D nanomaterial sensors.

Sub-10 nm Tunable Hybrid Dielectric Engineering on MoS2 for Two-Dimensional Material-Based Devices

The successful realization of high-performance 2D-materials-based nanoelectronics requires integration of high-quality dielectric films as a gate insulator. In this work, we explore the integration of organic and inorganic hybrid dielectrics on MoS2 and study the chemical and electrical properties of these hybrid films. Our atomic force microscopy, X-ray photoelectron spectroscopy (XPS), Raman, and photoluminescence results show that, aside from the excellent film uniformity and thickness scalability down to 2.5 nm, the molecular layer deposition of octenyltrichlorosilane (OTS) and Al2O3 hybrid films preserves the chemical and structural integrity of the MoS2 surface. The XPS band alignment analysis and electrical characterization reveal that through the inclusion of an organic layer in the dielectric film, the band gap and dielectric constant can be tuned from ∼7.00 to 6.09 eV and ∼9.0 to 4.5, respectively. Furthermore, the hybrid films show promising dielectric properties, including a high breakdown field of ∼7.8 MV/cm, a low leakage current density of ∼1 × 10-6 A/cm2 at 1 MV/cm, a small hysteresis of ∼50 mV, and a top-gate subthreshold voltage swing of ∼79 mV/dec. Our experimental findings provide a facile way of fabricating scalable hybrid gate dielectrics on transition metal dichalcogenides for 2D-material-based flexible electronics applications.

In-situ XPS study of ALD ZnO passivation of p-In 0.53 Ga 0.47 As

The effects of ALD ZnO passivation of ammonium hydroxide cleaned p-In0.53Ga0.47As is studied in detail with in-situ x-ray photoelectron spectroscopy (XPS), and metal-oxide-semiconductor capacitors (MOSCAPs) are fabricated in order to judge the effectiveness of ZnO as a passivation layer. Diethylzinc (DEZ) and water are used as precursors. Multiple DEZ pulses are used in the first ALD cycle in order to determine the oxide cleanup ability of DEZ. XPS results indicate that DEZ can chemically reduce Ga3+ and As5+ to Ga1+ and As3+ respectively, with the majority of change occurring before the first water pulse. DEZ is found to have minimal oxide cleanup ability, with the overall the amount of As oxide reduced by approximately 15% and Ga oxide remaining unchanged. ZnO passivated MOSCAPs with HfO2 dielectric show significant improvement over MOSCAPs without ZnO passivation. Accumulation frequency dispersion, hysteresis and Dit are all reduced dramatically.