161 research outputs found

    GaN-based Metal-Oxide-Semiconductor Devices

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    Feature Papers in Electronic Materials Section

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    This book entitled "Feature Papers in Electronic Materials Section" is a collection of selected papers recently published on the journal Materials, focusing on the latest advances in electronic materials and devices in different fields (e.g., power- and high-frequency electronics, optoelectronic devices, detectors, etc.). In the first part of the book, many articles are dedicated to wide band gap semiconductors (e.g., SiC, GaN, Ga2O3, diamond), focusing on the current relevant materials and devices technology issues. The second part of the book is a miscellaneous of other electronics materials for various applications, including two-dimensional materials for optoelectronic and high-frequency devices. Finally, some recent advances in materials and flexible sensors for bioelectronics and medical applications are presented at the end of the book

    Graphene: Piecing it together

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    Graphene has a multitude of striking properties that make it an exceedingly attractive material for various applications, many of which will emerge over the next decade. However, one of the most promising applications lie in exploiting its peculiar electronic properties which are governed by its electrons obeying a linear dispersion relation. This leads to the observation of half integer quantum hall effect and the absence of localization. The latter is attractive for graphene-based field effect transistors. However, if graphene is to be the material for future electronics, then significant hurdles need to be surmounted, namely, it needs to be mass produced in an economically viable manner and be of high crystalline quality with no or virtually no defects or grains boundaries. Moreover, it will need to be processable with atomic precision. Hence, the future of graphene as a material for electronic based devices will depend heavily on our ability to piece graphene together as a single crystal and define its edges with atomic precision. In this progress report, the properties of graphene that make it so attractive as a material for electronics is introduced to the reader. The focus then centers on current synthesis strategies for graphene and their weaknesses in terms of electronics applications are highlighted.Comment: Advanced Materials (2011

    Plasma-assisted atomic layer deposition of III-nitride thin films

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    Ankara : Materials Science and Nanotechnology Program of The Graduate School of Engineering and Science of Bilkent University, 2014.Thesis (Ph. D.) -- Bilkent University, 2014.Includes bibliographical references leaves 127-153.III-nitride compound semiconductors and their alloys have emerged as versatile and high-performance materials for a wide range of electronic and optoelectronic device applications. Besides possessing very unique material properties individually, members of the III-nitride family with wurtzite (hexagonal) crystal structure also exhibit direct band gaps, which cover a wide range with values of 6.2, 3.4 and 0.64 eV for AlN, GaN and InN, respectively. In this respect, ternary and quaternary alloys of this family are particularly important since their bandgaps can easily be tuned by adjusting the alloy composition. Although high quality IIInitride thin lms can be grown at high temperatures (>1000 XC) with signi cant rates, deposition of these lms on temperature-sensitive device layers and substrates necessitates the adaptation of low-temperature methods such as atomic layer deposition (ALD). ALD is a special type of chemical vapor deposition, in which the substrate surface is exposed to sequential pulses of two or more precursors separated by purging periods. When compared to other low-temperature thin lm deposition techniques, ALD stands out with its self-limiting growth mechanism, which enables the deposition of highly uniform and conformal thin lms with sub-angstrom thickness control. Moreover, alloy thin lms can be easily deposited by ALD, where lm composition is digitally controlled by the relative number of subcycles. In this thesis, we report on the development of plasma-assisted ALD (PAALD) processes for III-nitrides, and present detailed characterization results for the deposited thin lms and fabricated nanostructures. PA-ALD of polycrystalline wurtzite AlN thin lms was realized at temperatures ranging from 100- 500 XC using trimethylaluminum (AlMe3) as the Al precursor. Films deposited at temperatures within the ALD window (100-200 XC for both ammonia (NH3) and N2/H2 plasma processes) were C-free and had relatively low O concentrations (<3 at.%). We also demonstrated the conformality of AlMe3-NH3 plasma process by fabricating high surface area AlN hollow nano bers using electrospun nylon nano ber mats as sacri cial templates. Our initial e orts for depositing GaN and InN resulted in thin lms with high O concentrations. Although - at rst - the most probable source of this contamination was presumed as the O-containing impurities in the unpuri ed 5N-grade NH3 gas, subsequent experiments revealed the true source as the quartz tube of inductively coupled RF-plasma (ICP) source itself. In view of these circumstances, the choice of N-containing plasma gas (NH3, N2/H2 or N2) determined the severity of O incorporation into AlN and GaN lms deposited by PA-ALD. As an e ort to completely avoid this plasma-related oxygen contamination problem, we replaced the original quartz-based ICP source of the ALD system with a stainless steel hollow cathode plasma (HCP) source. Thereby we demonstrated the low-temperature hollow cathode PA-ALD (HCPAALD) of crystalline AlN, GaN and AlxGa1−xN thin lms with low impurity concentrations (O, C <1 at.%) using AlMe3 and trimethylgallium (GaMe3) as the Al and Ga precursors, respectively. Optical band edge values of the AlxGa1−xN lms shifted to lower wavelengths with the increasing Al content, indicating the tunability of band edge values with alloy composition. HCPA-ALD of InN was also investigated within the scope of this study. Initial results revealed the possibility to obtain single-phase wurtzite InN thin lms using cyclopentadienyl indium (CpIn) as the In precursor.Özgit-Akgün, ÇağlaPh.D

    Deposition and characterization studies of boron carbon nitride (BCN) thin films prepared by dual target sputtering

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    As complementary metal-oxide semiconductor (CMOS) devices shrink to smaller size, the problems related to circuit performance such as critical path signal delay are becoming a pressing issue. These delays are a result of resistance and capacitance product (RC time constant) of the interconnect circuit. A novel material with reduced dielectric constants may compromise both the thermal and mechanical properties that can lead to die cracking during package and other reliability issues. Boron carbon nitride (BCN) compounds have been expected to combine the excellent properties of boron carbide (B4C), boron nitride (BN) and carbon nitride (C3N4), with their properties adjustable, depending on composition and structure. BCN thin film is a good candidate for being hard, dense, pore-free, low-k dielectric with values in the range of 1.9 to 2.1. Excellent mechanical properties such as adhesion, high hardness and good wear resistance have been reported in the case of sputtered BCN thin films. Problems posed by high hardness materials such as diamonds in high cutting applications and the comparatively lower hardness of c-BN gave rise to the idea of a mixed phase that can overcome these problems with a minimum compromise in its properties. A hybrid between semi-metallic graphite and insulating h-BN may show adjusted semiconductor properties. BCN exhibits the potential to control optical bandgap (band gap engineering) by atomic composition, hence making it a good candidate for electronic and photonic devices. Due to tremendous bandgap engineering capability and refractive index variability in BCN thin film, it is feasible to develop filters and mirrors for use in ultra violet (UV) wavelength region. It is of prime importance to understand process integration challenges like deposition rates, curing, and etching, cleaning and polishing during characterization of low-k films. The sputtering technique provides unique advantages over other techniques such as freedom to choose the substrate material and a uniform deposition over relatively large area. BCN films are prepared by dual target reactive magnetron sputtering from a B4C and BN targets using DC and RF powers respectively. In this work, an investigation of mechanical, optical, chemical, surface and device characterizations is undertaken. These holistic and thorough studies, will provide the insight into the capability of BCN being a hard, chemically inert, low-k, wideband gap material, as a potential leader in semiconductor and optics industry

    Yttrium and Scandium in Solution-processed Oxide Electronic Materials.

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    Large area electronics are critical for many novel applications such as smart windows, wearable electronics and Internet of Things. Among candidate materials, metal oxides have relatively good performance and stability and can be deposited by low-cost solution processes. This thesis explores the roles of rare-earth elements yttrium and scandium in solution-processed metal oxide thin films including semiconducting scandium- or yttrium-doped ZTO, conducting scandium- or yttrium-doped zinc oxide, and insulating yttrium-scandium oxide. Yttrium and scandium can act as oxygen getters and stabilizers, and the use of higher-order alloys can improve film thermal stability and electrical performance. First, thin film transistors (TFTs) are used to characterize undoped ZTO films as a baseline. The device performance of solution-processed ZTO TFTs depends on ink Zn to Sn ratio and annealing temperature, optimized to be 7:3 and 480⁰C, respectively. The optimized ZTO has a shallow donor energy level of 7meV and a steep exponential subgap band tail with a percolation energy of 3meV. Sputtered Mo forms an excellent ohmic contact to solution-processed ZTO with a width-normalized contact resistance of 8.7Ω•cm and a transfer length of 0.34μm, making the technology suitable for future sub-micron channel length devices. Yttrium enhances performance of ZTO TFTs at low concentrations (3at%). High yttrium concentrations slightly improve TFT negative bias illumination stress stability by reducing oxygen vacancy-related defects. Second, the introduction of scandium or yttrium in solution-processed ZnO decreases the conductivity by three orders of magnitude, which is ascribed to formation of insulating structures along grain boundaries. Scandium or yttrium also make the resistivity of ZnO more thickness-dependent than undoped ZnO after forming gas anneal, by causing surface depletion and grain disruptions in the film. Third, solution-processed (YxSc1-x)2O3 insulating alloys have comparable dielectric performance to vacuum deposited (YxSc1-x)2O3, with high breakdown field > 4MV/cm, low leakage current and low dielectric frequency dispersion. Even after 900°C anneals induce crystallization, the alloys maintain a high breakdown field. The yttrium- and scandium- doped solution-processed oxides developed here form a complete suite of electronic materials suitable for fabrication of future large-area electronic devices.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133324/1/wbhu_1.pd

    Wide Bandgap Based Devices: Design, Fabrication and Applications, Volume II

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    Wide bandgap (WBG) semiconductors are becoming a key enabling technology for several strategic fields, including power electronics, illumination, and sensors. This reprint collects the 23 papers covering the full spectrum of the above applications and providing contributions from the on-going research at different levels, from materials to devices and from circuits to systems

    Coatings for ALD Reactors to Prevent Metal Contamination on Semiconductor Products

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    Atomic layer deposition (ALD) is a promising processing method for the next generation semiconductor devices. Major advantages of ALD include conformality, uniformity over large areas, precise thickness control, repeatability and high quality of films produced. ALD thin film deposition is done inside an ALD reactor. Typical construction materials of ALD reactors include metal alloys such as stainless steel, aluminum and titanium. These materials contain multiple metallic elements that can be detrimental to the performance, reliability and yield of semiconductor devices. In order to process semiconductor devices with ALD, metal impurity levels originating from the ALD reactor must be controlled. Allowed levels of metal impurities in semiconductor processing are stringent and showing a tightening trend. This has led into the development of new methods for contamination control together with the adoption of more sensitive and robust detection methods for metallic impurities, such as inductively coupled plasma mass spectrometry (ICP-MS). This master thesis focuses on the metallic impurities originating from an ALD reactor and their prevention with ALD coatings. Three typical construction materials, aluminum, titanium and stainless steel were examined. The studied coatings were ALD deposited aluminum oxide (Al2O3), hafnium oxide (HfO2) and their nanolaminate (Al2O3/HfO2). The ability of the coatings to prevent metal impurity transfer from the metals to silicon substrates through the gas phase was studied by exposing the coated metals to two ALD precursors, trimethyl aluminum (TMA) and tris(dimethylamino) cyclopentadienyl hafnium (CpHf(NMe2)3). Metal impurity concentrations on silicon were measured with ICP-MS. Since academic literature concerning control of metal contamination from ALD reactors does not directly exist, the literature part of this thesis was based on relevant related topics. The selected topics included the development of semiconductor industry, role of ALD in this development and new ALD materials and chemistries required. Additionally, protective ALD films and the effects of metal impurities in semiconductor products were reviewed. The overall conclusion of this study was that the ALD coatings provide a worthy solution for metal contamination control. Some differences between the passivation efficiencies of different metal – coating systems were found
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