Semiconductor Research Research Articles

In-Situ Studies on 2D Materials

The investigation of 2D materials such as graphene and transition metal dichalcogenides for beyond CMOS device concepts emphasizes the importance of surface and interfacial reactions. A fundamental understanding of such reactions in the context of materials integration for devices greatly benefits from in-situ characterization methods where processes such as surface cleaning, film deposition, and annealing can be simulated and subsequently correlated to device behavior. This invited talk will review our recent work on in-situ characterization of 2D materials in the context of device applications and the correlation of the physical and electrical characterization.This research is supported in part by the STARNet Center for Low Energy Systems Technology, sponsored by the Semiconductor Research Corporation (SRC) and DARPA, the SWAN Center sponsored by the SRC Nanoelectronics Research Initiative and NIST, and by an IBM Faculty Award.

Semiconductor Research Corporation: A Case Study in Cooperative Innovation Partnerships

In the study of innovation institutions, it is important to consider how different institutional models can affect a research organization in conducting or funding successful work. As an industry collaborative, Semiconductor Research Corporation (SRC) provides an example of a privately funded institution that leverages the inputs of several member companies, along with federal funding, to accomplish innovation in its mission area. SRC has several component programs, all attempting to find innovative solutions to semiconductor problems, but on different time scales, and in different technology areas. But how does SRC use its resources to ensure these goals? Through data gathered from semi-structured qualitative interviews and SRC documentation, this paper addresses that question. SRC has found a way to leverage industry money to motivate and develop a robust field of university research for over 30 years. SRC uses several mechanisms for maintaining an application focused, member-centered decision process, institutional flexibility, and strong ties between industry contributors and university researchers. SRC has continued to keep its members satisfied by training thousands of graduate students for employment in their member companies, by focusing on precompetitive research that addresses industry requirements, and doing so in a manner that operates leanly, with low overhead to its funders. Given these successes, we identify aspects of SRC operations, such as a focus on its member company needs, frequent interactions between funders and researchers, flexible funding mechanisms, and focus on workforce development, that may be diffusible to innovation institutions, including federal research efforts.

GaN Switches in Pulsed Power: A Comparative Study

Present research in widebandgap semiconductors is concentrated predominantly in continuous-wave applications. While their applicability for pulsed power is recognized, little work has been done in taking advantage of the individual characteristics, such as the large drift velocities, of the candidate materials. Analysis of the relative merits of the key semiconductor technologies - Si, GaAs, SiC, and GaN - in the pulsed-power regime is presented, including limitations associated with majority carrier operation and thermal transients. We will also discuss a GaN photoconductor with a vertical topology, which is particularly well suited to higher current applications and also is geometrically more applicable for integration to transmission lines without degrading the high blocking field (2 MV/cm) now available. The relation between the blocking voltage and conduction current typical of majority carrier operation is analyzed and we will show how optical carrier generation provides the much higher switching power associated with bipolar operation.

(Invited) Electrical Characterization of Defects in Al2O3

Nanocrystalline high-k dielectrics play a major role in semiconductor research and development. The semiconductor industry faces nanocrystalline dielectrics for MIM capacitors in DRAM devices [1] and rf applications, as well as for gate dielectrics in sub 45 nm devices.However, the use of crystalline dielectrics lead to new effects like trapping, stress induced leakage currents [2, 3], change in the field extrapolation model of lifetime [4] and an increase of dielectric absorption effects [5]. Most of the described effects are connected to the formation of defect states within the bandgap of the dielectric material. We will review our work on electrical characterization of amorphous and crystalline dielectrics of materials like Al2O3, HfO2, ZrO2 and SrZrO. The time constants of the dielectric absorption of the dielectrics differ very strongly and mainly for the crystalline dielectrics they show strong load voltage dependence. This can be attributed to a very effective tunneling process into a defect band in the high-k-Material at voltages of 0.6-0.7 V. Additionally, optical stimulated leakage current measurements at 15 K will be shown. Here, defects states in the dielectric and at the interface dielectric-semiconductor can be optically stimulated with IR-light for different sub-band-gap energies.By the different described methods a detailed characterization of the energy of the investigated bulk and interface traps of the high-K material in combination with Si and GaN substrates are carried out.[1] J. Heitmann, A. Avellan, T. Boescke, E. Erben, B. Hintze, S. Jakschik, S. Kudelka, and U. Schroeder, ECS. Trans. 2,217 (2006).[2] D. Zhou, U. Schroeder, J. Xu, J. Heitmann, G. Jegert, W. Weinreich, M. Kerber, S. Knebel, E. Erben, and T. Mikolajick, J. of Appl. Phys. 108 (2010) 124104.[3] A. Paskaleva, M. Lemberger, A.J. Bauer, W. Weinreich, J. Heitmann, E. Erben, U. Schröder, and L. Oberbeck, J. Appl. Phys. 106 (2009) 054107.[4] R. Agaiby, P. Hofmann, D. Zhou, M. Kerber, J. Heitmann, U. Schroeder, E. Erben, L. Oberbeck, IEEE Elect. Dev. Lett. 30 (4) (2009) 340-342.[5] M. Kerber, C. Fachmann, J. Heitmann, S. Kudelka, U. Schröder, H. Reisinger, J. Vac. Sci. Technol. B 27(1) (2009) 321-324.

Nitride Semiconductors

AbstractThe 10th International Conference on Nitride Semi‐ conductors (ICNS‐10) was held in Washington, DC, USA from 25th to 30th August 2013. The conference continues the successful series of biennial events started in Nagoya in 1995, and followed by meetings in Tokushima (1997), Montpellier (1999), Denver (2001), Nara (2003), Bremen (2005), Las Vegas (2007), Jeju (2009) and most recently Glasgow, Scotland in 2011.Despite ongoing global economic challenges, the conference was very well attended with 893 attendees from 31 countries enjoying a summer week in Washington, experiencing American culture, through tours of some of America's most historical monuments or of nine world‐famous museums, in addition to the scientific program. The steady attendance is testament to the continuing development of III‐nitrides as a material for a wealth of applications, including those needed for a 'greener' world, with increasing applications in more powerful and efficient lighting, electrical power manipulation, and electric vehicles.A total of 932 abstracts were submitted to the conference, leading to 271 oral and 504 poster presentations. The field continues to grow and diversify, and as a result, the conference series ran four parallel sessions. The meeting was divided into 20 different symposia, covering the entire spectrum of III‐nitride semiconductor research and application, extending to cover newer, or less developed concepts such as solar cells and sensor applications.The organizers are very grateful to the 52 members of the program committee who worked tirelessly to solicit and then rank the submissions, as well as identifying topics and stimulating invited speakers. We are particularly grateful to the subject chairs (A. Doolittle, M. Wraback and D. Jena) and regional chairs (F. Ponce, Y. Nanishi and A. Krost) for their invaluable help and advice, and to Z. Sitar, S. Keller, W. Goetz, L. Schowalter and T. P. Chow for coordinating the stimulating rump sessions. Many thanks are due to the International Advisory Committee for their guidance concerning the event arrangements, conference structure and invited speakers. We would especially like to acknowledge the sponsors and agencies for all their financial support, particularly the Office of Naval Research, Army Research Office, Sandia National Laboratory, National Science Foundation, Zeiss, Nichia, Laytec, and Nitride Semiconductors Foundation of Japan who together sponsored 94 young scientists with travel support. Furthermore we thank Aixtron, Osram, Plasma‐Therm, Crystal IS and Dow Electronic Materials for sponsorship of social functions. We also thank the 33 exhibitors who participated in the meeting. Finally, we especially want to thank the Materials Research Society and the Gaylord National Resort for meeting and local arrangements assistance.We received 182 submissions for the conference proceedings to be published in physica status solidi, using their standard evaluation procedures. Of these, 158 have been accepted for publication in this special volume, with 13 being accepted for the special sections: Phys. Status Solidi A. We are grateful to the editorial support provided by Stefan Hildebrandt, Julia Hübner and their team in bringing the proceedings together, as well as to our Guest co‐Editors (D. D. Koleske, H. Amano and M. Kuball) who worked diligently to arrange quality reviews of submitted manuscripts.Finally, we thank all those who attended and contributed to making ICNS‐10 such an enjoyable conference and we look forward to meeting you all again in Bejing at ICNS‐11 in 2015. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrochemical Synthesis of Red Fluorescent Silicon Nanoparticles

Herein, we report on the preparation of red fluorescent Si nanoparticles stabilized with styrene. Nano-sized Si particles emit fluorescence under UV excitation, which could be used to open up new applications in the fields of optics and semi-conductor research. Unfortunately, conventional methods for the preparation of red fluorescent Si nanoparticles suffer from the lack of a fully-established standard synthesis protocol. A common initial approach during the preparation of semi-conductors is the etching of crystalline Si wafers in a HF/ ethanol/H2O bath, which provides a uniformly-etched surface of nanopores amenable for further nano-sized modifications via tuning of various parameters. Subsequent sonication of the etched surface crumbles the pores on the wafer, resulting in the dispersion of particles into the solution. In this study, we use styrene to occupy these platforms to stabilize the surface. We determine that the liberated silicon particles in ethanol solution interact with styrene, resulting in the substitution of Si-H bonds with those of Si-C as determined via UV photocatalysis. The synthesized styrene-coated Si nanoparticles exhibit a stable, bright, red fluorescence under excitation with a 365 nm UV light, and yield approximately 100 mg per wafer with a synthesis time of 2 h. We believe this protocol could be further expanded as a cost-effective and high-throughput standard method in the preparation of red fluorescent Si nanoparticles.

Progress in next-generation organic electroluminescent materials: material design beyond exciton statistics

Exciton (or spin) statistics is a physical principle based on the statistics of spin multiplicity. In electroluminescence, injected electrons and holes have randomized spin states, and usually form singlet or triplet excitons in the ratio of 1:3. Exciton statistics determines that the upper limit of internal quantum efficiency is 25% in fluorescent devices, since only singlet exciton can decay radiatively. However, both experimental and theoretical evidence indicate that the actual efficiency can exceed the exciton statistics limit of 25% by utilizing materials with special electronic structure and optimized device structures. These results bring light to break through the exciton statistics limit and develop new-generation fluorescent materials with low cost and high efficiency. Recently, the exciton statistics, which has attracted great attention in the past decade, is being rejuvenated due to the discovery of some fluorescent materials with abnormally high efficiencies. In view of their significance in theoretical research of organic semiconductors and developing new-generation OLED materials, such materials are widely investigated in both academic institutions and industry. Several key issues still require further clarification for this kind of materials, such as the molecular design concepts. Herein, we review the progress of the materials with efficiency exceeding the exciton statistics limit, and the routes to improve exciton utilization efficiency. In the end, we present an innovative pathway to fully harvest the excitons in fluorescent devices, namely, “hot exciton” model and relevant fluorescence material with hybridized local and charge-transfer (HLCT) excited state.

Automatic TCAD model calibration for multi-cellular Trench-IGBTs

TCAD simulators are a consolidate tool in the field of the semiconductor research because of their predictive capability. However, an accurate calibration of the models is needed in order to get quantitative accurate results. In this work a calibration procedure of the TCAD elementary cell, specific for Trench IGBT with a blocking voltage of 600V, is presented. It is based on the error minimization between the experimental and the simulated terminal curves of the device at two temperatures. The procedure is applied to a PT-IGBT and a good predictive capability is showed in the simulation of both the short-circuit and turn-off tests.

A comparison between minimum variance control and other online compensation methods for specimen drift in transmission electron microscopy

Transmission electron microscopes (TEMs) are the tools of choice in materials science, semiconductor, and biological research and it is expected that they will be increasingly used to autonomously perform high-volume, repetitive, nano-measurements in the near future. Thus, there is a clear need to develop automation strategies for these microscopes. In particular, an important feature in need of automation is specimen drift compensation, which is a common cause of image blurring in long-exposure TEM images, especially at high magnifications. In this paper, a systematic online approach to specimen drift compensation, called adaptive minimum variance control, is discussed in detail. The method makes use of an identified drift model, continuously updated from online drift measurements, to predict and ameliorate future drift values, significantly reducing their variance. The method's performance, measured in terms of drift variance reduction, is illustrated using both experimental and simulated data, and it is then compared with the performance of two pragmatic model-free methods: last data point prediction and linear extrapolation prediction.

Focus on analytical equipment and diagnostics

Focus on analytical equipment and diagnostics

Perspectives on future directions in III-N semiconductor research

The family of III-V nitride semiconductors has garnered significant research attention over the last 20–25 years, and these efforts have led to many highly successful technologies, especially in the area of light emitting devices such as light emitting diodes for solid state white lighting and lasers for high density optical read/write memories. These applications have taken advantage of a key material property of the III-N materials, namely a direct, tunable (0.7–6.2 eV, λ ∼ 200 nm to 1.7 μm) bandgap and have been accomplished despite a relatively poor level of material quality. But a direct, tunable bandgap is only one of many interesting properties of III-N materials of interest to potential future technologies. A considerable list of first and second order properties make this family of semiconductors even more attractive—namely, electric polarization, piezoelectricity, high breakdown field, pyroelectricity, electro-optic and photo-elastic effects, etc. The first few of these have found much utility in the development of high power transistors that promise significant commercial success in both communications and power switching applications. As these areas begin to flourish, it is reasonable to begin to explore what might be next for this versatile family of semiconductors. Here are highlighted three areas of significant potential for future III-N research—atomic layer epitaxy of complex heterostructures, variable polarity homo- and hetero-structures of arbitrary geometries, and nanowire heterostructures. Early results, key technical challenges, and the ultimate potential for future technologies are highlighted for each research path.

Abnormal Temperature-Dependent Electron Transport in Hole Transport Material N,N′-Diphenyl-N,N′-bis(3- methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD)

Charge transport is important both in the research and application of organic semiconductors. For hole transport materials, most works focus on the transport characteristics of holes while less attention is paid to that of electrons. In this study, electron currents in N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD) thin films were studied. It is found that temperature dependence of electron conduction of TPD varies with driving voltage: in low voltage range, the electron conduction increases with temperature, while in the high voltage range it decreases abnormally with increasing temperature. Neither trapped-charge-limited current with exponential distribution of traps nor trap free space-charge-limited current with electric-field-dependent mobility could be used to interpret all the observed phenomena. The inability of current models to explain the phenomena indicates that the electron transport mechanism of TPD is different from that of holes.

Use of dynamic compression to probe semiconductor response at large strains

AbstractLarge strains in semiconductors are expected to be more common in future electronic devices utilizing nanostructure components. Hydrostatic pressure (HP) and uniaxial stress (US) loading have inherent limitations for probing the desired strain conditions. Uniaxial strain loading, achieved in dynamic compression experiments, is particularly attractive for attaining well‐defined, large strains and to complement HP and US loading. Recent dynamic compression studies on III–V semiconductors (GaN, GaP, and GaAs) are summarized to review notable findings ranging from improved deformation potentials to free carrier properties. These findings demonstrate the benefits of dynamic compression experiments for semiconductor research.

Role of Simulation Technology for the Progress in Power Devices and Their Applications

The modern power electronics era started with the commercialization of the silicon-controlled rectifier in 1957, since when power electronics systems have been installed in a wide range of applications from appliances to traction and utility systems as the technology has advanced. Meanwhile, simulation tools have played an important role in the research and development of power semiconductors and power electronics systems. As power devices and power electronics become increasingly important technologies in today's electric society, it is worth examining the overall integration of power electronics design. This paper reviews the history of simulation technology with reference to power device modeling and discusses the future of power electronics system design.

光電子分光法による有機半導体の電子状態と界面の特徴

This article describes recent progress in organic semiconductor research with ultraviolet photoelectron spectroscopy (UPS). Origins of the energy level alignment at organic-conductor interfaces and the charge mobility in organic semiconductor systems are the most important subjects, which have been left to be elusive. Direct experimental detection of very low electronic density-of-states in the band gap is necessary to unravel mysteries of the energy level alignment. Experimental measurements of the energy band dispersion give information about the intermolecular interaction and the effective mass of transporting hole, and experimental detection of electron-phonon coupling at the highest occupied molecular orbital (HOMO) is indispensable to comprehend impacts of the coupling on the hole transport. We summarize our recent challenges on UPS measurements of organic semiconductors, which give the band dispersion of the HOMO, the HOMO hole-vibration coupling and the band-gap states appearing near the interface.

Al CMP for Low Resistance Gate Fill for 20nm and Beyond Replacement Metal Gate

ABSTRACTAluminum (Al) gate fill has been implemented in Replacement Metal Gate (RMG) due to its low resistivity. Titanium (Ti) has been widely used as wetting layer for Al to fill the gates. For low resistance gate fill in structures with small feature size and high aspect ratio, Ti-Al metal fill becomes increasingly more challenging as we move from 20nm into 14nm FinFET and 3D type structures.Cobalt (Co) is a good wetting film for Al with better fill performance and lower resistance than Ti-Al based process. However, due to the difference in corrosion potential between Al and Co, Chemical Mechanical Planarization (CMP) creates pitting type defects on Al-Co film that increases resistance variability across pattern density. CMP induced corrosion is separated in two parts; first is the static Co corrosion happened in the acidic chemical environment in the Al slurry. Second is the galvanic corrosion from Co-Al metal boundary due to high metal electrical potential. Static corrosion can be resolved by adding a Co corrosion inhibitor in the slurry formulation1. Galvanic corrosion can be minimized by controlling Co thickness deposition and formation of complete intermetallic phase. By controlling the removal rate with respect to corrosion rate we were able to suppress corrosion significantly.We looked into compositions where the corrosion potential (Ecorr) gap between Al and Co is reduced to ≤10mV leading to reduced galvanic currents. Stabilization of the corrosion currents in both Al and Co was observed using potentiodynamic scans. The effect of pH, several oxidizers and additives on the open circuit potentials (Eoc) of Al and Co was investigated and it was found that solutions of KMnO4, saccharides and sulfonate group containing compounds help reduce the Ecorr gap in between Al and Co to ∼10 mV.Controlling the Al gate height across pattern densities and gate lengths to within few nm is another challenge for Al CMP. The industry widely used approach is to clear all Al using a slurry with high selectivity to dielectric, followed by a CMP step using a non-selective Al-to-oxide slurry. Both polishing steps need to be optimized in parallel in order to remove the incoming spacer SiN divot, minimize Al loss on gates with high pattern density or long gate length, minimize oxide loss on large open areas while maintaining low defectivity.In this paper we are presenting an innovate Al CMP process that demonstrated low gate resistance with tight distribution up to 80% pattern density. This work has been supported by the independent Bulk CMOS and SOI technology development projects at the IBM Microelectronics Division Semiconductor Research & Development Center, Hopewell Junction, NY 12533.

Quantitative Cathodoluminescence Opens New Areas of Investigation in Semiconductor Research and Production

The increasing demand for new opto-electronics devices such as solar cells, laser diodes (LD), and high-brightness light-emitting diodes (HBLED), combined with the economic necessity to achieve lower energy consumption levels and higher device yields, is motivating researchers to develop new materials. The semiconductor industry is actively looking for alternatives to silicon, for example, to address new niche market applications in power devices. Constant efforts employed to reduce production costs are leading manufacturers to grow GaN on silicon substrate, creating new technical challenges, especially regarding the control of defect density on wafer. For all these reasons many studies are being initiated to improve understanding of the fundamental physical properties and behavior of compound semiconductor materials used in quantum wells, quantum dots and nanowire-like structures. Cathodoluminescence (CL) is a spectroscopy method that can generate reliable, quantitative, and stable data for research as well as prepare a basis for quality control during production.

Diamond MESFET performance improvement by layout optimisation

Hydrogen terminated diamond is a promising material for metal semi-conductor field effect transistor (MESFETs) fabrication and research effort is focused on diamond quality improvement. In this reported work, the focus of attention is on device layout and structure to improve RF performances, designed on the basis of diamond physical properties, taking into account the characterisation of previously fabricated devices. Significant increase of current gain cutoff frequency fT, from 3.4 to 6.7 GHz, has been obtained, while maximum oscillation frequency fMAX is raised from 10.4 to 11.8 GHz.

Review of Spark Discharge Generators for Production of Nanoparticle Aerosols

In the growing field of nanotechnology there is an increasing need to develop production methods for nanoparticles, especially methods that provide control and reproducibility. The spark discharge generator (SDG) is a versatile device for the production of nanoparticle aerosols. It can produce aerosol nanoparticles in the entire nanometer range (1–100 nm), and beyond. Depending on requirements, and the system used, these nanoparticles can be completely contamination free and composed of one or more materials. This provides a unique opportunity to create new materials on the nanoscale. Already in use in semiconductor, materials, health and environmental research, the SDG shows promise for yet more applications. If needed, particle production by the SDG could be scaled up using parallel generators facilitating continuous high-volume production of aerosol nanoparticles. Still, there is a surprisingly low knowledge of fundamental processes in the SDG. In this article we present a thorough review of the most common and relevant SDGs and the theory of their operation. Some possible improvements are also discussed. Copyright 2012 American Association for Aerosol Research

Bone cement and the implications for anaesthesia

Poly(methyl methacrylate) (PMMA) was developed in 1928 and was first marketed under the name of ‘Plexiglas’. Since then, PMMA has been used in a huge number of applications, including transparent glass substitutes in windows, semiconductor research, and for the bodies of electric guitars. PMMA has a good degree of biocompatibility, which has made it an important component of replacement intraocular lenses, dentures, and dental filling composite materials. In orthopaedic surgery, PMMA bone cement is used to affix implants and to remodel lost bone. The medical orthopaedic use of PMMA is universally credited to Sir John Charnley, who was inspired by his dentist to use dental acrylic for prosthetic fixation in total hip replacement (THR) procedures in 1957. In 1965, he began to use bone cement (CMW Bone Cement TM ) that was developed specifically for THRs rather than dental acrylic. Bone cement is now routinely used in a variety of orthopaedic procedures. The microscopic structure of bone cement comprises two substances glued together. The so-called ‘pearls’ in bone cement consist of small particles of pre-polymerized PMMA, which are present as white powder. The second substance is a liquid monomer of methyl methacrylate (MMA). Both substances are mixed together in theatre after the addition of a catalyst that initiates the polymerization of the monomer fluid. When the bone cement hardens, the individual pearls are entrapped and glued within the net of the polymerized monomer, but no chemical binding occurs between the pearls and the polymerized