Si/SiC bonded wafer: a route to carbon free SiO2 on SiC

This paper describes the thermal oxidation of Si/SiC heterojunction structures, produced using a layer-transfer process, as an alternative solution to fabricating SiC metal-oxide-semiconductor (MOS) devices with lower interface state densities (Dit). Physical characterization demonstrate that the transferred Si layer is relatively smooth, uniform, and essentially monocrystalline. The Si on SiC has been totally or partially thermally oxidized at 900–1150 °C. Dit for both partially and completely oxidized silicon layers on SiC were significantly lower than Dit values for MOS capacitors fabricated via conventional thermal oxidation of SiC. The quality of the SiO2, formed by oxidation of a wafer-bonded silicon layer reported here has the potential to realize a number of innovative heterojunction concepts and devices, including the fabrication of high quality and reliable SiO2 gate oxides

Feasibility Study for Development of Statewide Evapotranspiration Network

Information was collected on existing mesonets, potential evapotranspiration networks, and stakeholder needs, in support of a comprehensive feasibility study for a Texas statewide evapotranspiration network. This report summarizes the data and information collected from interviews and online resources regarding the purpose, design, operation, and value of these mesonets. It analyzes existing network data within Texas and evaluates the costs and benefits associated with operating a more comprehensive or integrated network. Finally, it presents options for a sustainable Texas mesonet based on successes elsewhere and the specific needs and resources of Texas. A mesonet here refers to a set of weather stations designed to detect and monitor weather phenomena ranging in size from several miles to hundreds of miles (the "mesoscale"). Such disturbances include flooding and thunderstorms (i.e. convective precipitation), high winds, droughts, and heatwaves. Instruments may be located as high as 10 m above the ground, and stations are generally located to avoid influences from urban landscapes, irrigation, forests, and large bodies of water. This report restricts the term mesonet to networks that serve a variety of needs or stakeholders. ET (Evapotranspiration) networks differ in both their objectives and measurements. Their objective is to determine the atmospheric demand for water evaporation and transpiration from land covered by a well-watered reference crop – either alfalfa or clipped grass. Such data is valuable for irrigation scheduling for agricultural production and for improving efficiencies in landscape watering for homes and businesses. ET networks use specific instruments often at 2 m heights sited well within a homogenous field of a well-maintained reference crop. Requirements of growers and stakeholders often drive the siting and spacing. An ET network has a particular specialized use while a mesonet is more of a multi-purpose network. Many existing mesonets in other states were originally established for agricultural purposes, while others were established in support of public safety. Most have been in operation for an average of twenty years and by now serve a broad range of sectors and constituencies. In Texas, there are three mesonets that serve a variety of purposes: the West Texas Mesonet, the Lower Colorado River Authority (LCRA) Hydromet Network, and the TexMesonet. There is one dedicated ET network, the TexasET Network, and there are numerous other single-purpose networks. All surveyed mesonets and ET networks measure air temperature, relative humidity, wind, and precipitation. Solar radiation is measured at all stations in the TexasET and TexMesonet networks, but only partially in the other two networks. In addition, many also measure soil temperature and soil moisture at a variety of subsurface levels as well as wind or temperature at multiple above-ground levels. Data transmission from individual stations is predominantly by cellular network. Users access the data via web sites, text alerts, apps, and through retransmission of data to larger aggregation networks such as the Meteorological Assimilation Data Ingest System, the National Mesonet Program, and MesoWest. Most mesonets quality control their data to either World Meteorological Organization or National Weather Service standards. Individual startup costs range from $6,200 to$25,000 per station, and network maintenance and operating costs range from $1,600 to$6,000 per station. Differences in cost largely reflect differences in instrumentation and maintenance needs. Maintenance costs for ET stations can be high due to irrigation infrastructure and land management required to maintain the reference grasses. Staffing needs depend on the mix of employees and outside contractors; labor-intensive tasks include station, instrumentation, and communication maintenance, calibration, product development, and administration. The benefits gained from fully functional ET networks are substantial. Analyses of benefits of existing ET networks find typical water savings of several inches per year on irrigated cropland, implying potential water savings exceeding one million acre-feet per year within the agriculture sector alone. Overall, the potential economic return on investment is substantial, with one study estimating it at 20:1. Mesonet business models range from comprehensive centralized networks with fully integrated operations to secondhand aggregators of data from existing networks. Most of the successful networks examined in this report operate on a partnership model with some centralized tasks and funding and some tasks and funding shouldered at the local level. Nearly all mesonets function through university or multi-university partnerships. In most cases, data is free of charge. In Texas, an appropriate model would be a consortium model, consisting of the Texas Water Development Board, universities such as Texas Tech University, Texas A&M University, and the University of Texas, and other statewide or regional stakeholders/operators such as the the Texas A&M Agrilife Extension Service, Lower Colorado River Authority and the Electricity Reliability Council of Texas. Additional stakeholder participation can be formalized through an advisory board. Successful mesonets elsewhere have avoided challenges which can potentially lead to failure of the network, including: 1. lacking an overall network vision; 2. failing to properly engage potential stakeholders; 3. misdiagnosing local needs; 4. lacking diversification in revenue streams; 5. not fully exploring potential government partners; 6. not properly budgeting for maintenance costs; understaffing; 7. lacking data and metadata standards; 8. insufficient communications infrastructure; and 9. not providing reliable web/automated dissemination of data.Texas Water Development Boar

The optimization of 3.3 kV 4H-SiC JBS diodes

The article reports a comprehensive study optimizing the OFF- and ON-state characteristics of 3.3 kV junction barrier Schottky (JBS) diodes made using nickel, titanium, and molybdenum contact metals. In this design, the same implants used in the optimized termination region are used to form the P-regions in the JBS active area. The width and spacing of the P-regions are varied to optimize both the ON- and OFF-state of the device. All the diodes tested displayed high blocking voltages and ideal turn-on characteristics up to the rated current of 2 A. However, the leakage current and the Schottky barrier height (SBH) were found to scale with the ratio of Schottky to p + regions. Full Schottkys, without p + regions, and those with very wide Schottky regions had the lowest SBH (1.61 eV for Ni, 1.11 eV for Mo, and 0.87 eV for Ti) and the highest leakage. Those diodes with the lowest Schottky openings of 2 μm had the lowest OFF-state leakage, but they suffered severe pinching from the surrounding p + regions, increasing their SBH. The best performing JBS diodes were Ni and Mo devices with the narrowest pitch, with the p + implants/Schottky regions both 2 μm wide. These offered the best balanced device design, with excellent OFF-state performance, while the Schottky ratio guaranteed a relatively low forward voltage drop

3.3 kV SiC JBS diodes employing a P2O5 surface passivation treatment to improve electrical characteristics

3.3 kV Schottky barrier diodes and Junction Barrier Schottky diodes have been fabricated, employing a phosphorous pentoxide (P2O5) surface treatment prior to metal deposition in an attempt to further condition the power device’s interface. For SBD structures, the treatment consistently reduces the leakage current in molybdenum, tungsten and niobium SBDs, for the tungsten treatment by more than four orders of magnitude. X-ray photoelectron spectroscopy (XPS) analysis on the treated SBD interface revealed formation of a metal phosphate between P2O5 and the metal. When compared to an untreated sample, the P2O5 treatment has increased the valence band to fermi level offset by 0.2 eV to 3.25 eV, indicating that the treatment results in a degenerately n-doped SiC surface. When applied to fully optimised 3.3 kV JBS power structures utilizing a hybrid JTE design, P2O5 treatments improved blocking capabilities across the entire dataset by as much as 1,000

Integration of HfO2 on Si/SiC heterojunctions for the gate architecture of SiC power devices

In this paper we present a method for integrating HfO2 into the SiC gate architecture, through the use of a thin wafer bonded Si heterojunction layer. Capacitors consisting of HfO2 on Si, SiC, Si/SiC, and SiO2/SiC have been fabricated and electrically tested. The HfO2/Si/SiC capacitors minimize leakage, with a breakdown electric field of 3.5 MV/cm through the introduction of a narrow band gap semiconductor between the two wide band gap materials. The Si/SiC heterojunction was analyzed using transmission electron microscopy, energy dispersive x-ray, and Raman analysis, proving that the interface is free of contaminants and that the Si layer remains unstressed

Feasibility Study for Development of Statewide Evapotranspiration Network

Information was collected on existing mesonets, potential evapotranspiration networks, and stakeholder needs, in support of a comprehensive feasibility study for a Texas statewide evapotranspiration network. This report summarizes the data and information collected from interviews and online resources regarding the purpose, design, operation, and value of these mesonets. It analyzes existing network data within Texas and evaluates the costs and benefits associated with operating a more comprehensive or integrated network. Finally, it presents options for a sustainable Texas mesonet based on successes elsewhere and the specific needs and resources of Texas. A mesonet here refers to a set of weather stations designed to detect and monitor weather phenomena ranging in size from several miles to hundreds of miles (the "mesoscale"). Such disturbances include flooding and thunderstorms (i.e. convective precipitation), high winds, droughts, and heatwaves. Instruments may be located as high as 10 m above the ground, and stations are generally located to avoid influences from urban landscapes, irrigation, forests, and large bodies of water. This report restricts the term mesonet to networks that serve a variety of needs or stakeholders. ET (Evapotranspiration) networks differ in both their objectives and measurements. Their objective is to determine the atmospheric demand for water evaporation and transpiration from land covered by a well-watered reference crop – either alfalfa or clipped grass. Such data is valuable for irrigation scheduling for agricultural production and for improving efficiencies in landscape watering for homes and businesses. ET networks use specific instruments often at 2 m heights sited well within a homogenous field of a well-maintained reference crop. Requirements of growers and stakeholders often drive the siting and spacing. An ET network has a particular specialized use while a mesonet is more of a multi-purpose network. Many existing mesonets in other states were originally established for agricultural purposes, while others were established in support of public safety. Most have been in operation for an average of twenty years and by now serve a broad range of sectors and constituencies. In Texas, there are three mesonets that serve a variety of purposes: the West Texas Mesonet, the Lower Colorado River Authority (LCRA) Hydromet Network, and the TexMesonet. There is one dedicated ET network, the TexasET Network, and there are numerous other single-purpose networks. All surveyed mesonets and ET networks measure air temperature, relative humidity, wind, and precipitation. Solar radiation is measured at all stations in the TexasET and TexMesonet networks, but only partially in the other two networks. In addition, many also measure soil temperature and soil moisture at a variety of subsurface levels as well as wind or temperature at multiple above-ground levels. Data transmission from individual stations is predominantly by cellular network. Users access the data via web sites, text alerts, apps, and through retransmission of data to larger aggregation networks such as the Meteorological Assimilation Data Ingest System, the National Mesonet Program, and MesoWest. Most mesonets quality control their data to either World Meteorological Organization or National Weather Service standards. Individual startup costs range from $6,200 to$25,000 per station, and network maintenance and operating costs range from $1,600 to$6,000 per station. Differences in cost largely reflect differences in instrumentation and maintenance needs. Maintenance costs for ET stations can be high due to irrigation infrastructure and land management required to maintain the reference grasses. Staffing needs depend on the mix of employees and outside contractors; labor-intensive tasks include station, instrumentation, and communication maintenance, calibration, product development, and administration. The benefits gained from fully functional ET networks are substantial. Analyses of benefits of existing ET networks find typical water savings of several inches per year on irrigated cropland, implying potential water savings exceeding one million acre-feet per year within the agriculture sector alone. Overall, the potential economic return on investment is substantial, with one study estimating it at 20:1. Mesonet business models range from comprehensive centralized networks with fully integrated operations to secondhand aggregators of data from existing networks. Most of the successful networks examined in this report operate on a partnership model with some centralized tasks and funding and some tasks and funding shouldered at the local level. Nearly all mesonets function through university or multi-university partnerships. In most cases, data is free of charge. In Texas, an appropriate model would be a consortium model, consisting of the Texas Water Development Board, universities such as Texas Tech University, Texas A&M University, and the University of Texas, and other statewide or regional stakeholders/operators such as the the Texas A&M Agrilife Extension Service, Lower Colorado River Authority and the Electricity Reliability Council of Texas. Additional stakeholder participation can be formalized through an advisory board. Successful mesonets elsewhere have avoided challenges which can potentially lead to failure of the network, including: 1. lacking an overall network vision; 2. failing to properly engage potential stakeholders; 3. misdiagnosing local needs; 4. lacking diversification in revenue streams; 5. not fully exploring potential government partners; 6. not properly budgeting for maintenance costs; understaffing; 7. lacking data and metadata standards; 8. insufficient communications infrastructure; and 9. not providing reliable web/automated dissemination of data.Texas Water Development Boar