We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

In the past several years, research in each of the wide‐band‐gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high‐temperature electronics and short‐wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high‐power operation. The present advanced stage of development of SiC substrates and metal‐oxide‐semiconductor technology makes SiC the leading contender for high‐temperature and high‐power applications if ohmic contacts and interface‐state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high‐temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light‐emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN‐based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short‐wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN‐based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe‐based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide‐band‐gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.

Large‐band‐gap SiC, III‐V nitride, and II‐VI ZnSe‐based semiconductor device technologies

Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications from power conditioning to microwave transmitters for communications and radar. Of the various materials and device technologies, the AlGaN/GaN high-electron mobility transistor seems the most promising. This paper attempts to present the status of the technology and the market with a view of highlighting both the progress and the remaining problems.

AlGaN/GaN HEMTs-an overview of device operation and applications

Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC- and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation.

A Survey of Wide Bandgap Power Semiconductor Devices

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

4.5kV 60A SICGT of 6mm times 6mm chip size has been developed, which has the largest electric power handling capability among the reported SiC switching devices. Due to the fast turn-on time of 0.08mus and the fast turn-off time of 2.3mus at 250degC, SICGT can realize a low power loss as compared with 4.5kV Si GTOs and 4.5W Si IGBTs. A PWM half bridge inverter was built by using a couple of SICGT modules. Each module consists of one SICGT and two SiC pn diodes in a TO3 type package. The inverter achieved an output power of 20 kVA at V DC of 2kV and carrier frequency of 2kHz, This represents the largest output power among the reported SiC inverters

4.5 kV 60A SICGT and its Half Bridge Inverter Operation of 20kVA Class

We report on the development of the first 1 cm x 1 cm SiC Thyristor chip capable of blocking 5 kV. This demonstrates the present quality of the SiC substrate and epitaxial material. A forward drop of 4.1 V at 100 A and 25°C has been measured. The turn-on delay is found to be a strong function of the gate current. At a gate current of 0.5 A, a turn-on delay of 250 ns is observed for an anode to cathode current of 200 A. The turn-on delay reduces to 72 ns for an IG = 1.5 A. The turn-on rise time is a strong function of the anode to cathode voltage, VAK. At VAK =230 V, the turn-on rise-time is 300 ns for IAK =200 A. The rise-time reduces to 26 ns for VAK = 500 V.

A 1cm × 1cm, 5kV, 100A, 4H-SiC Thyristor Chip for High Current Modules

PURPOSE: A carbonized silicon MOS(Metal Oxide Semiconductor) FET(Field Effect Transistor) is provided to obtain a breakdown voltage in a forward breakdown mode which is almost similar to a breakdown voltage of a bulk semiconductor. CONSTITUTION: The carbonized silicon MOSFET comprises: an U-shaped gate transistor; N-type carbonized silicon layer; a bulk mono crystal carbonized silicon substrate of N-type conductivity; a first epitaxial layer of N-type conductive carbonized silicon; a second epitaxial layer of P-type conductive carbonized silicon; a first trench extended downward through the second epitaxial layer into the first epitaxial layer; a second trench adjacent to the first trench extended downward through the second epitaxial layer into the first epitaxial layer; an N-type conductive carbonized silicon region which is formed between the first and the second trenches and has an upper surface in an opposite region of the second epitaxial layer; a P-type carbonized silicon region formed in the first epitaxial layer under the second trench; a gate and a source contacts formed inside the first and the second trenches respectively; and a drain contact formed on the substrate.

Carbonized silicon metal-oxide-semiconductor field effect transistor

Power devices are susceptible to failure by terrestrial neutron single-event burnout (SEB) while in the high-voltage blocking state and above a VDS threshold for that device. Typically, the SEB failure rate is measured at a high blocking voltage, with the source and gate at ground potential. Here the effect of a negative gate bias, commonly applied during MOSFET switching to the blocking state, on the SEB failure rate is examined. It is observed that the SEB failure rate is only weakly dependent on the negative gate bias, because it does not significantly affect the peak field in the drift region where avalanche breakdown is initiated. A negative gate bias of -8VGS in the device blocking state at 1100VDS only results in a 6% increase in the MOSFET SEB failure rate.

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Gate Bias Effects on SiC MOSFET Terrestrial-Neutron Single-Event Burnout

With the steep expansion of the n-type 4H-SiC power metal-oxide-semiconductor field-effect transistor (MOSFET) market space, gate oxide reliability is gaining more and more attention. Although there exist several reports dealing with the bias temperature instability (BTI) under both positive and negative gate biases, gate oxide lifetime evaluations predominantly focus on positive gate bias time-dependent dielectric breakdown (TDDB) stresses for n-channel SiC MOSFETs. In this work we address that gap. From the negative gate bias TDDB data measured at 175 °C and at a gate oxide electric field of about 4 MV/cm, an intrinsic lifetime of 1E8 hours has been predicted, which closely matches with the results obtained from similar devices under positive gate stress. Also, in this work the correlation between failure location in a MOSFET unit cell and the failure signatures during TDDB stress have been established, and an explanation from a device physics standpoint has been provided. The identification of the failure location in the unit cell from in-situ gate leakage data without the need of physical failure analysis can turn out to be key during the early phase of a new process development activity.

John W. Palmour

Papers

4.5 kV 60A SICGT and its Half Bridge Inverter Operation of 20kVA Class

A 1cm × 1cm, 5kV, 100A, 4H-SiC Thyristor Chip for High Current Modules

Carbonized silicon metal-oxide-semiconductor field effect transistor

Gate Bias Effects on SiC MOSFET Terrestrial-Neutron Single-Event Burnout

Negative Gate Bias TDDB evaluation of n-Channel SiC Vertical Power MOSFETs