Materials Science Forum Vols. 821-823

Abstract: Ion implantation in silicon carbide (SiC) induces defects during the process. Implantation free processing can eliminate these problems. The junction termination extension (JTE) can also be formed without ion implantation in SiC bipolar junction transistor (BJT) using a well-controlled etching into the epitaxial base layer. The fixed charges at the SiC/SiO₂ interface modify the effective dose of the JTEs, leakage current, and breakdown voltage. In this paper the influence of fixed charges (positive and negative) and also interface trap density at the SiC/SiO₂ interface on the breakdown voltage in 4.5 kV 4H-SiC non-ion implanted BJT have been simulated. SiO₂ as a surface passivation layer including interface traps and fixed charges has been considered in the analysis. Simulation result shows that the fixed charges influence the breakdown voltage significantly more than the interface traps. It also shows that the positive fixed charges reduce the breakdown voltage more than the negative fixed charges. The combination of interface traps and fixed charges must be considered when optimizing the breakdown voltage.

Abstract: A single-mask junction termination extension withtrench structures is formed to realize a 4.5 kV implantation-free 4H-SiCbipolar junction transistor (BJT). The trench structures are formed on the baselayer with dry etching using a single mask. The electric field distributionalong the structure is controlled by the number and dimensions of the trenches.The electric field is distributed by the trench structures and thus the electricfield crowding at the base and mesa edges is diminished. The design isoptimized in terms of the depth, width, spacing, and number of the trenches toachieve a breakdown voltage (V_B) of 4.5 kV, which is 85% of thetheoretical value. Higher efficiency is obtainable with finer lithographicresolution leading to smaller pitch, and higher number and narrower trenches.The specific on-resistance (R_ON) of 20 mΩ.cm² is measuredfor the small-area BJT with active area of 0.04 mm². The BV-R_ONof the fabricated device is very close to the SiC limit and by far exceeds thebest SiC MOSFETs.

Abstract: Ultrahigh-voltage SiC flip-type n-channel implantation and epitaxial (IE)-IGBTs were developed, and the static and dynamic performance was investigated. A large device (8 mm × 8mm) with a blocking voltage greater than 16 kV was achieved, and an on-state current of 20 A was obtained at the low on-state voltage (V_on) of 4.8 V. R_onA_diff was 23 mΩ·cm² at V_on = 4.8 V. In order to evaluate the switching characteristics of the IE-IGBT, ultrahigh-voltage power modules were assembled. A chopper circuit configuration was used to evaluate the switching characteristics of the IE-IGBT. Smooth turn-off waveforms were successfully obtained at V_CE = 6.5 kV and I_CE = 60 A in the temperature range from room temperature to 250°C.

Abstract: In this work, we report our recently developed 27 kV, 20 A 4H-SiC n-IGBTs. Blocking voltages exceeding 24 kV were achieved by utilizing thick (210 μm and 230 μm), lightly doped N-drift layers with an appropriate edge termination. Prior to the device fabrication, an ambipolar carrier lifetime of greater than 10 μs was measured on both drift regions by the microwave photoconductivity decay (μPCD) technique. The SiC n-IGBTs exhibit an on-state voltage of 11.8 V at a forward current of 20 A and a gate bias of 20 V at 25 °C. The devices have a chip size of 0.81 cm² and an active conducting area of 0.28 cm². Double-pulse switching measurements carried out at up to 16 kV and 20 A demonstrate the robust operation of the device under hard-switched conditions; coupled thermal analysis indicates that the devices can operate at a forward current of up to 10 A in a hard-switched environment at a frequency of more than 3 kHz and a bus voltage of 14 kV.

Abstract: Thick multi-layer 4H-SiC epitaxial growth was investigated for very high-voltage Si-face p-channel insulated gate bipolar transistors (p-IGBTs). The multi-layer included n⁺ buffer, p⁺ field stop, and thick p^- drift layers. Two processes were employed to enhance the carrier lifetime of the p^- drift layer: carbon ion implantation/annealing and hydrogen annealing, and the enhanced carrier lifetime was confirmed by the open-circuit voltage decay measurement. Using the grown thick multi-layer 4H-SiC, simple pin diodes were fabricated instead of p-IGBTs to demonstrate efficient conductivity modulation in the thick p^- drift layer. While the on-state voltage was high at room temperature, it decreased significantly at elevated temperatures, and attained 3.5 V at 100 A/cm² at 200°C for the diode with the carrier lifetime enhancement processes, indicating sufficient conductivity modulation.

Abstract: Silicon Carbide is a promising material to overtake the limitations of Si sensors used for in vivo detection. Here, two different nanodevices are presented. The first one is a SiC NWFET used for electrical detection of DNA molecules. The addition of DNA probe molecules increases the current by 25% and the hybridization with DNA targets increases by 80%. This confirms the efficiency of our sensor to detect DNA. The second one is a Metal Insulator Semicondutor capacitor composed of DNA functionalized SiC nanopillar arrays embedded in a sol-gel silicon dioxide matrix. Capacitance measurements show a singular response between 80 and 100 Hz which is attributed to the presence of DNA molecules.

Abstract: This paper presents the characteristics and performance of a range of Silicon Carbide (SiC) CMOS integrated circuits fabricated using a process designed to operate at temperatures of 300°C and above. The properties of Silicon carbide enable both n-channel and p-channel MOSFETS to operate at temperatures above 400°C [1] and we are developing a CMOS process to exploit this capability [4]. The operation of these transistors and other integrated circuit elements such as resistors and contacts is presented across a temperature range of room temperature to +400°C. We have designed and fabricated a wide range of test and demonstrator circuits. A set of six simple logic parts, such as a quad NAND and NOR gates, have been stressed at 300°C for extended times and performance results such as propagation delay drive levels, threshold levels and current consumption versus stress time are presented. Other circuit implementations, with increased logic complexity, such as a pulse width modulator, a configurable timer and others have also been designed, fabricated and tested. The low leakage characteristics of SiC has allowed the implementation of a very low leakage analogue multiplexer showing less than 0.5uA channel leakage at 400°C. Another circuit implemented in SiC CMOS demonstrates the ability to drive SiC power switching devices. The ability of CMOS to provide an active pull up and active pull down current can provide the charging and discharging current required to drive a power MOSFET switch in less than 100ns. Being implemented in CMOS, the gate drive buffer benefits from having no direct current path from the power rails, except during switching events. This lowers the driver power dissipation. By including multiple current paths through independently switched transistors, the gate drive buffer circuit can provide a high switching current and then a lower sustaining current as required to minimize power dissipation when driving a bipolar switch.

Abstract: Among particle detectors, particle detectors based on the wide gap semiconductor materials are many used in the nuclear area. For the reliable uses in hard and severe environment, the 4H-SiC is mainly used to the realization of nuclear detector components. This is a part of the topic of the I_SMART European project which proposes to study the nuclear detection of the thermal and fast neutron and gamma rays. In this paper, we deal with the Monte Carlo simulation results of interactions between particles and 4H-SiC detector. In particular, simulation works present the results between fast neutron and 4H-SiC sensor with a comparison between the simulation and experimental results. This article tries to point out the effect of the space charge region depletion, in particular the electric field on the signal response strength.

Abstract: 4H-SiC ultraviolet photodetectors based on Schottky barriers have been formed on lightly doped n-type epitaxial layers grown by chemical vapor deposition method on industrial substrates. The diode structures were irradiated at 25°C with 167 MeV Xe ions at a fluence of 6x10⁹ cm^-2. Comparative studies of the optical and electrical properties of initial and irradiated structures with Schottky barriers were carried out in temperature range 23-180°C. Swift heavy ion stimulated changes in photosensitivity and electrical characteristics of the initial and irradiated detectors are explained in terms of the fluctuation traps model with the subsequent thermal dissociation.

Abstract: High gain photoconductive switching using Si and GaAs was studied previously for pulsed high voltage switching. A laser is used to generate charge carriers within the material to render the bulk conductive. We have begun the study of photoconductive switching using wide bandgap materials. These materials appear to operate in a non-high gain mode and the on resistance can be directly controlled with the laser intensity over many decades. It is presently believed that the conduction mechanism may be due to (a) excitation of deep states or (b) multi-photon pumping of carriers from the valance band. We present the study of the physics processes and development of a device operating at >20-kV.