Materials Science Forum Vols. 717-720

Abstract: We report two improvements of our all-silicon carbide (SiC) micromachined capacitive diaphragm-based pressure sensors: Ti/TaSi2/Pt contact metallization to enhance temperature cycling durability and a 0.5 μm-thin sensing gap to further improve sensor sensitivity. Three sensors with 0.5 μm and 1.5 μm sensing gaps were packaged individually in high temperature ceramic packages and characterized to designed (static) pressures of 2.1 MPa (300 psi), 3.4 MPa (500psi) and 6.9 MPa (1000 psi) up to 550°C. For the 3.4 MPa range sensor (0.5 μm gap, 70 μm diaphragm radius), a sensitivity of 0.06 fF/Pa and a nonlinearity of 2.0% was obtained at 550°C in contact mode operation. In comparison, the 2.1 MPa range sensor (1.5 μm gap, 95 μm diaphragm radius) demonstrated a sensitivity of 0.07 fF/Pa and a nonlinearity of 4.6% at 550°C in contact mode operation. The 6.9 MPa range sensor (1.5 μm gap, 70 μm diaphragm radius) demonstrated a sensitivity of 0.03 fF/Pa and a nonlinearity of 4.0% at 500°C, also in contact mode.

Abstract: Smart sensor systems that can operate at high temperatures are required for a range of aerospace applications such as propulsion [1]. For future aerospace propulsion systems to meet the requirements of decreased maintenance, improved performance, and increased safety, the inclusion of intelligence into the propulsion system design and operation is necessary. This implies the development of sensor systems able to operate under the harsh environments present in an engine. Likewise, applications such as Venus exploration missions require systems that can operate in the harsh environments present on the Venus planetary surface. More sensor systems added to the aircraft increases the number of wires and the associated weight, complexity, and potential for failure. Thus, there is a need not only for high temperature sensors and electronics, but also for high temperature wireless technology. This implies the integration of sensors, electronics, wireless circuits, and power into a single system. In this paper, we demonstrate a significant step towards this goal, i.e., for the first time the integration of a pressure sensor with a SiC JFET logic-gate ring oscillator that operates at 500 °C; the sensor output signal is extracted from the small-signal ring oscillation frequency detected at the powersupply end of the DC power wires.

Abstract: The demands of modern high-performance power electronics systems are rapidly surpassing the power density, efficiency, and reliability limitations defined by the intrinsic properties of silicon-based semiconductors. The advantages of silicon carbide (SiC) are well known, including high temperature operation, high voltage blocking capability, high speed switching, and high energy efficiency. In this discussion, APEI, Inc. presents two newly developed high performance SiC power modules for extreme environment systems and applications. These power modules are rated to 1200V, are operational at currents greater than 100A, can perform at temperatures in excess of 250 °C, and are designed to house various SiC devices, including MOSFETs, JFETs, or BJTs.

Abstract: The majority carrier domain of power semiconductor devices has been extended to 10 kV with the advent of SiC MOSFETs and Schottky diodes. Twenty-four MOSFETs and twelve JBS diodes have been assembled in a 10 kV half H-bridge power module to increase the current handling capability to 120 A per switch without compromising the die-level characteristics. For the first time, a custom designed system (13.8 kV to 465/√3 V solid state power substation) has been successfully demonstrated with these state of the art SiC modules up to 855 kVA operation and 97% efficiency. Soft-switching at 20 kHz, the SiC enabled SSPS represents a 70% reduction in weight and 50% reduction in size when compared to a 60 Hz conventional, analog transformer.

Abstract: An all SiC 600V / 6 m hermetic half-bridge power module has been developed to operate at ambient temperatures of 200oC and with junction temperatures near 250oC. The modules use SiC trench JFET technology and can output over 100A at Tj=250oC. Double pulsed switching was performed up to temperatures of 150oC with a measured total switching energy of 0.73mJ

Abstract: We have developed a small-volume, high-power-output inverter with a high output power density using SiC power devices. To fully utilize the advantages of SiC power devices, it is necessary to reduce the inductance of the power module. This is done by using a double-layer ceramic substrate, attaining a low inductance of 5 nH. A double pulse test was carried out up to 60 A under a DC voltage of 600 V. The low inductance greatly reduced the surge voltage and the oscillation at the switching transient. The SiC inverter with a volume of 250 cc was assembled using three of the power modules. The cooling performance of the inverter was evaluated at a loss equivalent to an output power of 10 kW, and it was found that the inverter can output 10 kW at a junction temperature (Tj) of about 200°C.

Abstract: This paper presents the development and experimental evaluation of a 25kW, 700V galvanically isolated bidirectional converter based on silicon carbide (SiC) MOSFETs and Schottky diodes. Compared with a similarly rated silicon (Si) IGBT version, the SiC converter exhibits a 3% improvement in peak efficiency, 2.6 times reduction in total losses, and three times improvement in power density.

Abstract: In the aerospace industry where the weight and power density are important design parameters, high frequency operation results in smaller passive components. Furthermore, to achieve a large voltage conversion ratio, which is a goal for payload systems, the use of transformers increases the size and power losses of the system. To fulfill the space and weight requirements, a transformer-less SiC-based DC-DC multilevel converter providing high voltage conversion ratios without an extremely high duty cycle has been realized. The experimental high switching frequency and low current results for a conventional, 3-level and 4-level converter utilizing Si and SiC based COTS diodes are presented. SiC-based multilevel converters show a higher efficiency due to the low reverse recovery and fast switching of the diodes, which results in a higher voltage conversion ratio. This translates to a lower duty cycle to obtain the required output voltage, whilst eliminating the need for complex filtering even under light load conditions.

Abstract: Silicon-Carbide-based semiconductors offer realization of efficient high voltage components, with high switching speed and low conduction losses. SiC Schottky diodes with safe blocking capability of at least 4 kV were produced and characterized. A simulation model for loss determination was developed. Real losses were determined on a small scale test setup and chip temperature distribution was obtained from that, combined with FEM calculation. A full-size rectifier 100 kW/140 kV-SiC-rectifier module with six times higher power density than with conventional Si-technology was realized.

Abstract: This paper reports the design and experimental demonstration of a novel bi-directional solid-state disconnect (SSD) based on Silicon Carbide (SiC) depletion-mode junction field effect transistors (JFETs) for protecting critical sensitive components in high power systems. The SSD is able to provide a fast disconnect action upon receiving a preset trip current flowing through it and has a very low insertion loss, which makes it suitable for high power applications. For the application in 150kW six-phase power inverter systems, an insertion loss of less than 0.91% and a current fall time of less than 20μs for trip currents of about 800A have been demonstrated experimentally. To the best of our knowledge, there are no other solid-state disconnects available of comparable parameters.