Papers by Author: David C. Sheridan

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: Equivalent sized (4.5 mm2 die area), 1200 V, 4H-SiC, vertical trench Junction Field Effect Transistors (JFETs) were characterized in terms of DC and switching performance. The 100 mΩ Enhancement-Mode (EM) JFET was found to have natural advantages in safe operation being normally-off, whereas the Depletion-Mode (DM) JFET was found to have advantages with ~ twice as high saturation current, less on-resistance (85 mΩ) and no gate current required in the on-state. The JFETs were found to both have radically less (five to ten times) switching energies than corresponding 1200 V Si transistors, with the DM JFET and EM JFET having EON and EOFF of only 115 µJ and 173 µJ, respectively when tested at half-rated voltage (600 V) and 12 A.

Abstract: This work presents the progress in developing an all SiC based power module for use in high frequency and high efficiency applications. Using parallel combinations of 1200V enhancement mode SiC VJFETs (36mm2) and Schottky diodes (23mm2), a total on-resistance of only 10mOhm (2.7m-cm2) was achieved at ID=100A in a commercially available standard module configured as a half-bridge circuit. Careful attention to module layout, gate driver design, and the addition of optimized snubbers resulted in excellent switching waveforms with low total switching losses of 1.25mJ when switching 100A at 150oC.

Abstract: Recently 63 m, 100 m, and 125 m 1200 V normally-off SiC VJFETs have become commercially available and 99% efficiency has been demonstrated in a single-phase solar inverter using these components [1]. They exhibit low specific on-resistance (3 m∙cm2), high saturation current density (1000 A∙cm-2), and low switching losses. For some applications, including 30 to 100 kW inverter modules and those requiring high surge current capability, larger die size is required. This paper reports the static and dynamic performance of 15 mm2 1200 V normally-off VJFETs with 25 m on-resistance and 120 A saturation current at 25 °C.

Abstract: The design of analog integrated circuits, for instance, the operational amplifiers, have been widely perfected with devices and processes available in silicon. However, analogous circuits have been the subject of research in Silicon Carbide (SiC). Among SiC devices, 4H-SiC Lateral-Trench JFET (LTJFET) transistor offers advantages and new opportunities to make affordable and reliable analog integrated circuits for harsh environment. In this paper: (1) SiC LTJFET is characterized for modeling and simulation, (2) effect of temperature variation on SiC LTJFET threshold voltage and small signal parameters are reported, (3) gain performance and small signal parameters of the basic analog circuit block, Common Source (CS) amplifier, based on the variation of the load transistors threshold voltage (Vth) are studied and analyzed, and (4) frequency and transient response of the cascoded CS amplifier (CS-Cas) are reported.

Abstract: In this work, we report the most recent reliability results of the 1200-V SiC vertical-channel JFETs (VJFETs) under reverse and forward bias of the gate-source diode at temperatures up to 200 °C. The preliminary results indicate that continuous forward bias stress of the gate-source diode at 200 °C for 112 hours produced no observable change in the forward conduction or transient or reverse blocking characteristics of the vertical-channel JFET. This preliminary result suggests that devices based on this structure, such as the enhancement-mode (normally off) SiC VJFET, may not be effected by the recombination enhanced defect creation process and the associated increase in on-resistance, related to body-diode conduction in the SiC DMOSFET and the SiC lateral-channel depletion-mode JFET. Since the vertical-channel JFET has no body diode, no degradation is possible from the reverse conduction mode of operation.

Abstract: Prototype 800 V, 47 A enhancement-mode SiC VJFETs have been developed for high temperature operation (250 °C). With an active area of 23 mm2 and target threshold voltage of +1.25 V, these devices exhibited a 28 m room temperature on-resistance and excellent blocking characteristics at elevated temperature. With improved device packaging, on-resistance and saturation current values of 15 m and 100 A, respectively, are achievable.

Abstract: SiC Lateral Trench JFET (LTJFET) technology is demonstrated as a promising candidate for use in high-temperature wireless telemetry systems. 4H-SiC LTJFETs were designed, fabricated and characterized for DC, and small-signal AC and RF performance at different case temperatures. Four-fold drain current reduction was observed at 460°C as compared to RT measurements. The measured threshold voltage shift was less than 2.3 mV/°C from 21°C to 460°C. A simple common source amplifier built using a fabricated device demonstrated stable small-signal AC performance after 100 hrs of operation at 450°C. Small-signal RF measurements were carried out on the packaged devices at different temperatures. GMax above 8 dB was measured over the L-band frequency range at RT. The average degradation of small-signal power gain measured at f=250 MHz did not exceed 0.0125 dB/ °C over the temperature ranging from 21°C to 365°C.

Abstract: In this work we have demonstrated the high-temperature operations of 600 V/50 A 4HSiC vertical-channel junction field-effect transistors (VJFETs) with an active area of 3 mm2. Specific-on resistance (RONSP) in the linear region of a single die is less than 2.6 mW.cm2 while the drain-source current is over 50 A under a gate bias (VGS) of 3 V. A reverse blocking gain of 54 is obtained at gate bias ranging from -13 V to -23 V and drain-source leakage current (IRDS) of 200 μA. To demonstrate the use of SiC VJFETs for high-power applications, eight 3 mm2 SiC VJFETs are bonded in a high current 600-V module. RONSP in the linear region of these eight-paralleled SiC VJFETs is 2.8 mW.cm2 at room temperature and increased to 5.35 mW.cm2 at an ambient temperature of 175 °C in air, corresponding to a shift of 0.61%/°C from room temperature to 175 °C. Meanwhile, the forward current is over 360 A at room temperature and reduces to 188 A at 175 °C at drain-source bias (VDS) of 5.25 V and VGS of 3 V.

Abstract: In this work we report the most recent high-temperature long-term reliability results of the 600 V/14 A, 4H-SiC vertical-channel junction field-effect transistors (VJFETs). Two groups (A and B) devices were subjected to different thermal and electrical stresses. One device (Group A) reached 12,000 hours of continuous switching without a single failure. Four devices in Group A were thermally stressed at 250 °C over 4,670 hours in air, for which standard deviation of the specific on-resistance (RONSP) in linear region at gate bias (VGS) of 3 V were < 4.1% throughout the entire duration time. The off-state characteristics were evaluated by high temperature reverse bias (HTRB) tests. Three devices (Group A) were biased at 50% rated BVDS at 250 °C for 2,278 hours. A higher reverse bias at 80 % rated BVDS was then applied to 14 devices (group B) at 200 °C for 1,000 hours. Variations of the leakage current were negligible throughout the entire HTRB test for all tested devices.