David W. Berning

SiC power diodes provide breakthrough performance for a wide range of applications

The electrical performance of silicon carbide (SiC) power diodes is evaluated and compared to that of commercially available silicon (Si) diodes in the voltage range from 600 V through 5000 V. The comparisons include the on-state characteristics, the reverse recovery characteristics, and power converter efficiency and electromagnetic interference (EMI). It is shown that a newly developed 1500-V SiC merged PiN Schottky (MPS) diode has significant performance advantages over Si diodes optimized for various voltages in the range of 600 V through 1500 V. It is also shown that a newly developed 5000 V SiC PiN diode has significant performance advantages over Si diodes optimized for various voltages in the range of 2000 V through 5000 V. In a test case power converter, replacing the best 600 V Si diodes available with the 1500 V SiC MPS diode results in an increase of power supply efficiency from 82% to 88% for switching at 186 kHz, and a reduction in EMI emissions.

A monolithic CMOS microhotplate-based gas sensor system

A monolithic CMOS microhotplate-based conductance-type gas sensor system is described. A bulk micromachining technique is used to create suspended microhotplate structures that serve as sensing film platforms. The thermal properties of the microhotplates include a 1-ms thermal time constant and a 10/spl deg/C/mW thermal efficiency. The polysilicon used for the microhotplate heater exhibits a temperature coefficient of resistance of 1.067/spl times/10/sup -3///spl deg/C. Tin(IV) oxide and titanium(IV) oxide (SnO/sub 2/,TiO/sub 2/) sensing films are grown over postpatterned gold sensing electrodes on the microhotplate using low-pressure chemical vapor deposition (LPCVD). An array of microhotplate gas sensors with different sensing film properties is fabricated by using a different temperature for each microhotplate during the LPCVD film growth process. Interface circuits are designed and implemented monolithically with the array of microhotplate gas sensors. Bipolar transistors are found to be a good choice for the heater drivers, and MOSFET switches are suitable for addressing the sensing films. An on-chip operational amplifier improves the signal-to-noise ratio and produces a robust output signal. Isothermal responses demonstrate the ability of the sensors to detect different gas molecules over a wide range of concentrations including detection below 100 nanomoles/mole.

Silicon Carbide Power MOSFET Model and Parameter Extraction Sequence

A compact circuit simulator model is used to describe the performance of a 2-kV, 5-A 4-H silicon carbide (SiC) power DiMOSFET and to perform a detailed comparison with the performance of a widely used 400-V, 5-A Si power MOSFET. The models channel current expressions are unique in that they include the channel regions at the corners of the square or hexagonal cells that turn on at lower gate voltages and the enhanced linear region transconductance due to diffusion in the nonuniformly doped channel. It is shown that the model accurately describes the static and dynamic performance of both the Si and SiC devices and that the diffusion-enhanced channel conductance is essential to describe the SiC DiMOSFET on-state characteristics. The detailed device comparisons reveal that both the on-state performance and switching performance at 25degC are similar between the 400-V Si and 2-kV SiC MOSFETs, with the exception that the SiC device requires twice the gate drive voltage. The main difference between the devices is that the SiC has a five times higher voltage rating without an increase in the specific on-resistance. At higher temperatures (above 100degC), the Si device has a severe reduction in conduction capability, whereas the SiC on-resistance is only minimally affected

Large area, ultra-high voltage 4H-SiC p-i-n rectifiers

This paper reports the design, fabrication and high temperature characteristics of 1 mm/sup 2/, 4 mm/sup 2/ and 9 mm/sup 2/ 4H-SiC p-i-n rectifiers with 6 kV, 5 kV, and 10 kV blocking voltage, respectively. These results were obtained from two lots in an effort to increase the total power levels on such rectifiers. An innovative design utilizing a highly doped p-type epitaxial anode layer and junction termination extension (JTE) were used in order to realize good on-state as well as stable blocking characteristics. For the 1 mm/sup 2/ and 4 mm/sup 2/ rectifier, a forward voltage drop of less than 5 V was observed at 500 A/cm/sup 2/ and the peak reverse recovery current shows a modest 50% increase in the 25/spl deg/C to 225/spl deg/C temperature range. On the 10 kV, 9 mm/sup 2/ rectifier, a forward voltage drop of less than 4.8 V was observed at 100 A/cm/sup 2/ in the entire 25/spl deg/C to 200/spl deg/C temperature range. For this device, the reverse recovery characteristics show a modest 110% increase in the peak reverse recovery current from 25/spl deg/C to 200/spl deg/C. A dramatically low Q/sub rr/ of 3.8 /spl mu/C was obtained at a forward current density of 220 A/cm/sup 2/ at 200/spl deg/C for this ultra high voltage rectifier. These devices show that more than three orders of magnitude reduction in reverse recovery charge is obtained in 4H-SiC rectifiers as compared to comparable Si rectifiers.

Silicon carbide power MOSFET model and parameter extraction sequence

A compact circuit simulator model is used to describe the performance of a 2-kV, 5-A 4-H silicon carbide (SiC) power DiMOSFET and to perform a detailed comparison with the performance of a widely used 400-V, 5-A Si power MOSFET. The models channel current expressions are unique in that they include the channel regions at the corners of the square or hexagonal cells that turn on at lower gate voltages and the enhanced linear region transconductance due to diffusion in the nonuniformly doped channel. It is shown that the model accurately describes the static and dynamic performance of both the Si and SiC devices and that the diffusion-enhanced channel conductance is essential to describe the SiC DiMOSFET on-state characteristics. The detailed device comparisons reveal that both the on-state performance and switching performance at 25degC are similar between the 400-V Si and 2-kV SiC MOSFETs, with the exception that the SiC device requires twice the gate drive voltage. The main difference between the devices is that the SiC has a five times higher voltage rating without an increase in the specific on-resistance. At higher temperatures (above 100degC), the Si device has a severe reduction in conduction capability, whereas the SiC on-resistance is only minimally affected

Recent Advances in High-Voltage, High-Frequency Silicon-Carbide Power Devices

The emergence of high-voltage, high-frequency (HV-HF) silicon-carbide (SiC) power devices is expected to revolutionize commercial and military power distribution and conversion systems. The DARPA wide bandgap semiconductor technology (WEST) high power electronics (HPE) program is spearheading the development of HV-HF SiC power semiconductor technology. In this paper, some of the recent advances in development of HV-HF devices by the HPE program are presented and the circuit performance enabled by these devices is discussed

Failure dynamics of the IGBT during turn-off for unclamped inductive loading conditions

The internal failure dynamics of the insulated gate bipolar transistor (IGBT) for unclamped inductive switching (UIS) conditions are studied using simulations and measurements. The UIS measurements are made using a unique, automated nondestructive reverse bias safe operating area (RBSOA) test system. Simulations are performed with an advanced IGBT circuit simulator model for UIS conditions to predict the mechanisms and conditions for failure. It is shown that the conditions for UIS failure and the shape of the anode voltage avalanche sustaining waveforms during turn-off vary with the IGBT temperature, and turn-off current level. Evidence of single and multiple filament formation is presented and supported with both measurements and simulations.

Power MOSFET temperature measurements

Three temperature-sensitive electrical parameters are compared as thermometers for power MOSFET devices. The parameters are the forward drain-body diode voltage, the source-gate voltage, and the on-resistance. The results are also compared with temperatures measured with an infrared microradiometer. The procedure, apparatus, and circuits required to use each of the parameters as a thermometer are described. Some general considerations for measuring the temperature of power semiconductor devices are also discussed. Each parameter is found to be satisfactory for measuring the temperature of power MOSFETs. The sourcegate voltage measures a temperature nearest to the peak device temperature, and the drain-body diode voltage shows the least variation in calbiration from device to device.

Characteristics and utilization of a new class of low on-resistance MOS-gated power device

A new class of MOS-gated power semiconductor devices Cool MOS/sup TM/ has been introduced with a supreme conducting characteristic that overcomes the high on-state resistance limitations of high voltage power MOSFETs. From the application point of view, an immediate and very frequently asked question arises: does this device behave like a MOSFET or an insulated gate bipolar transistor (IGBT)? The goal of this paper is to compare and contrast the major similarities and differences between this device and the traditional MOSFET and IGBT. In this study, the new device is fully characterized for its (1) conduction characteristics, (2) switching voltage, current, and energy characteristics, (3) gate drive resistance effects, (4) output capacitance, and (5) reverse bias safe operating areas. Experimental results indicate that the conduction characteristics of the new device are similar to the MOSFET but with much smaller on-resistance for the same chip and package size. The switching characteristics of the Cool MOS are also similar to the MOSFET in that they have fast switching speeds and do not have a current tail at turn-off. However, the effect of the gate drive resistance on the turn-off voltage rate-of-rise (dv/dt) is more like an IGBT. In other words, a very large gate drive resistance is required to have a significant change on dv/dt, resulting in a large turn-off delay. Overall, the device was found to behave more like a power MOSFET than like an IGBT.

Issues in validating package compact thermal models for natural convection cooled electronic systems

A methodology is proposed for the validation of compact thermal models of electronic packages which utilizes data and simulations obtained from a simple but realistic system containing the package. The test system is the enclosure specified by the JEDEC Subcommittee, JC15.1 for thermal measurements in a natural convection environment. Simulations for a detailed model and several different compact models for a 88-pin plastic quad flat-package in the enclosure are in good agreement with experimental measurements of junction temperature. The study shows that the system must be well characterized, including accurate knowledge of circuit board thermal conductivity and accurate simulation of radiation heat transfer, to serve for validation purposes. For the package used in this study, system level considerations can outweigh package level considerations for predicting junction temperature. Given that the system is accurately modeled, the JEDEC enclosure can serve as a viable experimental validation tool for compact models.