Allen R. Hefner

Micro-differential scanning calorimeter for combustible gas sensing

Abstract A micron-scale differential scanning calorimeter (μDSC) has been produced on a silicon chip allowing for microscopic differential scanning calorimetry (DSC) measurements on small samples. The device consists of a suspended rectangular microhotplate with sample and reference zones at either end, each with a polysilicon microheater for temperature control. The temperature difference between the two zones is measured with a thermopile consisting of a series of successive polysilicon/metal junctions which alternate between the two zones. In a scanning differential calorimetry measurement, the two elements are heated simultaneously with a ramped temperature profile. A thermal process zone is defined on one of the elements, for example, a catalyst for chemical sensing, a material which exhibits a phase transition, or a chemically selective reactive material. When temperature is scanned the loss or gain of heat associated with the reaction or phase transition on the sample zone produces a difference signal on the thermopile. The device has a temperature range from 20 to 600xa0°C, and can be heated to that temperature in as little as 40xa0μs, while the cooling time constant is 5xa0ms. Thermal imaging was used to characterize heat flow across the device in response to a 40xa0μs voltage pulse applied to one side. At 4xa0ms after the pulse the heat distribution has become largely uniform across the device, showing that scans shorter than this time-scale will minimize the effects of heat loss from the sample to the reference zone. An example application shows the response to varying concentrations of methanol, ethanol, acetone, benzene, and hydrogen in air, when operated with periodic ramps to 570xa0°C of duration 3.5xa0s. The thermopile responds with a periodic waveform which is different for different gases, making the use of pattern recognition analytical methods for gas identification possible.

Automated parameter extraction software for advanced IGBT modeling

A software package for extracting parameters to be used in advanced IGBT models is presented. In addition, new model equations and extraction procedures are introduced that more accurately describe a wide range of IGBT types including the Warp-Speed IGBTs. The parameter extraction software package consists of five programs that extract the 20 physical and structural parameters needed in the most recent version of the Hefner IGBT model. Each program has a graphical user interface and uses the IEEE 488 bus to control the measurement instruments. Various algorithms are employed for fitting the IGBT model equations to measured data. The new software package enables users of the simulation software products to extract model parameters themselves and thus permits the simulation of new IGBT part numbers as soon as they are introduced.

High-Voltage capacitance measurement system for SiC power MOSFETs

Adequate modeling of a power Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is dependent on accurate characterization of the inter-electrode capacitances. With the advent of high-voltage silicon carbide (SiC) power MOSFETs, it has become important to develop a measurement system that can perform and record high-voltage capacitance versus voltage measurements on these devices. This paper describes a measurement apparatus that safely and accurately allows high voltage capacitance-voltage (CV) measurements to be performed. The measurements are based on conventional LCR (Inductance (L), Capacitance (C), and Resistance (R)) meter CV techniques but with added circuitry to interface the LCR meter to high voltage bias sources. The effects of the added circuitry are studied theoretically, and the CV measurement accuracy is verified with experimentation. High voltage capacitance voltage measurements are presented for both silicon and SiC power MOSFETs.

High-Voltage Isolated Gate Drive Circuit for 10 kV, 100 A SiC MOSFET/JBS Power Modules

A high-current, high-voltage-isolated gate drive circuit developed for characterization of high-voltage, high- frequency 10 kV, 100 A SiC MOSFET/JBS half-bridge power modules is presented and described. Gate driver characterization and simulation demonstrate that the circuit satisfies the gate drive requirements for the SiC power modules in applications such as the DARPA WBST-HPE solid state power substation (SSPS). These requirements include 30 kV voltage-isolation for the high-side MOSFETs, very low capacitance between the ground and floating driver sides, and 20 kHz operation. Block diagram and detailed discussion of principles of operation of the gate drive circuit are given, together with measured and simulated waveforms of performance evaluation.

Device Models, Circuit Simulation, And Computer-controlled Measurements For The IGBT

The implementation of the recently dcvel- oped IGBT device model into a circuit simulation program is described. It is shown that the circuit simulation program rapidly and robustly simulates the dynamic behavior of the IGBT for general external drive, load, and feedback circuit configurstions. The algorithms used to extract the IGBT de- vice parameters from computer-controlled measurements are also described, and it is shown that the model accurately de- scribes experimental results when the extracted parameters are used.

Electro-thermal simulation of 1200 V 4H-SiC MOSFET short-circuit SOA †

The purpose of this paper is to introduce a dynamic electro-thermal simulation and analysis approach for device design and short-circuit safe-operating-area (SOA) characterization using a physics-based electro-thermal Saber®* model. Model parameter extraction, simulation, and validation results are given for several commercially available 4H-silicon carbide (SiC) power MOSFETs with a voltage rating of 1200 V and with current ratings of 31.6 A and 42 A. The electro-thermal model and simulations are used to analyze the short-circuit SOA including the measured failure time (tfailure) and simulated device internal junction temperature (Tj) at failure for different gate voltages (VGS) and drain voltages (VDS).

Long-Term Stability Test System for High-Voltage, High-Frequency SiC Power Devices

This paper presents a test system developed for long-term stability characterization of 10 kV Silicon Carbide (SiC) power MOSFETs and SiC diodes under 20 kHz hard switching conditions. The system is designed to test a single power switch and a single power diode for continuous or burst switching conditions up to 5 kV and 5 A. The test system includes a 4.5 kV to 5 kV boost converter to emulate a 22.5 kW hard switching power converter. An additional DC-DC converter is used to recover the power processed by the boost converter. The design criteria, simulation, and construction of the test system are discussed in this paper and the system operation is demonstrated using various high voltage devices including 4.5 kV Silicon IGBTs, 10-kV SiC MOSFETs and 15 kV stacked silicon diodes.

Automated parameter extraction software for silicon and high-voltage silicon carbide power diodes

This paper presents an automated parameter extraction software package developed for constructing silicon (Si) and silicon carbide (SiC) power diode models, which is called DIode Model Parameter extrACtion Tools (DIMPACT). This software tool extracts the data necessary to establish a library of power diode component models and provides a method for quantitatively comparing between different types of devices and establishing performance metrics for device development. To verify the accuracy of DIMPACT, the extracted model parameter sets are incorporated into the circuit simulation software to compare model predictions with measured static and transient diode characteristics. In this paper, the DIMPACT parameter extraction results are demonstrated for a 45 V, 15 A Si Schottky diode; a 600 V, 200 A Si PiN diode; a 10 kV, 5 A SiC Junction Barrier Schottky (JBS) diode; and a 10 kV, 20 A SiC PiN diode. The validation results indicate that the model parameters extracted using DIMPACT are accurate.

Low-impedance time-domain reflectometry for measuring the impedance characteristics of low-impedance transmission lines

An experimental examination of a 10 Ω and a 2 Ω time-domain reflectometer (TDR) technique for measuring low-impedance transmission line characteristics is presented. TDR measurements using these systems are compared to those using a 50 Ω TDR system. The results show that the uncertainties in the characteristic impedance, ZC, of a low-ZC transmission line are a significant fraction of ZC for 50 Ω TDR measurements, whereas the fractional uncertainties are much less when using a low-impedance TDR. The fractional ZC uncertainties for the 50 Ω TDR increase as ZC decreases.