Simulation of a new hybrid Si/SiC power device for harsh environment applications

A new power device structure is proposed, conceived to operate in a high temperature, harsh environment, for example within a motor drive application down hole, as an inverter in the engine bay of an electric car, or as a solar inverter in space. The lateral silicon power device resembles a laterally diffused MOSFET (LDMOS), such as those implemented within silicon on insulator (SOI) substrates. However, unlike SOI, the Si thin film has been transferred directly onto a semi-insulating 6H silicon carbide (6H-SiC) substrate via a wafer bonding process. Thermal simulations of the hybrid Si/SiC substrate have shown that the high thermal conductivity of the SiC will have a junction-to-case temperature approximately 4 times less that an equivalent SOI device, reducing the effects of self-heating. Electrical simulations of a 600 V power device, implemented entirely with the silicon thin film, suggest that it will retain the ability of SOI to minimise leakage at high temperature, but does so with 50% less conduction losses

High temperature reliability of power module substrates

The thermal cycling reliability of candidate copper and aluminium power substrates has been assessed for use at temperatures exceeding 300°C peak using a combination of thermal cycling, nanoindentation and finite element modelling to understand the relative stresses and evolution of the mechanical properties. The results include the relative cycling lifetimes up to 350°C, demonstrating almost an order of magnitude higher lifetime for active metal brazed Al / AlN substrates over Cu / Si3N4, but four times more severe roughening and cracking of the Ni-P plating's on the Al / AlN (DBA) substrates. The nonlinear finite element modelling illustrated that the yield strength of the metal and the thickness of the ceramic are the main stress controlling factors, but comparisons with the cycling lifetime results demonstrated that the fracture toughness (resistance) of the ceramic is the over-riding controlling factor for the overall passive thermal cycling lifetimes. In order to achieve the highest substrate lifetime for the highly stressed high temperature thermal cycled applications, the optimum solution appears to be annealed copper, brazed on to a thicker than normal or higher fracture toughness Si3N4 ceramic

Accurate analytical modeling for switching energy of PiN diodes reverse recovery

PiN diodes are known to significantly contribute to switching energy as a result of reverse-recovery charge during turn-off. At high switching rates, the overlap between the high peak reserve-recovery current and the high peak voltage overshoot contributes to significant switching energy. The peak reverse-recovery current depends on the temperature and switching rate, whereas the peak diode voltage overshoot depends additionally on the stray inductance. Furthermore, the slope of the diode turn-off current is constant at high insulated-gate bipolar transistor (IGBT) switching rates and varies for low IGBT switching rates. In this paper, an analytical model for calculating PiN diode switching energy at different switching rates and temperatures is presented and validated by ultrafast and standard recovery diodes with different current ratings. Measurements of current commutation in IGBT/PiN diode pairs have been made at different switching rates and temperatures and used to validate the model. It is shown here that there is an optimal switching rate to minimize switching energy. The model is able to correctly predict the switching rate and temperature dependence of the PiN diode switching energies for different devices

Analytical modeling of switching energy of silicon carbide Schottky diodes as functions of dIDS/dt and temperature

SiC Schottky Barrier diodes (SiC SBD) are known to oscillate/ring in the output terminal when used as free-wheeling diodes in voltage-source converters. This ringing is due to RLC resonance among the diode capacitance, parasitic resistance, and circuit stray inductance. In this paper, a model has been developed for calculating the switching energy of SiC diodes as a function of the switching rate (dIDS/dt of the commutating SiC MOSFET) and temperature. It is shown that the damping of the oscillations increases with decreasing temperature and decreasing dIDS/dt. This in turn determines the switching energy of the diode, which initially decreases with decreasing dIDS/dt and subsequently increases with decreasing dIDS/dt thereby indicating an optimal dIDS/dt for minimum switching energy. The total switching energy of the diode can be subdivided into three phases namely the current switching phase, the voltage switching phase, and the ringing phase. Although the switching energy in the current switching phase decreases with increasing switching rate, the switching energy of the voltage and ringing phase increases with the switching rate. The model developed characterizes the dependence of diode's switching energy on temperature and dIDS/dt, hence, can be used to predict the behavior of the SiC SBD

An evaluation of silicon carbide unipolar technologies for electric vehicle drive-trains

Voltage sourced converters (VSCs) in electric vehicle (EV) drive-trains are conventionally implemented by silicon Insulated Gate Bipolar Transistors (IGBTs) and p-i-n diodes. The emergence of SiC unipolar technologies opens up new avenues for power integration and energy conversion efficiency. This paper presents a comparative analysis between 1.2-kV SiC MOSFET/Schottky diodes and silicon IGBT/p-i-n diode technologies for EV drive-train performance. The switching performances of devices have been tested between -75 °C and 175 °C at different switching speeds modulated by a range of gate resistances. The temperature impact on the electromagnetic oscillations in SiC technologies and reverse recovery in silicon bipolar technologies is analyzed, showing improvements with increasing temperature in SiC unipolar devices whereas those of the silicon-bipolar technologies deteriorate. The measurements are used in an EV drive-train model as a three-level neutral point clamped VSC connected to an electric machine where the temperature performance, conversion efficiency and the total harmonic distortion is studied. At a given switching frequency, the SiC unipolar technologies outperform silicon bipolar technologies showing an average of 80% reduction in switching losses, 70% reduction in operating temperature and enhanced conversion efficiency. These performance enhancements can enable lighter cooling and more compact vehicle systems

Comparative study of RESURF Si/SiC LDMOSFETs for high-temperature applications using TCAD modeling

This paper analyses the effect of employing an Si on semi-insulating SiC (Si/SiC) device architecture for the implementation of 600-V LDMOSFETs using junction isolation and dielectric isolation reduced surface electric field technologies for high-temperature operations up to 300 °C. Simulations are carried out for two Si/SiC transistors designed with either PN or silicon-on-insulator (SOI) and their equivalent structures employing bulk-Si or SOI substrates. Through comparisons, it is shown that the Si/SiC devices have the potential to operate with an offstate leakage current as low as the SOI device. However, the low-side resistance of the SOI LDMOSFET is smaller in value and less sensitive to temperature, outperforming both Si/SiC devices. Conversely, under high-side configurations, the Si/SiC transistors have resistances lower than that of the SOI at high substrate bias, and invariable with substrate potential up to −200 V, which behaves similar to the bulkSi LDMOS at 300 K. Furthermore, the thermal advantage of the Si/SiC over other structures is demonstrated by using a rectangle power pulse setup in Technology Computer-Aided design simulations

The impact of temperature and switching rate on the dynamic characteristics of silicon carbide schottky barrier diodes and MOSFETs

Silicon carbide Schottky barrier diodes (SiC-SBDs) are prone to electromagnetic oscillations in the output characteristics. The oscillation frequency, peak voltage overshoot, and damping are shown to depend on the ambient temperature and the metal-oxide- semiconductor field-effect transistor (MOSFET) switching rate (dIDS/dt). In this paper, it is shown experimentally and theoretically that dIDS/dt increases with temperature for a given gate resistance during MOSFET turn-on and reduces with increasing temperature during turn-off. As a result, the oscillation frequency and peak voltage overshoot of the SiC-SBD increases with temperature during diode turn-off. This temperature dependence of the diode ringing reduces at higher dIDS/dt and increases at lower dIDS/dt. It is also shown that the rate of change of dIDS/dt with temperature (d2IDS/dtdT) is strongly dependent on RG and using fundamental device physics equations, this behavior is predictable. The dependence of the switching energy on dIDS/dt and temperature in 1.2-kV SiC-SBDs is measured over a wide temperature range (-75 °C to 200 °C). The diode switching energy analysis shows that the losses at low dIDS/dt are dominated by the transient duration and losses at high dIDS/dt are dominated by electromagnetic oscillations. The model developed and results obtained are important for predicting electromagnetic interference, reliability, and losses in SiC MOSFET/SBDs

Modeling of turn-OFF transient energy in IGBT controlled silicon PiN diodes

Silicon PiN diodes are the most widely used rectifying technology in industry especially in voltage source converters. The PiN diodes are usually used as anti-parallel diodes across silicon IGBTs where they conduct current in the reverse direction as the current commutates between the phases of the converter. They tend to generate a considerable amount of energy losses during the turn-OFF transient due to the reverse recovery characteristics. The rate at which the diode is switched will determine the switching energy and will affect EMI, electrothermal stresses and reliability. Hence, it is vital to be able to predict the switching energy of the diode during its turn-OFF transient given the switching conditions so as to have a realistic approach towards predicting the operating temperature. The switching energy of PiN diodes is determined by the peak reverse recovery current, the peak diode voltage overshoot, the time displacement between them as well as the temperature dependency of these peaks. In this paper, a model is presented and validated over a temperature range of -75 °C to 175 °C and with switching speeds (dI/dt) modulated by the gate resistance on the low side IGBT ranging from 10 © to 1000 ©. Comparisons show consistency between model prediction and measurements result. The model is a novel method of accurately predicting the switching energy of PiN diodes at different switching rates and temperatures using the measurements of a single switching rate at different temperatures

An investigation of temperature sensitive electrical parameters for SiC power MOSFETs

This paper examines dynamic Temperature Sensitive Electrical Parameters (TSEPs) for SiC MOSFETs. It is shown that the output current switching rate (dIDS/dt) coupled with the gate current plateau (IGP) during turn-ON would be the most effective under specific operating conditions. Both parameters increase with the junction temperature of the device as a result of the negative temperature coefficient of the threshold voltage. The temperature dependency of dIDS/dt has been shown to increase with the device current rating (due to larger input capacitance) and external gate resistance (RGEXT). However, as dIDS/dt is increased by using a small RGEXT, parasitic inductance suppresses the temperature sensitivity of the drain and gate current transients by reducing the “effective gate voltage” on the device. Since the temperature sensitivity of dIDS/dt is at the highest with maximum RGEXT, there is a penalty from higher switching losses when this method is used in real time for junction temperature sensing. This paper investigates and models the temperature dependency of the gate and drain current transients as well as the compromise between the increased switching loss and the potential to implement effective condition monitoring using the evaluated TSEPs

A temperature gradient based Condition Estimation Method for IGBT Module

The paper presents a temperature gradient based method for device state evaluation, taking the insulated Gated Bipolar Transistor (IGBT) modules as an example investigation. Firstly, theoretical basis of this method is presented and the results from example calculation on temperature gradient indicate that the increased thermal resistance and power loss of IGBT modules would increase the temperature gradient. Then an electrical-thermal- mechanical finite element method (FEM) model of IGBT modules, which takes the material temperature-dependent characteristic into account, is utilized to estimate the temperature gradient distribution for both healthy and fatigue conditions. It is found that the temperature gradient varies with power loss. Furthermore, both the experimental and simulation investigation on the temperature gradient for different conditions were conducted, and it is concluded that the temperature gradient can not only track the change of power loss, but have a better sensitivity compared with temperature distribution. In addition, the temperature gradient can reflect the defects location and distinguish failures degree. In the end the influence on the temperature gradient distribution caused by solder fatigue, void and delamination are discussed