Sebastiano Russo

A Reliability Model for Power MOSFETs Working in Avalanche Mode Based on an Experimental Temperature Distribution Analysis

The on-state resistance of power MOSFET devices tasked to perform repetitive avalanche operations is subject to modifications caused by the growth of voids and cracks in the source metallization. Endurance tests are the traditional way to monitor these changes in order to assess device reliability. However, they are very time intensive, requiring even months of uninterrupted operations. An interesting alternative is assessment of reliability through a suitable model, but no standard techniques have been developed up until now to accomplish this task. A possible approach, dynamic analysis of the temperature distribution over the source metal, is presented in this paper. Coupling the results of the thermodynamic analysis with a reliability model, and based on the Coffin-Manson law, device degradation over time can be estimated and the level of reliability can be evaluated. The consistence of the obtained reliability prediction is confirmed by comparison with endurance test results. The described approach can be usefully applied to assess the reliability of MOSFETs in a large set of applications in the automotive field.

Reliability enhancement with the aid of transient infrared thermal analysis of smart Power MOSFETs during short circuit operation

Abstract The usage of novel measurement techniques enhances the capabilities of researchers and power device manufacturers to understand and address reliability problems in novel Smart Power Devices. Along this line of argument, this work describes a method to improve the reliability of the smart Power MOSFET devices by design. The design optimization process involves Silicon layout, interconnections, packaging and protection strategy as well. Accurate thermal transient analyses, made possible by the unique features of a custom infrared radiometric microscope experimental setup which allows dynamic temperature detection with a bandwidth of 1 MHz over the chip area, indicated the way to minimize peak temperature and to verify the effect of the optimization.

Stress analysis and lifetime estimation on power MOSFETs for automotive ABS systems

Stress analysis and lifetime estimation are required in order to guarantee higher and higher levels of reliability of automotive power electronic devices. Stress analysis is oriented to investigate the effects of all the possible physical cause of failures, according to the defined device mission. On the basis of the stress analysis, and of a suitable reliability model a life time prediction can be performed. This is useful to predict the suitability of the device under evaluation to the prescribed mission, as well as to improve the design of new generations of devices. An experimental technique is exploited in this paper to evaluate the stress exerted on planar power MOSFETs designed to equip automotive ABS systems. The technique is based on an accurate experimental analysis of electro-thermal cycles, exploiting a laboratory tool tailored around an infrared microscope. It enables an high resolution dynamic temperature mapping with a large bandwidth. Such a tool makes also possible the evaluation of the effects of charge trapping phenomena occurring on power MOSFETS as result of unavoidable gate overvoltages. According to a reliability model based on the Coffin Manson law, finally it is shown that gate voltage spikes can dramatically reduce the expected life time.

Fast transient infrared thermal analysis of smart Power MOSFETS in permanent short circuit operation

Automotive smart power MOSFETs are submitted to very high power dissipation when they operate in short circuit conditions. The consequential fast temperature cycling stresses the device structure and challenges its reliability. A not conventional 2D thermal measurement method permitted the thermal analysis of extremely fast thermal transients. This made feasible the definition of new smart power design rules to reduce stressing temperature peaks so improving significantly their reliability

Reliability of planar, Super-Junction and trench low voltage power MOSFETs

A strong demand of even more compact and reliable devices has powered in the last years the development of advanced power MOSFET structures. Among them, the planar STripFET™ has been introduced as an alternative to conventional trench gate MOSFET in low voltage (<60 V) applications. Moreover low voltage Super-Junction devices are also under development. In this paper a conventional trench gate MOSFET is compared in terms of reliability with a STripFET™ and a Super-Junction device. The comparison is accomplished through a reliability model taking advantage from a dynamic analysis of the temperature distribution over the metal source surface in an effort to correlate electric working conditions to thermo-mechanical stresses.

An Infrared Thermal Measuring System for Automotive Applications and Reliability Improvement

In the last years the global energy economy hangs in the balance, pushing up the research interest in novel and renewable energy sources and in innovative engines able to improve performances saving the efficiency. This frame requires the development of power electronics subsystems and the continuous increase of working temperatures; hence reliability has become the most critical requirement for any new device design. The temporal evolution of temperature distribution on the surface of a power electronic device undergoing an exerted stress plays a fundamental role in studying and improving reliability. A suitable scanning measuring system has been realized in order to allow the analysis of fast transient states and the localization of “hot-spots” which could be a cause of a premature failure and unreliability of the devices.

Reliability Assessment of Power MOSFETs Working in Avalanche Mode Based on a Thermal Strain Direct Measurement Approach

A strong demand of even more compact and reliable power electronic devices has powered in the last years the development of advanced device design techniques. A key role in these techniques is played by the reliability assessment, a procedure that estimates the expected lifetime of power devices according to given mission profiles. The reliability assessment of a low voltage MOSFET working in avalanche mode is faced in this paper through a new experimental approach based on the Coffin Manson law and a direct measurement of the thermal strain over the Source Aluminum layer. The consistence of the proposed technique is evaluated by comparing obtained estimations of the progressive increment of the on state resistance with estimations carried out from other reliability models and endurance tests results. The described approach can be usefully applied to assess the reliability of MOSFETs in applications typical of the automotive field were power devices are tasked to operate in avalanche mode, such as: brake pump drivers, electromagnetic valve control, direct high-pressure injection, starter-alternator and active suspension systems.

Molding Compounds Adhesion and Influence on Reliability of Plastic Packages for SiC-Based Power MOS Devices

Adhesion and interface compositions of epoxy phenolic molding compounds (EMCs) for high-temperature plastic packages are studied. Interfaces are obtained by molding two EMCs onto aluminum oxide-hydroxide surfaces (oxide onto thin film of AlSiCu) and two die passivation layers consisting of fluorinated polyimide and cyclotene. One compound (A) is a “green” type, containing organic phosphorous-based flame retardant, and the other compound (B) is a conventional type containing antimony (III) oxide and bromined resin flame retardants. A high-temperature storage test at 250 °C is employed to study chemical modifications occurring at the previously mentioned interfaces. A high-temperature reverse bias test at 225 °C is employed to study the influences of the EMC chemical formulations on the reliability of plastic packages for SiC-based power MOS devices. Green compound A shows poor adhesion onto Al oxide and high adhesion strength onto both polymer passivations. The failure mechanism is mainly cohesive on the polymer passivations. The conventional compound B shows a high degree of delamination because of poor adhesion compared with the green compound. SiC-based power MOS devices assembled in plastic packages with compound A show better reliability under HTRB test at 225 °C compared with compound B.

Reliability assessment of low-voltage MOSFETs driving inductive loads

Reliability and compactness are two aspects often fighting among themselves when speaking about power electronics, but, indeed, they are the keys for the success of any new circuit or device. Reliability, in particular, is the word of the moment, powering the development of advanced device design techniques having the reliability as a major goal. Endurance tests is the traditional way to evaluate the reliability of power devices. However, they are very time expensive, requiring even months of uninterrupted testing. An interesting alternative is the estimation of the reliability of a device through a suitable model, but, no standard techniques have been developed up to now to accomplish this task. A possible approach is followed in this paper to assess the reliability of Power MOSFETs driving inductive loads, by exploitation of a dynamic analysis of the temperature distribution over the source metal. Coupling such an analysis with a reliability model, carried out from the Coffin-Manson law, the device life time is estimated. Such a procedure is then used to assess the reliability of Power MOS devices tasked to control the brake pump in a modern vehicle. The consistence of the reliability estimation is confirmed by comparison with results of endurance tests. The described approach can be usefully applied to a large set of applications of MOSFETs in the automotive field.

Reliability assessment of power MOSFETs working in avalanche mode based on a thermal strain direct measurement approach

A strong demand for even more compact and reliable power electronic devices has powered the development of advanced design techniques. A key role is played in these techniques by the reliability assessment, a procedure that estimates the expected lifetime according to given mission profiles. The reliability assessment of a low voltage MOSFET working in avalanche mode is considered in this paper through an experimental approach based on the Coffin-Manson law. Differently from previously proposed techniques, based on a thermodynamic analysis, a direct measurement of the thermal strain over the source aluminum layer is instead exploited. The consistence of the proposed technique is evaluated by comparing estimation of the progressive increment of the on-state resistance with results of endurance tests and estimation obtained from previously presented reliability models. The described technique can be applied to assess the reliability of MOSFETs in applications typical of the automotive field, where they are tasked to power inductive loads in unclamped mode. More in general, the method can be exploited to characterize the front metal of MOSFET devices subjected to power cycling, or short-circuit stress tests.