M. Vellvehi

Irradiance-based emissivity correction in infrared thermography for electronic applications

This work analyzes, discusses, and proposes a solution to the problem of the emissivity correction present in infrared thermography when coatings with known emissivity cannot be deposited on the inspected surface. It is shown that the conventional technique based on two reference thermal images and the linearization of the blackbody radiation dependence on temperature is not a reliable and accurate solution when compared with the coating procedure. In this scenario, a new approach based on the direct processing of the output signal of the infrared camera (which is proportional to the detected irradiance) is proposed to obtain an accurate emissivity and surrounding reflections map, perfectly compensating the thermal maps. The results obtained have been validated using a module as a test vehicle containing two thermal test chips which incorporate embedded temperature sensors.

Study of novel techniques for reducing self-heating effects in SOI power LDMOS

Abstract Self-heating effects in silicon-on-insulator (SOI) power devices have become a serious problem when the active silicon layer thickness is reduced and buried oxide thickness is increased. Hence, if the temperature of the active region rises, the device electrical characteristics can be seriously modified in steady state and transient modes. In order to alleviate the self heating, two novel techniques which lead to a better heat flow from active silicon layer to silicon substrate through the buried oxide layer in SOI power devices are proposed. No significant changes on device electrical characteristics are expected with the inclusion of the novel techniques. The electro-thermal performance of lateral power devices including the proposed techniques is also presented.

Intelligent bidirectional power switch module for matrix converter applications

This work proposes a new intelligent power module integrating the bidirectional switch function with fast switching times, optimized for matrix converter applications. It includes the power transistors gate drivers, galvanic isolation between control and power stages, over-voltage protection devices, floating voltage power supplies and a control circuitry providing smart switching sequences for the current commutation strategy. In addition, its modular design allows easy replacement of damaged BDSs in an entire matrix converter and makes the power and signals interconnections easier. The structure of the bidirectional switch consists of a power substrate containing the power circuit and components (diodes, IGBTs, etc.) and a PCB on top with the control circuits. From the users point of view, the proposed module shows two power terminals (bidirectional switch function), two pins corresponding to the voltage power supply of the high-level control circuits, the bidirectional switch logic control signal pin (turn-on / turn-off) and other auxiliary control pins depending on the implemented commutation strategy (for example, the sign of the load current).

Transmission Fabry–Pérot interference thermometry for thermal characterization of microelectronic devices

The suitability of the thermometry based on transmission Fabry–Perot interferences in semiconductor devices and ICs under working conditions is experimentally shown. Usually, they work at short time scales producing internal temperature increments, which are crucial for understanding their failure mechanisms. Thanks to this technique, the temperature profile in semiconductor devices and ICs is extracted with a very good depth resolution (below 35 µm). By means of versatile apparatus, transmission Fabry–Perot and internal infrared laser deflection temperature measurements are simultaneously performed on a specific thermal test chip device. Concretely, the temperature evolution at various depths of the thermal test chip during the device heating and cooling processes is obtained. Experimental results are compared with the analytical model which thermally describes the thermal test chip behaviour during the heating process, achieving a very good agreement.

Hot spot analysis in integrated circuit substrates by laser mirage effect

This work shows an analytical and experimental technique for characterizing radial heat flow present in integrated circuits (ICs) when power is dissipated by integrated devices. The analytical model comes from the resolution of the Fermat equation for the trajectory of rays and supposing a spherical heat source dissipating a time-periodic power. An application example is presented; hence demonstrating how hot spots and heat transfer phenomena in the IC substrate can be characterized. The developed method may become a practical alternative to usual off-chip techniques for inspecting hot spots in ICs and to experimentally characterize heat flow in the semiconductor substrate.

Design of logic gates for high temperature and harsh radiation environment made of 4H-SiC MESFET

Silicon carbide MESFETs are very attractive devices for high frequency applications, and communications. Progresses in the manufacturing of high quality SiC substrates open the possibility to new circuit applications. SiC unipolar transistors, such as JFETs and MESFETs have also a promising potential for digital integrated circuits operating at high temperature (HT) and/or in harsh environments. An increasing demand for HT compliant circuits comes from intelligent power management, automotive industry, and intelligent sensors for harsh environment, space and aerospace as well. The present work is a demonstration of logic gates design with normally-on 4H-SiC MESFET devices using HT Spice models extracted from experimental measurements. A complete library of functional HT logic gates allows the implementation of complex logic embedded in power management circuitry.

Hot-Spot Detection in Integrated Circuits by Substrate Heat-Flux Sensing

This letter presents a novel approach to detect hot spots (HSs) in active integrated circuits (ICs) and devices. It is based on sensing the HS heat flux within the chip substrate with a probe-laser beam. As the beam passes through the die, it experiences a deflection directly proportional to the heat flux found along its trajectory (internal infrared laser deflection technique). The proposed strategy allows inspecting the chip through its lateral sides (lateral access), avoiding the metal and passivation layers placed over the die. The obtained results demonstrate the suitability of this technique to locate and characterize devices behaving as hot spots in nowadays IC CMOS technologies.

Lateral spread of implanted ion distributions in 6HSiC: simulation

In this paper, Monte Carlo simulation, using improved models for electronic stopping and 3D damage accumulation has been carried out to calculate the lateral distribution of ions implanted into 6HSiC crystal. Two dimensional concentration contour plots are used to show the lateral spread of implanted Al+ ions at mask edges. It appears that channeling strongly influences the shape of lateral distributions due to the capture of random implanted ions by axial channels lying parallel to the (0001) surface of 6HSiC which appears alternatively every 30° around the 〈0001〉 axis, according to the symmetry of the 6HSiC crystal. This phenomenon, if confirmed by SIMS 2D profiling, could have important consequences on the behavior of ion implanted lateral junctions of SiC devices.

The IBMCT: a novel MOS-gated thyristor structure

This paper addresses the analysis of the Insulated Base MOS-Controlled Thyristor (IBMCT), a novel MOS-thyristor structure compatible with IGBT process technology. The IBMCT turn-off process is based on the existence of a Floating Ohmic Contact (FOC) which allows fast hole removal from the p-body region. The device operation mode and its electrical characteristics are analyzed with the aid of 2-D numerical simulations. Experimental measurements confirm the ability to control both turn-on and turn-off processes by biasing the two independent gate electrodes. A comparison of the electrical characteristics with those obtained from IGBT and BRT is also provided.

An effective thermal conductivity measurement system

In the technical literature, there is a lack of reliable thermal parameters and, often, it is necessary to do in situ measurements for every particular material. An effective thermal conductivity measurement system has been designed and implemented to provide reliable and accurate values for that thermal parameter. The thermal conductivity of a given material is deduced from thermal resistance differential measurements of two samples. All parts of the implemented system as well as practical and theoretical solutions are described, including a power controller circuit exclusively conceived for this application. Experimental considerations to reduce the measurement error are exposed, as well as some results obtained for three different materials.