Highlighting IMB-CNM’s role in the 37th IEEE International Symposium on Power Semiconductor Devices and ICs

For the first time, researchers from the Power Devices and Systems Group (PDS) of IMB-CNM presented five contributions in the leading international conference on power semiconductor devices, the 37th IEEE International Symposium on Integrated Circuits and Power Semiconductor Devices (ISPSD). The event was held from June 1 to 5 in Kumamoto, Japan, and brought together the main global players in this field, both industrial and academic. 

The ISPSD is a premier international conference for the presentation and discussion of all aspects of power semiconductor device and power integrated circuit technologies. Power semiconductor devices are one of the key enabling technologies for the deployment of renewable energy solutions, smart grids for safe and efficient distribution of electrical energy, and the electrification of industrial processes as a tool for achieving our society's energy transition goals.

This year, five predoctoral researchers from the PDS group presented their contributions. Mariana Raya gave an oral presentation, while Emma Solà, Ferran Bonet, Conrad Ferrer, and Miquel Tutusaus participated in the poster session. All presentations addressed several of the most pressing problems affecting the integration and advanced characterization of power semiconductor devices, generating great interest and engaging scientific discussions with other participants. Furthermore, Xavier Jordà, a researcher at IMB-CNM, was a member of the Technical Program Committee and chaired the Packaging Technologies session during the conference.

Below is a summary of the content of the five contributions presented at ISPSD.

SiC MOSFET Chip Embedded Switching-Cell for Multilevel Converters

Presented by Mariana Raya.

Chip embedding is emerging as a promising advanced packaging technology, offering significant advantages over conventional methods in terms of performance, reliability and miniaturization. This integration approach allows an easy and cost effective solution to combine standard SMD components on top of PCB boards and power devices embedded inside the board itself. This feature was considered of main interest for the development of smart power modules integrating modular and scalable switching-cells in the framework of the Horizon Europe SCAPE project.

Mariana Raya explained the design, development and characterization of a smart switching-cell for multilevel converters, utilizing chip embedding technology and 750V, 12mΩ SiC power MOSFETs. The switching-cell design was optimized in terms of minimum partial inductance and thermal resistance. Simulation results align closely with experimental data, showing a junction to backside thermal resistance of 0.63 K/W and a parasitic inductance of 2.7nH at 10MHz. The electrical performance and functionality of the switching-cell was also experimentally validated up to 400V, 30A and 100kHz switching frequency, confirming the interest of chip embedding for smart power modules integration in the medium voltage/power range.

Chip-level Interconnection Techniques for Chip Embedding Integration of SiC MOSFETs

Presented by Emma Solà.

The basis of the chip-embedding approach consists in introducing the semiconductor power devices inside the printed circuit boards of a given converter circuit, achieving high levels of integration. The work presented by Emma Solà focused on the topside and backside die-level interconnection techniques needed for enabling the electrical contacts of the embedded devices. A novel in-house technique was presented to selectively re-metallize with Cu the contact pads of any device by hard shadow masking, to allow subsequent standard microvia contacts during the PCB manufacturing process. In this work the technique was used to re-metallize the gate and source pads of 750V-12mΩ SiC MOSFET dies, which were then attached to Cu lead-frames with a robust layer of sintered Ag micro/nano particles. These assemblies were successfully embedded for implementing elementary switching-cells used in multilevel power converters designed for electric traction applications in the framework of the SCAPE project.

Measurement of Free-Carrier Density in a 1.2 kV SiC Schottky Diode under Overstress Conditions

Presented by Ferran Bonet.

The development of new power devices based on novel materials and innovative structures requires advanced electro-thermal characterization techniques at the die level. Among these techniques, the Internal InfraRed-Laser Deflection (IIR-LD) method stands out as a powerful tool for measuring thermal and electrical variables inside devices during operation. Ferran Bonet was the first to demonstrate the successful application of the IIR-LD method to measure the carrier density profile in a 1.2 kV SiC Schottky diode under overcurrent conditions. This type of electrical overstress induces a high injection level into the drift region at the junction termination extension, effectively activating PiN diode behavior.

To do this, Bonet addressed key challenges in postprocessing IIR-LD data: decoupling temperature effects from carrier density in deflection signals and deconvolving for the laser beam’s relatively large diameter (~16 μm) from measured carrier concentration. Experimental results in the drift region show excellent agreement with simulations, revealing carrier densities ranging from 2.73×10¹⁶ to 3.47×10¹⁶ cm⁻³. Additionally, measurements in the substrate region indicate temperature-driven dopant ionization. All these results will be very relevant for the development of new generation of SiC devices in the Horizon Europe project SAFEPOWER.

Thermal Analysis of Current Crowding in IGBTs under Stressful Operation in Resonant Converters

Presented by Conrad Ferrer.

Temperature monitoring in power semiconductor devices is a key research area due to its impact on system’s reliability. Spatially-resolved measurement approaches provide surface thermal distributions allowing for the detection of hot-spots induced, for example, by current crowding phenomena. Conrad Ferrer presented for the first time, die-level electrical stress from current crowding conditions analysed by InfraRed (IR) thermography in an IGBT operating in a half-bridge resonant converter outside the zero-voltage switching (ZVS) regime from 150 to 75 kHz switching frequency. Custom IR image processing with Fourier coefficients and time reconstruction enabled non-invasive 10 µm sub-millisecond monitoring of the device’s thermal map during switching operation, identifying overheated areas in low-impedance regions at a tens of microsecond time scale.

Non-Intrusive Online Junction Temperature Monitoring in Si and SiC Power MOSFETs

Presented by Miquel Tutusaus.

With the increase of power electronic systems due to the decarbonization of the industry, it is important to assure a reliable operation under different stress conditions. In this sense, the junction temperature of power semiconductor devices is a key parameter to consider when designing and operating power systems to assure proper reliability. Nevertheless, on-line junction temperature measurement of power devices under high-voltage switching conditions is a very challenging task. Miquel Tutusaus presented a non-intrusive method based on a fast clamping circuit and a look-up table to utilize the ON-state voltage drop of power devices as a temperature sensitive electrical parameter (TSEP). This method allows junction temperature monitoring of Si and SiC MOSFETs during converter operation, achieving steady-state temperature measurement deviations below 1 °C. The proposed solution will be of main interest for industrial converters such as the induction heating cookers developed by the company BSH.