Lyubomir Kerachev

Study of Techniques for Flip-Chip Bonding to Organic Substrates for Low-Power Applications

This paper deals with the study of technologies for flip-chip assembly of CMOS integrated power converters on standard FR4 organic substrates. Tests for the characterization of commercially available technologies for microassemblies, such as anisotropic adhesive bonding, thermocompression bonding, thermosonic/ultrasonic bonding, and solder bonding, are carried out. The aim of this paper is to determine the most suitable flip-chip bonding technology for power CMOS circuits with more than 50 pads. First, the coupled design of the CMOS chip and the corresponding substrate dedicated to low-power microconversion (10 W) is presented. It is shown that the parasitic resistances and inductances of the interconnections increase the conduction and switching losses of the device. This leads to a temperature rise, which can limit the operating ratings of the circuit. The experimental results are provided to evaluate each technology for flip-chip assembly.

Characterization and Analysis of an Innovative Gate Driver and Power Supplies Architecture for HF Power Devices With High dv/dt

This paper presents a specific architecture for a low-side/high-side gate driver implementation for power devices running at high switching frequencies and under very high switching speeds. An electromagnetic interference (EMI) optimization is done by modifying the parasitic capacitance of the propagation paths between the power and the control sides, thanks to a specific design of the circuit. Moreover, to reduce the parasitic inductances and to minimize the antenna phenomenon, the paper studies which elements of the drivers’ circuitry must be brought as close as possible to the power parts. This is important when the ambient temperature of the power device becomes critical, for instance, in automotive and aeronautic applications. Simulations and experiments validate the advantages of the proposed architecture on the conducted EMI problem.

Concept and design of hybrid interleaved and isolated micro-converter for low power applications

In this paper, a hybrid interleaved and isolated micro-converter (5V/2A/1MHz) dedicated to low power conversion is presented. In order to be able to address a lot of different applications, its structure is isolated (implementation of a planar coupler) and uses interleaved parallel legs with coupled inductors (lowering internal losses). For very high integration purpose, two chips have been done: one dedicated to the control of the switching-cells and the other implementing the drivers and the power switches. The control part implements an original modular approach dedicated to provide the interleaved carriers and to guaranty the current balancing. The power part discusses the layout constraints to optimize the power density.

Design and Implementation of a Highly Integrated Dual Active Bridge Microconverter

This paper deals with the design and the implementation of an isolated and highly integrated low voltage, low power microconverter. A dual active-bridge topology is considered as a good candidate for reducing the number of passive elements. The design of a “power die” integrating power inverter legs and their driver circuits is carried out in order to benefit from the high level of integration and to reduce the amount of active components and the volume of the converter. Thus, a microconverter is built for 10 W power supply (5 V/2 A) and is operating at 1 MHz switching frequency. The measured efficiency of the converter is 88% for 6.5 W transferred power and 86% for 8.5 W transferred power without taking into account its control unit. The converter is operating in natural convection, and no cooling system is implemented. Therefore, a power density of 9.9 kW/L is achieved, which is beyond the state of the art of the conventional isolated converters whose power densities are around 1-2 kW/L at the same power level.

Implementation of monolithic multiple vertical power diodes in a multiphase converter

In this paper, an implementation of monolithic multiple power diodes into a multiphase converter structure with coupled inductors is presented. Advantages of interleaved converters are focused on filtering reduction while increasing the number of needed power devices. The large number of smaller active devices is one of the most important issues in these converter topologies. In this context, a concept based on the monolithic integration of multiple power diodes is developed. Reliability and cost effective solutions are the driving criteria to develop the assembly, the packaging and the interconnections of power devices at wafer level. The functionality of this structure is experimentally tested and validated. Finally, experimental results are presented and discussed.