EPSRC Centre for Power Electronics
University of Nottingham
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Feasibility Studies

Patterned Magnetic Cores (PaMaCore) for Efficient Power Devices

Dr Jonathan Terry, University of Edinburgh

The University of Edinburgh’s research into more-than-Moore technologies included integration of components comprising magnetic materials, such as micro-inductors. When there is a magnetic flux in the conductive core of devices such as inductors and transformers, circulating currents are induced within the core. These eddy currents oppose flow of the induced current generating resistive heating and power loss in the core. These losses are typically reduced in discrete components using laminated cores, but this doesn’t translate well to the magnetic cores of devices integrated on silicon.

This feasibility study investigated cores fabricated of patterned magnetic segments defined by photolithography. In combination with the use of magnetic seed layers, macro-patterned magnetic cores have been found to improve the electrical performance of micro-inductors in terms of Q-factor. On-going work is investigating micro-patterned segments, with dimensions close to those of individual magnetic domains, to determine whether further performance improvements can be achieved.

PaMaCore for Efficient Power Devices

Magnetic core comprising patterned segments of NiFe (left); with a crossbridge test structure for use in determining sheet resistance and line width of electroplated material (right).
 

 

 

Novel under-bump metallisation to enable low cost Pb-free solder interconnects for power electronics 

Professor Changqing Liu, Loughborough University

Recent regulations such as RoHS and WEEE directives have restricted the use of Lead-rich solders in high power electronics due to its toxicity. Zn-based solders promise to replace high lead solders for numerous advantages such as low cost, excellent mechanical strength, high thermal and electrical conductivity.

However, Zn-based solders react actively with substrate metals (e.g. Cu), forming excessive Cu-Zn IMCs at elevated temperature to make the joints prone to fracture, which requires a diffusion barrier known as Under-bump metallisation (UBM) to prevent continuous growth of IMCs.

In this feasibility study, a ternary amorphous NiWP metallization was developed that can keep amorphous at elevated temperature (e.g. 400°C) to effectively retard IMC growth and to significantly enhance the reliability of solder joints. The crystallization mechanism of this NiWP coating and its reaction with Zn-5Al solder will be further investigated in our future work in this project.

SEM & Related AFM Images

The SEM and the related AFM images (mean roughness included) of Ni-15W-10P alloys after various annealing (1) As-deposited stated; (2) Annealing at 400ºC for 2 hours; (3) Annealing at 750ºC for 2 hours.

 

 

 

Dielectric Properties of Thin Diamond Layers

Dr Oliver Williams, Cardiff University

This project will determine the dielectric properties and high voltage blocking capabilities of thin diamond films on silicon and select metals. This will determine the feasibility of using thin diamond layers as heat spreading layers in high power devices as well as its potential in MEMS technologies. It aims to demonstrate diamond’s capabilities as a passive material rather than an active electronic device material as this is an area where diamond has previously been shown to excel.

 

 

 

 

 

 

Structural and Functional Integration of Power Electronics for Harsh Environments

Dr David Flynn, Heriot-Watt University and Dr Robert Kay, Loughborough University

The overall vision of this feasibility study is to assess solutions for the structural and functional integration of Silicon Carbide (SiC) power electronic devices into bespoke ceramic packages for deployment in harsh environments. An innovative assembly and packaging process will be created that is based on the incorporation of SiC power devices utilising Solid Liquid Inter Diffusion (SLID) interconnects, within ceramic substrates that have been produced using Additive Manufacturing.  

David Flynn (a)

Additive Manufacturing of Ceramic & Conductive Track Fabrication
 
 

M+POWER: Magnetic Field Controlled Switching Device for Power IC Technology

Dr Petar Igic, Swansea University

In the recent years, significant research effort has been put into increasing component integration and extending the operating envelope through intelligent control and advanced operational diagnostics, increasing devices’ functionality and replacement of classical electromechanical devices with their solid-state counterparts, as well as, improving operational management and control including device, module and converter/drive status monitoring, diagnostics and prognostics. 

The main outcome from the M+POWER project is the design, fabrication and testing of a functional prototype of novel integrated current sensing device aimed for on-chip over-load/over-current protection of power devices. The current sensor will be based on a revolutionary new integrated magnetic FET featuring the extreme magnetic sensitivity and inherent magnetic controlled on-off switching phenomena. Since the proposed high-performance MagFET design and fabrication is compatible with CMOS SOI technology, it could be easily embedded in gate drivers controlling the “on” and “off” cycling of future SiC and GaN power devices used for high temperature applications.

 

 

P Igic-Fig.1

 

P Igic-Fig.2

 
 

EPSRC Centre for Power Electronics

Email: correspondence@powerelectronics.ac.uk