Innovative polymer thin films for power electronics

Published : 15 July 2019

Power electronics require the development of smaller and smaller devices that can withstand high currents and high voltages (> 500 V). In particular, the production of high-voltage thin capacitors (300 µm thick) requires the use of dielectric materials with a high breakdown field. This field has been explored for more than 10 years within the passive components laboratory at LETI. The main approach is the reduction of the capacitor sizes by increasing the dielectric constant of the materials, this often being done to the detriment of the breakdown field. The emergence of new markets, such as batteries for electric vehicles, is now pushing developments towards the use of dielectrics with lower dielectric constants but high breakdown field. Ceramics capacitors already exist and meet the specifications for high voltage applications but their size remains a disadvantage for their integration in high-performance circuits. A promising alternative is the use of polymers that can answer to the main challenges: reduction of the thickness by thin film deposition and resistance to high voltages.

The objective of this thesis is to develop, with techniques compatible with the semiconductor industry, polymer thin films capable of withstanding voltages of several hundred volts, to characterize them and to correlate their properties (including breakdown field and permittivity) to the composition and structure of the materials. Chemical Vapor Deposition (CVD) techniques will be favored because they allow conformal deposition of thin insulating layers in 3D structures. This work will take advantages of the solid expertise already acquired by CEA-LETI on the development of thin polymer films by innovative filament-assisted CVD techniques (such as iCVD). The thesis work will include the definition and selection of precursors compatible with the thin film deposition technique and the optimization of the deposition process to obtain materials that can sustain high voltages. The materials will be characterized using a wide range of physico-chemical characterization techniques (ellipsometry, FTIR, AFM, ToF-SIMS, XPS, …). A second part of the work will include the integration of materials in electronic devices and electrical tests of these components in order to highlight the relationships between the characteristics of dielectrics (including the breakdown field) and the microstructure of the polymers. This thesis may also lead to the identification of failure mechanisms in these materials.

This work will be carried out as part of a collaboration between the department of technology platforms and the RF components laboratory of the devices department. Thin film deposition and some characterizations will be carried out in a clean room. The fine characterizations will be carried out in collaboration with experts in materials characterization (nano-characterization platform) and with specialists in the electrical characterization of passive components.

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