Overview
Automotive, aerospace, and energy production industries can greatly benefit from the development of semiconductor based electronics operating at temperature higher than 150 °C. Wide bandgap semiconductors like SiC and GaN are key enablers as these allow electronics to function at much higher temperatures than silicon. Consequently devices made from these materials can handle more current and thus power compared to Si based ones. However, increasing operating temperatures compromise the performance and reliability of other components in the power electronic system, including capacitors and inductors, interconnects and packaging, and therefore complex cooling systems are required which adds complexity and volume to the device design.
This proposal directly addresses the specific technological challenges of the Call JTI-CS-2013-03-SGO-02-087 entitled “Technology development and fabrication of high-temperature high-frequency capacitors for power switch integration”, in which a thorough programme of work is proposed to develop optimized ceramic formulation and fabrication to provide highly reliable multilayer ceramic capacitors for high-temperature high-frequency capacitors for power switch integration.
The 24 month project will use as its base a new high-K ceramic material (SBFT - Strontium-Bismuth-Ferrum-Titanate) which extends power electronics operating temperature up to 200 C. The SBFT ceramic capacitor is characterized by a low thermal coefficient of capacitance (TCC) of less than 25% up to 200 C. The project will focus firstly on the production of samples with a variety of chemical modifications being performed, subsequently fabrication of MLCCs using non optimised, and optimised materials will be performed and samples delivered to the topic group leader for qualification.
Funding
Results
Executive Summary:
The objectives of the HITECA project was to fulfil the specific technological challenge of Call JTI-CS-2013-03-SGO-02-087 entitled “Technology development and fabrication of high-temperature high-frequency capacitors for power switch integration”.
HITECA team members have previously investigated a range of lead-free materials that could have the required properties that would enable it to be developed into a high temperature capacitor. NPL and SYF have each filed a Patent Application to protect a new high-K ceramic material (SBFT - Strontium-Bismuth-Ferrum-Titanate) with unprecedented energy storage performance up to 200 °C. The most innovative part of this material is that it can meet X7R and X8R characteristics in a totally different material chemistry, offering electrical properties that are not available in BaTiO3 based materials - such as low df and heat rise, low VC and high temperature stability).
The objectives of the project and an update of status at the end of the project are as follows:
a) Capacitor specifications for HF and HT switches: These issues were discussed with the Topic Manager and projects outputs defined. Two 4040 chip types of nominal 500V rated voltage and 1uF and 2.2uF capacitance value were specified.
b) Improve capacitor performance and reliability above 125 °C: The material developed in the previous project has been optimised and improvement to component reliability has been demonstrated. This was mainly achieved by optimising dopant levels and processing conditions.
c) Improve termination at high temperatures: This work has primarily been focussed on a plateable termination finish, but reliability results have been somewhat inconsistent using this finish, so an alternative material system which can be used for surface mount components but without a patented plateable finish has been evaluated with promising results.
d) Cost-effective electrodes: Euro Support have worked on adjusting the basic material formulation to allow use of a lower sintering temperature. These changes have not yet been successfully implemented into MLCC's.
e) Thick capacitors: This material system does not appear to suffer from issues relating to component thickness, so thick components have been made successfully.
f) Energy density and breakdown field. This is lower than desired, but allowed manufacture of the specified components within the project timescales.
At the end of the project, all deliverables have been met, but the project team are awaiting feedback on part performance from the Topic Manager.
NPL are submitting an article on Lead-free ceramics with high energy density and reduced losses for high temperature applications to Advanced Engineered materials magazine.
Syfer have submitted an article on MLCC's in automotive applications to Power Electronics Europe
Syfer have supplied parts to three interested customers (with NDA's) with a fourth NDA being prepared.
Further work is on going on material and process optimisation with a view to qualification and release in 2018.