Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Periodic Report Summary 1 - HITECA (technology development and fabrication of HIgh TEmperature high frequency CApacitors for power switch integration)

Project Context and Objectives:
Automotive, aerospace, and energy production industries will greatly benefit from the development of semiconductor based electronics operating at temperature higher than 150 °C. However, increasing operating temperatures compromise the performance and reliability of 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 device design.
This project directly addresses this issue which is 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”, and proposes a thorough programme of work aimed at the development and fabrication of an optimized ceramic formulation which can provide highly reliable multilayer ceramic capacitors for power switch integration. This directly addresses the CfP by making ‘major advances in designing high performance lightweight and small volume power systems for avionic applications’ by making available high temperature capacitors (at least 150 ºC steady-state, with a view at achieving 200 ºC over the project duration) suitable for high frequency filtering and for embedment within solid-state power modules’.
The project will additionally, ‘support other on-going activities targeting the demonstration of very compact converters by supporting the development of high performance high temperature ceramic (or equivalent performance) capacitors. This builds on a range of previous project within the Clean Sky Initiative.
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, and fabricated MLCCs (see Figure 1), have shown unique properties. 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 objective of the HITECA project is to make the following improvements relative to the current state of the art:
a) Capacitor specifications for HF and HT switches: In close co-operation with the Topic Manager (TM), the temperature characteristics required for the capacitor need to be defined. For applications at temperatures above 150°C it needs to be discussed, if these products still need to have a temperature characteristic that is in accordance with the X9R specification, because this is referring to a capacitance variation between -55 and 200°C with respect to a room temperature reference value.
b) Improve capacitor performance and reliability above 125 °C: The temperature range of the material’s performance and reliability will be extended. This means that the ceramic capacitor which can currently reliably operate at 125°C needs to be further developed to offer comparable performance at 150°C and later to 200°C. However, the sources of electrical failure in SBFT ceramic capacitors are not well understood. These may come from the SBFT ceramic (e.g. space charges, oxygen vacancies) or from the MLCC design (e.g., electrode metal migration to the ceramic layer).
c) Improve termination at high temperatures: Ensuring that the termination finish is compatible with the upper temperature rating is also a major priority in this project.
d) Cost-effective electrodes: An additional focus will be laid on the lowering of the firing temperature of the SBFT ceramic. This would allow the use of a higher Ag content in the inner electrodes which are now used with 30% of the expensive metal Pd.
e) Thick capacitors: In order to supply the high capacitance values that are likely to be required with this material, large, thick components are likely to be most common. In standard multilayer ceramic capacitors larger, thicker parts suffer from voltage related stress cracking which impacts the maximum capacitance values. This aspect will be investigated during the project.
f) Energy density and breakdown field: High energy density at the operated voltage is required to reduce the volume of stacked capacitors to deliver the required capacitance. For the new capacitors an energy density of > 1 J/cm3 will be aimed, which could be achieved by optimizing breakdown field to above 100 kV/cm.

Project Results:
1. A Technology Review Report was completed in February 2015. This report:
a) Reviewed capacitors currently available for high-frequency and high-temperature switches for avionic applications.
b) Benchmarked ceramic capacitors currently available from other suppliers.
c) Investigated physical and electrical mechanisms of ceramic oxides and multilayer ceramic capacitor (MLCC) degradation.
d) Detailed measurement and characterisation techniques to be used within the project.
D1.1 provided the background material required to successfully engineer a device sufficiently reliable for commercial development from a new material.

2. The Technology Roadmapping HITECA specification and range proposal was completed in February 2015. This report:
a) Reviewed the circuit requirements for the test part.
b) Introduced the prototype Inverter.
c) Road mapped the requirements of the Topic Manager.
d) Introduced HITECA range proposals.
e) Recommended test components to be manufactured for WP3 and WP4, together with expected performance over a range of temperatures and voltages.

3. Sample and product development. This work package forms the main body of the research and development work for this project.
a) Formulation development.
Ceramic powder formulation trials are carried out at Euro Support, producing ceramic discs which are characterised at Euro Support, with additional testing being carried out at NPL as necessary. Promising formulations are then submitted to Knowles UK for capacitor trials.
So far 8 bulk samples from Euro Support have been evaluated at Knowles, with many more intermediate (blended) samples also evaluated as MLCC’s. Mn and X7R doping levels have been found to be important to the formulation, but so far no material has outperformed the original ‘reference’ material. Recent understanding of the lattice structure of the material has led to promising disc results and further bulk samples are in manufacture.
b) Process optimisation
Knowles have spent much time investigating the process variables of the HITECA ‘reference’ formulation, with a view to optimising processing conditions for this material system in parallel to the formulation work. This work has highlighted a number of areas which are key to product reliability. This work is ongoing.

4. MLCC manufacture not optimised.
The parts as defined in 2. above were manufactured and tested using the ‘reference’ material and optimised processing conditions. Parts meeting the output targets for the project have been submitted to the topic manager. At the time of writing this report there has been no feedback on the test samples.

Potential Impact:
At this stage, it is uncertain whether an improved formulation version of the reference material will be available before the end of the project.
However, the output targets of the project have already been met, and we aim to make further parts for the topic manager, either with an improved formulation, or with a formulation tailored to high temperature performance.
Using processing improvement techniques developed during the course of the project, SYF are also developing the reference material for potential market release as a high voltage / AC range of MLCC’s. It is hoped that this work will be complete by the end of 2016.
1. The reference version of the material is in the process of being commercialised by SYF for use in a range of high voltage MLCC’s. The range may include AC and low voltage coefficient specific parts.
2. In order to achieve the above, ES will be supplying material to SYF as per any agreements made between NPL, ES and SYF.
3. Depending upon the outcome from the remainder of the technical work during the project, it is possible that the consortium may make a presentation or prepare an article for publication, in relation to the progress made and the products to be launched.
4. During the first period the project team submitted an abstract to ESREF2015, but the paper was rejected due to lack of detail.
5. A poster has been exhibited at the IOP dielectrics conference.


Mark Scharff, (Finance director)
Tel.: +44 1603 723336
Datensatznummer: 184121 / Zuletzt geändert am: 2016-06-08
Informationsquelle: SESAM