The usual bonding temperature with this method is about 300 °C. “We extended this method by including an ultrasound procedure to lower the process temperatures down to 200 °C”, explains Peter Ramm. In a patented method, the SLID technology was combined with the TSV concept and further developed to a high-performant and cost-efficient 3D-TSV technology. This allows for integration densities of millions of contacts per square centimeter. Based on this 3D technology, the researchers developed e.g. a miniaturized and wireless communicating tire pressure sensor in cooperation with the partners Infineon, Sensonor and SINTEF.
Hybrid Memory Cubes and Smart Sensor Systems
The high requirements on performance in some new IoT applications require even higher integration densities. In order to progress in this market segment, Fraunhofer EMFT signed a license agreement with XPERI Corp. in September 2016 and integrated two of the currently most advanced 3D integration technologies into its service portfolio: ZiBond und DBI (Direct Bond Interconnect). Both technologies can be carried out at comparatively low bonding temperatures of below 200 °C. “After all, DBI realizes a vision that had been discussed already 20 years ago – but it was considered as unrealizable that time: A kind of “hybrid” between dielectric bonding and metal bonding”, remembers Peter Ramm.
Within DBI technology, the components are connected both mechanically and electrically after sophisticated surface pretreatment of the deposited copper and oxide layers. Thus the complex through-plating procedure is no longer required, which allows for manufacturing the systems in a cost-effective manner – a basic requirement for access to mass markets such as consumer electronics.
This technology also enables “pitches” (structural width and clearance between the joints) of only 2 μm, thus allowing for highly integrated chip-stacks with enormous performance. This is of great interest for high-performance applications like processors: A current trend in this field deals with so-called memory cubes – where memory and processor are integrated in one 3D stack.
Particularly in the European research landscape there is another current tendency in the field of 3D integration: Smart Sensor Systems for IoT applications where sensors and electronics are integrated into one 3D system. This allows for processing huge data volumes already on the system level – before transmission to the Cloud. This approach could gain importance in the future: In case the number of connected devices will grow as tremendously as predicted in the Internet of Things vision, the “data highways” will be overcrowded very soon. More than that, the private data security increases significantly if the data processing is perfomed already within the sensor system, independent from the Cloud.
The challenge to realize such complex 3D systems lies mainly in the heterogeneity of the components – typically at least one sensor, one IC for data processing and one IC for data transmission. “In this field the new low temperature processes are the key to realize robust heterogeneous sensor systems with high performance and reliability”, says Peter Ramm.
* Katrin Tina Möbius is Communications and Marketing Specialist at the Fraunhofer EMFT.