(Invited) 3D Integration Processes for Advanced Sensor Systems and High-Perfomance RF Components
Authors: Weber Josef , Fernandez-Bolanos Montserrat , Ionescu Adrian Mihai , Ramm Peter 
Published: February 2020

Sensor systems are the key elements of today’s automotive, health care, environmental and Internet-of-Things (IoT) applications. By using MEMS sensors real-world data like physical or electrical parameters in production equipment, gas concentration in the environment or chemical parameters like th ph-value in fluids can be gathered, digitized and transfered wireless to cloud storage for further processing e.g. by means of big data algorithms.
Advanced sensors are in many cases based on nano-technologies for optimizing the data acquisition. These analogue data are processed by using state-of-the-art electronics like ultra-low power microcomputers and transceiver circuits.
3D integration processes are most suitable for high performant and reliable integration of sensor functions and electronic processing and minimize the footprint, weight and formfactor of the sensor/IC product.
Key application demonstrators of such heterogeneous 3D integrated systems were evaluated already in 2009 by Infineon, SINTEF and Fraunhofer for automotive sensors [1] and later in the European Integrating Project e-BRAINS by a consortium of Infineon, Siemens, IMEC, CEA, SINTEF, Tyndall, Fraunhofer, EPFL and others for bio-sensors (Magna, Infineon), infrared imagers (Sensonor, SINTEF), active medical implants (Sorin, 3D Plus) and smart gas sensors (Siemens, EPFL). A particular focus of the e-BRAINS project was the development of novel low-temperature processes for highly reliable 3D integrated sensor systems [2]. As another key application, we demonstrated high-performance communication devices with Infineon Technologies Austria, IMEC, Fraunhofer and EPFL. For high frequency components, Fraunhofer EMFT developed a specific fine-pitch 3D-TSV technology for RF-MEMS and RF-IC applications. High-performance RF test structures, antennas and 3D embedded high-Q RF inductors were designed and evaluated by EPFL and IMEC [3-4].
The application IoT is predicted as a third wave of MEMS proliferations, after automotive and mobile phones. A subset of IoT are “smart objects” showing local intelligence and awareness. We are in the phase of rapidly growing markets and increasing competition and we must reach for cost reduction, standardization and increasing functionality and performance. A corresponding key is simplification of processes and explicitly regarding the fabrication of device stacks by wafer bonding. Due to the heterogeneity of the components of the 3D integrated system – typically at least one sensor, one IC for data processing and one IC for data transmission, the bonding processes have to be optimised. Chemical and gas sensors are typically comprised of very sensitive layers as e.g. the coating of capacitive CO2 sensors [5] and sophisticated devices as vertically stacked SiNWs, fin or ISFET bio-sensors [6-7] and capacitive gas sensors based on CNT [8] and other technologies). Therefore new low temperature processes are the key to realize robust heterogeneous sensor systems with high performance and reliability [9]. Various bonding schemes, including oxide-oxide bond and variants of metal bond technologies - as thermocompression bonding, solid-liquid-interdiffusion (EMFT) and DBI® (XPERI) - will be discussed.
Additionally a 3D-TSV integration process for realizing RF structures like ultra compact antennas and inductors, which can be applied as a passive RF front-end for MEMS will be demonstrated.
References:
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[9] P. Ramm, M. Fernández-Bolaños, J. Weber Proc. nanoFIS 2017, Graz (2017)