The primary objective of the MICROPRINCE project has been to create the first worldwide open access foundry pilot line for micro-transfer-printing (μTP) and to demonstrate its capability for heterogeneous integration of different functional components in an industrial environment. Five different target applications were initially selected to represent the possibilities of the technology for smart system integration (SSI) ranging from III/V Hall plates for current sensors, optical filter elements for Human Eye Response (HER) sensors, μLEDs for automotive interior lightning as well as GaAs- & InP-based emitters, modulators and sensors for photonic integrated circuits (PICs) in life science. For the implementation of the pilot line and the process development for the selected target applications the following work was conducted till the end of the project: With respect to the pilot line installation the required tools for the adhesive deposition (coater/ developer), the micro-transfer-printing and the adhesive curing were specified, selected and installed in the XFAB MEMS cleanroom. Moreover, a Silane supply for an existing CVD chamber was established to allow the deposition of SiN on 8 inch source wafers. Based on these new equipment and already existing tools general process capabilities were investigated/ developed for a 3D-integration via µTP.
Moreover, in cooperation with the project partners TU Dresden a first μTP design aid tool was developed to relieve the co-design of source and target chips. Additionally, the new processes and materials were characterized and their reliability performance was tested in cooperation with the project partner IMWS. Concerning the transfer-printing of GaAs-based sensing elements in WP2, sensor ICs (target) and GaAs source chiplets with SiN tethers were prepared. Based on these materials, release and printing experiments (on BCB) were performed at XMF indicating issues with the chiplet warpage and, therefore, reduce print yields. Nevertheless, characterized samples indicated that GaAs transfer-printed Hall elements provide increased signal to noise ratio (SNR) of a factor of five, compared to chips with Silicon Hall plates. The main objectives of WP3 were process developments for the printing of filters on optical sensors. To achieve this goal, source wafers carrying HER filter were fabricated at the project partner OBJ. By further processing at ISIT (tether formation and release etch) these wafers were prepared for the transfer-printing. These print-ready filter devices were finally heterogeneously integrated at XMF. Optical measurements of the integrated sensors (Responsivity and dark current) indicated a full functionality of the HER sensors.The objectives of WP4 (printing silicon photonics for data transmission) cannot be achieved in the MICROPRINCE project since HUAWEI stepped out of the project early in the 2nd project year. Concerning WP 5, a new LED driver IC for transfer-printed RGB μLEDs was developed. Additionally, special GaN based blue and green LEDs for μTP were designed and fabricated in cooperation with the project partner TYN. These LEDs were afterwards directly printed on the driver IC in the XMF MEMS clean room. After metallization and packaging, the integrated µLEDs were tested indicating a promising performance. The main objective for WP6 has been the heterogeneous integration of active components in silicon photonic circuits. Therefore, InP and GaAs photodiodes (PDs) have been fabricated and revealed promising performance with respect to bandwidth (3dB of ~50 nm), dark current (as low as 200nA) and responsivity (0.85 A/W). Moreover these PDs have been packaged on Si photonic circuits and functional integrated spectrometers were build. Accordingly, the main goal of the MICROPRINCE project of building a pilot line for heterogeneous integration and showing its applicability for different material classes and target applications by the generation of demonstrator devices has been achieved.
