[en] In this paper, we introduce a method of isolating thermal conduction from silicon substrate for accommodating thermal-sensitive micro-devices. This method lies in fabrication of a low-stress photosensitive polyimide (PSPI) suspension structure which has lower thermal conductivity than silicon. First, a PSPI layer was patterned on a silicon wafer and hard baked. Then, a cavity was etched from the backside of the silicon substrate to form a membrane or a bridge-shape PSPI structure. After releasing, a slight deformation of about 20 nm was observed in the suspended structures, suggesting ultralow residual stress which is essential for accommodating micro-devices. In order to investigate the thermal isolation performance of the suspended PSPI structures, micro Pirani vacuum gauges, which are thermal-sensitive, had been fabricated on the PSPI structures. The measurement results illustrated that the Pirani gauges worked as expected in the range from 1– 470 Pa. Moreover, the results of the Pirani gauges based on the membrane and bridge structures were comparable, indicating that the commonly used bridge-shape structure for further reducing thermal conduction was unnecessary. Due to the excellent thermal isolation performance of PSPI, the suspended PSPI membrane is promising to be an outstanding candidate for thermal isolation applications. (paper)

[en] This work systematically investigated a high-κ Al₂O₃ material for low temperature wafer-level bonding for potential applications in 3D microsystems. A clean Si wafer with an Al₂O₃ layer thickness of 50 nm was applied as our experimental approach. Bonding was initiated in a clean room ambient after surface activation, followed by annealing under inert ambient conditions at 300 °C for 3 h. The investigation consisted of three parts: a mechanical support study using the four-point bending method, hermeticity measurements using the helium bomb test, and thermal conductivity analysis for potential heterogeneous bonding. Compared with samples bonded using a conventional oxide bonding material (SiO₂), a higher interfacial adhesion energy (∼11.93 J/m²) and a lower helium leak rate (∼6.84 × 10⁻¹⁰ atm.cm³/sec) were detected for samples bonded using Al₂O₃. More importantly, due to the excellent thermal conductivity performance of Al₂O₃, this technology can be used in heterogeneous direct bonding, which has potential applications for enhancing the performance of Si photonic integrated devices

[en] Electroplating is a popular method to produce solders in microelectromechanical systems (MEMS) encapsulation and interconnection applications. In this work, a fabrication process is introduced for the generation of three-dimensional (3D) Sn solder microstructures. An aluminum membrane was employed as the conducting layer while electroplating. Based on the proposed method, Sn solders with different heights can be easily obtained after reflow. Taking advantage of these 3D structures, MEMS packaging, electrical interconnections, hermetic seals and metal-armoring can be formed simultaneously in one step. Metal-armoring provided by the solder–solder contact can be used at the extremes of the suspension travel, greatly increasing the capability of shock resistance. The helium leak rates of the packaged samples are lower than the reject limit (5  ×  10⁻⁸ atm cc s⁻¹ based on MIL-STD-883E standard). The bonding strength of samples is measured by a die shear strength tests with an average value of 7.4 MPa. In addition, the ohmic behavior of the Sn solder bonding is verified as well. These excellent results show an outstanding packaging quality in MEMS encapsulation applications. (paper)

[en] This paper investigates low temperature ohmic contact formation of Au/Sb to n-type Si substrates through AuSb/NiCr/Au metal stacks. Liquid epitaxy growth is utilized to incorporate Sb dopants into Si substrate in AuSi melt. The best specific contact resistivity achieved is 0.003 Ω ⋅ cm"2 at 425 "oC. Scanning electron microscopy (SEM) reveals inverted pyramidal crater regions at the metal/semiconductor interface, indicating that AuSi alloying efficiently occurs at such sites. Secondary ion mass spectroscopy (SIMS) shows that Sb atoms are successfully incorporated into Si as doping impurities during the anneal process, and the Sb doping concentration at the contact interface is found to be higher than the solid solubility limit in a Si crystal. This ohmic contacts formation method is suitable for semiconductor fabrication processes with limited thermal budget, such as post CMOS integration of MEMS