In this research study, we present comprehensive characterizations of flexible silicon sensors fabricated using controlled spalling which uses fracture to produce thin films of single-crystal silicon directly from a bulk substrate. We characterized the property of the thin silicon film for sensing strain and temperature. The flexible sensor exhibits high sensitivity with a temperature coefficient of resistance of -0.16/°C, which is desirable for targeted health monitoring applications.

In this work, Pb-free microbumps at 50μm pitch with NiFe-based Ball-limiting-metallurgy (BLM) are fabricated and tested. Detailed microstructural analysis has been performed, which shows a uniform thin layer (~0.2μm) of FeSn 2 Intermetallic Compound (IMC) is formed between the Pb-free solder and NiFe BLM after the first reflow. In comparison, the NiCuSn IMC can grow more than 2μm in microbumps with the conventional Ni BLM or solder-caped Cu pillar after the first reflow. An excessive lateral “thermal-undercut” has been discovered in NiFe BLM structures during solder reflows due to good edge wettability of NiFe. A dual-layer BLM structure is proposed and demonstrated to mitigate the “thermal-undercut”. Moreover, addition of NiFe layer on a micro-Cu pillar structures have been demonstrated and characterized.

In this letter, the integration of CMOS-compatible thru-Si via (TSV) interconnects with deep-trench decoupling capacitors is demonstrated. Reliability test is performed with a 65-nm CMOS test chip on top of a 3-D Si interposer chip that contains 10 000 TSV interconnects. Multilayer stacking is also demonstrated, and capacitance density of 280 nF/mm(2) is achieved with two-layer Si interposer chip stacks.