Optofluidic Waveguiding for Biomedical Sensing

ABSTRACTWe review an optofluidic waveguiding lab-on-a-chip used to sense bioparticles. The sensor uses a liquid filled Anti-Resonant Reflecting Optical Waveguide (ARROW) that is interfaced with standard ridge waveguides. The ridge waveguides are coupled to off-chip lasers and detectors via optical fiber. A perpendicular intersection between the ARROW and a ridge waveguide is especially useful for detecting fluorescently tagged particles. Light coupled into the ridge waveguide can fluorescently excite these particles within a very small volume. Fluorescent signal can then be guided within the ARROW and subsequently off chip to a detector.We also discuss how such devices are fabricated. Both the ARROW and ridge waveguides are made using alternating thin films of tantalum oxide and silicon dioxide on silicon substrates. These thin films are deposited by either sputtering or plasma enhanced chemical vapor deposition (PECVD). The waveguides are patterned using a combination of standard photolithographic processes, reactive ion etching, and sacrificial etching. Low-loss optical guiding is very dependent on both the waveguide structure and the materials used. The latest processes for maximizing detection sensitivity are reviewed.We also present results using the optofluidic waveguiding sensor for detecting a variety of different types of particles such as fluorescently labeled nanobeads, viruses, ribosomes, and RNA.

Heterogeneous Integration of LSI Amplifier and the Tactile Sensor Using Stacking and Through-Si-Via Techniques

ABSTRACTWe have developed the tactile sensor using the microcantilevers with strain gauge film which can detect normal and shear forces simultaneously. In this work, the tactile sensor and the IC amplifier have been integrated heterogeneously to shorten the wire length by chip-on-chip stacking and reduce the noise in the output voltage. Standard deviation of the noise can be reduced from 27.6 mV to 3.3 mV by heterogeneous integration of the tactile sensor and the IC amplifier using Au wire bonding. By this heterogeneous integration, the device size and wiring numbers can be reduced, and installation of more sensors is allowed on fingertips of the robot. Moreover, through-silicon-via (TSV) holes were fabricated to mount an IC amplifier on the backside of the sensor chip, instead of using Au wires. Although TSV can be fabricated successfully, resistance to sacrificial etching process is problem. As a result, Si3N4 used instead of SiO2 has improved insulation between TSVs.

Fabrication of Suspending GAN Microstructures With Combinations of Anisotropic and Isotropic Dry Etching Techniques

A method for fabricating gallium nitride (GaN) based microelectromechanical (MEM) devices on silicon substrate was demonstrated. Various suspended GaN microstructures have been fabricated using ICP (Inductive coupled plasma)-based sacrificial etching of the underlying silicon with combination of both anisotropic and isotropic etching techniques, so that deeply released freestanding microstructures with minimized lateral undercut can be achieved. Cl2-based ICP-RIE (Reactive ion etching) dry etching technique is employed to pattern gallium nitride. The experimental results show that freestanding GaN microstructures with large air gap of high depth-to-width ratio can be realized by employing such two-step dry releasing technique. Fabrication results have been characterized by scanning electron microscope (SEM).