This work presents a three-dimensional flexible polyimide (PI) probe array with biodegradable polymer that offers desirable insertion capability. In order to avoid the recording sites position shifts slightly and damage neuron cells when the body moves, the flexible neural probes are more preferable than traditional Si-based neural probes. A sufficient buckling strength of flexible probe is critical for inserting flexible probe into the brain. Here, we used a biodegradable polymer, polyethylene glycol (PEG), to improve the mechanical stiffness of flexible probe. PEG, which is solid state at room temperature and dissolves when immersing in water, was coated onto the flexible probe and the mechanical stiffness of the flexible probe was increased before insertion into the biological tissue. The buckling strength of different probes was simulated using finite element analysis and measured by compression tester. The coated PEG flexible probe maintains sufficient stiffness to facilitate tissue penetration with solid PEG elastic modulus of 660±19 MPa but loses its strength within 25 minutes once immersed in saline. A microassembly method of three-dimensional flexible probe array was also proposed to integrate the flexible probe and their interconnections. In vitro test, the coated PEG flexible probe regained their original impedance of 12.8 kΩ at 1 kHz within 30 minutes of immersing in saline via water absorption and polymer’s biodegradable response.

SiO2 and Si3N4 layers to be used in the microfabrication of a neural probe were formed on Si substrate through plasma enhanced chemical vapor deposition (PECVD). To ensure their cytoconnpatibility, the surface properties and cytocompatibility of the PECVD-formed SiO2 and Si3N4 were investigated and compared. SEM images showed the SiO2 and Si3N4 layers consisted of nano-sized particles. In accordance with water contact angle measurement, the surface of both PECVD-formed SiO2 and Si3N4 layers were hydrophilic and there was no significant difference in wettability between them. A breast cancer cell line (MCF-7) was seeded on their surface to evaluate the cytocompatibility. After 3 days of cell culture, the adherent cells on PECVD-formed Si3N4 surface did not spread as well as those on Si or PECVD-formed SiO2, and the cells on the surface of PECVD-formed SiO2 and Si3N4 were significantly less than on Si. At day 7, however, there was no significant difference between them, in terms of cell morphology and number. Therefore, the PECVD-formed SiO2 and Si3N4 layers did not exhibit acute cytotoxicity and were as cytocompatible as tissue culture polystyrene.

This work presents a bio-degradable glass probes and its biocompatibility assessment for neural applications. The probes can be implanted into different sites of the human brain for recording and stimulating purposes. Current existing neural probe address the probe stiffness requirement for the penetration of brain tissue. However, this requirement normally resulted in the rigidity of the probe which is non-compatible with the brain tissue movement for long term implantation. The brain neuron cells will be damaged by too rigid probe substrate. In order to address this issue, bio-degradable glass probes having sufficient stiffness for a smooth brain insertion as well as ability to degrade after implantation; leaving behind the flexible circuitry substrate was being explored. The biodegradability of the proposed probe was evaluated.

This paper describes the integration of micro-electro-mechanical systems (MEMS) tri-axial force sensor using polyimide-based substrate for sensorised guide wire application. For tri-axial force sensor, piezoresistive silicon nanowires (SiNWs) are embedded into a cross cantilever design with a maneuverable stylus to allow the detection of force in all directions, and amplify the tactile forces at the tip for transverse directions. The electrical resistance changes in the four SiNWs are used to decode an arbitrary force applied onto the force sensor. Robustness of the force sensor is improved due to the novel design by incorporating a mechanical stopper at the tip of the stylus. Flip chip bonding using gold stud bumps is used to mount the force sensor on a substrate for characterization and to simplify the assembly process. The packaging process of the miniaturized sensorised guide wire was presented in this work.

Neural probe array is used for neural recording and simulation applications. It will be implanted into the motor cortex of a paralytic human to control robotic arm and perform tasks such as grasping an object. The major components are silicon (Si) probes, Si platform, application-specific integrated circuit (ASIC), polyimide flexible cable and wireless IC. In-plane Si probes are inserted into the Si platform to form a three-dimensional (3D) probe array. Wirebonding technique is used to integrate the ASIC and the probe array. Pad finishes play an important role in wire bonding as it would affect the reliability of the electrical connections. As such, the focus of the paper will be on the evaluation and characterization of an electroless nickel immersion gold (ENIG) pad finishing and its bonding parameters for wirebonding application. ENIG pad having a 0.1-µm gold (Au) thickness combined with an additional Au stud and wirebonding temperature of 200 °C are found to have comparable wirebonding capabilities as a 0.3-µm thick Au finishing pad. The wire pull test result and SEM observation between the ENIG and Au finishing pad at different bonding parameters were presented and discussed.

In this paper, a tilt sensing mechanism based on the capacitive micromachined ultrasound transducers (CMUTs) is presented. By measuring the difference in the time of flight of various pulse-echo signals from different CMUT transmitting elements to one common receiving element in the oil bath, the tilt angle of the oil surface can be determined. With the proposed device, the maximum tilt angles of 20° and 28° have been measured in the clockwise and counterclockwise directions, respectively, and the difference between the measured and the theoretical values of the tilt angle was found to be within 0.05° during the whole test.

In this work, an out-of-plane connection in an orthogonal assembly is demonstrated. The proposed method for the orthogonal connection will help to overcome critical issues faced in this type of connection, such as lead transfer and bonding plane mismatch. It proposed to utilize the laser assisted soldering technique to achieve the lead transfer in the connection. Being a highly flexible probe array, it is more conformal to the tissue, minimizing tissue damage after implantation. Compared to previous works, the proposed flexible probe array has excellent flexibility and can easily conform to the shape of tissue, preventing the micromotion of probe after implantation. The measured impedance at the typical frequency of action potential (1 kHz) is about 12.8 kΩ.

In this paper, the dynamic mechanical stability of the liquid-filled lenses was studied, in which acoustic excitation was used as broad band perturbation sources and the resultant response of the lens was characterized using non-contact laser Doppler vibrometer. To the best of our knowledge, it's the first time that the mechanical stability of liquid-filled lenses was experimentally reported. Both experimental results and theoretical analysis demonstrate that the resonance of the lens will shift to higher frequency while the vibration velocity as well as its magnitude will be reduced accordingly when the pressure in the lens cavity is increased to shorten the focal length. All of these results will provide useful references to help researchers design their own liquid-filled lenses for various applications.