Wei Mong Tsang

Ultra-thin flexible polyimide neural probe embedded in a dissolvable maltose-coated microneedle

The ultra-thin flexible polyimide neural probe can reduce the glial sheath growth on the probe body while its flexibility can minimize the micromotion between the probe and brain tissue. To provide sufficient stiffness for penetration purposes, we developed a drawing lithography technology for uniform maltose coating to make the maltose-coated polyimide neural probe become a stiff microneedle. The coating thicknesses under different temperature and the corresponding stiffness are studied. It has been proven that the coated maltose is dissolved by body fluids after implantation for a few seconds. Moreover, carbon nanotubes are coated on the neural probe recording electrodes to improve the charge delivery ability and reduce the impedance. Last but not least, the feasibility and recording characteristic of this ultra-thin polyimide neural probe embedded in a maltose-coated microneedle are further demonstrated by in vivo tests.

Annularly Grooved Diaphragm Pressure Sensor With Embedded Silicon Nanowires for Low Pressure Application

We present a nanoelectromechanical system piezoresistive pressure sensor with annular grooves on the circular diaphragm where silicon nanowires (SiNWs) are embedded as sensing elements around the edge. In comparison with our previous flat diaphragm pressure sensor, this new diaphragm structure enhances the device sensitivity by 2.5 times under pressure range of 0-120 mmHg. By leveraging SiNWs as piezoresistors, this improvement is even remarkable in contrast to other recently reported piezoresistive pressure sensing devices. In addition, with the miniaturized sensing diaphragm (radius of 100 μm) the sensor can be potentially used as implantable device for low-pressure sensing applications.

Development of silicon electrode enhanced by carbon nanotube and gold nanoparticle composites on silicon neural probe fabricated with complementary metal-oxide-semiconductor process

We present the fabrication of highly P-doped single crystal silicon electrodes on a silicon probe through complementary metal-oxide-semiconductor (CMOS)-compatible processes. The electrode with diameter of 50 μm and a separation of 200 μm is designed for recording/stimulating purposes. Electrochemical impedance spectroscopy indicates that the interfacial impedance of silicon electrodes at 1 KHz is 2.5 ± 0.4 MΩ, which is equivalent to the result reported from the gold (Au) electrode. To further enhance the charge storage capacity, composites of multi-wall carbon nanotubes (MWCNTs) and Au nanoparticles are electroplated onto the highly P-doped silicon electrode after surface roughness treatments. With optimized electroplating processes, MWCNTs and Au nanoparticles are selectively coated onto the electrode site with only a minimum enlargement in physical diameter of electrode (<10%). However, the typical impedance is reduced to 21 ± 3 kΩ. Such improvement can be explained by a boost in double-layer capacitan...

A Miniaturization Strategy for Harvesting Vibration Energy Utilizing Helmholtz Resonance and Vortex Shedding Effect

In this letter, we report a miniaturization strategy for harvesting a low-frequency random vibration energy with a piezoelectric energy harvesting (EH) system utilizing coupled Helmholtz resonance and vortex shedding effect. This is made possible by transferring the low-frequency vibration energy into a pressurized fluid, which is in turn converted into predefined, pressure-independent high-frequency energy harvested by the device. The vibration-pressurized fluid conversion extends the device sampling frequency band; enables efficient harvesting of broadband low vibration frequencies with small form factor. Proof of concept of the proposed strategy has been demonstrated with an AlN-based MEMS EH, which delivered an output power density of 95.5 mW/cm3 under a constant input airflow at 4.2 lbf/in2 pressure.

Development of flexible neural probes using SU-8/parylene

A new process for making SU-8 neural probe with fluidic channels and gold electrodes based on multilayered thin parylene and SU-8 is presented here. This approach can realize a thin 15 μm gap between electrode surface and neural cells. The thin gap will help to enhance the neural signal acquisition. Fluidic testing and mechanical testing are conducted to ensure the device reliability.

A microfabricated neural probe with porous si-parylene hybrid structure to enable a reliable brain-machine interface

To establish a reliable brain-machine interface (BMI), we report for the first time, a multifunctional porous silicon (PSi)-parylene neural probe using a CMOS compatible fabrication process. The biodegradable PSi shank serves as a mechanical stiffener for insertion process, then dissolves to leave only the polymeric structure to reduce stiffness mismatch between implant and cortical tissue, thus attenuates tissue responses. Moreover, its porous structure can serve as drug reservoir. The healing of the insertion trauma can be enhanced by continuously releasing pre-loaded drugs with the PSi degradation. Hence, the neural probe enables a more reliable BMI.

Silicon Nanowires embedded pressure sensor with annularly grooved diaphragm for sensitivity improvement

A NEMS piezoresistive pressure sensor with annular grooves on the circular diaphragm is presented here. Silicon Nanowires (SiNWs) are embedded as sensing elements at the edge of the diaphragm. This new diaphragm structure improves the device sensitivity by 2.5 times under a low pressure range of 0~120 mmHg with respect to our previously reported flat diaphragm pressure sensor. With the advantage of superior piezoresistive effect of SiNWs, this sensitivity improvement is even remarkable in contrast to other recently reported piezoresistive pressure sensing devices. Additionally, by leveraging the miniaturized sensing diaphragm (radius of 100 μm), the sensor can be potentially used as implantable device for low pressure sensing applications.

Correction to “A Miniaturization Strategy for Harvesting Vibration Energy Utilizing Helmholtz Resonance and Vortex Shedding Effect” [Feb 14 271-273]

In the above paper , there are two typos in the abstract and last page. The 95.5

Characterizations of silicon nanowires (SiNWs) embedded NEMS sensors and for potential biomedical applications

{\rm mW}/{\rm cm}^{3}

Polymeric C-shaped cuff electrode for recording of peripheral nerve signal

should be 95.5