Chia-Jung Chang

Die-level, post-CMOS processes for fabricating open-gate, field-effect biosensor arrays with on-chip circuitry

Field-effect sensors have been applied extensively to numerous biomedical applications. To develop biosensor arrays in large scale, integration with signal-processing circuits on a single chip is crucial for avoiding wiring complexity and reducing noise interference. This paper proposes and compares two CMOS-compatible processes that allow open-gate, field-effect transistors (OGFETs) to be fabricated at the die level. The polygates of transistors are removed to maximize the transconductance. The CMOS compatibility further facilitates the monolithic integration with circuitry. Based on images and electrical measurements taken at different stages of the post-CMOS processes, a more feasible and reliable process is identified. The robustness of the fabricated OGFETs against the micromachining process and against moisture is further examined and discussed. Finally, the capability of the OGFETs in detecting ion concentrations, biomolecules, and electrophysiological signals is demonstrated.

Fabrication of a SU-8-based polymer-enclosed channel with a penetrating UV/ozone-modified interior surface for electrokinetic separation of proteins

This paper introduces electrokinetic separation inside fully cross-linked epoxy-based polymer channels that were batch modified on the inner surfaces using a penetrating UV/ozone treatment from the outside. The treatment can employ either a 254 nm UV source in an ozone-rich environment or a stand-alone 172 nm UV source to directly generate C=O hydrophilic functional groups on the embedded polymer channel wall surfaces. Short-wavelength UV radiation was employed to break polymer surface bonds inside the channel. Ozone generated directly from air or supplied externally oxidized the reaction site on the activated polymer surface to generate the desired functional groups. An epoxy-based photoresist compound, SU-8 (MicroChem, MA), which is widely used in microfluidic systems, was employed to demonstrate the surface modification. Fourier transform infrared spectroscopy (FTIR) and high resolution x-ray photoelectron spectroscopy (HRXPS) were employed to characterize the functional groups that formed after the UV/ozone surface modification and to confirm the formation of O−H functional groups from the phenol group covalently bonded to the SU-8 surface, attributed mostly to the surface hydrophilicity modification. Water contact angles on the modified surface ranged from 72° to 12° depending on the processing time, UV power and ozone concentration. These angles were retained for at least 4 weeks after the process. Finally, the inner wall surfaces of the SU-8-enclosed channels were successfully modified using this technology, and rapid water transportation and EOF pumping were visualized inside the channel after surface modification. Successful electrokinetic separation of 10 mM BSA and 10 mM anti-rabbit IgG labeled with FITC inside the channel was also carried out. The polymer channel revealed a surface charge density of 75% of the zeta potential on a microslide glass surface, indicating the potential for molecule separation using polymer channels instead of glass channels. This simple process provides a novel way to integrate surface modification into microfluidic structures after fabrication for fully polymer-based lab-on-a-chip systems.

SU8 3D prisms with ultra small inclined angle for low-insertion-loss fiber/waveguide interconnection

This paper presents a simple method for fabricating SU8 three dimensional (3D) prisms with very small inclined-angles for optical-fiber/planar-waveguide interconnection with low insertion-loss by combining self-filling, molding and nano-lithography processes on plane surface. The prisms possess ultra low 3D inclined angle of 0.6° and a small surface roughness of 3.5 nm. It is demonstrated that the transmission efficiency of SOI waveguides improved about 4.6 times at the presence of SU8 prisms with a coupling loss of 11 dB per taper and radiation loss of 2.4 dB per taper.

A CMOS neuroelectronic interface based on two-dimensional transistor arrays with monolithically-integrated circuitry.

The ability to monitor and to elicit neural activity with a high spatiotemporal resolution has grown essential for studying the functionality of neuronal networks. Although a variety of microelectrode arrays (MEAs) has been proposed, very few MEAs are integrated with signal-processing circuitry. As a result, the maximum number of electrodes is limited by routing complexity, and the signal-to-noise ratio is degraded by parasitics and noise interference. This paper presents a single-chip neuroelectronic interface integrating oxide-semiconductor field-effect transistors (OSFETs) with signal-processing circuitry. After the chip was fabricated with the standard complementary-metal-oxide-semiconductor (CMOS) process, polygates of specific transistors were etched at die-level to form OSFETs, while metal layers were retained to connect the OSFETs into two-dimensional arrays. The complete removal of polygates was confirmed by high-resolution image scanners, and the reliability of OSFETs was examined by measuring their electrical characteristics. Through a gate oxide of only 7nm thick, each OSFET can record and stimulate neural activity extracellularly by capacitive coupling. The capability of the full chip in neural recording and stimulation was further experimented using the well-characterised escape circuit of the crayfish. Experimental results indicate that the OSFET-based neuroelectronic interface can be used to study neuronal networks as faithfully as conventional electrophysiological tools. Moreover, the proposed simple, die-level fabrication process of the OSFETs underpins the development of various field-effect biosensors on a large scale with on-chip circuitry.

Control the movement of a single dsDNA by DEP

In this paper we demonstrate the adoption of both electrophoresis (EP) and dielectrophoretic (DEP) forces to control the movement of a single DNA and stretch this DNA as a stretched bridge across two Al metal electrodes at specific positions. The moving speed of the single DNA molecule can also be manipulated from 0.615 to 2.285µm/s inside a nano-pore region by DEP controlling the opening size of the virtual nanopore. The control of stretched DNA linear structure and moving speed will be the first step toward single DNA base pair detection in rapid nano pore DNA sequencing technology in the future.

Proton exchange membranes based on aryl epoxy resin for fuel cells operated at elevated temperatures

This paper reports the characterization of a new type of low-cost proton exchange membrane (PEM) based on photo-patternable nano porous aryl epoxy resin (npAER) sulfonated by sulfanilic acid. The npAER PEM fabrication process involves solvent-casting nanoporous structure formation combined with standard photolithography steps for microstructure fabrication. The PEM was placed in the cathode of a half-fuel cell for testing in 0.5M H2SO4 at different temperatures with constant oxygen flow. When compared to commercial PEM Nafion®, this npAER PEM exhibits increased current density by about 170% as temperature increased from 60°C to 90°C, while the current density of Nafion® dropped by about 70%. The new npAER PEM demonstrates decent thermal stability, mechanical strength and proton transport ability at a higher temperature (90°C).

Thermally stable sulfonated nanoporous aryl epoxy resin as proton exchange membranes at elevated temperatures

This paper proposes a new proton exchange membrane (PEM) based on photochemically synthesized nano porous aryl epoxy resin (npAER) sulfonated by sulfanilic acid. The npAER PEM fabrication process involves solvent-induced nanoporous structure formation combined with photopolymerization for microstructure fabrication. The PEM was placed in the cathode of a half-fuel cell for testing in 0.5M H2SO4 at different temperatures with a constant oxygen flow. When compared to commercial PEM based on Nafion®, this npAER PEM exhibits increased current density from −0.456 (mA/cm2) to −1.14 (mA/cm2) as temperature increased from 60°C to 90°C, while Nafion® demonstrates current density drop by two orders of magnitude. The new npAER PEM shows decent thermal stability, mechanical strength and proton transport ability at a higher temperature (90°C).

Control single dsDNA molecule stretching and transportation by using virtual nanopore trapper

In this paper we demonstrate the adoption of both electrophoresis (EP) and dielectrophoretic (DEP) forces inside a nanoconfinement region to stretch single dsDNA molecule and control the moving speed. By adjusting DEP field inside the nanopore, the opening of the virtual nanopore can be manipulated to drag or trap dsDNA molecule in the virtual nanochannel region. EP force was applied to stretch the dsDNA across the virtual nanopore. The transportation speed of dsDNA molecules can be controlled in a range from 0.615 to 2.285 µm/s, slow enough for DNA sequencing. This virtual nanopore can be used as an electro-tweezers within micro/nano fluidic systems.