Lab-on-a-chip devices

Thisreviewcoversthekeypapersrelatingtothetheory,techniques and quantification of hydrophilically activated silicon wafer bonding. This begins with a review of the history and development of the art. Bond strength characterization is then reviewed followed first by models of physical deformation and then by plasma and radical activation techniques. In the interests of clarity and succinctness this review is not an attempt to exhaustively catalog all direct bonding wafer literature. Excluded are hydrophobic and UHV bonding, and the many papers applying bonding techniques to differing combinations of wafer materials. This paper concludes with a summery of the state of the art of direct wafer bonding and a summation of the current wafer-bonding model derived from the papers reviewed.

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A Review of Hydrophilic Silicon Wafer Bonding

In this paper, a review of surface-activation-based nanobonding technology for packaging and integration is presented. In this paper, the focus will be on nanobonding technology for electronic, photonic, and fluidic devices for miniaturized biomedical and environmental-sensing systems. We describe four different nanobonding techniques that have been developed and successfully implemented in a wide range of materials that include metals, semiconductors, flexible laminations, and ionic materials. Nanobonding technologies are particularly attractive because they offer void-free, strong, and nanoscale bonding at room temperature or at low temperature (<;200°C), and without the need for chemicals, adhesives, and high external pressure. Therefore, there are significant potential and opportunities for nanobonding technologies in the development of low cost, low loss, and high-speed miniaturized emerging systems based on a combination of electronic, fluidic, and photonic devices.

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Nanobonding Technology Toward Electronic, Fluidic, and Photonic Systems Integration

In this paper, we put forward a capacitive sensor for Lab-on-Chip applications using a charge-based capacitance measurement (CBCM) method. This simple and highly sensitive capacitive sensor is implemented in the TSMC 0.18 CMOS process to which we incorporate microfluidic structures for chemical sensing. The post-layout simulation, fabrication and preliminary Lab-on-Chip testing results are also reported.

A 0.18-μm CMOS capacitive sensor Lab-on-Chip

This review discusses various bonding strategies for fabricating microfluidic devices, with a special emphasis on the modification of the surface assisted by the use of chemicals to assemble microfluidic devices under mild conditions such as room temperature and atmospheric pressure. The paper includes an overview of the wide ranges of bonding methods used in the fabrication of microfluidic systems, such as anodic bonding, fusion bonding, thermal bonding, solvent bonding, and surface chemical bonding. Among these, surface chemical bonding plays a crucial role between the polydimethylsiloxane (PDMS) and thermoplastics in order to assemble a microfluidic device in a simple and facile manner. The first section reviews relevant research on the sealing for microfluidic devices; in the second section, the materials used for device fabrication are reviewed. The third section discusses the different sealing processes used in the fabrication of microfluidic devices on silicon, glass, thermoplastic, and elastomer. Overall, this review concludes with a discussion on the importance of the surface chemical modification for bonding an elastomer - PDMS - with rigid materials at room temperature under atmospheric pressure and detailed discussions on their bond strengths.

Microfluidic device fabrication mediated by surface chemical bonding

A sequential plasma activation process consisting of oxygen reactive ion etching (RIE) plasma and nitrogen radical plasma was applied for microfluidics packaging at room temperature. Si/glass and glass/glass wafers were activated by the oxygen RIE plasma followed by nitrogen microwave radicals. Then, the activated wafers were brought into contact in atmospheric pressure air with hand-applied pressure where they remained for 24 h. The wafers were bonded throughout the entire area and the bonding strength of the interface was as strong as the parents bulk wafers without any post-annealing process or wet chemical cleaning steps. Bonding strength considerably increased with the nitrogen radical treatment after oxygen RIE activation prior to bonding. Chemical reliability tests showed that the bonded interfaces of Si/Si could significantly withstand exposure to various microfluidics chemicals. Si/glass and glass/glass cavities formed by the sequential plasma activation process indicated hermetic sealing behavior. SiOx Ny was observed in the sequentially plasma-treated glass wafer, and it is attributed to binding of nitrogen with Si and oxygen and the implantation of N2 radical in the wafer. High bonding strength observed is attributed to a diffusion of absorbing water onto the wafer surfaces and a reaction between silicon oxynitride layers on the mating wafers. T-shape microfluidic channels were fabricated on glass wafers by bulk micromachining and the sequential plasma-activated bonding process at room temperature

Room-temperature microfluidics packaging using sequential plasma activation process

A sequential plasma activation process consisting of oxygen reactive ion etching (RIE) plasma and nitrogen radical activation was applied for microfluidics packaging at room temperature. Si/glass and glass/glass wafers were activated by the oxygen RIE plasma and nitrogen microwave radicals one after another. The activated wafers by the two-step process were brought into contact in air followed by keeping them in air for 24 h. The wafers were bonded throughout the entire area and the bonding strength of the interface was as strong as silicon and glass bulk without any post-annealing process and wet chemical cleaning steps. Bonding strength considerably increased with the nitrogen radical treatment after oxygen RIE activation prior to bonding. Chemical reliability tests showed that the bonded interfaces were significantly worked with various chemicals. Si/glass and glass/glass cavities formed by the sequential plasma activation process indicated hermetic sealing behavior. High bonding strength was thought to be due to a diffusion of absorbing water into wafer surface and a reaction between silicon oxynitride layers on the mating wafers. An amorphous layer of 7 nm thick was found at the Si/Si interface. Activation with N/sub 2/ radical for 1200 s after O/sub 2/ RIE plasma treatment for 60 s generated a new phase in the Si wafers across the amorphous layer, probably due to the implantation effect of N2 radical in Si wafer. T-shape microfluidics channels were fabricated on glass wafers by bulk micromachining and bonded by using the sequential plasma activation process at room temperature.

R. Maeda

Papers

Room-temperature microfluidics packaging using sequential plasma activation process

Sequential plasma activation process for microfluidics packaging at room temperature