Room temperature bonding of micromachined glass devices for capillary electrophoresis

https://doi.org/10.1016/S0925-4005(00)00351-8Get rights and content

Abstract

We report a simple method to bond glass at room temperature for microfluidic applications, which is based on rigorous cleaning [K. Fluri, G. Fitzpatrick, N. Chiem, D.J. Harrison, Integrated capillary electrophoresis devices with an efficient postcolumn reactor in planar quartz and glass chips, Anal. Chem. 68 (1996) 4285–4290; N. Chiem, D.J. Harrison, Microchip-based capillary, Anal. Chem. 69 (1997) 373–378; D. Sobek, A.M. Young, M.L. Gray, S.D. Senturia, A microfabricated flow chamber for optical measurements influids, Proc. IEEE Micro-Electromechanical Systems Workshop, Fort Lauderdale, FL, Feb 7–10, 1993, pp. 219–224.] of the glass substrates before bonding. Low applied pressure on micromachined glass substrates contacted at 20°C provides devices, which are robustly bonded. These devices are able to withstand routine handling, and be used for capillary electrophoresis for as long as 2 years. Separation efficiencies as high as 90,000 theoretical plates were observed at 6–8 kV applied, comparable to 100,000 observed in devices bonded at 440–650°C. A wide range of the same or different types of commercially available glass can be bonded without heat treatment, alleviating the need for a good match in thermal expansion coefficients between the glasses.

Introduction

Microfluidic devices etched in glass substrates provide an on-chip fluidic network in which chemical reactions, sample injection, and separation of reaction products can be pumped and driven using electrokinetic phenomena [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. Devices fabricated in glass have used a cover plate to close the channels in the etched plate, which was bonded at high temperatures to allow softening and flow of the glass plates [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. It would be convenient to lower the temperature required for bonding, or even to make the bonding step reversible, in order to reduce fabrication time and cost, and increase the flexibility of device usage.

Oxidized silicon wafer bonding has been extensively studied [12], [13]. Frequently, room temperature, intimate contact of the wafers gives a cold welded bond that is strong enough to allow further handling of the bonded structure without additional treatment. Glass bonding should be similar to oxidized semiconductor wafer bonding, however, the microscale roughness of Si is less than 5 Å [13], while that of glass is 50–70 Å for fired or mechanically polished glass [14]. Consequently, it is not obvious that the intimate contact of glass required for formation of a strong cold weld can be achieved. We recently reported that temperatures could be lowered to 440°C with extensive cleaning [16], while Wang et al. [17] have reported a chemical additive used in bonding silicon can be used to lower the bonding temperature of glass to about 90°C.

In this paper, we report a simple method to bond glass at room temperature that is based on rigorous cleaning [11], [16], [18]. This method was successfully used to bond a wide range of the same or different types of commercially available glass, without the need for thermal treatment. Microfluidic devices bonded with this method did not leak under normal operating conditions with either pressure or electrokinetically driven flow and showed good separation performance.

Section snippets

Materials and reagents

Borosilicate glass (Pyrex, Borofloat) was from Paragon Optical (Reading, PA). Photomask glass was from Agfa-Gevaert (Belgium) and cover-slip glass (Corning 0211) was from Corning Glass (Parkridge, IL). Microscope slides and Sparkleen detergent were from Fisher Scientific (Edmonton, Canada). Hollow diamond drill bits were from Lunzer (Saddle Brook, NJ). Crystal bond was from Aremco (Ossining, NY). The beads were Spherisorb ODSI (Phase Separations, Flintshire, UK), a porous C-18, Silica bead with

Conditions for the absence of interference fringes

The glass types tested for room temperature bonding (RT) are listed in Table 1. The first criteria of importance are the glass smoothness and its preparation during manufacture of the plates. The Pyrex used was ground and polished, while the borofloat, microscope slide, and cover slip glass (Corning 0211) were manufactured by a float process. The manufacturer's procedure for the photomask glass was not available, but it was either rolled or else ground and polished.

All of the glasses tested

Conclusion

The most important factors for successful room temperature bonding were the cleanliness and flatness of the glass surfaces. The separation performance and the durability of these RT bonded devices were comparable to that of devices prepared by high temperature bonding (>400°C). The availability of a low temperature bonding process that does not require additional chemical treatments should prove significant, greatly increasing the flexibility available in fabrication. Greater range in the

Acknowledgements

We thank the Natural Sciences and Engineering Council of Canada for support. NC thanks the Alberta Microelectronic Centre for a Research Fellowship and for the use of their facilities and G. McKinnon for helpful contributions. We are grateful to P. Myers of Phase Separations, UK, for donating the silica beads. DJH thanks M. Schmidt, M. Gray, and D. Sobek of MIT for valuable discussions.

References (20)

  • A. Manz et al.

    Micromachining of monocrystalline silicon and glass for chemical analysis systems: a look into next century's technology or just a fashionable craze?

    Trends Anal. Chem.

    (1991)
  • H.Y. Wang et al.

    Low temperature bonding for microfabrication of chemical analysis devices

    Sens. Actuators, B

    (1997)
  • D.J. Harrison et al.

    Capillary electrophoresis and sample injection systems integrated on a planar glass chip

    Anal. Chem.

    (1992)
  • K. Seiler et al.

    Planar glass chips capillary electrophoresis: repetitive sample injection, quantitation and separation efficiency

    Anal. Chem.

    (1993)
  • C.S. Effenhauser et al.

    Glass chips for high-speed capillary electrophoresis separations with submicrometer plate heights

    Anal. Chem.

    (1993)
  • D.J. Harrison et al.

    Micromachining a miniaturized capillary electrophoresis-based chemical analysis system on a chip

    Science

    (1993)
  • Z. Fan et al.

    Micromachining of capillary electrophoresis injectors and separators on glass chips and evaluation of flow at capillary intersections

    Anal. Chem.

    (1994)
  • S.C. Jacobson et al.

    Effects of injection schemes and column geometry on the performance of microchip electrophoresis devices

    Anal. Chem.

    (1994)
  • K. Seiler et al.

    Electroosmotic pumping and valveless control of fluid flow within a manifold of capillaries on a glass chip

    Anal. Chem.

    (1994)
  • D.J. Harrison et al.

    Micromachining chemical and biochemical analysis and reaction systems on glass substrates

There are more references available in the full text version of this article.

Cited by (0)

View full text