Bonding Characterization of Oxidized PDMS Thin Films
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Bonding Characterization of Oxidized PDMS Thin Films J.J. McMahon, Y. Kwon, J.-Q. Lu, T.S. Cale, and R.J. Gutmann Focus Center-New York, Rensselaer: Interconnections for Hyperintegration Center for Integrated Electronics Rensselaer Polytechnic Institute, Troy, New York-12180 ABSTRACT This paper reports on the use of poly(dimethylsiloxane) (PDMS) thin films to bond pairs of glass slides, borosilicate glass, and silicon substrates, with an emphasis on application for wafer-level three-dimensional (3D) heterogeneous integration technology platforms. PDMS films were spin-cast and cured, surface modified using low power oxygen plasma, and then bonded to various materials. These bonds were destructively tested using a four point bending technique. The critical adhesion energy obtained using surface modified PDMS to bond glass slides is 3.0 J/m2. Adhesion energies obtained using unmodified PDMS are 2.8, 1.8, and 1.6 J/m2 for bonded silicon, glass slides, and borosilicate glass, respectively. Correlation of these results to material surface and interface properties indicates that although PDMS has process advantages as a bonding material for heterogeneous integration, its adhesion strength is lower than that of other dielectric bonding glues. INTRODUCTION The field of microfluidic research is often divided into two areas: flow-through systems and microarrays. Flow-through systems deal with moving fluids, while arrayed systems involve stationary or ‘spotted’ fluids. The primary advantage of flow-through systems is that they offer increased capability in terms of manipulation of the fluids; the primary drawback is increased complexity in fabrication of devices. Recent research has demonstrated significant advances in flow-through microfluidic devices with significant functionality, such as mass spectrometry or integrated fluorescence sensors [1-3]. However, flow-through fluidic systems have yet to achieve high degrees of manufacturability for commercial markets, in general. System-on-a-chip (SoC) integration has been very successful in reducing cost through integration of silicon electronic functions [4]. However, when integrating non-electronic functions with silicon information processing electronics, material selection and processing options are limited. In particular, microelectromechanical systems (MEMS), electro-optical, and electro-biological devices often prove very difficult to integrate using existing SoC fabrication processes. One approach currently being pursued to alleviate some of these issues is 3D integration. Several 3D platforms show promise for reducing future electronic interconnect delays [5-8]. In addition to addressing long interconnects in advanced integrated circuits (ICs), the 3D approach used at Rensselaer can enable heterogeneous integration of non-electronic devices with ICs [9]. The 3D-SoC platform under development at Rensselaer is illustrated conceptually in Figure 1 [10]. Salient features of this 3D platform include: 1) Precise alignment (~1 µm) of large area (200 mm diameter) substrat
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