Silicon-To-Silicon Anodic Bonding via Intermediate Borosilicate Layer for Passive Flow Control Valves

Authors: Luc Conti, Dimitry Dumont-Fillon, Harald van Lintel, Eric Chappel

Abstract:

Flow control valves comprise a silicon flexible membrane that deflects against a substrate, usually made of glass, containing pillars, an outlet hole, and anti-stiction features. However, there is a strong interest in using silicon instead of glass as substrate material, as it would simplify the process flow by allowing the use of well controlled anisotropic etching. Moreover, specific devices demanding a bending of the substrate would also benefit from the inherent outstanding mechanical strength of monocrystalline silicon. Unfortunately, direct Si-Si bonding is not easily achieved with highly structured wafers since residual stress may prevent the good adhesion between wafers. Using a thermoplastic polymer, such as parylene, as intermediate layer is not well adapted to this design as the wafer-to-wafer alignment is critical. An alternative anodic bonding method using an intermediate borosilicate layer has been successfully tested. This layer has been deposited onto the silicon substrate. The bonding recipe has been adapted to account for the presence of the SOI buried oxide and intermediate glass layer in order not to exceed the breakdown voltage. Flow control valves dedicated to infusion of viscous fluids at very high pressure have been made and characterized. The results are compared to previous data obtained using the standard anodic bonding method.

Keywords: Anodic bonding, evaporated glass, microfluidic valve, drug delivery.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1317106

References:

[1] X. Zhang, N. Xiang, W. Tang, D. Huang, X. Wang, H. Yi, Z. Ni, “A passive flow regulator with low threshold pressure for high-throughput inertial isolation of microbeads,” Lab Chip, vol. 15(17), pp. 3473-3480, 2015.
[2] E. Chappel, D. Dumont-Fillon, S. Mefti, “Passive flow regulators for drug delivery and hydrocephalus treatment,” in Proc. SPIE 8976 Microfluidics, BioMEMS, and Medical Microsystems XII, San Francisco, USA, 2014, paper 89760S.
[3] E. Chappel, “Adjustable passive flow regulator,” European Patent EP2943708B1, 2017.
[4] J. Leib, U. Hansen, S. Maus, H. Feindt, K. Hauck, K. Zoschke, M. Toepper, “Anodic bonding at low voltage using microstructured borosilicate glass thin-films,” Proc. Electronic System-Integration Technology Conf. (ESTC) 3rd, Berlin, Germany, 2010, pp. 1-4.
[5] D. Dumont-Fillon, M. Hannebelle, H. van Lintel, E. Chappel, “Design of a Passive Flow Regulator Using a Genetic Algorithm,” in Proc. 30th Eurosensors Conf., Budapest, Hungary, 2016, Procedia Engineering vol.168, pp 1016-1019.
[6] A. Hanneborg, M. Nese, P. Ohlckers, “Silicon-to-silicon anodic bonding with a borosilicate glass layer,” J. Micromech. Microeng., vol. 1(3), pp. 139–144, 1991.
[7] M. Esashi, A. Nakano, S. Shoji, H. Hebiguchi, “Low-temperature silicon-to-silicon anodic bonding with intermediate low melting point glan,” Sensors Actuators A. Phys., vol. 23(1–3), pp. 931–934, 1990.
[8] W.-B. Choi, B.-K Ju, Y.-H. Lee, J.-W. Jeong, M. R. Haskard, N.-Y Lee, M.-Y. Sung, M.-H Oh, “Experimental analysis on the anodic bonding with an evaporated glass layer,” J. Micromech. Microeng., vol. 7, pp. 316-322, 1997.
[9] F. Koliatene, “Contribution à l’étude de l’existence des décharges dans les systèmes de l’avionique,” PhD Thesis, University of Toulouse III, France, 5 janvier 2009.
[10] S. Weichel, R. de Reus, M. Lindahl, “Silicon-to-silicon wafer bonding using evaporated glass,” Sensors and Actuators A-Phys., vol. 70(1-2), pp. 179–184, 1998.
[11] E. Tatar, M. M. Torunbalci, S. E. Alper, T. Akin, “A method and electrical model for the anodic bonding of SOI and glass wafers,” Proc. MEMS 2012, Paris, France, 2012, pp. 68-71.
[12] L. Cornaggia, L. Conti, M. Hannebelle, S. Gamper, D. Dumont-Fillon, H. van Lintel, P. Renaud, E. Chappel, “Passive flow control valve for protein delivery,” Cogent Engineering, 1413923, 2017.