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Sealing of Surface Micromachined Poly-SiGe Cavities

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Poly-SiGe for MEMS-above-CMOS Sensors

Part of the book series: Springer Series in Advanced Microelectronics ((MICROELECTR.,volume 44))

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Abstract

This chapter describes the sealing of polycrystalline SiGe (poly-SiGe) surface micromachined cavities for above-CMOS pressure sensor applications. Two different sealing techniques involving thin-film deposition are investigated: direct sealing and sealing by using an intermediate porous layer. The sealing materials studied include Si-oxide and aluminum. Both \(\mu \)c-SiGe and SiC are evaluated as porous layer. The maximum processing temperature is kept below \(460\,{^\circ }\)C to allow for the post-processing on top of standard CMOS. Section 5.1 gives a short overview about the most common sealing methods for pressure sensors and lists the main requirements the sealing layer needs to fulfill. Section 5.2 explains the fabrication process of the test structures. The measurement set up used to characterize the deflection of the sealed membranes deflection under different applied loads is introduced in Sect. 5.3. In Sect. 5.4 the theoretical analysis of the load-deflection behavior of square membranes is introduced, and with the help of finite element simulations a model adapted to our test structures is developed. Section 5.5 gives the results of the short- and long-term hermeticity tests performed on the sealed membranes. This section also describes the use of micro-venting holes drilled using Focus Ion Beam (FIB) in some of the sealed membranes to study the behavior of the diaphragms under 0-pressure-difference. This chapter ends with a conclusion (Sect. 5.6) listing the main aspects of the different sealing techniques studied and the reasons behind the selection of SACVD (Sub-Atmospheric Chemical Vapor Deposition) oxide as sealing layer for our pressure sensor.

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Authors and Affiliations

  1. CMOS Systems Department, IMEC, Kapeldreef 75, 3001, Leuven, Belgium

    Pilar González Ruiz & Kristin De Meyer

  2. Department of Metallurgy and Material Engineering, KU Leuven, Kapeldreef 75, 3001, Leuven, Belgium

    Ann Witvrouw

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  1. Pilar González Ruiz
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  2. Kristin De Meyer
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Correspondence to Pilar González Ruiz .

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Ruiz, P.G., Meyer, K.D., Witvrouw, A. (2014). Sealing of Surface Micromachined Poly-SiGe Cavities. In: Poly-SiGe for MEMS-above-CMOS Sensors. Springer Series in Advanced Microelectronics, vol 44. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-6799-7_5

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  • DOI: https://doi.org/10.1007/978-94-007-6799-7_5

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