Special Issue "Wafer Level Packaging of MEMS"

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A:Physics".

Deadline for manuscript submissions: closed (15 March 2018).

Special Issue Editor

Prof. Dr. Shuji Tanaka
E-Mail Website
Guest Editor
Department of Robotics, Graduate School of Engineering, Tohoku University 6-6-01 Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi 980-8579, Japan
Interests: MEMS (Micro Electro Mechanical Systems) and and micro/nanotechnology

Special Issue Information

Dear Colleagues,

Packaging is essential for the practical use of micro electro mechanical systems (MEMS), in terms of performance and reliability. The electronics market has been continuously requiring the downsizing and cost reduction of MEMS, and, thus, wafer-level packaging is becoming more important and replacing conventional die-level packaging. For example, the recent drastic reduction of die size found in inertial sensors has been driven by the progress of wafer-level packaging technology. One of important features of the wafer-level packaging of MEMS is that it often needs the device cavity, which is hermetically sealed. Therefore, hermetic/vacuum sealing and electrical feedthrough from the sealed cavity are key technologies. On the other hand, emerging devices need new types of packaging, for example, biocompatible and flexible packaging, which are also attracting a great deal of attention. Test, reliability control, wiring, dicing, chip-level integration and material development related to the wafer-level packaging of MEMS are also included in the scope of this Special Issue. Wafer-level packaging is strongly connected to the integration of multiple components, and, thus, papers about wafer-level integration are also welcome.

Prof. Dr. Shuji Tanaka
Guest Editor

Manuscript Submission Information

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Keywords

  • Wafer-level packaging
  • Wafer-level integration
  • Hermetic sealing
  • Vacuum sealing
  • Wafer bonding
  • Electrical feedthrough
  • TSV (Through Silicon Via)
  • Reliability
  • Biocompatibility

Published Papers (6 papers)

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Research

Open AccessArticle
Development and Characterization of Non-Evaporable Getter Thin Films with Ru Seeding Layer for MEMS Applications
Micromachines 2018, 9(10), 490; https://doi.org/10.3390/mi9100490 - 25 Sep 2018
Cited by 1
Abstract
Mastering non-evaporable getter (NEG) thin films by elucidating their activation mechanisms and predicting their sorption performances will contribute to facilitating their integration into micro-electro-mechanical systems (MEMS). For this aim, thin film based getters structured in single and multi-metallic layered configurations deposited on silicon [...] Read more.
Mastering non-evaporable getter (NEG) thin films by elucidating their activation mechanisms and predicting their sorption performances will contribute to facilitating their integration into micro-electro-mechanical systems (MEMS). For this aim, thin film based getters structured in single and multi-metallic layered configurations deposited on silicon substrates such as Ti/Si, Ti/Ru/Si, and Zr/Ti/Ru/Si were investigated. Multilayered NEGs with an inserted Ru seed sub-layer exhibited a lower temperature in priming the activation process and a higher sorption performance compared to the unseeded single Ti/Si NEG. To reveal the gettering processes and mechanisms in the investigated getter structures, thermal activation effect on the getter surface chemical state change was analyzed with in-situ temperature XPS measurements, getter sorption behavior was measured by static pressure method, and getter dynamic sorption performance characteristics was measured by standard conductance (ASTM F798–97) method. The correlation between these measurements allowed elucidating residual gas trapping mechanism and prediction of sorption efficiency based on the getter surface poisoning. The gettering properties were found to be directly dependent on the different changes of the getter surface chemical state generated by the activation process. Thus, it was demonstrated that the improved sorption properties, obtained with Ru sub-layer based multi-layered NEGs, were related to a gettering process mechanism controlled simultaneously by gas adsorption and diffusion effects, contrarily to the single layer Ti/Si NEG structure in which the gettering behavior was controlled sequentially by surface gas adsorption until reaching saturation followed then by bulk diffusion controlled gas sorption process. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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Open AccessArticle
Technology for 3D System Integration for Flexible Wireless Biomedical Applications
Micromachines 2018, 9(5), 213; https://doi.org/10.3390/mi9050213 - 02 May 2018
Cited by 1
Abstract
This paper presents a new 3D bottom-up packing technology for integrating a chip, an induction coil, and interconnections for flexible wireless biomedical applications. Parylene was used as a flexible substrate for the bottom-up embedding of the chip, insulation layer, interconnection, and inductors to [...] Read more.
This paper presents a new 3D bottom-up packing technology for integrating a chip, an induction coil, and interconnections for flexible wireless biomedical applications. Parylene was used as a flexible substrate for the bottom-up embedding of the chip, insulation layer, interconnection, and inductors to form a flexible wireless biomedical microsystem. The system can be implanted on or inside the human body. A 50-μm gold foil deposited through laser micromachining by using a picosecond laser was used as an inductor to yield a higher quality factor than that yielded by thickness-increasing methods such as the fold-and-bond method or thick-metal electroplating method at the operation frequency of 1 MHz. For system integration, parylene was used as a flexible substrate, and the contact pads and connections between the coil and chip were generated using gold deposition. The advantage of the proposed process can integrate the chip and coil vertically to generate a single biocompatible system in order to reduce required area. The proposed system entails the use of 3D integrated circuit packaging concepts to integrate the chip and coil. The results validated the feasibility of this technology. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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Open AccessArticle
Bonding-Based Wafer-Level Vacuum Packaging Using Atomic Hydrogen Pre-Treated Cu Bonding Frames
Micromachines 2018, 9(4), 181; https://doi.org/10.3390/mi9040181 - 13 Apr 2018
Abstract
A novel surface activation technology for Cu-Cu bonding-based wafer-level vacuum packaging using hot-wire-generated atomic hydrogen treatment was developed. Vacuum sealing temperature at 300 °C was achieved by atomic hydrogen pre-treatment for Cu native oxide reduction, while 350 °C was needed by the conventional [...] Read more.
A novel surface activation technology for Cu-Cu bonding-based wafer-level vacuum packaging using hot-wire-generated atomic hydrogen treatment was developed. Vacuum sealing temperature at 300 °C was achieved by atomic hydrogen pre-treatment for Cu native oxide reduction, while 350 °C was needed by the conventional wet chemical oxide reduction procedure. A remote-type hot-wire tool was employed to minimize substrate overheating by thermal emission from the hot-wire. The maximum substrate temperature during the pre-treatment is lower than the temperature of Cu nano-grain re-crystallization, which enhances Cu atomic diffusion during the bonding process. Even after 24 h wafer storage in atmospheric conditions after atomic hydrogen irradiation, low-temperature vacuum sealing was achieved because surface hydrogen species grown by the atomic hydrogen treatment suppressed re-oxidation. Vacuum sealing yield, pressure in the sealed cavity and bonding shear strength by atomic hydrogen pre-treated Cu-Cu bonding are 90%, 5 kPa and 100 MPa, respectively, which are equivalent to conventional Cu-Cu bonding at higher temperature. Leak rate of the bonded device is less than 10−14 Pa m3 s−1 order, which is applicable for practical use. The developed technology can contribute to low-temperature hermetic packaging. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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Open AccessArticle
Comprehensive Die Shear Test of Silicon Packages Bonded by Thermocompression of Al Layers with Thin Sn Capping or Insertions
Micromachines 2018, 9(4), 174; https://doi.org/10.3390/mi9040174 - 11 Apr 2018
Cited by 1
Abstract
Thermocompression bonding for wafer-level hermetic packaging was demonstrated at the lowest temperature of 370 to 390 °C ever reported using Al films with thin Sn capping or insertions as bonding layer. For shrinking the chip size of MEMS (micro electro mechanical systems), a [...] Read more.
Thermocompression bonding for wafer-level hermetic packaging was demonstrated at the lowest temperature of 370 to 390 °C ever reported using Al films with thin Sn capping or insertions as bonding layer. For shrinking the chip size of MEMS (micro electro mechanical systems), a smaller size of wafer-level packaging and MEMS–ASIC (application specific integrated circuit) integration are of great importance. Metal-based bonding under the temperature of CMOS (complementary metal-oxide-semiconductor) backend process is a key technology, and Al is one of the best candidates for bonding metal in terms of CMOS compatibility. In this study, after the thermocompression bonding of two substrates, the shear fracture strength of dies was measured by a bonding tester, and the shear-fractured surfaces were observed by SEM (scanning electron microscope), EDX (energy dispersive X-ray spectrometry), and a surface profiler to clarify where the shear fracture took place. We confirmed two kinds of fracture mode. One mode is Si bulk fracture mode, where the die shear strength is 41.6 to 209 MPa, proportionally depending on the area of Si fracture. The other mode is bonding interface fracture mode, where the die shear strength is 32.8 to 97.4 MPa. Regardless of the fracture modes, the minimum die shear strength is practical for wafer-level MEMS packaging. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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Open AccessArticle
Millimeter-Wave Substrate Integrated Waveguide Using Micromachined Tungsten-Coated Through Glass Silicon Via Structures
Micromachines 2018, 9(4), 172; https://doi.org/10.3390/mi9040172 - 09 Apr 2018
Cited by 3
Abstract
A millimeter-wave substrate integrated waveguide (SIW) has been demonstrated using micromachined tungsten-coated through glass silicon via (TGSV) structures. Two-step deep reactive ion etching (DRIE) of silicon vias and selective tungsten coating onto them using a shadow mask are combined with glass reflow techniques [...] Read more.
A millimeter-wave substrate integrated waveguide (SIW) has been demonstrated using micromachined tungsten-coated through glass silicon via (TGSV) structures. Two-step deep reactive ion etching (DRIE) of silicon vias and selective tungsten coating onto them using a shadow mask are combined with glass reflow techniques to realize a glass substrate with metal-coated TGSVs for millimeter-wave applications. The proposed metal-coated TGSV structures effectively replace the metallic vias in conventional through glass via (TGV) substrates, in which an additional individual glass machining process to form micro holes in the glass substrate as well as a time-consuming metal-filling process are required. This metal-coated TGSV substrate is applied to fabricate a SIW operating at Ka-band as a test vehicle. The fabricated SIW shows an average insertion loss of 0.69 ± 0.18 dB and a return loss better than 10 dB in a frequency range from 20 GHz to 45 GHz. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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Open AccessArticle
Wafer-Level Packaging Method for RF MEMS Applications Using Pre-Patterned BCB Polymer
Micromachines 2018, 9(3), 93; https://doi.org/10.3390/mi9030093 - 25 Feb 2018
Cited by 1
Abstract
A radio-frequency micro-electro-mechanical system (RF MEMS) wafer-level packaging (WLP) method using pre-patterned benzo-cyclo-butene (BCB) polymers with a high-resistivity silicon cap is proposed to achieve high bonding quality and excellent RF performance. In this process, the BCB polymer was pre-defined to form the sealing [...] Read more.
A radio-frequency micro-electro-mechanical system (RF MEMS) wafer-level packaging (WLP) method using pre-patterned benzo-cyclo-butene (BCB) polymers with a high-resistivity silicon cap is proposed to achieve high bonding quality and excellent RF performance. In this process, the BCB polymer was pre-defined to form the sealing ring and bonding layer by the spin-coating and patterning of photosensitive BCB before the cavity formation. During anisotropic wet etching of the silicon wafer to generate the housing cavity, the BCB sealing ring was protected by a sputtered Cr/Au (chromium/gold) layer. The average measured thickness of the BCB layer was 5.9 μm. In contrast to the conventional methods of spin-coating BCB after fabricating cavities, the pre-patterned BCB method presented BCB bonding layers with better quality on severe topography surfaces in terms of increased uniformity of thickness and better surface flatness. The observation of the bonded layer showed that no void or gap formed on the protruding coplanar waveguide (CPW) lines. A shear strength test was experimentally implemented as a function of the BCB widths in the range of 100–400 μm. The average shear strength of the packaged device was higher than 21.58 MPa. A RF MEMS switch was successfully packaged using this process with a negligible impact on the microwave characteristics and a significant improvement in the lifetime from below 10 million to over 1 billion. The measured insertion loss of the packaged RF MEMS switch was 0.779 dB and the insertion loss deterioration caused by the package structure was less than 0.2 dB at 30 GHz. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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