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Heterogeneous Integration Technologies Based on Wafer Bonding and Wire Bonding for Micro and Nanosystems

Time: Fri 2019-10-04 10.00

Location: Sal F3, Lindstedtsvägen 26, Stockholm (English)

Subject area: Electrical Engineering

Doctoral student: Xiaojing Wang , Mikro- och nanosystemteknik

Opponent: Professor Shuji Tanaka, Tohoku University

Supervisor: Professor Göran Stemme, Mikro- och nanosystemteknik; Professor Frank Niklaus, Mikro- och nanosystemteknik; Associate Professor Niclas Roxhed, Mikro- och nanosystemteknik

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Heterogeneous integration realizes assembly and packaging of separately manufactured micro-components and novel functional nanomaterials onto the same substrate. It has been a key technology for advancing the discrete micro- and nano-electromechanical systems (MEMS/NEMS) devices and micro-electronic components towards cost-effective and space-efficient multi-functional units. However, challenges still remain, especially on scalable solutions to achieve heterogeneous integration using standard materials, processes, and tools. This thesis presents several integration and packaging methods that utilize conventional wafer bonding and wire bonding tools, to address scalable and high-throughput heterogeneous integration challenges for emerging applications.

The first part of this thesis reports three large-scale packaging and integration technologies enabled by wafer bonding. Two low-temperature wafer-level vacuum packaging approaches are realized using narrow footprint metal-based sealing rings (Cu-Cu and Al-Au bonding, respectively). As Cu and Al are standard materials used in complementary metal-oxide-semiconductor (CMOS) wafers, these two methods can be used for system-on-chip (SoC) integration of vacuum packaged MEMS with CMOS circuits. Then, an integration method for transferring large-area 2D materials, including graphene, hexagonal boron nitride (h-BN), and molybdenum disulfide (MoS2), from their growth substrates to target substrates and formation of graphene/h-BN heterostructures by adhesive wafer bonding is demonstrated. Such a method would facilitate large-scale fabrication of novel 2D material-based devices.

The second part of this thesis describes two different heterogeneous assembly approaches enabled by wire bonding. The first work realizes scalable vertical integration of microchips that are in-plane fabricated from the source wafer into a separate receiving substrate. The contactless assembly of microchips is realized by magnetic assembly and the electrical contacting is achieved by wire bonding on the sidewalls of the vertically assembled microchips. The second work deals with transfer of carbon nanotubes and Si micro-structures from their growth/fabrication substrates to target substrates by utilizing wire bonder as an automated manipulation tool. These methods could be useful for high-throughput 3D integration of microstructures and nanomaterials for various applications.