John Heck

Demonstration of a High Speed 4-Channel Integrated Silicon Photonics WDM Link with Hybrid Silicon Lasers

The demonstration of a 4λ×10Gbps Silicon Photonics CWDM link integrating all optical components, electronics and packaging technologies required for system integration is reported. Further demonstration of the link operating at 50Gbps, 4λ×12.5Gbps, is also shown.

Hybrid III–V/Si Distributed-Feedback Laser Based on Adhesive Bonding

A hybrid evanescently coupled III-V/silicon distributed-feedback laser with an integrated monitor photodiode, based on adhesive divinyl siloxane-benzocyclobutene bonding and emitting at 1310 nm, is presented. An output power of ~2.85 mW is obtained in a continuous wave regime at 10°C. The threshold current is 20 mA and a sidemode suppression ratio of 45 dB is demonstrated. Optical feedback is provided via corrugations on top of the silicon rib waveguide, while a specially developed bonding procedure yields 40-nm-thick adhesive bonding layers, enabling efficient evanescent coupling.

1310-nm Hybrid III–V/Si Fabry–Pérot Laser Based on Adhesive Bonding

An evanescently coupled, hybrid III-V/Silicon Fabry-Pérot laser based on adhesive divinyl siloxane-benzocyclobutene (DVS-BCB) bonding is presented operating at 1310 nm. We obtain 5.2-mW output power in continuous-wave (CW) regime at 10 °C with a threshold current density of 2.83 kA/cm2 in an 800-μm -long device. A specially developed bonding procedure produces 50-nm-thick bonding layers, enabling the evanescent coupling.

Metal contact reliability of RF MEMS switches

It is well-recognized that MEMS switches, compared to their more traditional solid state counterparts, have several important advantages for wireless communications. These include superior linearity, low insertion loss and high isolation. Indeed, many potential applications have been investigated such as Tx/Rx antenna switching, frequency band selection, tunable matching networks for PA and antenna, tunable filters, and antenna reconfiguration. However, none of these applications have been materialized in high volume products to a large extent because of reliability concerns, particularly those related to the metal contacts. The subject of the metal contact in a switch was studied extensively in the history of developing miniaturized switches, such as the reed switches for telecommunication applications. While such studies are highly relevant, they do not address the issues encountered in the sub 100μN, low contact force regime in which most MEMS switches operate. At such low forces, the contact resistance is extremely sensitive to even a trace amount of contamination on the contact surfaces. Significant work was done to develop wafer cleaning processes and storage techniques for maintaining the cleanliness. To preserve contact cleanliness over the switch service lifetime, several hermetic packaging technologies were developed and their effectiveness in protecting the contacts from contamination was examined. The contact reliability is also very much influenced by the contact metal selection. When pure Au, a relatively soft metal, was used as the contact material, significant stiction problems occurred when clean switches were cycled in an N2 environment. In addition, various mechanical damages occurred after extended switching cycling tests. Harder metals, while more resistant to deformation and stiction, are more sensitive to chemical reactions, particularly oxidation. They also lead to higher contact resistance because of their lower electrical conductivity and smaller real contact areas at a given contact force. Contact reliability issues could also be tackled by improving mechanical designs. A novel collapsing switch capable of generating large contact forces (>300μN) was shown to be less vulnerable to contamination and stiction.

High-resolution aliasing-free optical beam steering

Many applications, including laser (LIDAR) mapping, free-space optical communications, and spatially resolved optical sensors, demand compact, robust solutions to steering an optical beam. Fine target addressability (high steering resolution) in these systems requires simultaneously achieving a wide steering angle and a small beam divergence, but this is difficult due to the fundamental trade-offs between resolution and steering range. So far, to our knowledge, chip-based two-axis optical phased arrays have achieved a resolution of no more than 23 resolvable spots in the phased-array axis. Here we report, using non-uniform emitter spacing on a large-scale emitter array, a dramatically higher-performance two-axis steerable optical phased array fabricated in a 300 mm CMOS facility with over 500 resolvable spots and 80° steering in the phased-array axis (measurement limited) and a record small divergence in both axes (0.14°). Including the demonstrated steering range in the other (wavelength-controlled) axis, this amounts to two-dimensional beam steering to more than 60,000 resolvable points.

Die-to-Die Adhesive Bonding Procedure for Evanescently-Coupled Photonic Devices

Recently demonstrated evanescent hybrid III-V/Si lasers are mostly based on molecular bonding of a III-V die on an SOI photonic wafer. This procedure requires ultra-clean and smooth bonding surfaces and might be difficult to implement in an industry-scale fabrication process. As an alternative, we present a die-to-die adhesive bonding procedure, using a DVS-BCB polymer. We achieved less than 100 nm-thick bonding layers that enable evanescent coupling between III-V and silicon. The process shows good robustness and bonding strength, with a break-down shear stress of 2 MPa. The process can be scaled-up to a multiple die-to- wafer bonding procedure. Silicon photonics, based on the silicon-on-insulator (SOI) mate- rial platform, is considered as the technology of choice for the inte- gration of photonic devices with microelectronic circuits. However, the fabrication of efficient light sources in silicon photonics is chal- lenging due to silicons indirect bandgap. Heterogeneous integration, achieved through the bonding of III-V semiconductor materials on a SOI platform, is the most promising approach to address this prob- lem. Among several schemes to couple the light from the III-V active medium into the SOI waveguide, 1 evanescent optical coupling is the most promising one and requires no additional coupling structures, 2 although the active material and the silicon waveguide need to be within several hundred nanometers. Several evanescent hybrid III-V/ Si lasers based on direct bonding were reported, 2-5 but this technique is very sensitive to surface topography, contamination or presence of particles and may not be sufficiently robust for industrial-scale fabri- cation where such strict requirements are difficult to meet. Compared to direct bonding, adhesive bonding is more tolerant to surface topography and particle contamination. It has been used for hybrid integration of photonic and electronic circuits. 6 Both ther- moplastic polymers, like SU-8 7 and thermosetting polymers, such as polyimide and BCB, 8 are used as adhesives. Our heterogeneous integration scheme assumes bonding unprocessed III-V dies on top of pre-patterned SOI waveguide circuits (see Fig. 1a). Precise bond- ing alignment is not required since the III-V dies are processed after the bonding. Post-bonding thermal budget should allow 350C proc- essing of the III-V components. Therefore, a thermosetting polymer, divinylsiloxane-bis-benzocyclobutene (DVS-BCB), also referred to as BCB, was chosen. It is a well-known material that is used both for wafer-to-wafer 8 and die-to-wafer bonding processes. 9 Recently, the fabrication of evanescently-coupled photodetectors, 10 hybrid III- V/Si lasers 11 and several other photonics devices 12 using BCB bonding has been demonstrated, but in these cases, a manual bond- ing procedure was used. This resulted in a difficult-to-control bond- ing procedure, which prevents scaling-up to an industrial-level fab- rication. In this paper, we report a machine-based BCB bonding process providing thin bonding layers (<100 nm), suitable for the fabrication of evanescently-coupled photonic devices, specifically hybrid III-V/Si lasers.

Thin-layer Au-Sn solder bonding process for wafer-level packaging, electrical interconnections and MEMS applications

The developed bonding process utilizes AuSn solder and provides liquid-proof sealing and multiple reliable electrical connections between the bonded wafers. The bond can withstand 300°C and features a thin bond line (2–3 µm), high bond strength, excellent bond gap control, and low stress due to small amount of bonding material. A Nb/Au seed layer was shown to be an optimal adhesion and barrier film.

Die-to-Die Adhesive Bonding for Evanescently-Coupled Photonic Devices

Heterogeneous integration of III-V semiconductor materials on the SOI (silicon-on-insulator) platform is a promising method for fabrication of active photonic devices. It requires a reliable and robust bonding procedure that also enables an effective optical coupling between III-V layers and SOI waveguides. Molecular bonding is usually used for this purpose, but due to its strict requirements for contamination-free and smooth bonding surfaces, it might not be sufficiently robust for industrial-scale fabrication. As an alternative technique, in this paper we present an adhesive bonding procedure based on the use of DVS-BCB. We developed a die-to-die adhesive bonding procedure, resulting in less than 100nm-thick bonding layers thereby enabling evanescent optical coupling between III-V layers and silicon waveguides. The process shows very good robustness and bonding strength (breakdownshear stress of 2MPa). In perspective, we plan to scale-up the process to a multiple die-to-wafer bonding procedure which would be suitable for industrial-scale fabrication.

1310 nm Evanescent Hybrid III-V/Si Laser Based on DVS-BCB Bonding

We present an evanescently-coupled, hybrid III-V/Silicon Fabry-Perot laser based on adhesive (DVS-BCB) bonding, operating at 1310 nm. Maximum optical power in a continuous-wave regime is 3 mW and the threshold current density is 2.41 kA/cm2.

Ceramic Via Wafer-Level Packaging for MEMS

We will present a novel approach to wafer level packaging for micro-electro-mechanical systems. Like most common MEMS packaging methods today, our approach utilizes a wafer bonding process between a cap wafer and a MEMS device wafer. However, unlike the common methods that use a silicon or glass cap wafer, our approach uses a ceramic wafer with built-in metal-filled vias, that has the same size and shape as a standard 150 mm silicon wafer. This ceramic via wafer packaging method is much less complex than existing methods, since it provides hermetic encapsulation and electrical interconnection of the MEMS devices, as well as a solderable interface on the outside of the package for board-level interconnection. We have demonstrated successful ceramic via wafer-level packaging of MEMS switches using eutectic gold-tin solder as well as tin-silver-copper solder combined with gold thermo-compression bonding. In this paper, we will present the ceramic via MEMS package architecture and discuss the associated bonding and assembly processes.Copyright