Indium-silver as solder materials for low temperature bonding had been introduced earlier. In theory the final bonding
interface composition is determined by the overall materials composition. Wafer bonding based multiple intermediate
layers facilitates precise control of the formed alloy composition and the joint thickness. Thus the bonding temperature
and post-bonding re-melting temperature could be easily designed by controlling the multilayer materials. In this paper, a
more fundamental study of In-Ag solder materials is carried out in chip-to-chip level by using flip-chip based
thermocompression bonding. Bonding at 180°C for various time duration under various bonding pressure is studied.
Approaches of forming Ag2In with re-melting temperature higher than 400°C at the bonding interface are proposed and
discussed. Knowledge learned in this process technology can support us to develop sophisticated wafer level packaging
process based wafer bonding for applications of MEMS and IC packages.
There is an increasing demand for tunable lasers in telecommunications networks for test equipment, optical components
and other applications. In DWDM systems, multiple data streams propagate concurrently on a single mode fiber.
DWDM networks are based on a DFB lasers operating at a wavelength defined by ITU wavelength grid. Statistical
variations associated with the manufacture of DFB laser results in yield losses. Continuously tunable external lasers are
developed to overcome the limitations of DFB lasers. Various laser tuning mechanisms are being explored to provide
external cavity tunable lasers to provide a stable single mode output.
The packaged tunable laser source (TLS) for DWDM network also need to include several optical elements for isolation
and data modulation like collimator, focusing lens, fiber pigtail, a modulator and output fiber segment. In this
publication, we propose a novel semi integrated miniature high frequency tunable laser design based on Silicon Optical
Bench (SiOB) concept. One of the mirrors is a movable MEMS structure changing the optical path length. We propose
micro optical design between laser diode and the MEMS mirror for efficient optical coupling and side mode suppression.
We also present the compatibility between the optical coupling and MEMS actuation range. We present the coupling
efficiency results over the tuning range. We also propose a method of monitoring the output power of the tunable laser
using waveguide coupler structures which are integrated in the silicon wafer and method of packaging in a miniature
package compatible to the industry standard form factor.
In this paper, the optical design of 4-channel WDM Transmission Optical Subassemblies (TOSA)/Receiver Optical
Subassemblies (ROSA) is reported. The TOSA and ROSA are being developed for uncooled modules for CWDM
applications and are compatible with the SFP/SFF form factor TOSA and ROSA. The physical dimension of OSA
together with the electronic circuitries is limited to 10×6×5 mm3. The designs of TOSA and ROSA are employed using
four thin film filters (TFFs) to select the specific channel wavelength, four 500 μm ball lenses, one 2.5 mm ball lens and
a high reflection mirror using folded optical configuration. The optical elements are to be assembled on a SiOB, except
the 2.5 mm ball lens. The simulation results are used to estimate the required optical components assembly accuracy.
Based on the simulation results, the tolerance requirement for tilting the mirror and first thin film filter is approximately
± 0.2° for the longest optical path namely Channel 4.
Silicon Optical Bench (SiOB) is a popular solution for passive assembly of optical module. In order to realize an optical
transmitter or receiver module, it is necessary to integrate high frequency optoelectronic components such as signal
photodiodes (PD) or laser diodes (LD) onto the SiOB. In this way, the module's electrical and optical performances can
be further improved, and a higher degree of miniaturization can be achieved. The challenge for this integration is not
only on the assembly accuracy for the LD and PD, it required the design of low loss electrical interconnect at high
frequency. However, the standard silicon substrate used in the SiOB has a high electrical loss especially at high
frequency. This imposed a limitation on the electrical interconnection length between the optoelectronic components and
their I/O interfaces. It is proposed here to design the electrical interconnection using a layer of SiO2 sandwiched between
two layers of metal layer. Simulations have demonstrated that by varying the thickness of the SiO2 layer, an optimum
electrical performance can be achieved.
An optical sub-assembly of MUX/DEMUX where optical devices are hybrid-integrated on a silicon optical bench (SiOB)
using a low cost passive alignment method was reported. A tight tolerance of positional and tilting angular accuracy is
required for optical devices attachment in order to maximize the coupling efficiency. The critical positioning transverse
to the optical axis merely depends on the symmetry, and accuracy of the position and shape of trenches. Any inaccuracy
primarily affects the non-critical positioning, i.e., z-axis & θz, in the direction along the optical axis; misalignment
accumulated and causes undesired insertion loss. All the piece parts, i.e., mirror, thin-film filters (TFFs), ball lens, SiOB
etc., have a defined tolerance in their dimensions and surfaces which increases the challenge in achieving high placement
accuracy along the optical axis. The effects from these inherent inaccuracies of the position and shape of trenches and
piece parts could be minimized by improve the bottom flatness, and proper procedure selection. Misalignment at each
axis, e.g. x-, y-, z-, θx, θy & θz was characterized and its effect to the coupling efficiency was discussed.
This paper presents design, simulation and fabrication of a wafer level packaged Microelectromechanical Systems
(MEMS) scanning mirror. In particular we emphasize on the process development and materials characterization of In-
Ag solder for a new wafer level hermetic/vacuum package using low temperature wafer bonding technology. The
micromirror is actuated with an electrostatic comb actuator and operates in resonant torsional mode. The mirror plate
size is 1.0 mm × 1.0 mm. The dynamic vibration characteristics have been analyzed by using FEM tools. With a single
rectangular torsion bar, the scanning frequency is 20 KHz. Besides, the hermetically sealed packaged is favored by
commercial applications. The wafer level package is successfully carried out at process temperature of 180°C. With
proper process design, we may lead the form a single phase of Ag2In at the bonding interface, in which it is an
intermetallic compound of high melting temperature. This new wafer level packaging approach allows us to have high
temperature stability of wafer level packaged scanning mirror devices. The wafer level packaged devices are able to
withstand the peak temperature in SMT (surface mount technology) manufacturing lines. It is a promising technology for
commercializing MEMS devices.
The high cost of optoelectronics components typically used for long-haul communication is prohibitive in the Fiber to
the Home (FTTH) and Passive Optical Networks (PONs). One method of cost reduction is through the reducing the cost
of the electronics in the transceiver and reducing the packaging cost. We report the development of low-cost 2.5-Gbps
optical transceiver for Gigabit Passive Optical Network (GPON) using CMOS driver ICs and chip-on-board assembly
method. We developed the Laser Diode Driver (LDD), Trans-impedance Amplifier (TIA), Limiting Amplifier (LA) and
the Clock and Data Recovery (CDR) using CMOS technology for short reach application and developed the burst mode
version of the ICs for PON applications. The ICs are designed in house and fabricated on a standard CMOS 8" wafer
with 0.18μm technology. The devices operate at 1.8V and are low power in nature, thus reducing the demand on power
dissipation. The transceiver consists of an un-cooled and direct modulated laser diode driven with a LDD, a high speed
PIN photo-diode with amplifier and CMOS ICs. The bare CMOS ICs are attached on a transceiver substrate that is
compliant with the small form-factor pluggable (SFP) package multisource agreement (MSA) and coupled to a 1310nm
FP laser TOSA and a PIN ROSA with LC connector. The integrated transceiver is characterized up to 2.5-Gbps. In this
publication, we present the detail of the module development, assembly methods and performance characterization at
In this study, a low-cost (with bare chips) and high (optical, electrical, and thermal) performance optoelectronic system with
a data rate of 10Gbps is designed and analyzed. This system consists of a rigid printed circuit board (PCB) made of FR4
material with an optical polymer waveguide, a vertical cavity surface emitted laser (VCSEL), a driver chip, a 16:1 serializer,
a photo-diode detector, a Trans-Impedance Amplifier (TIA), a 1:16 deserializer, and heat spreaders. The bare VCSEL, driver
chip, and serializer chip are stacked with wire bonds and then solder jointed on one end of the optical polymer waveguide on
the PCB via Cu posts. Similarly, the bare photo-diode detector, TIA chip, and deserializer chip are stacked with wire bonds
and then solder jointed on the other end of the waveguide on the PCB via Cu posts. Because the devices in the 3D stacking
system are made with different materials, the stresses due to the thermal expansion mismatch among various parts of the
system are determined.
Silicon photonic crystal (PhC) waveguide based resonator is designed by introducing a micro-cavity within the line
defect so as to form the resonant band gap structure for PhC. Free-standing silicon beam comprising this nanophotonic
resonator structure is investigated. The output resonant wavelength is sensitive to the shape of air holes and defect length
of the micro-cavity. The resonant wavelength shift in the output spectrum is a function of force loading at the center of a
suspended beam with PhC waveguide resonator. The sensing capability of this new nanomechanical sensor is derived as
that vertical deformation is about 20nm at center and the smallest strain is 0.005% for defect length.
A new method of coupling the light from a laser diode to a Single Mode Fiber (SMF) with large alignment tolerances
and without using coupling lenses is presented. A pseudo vertical tapered coupler is designed for light coupling between
laser diode and single mode fiber. It has a large input aperture which is about 100 times the size of the laser waveguide
cross-section. The tapered coupler provides single mode output and matches the mode size with the single mode fiber.
The tapered coupler is fabricated on a silicon optical bench and is located between the laser and the fiber through the
silicon micrfabrication process. The misalignment between the fiber and taper coupler can be very small since this is
controlled by high precision silicon optical bench patterning processes. The coupler relaxes the laser diode placement
accuracies and eliminates the need for a coupling lens. Design Studies showed that the tolerance between the laser diode
and taper coupler can be more than +/-5μm misalignment at x-y, and +/-0.5degree tilting angle tolerance and the
fabricated assembly results are encouraging with good placement tolerances and coupling efficiency. The laser to single
mode fiber coupling tolerances is greatly improved and passive alignment for laser and single mode fiber is realized. The
technology can be useful for multi channel optical assembly where significant device and process cost saving can be
achieved and is suitable for functional integration for silicon photonics.
A compact wavelength division multiplexing (WDM) module is designed using discrete micro optics
components assembled on silicon optical bench for multiple-channel transceivers. This design is optimized
for a 4-channel multiplexer (MUX) plus a 4-channel demultiplexer (DEMUX). In this design, the micro
optics components for the MUX and DEMUX are integrated, and the MUX and DEMUX share the same
space. This helps to minimize the number of components required and hence reduce the cost and size.
Therefore, the module is compact enough to be put in small standard packages (SFF/SFP).