SUCCESS STORY – Silicon Photonics Set the Pace on the Data Highway-- Steffen Arnold --Silicon Photonics Set the Pace on the Data Highway
Automated Packaging As Complete Solution

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Silicon Photonics Set the Pace on the Data Highway-- Steffen Arnold--Some years ago, silicon-photonics was already an important
topic with regard to fast telecommunication solutions, today
the focus lies more on datacom, implying that opticalinterconnect is not only used for long-haul data transmission,
but also for on-chip communication, chip-to-chip, chip-toboard, and so on. The major buzzwords in this context arecloud computing, fast Internet and a number of othercomputer-supported services requiring the highest possible
transmission rates.
Here, silicon photonics enable data rates to the magnitude ofTbit/s. However, it is far from easy to place the opticalcomponents on the silicon substrate or to handle the opticalconnectivity necessary to move data to / from the chips. To
pave the way to cost-optimized mass production it isnecessary to automate a number of complex positioning
tasks, adding also machine vision and active measurements.

But as soon as you break away from the wafer level to full
packaging technology, the costs soar upwards. The
integration of light sources at the wafer level and theconnection of the optical inputs and outputs prove to bedifficult. As a rule, the optical waveguides on silicon wafers
have a width ranging from 200 to 400 nm, and are thereforemuch smaller than optical mono-mode glass fibers with anaverage core diameter of approx. 9 µm. For these monomode glass fibers, it is necessary to apply some special ‘tricks’
to funnel the light in and out of the chip (tapers, gratings,etc.).
Managing such an automation task is indeed a major
challenge: It requires maximum precision in handling,
positioning and adjustment as well as the highest possible
production speed in order to serve mass markets. PI miCos, aPI subsidiary, has taken on this challenge and developed an
automated photonic assembly and alignment system which
has already proven itself in pre-production use.
The specialists for micro- and nanopositioning were able toleverage on a number of in-house technologies for this task.
This resulted in a turnkey automated solution which can beadapted well to various application requirements (Fig. 1).
Here, a silicon chip already diced from a complete wafer isassembled in a ceramic package and other optical elements
are then bonded to it, for example, a fiber array, positioned
with an sub-µm accuracy (Fig. 2).

Fig. 1

Automated solution for silicon photonic chip production andinspection: the system integrates several hardware components
and software for the automation of assembly and alignment,such as pick-and-place robot technology, image processing, ordevices for precision positioning (image: PI)

Silicon photonics employs fairly standard silicon
semiconductor processes to build the optical elements
required for sending, receiving, and distributing opticalinformation between CPUs and other electronic components.
To this purpose, optical components are integrated next tothe electronic components in the silicon substrate.
The resulting microchips can send data at terabit-per-second
rates via optical waveguides with very low power
consumption and heat generation. The various components
for manufacturing such semiconductor chips can already be
produced with commercial equipment. Production at wafer
level has become highly automated at reasonably low prices.

Fig. 2

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

Chip packaging: silicon substrate (I), fiber connection (II),external laser source (III) and flip-chip bonds (IV) (image: PI)

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SUCCESS STORY – Silicon Photonics Set the Pace on the Data Highway-- Steffen Arnold--

Nanopositioning, Image Processingand Robotics
Four different areas (Fig. 3) needed to be covered for theimplementation of this complex assembly and alignment
bench:Fig. 3

Schematic design: positioning system for fine adjustment (I),application-specific software and user interface (II), industrial
image processing (III) and conventional robotics for pick-andplace of the components (IV) (image: PI)

Micro- and nanopositioning, machine vision, robotics for thepick-and-place of the various components, as well as theapplication-specific software and graphical user interface (Fig.
5). The principal design and function of the system are
relatively easy to understand:The vision-guided robot picks up the components and places
them on intermediate holders. Then the photonic
components are positioned with high accuracy on the Si
substrate, employing a high resolution image processing
system (Fig. 4) based on cameras in the visible and shortwave
infrared range (SWIR).

Fig. 5

Fig. 4

Fine adjustment for fiber array. The light throughput is measured
and optimized via scan algorithms (image: PI)

Integrated image processing supports chip alignment prior toassembly (chip by STMicroelectronics) (image: PI)

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Silicon Photonics Set the Pace on the Data Highway-- Steffen Arnold--

The task is managed by a combination of linear positioners
and micro-fabrication robots operating in six degrees offreedom, the so-called SpaceFAB's from PI miCos (Fig. 6).

This enables the realization of fast and high-precision travel.
In contrast to serial kinematics, in parallel-kinematic systems
all the actuators act directly on the same platform, in otherwords there is no accumulation of guiding errors as in"stacked" systems, thus increasing accuracy greatly. But there
are also other advantages: for example, low moved mass andconsequently better dynamic performance equal for all
motion axes, no moving cables to cause friction, and aconsiderably more compact design.
The XY stages, which were developed especially for
applications in optical waveguide alignment, can be equippedwith rotary encoders or high-precision glass measuring scales
in a closed servo loop. Commanding the Hexapod system has
been made very easy.

Fig. 6

Exact alignment of the optical fibers on a silicon photonic chippackage using two SpaceFab positioning systems (image: PI)

The Parallel-Kinematic Principle
The parallel-kinematic SpaceFab principle is based on three
XY stages that jointly position a platform using three struts
with a constant length and a suitable joint configuration (Fig.
7).

Fig. 7

In contrast to serial kinematics, in parallel-kinematic systems all
the actuators act directly on the same platform (image: PI)

The Hexapod controller allows the user to set an arbitrary
point in space as center of rotation. This freely definable pivot
point is maintained independently of the motion, a feature
which has proven especially invaluable for optical adjustment.
This method allows extremely precise positioning of thephotonic components, and the so-called "first light" isachieved, based on the initial position feedback of thephotonics components supplied by the imaging system This
term states that optical signal continuity can be measured
and monitored.
This is a prerequisite for searching and detecting peaks in the
sub-micron range with a high level of accuracy. Successful finealignment is followed by an automated bonding cycle withepoxy resin, optionally with UV or thermal curing. This
customized pre-production automated solution for silicon
photonics reduces the entire manufacturing process to only afew minutes, which compares very favorably with the usual
40 minutes or more required today for manual production.
With their turnkey assembly and adjustment system, thespecialists for micro- and nanopositioning have contributed toa major advance in driving silicon photonics ahead andgetting closer to the needs of silicon photonics massproduction. It will be interesting to see how the future
develops.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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About PI
In the past four decades, PI (Physik Instrumente) with
headquarters in Karlsruhe, Germany has become the leading
manufacturer of nanopositioning systems with accuracies in
the nanometer range. With four company sites in Germany
and fifteen sales and service offices abroad, the privately
managed company operates globally.
Over 850 highly qualified employees around the world enable
the PI Group to meet almost any requirement in the field ofinnovative precision positioning technology. All keytechnologies are developed in-house. This allows thecompany to control every step of the process, from design
right down to shipment: precision mechanics and electronics
as well as position sensors.
The required piezoceramic elements are manufactured by its
subsidiary PI Ceramic in Lederhose, Germany, one of the
global leaders for piezo actuator and sensor products.
PI miCos GmbH in Eschbach near Freiburg, Germany, is a
specialist for positioning systems for ultrahigh vacuum
applications as well as parallel-kinematic positioning systems
with six degrees of freedom and custom-made designs.

Author

Dipl.-Phys. Steffen Arnold, Head of "Marketing and Products"
at PI (Physik Instrumente)

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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