Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Meso-Scale Actuator Design For The Integrated Dynamic
Alignment Of A Lenslet Array Within a Package
Stefan Wilhelm, Robert W. Kay, Marc P.Y. Desmulliez
Microsystems Engineering Centre (MISEC),
Institute for Integrated Systems (IIS),
School of Engineering and Physical Sciences, Heriot-Watt University,
Edinburgh EH14 4AS, Scotland, United Kingdom
Tel: +44 (0)131-451-8316
Keywords- LTCC, actuator, packaging, optical lenses
Abstract- This paper describes the design of an LTCCprocess
compatible meso-scale actuator for the six degrees of
freedom dynamic adjustment of micro-optical components, in
particular the alignment of a microlens array on top of a UV-
LED array. The lens array is specified to have an active area of
3mm x 3mm, the GaN array is 5mm x 5mm x 450!m. The focal
length is 65!m. The actuator must enable the collimation or
the focusing of the optical beams emanating from the LED array.
INTRODUCTION
A great variety of micro-devices encompasses multiple
interacting electronic, electro-mechanical, electrochemical
or optoelectronic components that require to be aligned statically
or dynamically (real-time). Static alignment can be
achieved with the help of high precision pick-and-place machines
with control feedback combined with a bonding process,
such as U.V. curable glue or flip-chip bonding using
reflowed solder balls. There are however instances where an
alignment has to be performed after the sealing of the package.
In such cases, structures with temporary actuation functionalities
designed within the micro-devices can be exposed
to external fields, providing thereby precise positioning
with the help of external or temporary internal feedback.
Dynamic alignment requires the manufacturing of permanent
actuators within the device and must fit the requirements
for power consumption, response time, force, deflection
range and long term reliability. Conventionally, the
function of the package is to provide electrical interconnection,
heat transfer and protection against mechanical, electromagnetic
and chemical influences. The additional ability
of the package to provide actuation and feedback elements
for aligning statically or dynamically opens up interesting
opportunities for new applications such as the microscope
on a chip, and greater ease of packaging by relaxing positioning
tolerances at the assembly stage. This paper aims to
offer an example of such a meso-sale actuation for optoelectronic
application using Low Temperature Cofired Ceramics
(LTCC). In that respect, a MEMS post process based solution
for the alignment of the microlens array has already
been reported in [1].
LTCC is an established multi-layer-process, which enables
to integrate electrical, fluidic or optical interconnections
and passive circuit components together with mechanical
structures in one solid ceramic body. Applications include
electrical packaging, RF-systems, micro-fluidics [2],
sensors [3] and actuators [4]. The 3D laminated device is
composed of paper-thin flexible sheets consisting of alumina,
glass and organic binders [5]. These so-called green
sheets can encompass layer-interconnection vias, cavities
and flexures, whose patterning can be performed using laser-machining,
powder blasting [6], punching and embossing
[7]. Metal tracks, resistors, solder masks, sacrificial inlays,
high-! materials and magnetic components like ferrite
[8] can be applied using thick-film screen-printing. After
being separately processed, the layers are laminated and cofired
into a single body at temperatures of approximately
900ºC.
The variety of applicable materials and the standardized
process make LTCC a preferred candidate for a meso-scale
actuator. The challenge is to devise a low-cost LTCCprocess
compatible design, which compensates for the accuracy
limits of the process whilst satisfying the requirements
of maximum stroke of 10!m for the application envisaged.
DESIGN OF THE PACKAGE ACTUATOR
Six degrees of freedom actuation of the optical system requires
the generation of translational forces and momentums
for three linear independent axes. In macro manipulators,
this is often realized by cascading independent polar
and linear axes. As complex three-dimensional structures
increase significantly the complexity of the LTCC manufacturing
process, actuation elements and restoring force elements
were selected, which can be placed “in plane” by
structuring single layers using screen and stencil printing.
Hence, the device requires planar actuation elements that
generate lateral and vertical forces. The optical system can
be rotated and tilted by generating these forces at a specified
distance of the rotation/tilt centre point.
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