Polymide V-groove joints for three - dimensional silicon transducers
Today, we can see a fast growing interest in silicon micromachined transducers following the ongoing
miniaturization trend around us. The sophisticated production methods associated with silicon
technology offer the possibility for low-cost highly miniaturized electro-mechanical devices.
However, the planar nature of the photolithography technique used in most silicon fabrication has a
large drawback when three-dimensional (3-D) microstructures are needed. This thesis presents a new 3-
D technique using polyimide V-groove (PVG) joints based on thermal shrinkage of polyimide in
V-grooves to overcome the planar limitation. These polyimide joints have been carefully investigated
and several important advantages compared to other techniques are demonstrated (i.e. very robust, selfassembly
small radii joints for accurate out-of wafer plane erection of silicon microstructures). Further
the new micro-joint can be used both in a static mode for 3-D sensor applications and in a dynamic,
actuator, mode. In the thesis two different applications are described.
The first application field is fluid dynamics and turbulence flows which are unsolved problems in
physics. Measurement and active control of turbulent flow fields are key issues in many technical
application areas. Miniaturized micromachined 3-D sensor with hot-wires in the same size as the
smallest turbulence scales can help researchers to study physical phenomena that are not yet
understood due to lack of sufficiently small sensors.
Development of a reliable fabrication process to fabricate the 3-D hot-wire sensors based on the
PVG-joint has successfully been realized. Experiments showed that the fabricated hot-wire sensors
have several important advantages over hand-made conventional metal hot-wire sensors. For example,
the fabricated silicon hot-wires have higher flow sensitive, response times smaller than 30 µs, no
drift over time, small hot-wire dimensions (500 × 5 × 2 µm3), potential for low cost fabrication
and array configuration. Turbulence characteristics of free-standing hot-wires fabricated by
micromaching have been investigated for the first time.
In the research field of micromechanics the focus has moved from single sensor and actuator devices
to more complex and sophisticated micro systems. The manufacturing approach for these small
micro-systems, consisting of assembly many small sub-components and micro-devices, is of great
importance for future success and expansion of microelectromechanical systems (MEMS). In
particular, micro-assembly is a key point for many micro-systems and one challenging technology is
the used of MEMS-based micro-robotics devices. The thesis contains a general review on both microrobotics
and three-dimensional microfabrication.
Several actuator applications are feasible with the new PVG-joint. In this thesis they are
exemplified by a micro-conveyer and the first MEMS-based walking micro-robot. The use of the PVG
joint with integrated heaters allows dynamic stroke up to 340 µm for a 1 mm long silicon structure,
using the large thermal expansion of polyimide. The lifetime exceeds 2x108 load cycles under 5 weeks
of continuous actuation. These polyimide joint actuators are used in asynchronously driven array
configuration where each actuator can be operated individually with integrated heaters. Several different
design in the form of micro-conveyers with maximum conveyance speed of 12mm/s and a load
capacity of 3500 µg and a robot with measured walking speed of 6 mm/s and a static load capacity of
6000 µg are presented.
Thorbjörn Ebefors, Instrumentation Laboratory, Department of Signals, Sensors and Systems (S3),
Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
iv Thorbjörn Ebefors
PVG Joints for Three-Dimensional Silicon Transducers v
I have found some errors in the papers included in this thesis (listed beneath). Although I have made
my best to avoid any errors there are undoubtedly several others and I sincerely apologize for those
that remain. I welcome hearing from readers about any factual errors or overlooked omissions in the
papers and publications included in this thesis. All mistakes and shortcomings, in particular in
language and style of presentation, are due myself as author.
Updates of this errata, and full information of the status of the submitted papers (i.e. Journal and page
information when/if they get published) will be available at the web site for this thesis at:
If you care to contribute to this errata, please send e-mail (for correct e-mail address see
School:Kungliga Tekniska högskolan
Source Type:Doctoral Dissertation
Date of Publication:01/01/2000