Download Polymer Micro Actuator

Gih-Keong Lau
Polymeric Thermal Actuator
For Effective In-plane Bending
Delft University of Technology
Precision and Microsystems Engineering
Mekelweg 2, 2628 CD Delft, The Netherlands
Tel: +31 15 2786547 Fax: +31 15 2783910
Email: [email protected]
Introduction
A novel thermal actuator design is proposed to
accomplish power-efficient in-plane bending. It
combines a metallic heater, a heat conducting structure
and an insulating polymer with a high thermal
expansion coefficient (CTE) . This composite design is
different from a conventional U-shape design with a hot
arm and a cold arm made of a single material [2].
Objective
The new design aims to achieve effective in-plane
actuation by improving heat transfer across a thick layer
of insulating layer and by transverse constraint. In
addition, it is aimed to reinforced the softer polymer
with the stiff microstructures.
Approach
Fig. 1 shows the novel design. The asymmetric
meandering structure is made of a heat conductive
silicon. It extends through the full thickness of the
polymer. Its top is covered by an aluminium film. SU8 is
selected as expansion material for its high CTE and its
considerable Young’s modulus.
Resistive heater
Current
Polymer confined in the gaps by the meandering
structures is similar in configuration to the parallel-plated
polymer strip. It can move more freely perpendicular to
the plate but less transversely. As a result of the plate
constraint, volumetric thermal expansion is accumulated
mostly in the perpendicular direction, resulting a higher
constrained linear CTE than a free linear CTE. In addition,
the longitudinal stiffness increases due to the transverse
constraint. The constraint effectively improves the
actuation capability of the thermal expandable polymer.
Results
A 500-µm long, 50-µm deep micro-machined
demonstrator is tested, showing large lateral
displacement (25um) (see Fig. 3) at a low voltage (less
than 2V) and low power (25 mW). This presents a
tremendous enhancement in displacement generation at
a low driving power for thermal actuators.
As it is power-efficient, the new design can potentially be
used for a wider range of applications, as compared to
conventional thermal actuators made of silicon or metals.
Potential applications include low-power micropositioning, low-temperature object manipulation, and
micro-instruments for material testing.
25
(a)
Heat conductor
(b)
Fig. 1 Schematic drawing shows (a) current flow path on top of the
composite actuator (b) a whole bending actuator comprising of Al/Si/SU8
composite.
Tip displacement (um)
Insulating
polymer
Insulating
polymer
20
15
10
5
0
0
0.5
1
Voltage (V)
1.5
2
Fig. 3 Lateral tip motion of the thermal actuator when activated
Fig. 2 Composite actuator devices: (left) SEM micrograph showing a
microfabricated device of SU8/Si composite before being released from
substrate; (right) optical image showing an activated actuator
undergoing a large magnitude of bending
Delft Centre for Mechatronics and Microsystems
Acknowledgement
This project is supported by the Delft Centre for
Mechatronics and Microsystems.
Delft University of Technology