Powerful polymeric thermal microactuator with embedded silicon microstructure

Lau, Gih Keong; Goosen, J.F.L.; Keulen, Fred van; Duc, Trinh Chu; Sarro, P.M.

doi:10.1063/1.2742599

Cited by 26 publications

(23 citation statements)

References 14 publications

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“…doi:10.1016/j.ijsolstr.2008.05.016 insulator. Experimental testing of a micro-machined device confirmed that the polymeric actuator with the embedded skeleton exhibits excellent actuation capability (Lau et al, 2006a(Lau et al, , 2007b.…”

Section: Introductionmentioning

confidence: 57%

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Thermo-elastic behavior of a polymeric layer bonded between rigid interfaces

Lau¹,

Goosen

Keulen

2008

International Journal of Solids and Structures

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a b s t r a c tA highly expandable polymeric material have been combined with a stiff skeleton material to form a powerful design of thermal micro-actuators. The bond interfaces with the skeleton laterally restrain deformation of the polymer and consequently direct its volumetric expansion in the transverse direction. A complete lateral constraint at the infinite bond width could maximize the apparent thermal strain of the bonded polymer. However, it is not sure how much strain enhancement can be achieved using a finite bond width. To answer this, we resort to an approximate thermo-elastic model and solve it using the mean-pressure method. This model leads to closed-form solutions to the thermally induced strains and stresses in a bonded polymer layer between rigid interfaces. The closed-form solution shows that the apparent strain of a bonded layer depends on the aspect ratio of the bond width to the layer thickness, besides Poisson's ratio. Furthermore, it further shows that a bond width five times the thickness of the SU-8 epoxy layer is sufficient to attain 95% of the maximum apparent strain, which is obtained at the infinite width.

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Section: Introductionmentioning

confidence: 57%

“…Such integration exploits the large thermal expansion and stiffness mismatches between the two materials to enhance the actuation performance of the polymer. This leads to a new class of powerful thermal micro-actuators (Lau et al, 2006a(Lau et al, , 2007b.…”

Section: Introductionmentioning

confidence: 99%

Thermo-elastic behavior of a polymeric layer bonded between rigid interfaces

Lau¹,

Goosen

Keulen

2008

International Journal of Solids and Structures

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“…The confinement of the polymer material causes a concentration of the thermal strains in the in-plane direction thus enhancing the total actuator displacement [7].…”

Section: Micro Gripper Design and Fabricationmentioning

confidence: 99%

“…The actuator is 85 µm wide and 30 µm thick. These dimensions have been chosen according to the analysis presented in [7] such that there is an effective confinement of the polymer material and a large transverse heat conduction coefficient, thus improving heat spreading across the insulating polymer. An integrated aluminium heater is defined on the top of the silicon structure.…”

Section: Micro Gripper Design and Fabricationmentioning

confidence: 99%

Finite element modelling and experimental characterization of an electro-thermally actuated silicon-polymer micro gripper

Krecinic

Duc

Lau

et al. 2008

J. Micromech. Microeng.

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This paper presents simulation and experimental characterization of an electro-thermally actuated micro gripper. This micro actuator can conceptually be seen as a bi-morph structure of SU-8 and silicon, actuated by thermal expansion of the polymer. The polymer micro gripper with an embedded comb-like silicon skeleton is designed to reduce unwanted out-of-plane bending of the actuator, while offering a large gripper stroke. The temperature and displacement field of the micro gripper structure is determined using a two-dimensional finite element analysis. This analysis is compared to experimental data from steady-state and transient measurements of the integrated heater resistance, which depends on the average temperature of the actuator. The stability of the polymer actuator is evaluated by recording the transient behaviour of the actual jaw displacements. The maximum single jaw displacement of this micro gripper design is 34 µm at a driving voltage of 4 V and an average actuator temperature of 170 • C. The transient thermal response is modelled by a first-order system with a characteristic time constant of 11.1 ms. The simulated force capability of the device is 0.57 mN per µm jaw displacement.

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“…Moreover, the thermal expansion of this actuator is enhanced due to the constraint effect of polymer layers between rigid silicon plates. 3 A calculation of compressed displacement of a constrained rubber between two rigid surfaces based on the hydrostatic pressure is reported in Ref. 4.…”

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confidence: 99%

Polymer constraint effect for electrothermal bimorph microactuators

Duc

Lau

Sarro

2007

Applied Physics Letters

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The authors report on the analysis of the polymer constraint effect and its use for a micromachined electrothermal bimorph actuator. The actuated displacement is enhanced due to the polymer constraint effect. Both the thermal expansion and apparent Young's modulus of the constrained polymer blocks are significantly improved, compared with the no constraint case. The calculation that agrees well with experimental results provides the means to optimize the design of the constrained polymer stack electrothermal microactuator. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2779929͔ Thermal expansion of polymer is currently widely used in microactuators to produce large motion at low temperature. In most of the polymeric electrothermal actuators reported in literature, a thin metal layer deposited on the top surface of the polymer structures is employed as heater. 1,2 Hence, the heat transfer interface between the heater and the polymer is rather limited. Since the polymer layers have low heat conduction rate, the actuator dimensions need to be small enough to get a good vertical temperature profile in the structure. Consequently, the resulting motion is quite limited. Moreover, the unintended vertical movement couples and interferes with the desired lateral movement of the structures.In this letter, we report on a silicon-polymer electrothermal bimorph actuator with a large motion range. This actuator has a silicon comb finger structure with a metal heater on top. The gaps between comb fingers are filled with polymer ͓see Fig. 1͑a͔͒. When the heater is activated, the generated heat is efficiently transferred to the surrounding polymer through the deep silicon comb finger structures that have a large heat transfer interface area with the polymer layers. The polymer layers expand along the lateral direction causing bending displacement of the bimorph cantilever actuator. Moreover, the thermal expansion of this actuator is enhanced due to the constraint effect of polymer layers between rigid silicon plates. 3 A calculation of compressed displacement of a constrained rubber between two rigid surfaces based on the hydrostatic pressure is reported in Ref. 4. The hydrostatic pressure theory is expanded here by taking into account the thermal expansion of constrained polymer as a function of the ratio between the dimensions of the rigid plate and the thickness of the polymer block. Finally, the thermal displacement of the actuator is then calculated using bimorph bending theory.It is assumed that the plates have infinite length, the thickness of the polymer block h is much smaller than the width w of the plate ͑h Ӷ w͒, and the polymer is incompressible ͑Poisson's ratio S = 0.5͒. When the temperature of the structure changes by ⌬T degree, the volume thermal expansion of a polymer block is given by 5where V is the initial volume of the polymer block and ␣ T is the thermal expansion coefficient ͑CTE͒ of the polymer. In the case of no constraint, the volume of the polymer block expands in three dimensions, as indicated b...

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Powerful polymeric thermal microactuator with embedded silicon microstructure

Cited by 26 publications

References 14 publications

Thermo-elastic behavior of a polymeric layer bonded between rigid interfaces

Thermo-elastic behavior of a polymeric layer bonded between rigid interfaces

Finite element modelling and experimental characterization of an electro-thermally actuated silicon-polymer micro gripper

Polymer constraint effect for electrothermal bimorph microactuators

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