WO2008114199A2

WO2008114199A2 - An actuator device and a method of manufacturing the same

Info

Publication number: WO2008114199A2
Application number: PCT/IB2008/050992
Authority: WO
Inventors: Murray F. Gillies; Marc W. G. Ponjee; Stefano Cattaneo; Mark T. Johnson; Jacob M. J. Den Toonder; Judith M. De Goede; Dirk J. Broer; Johannes T. A. Wilderbeek; Grietje N. Mol; Wim Talen
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-03-19
Filing date: 2008-03-17
Publication date: 2008-09-25
Also published as: WO2008114199A3

Abstract

An actuator device (100) comprising a substrate (102), an electrode structure (105) provided in and/or on the substrate (102), and an actuator unit (107) being movable relative to the substrate (102) upon application of an electrical signal to the electrode structure (105), wherein the actuator unit (107) is made of a dielectric material.

Description

An actuator device and a method of manufacturing the same

FIELD OF THE INVENTION

The invention relates to an actuator device.

Moreover, the invention relates to a method of manufacturing an actuator device.

BACKGROUND OF THE INVENTION

Biochips for (bio)chemical analysis, such as molecular diagnostics, will become an important tool for a variety of clinical, forensic and food applications. Such biochips incorporate a variety of laboratory steps in one desktop machine. In many protocols that may be desired to be carried out on a lab-on-a-chip the transportation of fluid and in particular of the bio-particles within that fluid, is crucial. For example, in a fully integrated DNA lab-on-a-chip platform, the biological material has to be transported to a lysing stage and then to PCR chambers, before being taken to an analysis stage. There are a variety of actuation methods available for the transportation of the bio- fluid. These include electrical actuation, electrophoresis and electroosmosis, capillary movement, pressure driving via MEMS, thermal gradients, etc.

The technology of MEMS (micro-electro-mechanical systems) is related to devices comprising an electronic part and a micromechanical component.

US 2003/0036215 Al discloses micromechanical devices that are capable of movement due to a flexible portion. The micromechanical device can have a flexible portion formed of an oxide and a transition metal.

However, the operation of a MEMS being activated by applying an electric force to an actuator component may be complex and may lack reliability.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide an efficiently operable actuator structure.

In order to achieve the object defined above, an actuator device and a method of manufacturing an actuator device according to the independent claims are provided. According to an exemplary embodiment of the invention, an actuator device (particularly for handling a fluid) is provided, the actuator device comprising a substrate, an electrode structure provided in and/or on the substrate and an actuator unit being movable relative to the substrate upon application of an electrical signal to the electrode structure, wherein the actuator unit is made of (particularly consists of) a dielectric material (i.e. an electrically insulating material).

According to another exemplary embodiment of the invention, a method of manufacturing an actuator device (particularly for handling a fluid) is provided, the method comprising forming an electrode structure in and/or on a substrate, forming an actuator unit being movable relative to the substrate upon application of an electrical signal to the electrode structure, and forming the actuator unit (particularly completely) of a dielectric material (i.e. an electrically insulating material).

In the context of this application, the term "dielectric material" may denote an electrical insulator, i.e. a substance that is highly resistant to an electric current. When a dielectric medium interacts with an applied electric field, charges may be redistributed within its atoms or molecules. This redistribution can alter the shape of an applied electrical field both inside the dielectric medium and in the region nearby. A dipole moment of such a substance may interact with an (inhomogeneous) electric field (or an electric field gradient) generated by an electrode structure. Thus, the term "electrically insulating material" may particularly denote the fact that the actuator unit may be free of electrically conductive material such as metal. In contrast to this, the actuator unit may consist of a dielectric material, and may be preferably formed by two or more different materials having different values of permittivity (ε_r). The term "micro-electro-mechanical systems" (MEMS) may denote the technology of integrating mechanical elements, sensors, actuators, and electronics on a common substrate through microfabrication technologies. Micro-electro-mechanical systems may be devices and machines fabricated using techniques generally used in microelectronics, particularly to integrate mechanical or hydraulic functions, etc. with electrical functions. Micro-electro-mechanical systems may integrate mechanical structures with microelectronics. Applications include sample handling systems, medical devices, and microfluidic devices.

The term "sample" may particularly denote any solid, liquid or gaseous substance to be analyzed, or a combination thereof. For instance, the substance may be a liquid or suspension, furthermore particularly a biological substance. Such a substance may comprise proteins, polypeptides, nucleic acids, lipids, carbohydrates or full cells, etc.

The "substrate" may be made of any suitable material, like glass, plastics, or a semiconductor. According to an exemplary embodiment, it may be advantageous to provide a substrate which is partially or (essentially) entirely transmissive for an electromagnetic radiation beam such as a light beam for reading out a sensor surface. The term "substrate" may be thus used to define generally the elements for layers that underlie and/or overlie a layer or portions of interest. Also, the "substrate" may be any other base on which a layer is formed, for example a glass or metal layer. The term "permittivity" of a medium may particularly denote a physical quantity that describes how an electric field affects or is affected by the medium.

The term "sample chamber" may particularly denote a three-dimensional volume which is provided to accommodate a sample. This volume may be, for instance, in the order of magnitude of milliliters, microliters or nano liters. The term "actuator device" may particularly denote any device having a mechanically movable/bendable/turnable component which may be employed to handle (such as to mix or to transport) a fluid (such as a liquid, particularly an aqueous sample, or a gas). Such an actuator device may be in an inactive state, in which an actuator unit (such as an actuator beam) statically rests on a surface of a substrate or in defined relationship to a substrate. When the actuator unit is activated using an electrical signal applied to an electrode structure provided in the environment of the actuator unit, the actuator unit may be moved under the influence of a force (which may originate from dielectrophoresis), that is to say an electric force acting on a dielectric structure provided in an electric field.

The term "electrical signal" may particularly denote an electric current or an electric voltage, and can be alternating or constant over a period of time. Thus, the electric signal can be an AC signal or a DC signal. When the electrode structure comprises a plurality of electrodes, such as in a finger electrode configuration, each of the individual electrode units may be provided with a separate electrical signal, for instance in a manner that alternating electrodes are provided with signals having a phase shift of 180° (π), or that the voltage on every electrode is shifted by 90° (π/2) with respect to the neighboring electrode.

According to an exemplary embodiment of the invention, an actuator unit (such as a movable beam) may be provided consisting of an insulating or electrically non- conductive material, so that an actuation of such an actuator unit by electrical signals of an electrode structure may be performed based on the phenomena of dielectrophoresis. Therefore, an actuator structure may be formed from one or more purely dielectric material(s), wherein applying an electrical signal of a predefined frequency may define whether a repelling or an attracting force presently acts on the actuator unit. Thus, without the need to introduce metallic materials in the manufacture process, it is possible to selectively generate a force acting on the actuator unit having any desired sign.

According to an exemplary embodiment of the invention, dielectrophoretic actuation of a MEMS structure may be made possible. A MEMS structure may therefore be provided which consists of a film enclosing particles with are polarized differently than the film. Such a MEMS structure can be actuated by AC (alternating current) electrical fields for pumping and/or mixing of biological fluids. Such a structure may comprise or consist of a substrate of multiple electrodes that can be supplied with a high frequency voltage. The structure to be actuated can be, for example, a high permittivity polymer film encapsulating particles with a low permittivity or can be a low permittivity film with high permittivity particles. In the case of the high permittivity film, the film can be a hydrophilic material, which absorbs water and therefore has a high permittivity. Upon applying a high frequency electric field from the electrodes, the enclosed particles may be polarized differently to the film and, via the dielectrophoretic effect, experience either an attractive or a repulsive force in the direction of the substrate. Since the particles are embedded in the film, the film also experiences either an attractive of repulsive force and is accordingly actuated.

An advantage of such a system of actuation is that both attractive and repulsive forces can be generated on the actuator simply by switching the frequency of the applied voltage. This can be used to repel the actuator and therefore avoid sticking of the actuator at the substrate. Further, there is no top electrode required as in electrostatic actuation and therefore the number of required processing steps is reduced since all electrodes may be integrated onto the substrate and may be defined together in one photolithographic step. Since only a high frequency field is applied via the electrodes there can be no electrolysis. Beyond this, since high frequency fields may be used, liquids containing charged species (such as blood) can be actuated without shielding of the applied field.

Next, further exemplary embodiments of the actuator device will be explained. However, these embodiments also apply to the method of manufacturing an actuator device. The actuator unit (for instance a bendable beam) may be free of an electrically conductive material. Therefore, any metallic material may be dispensable in the actuator unit because exemplary embodiments of the invention are not based on electrical forces acting on charged carriers of a conductive material, but is based on the phenomena of dielectrophoresis. Therefore, particularly an inhomogeneous electric field generated by the electrode structure may generate a selectable force acting on the actuator unit even when the latter does not comprise metal.

The actuator unit may comprise a material having an electrical permittivity differing from an electrical permittivity of a fluid surrounding the actuator unit such as a fluidic sample to be analyzed. If this is the case, that is to say when the actuator unit has a polarizability or permittivity which differs from the polarizability or permittivity of a surrounding fluid (such as an aqueous solution) it is possible to generate an electrical force even when the actuator unit is immersed in the fluid. By taking this measure, it is possible to generate mixing or pumping forces acting on the fluid, for instance in the context of a miniature lab-on-chip for life science or diagnostic applications.

Thus, the actuator unit may particularly comprise a material having a permittivity differing from a permittivity of an aqueous solution as the fluid. Consequently, it is possible to handle or treat a liquid sample such as a biological sample comprising proteins, blood, DNA, cells, etc. using the actuator according to an exemplary embodiment of the invention.

The actuator unit may comprise a first component and a second component (and may additionally comprise one or more further components), wherein the first component and the second component may have a different value of permittivity. The first component and the second component may be layers arranged on top of each other, or may be structures embedded or mixed relative to one another. When the two components have a different permittivity, namely one has a lower permittivity than the other one, an actuator device may be provided in which the actuator unit may be selectively moved in any desired direction under the influence of dielectrophoresis. A refinement of the response characteristic of the actuator unit may be obtained by designing the latter from different components with different dielectrophoretic properties.

The first component may provide a (layer-like or volumetric) matrix in which multiple (for instance spherical) particles formed by the second component are embedded. Therefore, the first component may be some kind of film in which for instance bead- like particles may be dispensed or distributed.

Still referring to the previous embodiment, the first component may have a higher permittivity than the second component. Alternatively, the first component may have a lower permittivity than the second component. In other words, it is possible to embed particles having a high permittivity in a low permittivity matrix, or vice versa.

The first component may be formed by a polymeric film. Such a polymeric film may be easy in manufacture (for instance using a conventional spinning technology), may be biocompatible and may be insoluble in water.

Particularly, the first component may be formed by a hydrophilic film capable of absorbing water. By taking this measure, the permeability of the first component may be brought to a value close to that of water since water contributions of an aqueous solution may accumulate in an interior of such a sponge-like hydrophilic film. The second component may be formed, for instance, by latex particles. When latex particles are embedded in a polymeric film, a high qualitative actuator unit may be generated which is very sensitive with regard to dielectric forces generated by the electrode structure.

The second component may be formed by gaseous (for example air) inclusions in the first component. Therefore, the actuator unit may be realized as some kind of aerogel, wherein the permittivity of the air inclusions may differ from a permittivity of a surrounding material of the actuator unit.

The actuator unit may have a first end portion connected to the substrate and may have a second end portion being movable/bendable relative to the substrate under the influence of an actuating force. By taking this measure, activating the actuator unit may make the actuator unit act as some kind of pump, since, when the actuator unit moves, a surrounding fluid may be moved as well under the influence of the mechanical moving actuator unit.

The electrode structure may comprise a plurality of individually controllable electrode units. For instance, such electrode units may be individual fingers of a finger electrode structure or an interdigitized structure. For example, each of the fingers may be supplied with a separate electrical excitation signal, so that a complex motion structure of the actuator unit may be obtained.

The electrode structure may be activatable by applying the electrical signal to the electrode structure to generate an adjustable force acting on the actuator unit. Particularly, by varying the frequency of an (AC) electrical signal, it may be adjusted whether the actuator unit is attracted by the electrodes or is repelled therefrom. For this purpose, the frequency may be selected to be larger or smaller than a so-called transition frequency (see also Fig. 4 and corresponding description). The substrate may but not necessarily comprise an electrically insulating layer between the electrode structure and the actuator unit. Such an electrically insulating layer which may be made, for instance, from silicon oxide (SiO₂) or silicon nitride (S13N4) may allow to avoid undesired electrolysis effects on the electrode structure. The actuator device may be adapted as a microfluidic device, that is to say as a device dimensioned, designed (regarding materials), capable or adapted to treat or handle microfluidic samples.

The actuator device may be a micro-electro-mechanical system (MEMS), for instance a micro-electro-mechanical pump. Such a micro-electro-mechanical pump may pump a fluid by moving the actuator unit in a specific direction. This will carry particles of the fluidic sample along the motion direction of the actuator unit. The MEMS may also be a micro-electro-mechanical fluid mixer. When the actuator unit is provided in a sample chamber in which two or more components shall be mixed together, oscillation of the actuator unit by generating alternating attracting and repulsive forces may mix the individual components. The MEMS may also be a microfluidic channel through which the fluidic sample is conveyed under the transporting influence of the moving actuator unit. The MEMS may also be a microfluidic valve for selectively opening or closing a fluidic path.

The actuator device may be a sensor device (particularly a biosensor device), a biochip, a lab-on-chip, an electrophoresis device, a sample transport device, a sample mix device, a cell lysing device, a sample washing device, a sample purification device, a sample amplification device, a polymerase chain reaction (PCR) device, a sample extraction device or a hybridization analysis device. Particularly, the microfluidic device may be implemented in any kind of life science or diagnostic apparatus.

The actuator device may be adapted in such a manner that the electrode structure is activatable by applying an electrical signal, generated by an electrical signal generator arranged externally of (i.e. off or apart from) the actuator device, to the electrode structure to generate an adjustable force acting on the actuator unit. In other words, it is possible to apply different types of electrical signals to the device, but it is not necessary that the signals are generated on the device. Indeed, particularly for very high frequencies it may be more appropriate that the signals are generated externally and are simply routed to the required actuator using wires and electrical switches (such as thin film transistors).

Next, further exemplary embodiments of the method of manufacturing an actuator device will be explained. However, these embodiments also apply to the actuator device. The particles (forming a second component of a multi-component dielectric actuator beam structure) may be mixed with a solution from which the matrix (forming a first component of a multi-component dielectric actuator beam structure) is formed by spin coating. In other words, before a solution for forming the matrix is hardened, spherical particles may be added during the spin coating procedure. This may result in a structure of homogeneously distributed particles surrounded by the film obtained by hardening the solution.

Alternatively, the matrix may be formed by spin coating, and the particles may be supplied to the matrix after the spin coating procedure. In other words, after hardening the matrix by spin coating, the particles may be added and may distribute within the matrix in a self-organizing manner.

Further alternatively, the particles may be formed as air- filled cavities in the matrix. These air- filled cavities may have a different permittivity than the surrounding material. According to an exemplary embodiment of the invention, a polymer film may be rolled out on a substrate of a biochip on/in which one electrode (or multiple separately addressable electrodes) is provided. When applying an electric field (particularly an alternating electric field), electric dipoles may be induced in the film so that an electric field is capable of generating a force acting on the polymer film. Thus, undesired effects resulting from electrolysis may be suppressed, and also electrically conductive samples (such as blood) may be treated with such a device.

Appropriate films for such a use may be polymeric films (such as films made of polyimide). Such films may have a thickness of several micrometers and may have an extension in length and width of tens to hundreds of micrometers. In such a film, beads may or may not be embedded. Such beads can be made of polystyrene and may have a dimension in the order of magnitude of hundreds of nanometers to several micrometers. Of course, other dimensions and materials are possible as well. The actuator film should be made of a material which is sufficiently flexible (and should therefore have a suitable Young modulus) to roll out under the influence of applied electric fields. It may be advantageous that the permittivity/polarizability of the actuator film differs sufficiently from the permittivity/polarizability of the surrounding medium such as a fluidic sample.

An biochip may be fabricated from one of the well-known large area electronics technologies, such as a-Si, LTPS (low-temperature polysilicon) or organic technologies. The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Fig. 1 shows an actuator structure according to an exemplary embodiment of the invention. Fig. 2 shows a conventional MEMS structure.

Fig. 3 shows an SEM image of a conventional actuator.

Fig. 4 schematically illustrates a dependency of a dielectrophoretic force on frequency, levitating particles (left hand side), and particles attracting to substrate (right hand side). Fig. 5 illustrates electrolysis occurring with electrostatic actuation.

Fig. 6 shows a MEMS device according to an exemplary embodiment of the invention.

DESCRIPTION OF EMBODIMENTS The illustration in the drawing is schematical. In different drawings, similar or identical elements are provided with the same reference signs.

In the following, referring to Fig. 1, a micro-electro-mechanical device 100 according to an exemplary embodiment of the invention will be explained.

The MEMS 100 is an actuator device for handling a fluidic sample 101 filled in a sample chamber defined or limited by a substrate 102 as well as by a lateral wall 103. The fluidic sample 101 may be a biological sample including molecules 104 to be detected.

Integrated within the substrate 102, a plurality of electrodes 105 are provided, wherein an alternating voltage U(f) may be applied to each individual one of the electrodes 105. For this purpose, a voltage supply unit 106 is provided which is capable of applying a corresponding or assigned one of exciting voltage signals U(f) to each of the electrodes 105 separately. In this context, U denotes an electric voltage and f denotes the frequency of the voltage.

Fig. 1 further illustrates an actuation beam 107 which is shown in a resting state (indicated with solid lines) and in an elongated state (indicated with dotted lines), wherein application of a corresponding electric signal to the electrodes 105 may cause the actuator beam 107 to move from one of the two states to the other one, or vice versa, as indicated by an arrow 108.

The actuator beam 107 consists of a dielectric material, that is to say an electrically non-conductive material in which a dipole moment may be induced in the presence of an external electric field. It is also possible to use a material for the actuator beam 107 which comprises permanent dipoles.

More particularly, the actuator beam 107 comprises a film or matrix 109 made of a polymeric material, wherein a plurality of particles 110 made of latex are embedded in the matrix 109. Since the polymeric material of the film 109 and the latex beads 110 have different values of the electric permittivity, application of a corresponding electric field by the electrodes 105 may cause selectively an attracting or a repulsive force between the electrodes 105 and the actuator beam 107.

The actuator beam 107 has a first end portion 111 connected to the substrate 102 and has a second end portion 112 which is freely movable relative to the substrate 102.

In the following, it will be described in more detail how a biochemical detection procedure can be carried out using the MEMS device 100.

The sample 101 to be analyzed comprises the particles 104. In Fig. 1, the particles 104 are presently accumulated on a left-hand side where they can be brought to a desired temperature using a heater 113. The heater 113 can be controlled by a control unit 114 such as a CPU (central processing unit) or a computer. The heater and other electrical components can also be controlled via a Large Area Electronics (LAE).

Furthermore, the control unit 114 also controls the voltage supply unit 106 to apply a specific sequence of electrical signals to the electrodes 105. After having brought the sample 104 to a desired temperature, a motion procedure may be carried out so that the actuating beam 107 acts as a pump to pump the molecules 104 to be detected from the heating position (that is to say close to the heating element 113) to a sensing position, that is to say to a sensor active surface 115 provided on the right-hand side of Fig. 1. At this sensor active surface 115, a plurality of capture molecules 116 are immobilized which may hybridize with the particles 104 (such a hybridization event is not shown in Fig. 1).

After hybridization, the particles 104 having fluorescence labels 117 attached thereto, may be irradiated with electromagnetic radiation generated by an electromagnetic radiation source such as a lamp or a laser 118. Fluorescence light emitted by the fluorescence labels 117 may be detected by a detector 119 such as a CCD device or a photodiode.

As can be taken from Fig. 1, the control unit 114 controls the heater 113, the voltage supply unit 106 and the sensor active surface 115 (if desired), but may also coordinate the lamp 118 and the detector 119.

Furthermore, an input/output unit 120 may be provided which allows a user to control and monitor an assay in accordance with specific user-defined preferences. The input/output unit 120 may comprise a display device such as a cathode ray tube, an LCD device, a plasma device, etc. Furthermore, input elements may be provided such as a keypad, a joystick, buttons, or even a microphone of a voice recognition system.

Therefore, by automatically actuating the electrically insulating actuator beam 107, a fluid transport of the sample 104 can be performed in the context of a biochemical experiment.

In the following, some aspects will be explained which may be useful for a detailed understanding of exemplary embodiments of the invention.

Recently, polymer composite structures may be used as fluid actuators. Electrostatically actuated polymer composite structures (PoIyMEMS) may be used for the manipulation of biological fluids. These structures can be seen in schematic cross-section in Fig. 2. Fig. 2 illustrates a MEMS 200 having a substrate 201, an under-electrode 202, an insulator 203 and an actuator unit 204 formed by a polyimide layer 205 and a chromium top electrode 206.

The structure 200 consists of the under-electrode 202 covered by an insulator 203 (for instance SiO₂ or acrylate film), and a second insulating film 205 (for instance polyimide or acrylate) also covered with an electrode 206. The second film 205 is structured and freed from the substrate 201 to 203 by photo-lithography and sacrificial layer etching. Upon applying a voltage difference between the two electrodes 202 and 206, the film 204 can overcome the force caused by internal stress and unroll. When the voltage is removed the film 204 rolls up again to its original position. The structures can be between 15 μm and 100 μm in length.

Fig. 3 shows a micrograph 300 of such a film in the rolled up state.

The structures can easily be actuated at frequencies of 20 Hz to 30 Hz, even in the presence of a fluid. This has been demonstrated for insulating silicone oil. It has also been shown that such structures can be used to mix fluids efficiently (see V.V. Khatavkar, P. D. Anderson, H.E.H. Meijer, J.M.J, den Toonder: "modeling micro-actuator motion in a micro- channel for local mixing", Poster presentation at the Gordon Conference on Microfluidics, August 2005, Oxford, UK). It is possible to combine a matrix array for electrostatic actuation. It is also possible to use pulsed AC driving of these polyMEMS structures 200 in order to avoid electrolysis and shielding of the electrodes 206 by the ions in the sample solution. However, the actuation principle is still electrostatic with the actuator always being unrolled with the application of the electrical potential as the actuation force is independent of the polarity of the potential.

An alternative to electrostatic actuation is magnetic field actuation though this tends to consume high amounts of power.

The principle of electrophoresis is relatively well known and easily understood. It is when charged particles are transported via an electrical field. There is, however, a different force that can be used to directly transport particles. This force is called dielectrophoresis and is possible when the polarisability of the particle is substantially different from that of the medium in which it is located. In the case of a water based solution the permittivity is approximately 80, and therefore many particles with a lower permittivity, such a latex beads, biological cells and hollow spheres can be transported. However, both surface conductivity and bulk conductivity may also play a role in determining the cross-over frequency of particles. For a spherical homogeneous dielectric particle suspended in an aqueous medium the dielectrophoretic force F_DEP above an array of inter digitized finger electrodes is given by:

F D₁ EP = 2πεJ - | R_Q[K(w)]AV² e ² (1)

where ε_m is the permittivity of the medium, r is the particle radius, d is the periodicity of the electrodes, A is a constant pertaining to the electrode geometry (A=2.76 for a planar parallel electrode array), K(w) the Clausius-Mossotti factor, V is the voltage and h is height of the particle above the electrodes. The dependence on the permittivity of the particle is incorporated in the Clausius-Mossotti factor. For a positive dielectrophoretic force F_DEP, particles are attracted to high field strength regions on the substrate while a negative dielectrophoretic force F_DEP results in particles collecting in the low field regions. A transition frequency between a negative and a positive dielectrophoretic force F DEP (see diagram 400 of Fig. 4) is known as the cross-over frequency and can vary between a few hundred kHz and several MHz depending on the conductivity, the dielectric constants of the medium and particle, and the size of the particle. Referring to Fig. 4, the particles 411 are situated above a linear array of interdigitzed electrodes 412 then they are either suspended at a height above the substrate 413 (image 410 in Fig. 4) or pulled down onto the substrate 413 (image 420 in Fig. 4). Which one of these states is obtained is dependent on the frequency of the applied voltage to the electrodes 412. It is inherent with electrostatic force modulation that the application of electrical fields always leads to an attractive force between the electrode 206 of the actuator 204 and the under electrode 202. A consequence of this is that the actuator 204 can never be repelled from the substrate 201 and is therefore prone to sticking. While the chances of sticking can be reduced by increasing the internal stress of the polyimide layer 205 this also increases the voltage needed to unroll the film 204 (this is in many cases already >80 V and should not be further increased). A second problem is that electrolysis can quickly occur, see image 500 in Fig. 5.

In order to avoid or suppress this the SiO₂ insulator 203 can be made of extremely high quality in order to avoid any leakage current. This is non-trivial considering that the insulator 203 is constantly submerged in water.

According to an exemplary embodiment of the invention as shown as a MEMS device 600 in Fig. 6, it is possible to incorporate particles 110 of a different polarisability into an actuator film 109 which is situated on an array of finger electrodes 105. The film 109 itself should be of a high permittivity (if the particles 110 are a low permittivity) or be fully permeable to water (for instance a hydrogel) so that it has the effective permittivity of water. Alternatively, the particles 110 can be of a high permittivity and the film 109 of a low permittivity. An alternating voltage is applied to the finger electrodes 105 with every second electrode 105 having a 180° phase difference from the preceding electrode 105. The film 109 in which the particles 110 are embedded is actuated together with the particles 110. An insulator is denoted with reference numeral 601.

To calculate the force exerted on one particle 110 of latex, it is possible to use formula (1), with ε_m= 80 x 8.85xlO^"12, d = 10 μm, r = 1 μm, h = 10 μm, Re[K(w)] = 1, V = 10 and A = 2.76. The force on a particle 110 is then calculated to be IxIO ⁹N. For comparison the electrostatic force on a rolled-out sheet of foil with electrodes on both sides is given by;

Tj insulator

(2)

2t^l

where in this case A is area, ε_m is the permittivity of the insulator, V the voltage and t the thickness of the insulator. For an area of 1 m², a voltage of 10 V and thickness of 10 μm then the force is 18 N. The number of particles therefore required for the dielectrophoretic force to be equal to the electrostatic actuation is then 1.7 x 10¹⁰ per m². The total volume that these particles is 7.IxIO^"8 m³. Thus for a Im² film of 10 μm then the fraction of particles in the film is 7%. This is only a rough calculation but illustrates that the magnitude of the dielectrophoretic force is sufficient to match that of traditional electrostatic actuation and can therefore actuate the film.

According to an exemplary method of incorporating the particles 110 into the film 109 is simply to mix the particles 110 with the solution from which the film 109 is to be spin coated. This will lead to a homogenous distribution of the particles 110 through the film 109. It may be advantageous to use latex particles which have active groups attached in order to cross-link to the film 109 material and so hold the particles 110 in place.

According to another exemplary embodiment of the invention, rather than mixing the particles 110 in the material from which the layer 109 is spun it is also possible to spin the material. The material 109 and the particles 110 can be chosen to adhere specifically to each other. After spinning of the film 109 a suspension containing the particles 110 can be flushed through the sample and self-assembly will occur on the surface of the film 109. While materials can be chosen to adhere to each other it is also possible to mix a material through the film 109 that contains a reactive group. The group for which it is reactive may then be attached to the particles.

According to another exemplary embodiment of the invention, it is possible to create different volumes of different permittivity within the film 109. Any other method which also results in this would also be acceptable, for example air filled cavities in the film 109 as in an aerogel.

It is also possible to create a DEP force on a homogeneous film which is impermeable to water and has a different permittivity from the medium. Finally, it should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of software or hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. An actuator device (100), the actuator device (100) comprising: a substrate (102); an electrode structure (105) provided in and/or on the substrate (102); an actuator unit (107) being movable relative to the substrate (102) upon application of an electrical signal to the electrode structure (105); wherein the actuator unit (107) is made of a dielectric material.

2. The actuator device (100) according to claim 1, wherein the actuator unit (107) is free of an electrically conductive material and/or is free of a semiconducting material.

3. The actuator device (100) according to claim 1, wherein the actuator unit (107) comprises a material having a permittivity differing from a permittivity of a fluid (101) surrounding the actuator unit (107).

4. The actuator device (100) according to claim 1, wherein the actuator unit (107) comprises a material having a permittivity differing from a permittivity of water.

5. The actuator device (100) according to claim 1, wherein the actuator unit (107) comprises a first component (109) and a second component (110), wherein the first component (109) and the second component (110) have a different permittivity.

6. The actuator device (100) according to claim 5, wherein the first component (109) provides a matrix in which particles forming the second component (110) are embedded.

7. The actuator device (100) according to claim 6, wherein the first component (109) has a higher permittivity than the second component (110).

8. The actuator device (100) according to claim 6, wherein the first component (109) has a lower permittivity than the second component (110).

9. The actuator device (100) according to claim 6, wherein the first component (109) is formed by a polymer film.

10. The actuator device (100) according to claim 6, wherein the first component (109) is formed by a hydrophilic film capable of absorbing water.

11. The actuator device (100) according to claim 6, wherein the second component (110) is formed by latex particles.

12. The actuator device (100) according to claim 6, wherein the second component (110) is formed by gaseous inclusions within the first component (109).

13. The actuator device (100) according to claim 6, wherein the particles forming the second component (110) have an electrical conductivity differing from an electrical conductivity of a fluid (101) surrounding the actuator unit (107).

14. The actuator device (100) according to claim 1, wherein the actuator unit (107) has a first end portion (111) coupled to the substrate (102) and has a second end portion (112) being freely movable relative to the substrate (102).

15. The actuator device (100) according to claim 1, wherein the electrode structure (105) comprises a plurality of individually controllable electrode units.

16. The actuator device (100) according to claim 1, comprising an electrical signal generator (106), wherein the electrode structure (105) is activatable by applying the electrical signal to the electrode structure (105) using the electrical signal generator (106) to generate an adjustable force acting on the actuator unit (107).

17. The actuator device (100) according to claim 1, adapted in such a manner that the electrode structure (105) is activatable by applying an electrical signal, generated by an electrical signal generator (106) arranged externally of the actuator device (100), to the electrode structure (105) to generate an adjustable force acting on the actuator unit (107).

18. The actuator device (100) according to claim 16 or 17, wherein the electrical signal is an alternating electrical signal having an adjustable frequency, wherein adjusting the frequency using the electrical signal generator (106) adjusts the force acting on the actuator unit (107) to be selectively attracting or repulsive.

19. The actuator device (100) according to claim 1, wherein the substrate (102) comprises an electrically insulating layer between the electrode structure (105) and the actuator unit (107).

20. The actuator device (100) of claim 1, adapted as a microfluidic device.

21. The actuator device (100) of claim 1, adapted as a micro-electro-mechanical system, particularly as one of the group consisting of a micro-electro-mechanical pump, a micro-electro-mechanical fluid mixer, a microfluidic channel, and a microfluidic valve.

22. The actuator device (100) of claim 1, adapted as at least one of the group consisting of a sensor device, a biosensor device, a biochip, a lab-on-chip, an electrophoresis device, a sample transport device, a sample mix device, a cell lysing device, a sample washing device, a sample purification device, a sample amplification device, a polymerase chain reaction device, a sample extraction device, and a hybridization analysis device.

23. A method of manufacturing an actuator device (100), the method comprising: forming an electrode structure (105) in and/or on a substrate (102); forming an actuator unit (107) being movable relative to the substrate (102) upon application of an electrical signal to the electrode structure (105); forming the actuator unit (107) of a dielectric material.

24. The method of claim 23, wherein the actuator unit (107) is formed based on a first component (109) and a second component (110) having different values of permittivity, wherein the first component (109) provides a matrix in which particles forming the second component (110) are embedded.

25. The method of claim 24, wherein the particles are mixed with a solution from which the matrix is formed by spin coating.

26. The method of claim 24, wherein the matrix is formed by spin coating and the particles are supplied to the matrix after finishing the spin coating.

27. The method of claim 24, wherein the particles are formed as air- filled cavities within the matrix.

28. The method of claim 23, comprising forming a large area electronics platform, particularly low-temperature polysilicon, for addressing electrical components on the actuator device (100) .