An electric based micro-fluidic device using active matrix principle

FIELD OF THE INVENTION

The invention relates to an electric based micro-fluidic device using active matrix principle, for the use in medical and health and wellness products, in particular biochips or bio-systems.

BACKGROUND OF THE INVENTION

Micro-fluidic chips are becoming a key foundation for these products. In all microfluidic devices, there is a basic need to control fluid flow, that is, fluids must be transported, mixed, separated and directed through a micro-channel system consisting of channels with a typical width of 0,1 mm. Various actuation mechanisms have been developed and are used. The US 2004124384 Al discloses an electrostatic deformable thin film, but as an opening and closing element of a micro valve.

SUMMARY OF THE INVENTION So it is the object of the present invention to achieve a programmable electrical actuator in microstructure, for the use in medical, health and wellness products, in particular biochips or bio-systems.

The stated object is achieved for electric based microfluidic device for biosensors by the features of patent claim 1. Further embodiments of this system are characterized in the dependant claims

2 - 10

The stated object is also achieved for operating such a system especially for biosensors, by characterizing features of a method of patent claim 11.

A further embodiment of this method is characterized in dependent claim 12. An electric based microfluidic device using active matrix principle, for the use in medical and health and wellness products, in particular biochips or bio-systems, wherein an 2-dimensional matrix array of poly-MEMS actuators (PMA) is arranged in a 2-dimenional system in which each single actuator is electrically/electronically steered independently from each other, in order to be able to generate a pattern of activation in the matrix. By

independent possibility of activation of each PMA, each pattern of activation can be generated, so that each kind of selected fluid pumping effect can be achieved. This is a very advantageous feature for the use in biosensor micro structured arrangement, in order to optimize a very selective steering of the micro-flux. An advantageous embodiment is, that the actuators of the matrix are divided into columns and rows, wherein each column- MEM is at one electronic port parallel be activated by an activation driver, each column-MEM (PMA) is at the other electronic port parallel be activated by a select driver, so that each actuator can be addressed by selecting a column and a row, so that the selected MEM (PMA) at the cross-point will be activated by these electrical 2-dimensional generation coordinates. By this each single PMA can be driven or activated in a very easy and effective way.

A further embodiment of the invention applies easy means, for predetermination and coordination of activation pattern, by applying electronic calculation and steering means, in order to calculate voltage steering signals for the actuator driver and the select driver, to access a predetermined activation pattern in the micro fluidic device.

A further advantageous embodiment of the invention is, that each PMA consist of a foil electrode and an activation electrode, wherein the activation electrode is accessed by a transistor switch, which base contact is switched in parallel to each other PMA of its row, and one of the source/drain-contacts is connected in parallel to the other column- PMA, and the other source/drain-contact is each connected to the activation electrode of its PMA. By using such thin film transistors, the system can be completely arranged on a common substrate or carrier.

This will be supported by the further embodiment in which each foil electrode is in galvanic contact with an overall common foil electrode. In a further embodiment, further electronic elements like temperature sensors and/or anemometer elements in microstructures and/or light emitting diodes are integrated on the array substrate. By this the array can be supported by local sensors, in order to optimize the activation of the array.

A further embodiment is, that in parallel to the foil-electrode/actuation- electrode-arrangement a memory element like a capacitor is applied, in order to hold electronically memory of a steered state of each PMA. By this, activation of the PMA can be generated only by a pulse signal. The capacitor holds memory of the activation position of the PMA.

The PMA can be formed or developed as a small coiled foil, or a small cylindrical tube, or what ever. Essential is, that these elements will be deformed by an activation signal, so that it can move fluids, as pumping through channels of cavities of microstructures. Finally, a method to operate an electric micro fluid device is advantageously be used, wherein in a calculation unit or in calculation means, signals or series of signals Vi as a function of time t are calculated and then be steered out by coordinated steering of the actuator driver and the select driver, in order to generate predetermined pattern of PMA activation. A Further embodiment of this method is given in that the signals of the further applied/integrated sensor elements are being recognized in evaluation of aforesaid steering signals.

DRAWINGS Different embodiments of the invention are shown in Fig. 1 to Fig. 6.

A convenient polymer micro-actuator geometry 1 that can be exploited is shown in Fig. 1. It shows a double layer composite structure consisting of a polymer film 2 (in this case an aery late) and a conductive film 3 (in this case chromium), made in our laboratory. The processing is tuned such that the structure curls upward, being attached at one end. When a voltage difference is applied between the electrode 4 underneath the actuator and the conductive film 3 that is part of the actuating structure, an electrostatic force will pull the structure towards the substrate. Consequently, it will roll out and flatten out on the substrate. When the voltage is removed the slab will return to its original curled shape by elastic recovery. The actuation effect is bi- stable, and the position of the actuator tip is a function of the applied voltage. For this particular PMA design, the "unroll" voltage Vun is 11 V, and the "elastic recovery" voltage Ver is 5V. These values can be tuned typically between IV and 100V depending on the dimensions and mechanical properties of the PMA.

It should be understood that the geometry sketched in Fig. 1 is just one possible embodiment, and many other geometries are conceivable: straight beams, cylindrical rods, etc. The actuation of the polymer micro-actuators in a (biological) fluid will induce fluid flow, i.e. fluid manipulation. A typical frequency that results in effective fluid flow is between 1 and 100 Hz. To achieve efficient fluid manipulation (transportation, mixing, routing, or other), it is essential that the micro-actuators, or groups of them, can be addressed individually. This would enable the creation of complex fluid flow patterns. The (groups of)

actuators could then be actuated slightly out of phase, creating e.g. a wave-like motion of the collective actuators which would result in a transporting flow. The out-of-phase actuation of groups of actuators will result in chaotic mixing patterns, if done with proper timing. Other, specific flow patterns can be achieved as well by controlled local addressing of the actuators. This asks for a means to create local electric fields at the positions of individual (groups of) polymer micro-actuators, i.e. the electrodes will have to be individually addressed. This description provides a solution to this requirement, using active matrix technology. Large area electronics, and specifically active matrix technology using for example Thin Film Transistors (TFT), is commonly used in the field of flat panel displays for the drive of many display effects e.g. LCD, OLED and electrophoretic.

Here the control of an array of electric actuators is improved, preferably based upon the poly-MEM (Micro Electro Mechanical) actuator (PMA) principles, specifically for use in a micro-fluidic device such as a biochip or bio-system. The PMA array may be controlled using the passive matrix approach. Preferably, the PMA will be controlled using a large area electronics based programmable electrode array. More preferably, the electrode array is arranged in the form of an active matrix array. It may however optionally comprise additional elements such as heating elements, other sensing elements such as photo-sensors, temperature sensors etc.

The device will be able to realize a variety of defined patterns of electrical actuation of the poly MEM elements. Preferably the device will further be able to realize a series of controllable dynamically changeable defined patterns of electrical actuation of the poly MEM elements. In preferred embodiments, it is desired to make use of the high addressing speed of the active matrix device to independently actuate any of the PMA at the preferred frequency ranges of 1-lOOHz described in the introduction. Fig. 2 shows a first embodiment of the invention as a circuit plan of the electrical features. In this first embodiment, we propose to generate defined patterns of electrical actuation of the poly MEM elements 1 by controlling the magnitude of the voltage at a set of actuation electrodes in the form of a passive matrix array. In this embodiment, the array of electrodes can be connected to external voltage drivers. This is shown schematically in Fig. 2. In order to realize this passive matrix layout, it is necessary that both the actuation and foil electrodes are structured in the form of lines orientated at an angle to each other. In the example of Fig. 2, the actuation electrodes have been structured in the form of columns, whilst the foil electrodes have been structured in the form of rows. In order for a passive matrix system to operate successfully, we require that the PMA exhibits a voltage threshold.

As shown in the introduction, this is the case; a voltage of around Vur is required to unroll the foil, whereby a voltage of around Vt will be insufficient to initiate the unrolling.

Using the examples of threshold discussed above, it is possible to configure a passive matrix PMA based electro-transport system. In this example, every PMA in the matrix comprises 2 electrodes, which are configured in the form of rows -the foil electrodes 4- and columns -the actuation electrodes 3 -to form an array of PMA.

The position numbers 3 for the actuation electrode and 4 for the foil electrodes are functionally equal with the nomenclature of the position numbers in Fig. 1.

Each row and each column can be individually attached to a voltage source. For example, the row electrodes may be connected to a select driver 10 -e.g. a standard-shift register similar to a gate driver for an AMLCD-, which can switch between OV and Vt. The column electrodes are then connected to the actuation driver 20. The actuation driver 20 could be just a standard voltage data driver as used for e.g. passive or active matrix liquid crystal displays (LCD), with outputs which may have either OV or (Vur- Vt) levels. Operation is as follows:

In the rest state, all row electrodes are set to OV. In this case, no PMA can be unrolled as the voltage across the electrodes cannot exceed Vt (i.e. below the threshold).

To unroll a given PMA, the row electrode associated with the row of PMA incorporating the required PMA is switched to -Vt. All other rows are held at OV. The voltage in the column electrode where the PMA is situated is set to its release voltage of +(Vur-Vt). The voltage across the electrode of the required PMA is now Vur, resulting in the unrolling of the PMA.

The voltage in all other columns is held at a voltage, which will not unroll the PMA (in this example OV). If the PMA need no longer be unrolled, the row electrode is again set to OV, at which point the PMA will roll up again.

It is also possible to actuate more than one PMA in a given row simultaneously by applying an actuation signal (voltage = Vur- Vt) to more than one column in the array (see Fig. 2). It is possible to actuate PMA in different lines by activating another row (row voltage -Vt) and applying an actuating signal (voltage = Vur- Vt) to one or more columns in the array.

A weakness of the passive matrix approach is that it is not possible to simultaneously and independently actuate PMA in different rows at the same time. This limits the number of actuation patterns which may be realized.

Fig. 3 shows a further embodiment. In this embodiment, it is proposed to generate a larger number of defined patterns of electrical actuation of the poly MEM elements 1 by independently controlling the magnitude of the voltage at a set of actuation electrodes. In the most simple embodiment, the array of electrodes can be connected to external voltage sources using the large area electronics as a simple switch 11, designed to route the voltage from the external sources to one or more of the electrodes. This is shown in Fig. 3 (top). For this embodiment, the switches could be realized as (thin film) transistor (TFT) switches (shown in Fig. 3 bottom), diode switches or MIM (metal-insulator-metal) diode switches, and addressing of one or more individual electrodes can be carried out using the well known active matrix driving principles.

In the case of a transistor based active matrix array, the operation of the illustrated device to independently control a single poly-MEM actuator (PMA) is as follows

In the non-addressing state, all select lines are set to a voltage where the switches are non-conducting. In this case, no PMA are being controlled.

To control a given PMA (and therefore causing it to roll or unroll), the switches in the entire line of compartments incorporating the required PMA are switched into the conducting state (by e.g. applying a select signal).

The control signal (e.g. a voltage) in the column where the PMA is situated is set to its desired level. This signal is passed through the switch to the actuation electrode of the PMA, resulting in the PMA changing its form (i.e. unrolling).

The control signals in all other columns are held at a level which will not change the form of the remaining PMA of the row (in this example, they will remain in their rolled state). The select signals of all other rows will be held in the non-select state, so that the other PMA are attached to the same column via non-conducting switches and will not be controlled.

After the PMA is set into the desired state, the switches in the line are again set to the non-conducting state, preventing further change in the shape of the PMA (unless the voltage across the PMA leaks away, at which point the PMA rolls up again).

The device will then remain in the non-addressed state until the following control signal is required to change the form of the first or another of the PMA, at which point the above sequence of operation is repeated.

It is also possible to control more than one PMA in a given row simultaneously by applying a control signal to more than one column in the array during the selected period. It is possible to sequentially control PMA in different rows by activating another row (using the select driver) and applying a control signal to one or more columns in the array.

It is possible to address the system such that the PMA is only activated whilst the control signal is present. However, in a preferred embodiment, it is advantageous to incorporate a memory device into the PMA -e.g. a storage capacitor element 12 in parallel to the PMA electrodes, or a transistor based memory element-, whereby the control signal is remembered after the select period is completed (see Fig. 4). This makes it possible to have a multiplicity of PMA at any point across the array in either their rolled or unrolled form simultaneously. Of course, if a memory device is available, a second control signal will explicitly be required to bring the PMA back to its rolled form.

In a preferred series of embodiments, the active matrix PMA electro transport device is realized using thin film transistor (TFT) technology to ensure that all PMA can be independently driven (see Fig. 3). TFT are well known switching elements in thin film, large area electronics, and have found extensive use in e.g. flat panel display applications. Industrially, the major manufacturing methods for TFT are based upon either amorphous-Si (a-Si) or low temperature polycrystalline Si (LTPS) technologies, whilst other technologies such as organic semiconductors or other non-Si based semiconductor technologies (such as CdSe) can be used.

Whilst offering somewhat less flexibility than using TFT, it is also possible to realize an active matrix based PMA electro transport device using the technologically less demanding thin film diode technology or metal-insulator-metal (MIM) diode technology. Fig. 5 shows a further embodiment in which TFT are exchanged against double diode arrangement. Whilst offering somewhat less flexibility than using TFT, it is also possible to realize an active matrix PMA based electro -transport device using the technologically less demanding thin film diode technology. Diode active matrix arrays (as have been used for e.g. active matrix LCD) can be driven in several known ways, one of which is the double diode with reset (D2R) approach.

The pixel circuit of this active matrix array is shown in Fig. 5. The diode matrix has two diodes per PMA, one to provide control data to the actuator electrode via the control line and one to remove control data from the electrode via a common reset line. The blocking range, that is the voltage range where the diodes are non-conducting, is determined

by the external voltages and therefore adjustable. This is a major advantage where higher operating voltage PMA are required. Higher voltages can easily be accommodated by providing diodes in series (as this prevents breakdown of separate diodes at high reverse voltage - the voltage is split across the diodes) - see Fig. 5. The number of external connections is equal to the number of rows plus columns plus one (the reset line). The circuit is independent of the diode characteristics and Pin or Schottky diodes can be chosen. The circuit can be made redundant for short or open circuit errors by using extra diodes in series or parallel (see Fig. 5). Optionally, the rows are driven using a reset method with five voltage levels. A PIN (or Schottky - IN) diode can be formed using a simple 3-layer process.

An amorphous semiconductor layer, a stack of p-doped, intrinsic, and n-doped regions, is sandwiched between top and bottom metal lines, which are oriented perpendicular. The electrical properties are hardly alignment sensitive.

Fig. 6 shows a further embodiment of the invention. Whilst offering somewhat less flexibility than using TFT, it is also possible to realize an active matrix PMA based electro-transport device using the technologically less demanding metal-insulator-metal (MIM) diode 13 technology.

Traditionally, MIM diode 13 active matrix arrays -as are used for active matrix LCD have a layout similar to the passive matrix as discussed in embodiment 1. However, a MIM diode is introduced as a non-linear resistance element in series with each component, to allow for active matrix addressing.

The MIM device is created by separating 2 metal layers by a thin insulating layer (examples are hydrogenated silicon nitride sandwiched between Cr or Mo metals, or Ta2O5 insulator between Ta metal electrodes), and is conveniently realized in the form of a cross over structure. The MIM connects the selection line or the control data line (shown) to the actuation electrode. Both metal layers and also the insulating layer can be realized on the same substrate. The PMA connections can be completed (Fig. 6) by adding a second line electrode to the foil (for providing the select signal) to the first substrate and separating it with a further (thicker) insulating layer as a crossover. The PMA device of Fig. 1 works by applying a voltage across the two electrodes to unroll the device. In the device as illustrated, the electrode on the substrate is covered by an insulator, whilst the electrode on the polymer is uncovered. It is therefore advantageous to hold the voltage of the latter, uncovered, electrode as close as possible to the potential of the liquid in which it is operating. This will suppress the occurrence of

electrolysis (which occurs above about 2 V if the fluid is water) and other electrode corrosion. In the case of the active matrix embodiments, this means that the uncovered electrode can advantageously form the common electrode (being held e.g. at OV).

In the case of the passive matrix, the uncovered electrode can advantageously form the select electrode, being held at OV when in the non-select state (for most of the time) and only receiving the select voltage when the line is actually selected (only once per frame of addressing - typically <1% of the time). This will also limit electrolysis and corrosion.