Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The liquid conveying element 10 is configured by arranging an upper substrate 12 and a liquid conveying substrate 13 having a plurality of rectangular electrodes 131 for driving so as to form a gap therebetween by means of a spacer 18, and the liquid droplet 15 to be conveyed is held in the gap between the two substrates. It is desired that the upper substrate 12 and the liquid conveying substrate 13 are substantially disposed in parallel to each other. The diagram is a bird's-eye view of the liquid conveying element 10 illustrating a part of the spacer 18 and the upper substrate 12 in a sectional view.
For the spacer 18, a double-sided tape for electronic appliance of 10 μm to 1000 μm in thickness, for example, a double-sided tape using a polyester film base and an acrylic adhesive is used. For the further reduction of the thickness, a spacer formed of a photosensitive material such as photoresist may be used. Alternatively, a difference in level may be provided in the upper substrate 12 or the liquid conveying substrate 13 through the semiconductor manufacturing process using Deep RIE (Deep Reactive Ion Etching) or the like.
For the upper substrate 12, a glass plate having an upper substrate water repellent layer 121 on the water droplet 15 side is used. As other material used for the upper substrate 12, a substance with high flatness is preferable, and if transparency is necessary for the observation of movement of the liquid droplet 15, quartz, PMMA (polymethacrylic methyl (polymethylmethacrylate, acrylic resin)), and others may be used. The upper substrate water repellent layer 121 is made of fluorine resin, and water repellent materials other than fluorine resin include silicone resin. The water repellency mentioned here means water contact angle of 90° or more. In this embodiment, in order to describe the conveyance of liquid, a reactor and a sensor are not formed on the upper substrate 12. However, the same conveyance is possible even when the upper substrate on which the reactor and the sensor are disposed is used. The liquid conveying substrate 13 will be described later.
According to a signal outputted from the system device 19, the first axial voltage control device 16 and the second axial voltage control device 17 change over first axial liquid conveying switches 1611 to 1622 and second axial liquid conveying switches 1711 to 1722, and the electric state of the rectangular electrode group 131 is controlled to one of the ground, potential given from power source, and floating, thereby conveying the liquid droplet 15.
Silicon is used as the material of the base substrate 1351, silicon oxide is used for the bottom insulating layer 1352 and the insulating layer between electrode columns 1353, tungsten is used for the rectangular electrode 131, the first axial coupling conductor 132, and the second axial coupling conductor 133, silicon nitride of 75 nm is used for the dielectric layer 1354, and fluoropolymer resin is used for the water repellent layer 1355 on the liquid conveying substrate. If transparency is necessary for the observation of movement of the liquid droplet 15, as other material used for the base substrate 1351, glass and quartz may be used. As other materials for the bottom insulating layer 1352 and the insulating layer between electrode columns 1353, highly insulating materials such as silicon nitride may be used. When insulator such as glass or quartz is used for the base substrate 1351, the bottom insulating layer 1352 is not always necessary. As other materials for the rectangular electrode 131, the first axial coupling conductor 132, and the second axial coupling conductor 133, aluminum, gold, platinum and other metal materials may be used, and ITO (indium tin oxide) is preferred if transparency is important. As other materials for the dielectric layer 1354, high dielectric materials are preferable, for example, metal oxides and metal nitrides such as silicon oxide, alumina, tantalum oxide, BST (Barium Strontium Titanate), zirconium oxide, hafnium oxide, alumina, titanium oxide, and lanthanum oxide, and insulators by combining these materials such as hafnium aluminate (HfAlO) may be used. As other materials for the water repellent layer 1355 on the liquid conveying substrate, silicone resin may be used. The water repellency mentioned here means water contact angle of 90° or more.
Before starting the conveyance of the liquid droplet 15, the first axial electrode columns 1311 to 1322 and the second axial electrode columns 1331 to 1342 are in a floating state, or the first axial electrode columns 1313 and 1314 are at a set potential V1, the second axial electrode columns 1333 and 1334 are at a set potential V2, and other electrode columns are in a floating state (provided V1>V2) for the purpose of stopping the liquid droplet 15. At this time, a part of the liquid droplet 15 is in contact with the first axial electrode column 1315 and the second axial electrode columns 1334 and 1335 via the dielectric layer 1354.
Next, the first axial liquid conveying switches 1615 and 1616 and the second axial liquid conveying switches 1713 and 1714 are changed over so that the potential of the first axial electrode columns 1315 and 1316 passing through the destination position 141 may be at the set potential V1 and the potential of the second axial electrode columns 1333 and 1334 passing through the destination position 141 may be at the set potential V2. For example, when silicon nitride of 100 nm in thickness is used for the dielectric layer, the set potentials are V1=15 and V2=−15. At the destination position 141, the first axial electrode columns 1315 and 1316 and the second axial electrode columns 1333 and 1334 cross with each other. A potential difference occurs via the liquid droplet 15 between these electrode columns, and the apparent wettability of the surface is increased by electrowetting. Therefore, the liquid droplet 15 moves to the destination position 141. In the diagram, the first axial electrode columns 1315 and 1316 in the state of potential V1 are hatched by vertical lines, and the second axial electrode columns 1333 and 1334 in the state of potential V2 are hatched by lateral lines so as to be distinguished from the other electrode columns. At this time, even if the first axial electrode columns 1315 and 1316 are in the state of the potential V2 and the second axial electrode columns 1333 and 1334 are in the state of the potential VI, the liquid droplet 15 moves to the destination position 141. In other words, the nearby liquid droplet 15 moves to the region adjacent to the first axial electrode column set at the potential V1 (or V2) and the second axial electrode column set at the potential V2 (or V1).
When two adjacent first axial electrode columns and two adjacent second axial electrode columns are selected from the first axial electrode columns 1311 to 1322 of 12 rows and the second axial electrode rows 1331 to 1342 of 12 columns, respectively, the number of combinations of the selected columns is 121. In other words, by combining the twelve first axial liquid conveying switches 1611 to 1622 and the twelve second axial liquid conveying switches 1711 to 1722, the liquid droplet can be conveyed to 121 different positions on the liquid conveying substrate 13.
Also, by varying the number of the first axial electrode columns and the second axial electrode columns to which the potential difference is applied, the effective area of the crossing region of the first axial electrode columns and the second axial electrode columns to which the potential difference is applied can be changed. With respect to the relation between the liquid droplet and the area of the region, the effective area of the region is designed to be slightly smaller than the contact area of the liquid droplet to be conveyed and the liquid droplet conveying substrate 13. Since the amount of liquid droplet 15 is equal to the product of contact area of the liquid droplet and the liquid conveying substrate 13 and the interval between the upper substrate 12 (
Further, since the liquid conveying element 10 includes all electrodes necessary for the conveyance of the liquid on the liquid conveying substrate 13, it can also be used as an open-type liquid conveying element without using the upper substrate 12 and the spacer 18.
In addition to the method described above, by appropriately changing the method of applying the voltage, the liquid droplet conveying capacity can be enhanced.
Before the conveyance of the liquid droplet 15, for the purpose of stopping the liquid droplet 15, the first axial electrode columns 1313 and 1314 and the second axial electrode columns 1333 and 1334 repeat the period where one electrode columns are set at V1 and the other electrode columns are set at V2. In the period when the potential changes from V1 to V2 (or V2 to V2), both the electrode columns go through a floating state. The repetition may be stopped when the position of the liquid droplet 15 is stabilized. Also, although a deviation between the liquid droplet and the electrode shape may occur, both the electrode columns may be set in a floating state.
Next, when conveying the liquid droplet 15 to the destination position 141, the first axial electrode columns 1313 and 1314 are switched to a floating state, and simultaneously, the first axial electrode columns 1315 and 1316 and the second axial electrode columns 1333 and 1334 are switched so as to repeat the period where the potential of one electrode columns is at V1 and the potential of the other electrode columns is at V2. From the time when the switching is carried out, the conveyance of the liquid droplet 15 to the destination position 141 is started. When the potential is changed from V1 to V2 (or V2 to V1), both the electrode columns go through the floating state. The repetition period of potential of the electrode columns is set from 1 millisecond to 1 second.
When the selected first axial electrode columns and the second axial electrode columns are set in a floating state and the apparent surface wettability returns to its initial state, a restoring force to return the shape of the liquid droplet to its original shape occurs. Also, when it comes to the opposite potential state, an electric charge is induced at the lower surface of the liquid droplet 15, and a repulsive force occurs in both the electrode columns. These two generated forces form a conveying power of the liquid droplet, and the conveying force of the liquid droplet 15 can be enhanced. The first axial voltage control device and the second axial voltage control device may switch the polarity of voltage at a specified interval by applying voltages of mutually opposite phases.
Further, in this voltage application method, when conveying the liquid droplet 15, the position of the liquid droplet can be corrected even if the liquid droplet 15 is slightly deviated from the destination position.
The process of dividing the liquid droplet 15 into two droplets 151 and 152 will be described with reference to
Next,
Meanwhile, through the procedure reverse to that described above, two droplets can be combined into one droplet by applying driving forces to the two droplets 151 and 152 in approaching directions.
(A) A thermal oxidation process is performed to the base substrate (silicon) 1351 to form a silicon oxide film layer of 300 nm in thickness to be the bottom insulating layer 1352 on the surface thereof.
(B) As a conductor layer 1356 for forming the lower layer conductor 1359 which is a part of the first axial coupling conductor 132, a titanium nitride/tungsten layer is deposited to have a thickness of 20 nm/150 nm by chemical vapor deposition method.
(C) After a pattern is formed by photolithography, the conductor layer 1356 is etched to form the lower layer conductors 1359.
(D) A silicon oxide film layer is deposited as the insulating layer between electrode columns 1353.
(E) Photolithography and etching are performed to form through holes for plugs 1357. Subsequently, a titanium nitride/tungsten layer is deposited by chemical vapor deposition method, and etching back is performed to form the plugs 1357.
(F) As the conductor layer 1358 for the rectangular electrode 131 and the second axial coupling conductor 135, a titanium nitride/tungsten layer is deposited to have a thickness of 20 nm/150 nm by chemical vapor deposition method.
(G) After a pattern is formed by photolithography, the conductor layer 1358 is etched to form a rectangular electrode 131 and second axial coupling conductors 133.
(H) As the dielectric layer 1354, silicon nitride is deposited to have a thickness of 75 nm by chemical vapor deposition method. For connecting the wiring positions of external power source and rectangular electrode 131, a pattern is formed by photolithography, and then the dielectric layer 1354 covering the wiring positions is removed by etching.
(I) Fluorine-based resin to be used as the water repellent layer 1355 is spin-coated.
In this method, the etching back is performed to embed the metal film, thereby forming the plugs 1357. However, it is also possible to form the plugs 1357 simultaneously with the rectangular electrode 131 and the second axial coupling conductors 133 by omitting this process.
The electrodes coupled in the x-axis direction in the diagram are hatched so as to be distinguished. They are disposed so that the positions of the centers of gravity of the electrodes coincide with the positions of the centers of gravity of the rectangular electrodes 131 of the liquid conveying substrate 13 in
All conductors for connecting the rectangular electrodes 131 in an x direction in the diagram are referred to as first axial coupling conductors 132, and all conductors for connecting them in a y direction in the diagram are referred to as second axial coupling conductors 133. The rectangular electrodes 131 connected in an x direction by the first axial coupling conductors 132 are regarded as one electrode column in each row, and they are called first axial electrode columns 1323 to 1324. Also, the rectangular electrodes 131 connected in a y direction by the second axial coupling conductors 133 are regarded as one electrode column in each column, and they are called second axial electrode columns 1343 to 1344. In the diagram, the rectangular electrodes 131 constituting the first axial electrode columns 1323 to 1324 and the first axial coupling conductors 132 are hatched. Also, in the crossing region 1361 of the first axial coupling conductor 132 and the second axial coupling conductor 133, the coupling conductor positioned in the lower layer is drawn by dotted lines.
In the crossing region 1361 of the first axial coupling conductor 132 and the second axial coupling conductor 133, a dielectric layer between electrodes 1353 (
Also, when the liquid droplet 15 is in contact with the rectangular electrode 131 via the dielectric layer 1354, an electric capacity between rectangular electrodes 131 via the liquid droplet (hereinafter, referred to as electric capacity between electrodes) is formed.
The larger the electric capacity between electrodes and the smaller the electric capacity between wirings, the liquid droplet can be conveyed at the lower potential difference. Supposing that the ratio of the electric capacity between wirings and the electric capacity between electrodes is larger than 1:100 and ε≅ε′, h≅H, and d>100 nm are satisfied, D>1 μm can be obtained. Also, supposing that the number of electrode columns is N, the total area S of the rectangular electrode group is about 2N2D2. Therefore, if N<1000 and S<100×100 cm2 are satisfied, D<1 mm can be obtained. Further, the range of the area D2 of the rectangular electrode 131 is 1 μm2<D2<1 mm2. Also in the case of electrodes with different shape other than the rectangular electrode such as the hexagonal electrode 331 shown in
The chemical reaction analysis element 50 is configured by arranging the liquid conveying substrate 13 and the sensor-reactor substrate 52 in parallel so as to form a gap by means of the spacer 18 therebetween, and the droplets 251 to 254 to be conveyed are held in the gap.
The sensor-reactor substrate 52 comprises temperature regulators 521 and 522 for regulating the temperature of the droplets 551 to 554, thermometers 523 and 524 disposed at the center of the temperature regulators 521 and 522 for measuring the temperature of the droplets, a sensor 525 for detecting specific molecules and ions in the droplets, and a reactor 526 having a catalyst for promoting chemical reaction of specific molecules and ions in the droplets.
According to the signal outputted from the system device 59, the first axial voltage control device 16 and the second axial voltage control device 17 change over the first axial liquid conveying switches 1610 to 1621 and the second axial liquid conveying switches 1710 to 1721 to control the electric state of the rectangular electrodes 131 to one of the ground, potential given from power source, and floating, thereby conveying the liquid droplets 551 to 554. In addition to the control of the conveyance of liquid drops, the system device 59 also performs the control of the temperature regulators 521 and 522 and processing of the signals outputted from the thermometers 523 and 524 and the sensor 525.
The droplets 251 to 252 are conveyed along a route 228. On the route 228, the droplets 251 to 252 are combined in one droplet and then conveyed to the temperature regulator 221 to be heated or cooled. The temperature of the droplet at this time is monitored by the temperature sensor 223 (temperature regulating step). Next, the droplet is conveyed to the reactor 226, and the chemical substance or biological substance in the reactor is reacted with the substance in the liquid droplet (chemical reaction step). Then, the liquid droplet is conveyed to the temperature regulator 222 to be heated or cooled. The temperature of the droplet at this time is monitored by the temperature sensor 224 (temperature regulating step). Finally, the droplet is conveyed to the sensor 225, and the amount of chemical substance or biological substance contained in the droplet is monitored (analysis step).
The conveying route of the droplets 251 to 254 can be freely selected within a two-dimensional plane. By changing the conveying route in accordance with the purpose, processes such as the basic operation of mixing and dividing of liquid droplets, the temperature regulating step by the temperature regulators 221 and 222 and the temperature sensors 223 and 224, the chemical reaction step by the reactors 226 and 227, and the analysis step by the sensor 225 can be combined freely in accordance with the purpose of the user. Moreover, by changing the conveying route of liquid, the order of the detection by sensor, the temperature detection by temperature regulator, and the reaction by reactor can be controlled.
Number | Date | Country | Kind |
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JP2006-183979 | Jul 2006 | JP | national |