Dielectric layer for digital microfluidic devices

Abstract

An electrowetting system is disclosed. The system includes a plurality of electrodes configured to manipulate fluid droplets in a microfluidic space. Each electrode is coupled to a circuit operable to selectively apply a driving voltage to the electrode. The system includes a dielectric stack comprising a first dielectric pair, the first dielectric pair comprising a first layer having a first dielectric constant and a second layer having a second dielectric constant.

Description

[0001] background

[0002] Digital microfluidics (DMF) devices utilize independent electrodes to actuate, split, and connect droplets in confined environments, thus providing a “lab-on-a-chip” capability. DMF devices have been used to actuate a wide range of volumes (nanoliches (nL) to microliters (μL)) and are alternatively referred to as electrowetting on dielectrics or “EWoD” to further distinguish this approach from competing microfluidic systems that rely on electrophoretic flow and / or micropumps. In electrowetting, a continuous or pulsed electrical signal is applied to the droplet, resulting in a switching of its contact angle. Liquids capable of electrowetting hydrophobic surfaces often include polar solvents, such as water, or ionic liquids, and are frequently characterized by ionic substances, such as aqueous electrolyte solutions. Wheeler provides a 2012 review of electrowetting techniques in “Digital Microfluidics,” Annu. Rev. Anal. Chem. 2012, 5:413-40. This technique allows for sample preparation, determination, and synthetic chemistry using both trace amounts of samples and reagents.

[0003] EWoD digital microfluidic devices have two main architectures: open systems and closed systems. Generally, both EWoD configurations include a baseplate characterized by a stack of propulsion electrodes, an insulating dielectric layer, and a hydrophobic layer providing the working surface. However, the closed system also features a top plate parallel to the baseplate and including a top electrode that serves as a common counter electrode for all propulsion electrodes. The top and base plates are provided in a spaced relationship defining the microfluidic region to allow droplet movement within the microfluidic region when a propulsion voltage is applied between the bottom electrode array and the top electrode. When a droplet is placed on the working surface, the electrode actuation causes the droplet to deform and, depending on the applied voltage, to wet or dewet from the surface. When the electrode matrix of the device is driven, each pixel of the DMF device receives a voltage pulse (i.e., the voltage difference between the two electrodes associated with that pixel) or a time sequence of voltage pulses (i.e., a “waveform” or “drive sequence”) to achieve a transition from one electrowetting state of the pixel to another.

[0004] Most literature on EWoDs deals with so-called “segmented” devices, where a dozen to several hundred electrodes are directly driven by a controller. While segmented devices are easy to manufacture, the number of electrodes is limited by space and drive constraints, and the devices need to be designed for specific applications. Therefore, performing large-scale parallel measurements, reactions, etc., in segmented devices can prove relatively problematic. In contrast, “active matrix” devices (also known as active matrix EWoDs or AM-EWoDs) can have thousands, hundreds of thousands, or even millions of addressable electrodes and offer a universal panel that can be used for many different applications.

[0005] Electrodes in AM-EWoD arrays are often switched by transistor matrices such as thin-film transistors (TFTs), but electromechanical switches can also be used. TFT-based thin-film electronics can control voltage pulses to address the EWoD array using various circuit arrangements. TFT arrays are highly desirable for this application because they have thousands of addressable transistors, allowing for massive parallelization of droplet processes. Driving circuitry can be integrated onto the AM-EWoD array substrate, and TFT-based electronics are well-suited for AM-EWoD applications.

[0006] As shown above, conventional DMF systems rely on the continuous actuation of droplets on an array, which over time leads to undesirable electrochemical reactions. This, in turn, results in the degradation of the dielectric layers covering the transistor matrix, often composed of dielectrics and / or hydrophobic materials. Preventing electrochemical degradation is a challenging task, given the aqueous solvents, salts, and acids of many DMF reagents and the relatively high voltages typically applied in the ±15V to ±30V range within the device. In many segmented DMF devices reported in the literature, protection against electrochemical degradation is achieved through dielectric layers, typically hundreds of nanometers thick, usually made of alumina, silica, poly(p-phenylene oxide), or other common dielectrics. In such segmented devices, the thickness of the dielectric necessitates very high actuation potentials, in some cases on the order of hundreds of volts, to achieve proper actuation of the droplets through the thick dielectric. However, such high voltages are often impractical in conventional TFT-based AM-EWoD devices, as operation exceeding the ±30V range can easily damage the TFT circuitry. The need to maintain the actuation voltage within ±30V has led to the adoption of optimized structures based on thin layers of high dielectric constant (“κ” or “k”) materials, which reduces the voltage of droplets actuating DMF devices. The use of advanced, high-quality deposition techniques such as atomic layer deposition (ALD) may help enable the fabrication of thin, high-k dielectric layers capable of protecting DMF devices from electrochemical degradation. However, the implementation of these layer fabrication techniques is often costly and suffers from low production yields. Invention Overview

[0008] An electrowetting system is disclosed. The system includes a plurality of electrodes configured to manipulate fluid droplets in a microfluidic space. Each electrode is coupled to circuitry operable to selectively apply a driving voltage to the electrode. The system includes a dielectric stack comprising a first dielectric pair, the first dielectric pair comprising a first layer having a first dielectric constant and a second layer having a second dielectric constant. The second dielectric constant is greater than the first dielectric constant. The dielectric stack also includes a second dielectric pair comprising a third layer having a third dielectric constant and a fourth layer having a fourth dielectric constant. The fourth dielectric constant is greater than the third dielectric constant. The thickness ratio of the fourth layer to the thickness of the third layer (T4:T3) is in the range of about 2:1 to about 8:1. The second dielectric is thinner than the first dielectric pair.

[0009] In one embodiment, this application provides an electrowetting system for performing droplet manipulation, comprising: a plurality of electrodes configured to manipulate fluid droplets in a microfluidic space, wherein each electrode is coupled to circuitry configured to selectively apply a drive voltage to the electrode; and a dielectric stack comprising: a first dielectric pair including a first layer and a second layer, wherein the dielectric constant of the second layer is greater than that of the first layer; and a second dielectric pair including a third layer and a fourth layer. The dielectric constant of the fourth layer is greater than that of the third layer. The ratio T4:T3 is in the range of about 2:1 to about 8:1, where T3 is the thickness of the third layer and T4 is the thickness of the fourth layer. The second dielectric is thinner than the first dielectric pair.

[0010] In another embodiment, this application provides an electrowetting system for performing droplet manipulation, the system comprising: a plurality of electrodes configured to manipulate fluid droplets in a microfluidic space, wherein each electrode is coupled to a circuit configured to selectively apply a driving voltage to the electrode; and a dielectric stack comprising: a first dielectric layer, and a thin dielectric pair comprising a second dielectric layer and a third dielectric layer, wherein: the dielectric constant of the third dielectric layer is greater than the dielectric constant of the second layer; ratio T H :T L In the range of approximately 3:1 to approximately 8:1, where T H T is the thickness of the third dielectric layer. L The thickness of the second dielectric layer is shown; the dielectric layer is thinner than the first dielectric layer.

[0011] In another embodiment, this application provides an electrowetting system for performing droplet manipulation, the system comprising: a plurality of electrodes configured to manipulate fluid droplets in a microfluidic space, wherein each electrode is coupled to a circuit configured to selectively apply a driving voltage to the electrode; and a dielectric stack comprising: a first dielectric layer and a second dielectric layer, wherein: the dielectric constant of the second dielectric layer is greater than the dielectric constant of the first dielectric layer; and the second dielectric layer is thinner than the first dielectric layer. Brief description of the attached diagram

[0013] Figure 1A This is a cross-sectional schematic diagram of a cell in an example EWoD device.

[0014] Figure 1B The EWoD operation is shown in DC top plane mode.

[0015] Figure 1C This illustrates EWoD operation with top plane switching (TPS).

[0016] Figure 1D This is a schematic diagram of a TFT connected to the gate line, source line, and drive electrode.

[0017] Figure 2 This is a schematic diagram of an exemplary TFT backplane for controlling droplet operation in an AM-EWoD propulsion electrode array.

[0018] Figure 3 This is a schematic diagram of a high-performance stack of a TFT array covered with alternating low-k and high-k dielectric layers.

[0019] Figure 4 This is a schematic diagram of a dielectric stack characterized by a single-layer, relatively inexpensive low-k dielectric and dielectric pairs consisting of low-k and high-k layers formed by atomic layer deposition.

[0020] Figure 5 This is a schematic diagram of a dielectric stack characterized by a single layer of relatively inexpensive low-k dielectric and a high-k layer formed by atomic layer deposition.

[0021] definition

[0022] Unless otherwise stated, the following terms have the specified meanings.

[0023] The “actuation” or “activation” of one or more electrodes refers to the change in the electrical state of one or more electrodes, which, in the presence of a droplet, results in manipulation of the droplet. Electrode activation can be accomplished using alternating current (AC) or direct current (DC). When using AC signals, any suitable frequency can be employed.

[0024] "Droplet" refers to a volume of liquid that electrowets a hydrophobic surface and is at least partially confined by a carrier liquid and / or, in some cases, a gas or gas mixture such as ambient air. For example, a droplet may be completely surrounded by a carrier liquid or may be confined by the carrier liquid and one or more surfaces of the EWoD device. Droplets can take various shapes; non-limiting examples typically include disc-shaped, strip-shaped, truncated spheres, ellipsoids, spheres, partially compressed spheres, hemispheres, ovoids, cylindrical shapes, and various shapes formed during droplet operation such as merging or splitting, or due to contact between such shapes and one or more working surfaces of the EWoD device; droplets may include polar fluids such as water, as in the case of aqueous or non-aqueous compositions, or may be mixtures or emulsions comprising aqueous and non-aqueous components. Droplets may also include dispersions and suspensions, such as magnetic beads in an aqueous solvent. In various implementations, the droplet may include biological samples or portions of biological samples, such as whole blood, lymph, serum, plasma, sweat, tears, saliva, sputum, cerebrospinal fluid, amniotic fluid, semen, vaginal secretions, serous fluid, synovial fluid, pericardial fluid, peritoneal fluid, pleural fluid, exudate, exudate, cystic fluid, bile, urine, gastric juice, intestinal juice, fecal samples, liquids containing single or multiple cells, liquids containing organelles, fluidized tissues, fluidized organisms, liquids containing multicellular organisms, biological swabs, and biological wash solutions. Furthermore, the droplet may include one or more reagents, such as water, deionized water, saline solutions, acidic solutions, alkaline solutions, detergent solutions, and / or buffer solutions. Other examples of droplet contents include reagents, such as reagents for biochemical protocols, nucleic acid amplification protocols, affinity-based assay protocols, enzyme assay protocols, gene sequencing protocols, protein sequencing protocols, and / or reagents for protocols for analyzing biological fluids. Further examples of reagents include those used in biochemical synthetic methods, such as reagents for synthesizing oligonucleotides and nucleic acid molecules with applications found in molecular biology and medicine. Oligonucleotides can contain natural or chemically modified bases and are most commonly used as antisense oligonucleotides, small interfering therapeutic RNA (siRNA) and their bioactive conjugates, primers for DNA sequencing and amplification, probes for detecting complementary DNA or RNA via molecular hybridization, tools for targeting the introduction of mutations and restriction sites in the context of gene editing technologies such as CRISPR-Cas9, and tools for synthesizing artificial genes. In further examples, droplet contents may include reagents for peptide and protein production, for example, through chemical synthesis, expression in living organisms such as bacterial or yeast cells, or through the use of biomechanics in in vitro systems.

[0025] A "droplet region" refers to the area enclosed around a droplet. In the context of droplets covering a pixelated surface, pixels located within a droplet region are called "droplet pixels" or "pixels of a droplet." When referring to a portion of a droplet, pixels located within that portion are called "partial pixels" or "partial pixels."

[0026] The terms “DMF device,” “EWoD device,” and “droplet actuator” refer to electrowetting devices used to manipulate droplets.

[0027] "Droplet manipulation" refers to any manipulation of one or more droplets on a microfluidic device. For example, droplet manipulation may include: loading droplets into a DMF device; dispensing one or more droplets from a source reservoir; splitting, separating, or dividing a droplet into two or more droplets; moving a droplet from one location to another in any direction; merging or combining two or more droplets into a single droplet; diluting a droplet; mixing a droplet; agitating a droplet; deforming a droplet; holding a droplet in place; incubating a droplet; heating a droplet; evaporating a droplet; cooling a droplet; processing a droplet; delivering a droplet out of the microfluidic device; other droplet manipulations described herein; and / or any combination of the foregoing. The terms "merge," "merging," "combine," "combining," etc., are used to describe the formation of a single droplet from two or more droplets. It should be understood that when such terms are used with respect to two or more droplets, any combination of droplet manipulations sufficient to result in the combination of two or more droplets into a single droplet may be used. For example, “merging droplet A with droplet B” can be achieved by delivering droplet A to contact with stationary droplet B, delivering droplet B to contact with stationary droplet A, or delivering droplets A and B to contact each other. The terms “split,” “separate,” and “divide” are not intended to imply any particular result regarding the volume of the resulting droplets (i.e., the volumes of the resulting droplets can be the same or different) or the number of resulting droplets (the number of resulting droplets can be 2, 3, 4, 5, or more). The term “mixing” refers to droplet manipulation that results in a more uniform distribution of one or more components within the droplet. Examples of “loading” droplet manipulation include, but are not limited to, microdialysis loading, pressure-assisted loading, robotic loading, passive loading, and pipette loading. Droplet manipulation can be electrode-mediated. In some cases, droplet manipulation is further facilitated by using hydrophilic and / or hydrophobic regions on the surface and / or by physical barriers.

[0028] Unless otherwise stated, the term "low k" refers to materials with a dielectric constant (relative to vacuum) of less than 10. The term "high k" refers to materials with a dielectric constant of 10 or greater.

[0029] A “drive sequence” or “pulse sequence” refers to the entire voltage-to-time profile used to actuate pixels in a microfluidic device. Often, such a sequence will include multiple elements (where a given element includes a substantially constant voltage applied over a period of time), which may be referred to as a “voltage pulse” or “drive pulse.” The term “drive scheme” refers to a set of one or more drive sequences sufficient to perform one or more manipulations on one or more droplets during a given droplet operation. Unless otherwise stated, the term “frame” refers to a single update of all pixel rows in a microfluidic device.

[0030] "Nucleic acid molecules" are a collective term for single-stranded or double-stranded, sense or antisense DNA or RNA. These molecules are composed of nucleotides, which are monomers consisting of three parts: a pentose sugar, a phosphate group, and a nitrogenous base. If the sugar is a ribose, the polymer is RNA (ribonucleic acid); if the sugar is derived from ribose as deoxyribose, the polymer is DNA (deoxyribonucleic acid). Nucleic acid molecules vary in length, from common oligonucleotides of about 10 to 25 nucleotides used for gene detection, research, and forensics to relatively long or very long prokaryotic and eukaryotic genes with sequences of about 1,000, 10,000 nucleotides or more. Their nucleotide residues can be entirely naturally occurring or at least partially chemically modified, for example, to slow down degradation in vivo. The molecular backbone can be modified, for example, by introducing nucleoside organothiophosphate (PS) nucleotide residues. Another modification used for the medical application of nucleic acid molecules is 2' sugar modification. Modifying the 2' sugar is thought to increase the effectiveness of therapeutic oligonucleotides by enhancing their target binding ability, especially in antisense oligonucleotide therapies. The two most commonly used modifications are 2'-O-methyl and 2'-fluoro.

[0031] When a liquid in any form (such as droplets or a continuous body, whether moving or stationary) is described as being “on,” “at,” or “over” an electrode, array, matrix, or surface, such a liquid may be in direct contact with the electrode / array / matrix / surface, or may be in contact with one or more layers or films interposed between the liquid and the electrode / array / matrix / surface.

[0032] When a droplet is described as being “in,” “on,” or “loaded” on a microfluidic device, it should be understood that the droplet is arranged on the device in a manner that facilitates one or more droplet operations on the droplet using the device, in a manner that facilitates sensing the properties of the droplet or signals from the droplet, and / or the droplet has already undergone droplet operations on a droplet actuator.

[0033] The word "each," when used with respect to multiple items, is intended to identify a single item in a set, but does not necessarily refer to every item in the set. Exceptions may occur if explicitly stated otherwise or clearly specified in the context.

[0034] Although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of the example implementation, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0035] Detailed Explanation

[0036] This disclosure provides a novel and improved multilayer dielectric stack combining high performance and resistance to electrochemical degradation. The dielectric stack can be used, for example, in TFT-based DMF devices. The stack includes one or more layers with relatively low dielectric constants, combined with one or more layers with high dielectric constants to improve performance, providing better protection against electrical breakdown. Unbound from any particular theory, it is believed that the presence of alternating layers of multiple dielectric constants, e.g., low dielectric constant layers followed by high dielectric constant layers, then low dielectric constant layers, and so on, minimizes the possibility of pinhole formation across the entire thickness of the stack when operating under higher voltages and / or corrosive solutions. The fabrication of the multilayer dielectric stack can be performed using relatively expensive and time-consuming deposition techniques, employing high-performance and durable DMF devices. Conversely, higher-output layer deposition methods can be used where long-term performance is less critical and manufacturing costs are a greater concern. In summary, the dielectric stack of this application is suitable for achieving an optimal balance between expected results and operating costs.

[0037] The benefits of high-k dielectric materials are understood in materials science and electrical engineering. The dielectric constant k typically describes a material's ability to store electrical energy in an electric field. Generally, as the dielectric constant of a material increases, the amount of electric field passing through it decreases. Therefore, high-k dielectric materials are used to homogenize electric fields and prevent concentrated electric field gradients, which can, for example, lead to unwanted electrical switching in electrical components such as transistors. The continuity of the dielectric layer is crucial because variations in thickness or composition can create paths for short circuits and breakdowns.

[0038] DMF equipment

[0039] Before proceeding further, it is desirable to describe the structure of a conventional DMF device. Figure 1AA schematic cross-sectional view of a cell in an exemplary conventional enclosed EWoD device is shown, wherein droplets 104 are surrounded laterally by a carrier liquid 102 and sandwiched between a top hydrophobic layer 107 and a bottom hydrophobic layer 110. A push electrode 105 can be directly driven or switched by a transistor array arranged to be driven by data (source) lines and gate (select) lines, producing a so-called active matrix (AM) EWoD. A dielectric stack 108 is positioned between the electrode 105 and the bottom hydrophobic layer 110. Cell spacing is typically in the range of about 50 micrometers (μm) to about 500 μm.

[0040] The drive closed system EWoD has two main modes: "DC top surface" and "top surface switching (TPS)". Figure 1B EWoD operation in DC top-side mode is illustrated, where the top-side electrode 106 is set to a zero-volt potential, for example, by grounding. As a result, the potential applied across the cell is the voltage on the active pixel, i.e., pixel 101 has a different voltage than the top surface, causing conductive droplets to be attracted to the electrode. In active-matrix TFT devices, this limits the pixel drive voltage in the EWoD cell to approximately ±15V, because in commonly used amorphous silicon (a-Si) TFTs, the maximum voltage ranges from approximately 15V to approximately 20V due to the electrical instability of the TFT under high-voltage operation. Figure 1C The display uses a TPS to drive the cell. In this case, by supplying power to the top electrode out of phase with the active pixel, the driving voltage is doubled to ±30V, so that the top surface voltage is added to the voltage provided by the TFT.

[0041] Amorphous silicon TFT panels typically have one transistor per pixel, although configurations with two or more transistors have also been considered. For example... Figure 1D As shown, the transistor is connected to the gate line, source line (also called the "data line"), and push electrode. When there is a sufficiently large positive voltage on the TFT gate, there is a low impedance between the source line and the pixel (Vg "on"), so the voltage on the source line is transferred to the pixel electrode. When there is a negative voltage on the TFT gate, the TFT is high impedance, and the voltage is stored on the pixel storage capacitor and is unaffected by the voltage on the source line when other pixels are addressed (Vg "off"). If no movement is needed, or if the droplet is intended to be moved away from the push electrode, there is 0 V on the pixel electrode, meaning there is no voltage difference relative to the top plate. Ideally, the TFT should act as a digital switch. In reality, when the TFT is in the "on" setting, there is still a certain amount of resistance, so the pixel takes time to charge. Additionally, when the TFT is in the "off" setting, voltage may leak from Vs to Vp, causing crosstalk. Increasing the capacitance of the storage capacitor reduces crosstalk, but at the cost of making the pixel more difficult to charge.

[0042] The drivers of the TFT array receive instructions related to droplet operations from a processing unit. The processing unit can be, for example, a general-purpose computer, a special-purpose computer, a personal computer, or other programmable data processing device that provides processing capabilities, such as storing, interpreting, and / or executing software instructions and controlling the overall operation of the device. The processing unit is coupled to a memory that includes programmable instructions to direct the processing unit to perform various operations, such as, but not limited to, providing input instructions to the TFT drivers to instruct them to generate electrode drive signals, according to embodiments herein. The memory may be physically located within the DMF device or within a computer or computer system that interfaces with the device, and stores programs and data as part of a working set of one or more tasks performed by the device. For example, the memory may store programmable instructions for executing drive schemes described in conjunction with a set of droplet operations. The processing unit executes programmable instructions to generate control inputs, which are transmitted to the drivers to implement one or more drive schemes related to a given droplet operation.

[0043] Figure 2 This is a schematic diagram of an exemplary TFT backplane for controlling droplet operation in an AM-EWoD advance electrode array. In this configuration, the elements of the EWoD device are arranged in a matrix form defined by the source and gate lines of the TFT array. A source line driver provides a source level corresponding to droplet operation. A gate line driver provides a signal for turning on the transistor gate of the electrode, which is actuated during operation. Figure 2 The diagram shows the signal lines for the data and gate lines. Gate line drivers can be integrated into a single integrated circuit. Similarly, data line drivers can be integrated into a single integrated circuit. The integrated circuit can include complete gate and source driver assemblies as well as a controller. Commercially available controller / driver chips include those commercialized by Ultrachip Inc. (San Jose, California), such as UC8120; UC8130; UC8124; UC8137; UC8142; UC8143; UC8151; UC8152; UC8154; UC8155; UC8157; UC8176; UC8159; UC8111; UC8112; UC8113; UC8118; UC8119, as well as those available from Solomon Systech (Hong Kong, China), including SSD1633; SSD1681; SSD1675B; SSD1680 / 80A; SSD1619A; SSD1683; SPD1656; SSD1677; and SSD1603. Figure 2The matrix consists of 1024 source lines and a total of 768 gate lines, although both numbers can be varied to suit the size and spatial resolution of DMF devices. Each element of the matrix includes a potential for controlling the corresponding pixel electrode. Figure 1D The TFTs are of the type shown, and each TFT is connected to a gate line and a source line.

[0044] Improved dielectric layer stacking

[0045] In some embodiments, this document provides a dielectric stack with a multilayer structure, characterized by alternating layers of materials having different dielectric constants, such as low or high, to achieve an optimized balance between high DMF device performance and long lifetime. In this case, the device is protected from degradation and successfully performs DMF operation.

[0046] The stack according to some embodiments taught herein includes two or more “dielectric pairs”, each pair being characterized by two adjacent dielectric layers. The two dielectric layers of a dielectric pair are directly adjacent, although additional intermediate layers or coatings may be present if desired. The first layer of the dielectric pair includes a first material characterized by a first dielectric constant, while the second layer includes a second material having a second dielectric constant, wherein the second dielectric constant is higher than the first dielectric constant. Therefore, for the purposes of this disclosure, the first layer may be classified as a “low-k” layer, where k 11 The second layer, which represents its dielectric constant, can be called a "high-k" material, characterized by its second dielectric constant k. 12 , where k 12 >k 11 The second dielectric pair includes those with a dielectric constant of k. 21 The layer and dielectric constant are k 22 The layers, where k 22 >k 21 More generally, each consecutive dielectric pair can be labeled with a natural number "m", where k m1 It is the dielectric constant of the lower k layer of the m-th dielectric pair, k m2 It is the dielectric constant of the higher k layer of the m-th dielectric pair, such that k m2 >k m1 In a dielectric stack characterized by a total of “n” dielectric pairs, each pair can be labeled in ascending order from the first (m=1) to the last (m=n).

[0047] The thickness of each individual layer is classified in a similar manner, where the thickness of the first layer of the m-th dielectric pair is labeled "T". m-1 The thickness of the second layer of the m-th dielectric pair is marked as "T". m-2 The thickness of the layer or dielectric pair can be measured along a direction perpendicular to the upper surface of the glass substrate, such as... Figure 3 As shown in axis 30.

[0048] Still referencing Figure 3 The multilayer dielectric stack 32 shown is characterized by a total of four dielectric pairs (n=4), which are spatially arranged to form a stack covering a glass substrate having a TFT driving electrode array 34. First, the thicker dielectric pair 36 (m=1) consists of a low-k first layer 311 and a high-k second layer 312. The thicknesses of layers 311 and 312 are approximately equal, such that the ratio T... 12 :T 11 The ratio is approximately 1:1, although variations ranging from approximately 0.5:1 to approximately 1.5:1 or from approximately 0.75:1 to approximately 1.25:1 can be considered. The first dielectric pair 31 is the thickest in the structure and accounts for approximately half of the total thickness of the dielectric stack. The second dielectric pair 33 (m=2), the third dielectric pair 35 (m=3), and the fourth dielectric pair 37 (m=4) are all thinner than the first dielectric pair 31.

[0049] As described above, each of the second, third, and fourth dielectric pairs includes a thickness of T. m-1 The low-k layer and the thickness of T m-2 The high k layer. However, unlike the first dielectric pair, the relative thickness of the layers makes T such that for m = 2, 3, or 4. m-2 :T m-1 The ratio is approximately 5:1. Therefore, the characteristics of a stack of 32 layers are shown in Table 1. In this table, each layer is labeled with the above code; for example, the first layer of the first pair is labeled "1-1", the second layer of the second pair is labeled "1-2", and so on.

[0050]

[0051] There is no theoretical limit to the number of thinner dielectric pairs in the stack (i.e., n-1). ALD technology allows the deposition of near-atomic-thin layers, the only requirement being that the layer has sufficient thickness to achieve a satisfactory level of uniformity and is free of blotches. In exemplary embodiments, the number of thinner dielectric pairs can be 1, 2, 3, 4, 5, 10, 15, 20, or even higher. Furthermore, the ratio T of the thinner dielectric pairs... m-2 :T m-1 The ratio can be greater than or less than about 5:1. In one embodiment, the ratio can range from about 2:1 to about 10:1, or more specifically, from about 2:1 to about 8:1, about 3:1 to about 8:1, about 4:1 to about 6:1, or about 4.5:1 to about 5.5:1. The total thickness of the stack is generally from about 100 nm to about 300 nm, but other values ​​are also acceptable to achieve the desired level of performance and stack corrosion resistance.

[0052] Multilayer stacking can be created by forming alternating layers of low-k and high-k materials using atomic layer deposition (ALD) technology, which is particularly well-suited for manufacturing high-quality layers. If reducing manufacturing costs is paramount, industrial vapor deposition methods can be applied. Figure 3 The embodiment shown in the figure illustrates a first, thicker dielectric pair 31 at the bottom of the stack. However, different arrangements are acceptable, such as those where one or more of 33, 35, and 37 are on opposite sides of 31, or where 31 is the uppermost dielectric pair. Furthermore, Figure 3 Each low-k layer is depicted at the bottom of its respective dielectric pair, but other configurations in which low-k layers are located at the top of their dielectric pairs are also conceivable.

[0053] In the initial step of ALD, a substrate is provided on which a dielectric stack will be coated. The substrate is often cleaned before coating, for example, with ethanol or isopropanol. The substrate can be any material, as long as it is stable during the atomic layer deposition (ALD) and sputtering steps described below. For example, the substrate can be a printed circuit board, coated glass such as ITO-coated glass, or an active matrix TFT backplane microfabricated on glass or other substrate materials. The next step is to deposit a first layer on the substrate using atomic layer deposition, typically plasma-assisted ALD or (hot) water vapor-assisted ALD. For example, a first layer of alumina can be fabricated using trimethylaluminum (Al(CH3)3) or Ta[(N(CH3)2)3NC(CH3)3] combined with oxygen plasma at a substrate temperature of approximately 180°C and a low pressure (less than 100 mbar). Alternatively, a layer of alumina can be deposited using a trimethylaluminum-water method. Atomic layer deposition can be performed at a rate greater than 0.1 nm / min, for example, 0.2 nm / min or greater. The final thickness of alumina or hafnium oxide is typically between 9 nm and 80 nm. Bent and colleagues, in their paper "A brief review of atomic layer deposition: from fundamentals to applications,"... Materials Today The details of these ALD methods are described in (2014), Volume 17, Issue 5, pp. 236-46, the full contents of which are incorporated herein by reference.

[0054] In some implementation schemes, Figure 3 The high-performance dielectric stack uses aluminum oxide (Al₂O₃) as the low-k material and hafnium oxide (HfO₂) as the high-k material. The target total thickness is approximately 200 nm, resulting in the thickness of each layer as shown in Table 2.

[0055]

[0056] Alumina was chosen as a low-k dielectric in part due to its availability and ease of use in ALD deposition combined with its relatively high dielectric breakdown strength. Other materials used for low-k dielectrics include silicon dioxide (SiO2) and silicon nitride (Si3N4). Hafnium oxide was chosen primarily because it combines a high dielectric constant with biocompatibility. Other suitable high-k dielectrics include tantalum oxide (Ta2O5), zirconium oxide (ZrO2), and lanthanum oxide (La2O5).

[0057] To provide comprehensive protection for TFTs, stacking can be accomplished using one or more polymers and a hydrophobic layer, such as a silane adhesion promoter film to which a protective coating is applied. The protective coating comprises polymeric materials deposited on electronic circuits and other devices as electrical insulation, moisture protection, and protection against corrosion and chemical attack. Common protective materials include poly(p-phenylene dimethyl)ethylene, a class of polymers whose backbone consists of a p-phenylene dicyclic ring linked by 1,2-ethanediyl bridges (-CH2-CH2-). "Poly(p-phenylene dimethyl)ethylene N" is an unsubstituted polymer obtained by polymerizing a p-xyleneyl precursor. Derivatives of poly(p-phenylene dimethyl)ethylene can be obtained by substituting hydrogen atoms on the benzene ring or aliphatic bridges with other functional groups. The most common of these variants is "poly(p-phenylene dimethyl)ethylene C," in which one hydrogen atom in the aromatic ring is replaced by chlorine. Another common halogenated variant is "poly(p-phenylene dimethyl)ethylene AF-4," in which four hydrogen atoms on the aliphatic chain are replaced by fluorine atoms. Poly(p-phenylene dimethyl)ethylene layers can be formed using methods well known to those skilled in the art, such as chemical vapor deposition (CVD).

[0058] The protective coating can then cover a hydrophobic, chemically inert top layer, which forms the bottom surface of the microfluidic space. In some embodiments, the surface layer material includes fluorinated and perfluoropolymers, such as Teflon AF, fluorinated polysiloxanes, and products marketed under the trade name CYTOP. TM A family of fluoropolymers purchased from (AGC Chemicals Company, Japan), and marketed under the brand name FLUOROPEL. TM Commercially available perfluoroalkyl polymers (Cytonix, Maryland).

[0059] In some embodiments, a dielectric stack is provided that is suitable for situations where manufacturing cost is given higher priority and a relatively inexpensive, high-capacity dielectric deposition method is preferred. For devices where long-term performance is less critical and / or where the use of corrosive substances is not considered, the majority of the dielectric stack can be formed using lower-cost materials and inexpensive, high-capacity dielectric deposition methods such as plasma-enhanced chemical vapor deposition (PECVD). Smaller portions of the stack can be fabricated using more complex and expensive high-quality deposition techniques such as ALD. The smaller portions can take the form of one of the thinner dielectric pairs described above, characterized by T m-2 :T m-1 The ratio is approximately 5:1. In one embodiment, the ratio may range from approximately 2:1 to approximately 10:1, or more specifically, from approximately 3:1 to approximately 8:1, from approximately 4:1 to approximately 6:1, or from approximately 4.5:1 to approximately 5.5:1. This combined approach may help prevent pinhole formation and can also significantly reduce costs and deposition time while increasing yield. In some embodiments, the dielectric stack has a total thickness from approximately 70 nm to approximately 300 nm.

[0060] Figure 4 The construction 40 according to some embodiments of this application is illustrated schematically. A relatively thick first layer 44 is deposited on a glass substrate having a TFT array 42 using a low-cost technique such as plasma-enhanced chemical vapor deposition (PECVD). The first layer 44 constitutes at least half the thickness of the dielectric stack and is formed of a low-k material such as silicon nitride (Si3N4), which can typically be formed by PECVD in just a few minutes. A dielectric pair 46 is then formed on the first layer 44. The dielectric pair consists of materials having a thickness T... L The low-k first layer 461 and having a thickness T H The second layer, composed of high k, consists of 462. The ratio T H :T L The ratio is typically approximately 5:1. Both layers of the dielectric pair are formed using a slower, higher-quality deposition method such as ALD. In one embodiment, layer 461 may be made of alumina or silicon dioxide, while layer 462 may be made of hafnium oxide.

[0061] In some embodiments, this application provides a simplified dielectric stack for disposable devices intended for short-duration operation. Due to factors such as cost and manufacturing yield, the dielectric stack comprises a first, relatively thick, low-k dielectric layer formed by an industrial vapor deposition method such as PECVD. A thinner second layer of high-k material is deposited on the first layer by a higher-quality deposition method such as ALD to form a simple two-layer stack with a total thickness of about 70 nm to about 300 nm.

[0062] Figure 5The construction 50 according to some embodiments of this application is illustrated schematically. A glass substrate having a TFT array 52 is first subjected to the deposition of a low-k dielectric layer 54 via PECVD. Then, a thinner, high-k dielectric layer comprising hafnium oxide 56 is formed via ALD. This combined approach may help prevent pinhole formation and can also significantly reduce cost and deposition time while increasing yield. In one embodiment, the ratio T... L :T H The ratio is approximately 5:1, where T L It is the thickness of the low-k dielectric layer, T H This refers to the thickness of the high-k dielectric layer. However, this ratio can range from about 2:1 to about 10:1, or more specifically, from about 3:1 to about 8:1, about 4:1 to about 6:1, or about 4.5:1 to about 5.5:1. In some embodiments, the dielectric stack has a total thickness from about 70 nm to about 300 nm.

[0063] The stack can be completed with a single or multiple polymer and / or hydrophobic layers for further protection. In one embodiment, one or more polymer dielectric layers may be present on top of the dielectric stack, and then the polymer dielectric layers are covered with a hydrophobic layer. Alternatively, only a single hydrophobic layer may be present on top of the dielectric stack. In one example, the stack is covered with a silane adhesion promoter film, on which a protective coating, such as poly(p-phenylene dimethyl)C, is formed. As described above, the protective coating may in turn cover a hydrophobic, chemically inert outer layer, such as Teflon, fluorinated polysiloxane, or CYTOP, on the bottom surface forming the microfluidic space. TM Or FLUOROPEL TM In addition to the hydrophobic outer layer, materials such as poly(p-phenylene dimethyl) AF-4 or poly(p-phenylene dimethyl) HT can serve as additional protection and as an external hydrophobic layer, both contained within a single layer.

[0064] In some implementations that do not include a high-k dielectric, the adhesive and polymer layers provide all the additional protection for the device, in addition to a relatively thick low-k dielectric layer.

[0065] It will be apparent to those skilled in the art that many changes and modifications can be made to the embodiments of the technology described herein without departing from the scope of the invention. Therefore, the entire foregoing description should be interpreted as illustrative rather than restrictive. It will be understood from the teachings above that the functionalities implemented on the processing unit described herein can be implemented or accomplished using any suitable implementation environment or programming language, such as C, C++, Cobol, Pascal, Java, JavaScript, HTML, XML, dHTML, assembly, or machine code programming. All contents of the foregoing patents and applications are incorporated herein by reference in their entirety. In the event of any inconsistency between the contents of this application and the contents of any patents and applications incorporated herein by reference, the contents of this application should be controlled to the extent necessary to resolve such inconsistency.

[0066] This disclosure includes the following implementation plan:

[0067] 1. An electrowetting system for performing droplet operations, the system comprising:

[0068] Multiple electrodes configured to manipulate fluid droplets in a microfluidic space, wherein each electrode is coupled to a circuit operable to selectively apply a driving voltage to the electrode; and

[0069] Dielectric stack, comprising:

[0070] A first dielectric pair comprising a first layer having a first dielectric constant and a second layer having a second dielectric constant, wherein the second dielectric constant is greater than the first dielectric constant, and

[0071] A second dielectric pair comprising a third layer having a third dielectric constant and a fourth layer having a fourth dielectric constant, wherein:

[0072] The fourth dielectric constant is greater than the third dielectric constant;

[0073] The ratio T4:T3 ranges from approximately 2:1 to approximately 8:1, where T3 is the thickness of the third layer and T4 is the thickness of the fourth layer; and

[0074] The total thickness of the second dielectric pair is thinner than the total thickness of the first dielectric pair.

[0075] 2. The electrowetting system according to embodiment 1, wherein the ratio T4:T3 is in the range of about 4.5:1 to about 5.5:1.

[0076] 3. The electrowetting system according to embodiment 1, wherein the first layer and the third layer each comprise materials independently selected from alumina (Al2O3), silicon dioxide (SiO2) and silicon nitride (Si3N4).

[0077] 4. The electrowetting system according to embodiment 1, wherein the second layer and the fourth layer each comprise a material independently selected from hafnium oxide (HfO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), zirconium oxide (ZrO2), yttrium oxide (Y2O3), and lanthanum oxide (La2O5).

[0078] 5. The electrowetting system according to embodiment 1, wherein the first, second, third and fourth layers are formed by atomic layer deposition (ALD).

[0079] 6. The electrowetting system according to embodiment 1 further includes a third dielectric pair and a fourth dielectric pair, the third dielectric pair comprising a fifth layer having a fifth dielectric constant and a sixth layer having a sixth dielectric constant, and the fourth dielectric pair comprising a seventh layer having a seventh dielectric constant and an eighth layer having an eighth dielectric constant.

[0080] The sixth dielectric constant is greater than the fifth dielectric constant;

[0081] The ratio T6:T5 is in the range of about 3:1 to about 8:1, where T5 is the thickness of the fifth layer and T4 is the thickness of the fourth layer;

[0082] The third dielectric is thinner than the first dielectric.

[0083] The eighth dielectric constant is greater than the seventh dielectric constant;

[0084] The ratio T8:T7 ranges from approximately 3:1 to approximately 8:1, where T7 is the thickness of the seventh layer and T8 is the thickness of the eighth layer; and

[0085] The fourth dielectric is thinner than the first dielectric.

[0086] 7. The electrowetting system according to embodiment 1 further includes 1 to 10 additional dielectric pairs, wherein:

[0087] Each additional dielectric is thinner than the first dielectric pair; and

[0088] Each additional dielectric pair comprises two layers, wherein one of the two layers has a higher dielectric constant than the other of the two layers.

[0089] 8. The electrowetting system according to embodiment 7, wherein each layer of each thin dielectric pair is formed by atomic layer deposition (ALD).

[0090] 9. An electrowetting system for performing droplet operation, the system comprising:

[0091] Multiple electrodes configured to manipulate fluid droplets in a microfluidic space, wherein each electrode is coupled to a circuit operable to selectively apply a driving voltage to the electrode; and

[0092] Dielectric stack, comprising:

[0093] A first dielectric layer having a first dielectric constant, and

[0094] A thin dielectric pair comprising a second dielectric layer having a second dielectric constant and a third dielectric layer having a third dielectric constant.

[0095] The third dielectric constant is greater than the second dielectric constant;

[0096] Ratio T H ∶T L In the range of approximately 3:1 to approximately 8:1, where T H T is the thickness of the third dielectric layer. L The thickness of the second dielectric layer; and

[0097] The dielectric layer is thinner than the first dielectric layer.

[0098] 10. The electrowetting system according to embodiment 9, wherein the dielectric constant of the third dielectric layer is greater than the dielectric constant of the first dielectric layer.

[0099] 11. The electrowetting system according to embodiment 9, wherein the first dielectric layer comprises silicon nitride aluminum oxide (Al2O3), silicon dioxide (SiO2) or silicon nitride (Si3N4).

[0100] 12. The electrowetting system according to embodiment 9, wherein the first dielectric layer is formed by plasma-enhanced chemical vapor deposition (PECVD).

[0101] 13. The electrowetting system according to embodiment 9, wherein the second dielectric layer comprises a material selected from alumina (Al2O3) and silicon dioxide (SiO2).

[0102] 14. The electrowetting system according to embodiment 9, wherein the third dielectric layer comprises a material selected from hafnium oxide (HfO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), zirconium oxide (ZrO2), yttrium oxide (Y2O3), and lanthanum oxide (La2O5).

[0103] 15. The electrowetting system according to embodiment 9, wherein the second dielectric layer and the third dielectric layer are formed by atomic layer deposition (ALD).

[0104] 16. An electrowetting system for performing droplet operations, the system comprising:

[0105] Multiple electrodes configured to manipulate fluid droplets in a microfluidic space, wherein each electrode is coupled to a circuit operable to selectively apply a driving voltage to the electrode; and

[0106] Dielectric stack, comprising:

[0107] First dielectric layer, and

[0108] Second dielectric layer,

[0109] The dielectric constant of the second dielectric layer is greater than that of the first dielectric layer; and

[0110] The second dielectric layer is thinner than the first dielectric layer.

[0111] 17. The electrowetting system according to embodiment 16, wherein the first dielectric layer comprises silicon aluminum nitride (Al2O3), silicon dioxide (SiO2) and silicon nitride (Si3N4).

[0112] 18. The electrowetting system according to embodiment 16, wherein the first dielectric layer is formed by plasma-enhanced chemical vapor deposition (PECVD).

[0113] 19. The electrowetting system according to embodiment 16, wherein the second dielectric layer comprises a material selected from hafnium oxide (HfO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), zirconium oxide (ZrO2), yttrium oxide (Y2O3), and lanthanum oxide (La2O5).

[0114] 20. The electrowetting system according to embodiment 16, wherein the second dielectric layer is formed by atomic layer deposition (ALD).

Claims

1. An electrowetting system for performing droplet operations, the system comprising: Multiple electrodes configured to manipulate fluid droplets in a microfluidic space, wherein each electrode is coupled to a circuit operable to selectively apply a driving voltage to the electrode; and Dielectric stack, comprising: A first dielectric pair comprising a first layer having a first dielectric constant and a second layer having a second dielectric constant, wherein the second dielectric constant is greater than the first dielectric constant, and A second dielectric pair comprising a third layer having a third dielectric constant and a fourth layer having a fourth dielectric constant, wherein: The fourth dielectric constant is greater than the third dielectric constant; The ratio T4:T3 ranges from 2:1 to 8:1, where T3 is the thickness of the third layer and T4 is the thickness of the fourth layer; and The total thickness of the second dielectric pair is thinner than the total thickness of the first dielectric pair.

2. The electrowetting system according to claim 1, wherein the ratio T4:T3 is in the range of 4.5:1 to 5.5:

1.

3. The electrowetting system according to claim 1, wherein the first layer and the third layer each independently comprise a material selected from alumina (Al2O3), silicon dioxide (SiO2), and silicon nitride (Si3N4).

4. The electrowetting system according to claim 1, wherein the second layer and the fourth layer each independently comprise a material selected from hafnium oxide (HfO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), zirconium oxide (ZrO2), yttrium oxide (Y2O3), and lanthanum oxide (La2O3).

5. The electrowetting system according to claim 1, wherein the first, second, third and fourth layers are formed by atomic layer deposition (ALD).

6. The electrowetting system according to claim 1, further comprising a third dielectric pair and a fourth dielectric pair, the third dielectric pair comprising a fifth layer having a fifth dielectric constant and a sixth layer having a sixth dielectric constant, and the fourth dielectric pair comprising a seventh layer having a seventh dielectric constant and an eighth layer having an eighth dielectric constant. The sixth dielectric constant is greater than the fifth dielectric constant; The ratio T6:T5 is in the range of 3:1 to 8:1, where T5 is the thickness of the fifth layer and T6 is the thickness of the sixth layer; The third dielectric is thinner than the first dielectric. The eighth dielectric constant is greater than the seventh dielectric constant; The ratio T8:T7 is in the range of 3:1 to 8:1, where T7 is the thickness of the seventh layer and T8 is the thickness of the eighth layer; and The fourth dielectric is thinner than the first dielectric.

7. The electrowetting system of claim 1, further comprising 1 to 10 additional dielectric pairs, wherein: Each additional dielectric is thinner than the first dielectric pair; and Each additional dielectric pair comprises two layers, wherein one of the two layers has a higher dielectric constant than the other of the two layers.

8. The electrowetting system of claim 7, wherein each layer of each additional dielectric pair is formed by atomic layer deposition (ALD).

9. An electrowetting system for performing droplet operation, the system comprising: Multiple electrodes configured to manipulate fluid droplets in a microfluidic space, wherein each electrode is coupled to a circuit operable to selectively apply a driving voltage to the electrode; and Dielectric stack, comprising: A first dielectric layer having a first dielectric constant, and A thin dielectric pair comprising a second dielectric layer having a second dielectric constant and a third dielectric layer having a third dielectric constant. The third dielectric constant is greater than the second dielectric constant; Ratio T H ∶T L In the range of 3:1 to 8:1, where T H T is the thickness of the third dielectric layer. L The thickness of the second dielectric layer; and The thin dielectric layer is thinner than the first dielectric layer.

10. The electrowetting system according to claim 9, wherein the dielectric constant of the third dielectric layer is greater than the dielectric constant of the first dielectric layer.

11. The electrowetting system according to claim 9, wherein the first dielectric layer comprises aluminum oxide (Al2O3), silicon dioxide (SiO2), or silicon nitride (Si3N4).

12. The electrowetting system of claim 9, wherein the first dielectric layer is formed by plasma-enhanced chemical vapor deposition (PECVD).

13. The electrowetting system of claim 9, wherein the second dielectric layer comprises a material selected from alumina (Al2O3) and silicon dioxide (SiO2).

14. The electrowetting system of claim 9, wherein the third dielectric layer comprises a material selected from hafnium oxide (HfO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), zirconium oxide (ZrO2), yttrium oxide (Y2O3), and lanthanum oxide (La2O3).

15. The electrowetting system of claim 9, wherein the second dielectric layer and the third dielectric layer are formed by atomic layer deposition (ALD).

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