Nanopore cell having seamless working electrode and method for forming same

Abstract

The nanopore cell may include a seamless porous electrode and a well having a hydrophobic sidewall. The seamless porous electrode may be formed by depositing a porous electrode material on a planar electrode support layer formed from conductive layer islands and a dielectric layer. The porous electrode material may form a uniform, seamless column and may be protected during fabrication by depositing a selectively removable protective layer thereon. The well may be formed by forming a hydrophobic cladding on the protective layer and then patterning it. The protective layer may be removed to expose the seamless porous electrode at the bottom of the well.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 029,936, filed May 26, 2020, the entire contents of which are incorporated herein by reference.

[0002] Incorporation by Reference All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. [Background technology]

[0003] background Nanopore membrane devices with pore sizes on the order of one nanometer in inner diameter have shown promise in rapid nucleotide sequencing. When an electric potential is applied across a nanopore immersed in a conducting fluid, there can be a small ionic current due to the conduction of ions across the nanopore. The size of the current is sensitive to the pore size and the type of molecule placed within the nanopore. The molecule can be the nucleotide itself (e.g., as part of a nucleic acid) or a specific tag attached to a specific nucleotide, thereby allowing detection of the nucleotide at a specific position in the nucleic acid. As a way to measure the resistance of the molecule, the voltage in a circuit with the nanopore (e.g., with an integrating capacitor) can be measured to detect which molecule is within the nanopore.

[0004] Despite the success of nanopore-based sequencing sensor chips in some applications, improvements are still desired. For example, improvements in nanopore well structures and methods are needed. In some cases, it has been found that the working electrodes of nanopore-based sequencing sensor chips are preferably made from porous electrode materials to maximize capacitance and surface area. A reliable porous working electrode with the desired properties (such as wettability and proper capacitance) is important for the operation of nanopore-based sequencing devices, so methods are implemented to protect the working electrode during fabrication. In particular, the working electrode needs to be protected during deposition and patterning of the hydrophobic cladding to form the well of the nanopore cell. Some methods of protecting the porous working electrode include the application of a protective layer (such as a dielectric layer) that is used as a buffer layer or sacrificial layer to protect the porous working electrode during subsequent steps. In many cases, it is desirable to easily remove the protective layer by chemical processes and thus expose and operate the porous working electrode. However, the chemicals used to remove the protective layer can potentially attack other layers if not taken into account in the structure and process of forming the porous electrode and nanopore cell. Summary of the Invention

[0005] Quick Overview Thus, nanopore cells and nanopore formation methods are described in accordance with embodiments of the present disclosure. The nanopore cells and methods for forming the nanopore cells ensure that the working electrode is structurally sound such that chemical removal of the protective layer does not adversely affect other components of the nanopore cell. In particular, the nanopore cells and nanopore cell formation methods ensure that the working electrode is formed of a seamless column of porous material, thereby reducing the possibility of chemicals penetrating and damaging other layers of the nanopore cell.

[0006] An embodiment relates to a method for forming a nanopore cell. The method may include providing a device structure having a conductive layer disposed on top of a substrate and an interconnect dielectric layer covering the conductive layer. The method includes removing a portion of the interconnect dielectric layer to form a planar electrode bearing surface. The planar electrode bearing surface has exposed islands of the conductive layer surrounded by remaining portions of the interconnect dielectric layer. The method further includes depositing a porous electrode material onto the planar electrode bearing surface to form a seamless porous electrode layer. The seamless porous electrode layer has columns of porous electrode material. The method further includes depositing a protective layer onto the seamless porous electrode layer, patterning the seamless porous electrode layer and the protective layer to form working electrode islands, depositing and patterning a hydrophobic cladding onto the working electrode islands to form sidewalls of a well of the nanopore cell, and removing at least a portion of the protective layer to expose the porous electrode layer. The exposed porous electrode layer forms at least a portion of a bottom wall of the well of the nanopore cell.

[0007] Some embodiments may include a nanopore cell. The nanopore cell may have a substrate, an electrode backing layer covering the top of the substrate, and a well. The electrode backing layer may have a conductive layer island surrounded by an interconnect dielectric layer and a flat top surface formed by the conductive layer island and the interconnect dielectric layer. The well may have a seamless porous working electrode island disposed on the flat top surface of the electrode backing layer, a hydrophobic cladding surrounding the seamless porous working electrode island and patterned to form a sidewall of the well, and a cavity formed by the hydrophobic cladding and the seamless porous working electrode island. The seamless porous working electrode island may have a column of porous electrode material. In some embodiments, the seamless working electrode island further has a protective layer disposed on the column of porous electrode material, the protective layer configured to be selectively removable to expose the porous electrode material to the cavity.

[0008] A better understanding of the nature and advantages of embodiments of the present invention may be obtained by reference to the following detailed description and accompanying drawings. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 shows one embodiment of a cell in a nanopore-based sequencing chip. [Diagram 2] FIG. 2 shows an embodiment of a cell for performing nucleotide sequencing using Nano-SBS technology. [Diagram 3] FIG. 3 shows an embodiment of an electrochemical cell of a nanopore-based sequencing chip having a TiN working electrode with increased electrochemical capacitance. [Figure 4] FIG. 4 shows a further embodiment of circuitry within a cell of a nanopore-based sequencing chip, in which the voltage applied to the nanopore can be configured to vary over the period during which the nanopore is in a particular detectable state. [Diagram 5] FIG. 5 illustrates the double layer that forms at any interface between a conductive electrode and an adjacent liquid electrolyte. [Figure 6] FIG. 6 illustrates the pseudocapacitive effect that can form simultaneously with the formation of a double layer at the interface between a conductive electrode and an adjacent liquid electrolyte. [Figure 7] 7A-7G show one embodiment of a process for constructing an electrochemical cell of a nanopore-based sequencing chip with a TiN working electrode using chemical mechanical planarization. [Figure 8] 8A-8F show one embodiment of a process for constructing an electrochemical cell of a nanopore-based sequencing chip with a TiN working electrode using photolithography and dry etching. [Figure 9] FIG. 9 illustrates a seam that may be formed in a working electrode constructed using the process illustrated in FIGS. 7A-7G and 8A-8F. [Figure 10] FIG. 10 is a photomicrograph showing a TiN electrode layer formed using the process shown in FIGS. 7A-7G. [Figure 11]FIG. 11 is a photomicrograph showing a TiN electrode layer formed using the process shown in FIGS. 8A-8F. [Figure 12] 12A-12F show one embodiment of a process for constructing an electrochemical cell of a nanopore-based sequencing chip with a seamless working electrode. [Figure 13] FIG. 13 shows a seamless electrode constructed using the process shown in FIGS. 12A-12F. [Figure 14] 14A and 14B are photomicrographs of an example of an array of seamless electrodes formed by the method of FIGS. 12A-12F. [Figure 15] FIG. 15 is a photomicrograph of an example of a seamless TiN electrode layer formed by the method of FIGS. 12A-12F. [Figure 16] FIG. 16 is a flow chart illustrating a method for forming a nanopore cell using seamless electrodes.

[0010] term "Nanopore" refers to a pore, channel, or passageway formed or otherwise provided in a membrane. The membrane may be an organic membrane, such as a lipid bilayer, or a synthetic membrane, such as a membrane made of polymeric materials. The nanopore may be located adjacent to or in close proximity to a sensing circuit, such as a complementary metal oxide semiconductor (CMOS) or field effect transistor (FET) circuit, or an electrode connected to such a sensing circuit. In some examples, the nanopore has a characteristic width or diameter on the order of about 0.1 nanometers (nm) to about 1000 nm. Some nanopores are proteins.

[0011] A "well" in a nanopore device refers to the structure formed by the insulating walls and the working electrode, which may have an electrolyte. A "well profile" refers to a structural description of the well, and may include measurements of the angle and sharpness of the well edges. A "cell" of a nanopore device may have the well, the nanopore (e.g., in the membrane across the well), and the working electrode, as well as other circuitry, such as data acquisition circuitry, at various stages of operation.

[0012] "Dielectric material" refers to an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, charges do not flow through the material as in a conductor, but shift only slightly from their average equilibrium position, resulting in dielectric polarization. "Conducting layer" refers to a layer of material that allows electric current to flow in one or more directions. Metal wire is a common conductor.

[0013] "Porous material" refers to a material that contains pores or voids on the surface of the material. "Spongy material" refers to a material that has an open porous structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Detailed Description In a nanopore device, a membrane may be formed over a well of a dielectric layer. For example, the membrane may include a lipid monolayer formed over the dielectric layer. When the membrane reaches the opening of the well, the lipid monolayer may transition to a lipid bilayer that spans across the opening of the well. The structure of the well and the materials forming the well may play an important role in the formation of the membrane and the insertion of the nanopore into the membrane, and interactions between the materials forming the well may also affect the operation of the nanopore device.

[0015] The following description includes an overview of the structure and operation of the nanopore cell. The structure of the well, the materials forming the well, and the effects of their interactions are also discussed. Problems resulting from interactions between the chemicals used to remove the protective layer and the porous working electrode are also described, along with proposed solutions.

[0016] I. Overview of Nanopore Cells This section introduces the operation of nanopore cells, the construction and use of the cells, and circuits for measuring signals. It explains the capacitive effect at the working electrode (called double-layer capacitance), and describes an exemplary process for constructing a porous working electrode.

[0017] A. Cell operation FIG. 1 shows one embodiment of a cell 100 in a cell array forming a nanopore-based sequencing chip. A membrane 102 is formed on the surface of the cell. In some embodiments, the membrane 102 is a lipid bilayer. A bulk electrolyte 114 containing a protein nanopore transmembrane molecular complex (PNTMC) and an analyte of interest (e.g., a single polymer molecule such as DNA) may be placed directly on the surface of the cell. A single PNTMC 104 may be inserted into the membrane 102 by electroporation. The individual membranes in the array are not chemically or electrically connected to one another. Thus, each cell in the array is an independent sequencer, generating data specific to a single polymer molecule associated with the PNTMC. The PNTMC 104 may modulate the ionic current through the otherwise impermeable bilayer.

[0018] The analog measurement circuit 112 is connected to a working electrode 110 (e.g., made of metal) that is covered by a volume of electrolyte 108 in a well formed in the oxide layer 106. The volume of electrolyte 108 is separated from the bulk electrolyte 114 by an ion-impermeable membrane 102. The PNTMC 104 provides the only path for ionic current to flow across the membrane 102 from the bulk liquid to the working electrode 110. The cell also has a counter electrode (CE) 116. The cell also has a reference electrode 117 that can act as an electrochemical potential sensor.

[0019] FIG. 2 shows an embodiment of a cell 200 for nucleotide sequencing by nanopore-based sequencing by synthesis (Nano-SBS) technology. In the nano-SBS technology, a sequencing template 202 and a primer are introduced into the cell 200. To this template-primer complex, four different tagged nucleotides 208, A, T, G, and C, are added in the bulk aqueous phase. When a correctly tagged nucleotide is complexed with a polymerase 204, the tail of the tag is positioned within the barrel of the nanopore 206. The tag held within the barrel of the nanopore 206 generates a unique ion-blocking signal 210, thereby electronically distinguishing the added base due to the different chemical structures of the tags.

[0020] B. Cell Structure and Use FIG. 3 shows an embodiment of an electrochemical cell 300 of a nanopore-based sequencing chip with a working electrode (e.g., TiN, which has high electrochemical capacitance). The cell 300 has a conductive or metal layer 301. The metal layer 301 connects the cell 300 to the rest of the nanopore-based sequencing chip. In some embodiments, the metal layer 301 is the top metal of a CMOS chip (e.g., metal 6 layer M6 of the underlying circuitry). The cell 300 further has a working electrode 302 and a dielectric layer 303 on top of the metal layer 301. In some embodiments, the working electrode 302 may be circular or octagonal in shape, with the dielectric layer 303 forming a wall surrounding the working electrode 302. The cell 300 further has a dielectric layer 304 on top of the working electrode 302 and the dielectric layer 303. The dielectric layer 304 forms an insulating wall surrounding a well 305.

[0021] In some embodiments, dielectric layer 303 and dielectric layer 304 together form a single dielectric piece. Dielectric layer 303 is the portion disposed horizontally adjacent to working electrode 302, and dielectric layer 304 is the portion disposed above and covering a portion of the working electrode. In some embodiments, dielectric layer 303 and dielectric layer 304 are separate dielectric pieces, which may be formed separately. Well 305 has an opening above the uncovered portion of the working electrode. In some embodiments, the opening above the uncovered portion of the working electrode may be circular or octagonal in shape.

[0022] Within the well 305, a volume of salt solution / electrolyte 306 is disposed above the working electrode 302. The salt solution 306 may include one of lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), lithium glutamate, sodium glutamate, potassium glutamate, lithium acetate, sodium acetate, potassium acetate, calcium chloride (CaClz), strontium chloride (SrClz), manganese chloride (MnClz), and magnesium chloride (MgClz). In some embodiments, the salt solution 306 has a thickness of about 3 microns (μm). The thickness of the salt solution 306 may range from 0 to 5 microns.

[0023] Dielectric materials used to form dielectric layers 303 and 304 include glass, oxide, silicon mononitride (SiN), and the like. The top surface of dielectric layer 304 may be silanized. The silanization forms a hydrophobic layer 320 on the top surface of dielectric layer 304. In some embodiments, hydrophobic layer 320 has a thickness of about 1.5 nanometers (nm). Alternatively, a dielectric material that is hydrophobic, such as hafnium oxide, may be used to form dielectric layer 304.

[0024] As shown in FIG. 3, the membrane may be formed on top of a dielectric layer 304 and span a well 305. For example, the membrane may have a lipid monolayer 318 formed on top of a hydrophobic layer 320, and when the membrane reaches the opening of the well 305, the lipid monolayer transitions to a lipid bilayer 314 that spans the opening of the well. The hydrophobic layer 320 facilitates the formation of the lipid monolayer 318 on the dielectric layer 304 and the transition from the lipid monolayer to the lipid bilayer. A bulk electrolyte 308 containing a protein nanopore transmembrane molecular complex (PNTMC) and an analyte of interest is placed directly above the well. A single PNTMC / nanopore 316 is inserted into the lipid bilayer 314 by electroporation. The nanopore 316 traverses the lipid bilayer 314 and provides the only path for ion flow from the bulk electrolyte 308 to the working electrode 302. The bulk electrolyte 308 may further include one of lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), lithium glutamate, sodium glutamate, potassium glutamate, lithium acetate, sodium acetate, potassium acetate, calcium chloride (CaCb), strontium chloride (SrCb), manganese chloride (MnCb), and magnesium chloride (MgCb).

[0025] The cell 300 has a counter electrode (CE) 310. The cell 300 also has a reference electrode 312 that acts as an electrochemical potential sensor. In some embodiments, the counter electrode 300 may be shared among multiple cells and is therefore also referred to as a common electrode. The common electrode may be configured to apply a common potential to a bulk liquid in contact with the nanopore in the measurement cell. The common potential and the common electrode are common to all measurement cells.

[0026] The working electrode 302 is a titanium nitride (TiN) working electrode with enhanced electrochemical capacitance. The electrochemical capacitance associated with the working electrode 302 can be increased by maximizing the specific surface area of ​​the electrode. The specific surface area of ​​the working electrode 302 is expressed as the number of electrodes per unit mass (e.g., m 2 / kg) or per unit volume (e.g., m 2 / m 3 , m 2 / m 3, or m -1 ), or per unit of base area (e.g., m 2 / m 2 ) Increasing the surface area increases the electrochemical capacitance of the working electrode, allowing more ions to be transferred at the same applied potential before the capacitor becomes charged. The surface area of ​​the working electrode 302 can be increased by making the TiN electrode "spongy" or porous. The TiN sponge creates a large effective surface area for soaking up and contacting the electrolyte. Techniques for making and using TiN are further described in U.S. Patent No. 10,174,371 to Foster et al.

[0027] Other materials that may be used to form the working electrode include ruthenium, as further described in Au et al., International Publication No. WO2020043653.

[0028] The capacitance associated with the membrane (C membrane ) and the capacitance associated with the working electrode (C electrochemical ) can be adjusted to achieve optimal overall system performance. The improvement in system performance is due to the electrochemical While maximizing C membrane This can be achieved by reducing C membrane can be tuned to produce the required RC time constant without requiring additional on-chip capacitance, thereby allowing for significant reduction in cell size and chip size.

[0029] In cell 300, the basal surface area of ​​the opening of well 305 (which is the same as the basal surface area of ​​lipid bilayer 314) and the basal surface area of ​​working electrode 302 are determined by the dimensions of dielectric layer 304 and dielectric layer 303, respectively. The basal area of ​​working electrode 302 is equal to or greater than the basal area of ​​the opening of well 305. Thus, the two basal surface areas are expressed as C membrane and C. electrochemical3, a portion of the working electrode 302 is covered by the dielectric 304, so that the covered portion is not in direct contact with the salt solution / electrolyte 306. By using a spongy, porous TiN working electrode, the electrolyte can diffuse vertically down the uncovered portion of the working electrode through the spaces between the columnar TiN structures and then horizontally to the covered portion of the working electrode 302 beneath the dielectric layer 304. As a result, the effective surface area of ​​the TiN in contact with the electrolyte is maximized, resulting in a high C electrochemical is the maximum.

[0030] C. Signal measurement circuit Figure 4 shows one embodiment of an intracellular circuit 400 of a nanopore-based sequencing chip, where the voltage or current applied to the nanopore can be configured to vary over the period of time that the nanopore is in a particular detectable state. Instead of showing a nanopore inserted into a membrane and the fluid surrounding it, Figure 4 shows an electrical model 402 that represents the electrical properties of the nanopore and membrane, and an electrical model 414 that represents the electrical properties of the working electrode.

[0031] The electrical model 402 includes a capacitor 406 (C membrane ) and a resistor 404 that models the resistance associated with the nanopore in different states (e.g., an open channel state or states corresponding to having different types of tags or molecules within the nanopore). The electrical model 414 has a capacitor 416 that models the capacitance associated with the working electrode. The capacitance associated with the working electrode is referred to as the electrochemical capacitance (C electrochemical ) is the electrochemical capacitance associated with the working electrode, C electrochemical includes double layer capacitance and may further include pseudo capacitance.

[0032] 4 also has a switch 408 coupled to a voltage 410 that can be switched on and off for purposes of measuring the resistance 404. In some embodiments, the voltage 410 is applied to an electrical model 402 representing the nanopore. After the capacitor 406 is fully charged (which may not be very long, as the membrane desirably has a low capacitance), the switch 408 can be opened and current can flow from one side of the capacitor 406 through the resistor 404 to the other side. Different resistor 404 values ​​will result in different currents flowing and therefore different voltage decays. The capacitor 416 can be large enough so as not to have a significant effect on the circuit.

[0033] After a specified amount of time, the voltage can be measured at the ADC (analog-to-digital converter) 412. This is because after a specified amount of time, the voltage change correlates with the resistance of the pore (and therefore the molecule within it), so that RC membrane Embodiments may also measure the amount of time it takes to reach a particular voltage, for example, by using a comparator, as described in U.S. Pat. No. 9,377,437.

[0034] D. Capacitive effect at the working electrode (double layer capacitance) It is desirable for the working electrode to have a high capacitance, thereby reducing impedance effects on the circuit that can cause the voltage level to shift slightly as a result of charge accumulation after multiple measurements involving the opening and closing of switch 408.

[0035] FIG. 5 illustrates a double layer that forms at the interface between a conductive electrode and an adjacent liquid electrolyte. The electrical model of the double layer is shown in FIG. 4 as electrical model 414, which models the capacitance associated with the working electrode. In the example shown, the electrode surface is negatively charged, so positively charged species accumulate in the electrolyte. In another example, the polarity of all charges may be opposite to the example shown. The charge in the electrode is balanced by dipole reorientation and accumulation of ions of the opposite charge in the electrolyte near the interface. The charges accumulated on both sides of the interface between the electrode and electrolyte are separated by a small distance due to the finite size of the charged species and solvent molecules in the electrolyte, acting like the dielectric of a conventional capacitor. The term "double layer" refers to the collection of electronic and ionic charge distributions near the interface between the electrode and electrolyte.

[0036] Figure 6 illustrates the pseudocapacitive effect that can form at the interface between a conductive electrode and an adjacent liquid electrolyte while forming a double layer similar to Figure 5. Figure 6 illustrates a double layer with the addition of pseudocapacitance from charge transfer resulting in adsorption, intercalation, or reduction-oxidation reactions limited by the available surface area (represented by the black circles).

[0037] E. Example of the construction process for a porous working electrode 7A-7G and 8A-8F illustrate an embodiment of a process for constructing an electrochemical cell of a nanopore-based sequencing chip with a TiN working electrode. Similar processes are described, for example, in U.S. Patent Application Serial No. 15 / 920,158, filed March 18, 2018, the contents of which are incorporated herein in their entirety. In particular, FIGS. 7A-7G illustrate one embodiment of a process for constructing an electrochemical cell of a nanopore-based sequencing chip with a TiN working electrode using chemical mechanical planarization, and FIGS. 8A-8F illustrate one embodiment of a process for constructing an electrochemical cell of a nanopore-based sequencing chip with a TiN working electrode using photolithography and dry etching. As described in more detail below, the processes result in a working electrode with the desired spongy and porous properties, but both of these methods can result in seams forming in the working electrode layer that can act as weak points and cause performance issues.

[0038] With reference to FIG. 7A, a receiving material 700 may be provided for constructing an electrochemical nanopore cell. The receiving material 700 may have a substrate 701, a conductive layer 702, and a dielectric layer 704 disposed thereon. The substrate 701 may be, for example, a CMOS substrate having circuitry for controlling the operation of the nanopore cell. The conductive layer 702 may be part of the circuitry that delivers signals from the cell to the remainder of the chip. In some cases, the conductive layer 702 may be the top metal layer of the circuitry, for example, the sixth metal layer. However, the conductive layer 702 is not limited to being the sixth metal layer of the underlying circuitry. In some cases, the conductive layer 702 may be an aluminum layer, for example, an aluminum interconnect metal associated with the substrate. As shown in FIG. 7A, the conductive layer 702 is surrounded by a layer of dielectric 704 (e.g., SiO2), which may be an interconnect dielectric disposed between the conductive components of the circuitry of the CMOS substrate as described above.

[0039] 7B, the first step in the process can be to etch a layer of dielectric 704 to form a via 706. The via 706 provides a cavity for forming the spongy and porous electrode desired for the nanopore cell. As shown in FIG. 7B, the via 706 has a sidewall 707 formed by the dielectric 704 that contacts a top surface 709 of the conductive layer 702.

[0040] In the next step shown in FIG. 7C, a spongy and porous electrode layer 708 is deposited to fill the vias 706 created in FIG. 7B. The spongy and porous electrode layer 708 may be a layer of TiN grown and deposited to form rough, sparse TiN columnar structures or columns of TiN crystals that provide a high specific surface area that may be in contact with the electrolyte. The spongy and porous TiN layer 708 may be deposited using a variety of deposition techniques including atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD) sputtering deposition, and the like. Although TiN is described herein as a preferred electrode material, it will be understood that other suitable porous electrode materials may be used.

[0041] 7D, in a further step, excess portions of TiN layer 708 may be removed. For example, chemical mechanical planarization (CMP) techniques may be used to remove the excess TiN layer. The remaining TiN deposited in via 706 forms a spongy, porous working electrode 710.

[0042] As mentioned above, it may be desirable to protect the porous working electrode 710 during further fabrication steps. Specifically, as described below with reference to FIG. 7F, the formation of the wells ultimately requires the formation of a hydrophobic cladding on the porous electrode. However, if the hydrophobic cladding is formed directly on the porous electrode, residues of the hydrophobic cladding may be embedded in the gaps or cavities of the porous electrode. The organic residues may make the electrode surface less wettable and prevent fluids from contacting the surface of the electrode. As a result, the effective surface area may be reduced, causing a significant reduction in double layer capacitance at the electrolyte-electrode interface. To alleviate this problem, a thin buffer or sacrificial protective layer, such as a SiO2 layer, may be formed on the electrode to protect the surface of the electrode before subsequent processing, such as deposition of a polyimide layer. After the wells are formed, the thin sacrificial layer may be removed from the top surface of the electrode. The thin buffer or sacrificial layer serves to protect the porous electrode layer from the hydrophobic layer during the well formation process. Thus, in a step prior to well formation, with reference to FIG. 7E, a protective layer 712 may be deposited on the working electrode 710. As mentioned above, the protective layer 712 may be used as a buffer or sacrificial layer to protect the working electrode 710 during fabrication so as to retain the desired wettability and capacitance for operation. As described in previously incorporated U.S. patent application Ser. No. 15 / 920,158, the protective layer 712 may be a dielectric material such as silicon oxide or a metallic material such as titanium. In either case, the protective layer may be selected to be selectively removable.

[0043] In the step shown in Figure 7F, hydrophobic cladding 714 can be formed and patterned to form a well 716 over the working electrode 710 and protective layer 712. As can be seen in Figure 7F, the presence of protective layer 712 prevents the hydrophobic cladding 714 from being formed directly over the working electrode 710. Once deposited and patterned, hydrophobic cladding 714 forms the sidewalls of well 716. The bottom of well 716 shown in Figure 7F initially has protective layer 712.

[0044] As can be seen in FIG. 7G, once the hydrophobic cladding is formed and patterned and processing is otherwise finalized, the protective layer 712 may be chemically removed to expose the working electrode 710 in the well 716. In particular, the protective layer 712 may be removed by applying a removal reagent including hydrofluoric acid (HF), nitric acid, or any other reagent that will adequately remove the protective layer 712. As an example, the protective layer 712 may be removed by a wet etching method using hydrofluoric acid (HF). The resulting nanopore cell 750 has an exposed working electrode 710 and a well 716 with a sidewall formed by the hydrophobic cladding 714.

[0045] An alternative process for constructing an electrochemical cell of a nanopore-based sequencing chip is provided in Figures 8A-8F. The process shown in Figures 8A-8F is similar to that shown in Figures 7A-7G, except that the working electrode and protective layer are patterned together using photolithography and dry etching rather than chemical mechanical planarization techniques as described in Figures 7A-7G. Specifically, Figure 8A shows the same receiving material 700 as in Figure 7A, having a substrate 701, a conductive layer 702, and a dielectric layer 704 disposed thereon, and Figure 8B shows the same etching of the dielectric 704 to form a via 706 to form a spongy and porous TiN electrode. As in Figure 7B, the via 706 has a sidewall 707 formed by the dielectric 704 that contacts the top surface 709 of the conductive layer 702.

[0046] Next, as shown in Figure 8C, a spongy, porous TiN layer 708 is deposited to fill the vias 706 created in Figure 8B, and a protective layer 812 is deposited on the porous TiN layer 708. Next, as shown in Figure 8D, the porous TiN layer 708 and protective layer 812 are patterned to create a working electrode 810 having a patterned protective layer 813. As mentioned above, the patterned protective layer 813 serves to protect the working electrode 810 during a subsequent well formation step described below with reference to Figure 8E.

[0047] With reference to Figure 8E, hydrophobic cladding 814 may be formed and patterned to form wells 816 similar to the process shown in Figure 7F. As discussed above with reference to Figure 7F, in Figure 8E it can be seen that the presence of protective layer 813 prevents the hydrophobic cladding 814 from being formed directly on the working electrode 810. Once deposited and patterned, hydrophobic cladding 814 forms the sidewalls of well 816, the bottom of which initially has protective layer 813.

[0048] As can be seen in FIG. 8F, once the hydrophobic cladding has been formed and patterned and processing is otherwise determined, the protective layer 813 may be chemically removed to expose the working electrode 810 in the well 816. In particular, the protective layer 813 may be removed by applying a removal reagent including hydrofluoric acid (HF), nitric acid, or any other reagent that will adequately remove the protective layer 813. As an example, the protective layer 813 may be removed by a wet etching process using hydrofluoric acid (HF). The resulting nanopore cell 850 has an exposed working electrode 810 and a well 816 with a sidewall formed by the hydrophobic cladding 814.

[0049] While the process described in Figures 7A-7G and 8A-8F above generally provides an electrochemical cell suitable for nanopore-based sequencing, several drawbacks associated with the growth of the porous electrode material have been observed. Specifically, it has been observed that while the deposition of the porous electrode material results in the growth of columns of electrode material having the desired porous properties, such growth occurs not only upward from the top of the conductive surface (i.e., top surface 709 shown in Figures 7B and 8B) as intended, but also perpendicular to this intended growth from the sidewalls of the deposition via (i.e., sidewalls 707 shown in Figures 7B and 8B). As a result, the columns growing upward from the top of the conductive surface and the columns growing laterally from the sidewalls of the deposition via collide with each other, forming a seam that continues to propagate until the deposition of TiN is complete.

[0050] FIG. 9 illustrates a seam that may form in a working electrode constructed using the process illustrated in FIGS. 7A-7G and 8A-8F. As can be seen in FIG. 9, columns of TiN 908 grow both vertically from the top surface 909 of the conductive layer 902 and horizontally from the sidewall 907 to form seam 918. Similar seams have been observed in examples fabricated using processes similar to those in FIGS. 7A-7G and 8A-8F. For example, seam 1018 may be observed in FIG. 10, which is a micrograph showing a TiN electrode layer formed using the process illustrated in FIGS. 7A-7G, and seam 1118 may be observed in FIG. 11, which is a micrograph showing a TiN electrode layer formed using the process illustrated in FIGS. 8A-8F.

[0051] It will be appreciated that the aforementioned seams formed in the non-planar vias result in undesirable voids that ultimately become weak points in the structure of the electrode layer (as can be seen in Figures 10 and 11). These voids and weak points can allow material to seep through the electrode layer and interact with or attack other layers of the nanopore cell, dramatically impacting the performance of the nanopore cell. In particular, removal reagents (such as HF or nitric acid-containing reagents) used to remove the protective layers described in the above process can seep through the voids formed by the described seams. For example, these reagents can attack the interconnect dielectric layers (e.g., layer 704 as shown in Figures 7A-7G and 8A-8F) that may be used to separate the conductive interconnects of the device. Ultimately, damage to these layers can cause misalignment of the well structure, shorting of the electrodes, and crosstalk between the electrodes, all of which can severely impact the performance of the nanopore cell.

[0052] II. Nanopore Cell with Seamless Electrodes A. Method for constructing a seamless working electrode To avoid the aforementioned seams and their associated drawbacks, a method for constructing a nanopore cell with a seamless working electrode is described. In particular, Figures 12A-12F show one embodiment of a process for constructing an electrochemical cell of a nanopore-based sequencing chip with a seamless working electrode.

[0053] As can be seen in FIG. 12A, the receiving material 1200 may be similar to the input material 700 described above with respect to FIGS. 7A and 8A, including a substrate 1201, a conductive layer 1202, and an interconnect dielectric layer 1204 disposed thereon.

[0054] In a next step, as shown in FIG. 12B, a planar electrode support layer 1205 may be formed by removing at least a portion of the interconnect dielectric layer 1204. The planar electrode support layer 1205 has both the conductive layer islands 1202 and the surrounding interconnect layer 1204 that remains after the removal of the portions thereof. Thus, the planar electrode support layer 1205 has a planar electrode support surface 1203 that has both the top surfaces of the conductive layer islands 1202 and the top surface of the surrounding interconnect layer 1204 that remains after the removal. The removal of the dielectric layer 1204 may be performed by blanket etching the dielectric layer 1204 to expose the islands of the conductive layer 702. In contrast to the previous process, there are no vias with sidewalls onto which the electrode material is deposited. Rather, the electrode material is deposited on a completely planar electrode support surface 1203.

[0055] In the next step shown in FIG. 12C, a porous electrode material 1208, such as TiN, may be deposited on the planar electrode support surface 1203. As can be seen from FIG. 12C, there are no via sidewalls for columnar growth of the porous electrode material in a vertical direction, so no seams are formed in the porous electrode material. Thus, the deposited porous electrode material 1208 forms uniform, seamless columns of porous electrode material. These uniform seamless columns are further shown in FIG. 13, which illustrates a seamless electrode layer constructed using the process shown in FIGS. 12A-12C. Once deposited, the seamless porous electrode material 1208 may be protected by depositing a protective layer 1212 thereon, as can also be seen in FIG. 12C. As mentioned above, the protective layer 1212 may be composed of a dielectric material or a metallic material. Examples of protective dielectrics that may be used include silicon oxide, titanium oxide, hafnium oxide, zirconium oxide, and the like. Other suitable dielectric materials (e.g., protective layer 1212) for use in embodiments of the present invention include, but are not limited to, oxides, nitrides (e.g., silicon mononitride or SiN), silicon oxide, silicon oxynitride, metal oxides, metal nitrides, metal silicates, transition metal oxides, transition metal nitrides, transition metal silicates, metal oxynitrides, metal aluminates, zirconium oxide, zirconium silicate, zirconium aluminate, hafnium oxide, titanium oxide, or combinations thereof. Those skilled in the art will recognize other dielectric materials suitable for use in the present invention. Examples of other materials that may be used as protective layers include titanium, aluminum, tantalum, tungsten, or non-porous titanium nitride. Those skilled in the art will recognize other metallic materials suitable for use in the present invention.

[0056] The porous electrode layer 1208 and protective layer 1212 are then patterned to create a patterned working electrode 1210 and protective layer 1213, as shown in FIG. 12D. The TiN and protective layer may be patterned together using photolithography and dry etching, or other suitable processes used to pattern such materials. The resulting working electrode is an island of uniform columns of TiN without the undesirable seams mentioned above, over which the protective layer is disposed.

[0057] In a further step, referring to FIG. 12E, a hydrophobic cladding 1214 may be formed and patterned on the electrode 1210 and protective layer 1213 to form a well 1216, similar to the process shown in FIG. 7F and FIG. 8E. As previously described with reference to FIG. 7F and FIG. 8E, the patterned hydrophobic cladding 1214 forms the sidewalls of the well 1216, the bottom of which initially includes the protective layer 1213 so as not to expose the working electrode 1210. Examples of hydrophobic materials that may be used include polyimide, epoxy, polybenzoxazole (PBO), benzocyclobutene (BCB). Those skilled in the art will recognize other hydrophobic materials suitable for use with the present invention.

[0058] Next, referring to FIG. 12F, once the fabrication process is otherwise complete, the protective layer 1213 may be chemically removed using a removal reagent, thereby exposing the working electrode 1210 to the well 1216. As discussed above, the protective layer 1213 may be chemically removed by a removal reagent containing HF, nitric acid, other suitable reagents, and / or combinations thereof, depending on the material selected for the protective layer 1212 / 1213. For example, if the protective layer 1212 / 1213 is comprised of silicon dioxide or the like, it may be removed using a buffered oxide etch (BOE) with a concentration ranging from 8:1 to 100:1 (NH4F:HF). On the other hand, if the protective layer 1212 / 1213 is comprised of a metallic material, a dilute HF / nitric acid mixture with a concentration ranging from 10:1:1 to 500:1:1 (H2O:HF:HNO3) may be used for removal. Those skilled in the art will appreciate other reagents suitable for use with the present invention. Depending on the protective material and the removal reagent, various processes may be used to remove the protective material. In some embodiments, protective layer 1213 may be removed by a wet etching process using any of the aforementioned reagents, although one of ordinary skill in the art would recognize other processes suitable for removal in the present invention. In contrast to the aforementioned methods, because electrode 1210 is formed of uniform seamless columns of TiN, it is highly unlikely that a removal reagent would penetrate and attack other layers, such as dielectric 1204.

[0059] FIG. 16 is a flow chart illustrating a method for forming a nanopore cell with seamless electrodes. The method 1600 includes, in step 1610, providing a device structure having a conductive layer disposed on top of a substrate and an interconnect dielectric layer overlying the conductive layer. Further details are provided in the description associated with FIG. 12A. In step 1620, a portion of the interconnect dielectric is removed to form a planar electrode support surface having exposed islands of the conductive layer surrounded by remaining portions of the interconnect dielectric layer. Further details are provided in the description associated with FIG. 12B. In step 1630, a porous electrode material is deposited on the planar electrode support surface to form a seamless porous electrode layer composed of columns of the porous electrode material. Further details are provided in the description associated with FIG. 12C and FIG. 13. In step 1640, a protective layer is deposited on the seamless porous electrode layer. Further details are provided in the description associated with FIG. 12C. In step 1650, the seamless porous electrode layer and the protective layer are patterned to form working electrode islands. Further details are provided in the description associated with FIG. 12D. In step 1660, a hydrophobic cladding is deposited and patterned to form the sidewalls of the wells of the nanopore cells. Further details are provided in the description associated with Figure 12E. In step 1670, a portion of the protective layer is removed to expose the porous electrode layer in the wells of the nanopore cells. Further details are provided in the description associated with Figure 12F.

[0060] B. Nanopore cell with seamless working electrode 12F shows a nanopore cell 1250 having a substrate 1201, an electrode backing layer 1205 covering the top of the substrate 1201, and a well 1216. The electrode support has a conductive layer island 1202 surrounded by an interconnecting dielectric layer 1204, and a flat top surface 1203 formed by the conductive layer island 1202 and the interconnecting dielectric layer 1204. The well 1216 has a seamless porous working electrode island 1210, a hydrophobic cladding 1214 that surrounds the seamless porous working electrode island 1210 and is patterned to form the sidewalls of the well 1216, and a cavity formed by the hydrophobic cladding 1214 and the seamless porous working electrode island 1210. The seamless porous working electrode island 1210 is disposed on the flat top surface 1203 of the planar electrode backing layer 1205 and is composed of a column of porous electrode material.

[0061] 14A and 14B are top and perspective view photomicrographs, respectively, of an example of an array of seamless electrodes formed by the method of FIGS. 12A-12E, and FIG. 15 is a SEM (scanning electron microscope) image showing an example of a nanopore device having a seamless TiN electrode layer 1510 formed by the method of FIGS. 12A-12E. As can be seen in each of these figures, the columns of electrode material have the desired porosity and uniformity, with no visible seams that could act as voids or weak points that allow removal reagents to permeate. Thus, electrode materials fabricated using the method of FIGS. 12A-12E may be better configured to prevent damage to other components of the nanopore well.

[0062] In the preceding description, for purposes of explanation, numerous details have been set forth in order to provide an understanding of various embodiments of the present technology. However, it will be apparent to one skilled in the art that certain embodiments may be practiced without some of these details or with additional details.

[0063] Where a range of values ​​is provided, each intervening value is understood to be between the upper and lower limits of the specifically disclosed range, to one tenth of the unit of the lower limit, unless the context clearly indicates otherwise. Smaller ranges are included between a stated value or intervening value in a stated range and another stated value or intervening value in that stated range. The upper and lower limits of these smaller ranges may be independently included or excluded in the range, and each range is also included in the present invention when either the upper or lower limit is included, neither is included, or both are included in the range, subject to any specifically excluded limit in the stated range. When a stated range includes one or both of the limits, the range excluding one or both of the included limits is also included.

[0064] As used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, a reference to a "method" includes a plurality of such methods. It will be further understood that as used herein, the terms "comprises" and / or "comprising" specify the presence of stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items and may be abbreviated as " / ".

[0065] Several embodiments of the present invention have been described above. However, those skilled in the art will recognize that various modifications, alternative structures, and equivalents may be used without departing from the spirit of the present invention. For example, in the above description, a polyimide layer is used as an example of a hydrophobic material for well formation, but other organic materials with hydrophobic surface properties, such as CYTOP, an amorphous fluoropolymer, may also be used in other embodiments. In addition, other dielectric materials with suitable etch selectivity and process compatibility, such as silicon nitride, zirconium oxide, and hafnium oxide, besides silicon oxide, may also be used to form the sacrificial layer. Furthermore, some well-known processes and elements have not been described to avoid unnecessarily obscuring the present invention. Furthermore, details of a particular embodiment may not always be present in the variations of that embodiment or may be added to other embodiments.

[0066] When a feature or element is referred to herein as being "on" another feature or element, it may be directly on the other feature or element, or intervening features and / or elements may also be present. In contrast, when a feature or element is referred to as being "directly" on another feature or element, there are no intervening features or elements. When a feature or element is referred to as being "connected," "attached," or "coupled" to another feature or element, it will be understood that it can also be directly connected, attached, or coupled to the other feature or element, or there may be intervening features or elements. In contrast, when a feature or element is referred to as being "directly connected," "directly connected," or "directly coupled" to another feature or element, there are no intervening features or elements. Although described or illustrated with respect to one embodiment, features and elements so described or illustrated may be applicable to other embodiments. It will also be understood by one skilled in the art that references to structures or features located "adjacent" to another feature may have portions that overlap or underlie the adjacent feature.

[0067] Spatially relative terms such as "under," "below," "lower," "over," "upper," and the like may be used herein to describe the relationship of one element or feature to another element or feature shown in the figures for ease of description. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, an element described as "below" or "below" the other element or feature would become "above" the other element or feature. Thus, the exemplary term "below" may encompass both an orientation of above and below. The device may be oriented in other ways (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly. Similarly, terms such as "upward," "downward," "vertical," "horizontal," and the like are used herein for descriptive purposes only, unless otherwise noted.

[0068] Although the terms "first" and "second" may be used herein to describe various features / elements (including steps), these features / elements should not be limited by these terms unless the context dictates otherwise. These terms may be used to distinguish one feature / element from another. Thus, a first feature / element described below may be referred to as a second feature / element, and similarly, a second feature / element described below may be referred to as a first feature / element without departing from the teachings of the present invention.

[0069] Throughout this specification and the claims that follow, unless the context dictates otherwise, the word "comprise" and variations such as "comprises" and "comprising" are meant to be used in conjunction with methods and articles (e.g., compositions and devices and devices that include methods). For example, the term "comprising" is understood to imply the inclusion of any element or step described herein, but not the exclusion of any other element or step.

[0070] As used herein and in the claims, including those used in the examples, unless expressly specified otherwise, all numbers may be interpreted as if they begin with the word "about" or "approximately", even if the term is not expressly indicated. The phrase "about" or "approximately" may be used when describing a size and / or location to indicate that the described value and / or location is within a reasonable expected range of values ​​and / or locations. For example, a numerical value may have a value of + / -0.1% of the stated value (or range of values), + / -1% of the stated value (or range of values), + / -2% of the stated value (or range of values), + / -5% of the stated value (or range of values), + / -10% of the stated value (or range of values), etc. Any numerical value provided herein should also be understood to include approximately that value, unless the context indicates otherwise. For example, if the value "10" is disclosed, then "about 10" is also disclosed. Any numerical range described herein is intended to include all subranges contained therein. It is also understood that when a value is disclosed as being "less than or equal to," "greater than or equal to" and possible ranges between values ​​are also disclosed, as would be understood by one of ordinary skill in the art. For example, when a value "X" is disclosed, "less than or equal to X" as well as "greater than or equal to X" (e.g., X is a numeric value) are also disclosed. It is also understood that throughout this patent application, data is provided in many different formats, and this data represents end and starting points, and ranges for any combination of data points. For example, when a specific data point "10" and a specific data point "15" are disclosed, it is understood that greater than, greater than, less than, less than, less than, and equal to 10 and 15 are considered to be disclosed, as well as between 10 and 15. It is also understood that each unit between two specific units is also disclosed. For example, when 10 and 15 are disclosed, 11, 12, 13, and 14 are also disclosed.

[0071] Although various exemplary embodiments have been described above, several modifications may be made to the various embodiments without departing from the scope of the invention, as set forth in the claims. For example, the order in which the various method steps described are performed may often be changed in alternative embodiments, and in other alternative embodiments, one or more method steps may be skipped entirely. Any feature of the various apparatus and system embodiments may be included in some embodiments and not in other embodiments. Thus, the foregoing description has been provided primarily for illustrative purposes and should not be construed as limiting the scope of the invention, as set forth in the claims.

[0072] The examples and figures contained herein show, by way of illustration and not limitation, specific embodiments in which the subject matter may be practiced. As previously mentioned, other embodiments may be utilized and derived therefrom, resulting in structural and logical substitutions and changes that may be made without departing from the scope of the present disclosure. Such embodiments of the subject matter of the present invention may be individually or collectively referred to herein by the term "invention" merely for convenience when more than one is actually disclosed, and without any intention to spontaneously limit the scope of this patent application to any single invention or inventive concept. Thus, although specific embodiments have been illustrated and described herein, any configuration calculated to achieve the same purpose may be substituted for the specific embodiment shown. The present disclosure is intended to cover any and all adaptations or variations of the various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those skilled in the art upon reviewing the above description.

[0073] All patents, patent applications, publications, and descriptions discussed herein are hereby incorporated by reference in their entirety for all purposes. None are admitted to be prior art.

Claims

1. 1. A method for forming a nanopore cell, comprising: a conductive layer disposed on top of the substrate; and an interconnect dielectric layer overlying said conductive layer; providing a device structure having removing portions of the interconnect dielectric layer to form a planar electrode bearing surface having exposed islands of the conductive layer surrounded by remaining portions of the interconnect dielectric layer; depositing a porous electrode material onto the planar electrode support surface to form a seamless porous electrode layer comprising columns of the porous electrode material; depositing a protective layer on the seamless porous electrode layer; patterning the seamless porous electrode layer and the protective layer to form a working electrode island; depositing and patterning a hydrophobic cladding on the working electrode island to form sidewalls of a well of the nanopore cell; removing at least a portion of the protective layer to expose the porous electrode layer to the well, the exposed porous electrode layer forming at least a portion of a bottom wall of the well of the nanopore cell; The method comprising:

2. The method of claim 1 , wherein the porous electrode material comprises porous TiN (titanium nitride).

3. The method of claim 1 , wherein the porous electrode material comprises a ruthenium-containing material.

4. 2. The method of claim 1, wherein removing the portion of the interconnect dielectric comprises blanket etching the portion of the interconnect dielectric.

5. The method of claim 1 , wherein the protective layer is comprised of a dielectric material.

6. The method of claim 1 , wherein the protective layer is comprised of silicon oxide.

7. The method of claim 1 , wherein the protective layer is comprised of a metallic material.

8. The method of claim 1 , wherein the protective layer is comprised of titanium.

9. The method of claim 1 , wherein removing at least a portion of the protective layer to expose the porous electrode layer comprises applying a removal reagent to the protective layer.

10. The method of claim 9 , wherein the removal reagent comprises hydrofluoric acid.

11. The method of claim 9 , wherein the removal reagent is applied using a wet etching process.

12. The method of claim 9 , wherein the removal reagent is applied to the protective layer without damaging the interconnect dielectric layer.

13. The method of any one of claims 1 to 12, wherein the seamless porous electrode layer and the protective layer are patterned using photolithography and dry etching.

14. A substrate; An electrode support layer covering an upper portion of the substrate, a conductive layer island; an interconnect dielectric layer surrounding said conductive layer island; a planar upper surface formed by said conductive layer islands and said interconnect dielectric layer; The electrode backing layer having A well, a seamless working electrode island disposed on the planar upper surface of the electrode backing layer and having columns of porous electrode material; a hydrophobic cladding that surrounds the seamless working electrode island and is patterned to form a sidewall of a well; a cavity formed by the hydrophobic cladding and the seamless working electrode island; The well having A nanopore cell having

15. The nanopore cell of claim 14 , wherein the porous electrode material comprises porous TiN (titanium nitride).

16. The nanopore cell of claim 14 , wherein the porous electrode material comprises a ruthenium-containing material.

17. 15. The nanopore cell of claim 14, wherein the seamless working electrode island further comprises a protective layer disposed over the column of porous electrode material, the protective layer configured to be selectively removable to expose the porous electrode material to the cavity.

18. The nanopore cell of claim 17 , wherein the protective layer is configured to be removed by application of a removal reagent.

19. The nanopore cell of claim 18 , wherein the removal reagent comprises hydrofluoric acid.

20. 20. The nanopore cell of claim 18, wherein the column of porous electrode material is configured to prevent the electrode backing layer from being damaged by the removal reagent.

21. The nanopore cell of claim 17 , wherein the protective layer is composed of a dielectric material.

22. The nanopore cell of claim 21 , wherein the protective layer is composed of silicon oxide.

23. The nanopore cell of claim 17 , wherein the protective layer is made of a metallic material.

24. 24. The nanopore cell of claim 23, wherein the protective layer is comprised of titanium.

25. The nanopore cell of any one of claims 14 to 24, wherein the conductive layer islands comprise aluminum.

26. The nanopore cell of any one of claims 14 to 24, wherein the interconnect dielectric comprises silicon oxide.

27. The nanopore cell of any one of claims 14 to 24, wherein the hydrophobic cladding comprises polyimide.

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