DIGITAL TIME RANGE READOUT CIRCUIT FOR BIOFET SENSORS

Abstract

Sensor readout circuit, comprehensive: a plurality (601) of cascaded logic gates (401; 403; 405; 501-1, 501-2, 501-N), wherein each logic gate comprises at least one BioFET sensor (404; 410); a delay extractor (610) configured to generate a pulse width signal (612) based on a time difference between an output signal from the plurality (601) of logic gates (401; 403; 405; 501-1, 501-2, 501-N) and a reference signal; and a counting module (614) configured to receive the pulse width signal (612) and output a digital count value corresponding to a width of the pulse width signal (612); the counting module (614) comprises: an AND gate (702) configured to receive the pulse width signal and a clock signal and to output a pulse count signal; and a digital counter (708) configured to receive the pulse counting signal and output the digital count value.

Description

BACKGROUND

[0001] Biosensors are devices for sensing and detecting biomolecules and operate based on electronic, electrochemical, optical, and mechanical detection principles. Biosensors that incorporate transistors are sensors that electrically sense charges, photons, and mechanical properties of bio-entities or bio-molecules. Detection can be performed by detecting the bio-entities or bio-molecules themselves or by interaction and reaction between specified reactants and bio-entities / bio-molecules. Such biosensors can be fabricated using semiconductor processes, can rapidly convert electrical signals, and can be easily incorporated into integrated circuits (ICs) and MEMS.

[0002] Additional circuitry is often required to read signals from the biosensors and generate a quantifiable detection signal. Such circuitry can generate an analog output signal or use an analog-to-digital (ADC) converter to measure an analog signal from the biosensor and generate a digital detection signal. Analog signals are easily affected by noise, and the circuit components used with analog signals can consume a large portion of the overall power of the biosensor system. Furthermore, integrating an ADC increases chip cost and area.

[0003] DE 10 2016 117 555 A1 describes a biologically sensitive field-effect transistor comprising: a substrate, a first control gate, and a second control gate. The substrate has a first side and a second side opposite the first side, a source region, and a drain region. The first control gate is arranged on the first side of the substrate. The second control gate is arranged on the second side of the substrate. The second control gate comprises a sensing film arranged on the second side of the substrate. A bias voltage between the source region and the second control gate is smaller than a threshold voltage of the second control gate. Further prior art is known from CA 2 619 000 C, US 2017 / 0 067 890 A1, DE 10 2007 048 727 A1, and US 2015 / 0 053 925 A1.

[0004] The invention is defined in the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying drawings. Note that, in accordance with industry practice, various features are not drawn to scale. Indeed, the dimensions of the various features may be arbitrarily exaggerated or reduced for clarity of description. Fig. 1 shows components of a sensing device according to some embodiments. Fig. 2 shows a cross-sectional view of an exemplary dual-gate back FET sensor according to some embodiments. Fig. 3A shows a cross-sectional view of an exemplary dual-gate back FET sensor according to some embodiments. The Fig. 3B and Fig. 3C illustrate the use of the dual-gate back FET sensor as a pH sensor according to some embodiments. The Fig. 4A-4C illustrate logic gates including a BioFET sensor, according to some embodiments. Fig. 5 shows several logic gates according to some embodiments using cascaded BioFET sensors. Fig. 6 shows a readout circuit for performing sensing using BioFET sensors according to some embodiments. Fig. 7 shows components of a counting module according to some embodiments. Fig. 8 shows another readout circuit for performing sensing using BioFET sensors according to some embodiments. Fig. 9 shows components of a counting module according to some embodiments. Fig. 10 shows another readout circuit for performing sensing using BioFET sensors according to some embodiments. Fig. 11 shows components of a counting module according to some embodiments. Fig. 12 shows a flowchart of an example method for measuring a sense signal from one or more BioFET sensors according to some embodiments. Fig. 13 shows a flowchart of another example method for measuring a sense signal from one or more BioFET sensors, according to some embodiments. Fig. 14 shows a flowchart of another example method for measuring a sense signal from one or more BioFET sensors, according to some embodiments. Fig. 15 shows a cross-sectional view of an exemplary dual-gate backside FET sensor that detects DNA, according to some embodiments. Fig. Figure 16A shows the binding mechanics of DNA on a receptor surface according to some embodiments. Fig. Figure 16B shows a change in threshold voltage for the exemplary dual-gate backside FET sensor based on appropriate analyte binding, according to some embodiments. Fig. 17 shows a cross-sectional view of an exemplary dual-gate back FET sensor having antibodies immobilized on its sensing layer, according to some embodiments. Fig. Figure 18 shows the binding mechanics of antigens and antibodies on a receptor surface according to some embodiments. DETAILED DESCRIPTION

[0006] The following disclosure provides many different embodiments or examples for implementing various features of the specified subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. For example, forming a first feature over or on a second feature in the following description may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed and / or arranged between the first and second features such that the first and second features need not be in direct contact. Additionally, the present disclosure may repeat reference numbers and / or letters in the various examples.This in itself does not impose any relationship between the various described embodiments and / or configurations.

[0007] Furthermore, spatially relative terms such as "below," "under," "lower," "above," "upper," and the like may be used herein for convenience of description to describe the relationship of one element or feature to other element(s) or feature(s) as shown in the figures. The spatially relative terms are intended to encompass various orientations of the device being used or operated in addition to the orientation shown in the figures. The device may be oriented in other ways (e.g., rotated 90 degrees or in other orientations), and the spatially relative terms used herein may also be interpreted accordingly. terminology

[0008] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein may be used in the practice or testing of embodiments consistent with the disclosure, those methods, apparatus, and materials are described now. All patents and publications mentioned herein are incorporated by reference for the purpose of describing and disclosing the materials and methods reported in the publications that could be used in connection with the present disclosure.

[0009] The acronym "FET," as used here, refers to a field-effect transistor. One example of a FET type is called a metal-oxide-semiconductor field-effect transistor (MOSFET). MOSFETs can be planar structures fabricated in and on the planar surface of a substrate, such as a semiconductor wafer. MOSFETs can also have a three-dimensional, fin-based structure.

[0010] The term "BioFET" refers to a FET comprising a layer of immobilized capture reagents that act as surface receptors to detect the presence of a target analyte of biological origin. A BioFET, according to some embodiments, is a field-effect sensor with a semiconductor transducer. One advantage of BioFETs is the possibility of label-free operation. In particular, BioFETs allow the avoidance of expensive and time-consuming labeling procedures, such as labeling an analyte with fluorescent or radioactive probes. The analytes for detection by a BioFET are typically of biological origin, such as, without limitation, proteins, carbohydrates, lipids, tissue fragments, or parts thereof.A BioFET may be part of a broader class of FET sensors that can also detect any chemical compound (known in the art as a "ChemFET") or any other element, for example, ions such as protons or metal ions (known as an "ISFET"). This disclosure relates to all types of FET-based sensors ("FET sensor"). One specific type of FET sensor described herein is a dual-gate back-side FET sensor.

[0011] "S / D" refers to the source / drain junctions, which form two of the four terminals of a FET.

[0012] The term "high-k" refers to a high dielectric constant. In the field of semiconductor device structures and fabrication processes, high-k refers to a dielectric constant higher than the dielectric constant of SiO2 (i.e., higher than 3.9).

[0013] The term “analysis” generally refers to a process or step involving physical, chemical, biological or biological analysis, including, without limitation, description, testing, measurement, optimization, separation, synthesis, addition, filtering, dissolution or mixing.

[0014] The term “assay” generally refers to a method or step that involves the analysis of a chemical or target analyte and includes, without limitation, cell-based assays, biochemical assays, high-throughput assays and screening, diagnostic assays, pH determination, nucleic acid hybridization assays, polymerase activity assays, nucleic acid and protein sequencing, immunoassays (e.g., antibody-antigen binding assays, ELISAs, and iqPCR), bisulfite methylation assays to detect the methylation pattern of genes, protein assays, protein binding assays (e.g., protein-protein, protein-nucleic acid, and protein-ligand binding assays), enzymatic assays, coupled enzymatic assays, kinetic measurements (e.g.,Protein folding kinetics and enzymatic reaction kinetics), enzyme inhibitor and activator screening, chemiluminescence and electrochemiluminescence assays, fluorescence assays, fluorescence polarization and anisotropy assays, absorbance and colorimetric assays (e.g., Bradford tests, Lowry tests, Hartree-Lowry tests, biuret tests, and BCA tests), chemical assays (e.g., for the detection of environmental pollutants and contaminants, nanoparticles, or polymers), and drug detection assays. The devices, systems, and methods described herein may utilize or adopt one or more of these tests for use with the FET sensor designs described herein.

[0015] The term "liquid biopsy" generally refers to a biopsy sample obtained from a subject's body fluid, as opposed to a tissue sample from the subject. The ability to perform assays using a body fluid sample is often preferable to using a tissue sample. The less invasive approach of using a body fluid sample has far-reaching consequences regarding patient well-being, the ability to conduct longitudinal disease monitoring, and the ability to obtain expression profiles even when tissue cells are not readily accessible, e.g., in the prostate. Assays used to detect target analytes in liquid biopsy samples include, without limitation, those described above. As a non-limiting example, a circulating tumor cell (CTC) assay can be applied to a liquid biopsy sample.

[0016] For example, a capture reagent (e.g., an antibody) immobilized on a FET sensor can be used to detect a target analyte (e.g., a tumor cell marker) in a liquid biopsy sample using a CTC assay. CTCs are cells that have migrated from a tumor into the blood vessels and circulate, for example, in the bloodstream. Generally, CTCs are present in the bloodstream at very low concentrations. To perform an assay on CTCs, CTCs are enriched from patient blood or plasma using various techniques known in the art. CTCs can be stained with specific markers using methods known in the art, including, without limitation, cytometry-based (e.g., flow cytometry)-based methods and immunohistochemistry (IHC)-based methods.For the devices, systems, and methods described herein, CTCs can be captured or detected using a capture reagent. In another example, the nucleic acids, proteins, or other cellular milieu of the CTCs can be used as target analytes for binding or detection by a capture reagent.

[0017] An increase in the target analyte that indicates or contains CTCs can help determine whether the subject has a cancer (e.g., one associated with the target analyte) likely to respond to a specific therapy, or can allow optimization of a therapeutic regimen, e.g., with an antibody to the target analyte. CTC measurement and quantification can provide information, for example, about tumor stage, response to therapy, disease progression, or a combination thereof. The information obtained by detecting the target analyte for CTCs can be used, for example, as a prognostic, predictive, or pharmacodynamic biomarker. Additionally, CTC assays can be used on a liquid biopsy sample either alone or in combination with further tumor marker analysis of solid biopsy samples.

[0018] The term “identification” generally refers to the process of determining the identity of a target analyte based on its binding to a capture reagent whose identity is known.

[0019] The term “measurement” generally refers to the process of determining the amount, type, or properties of a target analyte based on its binding to a capture reagent.

[0020] The term “quantification” generally refers to the process of determining the amount or concentration of a target analyte based on its binding to a capture reagent.

[0021] The term "detection" generally refers to the process of determining the presence or absence of a target analyte based on its binding to a capture reagent. Detection includes, without limitation, identification, measurement, and quantification.

[0022] The term “chemical” refers to a substance, compound, mixture, solution, emulsion, dispersion, molecule, ion, dimer, macromolecule such as a polymer or protein, biomolecule, deposit, crystal, chemical constituent or group, particle, nanoparticle, reagent, reaction product, solvent or liquid, each of which may be in solid, liquid or gaseous form and which may be the subject of analysis.

[0023] The term ‘reaction’ refers to a physical, chemical or biological transformation involving at least one chemical substance and which generally involves (in the case of chemical, biochemical and biological transformations) the breaking or formation of one or more bonds such as covalent, non-covalent, van der Waals, hydrogen or ionic bonds.The term “reaction” includes typical chemical reactions such as synthesis reactions, neutralization reactions, degradation reactions, replacement reactions, redox reactions, precipitation, crystallization, combustion reactions and polymerization reactions as well as covalent and non-covalent bonding, phase change, color change, phase formation, crystallization, dissolution, light emission, changes in light absorption or emission properties, temperature change or heat absorption or emission, conformational change and folding or unfolding of a macromolecule such as a protein.

[0024] "Capture reagent" as used herein is a molecule or compound capable of binding the target analyte or reagent, and which may be bound directly or indirectly to a substantially solid material. The capture reagent may be a chemical, and in particular, any substance for which there is a naturally occurring target analyte (e.g., an antibody, polypeptide, DNA, RNA, cell, virus, etc.) or for which a target analyte can be prepared, and the capture reagent may bind one or more target analytes in an assay.

[0025] "Target analyte" as used herein is the substance to be detected in the test sample using the present disclosure. The target analyte may be a chemical, and in particular, any substance for which a naturally occurring capture reagent (e.g., an antibody, polypeptide, DNA, RNA, cell, virus, etc.) exists or for which a capture reagent can be prepared, and the target analyte may bind one or more capture reagents in an assay. "Target analyte" also includes all antigenic substances, antibodies, and combinations thereof. The target analyte may include a protein, a peptide, an amino acid, a carbohydrate, a hormone, a steroid, a vitamin, a drug, for example, one administered for therapeutic purposes as well as one administered for illicit purposes, a bacterium, a virus, and metabolites or antibodies of any of the above substances.

[0026] "Test sample," as used herein, refers to the composition, solution, substance, gas, or liquid containing the target analyte to be detected and assayed using the present disclosure. The test sample may contain other components besides the target analyte, may have the physical properties of a liquid or gas, and may be of any size or volume, including, for example, a moving gas or liquid stream. The test sample may contain any other substances besides the target analyte, as long as the other substances do not interfere with the binding of the target analyte to the capture reagent or the specific binding of the first binding member to the second binding member. Examples of test samples include, without limitation, naturally occurring and non-naturally occurring samples, or combinations thereof. Naturally occurring test samples may be synthetic or synthesized.Naturally occurring test samples include body or body fluids isolated from any location in or on the body of a subject, such as, without limitation, blood, plasma, serum, urine, saliva or sputum, spinal fluid, cerebrospinal fluid, pleural fluid, nipple aspirate, lymph fluid, respiratory, intestinal and genitourinary tract fluid, tear fluid, breast milk, lymphatic system fluid, semen, fluid in an organ system, ascites, tumor cyst fluid, amniotic fluid and combinations thereof and environmental samples such as groundwater or wastewater, soil extracts, air and pesticide residues or food samples.

[0027] Detected substances may include, for example, nucleic acids (e.g., DNA and RNA), hormones, various pathogens (e.g., biological agents that cause illness or discomfort to the affected person, such as a virus (e.g., H7N9 or HIV), a protozoan (e.g., Palsmodium-causing malaria), or a bacterium (e.g., E. coli or Mycobacterium tuberculosis)), proteins, antibodies, various drugs or therapeutics, or other chemical or biological substances, such as hydrogen or other ions, non-ionic molecules or compounds, polysaccharides, small chemical compounds, such as entries in a chemical combinatorial library, and the like. Detected or determined parameters include, without limitation, pH changes, lactose changes, concentration changes, particles per unit time when a fluid is used to detect particles (e.g.,rare particles) flows over the device during a period of time, and other parameters.

[0028] As used herein, the term "immobilized," when used in reference to, for example, a capture reagent, essentially encompasses the attachment of the capture reagent at the molecular level to a surface. For example, a capture reagent can be immobilized on a surface of the substrate material using adsorption techniques, such as non-covalent interactions (e.g., electrostatic forces, van der Waals forces, and dehydration of hydrophobic interfaces), and covalent bonding techniques where functional groups or linkers enable the capture reagent to adhere to the surface. Immobilizing a capture reagent to a surface of a substrate material can be based on the properties of the substrate surface, the medium supporting the capture reagent, and the properties of the capture reagent.In some cases, a substrate surface can first be modified so that functional groups are attached to the surface. The functional groups can then bind to biomolecules or biological or chemical substances to immobilize them.

[0029] The term "nucleic acid" generally refers to a group of nucleotides linked together by a phosphodiester bond and refers to a naturally occurring nucleic acid to which a naturally occurring nucleotide present in nature is linked, such as DNA containing deoxyribonucleotides in which adenine, guanine, cytosine, and / or thymine are linked together, and / or RNA containing ribonucleotides in which adenine, guanine, cytosine, and / or uracil are linked together. In addition, non-naturally occurring nucleotides and non-naturally occurring nucleic acids are within the scope of the nucleic acid of the present disclosure. Examples include peptide nucleic acids (PNA), peptide nucleic acids with phosphate groups (PHONA), bridged / locked RNA (BNA / LNA), and morpholine nucleic acids.Further examples include chemically modified nucleic acids and nucleic acid analogues such as methylphosphonate DNA / RNA, phosphorothioate DNA / RNA, phosphoramidate DNA / RNA, and 2'-O-methyl DNA / RNA. Nucleic acids include those that can be modified. For example, a phosphoric acid group, a sugar, and / or a base in a nucleic acid can be labeled as necessary. Any substance for labeling nucleic acids in the art can be used for labeling. Examples of these include, without limitation, radioactive isotopes (e.g., 32P, 3H, and 14C), DIG, biotin, fluorescent dyes (e.g., FITC, Texas, cy3, cy5, cy7, FAM, HEX, VIC, JOE, Rox, TET, Bodipy493, NBD, and TAMRA), and phosphors (e.g., acridinium esters).

[0030] As used herein, aptamer refers to oligonucleic acids or peptide molecules that bind to a specific target molecule. The concept of using single-stranded nucleic acids (aptamers) as affinity molecules for protein binding is based on the ability of short sequences to fold into specific three-dimensional structures in the presence of a target, binding the target with high affinity and specificity. Aptamers can be oligonucleotide ligands selected for high-affinity binding to molecular targets.

[0031] The term "antibody," as used herein, refers to a polypeptide of the immunoglobulin family that can bind a corresponding antigen non-covalently, reversibly, and in a specific manner. For example, a naturally occurring IgG antibody is a tetramer having at least two heavy (H) chains and two light (L) chains linked by disulfide bonds. Each heavy chain comprises a heavy chain variable region (abbreviated herein as "VH") and a heavy chain constant region. The heavy chain constant region comprises three domains: CH1, CH2, and CH3. Each light chain comprises a light chain variable region (abbreviated herein as "VL") and a light chain constant region. The light chain constant region comprises a CL domain.The VH and VL regions can be further subdivided into regions of hypervariability called complementarity-determining regions (CDRs), interspersed with more conserved regions called framework regions (FRs). Each VH and VL consists of three CDRs and four FRs arranged from the amino terminus to the carboxyl terminus in the following order: FR1, CDR1, FR2, CDR2, FR3, CDR3, and FR4. The three CDRs constitute approximately 15–20% of the variable domains. The variable regions of the heavy and light chains contain a binding domain that interacts with an antigen. The constant regions of antibodies can mediate the binding of the immunoglobulin to host tissues or factors, such as various cells of the immune system (e.g., effector cells) and the first component (C1q) of the classical complement system.

[0032] The term "antibody" includes, without limitation, monoclonal antibodies, human antibodies, humanized antibodies, chimeric antibodies, and anti-idiotypic (anti-Id) antibodies (including, for example, anti-Id antibodies of the antibodies of the present disclosure). The antibodies may belong to any isotype / class (e.g., IgG, IgE, IgM, IgD, IgA, and IgY) or subclass (e.g., IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2).

[0033] The term "polymer" refers to any substance or compound consisting of two or more building blocks ("mers") that are repeatedly bonded together. For example, a "dimer" is a compound in which two building blocks have been bonded together. Polymers include both polycondensates and polymerizates. Examples of condensation polymers include polyamide, polyester, protein, wool, silk, polyurethane, cellulose, and polysiloxane. Examples of polymerizates are polyethylene, polyisobutylene, polyacrylonitrile, poly(vinyl chloride), and polystyrene. Other examples include polymers with enhanced electrical or optical properties (e.g., a nonlinear optical property), such as electrically conductive or photorefractive polymers. Polymers include both linear and branched polymers. Overview of an exemplary biosensor device

[0034] Fig. 1 shows an overview of components that may be included in a biosensor test platform 100. The biosensor test platform 100 includes a sensor array 102 having at least one sensor element for detecting a biological or chemical analyte, and a fluid delivery system 104 configured to deliver one or more fluid samples to the sensor array 102. The fluid delivery system 104 may be simple, such as a microfluidic well disposed over the sensor array 102 to hold a fluid over the sensor array 102. The fluid delivery system 104 may also include microfluidic channels for delivering various fluids to the sensor array 102. The fluid delivery system 104 may include any number of valves, pumps, chambers, and channels configured to deliver fluid to the sensor array 102.

[0035] A readout circuit 106 is provided, according to some embodiments, to measure signals from the sensors in the sensor array 102 and generate a quantifiable sensor signal indicative of the amount of a particular analyte present in a target solution. Various embodiments of the readout circuit 106 described herein utilize digital components to reduce power consumption and chip area.

[0036] A controller 108 can be used to send and receive electrical signals to both the sensor array 102 and the readout circuit 106 to perform the biological or chemical sensor measurement. The controller 108 can also be used to send electrical signals to the fluid delivery system 104, for example, to actuate one or more valves, pumps, or motors.

[0037] The sensor array 102 may comprise an array of BioFETs, with one or more of the BioFETs in the array functionalized to detect a specific target analyte. Different sensors may be functionalized using different capture reagents to detect different target analytes. Further details regarding an exemplary design of specific BioFETs are provided later.

[0038] The controller 108 may include one or more processing devices, such as a microprocessor, and may be programmable to control the operation of the readout circuit 106 and / or the sensor array 102. The details of the controller 108 itself are not important for understanding the embodiments described herein. However, the various electrical signals that may be sent and received by the sensor array 102 will be described in more detail later.

[0039] Details regarding the design and operation of the BioFET sensors themselves in the sensor array 102 are given first, followed by a detailed description of various readout circuit architectures using digital components. Dual-gate backside FET sensors

[0040] An exemplary type of BioFET sensor that may be used in sensor array 102 is the dual-gate backside FET sensor. Dual-gate backside FET sensors use semiconductor manufacturing techniques and biological capture reagents to form sensors in an array. While MOSFETs may have a single gate electrode connected to a single electrical node, the dual-gate backside FET sensor has two gate electrodes, each connected to a different electrical node. A first of the two gate electrodes is referred to herein as the "frontside gate," and the second of the two gate electrodes is referred to herein as the "backside gate." Both the frontside gate and the backside gate are configured to be electrically charged and / or discharged during operation, thereby affecting the electric field between the source / drain terminals of the dual-gate backside FET sensor.The front-side gate is electrically conductive, separated from a channel region by a front-side gate dielectric, and configured to be charged and discharged by an electrical circuit to which it is coupled. The back-side gate is separated from the channel region by a back-side gate dielectric and includes a biofunctionalized sensing layer disposed on the back-side gate dielectric. The amount of electrical charge on the back-side gate depends on whether a bio-detection response has occurred. In operation of dual-gate back-side FET sensors, the front-side gate is charged to a voltage within a predetermined voltage range. The voltage at the front-side gate determines a corresponding conductivity of the channel region of the FET sensor. A relatively small amount of change in the electrical charge at the back-side gate changes the conductivity of the channel region.It is this change in conductivity that indicates a bio-recognition reaction.

[0041] One advantage of FET sensors is the possibility of label-free operation. In particular, FET sensors allow the avoidance of expensive and time-consuming labeling processes, such as labeling an analyte with fluorescent or radioactive probes.

[0042] Fig. Figure 2 shows an exemplary dual-gate backside FET sensor 200 according to some embodiments. The dual-gate backside FET sensor 200 includes a control gate 202 formed over the substrate 214 and separated therefrom by an intervening dielectric 215 disposed on the substrate 214. The substrate 214 further includes a source region 204, a drain region 206, and a channel region 208 between the source region 204 and the drain region 206. In some embodiments, the substrate 214 has a thickness between approximately 100 nm and approximately 130 nm. The gate 202, the source region 204, the drain region 206, and the channel region 208 may be formed using any suitable CMOS process technology. The gate 202, the source region 204, the drain region 206, and the channel region 208 form a FET. An insulating layer 210 is disposed on the side of the substrate 214 opposite the gate 202.In some embodiments, the insulating layer 210 has a thickness of about 1 μm. In this disclosure, the side of the substrate 214 over which the gate 202 is disposed is referred to as the "front side" of the substrate 214. Similarly, the side of the substrate 214 on which the insulating layer 210 is disposed is referred to as the "back side."

[0043] An opening 212 is provided in the insulation layer 210. The opening 212 may be substantially aligned with the gate 202. In further embodiments, the opening 212 is larger than the gate 202 and may extend across multiple dual-gate backside FET sensors. An interfacial layer (not shown) may be disposed within the opening 212 on the surface of the channel region 208. The interfacial layer may serve to provide an interface for positioning and immobilizing one or more receptors for detecting biomolecules or bioentities. Further details regarding the interfacial layer are provided herein.

[0044] The dual-gate backside FET sensor 200 includes electrical contacts 216 and 218 to the drain region 206 and the source region 204, respectively. A front-side gate contact 220 may be formed for the gate 202, while a backside gate contact 222 may be formed for the active region 208. It should be noted that the backside gate contact 222 does not need to physically contact the substrate 214 or any interface layer above the substrate 214. Thus, while a FET may use a gate contact to control the conductivity of the semiconductor between the source and drain (e.g., the channel), the dual-gate backside FET sensor 200 allows receptors formed on a side opposite the gate 202 of the FET device to control conductivity, while the gate 202 provides another area to control conductivity.Therefore, the dual-gate back FET sensor 200 can be used to detect one or more specific biomolecules or bioentities in and / or around the opening 212, as described in more detail using various examples herein.

[0045] The dual-gate back-side FET sensor 200 may be connected to: additional passive components such as resistors, capacitors, inductors, and / or fuses; other active components such as p-channel field-effect transistors (PFETs), n-channel field-effect transistors (NFETs), metal-oxide-semiconductor field-effect transistors (MOSFETs), high-voltage transistors, and / or high-frequency transistors; other suitable components; and / or combinations thereof. It is further understood that additional features may be added to the dual-gate back-side FET sensor 200, and some of the described features may be replaced or eliminated for additional embodiments of the dual-gate back-side FET sensor 200.

[0046] Referring to Fig. 3A shows a cross-section of an exemplary dual-gate backside FET sensor 300 according to some embodiments. The dual-gate backside FET sensor 300 is an implementation of a dual-gate backside FET sensor 200. The previously described elements of Fig. 2 are therefore with element numbers from Fig. 2 and their descriptions are not repeated here. The dual-gate backside FET sensor 300 includes a gate 202, a source region 204, a drain region 206, and a channel region 208, with the source region 204 and the drain region 206 formed in the substrate 214. The gate 202, the source region 204, the drain region 206, and the channel region 208 form an FET. It should be noted that the various components of Fig. 3A are not intended to be drawn to scale and are exaggerated for visual convenience as would be understood by a person skilled in the relevant art.

[0047] In some embodiments, the dual-gate backside FET sensor 300 is coupled to various layers of metal interconnects 302 that electrically connect to the various doped regions and other devices formed in the substrate 214. The metal interconnects 302 may be formed using fabrication techniques well known to those skilled in the relevant art.

[0048] The dual-gate backside FET sensor 300 may include a bulk region 304 separated from the source region 204 and the drain region 206. The bulk region 304 may be used to bias the charge carrier concentration in the active region 208 between the source region 204 and the drain region 206. In some embodiments, a negative bias may be applied to the bulk region 304 to improve the sensitivity of the dual-gate backside FET sensor 300. In some embodiments, the bulk region 304 is electrically connected to the source region 204. In some embodiments, the bulk region 304 is electrically grounded.

[0049] The dual-gate back-side FET sensor 300 may be coupled to additional circuitry 306 fabricated in the substrate 214. The circuitry 306 may include any number of MOSFET devices, resistors, capacitors, and / or inductors to form a circuit that supports the operation of the dual-gate back-side FET sensor 300. The circuitry 306 may represent a readout circuit used to measure a signal from the dual-gate back-side FET sensor 300 indicative of analyte detection. The circuitry 306 may include amplifiers, analog-to-digital converters (ADCs), digital-to-analog converters (DACs), voltage generators, logic circuitry, and / or DRAM memory, to name a few examples. In some embodiments, the circuitry 306 includes digital components and does not measure an analog signal from the dual-gate back-side FET sensor 300.All or some of the components of additional circuitry 306 may be integrated into the same substrate 214 as the dual-gate back-side FET sensor 300. It should be understood that many FET sensors, each substantially similar to the dual-gate back-side FET sensor 300, may be integrated into the substrate 214 and coupled to the additional circuitry 306. In another example, all or some of the components of additional circuitry 306 are provided on a different semiconductor substrate than the substrate 214. In yet another example, some components of additional circuitry 306 are integrated into the same substrate 214 as the dual-gate back-side FET sensor 300, and some components of additional circuitry 306 are provided on a different semiconductor substrate than the substrate 214.

[0050] Still referring to the illustrative example of Fig. 3A, the dual-gate backside FET sensor 300 includes an interface layer 308 deposited over the insulating layer 210 and in the opening above the channel region 208. In some embodiments, the interface layer 308 has a thickness between about 20 Å and about 40 Å. The interface layer 308 may be comprised of a high-k dielectric such as hafnium silicate, hafnium oxide, zirconia, alumina, tantalum pentoxide, hafnium dioxide-alumina (HfO2-Al2O3) alloy, or any combination thereof. The interface layer 308 may serve as a support for the attachment of capture reagents, as described in more detail later in the section concerning biological sensing. A solution 312 is provided over the reaction site of the dual-gate back FET sensor 300 and a fluid gate 310 is disposed in the solution 312.The solution 312 may be a buffer solution containing capture reagents, targeting reagents, cleaning solution, or any other biological or chemical substance.

[0051] An exemplary operation of the dual-gate backside FET sensor 300 as a pH sensor will now be described. Briefly, the fluid gate 310 is used to provide electrical contact to the "second gate" of the dual-gate backside FET sensor. The solution 312 is provided over the reaction site of the dual-gate backside FET sensor 300, and the fluid gate 310 is disposed in the solution 312. The pH of the solution generally depends on the concentration of hydrogen ions [H +] in the solution. The accumulation of ions near the surface of the interface layer 308 above the channel region 208 influences the formation of the inversion layer in the channel region 208, which forms the conductive path between the source region 204 and the drain region 206. In some embodiments, a current I ds from the drain region 206 to the source region 204.

[0052] The Stream I dscan be measured to determine the pH of solution 312. In some embodiments, fluid gate 310 is used as the gate of the transistor during sensing, while gate 202 remains floating. In some embodiments, fluid gate 310 is used as the gate of the transistor during sensing, while gate 202 is biased to a given potential. For example, depending on the application, gate 202 may be biased to a potential between -2 V and 2 V while fluid gate 310 is swept through a range of voltages. In some embodiments, during sensing, fluid gate 310 is biased (or grounded) to a given potential, while gate 202 is used as the gate of the transistor (e.g., its voltage sweeps through a range of potentials).The fluid gate 310 may be formed from platinum or one or more other materials commonly used for reference electrodes in electrochemical analysis. An example of a reference electrode is an Ag / AgCl electrode, which has a stable potential value of approximately 0.230 V.

[0053] Fig. Figure 3B shows ions in solution that bind to a surface of the interfacial layer 308. A topmost atomic layer of the interfacial layer 308 is represented as the various free [O - ]-, [OH]- and [OH2 +] bonds. As the ions accumulate on the surface, the total surface charge influences the transistor's threshold voltage. As used herein, the threshold voltage is the minimum potential between the gate and source of a FET sensor required to establish a conductive path of minority carriers between the source and drain of the FET sensor. The total charge is also directly related to the pH of the solution, as a higher accumulation of positive charge indicates a lower pH, while a higher accumulation of negative charge indicates a higher pH.

[0054] Fig. Figure 3C shows an example change in threshold voltage resulting from varying pH values ​​in an n-channel FET sensor. As can be observed in this example, an increase in threshold voltage of 59 mV roughly corresponds to an increase in the pH of the solution by one. In other words, a pH change of one results in a total surface charge equivalent of 59 mV when measured as the voltage required to turn on the transistor.

[0055] Changing the threshold voltage of the dual-gate backside FET sensor 300 also changes the time required to form a conductive path between the source region 204 and the drain region 206 for a given voltage input at either the fluid gate 310 or the gate 202. This time delay in "turning on" the FET sensor can be quantified using digital circuitry, according to some embodiments, and used to determine an analyte concentration. Readout circuits

[0056] The Fig. 4A-4C illustrate example logic gates that utilize a BioFET sensor as at least one of the transistors in the logic circuit, according to some embodiments. Fig. Figure 4A shows an inverter 401 comprising two transistors: a p-channel transistor 402 and a BioFET sensor 404. The BioFET sensor 404 may be a dual-gate backside FET sensor as described with reference to Fig. 3A-C. In the arrangement of inverter 401, a source terminal of p-channel transistor 402 is connected to a positive supply voltage (VDD), while a drain terminal of p-channel transistor 402 is connected to a drain terminal of BioFET sensor 404. A source terminal of BioFET sensor 404 is connected to ground. The gates of p-channel transistor 402 and BioFET sensor 404 are connected together and receive an input signal 406. An output signal 408 is generated at the drain terminals of p-channel transistor 402 and BioFET sensor 404. In an example where the BioFET sensor 404 is a dual-gate back-side FET sensor, the gate of the BioFET sensor 404 that receives the input signal 406 is a front-side gate (similar to the gate 202 in Fig. 3A), while a fluid gate is biased at a given potential between about 0 mV and about 500 mV.

[0057] The p-channel transistor 402 does not need to have a biological interface and does not need to be exposed to a solution during operation. The BioFET sensor 404 may have a surface (such as interface layer 308 for a dual-gate FET design) that is exposed to a solution carrying an analyte to be detected. The analyte may bind to capture molecules configured to bind only to that specific analyte. The capture molecules may already be bound to the surface of the BioFET sensor 404 before the solution carrying the analyte is introduced. In some embodiments, the BioFET sensor 404 represents one sensor output of an array of sensors, which may include a total of over 100, over 1,000, or over 10,000 BioFET sensors. In some embodiments, the BioFET sensor 404 represents multiple BioFET sensors arranged in an array format and electrically coupled at their common terminals.

[0058] The input signal 406 is inverted by the inverter 401 to generate the output signal 408. That is, a rising edge transition of the input signal 406 results in a falling edge transition of the output signal 408, while a falling edge transition of the input signal 406 results in a rising edge transition of the output signal 408. During a rising edge transition of the input signal 406, a positive voltage is applied to the gate of the BioFET sensor 404, turning it on (assuming the BioFET sensor 404 is an n-channel device). The time it takes for the BioFET sensor 404 to turn on depends on its threshold voltage. The binding of different charged analytes to the surface of the BioFET sensor 404 can change its threshold voltage, according to some embodiments.This delay in turning on the BioFET sensor 404 can be quantified in the output signal 408 as Δt, where Δt is the time delay in turning on the BioFET sensor 404 due to a change in the number of charged particles on or near the surface of the BioFET sensor 404. The addition or removal of charge can be caused by a change in the pH in the solution above the BioFET sensor 404 or by the binding of charged analytes to a surface of the BioFET sensor 404. The time delay Δt in the output signal 408 can be a positive delay or a negative delay, depending on the charge polarity present at or near the surface of the BioFET sensor 404, according to some embodiments.

[0059] Fig. 4B shows another example of an inverter 403 including a BioFET sensor 410 and an n-channel transistor 412. The BioFET sensor 410 may be similar to the BioFET sensor 404, except that the BioFET sensor 410 is a p-channel device, while the BioFET sensor 404 is an n-channel device. In the arrangement of the inverter 403, a source terminal of the BioFET sensor 410 is connected to a positive supply voltage (VDD), while a drain terminal of the BioFET sensor 410 is connected to a drain terminal of the n-channel transistor 412. A source terminal of the n-channel transistor 412 is connected to ground. The gates of the BioFET sensor 410 and the n-channel transistor 412 are connected together and receive an input signal 414. An output signal 416 is generated at the drain terminals of the BioFET sensor 410 and the n-channel transistor 412.

[0060] The input signal 414 is inverted by the inverter 403 to generate the output signal 416. Since the BioFET sensor 410 is a p-channel device in the inverter 403, a falling edge transition of the input signal 414 results in a delayed rising edge transition of the output signal 416. The time delay Δt is proportional to the change in the threshold voltage of the BioFET sensor 410. The time delay Δt in the output signal 416 may, according to some embodiments, be a positive delay or a negative delay, depending on the charge polarity present at or near the surface of the BioFET sensor 410.

[0061] Fig. Figure 4C shows another example of an inverter 405 including BioFET sensor 410 acting as the p-channel device and BioFET sensor 404 acting as the n-channel device. The gates of BioFET sensor 404 and BioFET sensor 410 are connected together and receive input signal 406 / 414. Output signal 408 / 416 is generated at the drain terminals of BioFET sensor 404 and BioFET sensor 410. Both the rising and falling edge transitions of input signal 406 / 414 are inverted and delayed at output signal 408 / 416, where the time delay is related to the change in the threshold voltages of BioFET sensor 404 and BioFET sensor 410, respectively.

[0062] Both BioFET sensor 404 and BioFET sensor 410 can be functionalized with the same capture probes to detect the same analyte. In some embodiments, BioFET sensor 404 is functionalized with a different capture probe than BioFET sensor 410, so that binding of a particular target analyte causes a time delay during rising edge transitions or during falling edge transitions.

[0063] By incorporating BioFET sensors as special transistors in a logic gate, the threshold voltage changes of the BioFET sensor can be calculated based on the time delay in the output signal. It should be noted that logic gates other than inverters can also be used to generate output signals with a time delay proportional to the detection output of the BioFET sensors. Accordingly, BioFET sensors can be incorporated into AND gates, NAND gates, OR gates, NOR gates, or XOR gates.

[0064] Fig. 5 shows a delay chain 500 that, according to some embodiments, includes N logic gate stages, labeled 501-1 through 501-N, that are cascaded together. In one embodiment, each logic gate stage includes at least two FET devices, where at least one of the FET devices is a BioFET sensor, such as the BioFET sensor 404 shown in logic gate stage 501-1 and logic gate stage 501-2. In another embodiment, each logic gate stage includes a BioFET sensor and at least one resistive element using known resistor-transistor logic (RTL) configurations. The delay chain 500 has an input signal 502 at a first logic gate 501-1 and generates an output signal 504 at the Nth logic gate (logic gate 501-N).The output signal of each logic gate stage is received as an input signal for a subsequent logic gate stage in the chain, with the exception of the Nth logic gate stage. As mentioned above, logic gate stages 501-1 through 501-N are shown as inverters, however, any logic gates may be cascaded together to form delay chain 500, as would be understood by one skilled in the relevant art.

[0065] By coupling multiple logic gates together, the time delay generated by each BioFET sensor is added together. If Δt is the time delay generated by a single inverter stage in which the BioFET sensor is activated, then the final time delay in the output signal 504 of the Nth stage is approximately equal to Δt * (N / 2). The total number of stages N is divided by 2 because half of the stages activate the BioFET sensor in the Fig. 5. In an example where both the n-channel and p-channel transistors of each of the inverter stages are BioFET sensors, the output signal of the Nth stage would be approximately equal to Δt * N.

[0066] In some embodiments, an output signal can be measured between any two stages in delay chain 500 to measure any BioFET sensors from the previous stages in the chain. For example, if an output signal is measured between the 8th and 9th stages of delay chain 500, the time delay of the output signal is proportional to the sensor activity of the BioFET sensors in stages 1-8, but not stages 9-N. In this way, multiple BioFET sensors can be measured within the same delay chain 500.

[0067] Fig. 6 shows an exemplary readout circuit 600 configured to quantify the time delay generated as a result of the operation of one or more BioFET sensors, according to some embodiments. Readout circuit 600 includes, according to some embodiments, a biosensitive delay chain 601 and a reference delay chain 604, each receiving the same input signal 602. Biosensitive delay chain 601 includes a sequence of cascaded logic circuits including at least one BioFET sensor. An example of biosensitive delay chain 601 is delay chain 500. Biosensitive delay chain 601 may include any type of cascade-coupled logic gates, with each stage of the chain including at least one BioFET sensor. Biosensitive delay chain 601 generates a sensor output signal 606, which may have a biosensitive delay in the time domain.

[0068] The reference delay chain 604 may include a sequence of logic gates cascaded to provide a reference output signal 608. According to some embodiments, the transistors forming the logic gates of the reference delay chain 604 do not have biosensing properties. In some embodiments, one or more of the transistors forming the logic gates of the reference delay chain 604 are functionalized with different capture reagents than those located on the BioFET sensors in the biosensitive delay chain 601. The transistors of the reference delay chain 604 may be physically located near the BioFET sensors of the biosensitive delay chain 601 such that a solution containing a target analyte is disposed over a surface of both the BioFET sensors of the biosensitive delay chain 601 and the transistors of the reference delay chain 604.In another example, the transistors of the reference delay chain 604 are physically located away from the BioFET sensors of the biosensitive delay chain 601 such that the transistors of the reference delay chain 604 are not in contact with any solution.

[0069] According to some embodiments, the reference delay chain 604 includes the same number and type of logic gate stages as the biosensitive delay chain 601. In one example, the reference delay chain 604 is configured such that a time delay between the input signal 602 and the reference output signal 608 is substantially equal to a time delay between the input signal 602 and the sensor output signal 606 when no target analytes are bound to the BioFET sensors in the biosensitive delay chain 601. Because both the biosensitive delay chain 601 and the reference delay chain 604 receive the same input signal 602, a difference in the time domain between the reference output signal 608 and the sensor output signal 606 is related to the amount of target analyte detected by the BioFET sensors of the biosensitive delay chain 601.

[0070] According to some embodiments, the reference delay chain 604 is removed, and the input signal 602 is also used as the reference output signal 608. In this arrangement, a time delay between the reference output signal 608 and the sensor output signal 606 in a control experiment is compared to a time delay between the reference output signal 608 and the sensor output signal 606 after the BioFET sensors have been exposed to a solution containing the target analyte to determine a concentration and / or presence of the target analyte.

[0071] A delay extractor 610 is used to determine the time-domain difference between the sensor output signal 606 and the reference output signal 608, according to some embodiments. The delay extractor generates a pulse width signal 612 with a width that depends on the output signals of the BioFET sensors. The delay extractor 610 may include an XOR gate configured to receive the output signal 606 and the reference output signal 608 as input signals and generate the pulse width signal 612 as an output signal. In one example, the pulse width signal 612 has a width in the nanosecond range (e.g., between 1 ns and 1000 ns).

[0072] According to some embodiments, the readout circuit 600 includes a counting module 614 that receives the pulse width signal 612 and outputs a digital count value corresponding to a width of the pulse width signal 612. The counting module 614 may include any digital counter circuit, as would be understood by one of ordinary skill in the art.

[0073] Fig. Figure 7 shows a view of the counting module 614 according to some embodiments. The counting module 614 includes an AND gate 702 configured to receive the pulse width signal 612 and a reference clock signal 704. The AND gate 702 generates a pulse count signal 706. The pulse count signal 706 includes a given number of clock cycles within a width of the pulse width signal 612. The reference clock 704 may have a frequency between approximately 800 MHz and 1.2 GHz.

[0074] The pulse count signal 706 is received by a counter 708, according to some embodiments. The counter 708 may include flip-flops or latches configured to count a number of clock cycles present in the pulse count signal 706. In one example, the counter 708 includes a sequence of JK flip-flops coupled to the output of a given JK flip-flop, which is connected in series with the clock input of the next JK flip-flop. A binary digital count value may be an output signal of the counter 708.

[0075] Fig. 8 shows another example readout circuit 800 configured to measure the operation of one or more BioFET sensors according to some embodiments. Readout circuit 800 includes a biosensitive oscillator 802 to generate an oscillating sensor output 804. Oscillator 802 may include a biosensitive delay chain 806, which may be similar to delay chain 500. As such, biosensitive delay chain 806 may include a sequence of cascade-coupled inverters including at least one BioFET sensor, or a sequence of any cascade-coupled logic circuits including at least one BioFET sensor.

[0076] To form the oscillating sensing output, the output signal of the biosensitive delay chain 806 is fed back through a feedback line 808 to be received as an input signal for the biosensitive delay chain 806. This creates a ring oscillator with a constantly oscillating sensor output 804 at a frequency based on the number of stages in the biosensitive delay chain 806, the size of the transistors used in the various stages, and the operation of the BioFET sensors in the biosensitive delay chain 806. For example, a target analyte bound to a surface of the BioFET sensors can increase the threshold voltage of the BioFETs, thereby decreasing a resulting frequency of the oscillating sensor output 804.

[0077] According to some embodiments, the readout circuit 800 includes a counting module 810 that receives the oscillating sensor output 804 and outputs a digital count value corresponding to a frequency of the oscillating sensor output 804. The counting module 810 may include any type of digital counter circuit, as would be understood by one of ordinary skill in the art.

[0078] Fig. 9 shows a view of the counting module 810 according to some embodiments. The counting module 810 includes an AND gate 902 configured to receive the oscillating sensor output 804 and a reference clock signal 904. The AND gate 902 generates a count signal 906. The count signal 906 includes a number of cycles of the oscillating sensor output 804 within one clock cycle of the reference clock 904. The number of cycles of the oscillating sensor output signal 804 may be counted to obtain a measure of the width of each cycle (which correlates with the frequency of the oscillating sensor output signal 904). The reference clock 904 may have a frequency between approximately 50 kHz and 150 kHz. In one example, a frequency of the reference clock 904 is selected to be at least 100 times lower, at least 1,000 times lower, or at least 10,000 times lower than a frequency of the oscillating sensor output signal 804.

[0079] The count signal 906 is received by a counter 908, according to some embodiments. The counter 908 may include flip-flops or latches configured to count a number of clock cycles present in the count signal 906. In one example, the counter 908 includes JK flip-flops cascade-coupled with the output of a given JK flip-flop coupled to the clock input of the next JK flip-flop. A binary digital count value may be output from the counter 908.

[0080] Fig. 10 shows another exemplary readout circuit 1000 configured to measure the operation of one or more BioFET sensors according to some embodiments. The readout circuit 1000 includes a biosensitive oscillator 802 to generate an oscillating sensor output 804, as described with reference to Fig. 8. The readout circuit also includes a reference oscillator 1002 configured to generate a reference oscillation signal 1004. According to some embodiments, the reference oscillation signal 1004 has a frequency substantially equal to a frequency of the oscillating sensor output signal 804 when no target analyte is bound to any of the BioFET sensors. In this way, any frequency change in the output signal of the oscillating sensor output 804 due to the presence of a target analyte results in a difference between the oscillating sensor output 804 and the reference oscillation signal 1004. The reference oscillation signal 1004 may have a frequency between about 150 MHz and about 250 MHz.

[0081] According to some embodiments, the transistors forming the logic gates of reference oscillator 1002 do not have biosensing properties. In some embodiments, one or more of the transistors forming the logic gates of reference oscillator 1002 are functionalized with different capture reagents than those located on the BioFET sensors in biosensitive oscillator 802. The transistors of reference oscillator 1002 can be physically disposed near the BioFET sensors of biosensitive oscillator 802 such that a solution containing a target analyte is disposed over a surface of both the BioFET sensors of biosensitive oscillator 802 and the transistors of reference oscillator 1002.In another example, the transistors of reference oscillator 1002 are physically located away from the BioFET sensors of biosensitive oscillator 802 so that the transistors of reference oscillator 1002 are not in contact with any solution.

[0082] The readout circuit 1000 also includes a mixer 1006 that receives the oscillating sensor output 804 and the reference oscillation signal 1004 as input signals. The mixer 1006 may be a digital downconverter that generates a downconverted signal 1008. In some embodiments, the mixer 1006 includes at least one D flip-flop, with the reference oscillation signal 1004 being received as the clock input of the D flip-flop and the oscillating sensor output 804 being received at the data input of the D flip-flop. The down-converted signal 1008 corresponds to a difference in oscillation frequency between the oscillating sensor output 804 and the reference oscillation signal 1004. When no detection occurs at the BioFET sensors, the down-converted signal 1008 has essentially no oscillating signal.However, when the target analyte binds to the BioFET sensors, the down-converted signal 1008 has an oscillation frequency substantially equal to the difference in oscillation frequency between the oscillating sensor output signal 804 and the reference oscillation signal 1004, and corresponding to the amount of target analyte present. When the BioFET sensors are used as pH sensors, a change in pH of one may be approximately equivalent to a 2 MHz shift in the frequency of the oscillating sensor output 804, according to some embodiments.

[0083] According to some embodiments, the readout circuit 1000 includes a counting module 1010 that receives the down-converted signal 1008 and outputs a digital count value corresponding to a frequency of the down-converted signal 1008. The counting module 1010 may include any type of digital counter circuit, as would be understood by one of ordinary skill in the art.

[0084] Fig. 11 shows a view of the counting module 1010 according to some embodiments. The counting module 1010 includes an AND gate 1102 configured to receive the down-converted signal 1008 and a reference clock signal 1104. The AND gate 1102 generates a count signal 1106. The count signal 1106 includes a number of cycles of the down-converted signal 1008 within one clock cycle of the reference clock 1104. The number of cycles of the down-converted signal 1008 may be counted to obtain a measure of the width of each cycle (which correlates with the frequency of the down-converted signal 1008). The reference clock 1104 may have a frequency between about 5 kHz and about 50 kHz. In one example, a frequency of the reference clock 1104 is selected to be at least 100 times lower, at least 1,000 times lower, or at least 10,000 times lower than a frequency of the down-converted signal 1008.

[0085] The count signal 1106 is received by a counter 1108, according to some embodiments. The counter 1108 may include flip-flops or latches configured to count a number of clock cycles present in the count signal 1106. In one example, the counter 1108 includes a sequence of JK flip-flops coupled to the output of a given JK flip-flop, which is coupled to the clock input of the next JK flip-flop in the sequence. A binary digital count value may be output from the counter 1108.

[0086] In Fig. 12, an exemplary method 1200 is shown. The method 1200 may be performed by the readout circuit 600 to measure the sensor output from one or more BioFET sensors in a sensor array. Other operations related to signal filtering or any other signal processing not shown in the method 1200 may be performed either before, between, or after the illustrated operations of the method 1200. The various operations of the method 1200 may be performed in a different order than that shown.

[0087] At block 1202, a biosensor signal is generated. The biosensor signal may be an output of a cascaded sequence of logic gates, each logic gate including at least one BioFET sensor. In one example, each of the cascaded logic gates is an inverter circuit, and a time delay between an input signal of the cascaded sequence of logic gates and the biosensor signal at the output corresponds to the detection of a target analyte.

[0088] At block 1204, a reference signal is generated. The reference signal may be generated by a further cascaded sequence of logic gates arranged similarly to those that generate the biosensor signal. In some embodiments, these cascaded sequences of logic gates do not include BioFET sensors.

[0089] At block 1206, a time delay difference between the biosensor signal and the reference signal is determined. The determined time delay difference may correspond to a concentration of the target analyte bound to the BioFET sensors. The biosensor signal may be delayed in the time domain compared to the reference signal due to changes in the threshold voltages of the BioFET sensors.

[0090] At block 1208, a pulse width signal is generated based on the determined time difference. The pulse width signal may be generated using an XOR gate that receives the biosensor signal and the reference signal as inputs. A pulse width corresponds to a time difference between the biosensor signal and the reference signal.

[0091] At block 1210, a digital count value corresponding to a width of the pulse width signal is determined. A counting module may be used to determine the digital count value, which includes a counter and also uses a reference clock to obtain a number of clock cycles for a given pulse width. The reference clock may have a frequency between approximately 800 MHz and 1.2 GHz. The counter may use cascaded JK flip-flops, with the output of a given JK flip-flop coupled to the clock input of the next JK flip-flop.

[0092] In Fig. 13, an exemplary method 1300 is shown. Method 1300 may be performed by readout circuitry 800 to measure the sensor output from one or more BioFET sensors in a sensor array. Other operations related to signal filtering or any other signal processing not shown in method 1300 may be performed either before, between, or after the illustrated operations of method 1300. The various operations of method 1300 may be performed in a different order than that shown.

[0093] At block 1302, an oscillating biosensor signal is generated. The oscillating biosensor signal may be an output signal of a cascaded sequence of inverters, with the output signal also being fed back to be received as an input signal for the cascaded sequence of inverters. Each of the inverters includes at least one BioFET sensor. A frequency of the oscillating biosensor signal is based on the number of inverter stages, the size of the transistors used for the various inverters, and the operation of the BioFET sensors.

[0094] At block 1304, a digital count corresponding to a frequency of the oscillating biosensor signal is determined. A counting module may be used to determine the digital count, which includes a counter and also uses a reference clock to obtain a given number of cycles of the oscillating biosensor signal for one cycle of the reference clock. The reference clock may have a frequency between approximately 50 kHz and 150 kHz. In one example, a frequency of the reference clock is selected to be at least 100 times lower, at least 1,000 times lower, or at least 10,000 times lower than a frequency of the oscillating biosensor signal. The counter may use cascaded JK flip-flops coupled to the output of a given JK flip-flop, which is coupled to the clock input of the next JK flip-flop.

[0095] In Fig. 14, an exemplary method 1400 is shown. Method 1400 may be performed by readout circuitry 1000 to measure the sensor output from one or more BioFET sensors in a sensor array. Other operations related to signal filtering or any other signal processing not shown in method 1400 may be performed either before, between, or after the illustrated operations of method 1400. The various operations of method 1400 may be performed in a different order than that shown.

[0096] At block 1402, an oscillating biosensor signal is generated. The oscillating biosensor signal may be an output signal of a cascaded sequence of inverters, with the output signal also being fed back to be received as an input signal for the cascaded sequence of inverters. Each inverter includes at least one BioFET sensor. A frequency of the oscillating biosensor signal is based on the number of inverter stages, the size of the transistors used for the various inverters, and the operation of the BioFET sensors.

[0097] At block 1404, an oscillating reference signal is generated. The oscillating reference signal may be generated by another cascaded sequence of logic gates arranged similarly to those that generate the oscillating biosensor signal. In some embodiments, these cascaded sequences of logic gates do not include BioFET sensors. According to some embodiments, the oscillating reference signal has a frequency substantially equal to a frequency of the oscillating biosensor signal when no target analyte is bound to any of the BioFET sensors. In this way, any frequency change of the oscillating biosensor signal due to the presence of a target analyte results in a difference between the oscillating biosensor signal and the oscillating reference signal. The oscillating reference signal may have a frequency between about 150 MHz and about 250 MHz.

[0098] At block 1406, the oscillating reference signal is subtracted from the oscillating biosensor signal using a mixer component. The subtraction results in a down-converted signal output. The down-converted signal corresponds to a difference in the oscillation frequency of the oscillating biosensor signal and the oscillating reference signal. When the BioFET sensors are used as pH sensors, a change of one in pH may approximately correspond to a 2 MHz shift in the frequency of the oscillating biosensor signal.

[0099] At block 1408, a digital count corresponding to a frequency of the down-converted signal is determined. A counting module may be used to determine the digital count, which may include a counter and also use a reference clock to obtain a given number of cycles of the down-converted signal for one cycle of the reference clock. The reference clock may have a frequency between about 5 kHz and about 50 kHz. In one example, a frequency of the reference clock is selected to be at least 100 times lower, at least 1,000 times lower, or at least 10,000 times lower than a frequency of the down-converted signal. The counter may use cascaded JK flip-flops coupled to the output of a given JK flip-flop, which is coupled to the clock input of the next JK flip-flop. Chemistry, biology and interface

[0100] The devices, systems, and methods described in this application can be used to monitor interactions between various entities. These interactions include biological and chemical reactions to detect a target analyte in a test sample. As an example, reactions including physical, chemical, biochemical, or biological changes can be monitored to detect the generation of intermediates, byproducts, products, and combinations thereof. Additionally, the devices, systems, and methods of the invention can be used to detect these reactions in various assays as described herein, for example, without limitation, circulating tumor cell assays used in liquid biopsies and chelation assays for the detection of heavy metals and other environmental pollutants.Such assays and reactions can be monitored in a single format or in an array format, for example, to detect multiple target analytes. Biological sensor examples with double-gate backside FET sensor

[0101] Referring to Fig. 15 shows an exemplary biosensor test using the method described above in Fig. 3. A probe DNA 1504 (an example of a capture reagent) is bound to the interfacial layer 308 via a linker molecule 1502. The linker molecule 1502 may have a reactive chemical group that binds to a portion of the interfacial layer 308. An example of linking molecules is thiols. Linker molecules may also be formed by silanizing the surface of the interfacial layer 308 or by exposing the surface of the interfacial layer 308 to ammonia (NH3) plasma to form reactive NH2 groups on the surface. The silanization process involves sequentially exposing the surface of the interfacial layer 308 to various chemicals to build up covalently bonded molecules on the surface of the interfacial layer 308, as generally understood by one of ordinary skill in the relevant art.The probe DNA 1504 represents single-stranded DNA. The double-gate back-side FET sensor used in . Fig. 15 is a BioFET sensor within a sensor array present on a chip according to some embodiments.

[0102] The probe DNA 1504 can be immobilized on the interfacial layer 308 before exposing the FET sensor to the fluid sample 1501. The fluid sample 1501 can be delivered to the surface of the FET sensor using a fluid delivery system. The fluid sample 1501 can comprise the appropriate single-stranded DNA sequence 1506 that binds strongly to its appropriate probe DNA 1504. The binding of additional DNA increases the negative charge present on the interfacial layer 308 and directly above the channel region 208 of the FET sensor.

[0103] DNA binding is conceptually in Fig. 16A. Here, probe DNA with the nucleic acid sequence TCGA binds to its complementary matching strand with the nucleic acid sequence AGCT. Any mismatched sequences do not hybridize with the probe DNA sequences. Binding of the matching DNA increases the negative charge built up at the interface of the interfacial layer 308. In the Fig. In the example shown in Figure 16A, the interface layer 308 is hafnium oxide.

[0104] Fig. Figure 16B shows a shift in the threshold voltage of the dual-gate backside FET sensor when a matching DNA is bound to the surface of the interface layer 308. In short, a voltage can be applied to the fluid gate 310 until the FET sensor "turns on" and current flows between the drain region 206 and the source region 204. In another example, a voltage is applied to the gate 202 to turn on the FET sensor while the fluid gate 310 is biased to a predetermined potential. When more negative charge is present at the interface layer 308 due to the complementary DNA binding, a higher voltage is required to form the conductive inversion layer in the channel region 208. Thus, according to some embodiments, a higher voltage can be applied to the reference electrode 310 or the gate 202 before the FET sensor conducts and Ids flows.This difference in threshold voltage can be measured and used to determine not only the presence of the matching DNA target sequence, but also its concentration. It should be understood that a net positive overall charge at the interfacial layer 308 causes the threshold voltage to decrease rather than increase. Additionally, the change in threshold voltage has the opposite sign for an n-channel FET compared to a p-channel FET.

[0105] Referring to Fig. 17, another exemplary biosensor test is performed using the dual-gate back-side FET sensor. Probe antibodies 1704 (another example of capture reagents) are bound to the interfacial layer 308 via linker molecules 1702. The linker molecules 1702 may include a reactive chemical group that binds to a portion of the interfacial layer 308. A sample solution 1701 may be provided over the probe antibodies 1704 to determine whether the appropriate antigens are present in the sample solution 1701.

[0106] Referring to Fig. Figure 18 shows the binding process of matching antigens to probe antibodies 1704. Here, matching antigens bind to the antibodies of the immobilized probe, while non-matching antigens do not bind. Similar to the DNA hybridization method described above, the matching antigens change the accumulated charge present at the interface layer 308. The shift in threshold voltage due to the accumulated charge from the matching antibodies binding to the probe antibodies is measured in essentially the same manner as described above with reference to Fig. 16B is described. Concluding remarks

[0107] Embodiments of a readout circuit for use with BioFET sensors are described herein. According to some embodiments, a sensor readout circuit includes a plurality of cascaded logic gates, a delay extractor, and a counting module. Each logic gate of the plurality of logic gates includes at least one BioFET sensor. The delay extractor is configured to generate a pulse width signal based on a time difference between an output signal from the plurality of logic gates and a reference signal. The counting module is configured to receive the pulse width signal and output a digital count value corresponding to a width of the pulse width signal.

[0108] According to some embodiments, a sensor readout circuit comprises a plurality of cascade-coupled inverters, each inverter comprising at least one BioFET sensor. An output signal from the plurality of inverters is fed back to be received as an input signal for the plurality of inverters, thereby forming a ring oscillator. The sensor readout circuit also includes a counting module configured to receive the output signals from the plurality of inverters and output a digital count value corresponding to a frequency of the output signals from the plurality of inverters.

[0109] According to some embodiments, a sensor readout circuit includes a plurality of inverters, a mixer, and a counting module. The plurality of inverters are cascade-coupled, each inverter including at least one BioFET sensor, and an output signal of the plurality of inverters is fed back to be received as an input signal for the plurality of inverters. The mixer receives the output signals of the plurality of inverters and an oscillating reference signal and generates a down-converted signal corresponding to a difference in an oscillation frequency of the output signals of the plurality of inverters and the oscillating reference signal. The counting module is configured to receive the down-converted signal and output a digital count value corresponding to a frequency of the down-converted signal.

Claims

[1] Sensor readout circuit comprising: a plurality (601) of cascade-coupled logic gates (401; 403; 405; 501-1, 501-2, 501-N), each logic gate comprising at least one BioFET sensor (404; 410); a delay extractor (610) configured to generate a pulse width signal (612) based on a time difference between an output signal from the plurality (601) of logic gates (401; 403; 405; 501-1, 501-2, 501-N) and a reference signal; and a counting module (614) configured to receive the pulse width signal (612) and output a digital count value corresponding to a width of the pulse width signal (612); wherein the counting module (614) comprises: an AND gate (702) configured to receive the pulse width signal and a clock signal and to output a pulse count signal; and a digital counter (708) configured to receive the pulse count signal and output the digital count value. [2] The sensor readout circuit of claim 1, further comprising a second plurality (604) of cascade-coupled logic gates, wherein the reference signal is an output signal of the second plurality (604) of logic gates. [3] The sensor readout circuit of claim 2, wherein an input of the plurality (601) of cascade-coupled logic gates (401; 403; 405; 501-1, 501-2, 501-N) and an input of the second plurality (604) of cascade-coupled logic gates are connected to receive a same input signal. [4] Sensor readout circuit according to one of the preceding claims, wherein the plurality (601) of logic gates (401; 403; 405; 501-1, 501-2, 501-N) comprises a plurality of inverters. [5] Sensor readout circuit according to one of the preceding claims, wherein the delay extractor (610) comprises an XOR logic gate. [6] Sensor readout circuit according to one of the preceding claims, wherein the clock signal has a clock frequency between 800 MHz and 1.2 GHz. [7] Sensor readout circuit according to one of the preceding claims, wherein the BioFET sensor is a dual-gate BioFET sensor. [8] A sensor readout circuit according to any preceding claim, wherein the BioFET sensor in each of the logic gates comprises a functionalized surface (308) exposed to a fluid in a microfluidic well or microfluidic channel. [9] Sensor readout circuit, comprising: a plurality (802) of inverters coupled in cascade, each inverter comprising at least one BioFET sensor (404; 410), wherein an output signal of the plurality (802) of inverters is fed back to an input of the plurality (802) of inverters (401; 403; 405; 501-1, 501-2, 501-N); and a counting module (810) configured to receive the output signals of the plurality (802) of inverters and to output a digital count value corresponding to a frequency of the output signals of the plurality of inverters; where the counting module includes: an AND gate (902) configured to receive the output signal of the plurality (802) of inverters and a clock signal (904) and to output a count signal (906); and a digital counter (908) configured to receive the count signal (906) and output the digital count value. [10] Sensor readout circuit according to claim 9, wherein the clock signal has a clock frequency between 50 kHz and 150 kHz. [11] Sensor readout circuit according to one of claims 9 to 10, wherein the BioFET sensor is a double-gate BioFET sensor. [12] Sensor readout circuit according to one of claims 9 to 11, wherein the frequency of the output signals of the plurality of inverters is between 150 MHz and 250 MHz. [13] The sensor readout circuit of any one of claims 9 to 12, wherein the BioFET sensor in each of the inverters has a functionalized surface (308) exposed to a fluid in a microfluidic well or microfluidic channel. [14] Sensor readout circuit comprising: a plurality (802) of inverters coupled in cascade, each of the inverters comprising at least one BioFET sensor (404; 410), wherein an output signal of the plurality (802) of inverters is fed back as an input signal to the plurality (802) of inverters; a mixer (1006) configured to receive the output signal of the plurality (802) of inverters and an oscillating reference signal and to generate a down-converted signal corresponding to a difference in an oscillation frequency of the output signal of the plurality (802) of inverters and the oscillating reference signal; and a counting module (1010) configured to receive the down-converted signal and to output a digital count value corresponding to a frequency of the down-converted signal; wherein the counting module (1010) comprises: an AND gate (1102) configured to receive the down-converted signal and a clock signal and to output a count signal; and a digital counter (1108) configured to receive the count signal and output the digital count value. [15] The sensor readout circuit of claim 14, further comprising a second plurality (1002) of cascade-coupled inverters, wherein an output signal of the second plurality (1002) of inverters is fed back as an input signal to the second plurality (1002) of inverters, and wherein the oscillating reference signal is the output signal of the second plurality (1002) of inverters. [16] A sensor readout circuit according to claim 14 or 15, wherein the mixer (1006) comprises a flip-flop having a clock input coupled to the oscillating reference signal. [17] Sensor readout circuit according to one of claims 14 to 16, wherein the clock signal has a frequency between 5 kHz and 50 kHz.

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