Method and device for controlling a fet

Abstract

The present invention relates to a gate driver system (100) for driving a gate (112) of a field- effect transistor (110) in contact with a liquid. The system (100) includes the field-effect transistor with a gate (112), source (111), and drain (113) for biasing. It features a first drive electrode (120) for applying a driving signal to achieve a voltage at the gate. A first sense electrode (130) is used for measuring the gate voltage, providing a first feedback signal indicative of this voltage. The first drive electrode and / or the second drive electrode is an on- chip metal electrode. A feedback control system (140) is incorporated to regulate the gate voltage by controlling the first drive electrode using the first feedback signal. This system (100) is designed to ensure precise control of the gate voltage.

Description

[0001] Method and Device for controlling a FET

[0002] Field of the Invention

[0003] The present invention relates to the field of controlling field-effect transistors (FETs). More specifically it relates to a method and a device for regulating the gate voltage of a FET interfaced with microfluidic environments.

[0004] Background of the Invention

[0005] The field of bio-sensing has seen significant advancements in recent years, particularly with the integration of microfluidic technology and electronic sensing elements. In this domain, the ability to detect and quantify the presence of various substances within a liquid medium is of paramount importance. These substances can range from simple ions to complex biomolecules, and their detection is crucial in a wide array of applications, including life sciences research, medical diagnostics, environmental monitoring, and more.

[0006] One of the challenges in the field is the detection of very low concentrations of substances within a fluidic cell. The fluidic cell typically contains the liquid sample along with the sensing element, which must interact with the target substances to provide a measurable response. The sensing elements, often based on electronic components such as field-effect transistors (FETs), must be highly sensitive and capable of providing rapid feedback to be useful in time-sensitive applications.

[0007] The use of FETs, including graphene field-effect transistors (GFETs), has been explored due to their high sensitivity and the potential for miniaturization. These transistors operate by modulating electrical signals in response to changes in their environment, such as the presence of specific substances that bind to their sensitive layers. However, the operation of these devices in a fluidic environment introduces several challenges.

[0008] One of the primary issues is the establishment of a stable and reliable reference potential within the fluidic cell. The liquid medium can interact with the electrodes, leading to potential drifts due to chemical reactions. This instability can significantly affect the accuracy and reliability of the sensing system. To address this, reference electrodes made of chemically stable materials, such as silver / silver chloride (Ag / AgCI), are often used. These electrodes are designed to maintain a stable potential but introduce additional complexities due to their intrinsic resistances and capacitances.

[0009] Moreover, the liquid itself, along with the construction of the GFET, contributes additional resistances and capacitances, resulting in a high time constant for the sensing system. This high time constant limits the speed at which the system can respond to changes, which is a significant drawback for applications requiring rapid detection and analysis.

[0010] Despite the progress made in the field there remains a need for further advancements. The existing solutions still face limitations in terms of the speed and stability of the sensing system, particularly when dealing with the complex interplay of resistances, capacitances, and the need for a stable reference potential.

[0011] In summary, while the field of bio-sensing has made strides in integrating electronic sensing elements with microfluidic technology, there is an ongoing need for improvements in the stability, speed, and reliability of these systems. Addressing these challenges, as well as providing a cost-effective and modular solution for biomarker detection, is crucial for the advancement of bio-sensing applications across various disciplines.

[0012] Summary of the Invention

[0013] The aim of the invention is to provide a biosensing system avoiding, or at least mitigating, the drawbacks of known biosensing systems.

[0014] This is achieved using a biosensing system according to claim 1 or using a method according to claim 21.

[0015] A particular aim of the invention is to provide a cost-effective biosensing system providing not only a high sensitivity but also a modular solution for a large spectrum of applications.

[0016] It is an advantage of embodiments of the present invention that a stable, rapid, reliable and scalable (modular) solution is obtained for measurement of bio-markers in a fluid. Depending claims 2 to 20, and 22 to 31 are related to particular advantageous embodiment of the system and of the method. Some particular embodiments allow -near up to simultaneously- multiple markers detection in a same or in different fluids so as to provide a cost effective for a wider range of different applications, furthermore supported by the on-chip solution. Other particular embodiments, notably relying on multiplexing-, demultiplexing- and / or address-based circuits, provide not only scalability, robustness but also allow up to support an implementation of improved signal processing technic for accurate and rapidly detecting the presence and / or concentration of one or more substances.

[0017] It is an object of embodiments of the present invention to enable fast and stable voltage regulation at the gate of a field-effect transistor in contact with a liquid. This objective is accomplished by a gate driver system or method for driving a gate of a field-effect transistor in contact with a liquid according to the invention. This may for example be advantageous for improved biosensing performance or chemical sensitivity.

[0018] Embodiments of the present invention relate to a gate driver system for driving a gate of a field-effect transistor in contact with a liquid, the gate driver system comprising: the fieldeffect transistor, wherein the field-effect transistor comprises the gate, and a source and a drain for biasing the field-effect transistor, a first drive electrode configured for applying a first driving signal to obtain a voltage at the gate, a first sense electrode configured for measuring the voltage at the gate thereby obtaining a first feedback signal indicative of the voltage at the gate, a feedback control system for regulating the voltage at the gate by controlling the first drive electrode using the first feedback signal. The first drive electrode or the first sense electrode is an on-chip metal electrode. It is an advantage of embodiments of the present invention that the maximum frequency limit for gate-source voltage modulation is increased by providing an on-chip metal electrode for the first drive electrode and / or for the first sense electrode in comparison with a system where only reference electrodes are used for the first drive electrode and the first sense electrode.

[0019] In embodiments of the present invention, the first drive electrode is an on-chip metal electrode and the gate driver system may comprise a second drive electrode configured for applying a second drive signal to obtain a voltage at the gate, wherein the second drive electrode is a reference electrode and wherein the feedback control system is configured for also controlling the second drive electrode for regulating the voltage at the gate. This embodiment provides the advantage of enabling more precise control of the gate voltage by utilizing both an on-chip metal electrode and a reference electrode for driving the gate voltage. It is thereby advantageous that the reference electrode is less prone to drift than the on-chip metal electrode.

[0020] In embodiments, the gate driver system may comprise a second sense electrode, configured for measuring the voltage at the gate thereby obtaining a second feedback signal indicative of the voltage at the gate, wherein the feedback control system is configured for also using the second feedback signal for regulating the voltage at the gate. It is an advantage of embodiments of the present invention that the feedback accuracy for the regulation of the gate voltage is improved by incorporating a second sense electrode.

[0021] In embodiments, the first sense electrode or the second sense electrode may be an on- chip metal electrode. It is an advantage of embodiments of the present invention that a more integrated gate driver system is obtained which has a potentially faster response time for sensing the gate voltage. It is, moreover, an advantage of embodiments of the present invention that the on-chip metal electrodes are compatible with a CMOS process allowing a further integration.

[0022] In embodiments, the first sense electrode or the second sense electrode may be a reference electrode. It is an advantage of embodiments of the present invention that a stable reference for sensing the gate voltage is used.

[0023] In embodiments, one or more of the reference electrodes may be an Ag / AgCI electrode. It is an advantage of embodiments of the present invention that a well-established and chemically stable reference electrode material is used.

[0024] In embodiments of the present invention the FET may be a chemical field-effect transistor (ChemFET). In embodiments of the present invention the FET may be an ion sensitive field-effect transistor (ISFET).

[0025] In embodiments of the present invention, the field-effect transistor may be a graphene field-effect transistor (GFET). It is an advantage of embodiments of the present invention that the unique properties of graphene for sensitive and responsive gate control in the field-effect transistor are used.

[0026] Embodiments of the present invention relate to a biosensing system for detecting a substance in a fluid, the biosensing system comprising a gate driver system according to any embodiments of the first aspect, wherein the gate of the field-effect transistor is sensitive to the substance, and wherein the biosensing system comprises a control device which is configured for regulating the voltage at the gate of the field-effect transistor using the gate driver system and which is configured for determining a characteristic of the field-effect transistor for detecting the substance.

[0027] In a third aspect embodiments of the present invention relate to a method for driving and regulating a gate voltage of a field-effect transistor in contact with a liquid, the method comprising: applying a first driving signal to obtain a voltage at the gate of the field-effect transistor using a first drive electrode, measuring the voltage at the gate with a first sense electrode to obtain a first feedback signal indicative of the voltage at the gate, wherein the applied voltage is regulated using a feedback control system based on the first feedback signal. The first drive electrode and / or the first sense electrode is an on-chip metal electrode.

[0028] In embodiments of the present invention the method may include using a second drive electrode for applying a second drive signal to obtain a voltage at the gate wherein the first drive electrode is an on-chip metal electrode and the second drive electrode is a reference electrode. It is advantage of embodiments of the present invention that dual driving signals are provided for more precise gate voltage control.

[0029] In embodiments, the method of measuring the voltage at the gate may include using a second sense electrode to obtain a second feedback signal indicative of the voltage at the gate, wherein the applied voltage is regulated using the feedback control system based on the first feedback signal and / or on the second feedback signal. It is an advantage of embodiments of the present invention that enhanced feedback is provided for more accurate voltage regulation.

[0030] In embodiments, the first sense electrode or the second sense electrode may be an on- chip metal electrode. It is an advantage of embodiments of the present invention that a more integrated approach to sensing the gate voltage is provided.

[0031] In embodiments, the first sense electrode or the second sense electrode may be a reference electrode. It is an advantage of embodiments of the present invention that a stable reference for sensing the gate voltage is provided.

[0032] In embodiments, the applied first driving signal and / or second driving signal may be modulated. It is an advantage of embodiments of the present invention that modulation of the driving signals for potentially improved characterization of the FET is provided.

[0033] It is an advantage of embodiments of the present invention that a gate driver system can be provided which allows for rapid modulation of the gate-source voltage of a field-effect transistor (FET), such as a graphene field-effect transistor (GFET), in contact with a liquid. It is a further advantage of embodiments of the present invention that the gate voltage can be precisely controlled using a combination of on-chip metal electrodes and reference electrodes, such as Ag / AgCI electrodes, which can be beneficial for bio-sensing applications where the detection of low concentrations of substances is critical. It is yet another advantage of embodiments of the present invention that the time constant of the sensing system can be reduced, allowing for higher frequency feedback and better sensing loop stability, which is particularly advantageous in life science and medical applications where rapid detection is essential. It is an advantage of embodiments of the present invention that the use of on-chip metal electrodes for applying the gate voltage to the FET can lead to a reduction in the overall resistance and parasitic capacitances, which in turn can increase the maximum frequency limit for gate-source voltage modulation. It is a further advantage of embodiments of the present invention that the feedback control system can actively drive the gate voltage using one or more force electrodes based on the input of one or more sense electrodes, providing a higher frequency feedback path and improving the stability of the sensing loop. It is a further advantage of embodiments of the present invention that CMOS integration is enhanced by the use of on-chip metal electrodes. Driving and sensing may be performed by using circuit elements arranged in a CMOS semiconductor technology.

[0034] It is an advantage of embodiments of the present invention that the simultaneous driving of the reference electrode and the on-chip metal electrode can significantly increase the modulation frequency, potentially by a factor of 5 to 10, which is beneficial for faster readout times of the GFET-based biosensor.

[0035] The arrangement of electrodes can be detected optically, and the employed force and sense method can be inspected using an oscilloscope, facilitating the detection of the use of the patented solution by others.

[0036] It is an advantage of embodiments of the present invention that the biosensing system can detect substances in a fluid with high sensitivity and speed. The biosensing system may therefore comprise a control device configured for regulating the voltage at the gate of the FET using the gate driver system and for determining a characteristic of the FET for detecting the substance. The control device may be arranged in CMOS semiconductor technology. It is a further advantage of embodiments of the present invention that the method for driving and regulating a gate voltage of a FET in contact with a liquid can include the steps of applying a driving signal using on-chip metal electrodes, measuring the voltage at the gate to obtain feedback signals, and regulating the applied voltage using a feedback control system based on these signals, thereby achieving precise control over the gate voltage for enhanced sensing capabilities.

[0037] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims. The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

[0038] Brief description of the drawings

[0039] FIG. 1 is a schematic drawing of a prior art gate driver system wherein the liquid gate voltage of a FET is controlled using an external reference electrode.

[0040] FIG. 2 is an electric circuit which serves as a model of a reference electrode which may be used in a gate driver system according to embodiments of the present invention.

[0041] FIG. 3 is a schematic drawing of a gate driver system comprising a first drive electrode which is an on-chip metal electrode and a first sense electrode which is an on-chip metal electrode according to embodiments of the present invention.

[0042] FIG. 4 is an electric circuit which serves as a model of an on-chip metal electrode used in a gate driver system according to embodiments of the present invention.

[0043] FIG. 5 is a schematic drawing of a gate driver system comprising a first drive electrode which is an on-chip metal electrode, a second drive electrode which is a reference electrode, and a first sense electrode which is a reference electrode according to embodiments of the present invention.

[0044] FIG. 6 is a schematic drawing of a gate driver system comprising a first drive electrode which is a reference electrode, a first sense electrode which is an on-chip metal electrode, and a second sense electrode which is a reference electrode according to embodiments of the present invention.

[0045] FIG. 7 is a schematic drawing of a gate driver system comprising a first drive electrode which is an on-chip metal electrode, a second drive electrode which is a reference electrode, a first sense electrode which is an on-chip metal electrode, and a second sense electrode which is a reference electrode according to embodiments of the present invention.

[0046] FIG. 8 is a biosensing system according to embodiments of the present invention.

[0047] FIG. 9 is a simulation model of a gate driver system comprising an array of 256 GFETs with distributed on-chip gate electrodes according to embodiments of the present invention. FIG. 10 shows the simulation results of various gate driving systems according to embodiments of the present invention.

[0048] FIG. 11 shows an exemplary flow chart of a method in accordance with embodiments of the present invention.

[0049] FIG. 12 shows a schematic view of a biosensing system with an array of field effect transistors according to embodiments of the present invention

[0050] In the different figures, the same reference signs refer to the same or analogous elements.

[0051] Detailed description of Illustrative Embodiments

[0052] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0053] The terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0054] Moreover, the terms top and over and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

[0055] It is to be noticed that the term "comprising", also used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be interpreted as being limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. The term "comprising" therefore covers the situation where only the stated features are present and the situation where these features and one or more other features are present. The word "comprising" according to the invention therefore also includes as one embodiment that no further components are present. When the word "comprising" is used to describe an embodiment in this application, it is to be understood that an alternative version of the same embodiment, wherein the term "comprising" is replaced by "consisting of", is also encompassed within the scope of the present invention.

[0056] Similarly, it is to be noticed that the term "coupled" should not be interpreted as being restricted to direct connections only. The terms "coupled" and "connected", along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression "a device A coupled to a device B" should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "Coupled" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

[0057] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0058] Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0059] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0060] Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention.

[0061] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0062] The following terms are provided solely to aid in the understanding of the invention.

[0063] As used herein, and unless otherwise specified, the term "gate driver system" refers to an assembly of components designed to control the voltage level at the gate terminal of a fieldeffect transistor (FET), which is a specific type of transistor that uses an electric field to control the flow of current. The gate driver system includes the necessary circuitry and connections to apply driving signals, measure feedback signals, and adjust the driving signals based on the feedback to maintain desired gate voltage levels. Examples of specific embodiments of a gate driver system may include systems with various types of FETs such as graphene field-effect transistors (GFETs), and may be used in biosensing applications or for detecting chemical substances.

[0064] As used herein, and unless otherwise specified, the term "field-effect transistor (FET)" refers to a semiconductor device that controls current flow through a channel using an electric field induced by a voltage applied to its gate terminal. The FET includes three main terminals: the gate, the source, and the drain. The source and drain are the terminals through which current enters and exits the transistor, respectively, and the gate is the control terminal that modulates the current flow through the channel between the source and drain. In embodiments of the present invention the gate is in contact with a liquid, meaning that it is in electrical contact with the liquid (e.g. through an ohmic or a capacitive coupling or a combination of both). Examples of specific embodiments of FETs include but are not limited to MOSFETs, JFETs, and GFETs, with variations such as enhancement-mode or depletion-mode types, and they may be constructed from materials like silicon, gallium arsenide, or graphene. ChemFETs or ISFETs may be used.

[0065] As used herein, and unless otherwise specified, the term "on-chip metal electrode" refers to a conductive metal structure that is fabricated as part of an integrated circuit (IC) on a semiconductor chip. Examples of specific embodiments of on-chip metal electrodes include aluminum, copper, palladium, nickel, platinum, gold that are patterned during the semiconductor manufacturing process to form part of the circuitry on a silicon, gallium arsenide, or other semiconductor material-based chip. Also combinations of these metals may be used (e.g. nickel / palladium / gold). The on-chip metal electrode which is used as drive electrode or as sense electrode is in contact with the liquid of the gate driver system. They may be positioned on the chip. In an embodiment they are near to the FET to be measured. They may for example be neighboring the FET.

[0066] As used herein, and unless otherwise specified, the term "reference electrode" refers to an electrode that has a stable and well-defined electrochemical potential. It may be used as a reference point for the measurement or control of the potential the gate of a FET in a gate driver system in accordance with embodiments of the present invention. The reference electrode is typically used in electrochemical applications to ensure accurate voltage measurements and control. Examples of specific embodiments of reference electrodes include standard hydrogen electrodes, silver / silver chloride (Ag / AgCI) electrodes, and calomel electrodes, among others. Any electrode which provides a stable reference voltage may be used.

[0067] An "Ag / AgCI reference electrode" may comprise a silver wire coated with silver chloride. It is suitable as reference electrode due to its stable and well-defined potential. The Ag / AgCI electrode is often used in conjunction with a salt bridge or electrolyte solution to maintain its potential during use. As used herein, and unless otherwise specified, the term "graphene field-effect transistor (GFET)" refers to a field-effect transistor that utilizes graphene as the channel material through which current flows. Graphene is a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice, known for its exceptional electrical, thermal, and mechanical properties. GFETs leverage the high electron mobility of graphene to achieve highspeed operation and sensitivity, making them suitable for a wide range of applications, including high-frequency electronics and biosensors. Examples of specific embodiments of GFETs include GFET-based sensors for detecting biological molecules, GFETs for high-speed digital circuits, and GFETs for flexible electronics.

[0068] As used herein, and unless otherwise specified, the term "biosensing system" refers to a system designed to detect the presence or concentration of biological substances in a fluid. The system typically includes a sensor element that interacts with the substance to produce a measurable response, such as a change in electrical properties, and a control device that interprets this response to determine the characteristics of the substance. Examples of specific embodiments of biosensing systems include glucose monitors for diabetic care, DNA sensors for genetic testing, DNA sequences of viruses, cortisol, and immunoassays for detecting pathogens or biomarkers.

[0069] Where in embodiments of the present invention reference is made to a pathway configurator, reference is made to an electronic control module, circuit, or subsystem configured to selectively assign and manage the electrical function of one or more electrodes within the biosensing system. The pathway configurator establishes and controls the electrical connections between distributed on-chip metal electrodes and / or off-chip reference electrodes and the feedback control system.

[0070] In particular, the pathway configurator determines whether each electrode operates as a drive electrode, configured to apply a driving signal to the liquid in contact with the gate of a field-effect transistor, or as a sense electrode, configured to measure an electrical potential at the gate and provide a feedback signal indicative of the gate voltage.

[0071] In embodiments of the present invention, the pathway configurator includes multiplexing and / or demultiplexing circuit structures (for example, analog switches, cross- point switches, or address-based selectors) enabling dynamic reconfiguration of electrode roles. This allows for the simultaneous or sequential operation of electrodes as sense or drive electrodes according to the needs of the gate driver system and the biosensing application. In embodiments of the present invention, the pathway configurator may be controlled by the control device (for example, a digital processor or microcontroller), which issues configuration commands via an internal connection or communication bus. This enables the system to dynamically adapt electrode assignments in real time based on operational parameters, such as the detection of specific substances, gate voltage regulation requirements, or optimization of signal fidelity and loop stability.

[0072] In embodiments of the present invention, the pathway configurator may manage connections to both on-chip metal electrodes and off-chip reference electrodes (e.g., Ag / AgCI electrodes). The configurator ensures that the appropriate electrode combinations are established for optimized feedback control, allowing the gate driver system to leverage the stability of reference electrodes and the fast response characteristics of on-chip metal electrodes.

[0073] In embodiments of the present invention, the pathway configurator can be implemented in CMOS semiconductor technology, integrated with the feedback control system and other analog or digital circuitry on the same substrate, thereby enabling a compact and scalable biosensing system design.

[0074] The invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the technical teaching of the invention, the invention being limited only by the terms of the appended claims.

[0075] The present invention relates to a gate driver system (100) and a biosensing system (200) that utilize field-effect transistors (FETs) (110) for detecting substances in a fluid (170) and methods (300) for driving and regulating gate voltages of such transistors. The invention encompasses several aspects and embodiments, each designed to improve the precision, integration, and response time of the gate voltage control in contact with a liquid environment.

[0076] In FIG. 1 a schematic drawing of a prior art gate driver system is shown wherein an external reference electrode controls the liquid gate voltage of a FET (110). The reference electrode, typically an Ag / AgCI electrode, provides a stable chemical potential for electrochemical measurements. In this example the voltage source for applying the gate control voltage (GCV) is represented by the amplifier. It is understood that different voltage sources may be used. The output of the reference electrode is in contact with the liquid in the microfluidic cell. The reference electrode can be modelled by an electric circuit including the chemical potential Ve of the electrode and resistive and capacitive effects as shown in FIG. 2. In this model Cl may for example be 0.53 nF, R1 may for example be 30 kO and R2 may for example be 500 O. Due to the significant series resistance of the liquid and the reference electrode, and the FET (110) having a significant double-layer capacitance the frequency at which the gate voltage of the FET can be modulated is limited. In embodiments of the present invention the FET may be a GFET. In embodiments of the present invention the gate dimension of the GFET may be 100 pm x 100 pm. The GFET for example have a gate capacitance of 2 nF. The theory for the double layer capacitance and how it can be measured is for instance described in Ulibarri, A. (2018). Measuring the Double Layer Capacitance of Electrolyte Solutions U.pdf [Senior Theses, Linfield College],

[0077] Depending on the application, there are several liquids possible, what leads then also to a big variety of resistances. As examples may serve: DI water: 18 MOhm cm, distilled water: 0.3 MOhm cm to 2 MOhm cm. Phosphate buffered saline (PBS)XO.Ol: 5 kOhm cm, wherein 0.01 refers to a 100-fold dilution of PBSxl. The settling of the voltage at the graphene surface, when the gate control voltage is varied, is ruled by the time constant resulting from the combination of the GFET capacitance and the overall resistance. This sets an upper limit to the gate-source voltage modulation frequency as e.g. the following example might show. For PBS x 0.01 and one single 100 pm x 100 pm GFET electrically connected (with no common source connection to other GFETs of a GFET matrix), and short hose between the Ag / AgCI probe, the GFET might be operated at 100Hz modulation frequency with 20mV gate control voltage modulation amplitude (40mVpp). It should be noted, that the amount of modulation reaching the GFET is proportional to the applied gate control voltage modulation, thus the GFET could be operated at maybe 500Hz with 100 mV modulation amplitude.

[0078] It is an object of embodiments of the present invention to increase the maximum frequency limit at which the gate of the FET can be modulated.

[0079] Embodiments of the present invention relate to a gate driver system (100) for driving a gate (112) of a field-effect transistor (110) in contact with a liquid (170). Exemplary embodiments of such a gate driver system are schematically drawn in FIG. 3, FIG. 5, FIG. 6, FIG. 7, FIG. 8 and FIG. 9. The gate driver system (100) includes the field-effect transistor (110) itself, which comprises the gate (112), and a source (111) and a drain (113) for biasing the transistor. A first drive electrode (120), is configured for applying a first driving signal (DI) to obtain a voltage at the gate (112). A first sense electrode (130) is configured for measuring this voltage, thereby obtaining a first feedback signal (FBI) indicative of the voltage at the gate (112). The first drive electrode (120) and / or the first sense electrode (130) is an on-chip metal electrode. A feedback control system (140) is then used for regulating the voltage at the gate (112) by controlling the first drive electrode (120) using the first feedback signal. The feedback control system (140) may include elements (143) to improve loop stability, such as offset compensation. In the exemplary embodiment illustrated in FIG. 3 a feedback voltage (FBI) is subtracted from a gate control voltage (GCV) by a subtractor (141) and the result is input to an amplifier 142. The output of the amplifier may be fed to an optional loop compensation module to improve loop stability. In the exemplary embodiment illustrated in FIG. 3 the output of the feedback control system is connected to the first drive electrode (120) by means of an on-die metal electrode contact (181). The output (FBI) of the sense electrode (130) is connected to the feedback control system (140) by means of an on-die metal electrode contact (182).

[0080] The first driving electrode (120) and the first sensing electrode (130) may be on-chip metal electrodes, as depicted in FIG. 3, which shows a schematic drawing of a gate driver system with on-chip metal electrodes used to apply and measure the gate voltage.

[0081] The on-chip metal electrode, same as the reference electrode, can be modeled by an electrical circuit including the double-layer capacitance and faradaic conduction occurring when the voltage reaches chemical potentials of redox reactions occurring at the electrode. This effect can be modeled by e.g. diodes. Thus a model according FIG. 4 can be derived and is applied to the configuration of FIG. 3 with the on chip / on die metal electrode. In this model Cl may for example be 200 nF, R1 may for example be 800 O, R2 may for example be 20 kO, and C2 may for example be 2 nF.

[0082] In some embodiments, the gate driver system (100) may include a first drive electrode (120), which is an on-chip metal electrode, for applying a first drive signal (DI) to obtain a voltage at the gate (112) and a second drive electrode (150), which is a reference electrode, for applying a second drive signal (D2) to obtain a voltage at the gate (112). The feedback control system (140) is configured to control both the first drive electrode (120), via on-die metal electrode contact (181), for generating a first drive signal (DI) and the second drive electrodes (150) for generating a second drive signal (D2) for regulating the voltage at the gate (112), as shown in FIG. 5. This configuration combines the benefits of an on-chip metal electrode resulting in increased dynamics with the stable chemical potential provided by a reference electrode. The maximum frequency limit for gate-source voltage modulation can be increased by combining a reference electrode with an on-chip electrode, adding a higher frequency path to the gate of the FET (110). In the exemplary embodiment illustrated in FIG. 5 the first sense electrode (130) is a reference electrode and generates a feedback signal (FBI) which is indicative for the gate voltage. An exemplary model of a reference electrode is shown in FIG. 2 which represents the impedance characteristics of a reference electrode when immersed in a liquid.

[0083] In the embodiment illustrated in FIG. 6 the gate driver system (100) comprises a first driver electrode (120) which is a reference electrode, a first sense electrode (130) which is an on-chip metal electrode, and a second sense electrode (160) which is a reference electrode. The first feedback signal (FBI) of the first sense electrode and the second feedback signal (FB2) of the second reference electrode are used as feedback signals for the feedback control system (140) for regulating the voltage at the gate by controlling the first driver electrode (120). By using the first sense electrode which is an on-chip metal electrode and the second reference electrode which is a reference electrode a stable feedback loop is obtained which moreover has an increased maximum frequency limit compared to gate driver system which does not comprise an on-chip metal electrode.

[0084] Further embodiments may comprise a first drive electrode (120), which is an on-chip metal electrode, for applying a first drive signal (DI) to obtain a voltage at the gate (112) and a second drive electrode (150), which is a reference electrode, for applying a second drive signal (D2) to obtain a voltage at the gate (112), a first sense electrode (130), which is an on- chip metal electrode, for obtaining a first feedback signal (FBI) indicative of the voltage at the gate (112) a second sense electrode (160), which is a reference electrode, for obtaining a second feedback signal (FB2) indicative of the voltage at the gate (112). The feedback control system (140) uses both feedback signals (FBI, FB2) for regulating the voltage to a gate control voltage (GCV) which is applied at the input of the feedback control system (140). This is illustrated in FIG. 7, The feedback signal for regulating the gate voltage is a combination of a first feedback signal (FBI) from the first sense electrode (130) and a second feedback signal (FB2) from the second sense electrode (160).

[0085] In embodiments of the present invention the output (FBI) of the sense electrode (130) may be connected to the feedback control system (140) by means of an on-die metal electrode contact (182). In embodiments of the present invention the output of the feedback control system may be connected to the first drive electrode (120) by means of an on-die metal electrode contact (181).

[0086] In some embodiments, the reference electrodes may be Ag / AgCI electrodes, known for their chemical stability. The field-effect transistor (110) may be a graphene field-effect transistor (GFET), leveraging the unique properties of graphene for sensitive and responsive gate control.

[0087] Embodiments of the present invention relate to a biosensing system (200) for detecting a substance in a liquid (170). An schematic drawing of such a biosensing system (200) is shown in FIG. 8. This system incorporates a gate driver system (100) according to embodiments of the present invention. The gate (112) of the FET (110) is sensitive to the substance, and the biosensing system (200) includes a control device (210) for regulating the voltage at the gate (112) using the gate driver system (100) and for determining a characteristic of the FET (110) for detecting the substance. The biosensing system (200) may include a microfluidic cell that comprises the FET (110) and a liquid carrying substances to be measured. The liquid (170) has a limited conductivity, with examples provided for different types of water and solutions.

[0088] The control device (210) may for example be configured for modulating the voltage at the gate of the FET by providing a modulating voltage as gate control voltage as input to the feedback control system (140). The control device (210) may for example be configured for modulating the gate voltage of the FET (e.g. with reference to the source or to the ground), applying a drain source voltage to the FET and measure the drain source current of the FET. The gate voltage may for example be modulated by toggling between plus and minus a predefined bias voltage around a given bias point. The drain source current in function of the gate voltage or any specific feature thereof may be a characteristic feature of the FET which may be used for detecting the substance. Detecting the substance may also imply determining a quantity of the substance. The FET may be a GFET and the control device may be configured for determining the Dirac voltage of the GFET. In embodiments of the present invention the control device may be a processing device. The control device and the feedback control system may be realized under use of a CMOS semiconductor technology in an integrated circuit. The FET (e.g. GFET) and the on-chip metal electrodes may be arranged on the surface, as the on- chip metal electrodes are compatible to the CMOS semiconductor technology.

[0089] Embodiments of the present invention relate to a method (300) for driving and regulating a gate voltage of a FET (110) in contact with a liquid (170). An exemplary flow chart of such a method is shown in FIG. 11. The method involves applying (310) a first driving signal (DI) using a first drive electrode (120), measuring (320) the voltage at the gate (112) with a first sense electrode (130) to obtain a first feedback signal (FBI), and regulating (330) the applied voltage using a feedback control system (140) based on the first feedback signal (FBI). The first drive electrode and / or the first sense electrode is an on-chip metal electrode. The method may include using a second drive electrode (150) for applying a second driving signal (D2) and a second sense electrode (160) to obtain a second feedback signal (FB2), for enhanced feedback and voltage regulation. The applied first and / or second driving signals may be modulated to improve driving, sensing and control of the gate voltage. The gate voltage of the FET may be modulated to improve sensing, with a need for a small time constant to allow higher frequency modulation. The time constant of the sensing system is affected by leakages, resistances, and capacitances of the electrodes, the liquid, and the FET construction. The maximum frequency limit can be further increased by actively driving the gate voltage using force / sense electrodes, which are on-chip metal electrodes. The stability of the gate voltage can be improved by additionally providing a reference electrode for providing a driving signal. The stability of the sensing of the gate voltage can be improved by additionally providing a reference electrode for providing a feedback signal.

[0090] FIG. 9 shows a simulation model of an array of 256 GFETs with distributed on-chip gate electrodes. The gates of the GFETs are driven using a gate driver system in accordance with embodiments of the present invention. The gate complex of the GFET may be made sensitive to substances by applying one or more sensitive layers such as a graphene layer, also combined with may be additional layers for functionalizing the Graphene layer further to be sensitive to specific substances. The applied voltages on gate, source, and drain of the GFETs are referenced to ground.

[0091] In embodiments of the present invention the liquid within the microfluidic cell, carrying the substances to be measured, adds resistances and capacitances to the system. The resistance of a cube of liquid (100 pm side length) would be 500kOhm (conductivity of PBS x 0.01 ).

[0092] In embodiments of the present invention on-chip metal electrodes alongside the GFET are used to regulate the gate voltage of the GFET. In FIG. 9 on-chip drive electrodes 120 are alternating with GFETs 110. A typical distance between an on chip electrode and a GFET gate might range from 5 pm till 100 pm and is mainly determined by layout rules of the manufacturing process. As materials for the on chip electrodes e.g. Pt and Au might be used, but also other CMOS compatible metals might be suitable, that have a good chemical resistance for the used liquid based chemistry, as well as Ag and AgCl. As described already earlier, GFETs have e.g. 1 nF capacitance between the gate and the source and e.g. 1 nF between the gate and the drain, thus 2 nF in total. The resistance from the Ag / AgCI probes to the microfluidic cell is 5 mOhm with the probe connected to the microfluidic cell through a 1 cm long and 0.5 mm diameter wide hose. The Ag / AgCI electrodes may for example be used as sense electrode 130 or as drive electrode 150.

[0093] FIG. 10 shows simulation results of various gate driving methods.

[0094] Trace A displays the gate voltage in function of time when driving the gate of the FET using a prior art passive gate driver system through an Ag / AgCI electrode in the liquid which is in contact with the gate.

[0095] Trace B shows the gate voltage in function of time when driving the gate using a gate driver system in accordance with an embodiment of the present invention which comprises a first driver electrode which is an Ag / AgCI reference electrode and with feedback taken at a first sense electrode which is an on-chip metal electrode and at a second sense electrode which is an Ag / AgCI reference electrode as illustrated in FIG. 6.

[0096] Trace C shows the gate voltage in function of time when driving the gate using a gate driver system in accordance with an embodiment of the present invention which comprises a first driver electrode which is an on-chip metal electrode and second driver electrode which is an Ag / AgCI electrode with feedback taken at a first sense electrode which is an on-chip metal electrode and with feedback taken at a second sense electrode which is an Ag / AgCI electrode as illustrated in FIG. 7. This is the preferred embodiment, resulting in faster settling times for a FET-based sensor (e.g. GFET-based sensor).

[0097] It is an advantage that the gate voltage of the FET settles faster when using a gate driver system or method in accordance with embodiments of the present invention. When using a gate driver system in accordance with embodiments of the present invention for modulating the gate voltage, it is advantageous that the modulation frequency can be increased by a factor 5 to 10 in comparison with a prior art gate driver. This improvement is attributed to the reduced resistance and parasitic capacitances when using on-chip electrodes.

[0098] It is an advantage of embodiments of the present invention that the feedback control system allows to obtain a stable voltage at the gate of the FET. This feedback control system may include elements for loop stability and offset compensation.

[0099] In embodiments of the present invention the FET is housed in a microfluidic cell which contains the liquid with substances to be measured.

[0100] Embodiments of the present invention relate to a biosensing system (200) for detecting a presence and / or a concentration of a substance in a liquid sample (170) for a given application. An exemplary embodiment of such a system is shown in FIG. 12. The biosensing system (200) comprises an on-chip array (290) of field-effect transistors (110). Each field-effect transistor (110) has a gate (112) configured to receive a liquid sample (170) and is individually functionable to interact with the substance. Some of the transistors may be functionalized to interact with the substance. Some may not be functionalized to interact with the substance. They may for example be unfunctionalized. The presence of more than one substance may be detected or the concentrations of more substances may be measured. In that case sets of fieldeffect transistors are functionalised to different substances.

[0101] The biosensing system comprises a gate driver system (100) for driving the gates of said field-effect transistors which are in contact with the liquid sample. The gate driver system (100) comprises a feedback control system (140) configured to use one or more feedback signals, each feedback signal being representative of a measured voltage of the liquid sample, said voltage being provided by one or more sense electrodes (130, 160) to control a drive voltage applied to the liquid sample by one or more drive electrodes (120, 150) so as to apply a desired voltage at said gates (112).

[0102] The biosensing system, moreover, comprises a control device (210) configured to determine a characteristic of each field effect transistor (110) or group of field effect transistors of said on-chip array (290) of field effect transistors for detecting the presence and / or the concentration of the substance in the liquid sample.

[0103] The characteristic of each field effect transistor (110) or group field effect transistors is obtained by providing the desired to the feedback control system of the gate driver system.

[0104] The on-chip array of field-effect transistors (110) comprises a plurality of distributed on-chip metal electrodes (120,130), and the gate driver system comprises an electrodes pathway configurator (260) for operating each of said plurality of distributed on-chip metal electrodes either as one of said one or more sense electrodes or as one of said one or more drive electrodes;

[0105] In embodiments of the present invention the field-effect transistors (110) of the on- chip array are preferably graphene field-effect transistors (GFET).

[0106] In embodiments of the present invention a characteristic of a group of field effect transistors is obtained by combining the characteristics of individual field effect transistors. The group may for example be the complete array or a subset of the array. The group may comprise transistors which are functionalized for the same substance. Combining the characteristics may, for example, involve processing, aggregating, or analysing the characteristics in various ways, such as averaging, summing, weighting, filtering, or applying statistical or computational methods to derive a combined value or outcome.

[0107] FIG. 12 shows a schematic view of an exemplary embodiment of a biosensing system 200 with an array 290 of field-effect transistors 110 with distributed on-chip metal electrodes 430 for detecting a presence and / or a concentration of at least one substance in a liquid sample, notably for a medical, health or monitoring application.

[0108] In embodiments of the present invention the field-effect transistors are graphene field effect transistors.

[0109] The illustrated biosensing system is a modular system 200 comprising on-chip analogue structure 205, notably comprising the on-chip array 290 of field-effect transistors 110 with distributed on-chip metal electrodes 430 and an array biasing unit 270 for biasing the fieldeffect transistors and reading operational electrical quantities, being operationally connected to a digital control device 210 via a connection 202, the control device being configured to determine a characteristic of said on-chip array of field-effect transistors for detecting a presence and / or a concentration of a given substance in the liquid sample by to the on-chip array of field-effect transistors.

[0110] Preferably, the control device 210 is an on-chip control device, e.g. being integrated with or attached to the analogue structure 205, e.g. by means of on chip digital control building blocks on the same substrate of the analogue structure 205 in view of an on-chip solution.

[0111] In the exemplary embodiment, the internal connection 202 provides data and / or signals exchanges between the control device 210 and the analogue structure 205, the control device and / or the analogue structure being provided with Analogue-to-Digital converter(s) (ADC) and Digital-to-analogue converter(s) (DAC) 295 for providing analogue signal and / or digital data exchange between the two blocks. The biosensing system is also provided with a communication interface 201 for providing digital data exchange with an external device (not illustrated) as well as operational control and powering.

[0112] The control device may comprise a digital processor 211, a memory 212 for storing instructions and data, a communication module 213 for managing instructions and data exchange on the communication interface 201, and a register 214 for providing instructions and data exchange between the control device and the units of the analogue structure 205 through the internal connection 202.

[0113] Complementarily, the on-chip analogue structure 205 may comprise an additional analogue signal / powering bus 203 for operating an external structure (not illustrated). The external structure may comprise additional GFETs e.g. one or more GFET, or an array of GFET, for improving robustness of the detection and / or providing detection of other substances. Alternatively or complementarily, the external structure may comprise one or more sensing elements e.g. for sensing environmental phenomena, such as a temperature sensor.

[0114] Each field-effect transistor of the array 205 (eventually of the external structure) comprises a gate configured to receive the liquid sample (thereafter also referred as liquid gate) and being individually functionable to a predefined substance whose presence and / or concentration has to be detected in the provided liquid sample.

[0115] In order to allow the control device to determine the specific voltage (Dirac voltage) of GFETs, notably of the first, second and / or third subset, of the array, the biosensing system, as previously described, thus comprises a gate driver system 100 for driving the liquid gates of the field-effect transistors being in contact with the liquid sample.

[0116] The gate driver system 100, that in this embodiment is advantageously part of the on- chip analogue structures 205 for providing a compact and performant solution, comprises an on-chip feedback control system 140 (also called closed-loop control system) that is operationally connected to one or more sense electrodes for (locally) sensing voltage of the liquid sample, one or more drive electrodes for (locally) applying a desired voltage at said liquid gates.

[0117] The control device can thus provide a desired voltage to be applied to the liquid-gates of the field-effect transistors (in view of determine a characteristic, e.g. the Dirac voltage of the field-effect transistors) to the gate driver system. The feedback control system 140 can thus - continuously or iteratively- regulate (control) the drive voltage(s) that is / are (locally) applied to the liquid sample by the one or more drive electrodes according to one or more (locally) measured voltages of the liquid sample provided by the one or more sense electrodes for obtaining the desired voltage at the liquid gates.

[0118] Advantageously, the gate driver system 100 comprises an electrodes pathway configurator 260 for managing each connection between the sense and the drive electrodes and the feedback control system 200.

[0119] In particular, the electrodes pathway configurator 260 is configured to enable (or disable) a connection with each of one or more external (off-chip) reference electrodes that can be thus configured to be operated either as drive or sense electrode by the feedback control system 140. This configuration allows a scalability and performance optimization of field-effect transistors' gate driving, e.g. providing accurate and fast gating being focused on gates of one or more field-effect transistors of interest.

[0120] Alternatively or complementarily, the electrodes pathway configurator can advantageously provide a configuration of each of the distributed on-chip metal electrodes 430 either as one of the sense electrode(s) or as one of the drive electrode(s) operated by the feedback control system 200 for regulating the gate voltage of the field-effect transistors, e.g. for sake of faster settling time as previously outlined and illustrated in Fig.10.

[0121] In one embodiment, the electrodes pathway configurator comprises a demultiplexingbased circuit structure for allowing the feedback control system to provide a same drive signal to one up to a plurality of selected electrodes within the distributed on-chip metal electrodes and the connected external reference electrodes, these selected electrodes operating thus as drive electrodes. Complementarily, the electrodes pathway configurator comprises a multiplexing-based circuit structure for allowing the feedback control system to acquire one or more feedback signals from one up to a plurality of selected electrodes within the distributed on-chip metal electrodes and the connected external reference electrodes, these selected electrodes operating thus as sense electrodes.

[0122] The electrodes pathway configurator is preferably controllable by the control device (via the connection 202) so as to provide e.g. an initial configuration, a reconfiguration, and / or a dynamic modification (i.e. during operation of the biosensing system) of the configuration of the sense and / or drive electrodes in connection with the feedback control system 200.

[0123] The electrodes pathway configurator can thus allow the control device to dispose to an adequate electrodes configuration that can apply the desired voltage in a faster and more accurate way to the gates of the Field-effect transistor(s) e.g. as shown in Figure 10, configuration that can be modified according to characteristics of the liquid sample and / or Field-effect transistors (spatial) configuration of and / or locations in the array in order to provide accurate and rapid applications.

[0124] The pathway configurator 260 of the Fig. 12 is an on-chip electronic control module that is implemented in CMOS semiconductor technology and integrated with the feedback control system 140 (and eventually other analog or digital circuitry) on the same substrate. The pathway configurator includes multiplexing and / or demultiplexing circuit structures (for example, analog switches, cross-point switches, or address-based selectors) for enabling dynamic reconfiguration of electrode roles according to the needs of the gate driver system and / or of the biosensing application. In the illustrated embodiment, the pathway configurator 260 is advantageously controlled by the control device 210 which issues configuration commands notably by setting parameters in the register 214 that is accessible to the pathway configurator via the internal connection or communication bus 202. The register 214 of the illustrated embodiment is a memory that is used to operate the pathway configurator, notably by storing one or more instruction, operational and / or status parameters, notably for setting a new configuration, timely triggering and / or synchronizing a new configuration change, for monitoring the current status of the configuration. The register 214 can be integrated in the digital processor 211, or be a portion of the memory 212, or a dedicated (stand-alone) memory.

[0125] The pathway configurator can be thus configured to regularly check the register for waiting for new parameters (polling-based mode), alternatively it can be configured to read a new parameter when a new entry in the register is signalized to the pathway configurator (interrupt-based mode). The pathway configurator is also configured to write in the register so as to update operational and / or status parameters.

[0126] This enables the system to dynamically adapt electrode assignments in real time based on operational parameters, such as the detection of specific substances, gate voltage regulation requirements, or optimization of signal fidelity and loop stability.

[0127] Even if the field-effect transistors 110 of the illustrated array 290 are aligned in columns and rows wherein the distributed on-chip metal electrodes 430 are disposed in alternation with the field-effect transistors, others arrangements of the field-effect transistors and / or distributed on-chip metal electrodes are possible. In some embodiments, the field-effect transistors are aligned along two or more parallel or inclined lines and / or disposed according to a regular or recurrent geometric pattern. In one embodiment, wherein the number of the on-chip metal electrodes is equal or a divisor of the number of the field-effect transistors of the on-chip array 110, each of the distributed on-chip metal electrodes can be located near (e.g. a distance of 5 pm till 100 pm from the liquid gate of the GFET gate) to each field-effect transistor or near to a group of field-effect transistors.

[0128] In another embodiment, where the number of on-chip metal electrodes are a multiple of the number of the field-effect transistors of the on-chip array 110, at least two on-chip metal electrodes are located in proximity of each field-effect transistor so as one of these electrodes can be configured as drive electrode and the other as a sense electrode via the electrodes pathway configurator. As described above, the on-chip metal electrodes can be made of platinum (Pt) and / or of Gold (Au), eventually of other CMOS compatible metals. In embodiments of the present invention each field-effect transistor 110 of the on-chip array (290) of field-effect transistors 110 comprises a source 111 and a drain 113 for biasing the field-effect transistor.

[0129] In embodiments of the present invention the control device is configured to collectively operate the group of field-effect transistors, for example by managing and / or using and / or measuring, an electrical quantity at the sources and / or at the drains of the group of field-effect transistors.

[0130] In embodiments of the present invention the control device is configured for individually operating each field-effect transistor, for example by managing and / or using and / or measuring, an electrical quantity at the source and / or at the drain of each field-effect transistor of the array for determining said characteristic.

[0131] As above described, each graphene field-effect transistor of the array has a drain source current versus gate source voltage transfer function with a local minimum for a specific voltage (called Dirac voltage) which can be made sensitive to a presence and / or to a concentration of the given substance by a functionalization of the liquid gate of the field-effect transistor (i.e. the graphene channel thereof). The control device can thus be configured to determine the Dirac voltage as a (dynamic) characteristic of one or a group of graphene fieldeffect transistor(s) allowing a (dynamic) determination of the presence and / or a concentration of the given substance in the liquid sample being in contact with the gates of the graphene field-effect transistor(s).

[0132] The individual functionalization of each liquid gate of the array provides thus a modular and robust solution to a large spectre of applications. In fact, a plurality of field-effect transistors of the array (forming a first subset of the array) can be functionalized to be sensitive to a first substance so as to provide not only accuracy but also robustness against transistors failures and disruptions. It has been observed that one or more field-effect transistors of the array are inoperative, e.g. due to manufacturing or functionalize processes, or become inoperative, e.g. due to aging, delamination or substrate breaking, and accumulation of impurities carried by the liquid sample. These field-effect transistors are thereafter referred as flawed filed-effect transistors.

[0133] The control device can thus dynamically modify the desired voltage to be applied to the liquid gates so as to determine the characteristic (e.g. Dirac voltage) on which a detection of the substance and / or the concentration of the substance relies. In one embodiment, the control device can dynamically increase the desired voltage so as to gate the field-effect transistor by a ramp-shaped voltage allowing a determination of the specific drain source current versus gate source voltage transfer function of the gated field-effect transistors of the array. Alternatively, in view of providing a less time- and power consuming process as well as of avoiding a rapid aging of the GFET due to important variation of the gating voltages, the control device can be configured to alternate or modulate the desired voltage around a current estimate of the specific voltage (i.e. Dirac voltage), e.g. between two values one being less and the other being greater than such current estimate, so as to allow a track of a possible modification of the specific voltage notably due to a presence or concentration of the given substance on which the field-effect transistors are sensible. When a modification of the specific voltage is detected or observed, the current estimate can be adequately updated in view of adequately alternate or modulate the desired voltage.

[0134] In embodiments of the present invention a characteristic of a group of field-effect transistors 110 of the on-chip array 290 is based on the specific voltage of one or more fieldeffect transistors of the group.

[0135] In embodiments of the present invention the first subset and / or the second subset may be groups.

[0136] In embodiments of the present invention a characteristic of a group of field effect transistors is obtained by combining the characteristics of individual field effect transistors.

[0137] Advantageously the biosensing system of Fig. 12, is configurable to allow the control device to acquire the drain source currents of all the field-effect transistors of the array (individually, in a group or in a collectively mode) notably via the array biasing unit 270. In the illustrated embodiment, the array biasing unit 270 comprises an address-based circuit providing the (measured) drain source current of single up to a group of field-effect transistors of the array being addressed by control device. The query and the current values are provided via the internal connection 202 and the ADC / DAC unit 295.

[0138] In a preferred embodiment, the control device 210 is thus configured to -individually, in a group or collectively - acquire the drain source current of selected field-effect transistors of the array in view of determine such characteristic (e.g. Dirac voltage) related uniquely to a given list of selected field-effect transistors (e.g. field-effect transistors of interest).

[0139] Moreover, the modularity of the biosensing system allows to functionalize another plurality of field-effect transistors, i.e. forming a second distinct subset (i.e. a non-overlapping subset with respect to the first subset), so as to be sensitive to a second substance, e.g. that can be complementarily or alternatively required by an application. Thus, the control device T1 can be configured to separately acquire the drain source current(s) of the field-effect transistors of the first subset of array separately from the drain source current(s) of the second of the field-effect transistors of the first subset of array so as to be able to determine a first and a second characteristics, each related to a different subset of fiend-effect transistors.

[0140] In embodiments of the present invention the control device is able to collectively operate the first and / or second subset, of the array to determine said first and / or second characteristic. In embodiments of the present invention operation of the field effect transistor may imply managing and / or using and / or measuring, an electrical quantity at the source and / or at the drain and / or at the gate of the field effect transistor. In view of determining such characteristics, the control device can dynamically increase the desired voltage so as generate a collective ramp-shaped gate voltage at each liquid gate of the field-effect transistors of the first and second subset of the array. Alternatively, the control device can be configured to alternate or modulate the desired voltage around both a first current estimate of the specific voltage (i.e. Dirac voltage) of the first subset and a second current estimate of the specific voltage of the second subset, e.g. between two values one being less to both the estimates and the other being greater than both the estimates. Distinct acquisitions of the drain source current(s) of the field-effect transistors of the two subsets provides an individual track of variations of the specific voltage related to the first subset and variations of the specific voltage related to the second subset. The first and the second estimates can be thus updated according to detected modifications.

[0141] Advantageously, the field-effect transistors of a third distinct subset of the array are not functionalized so as to use the related specific voltage as a (dynamic) reference specific voltage (i.e. reference Dirac voltage) notably for reducing up to eliminate Dirac offsets and drifts of Dirac voltages of functionalized GFETs, notably caused by aging and common liquid contaminations. The control device can be thus configured to alternate or modulate the desired voltage around both the current estimates of the specific voltage of the first, second and third subset. Distinct acquisitions of the drain source current(s) of the field-effect transistors of the three subsets provides individual tracks of variations of the specific voltage related to each the first, second and third subset while estimates can be then updated according to detected modifications.

[0142] As it has been observed that one or more field-effect transistors of the array are inoperative or become inoperative, the control device is advantageously configured to detect a flawed field-effect transistor based on measurement and / or monitoring of an electrical quantity at the source and / or at the drain of such field-effect transistor, notably via the array biasing unit 270, in particular based on the (measured) drain source current of such field-effect transistor.

[0143] The control device can thus detect a flawed field-effect transistor by comparing a given electrical quantity (e.g. voltage or current) of a given field-effect transistor with one or more of the followings:

[0144] - a given threshold, notably a maximal threshold and minimal threshold;

[0145] - a prior electrical quantity being previously measured for the same field-effect transistor or being mathematical or statistical extracted or inferred from a series of previously collected electrical quantities of the same field-effect transistor, notably during a calibration process;

[0146] - a common electrical quantity being mathematical or statistical extracted or inferred from a series of collected electrical quantities of others field-effect transistors of the array.

[0147] In case of a comparison indicating that the checked field-effect transistor shows an unusual electrical quantity that is a hint of a flawed field-effect transistor, the control unit can remove said flawed field effect transistor from the group of field-effect transistors (e.g. from the array or from the related subset, e.g. the first, second or third subset, or from the fieldeffect transistor of interest) being selected for detecting the characteristic (notably the Dirac Voltage) in view of determining a presence or a concentration of a given substance. In the illustrated embodiment, the control device removes the identified flawed field-effect transistor from the list of selected field-effect transistors whose drain source currents are acquired (via the array biasing unit 270) for determining the characteristic (e.g. specific voltage, Dirac voltage) of such list (e.g. representing the first, second or third subset).

[0148] In embodiments of the present invention the control device is configured to detect a flawed field-effect transistor within the first of second subset of field effect transistors. In embodiments of the present invention this flawed transistor is excluded for the determination of the first characteristic and / or of the second characteristic.

[0149] The biosensing system can advantageously comprise an on-chip temperature sensor 280 for sensing a temperature of a portion of the biosensing system, preferably of the on-chip array of field-effect transistors. The control device can thus be configured to acquire a temperature provided by the temperature sensor in view of use the sensed temperature e.g. for regulating the biasing of the field-effect array, and / or for more accurately determining the characteristic of one or more of said field-effect transistors of the array for detecting a presence and / or the concentration of a given substance in the liquid sample.

[0150] In embodiments of the present invention the biosensing system (200) comprises a microfluidic cell arrangement for carrying the liquid sample to a first group of field-effect transistors of the on-chip array of field-effect transistors and to carry a second liquid sample to a second group of field-effect transistors of the on-chip array of field-effect transistors.

[0151] In embodiments of the present invention the first group comprises the first subset of field-effect transistors and the second group comprises the second subset of field-effect transistors. In embodiments of the present invention the first group comprises a portion of the first subset of field-effect transistors and a portion of the second subset of field-effect transistors and the second group comprises another portion of the first subset of field-effect transistors and another portion of the second subset of field-effect transistors.

[0152] The illustrated biosensing enables a method for operating an on-chip array of fieldeffect transistors, notably above described and illustrated in Fig.12, notably for regulating the gate voltage of the liquid gates of the field-effect transistors of the array, wherein the fieldeffect transistors are preferably GFETs.

[0153] The method for operating an on-chip array of field-effect transistors, each field-effect transistor having a liquid gate configured to receive a liquid sample and being individually functionable to a substance, wherein the on-chip array comprises a plurality of distributed on- chip metal electrodes, comprises the following steps: i) provide one or more drive electrodes and one or more sense electrodes by selectively operating each of said plurality of distributed on-chip metal electrodes either as one of said one or more sense electrodes or as one of said one or more drive electrodes, and bringing them in contact with the liquid sample; ii) applying a drive voltage to the liquid sample to obtain a desired voltage at the liquid gate of the field-effect transistor using said one or more drive electrodes (120), ii) measuring a voltage of the liquid gate with said one or more sense electrodes (130) to obtain one or more feedback signals indicative of said measured voltage; wherein the step ii) comprises regulating the applied voltage using a feedback control system based on said one or more feedback signals, and wherein said step i) comprises selectively configuring each of said plurality of distributed on-chip metal electrodes to operate either as one of said one or more sense electrodes or as one of said one or more drive electrodes. In embodiments of the present invention the method comprises functionalizing the gate of at least one field-effect transistor (110) of the on-chip array (290) to a substance, determining a characteristic of said at least one field-effect transistor by applying the desired voltage at the gate of said at least one field-effect transistor and preferably by acquiring a drain source current of said at least one field-effect transistor; and detecting a presence and / or a concentration of the substance in the liquid sample based on said characteristic.

[0154] The step i) can advantageously comprise:

[0155] - providing a first off-chip reference electrode, preferably even a second off-chip reference electrode, to be in contact with the liquid sample.

[0156] In embodiments of the present invention the first reference electrode, preferably even the second reference electrode, is operated as a drive electrode or as a sense electrode, preferably one of the first and the second reference electrode is operated as a drive electrode, the other as a sense electrode.

[0157] The step i) can further comprise:

[0158] - configuring at least one of said plurality of distributed on-chip metal electrodes to operate as one of said one or more sense electrodes, and

[0159] - configuring at least one of said plurality of distributed on-chip metal electrodes to operate as one of said one or more drive electrodes.

[0160] The step ii) may comprise:

[0161] - determining a processed feedback signal by mathematically combining and / or statistically inferring said one or more feedback signals, and

[0162] - regulating the applied voltage using the processed feedback signal.

[0163] The method can advantageously comprise the followings steps: iv) functionalizing the gate of at least one field-effect transistor of the on-chip array, preferably of each field-effect transistor of a first subset of the on-chip array , to a first substance; v) detecting a characteristic of said at least one field-effect transistor, preferably of the field-effect transistors of the first subset, by applying the desired voltage at the liquid gate of said at least one field-effect transistor, preferably of the field-effect transistors of the first subset ; and vi) detecting a presence and / or a concentration of the substance in the liquid sample based on said characteristic; wherein step v) can advantageously comprise: - determining a first given value being lower than a current estimate of the specific voltage of said at least one field-effect transistor, preferably of the field-effect transistors of the first subset;

[0164] - determining a second given value being higher than said current estimate;

[0165] - modulating or alternating the desired voltage between the first and the second given value; and to

[0166] - update the current estimate according to one or more measures of the drain source currents of said at least one field-effect transistor, preferably of the field-effect transistors of the first subset; wherein the characteristic is preferably the specific voltage (or Dirac voltage) of the field-effect transistors.

[0167] The method can advantageously comprise the following steps in view of providing a more accurate and robust detection:

[0168] -in addition to step iv), keeping the liquid gate of each field-effect transistor of a second subset of the on-chip array not functionalized, the second subset being distinct from the first subset; and wherein

[0169] - the step v) comprises detecting a characteristic of the field-effect transistors of the second subset; and wherein

[0170] - the step vi) comprises detecting the presence and / or the concentration of the substance in the liquid sample also based on both the two characteristics, preferably based on a difference between the detected characteristic of the first subset and the detected characteristic of the second subset; wherein step v) can advantageously comprise:

[0171] - determine a first given value being lower than a first current estimate of the specific voltage of the field-effect transistors of the first subset and lower than a second current estimate of the specific voltage of the field-effect transistors of the second subset;

[0172] -determine a second given value being higher than the first and the second current estimate;

[0173] - modulate or alternate the desired voltage between the first and the second given value;

[0174] - update the first current estimate according to one or more measures of the drain source currents of the field-effect transistors of the first subset, and to - update the second current estimate according to the drain source currents of the field-effect transistors of the second subset.

[0175] In a preferred embodiment, step v) comprises acquiring drain source currents of a list of selected field-effect transistors in view of determine the characteristic, the characteristic being preferably the specific voltage (i.e. Dirac voltage).

[0176] The method can advantageously comprise following steps in view of detecting a different substance, e.g. in complement or in alternative of the first substance:

[0177] - functionalize the liquid gate of each field-effect transistor of a first subset of the on- chip array to a substance;

[0178] - functionalize the liquid gate of each field-effect transistor of a second subset of the on-chip array to the different substance, the second subset being distinct from the first subset;

[0179] - keeping the liquid gate of each field-effect transistor of a third subset of the on-chip array not functionalized, the third subset being distinct from the first and the second subset;

[0180] - detecting a presence and / or a concentration of the substance in the liquid sample based on a characteristic of the field-effect transistors of the first subset and on a characteristic of the field-effect transistors of the third subset;

[0181] - detecting a presence and / or a concentration of said different substance in the liquid sample based on a characteristic of the field-effect transistors of the second subset and on a characteristic of the field-effect transistors of the third subset.

[0182] Complementarily:

[0183] - step v) can advantageously comprise:

[0184] - determine a first given value being: lower than a first current estimate of the specific voltage of the field-effect transistors of the first subset, and lower than a second current estimate of the specific voltage of the field-effect transistors of the second subset, and lower than a third current estimate of the specific voltage of the field-effect transistors of the third subset;

[0185] - determine a second given value being higher than the first, the second and the third current estimate;

[0186] -modulate or alternate the desired voltage between the first and the second given value; -update the first current estimate according to one or more measures of the drain source currents of the field-effect transistors of the first subset,

[0187] -update the second current estimate according to the drain source currents of the field-effect transistors of the second subset, and to

[0188] -update the third current estimate according to the drain source currents of the field-effect transistors of the third subset.

[0189] In one embodiment, step v) further comprise:

[0190] - detecting a flawed field-effect transistor within the array, preferably within the first or second or third selected subset of the field-effect transistors; and

[0191] - detect the characteristic of said field-effect transistors without the detected flawed field effect transistor (e.g. removing it from said first or second or third selected subset of the field-effect transistors); in a preferred embodiment by removing the detected flawed fieldeffect transistor from the list of drain source currents being acquired in view of determining the characteristic (e.g. Dirac voltage).

[0192] The step of detecting a flawed field-effect transistor may comprise:

[0193] - comparing a given electrical quantity (e.g. voltage or current) of a given field-effect transistor with one or more of the followings: a given threshold, notably a maximal threshold and minimal threshold; a prior electrical quantity being previously measured for the same field-effect transistor or being mathematical or statistical extracted or inferred from a series of previously collected electrical quantities of the same field-effect transistor, notably during a calibration process; a common electrical quantity being mathematical or statistical extracted or inferred from a series of collected electrical quantities of others field-effect transistors of the array.

[0194] It is to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope of this invention. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.

Claims

Claims1.- A biosensing system (200) for detecting a presence and / or a concentration of a substance in a liquid sample (170) for a given application, the biosensing system (200) comprising :- an on-chip array (290) of field-effect transistors (110), each field-effect transistor (110) having a gate (112) configured to receive a liquid sample (170) and being individually functionable to interact with the substance;- a gate driver system (100) for driving the gates of said field-effect transistors being in contact with the liquid sample (170), the gate driver system (100) comprising a feedback control system (140) configured to use one or more feedback signals, each feedback signal being representative of a measured voltage of the liquid sample, said voltage being provided by one or more sense electrodes (130, 160), to control a drive voltage applied to the liquid sample by one or more drive electrodes (120, 150) so as to apply a desired voltage at said gates (112); and- a control device (210) configured to determine a characteristic of each field effect transistor (110) or a group of field effect transistors of said on-chip array (290) of field-effect transistors for detecting the presence and / or the concentration of the substance in the liquid sample by providing the desired voltage to the feedback control system of the gate driver system; wherein the on-chip array of field-effect transistors (110) comprises a plurality of distributed on-chip metal electrodes (120,130); and wherein the gate driver system comprises an electrodes pathway configurator (260) for operating each of said plurality of distributed on-chip metal electrodes either as one of said one or more sense electrodes or as one of said one or more drive electrodes; preferably the field-effect transistors (110) of the on-chip array being graphene field-effect transistors (GFET).

2. The biosensing system (200) according to the previous claim, wherein the field-effect transistors (110) of the on-chip array of field-effect transistors are aligned along two or more parallel lines and / or are disposed according to a recurrent or regular geometric pattern.3.- The biosensing system (200) according to any one of the previous claims, wherein the plurality of distributed on-chip metal electrodes are regularly and / or geometrically distributed among the on-chip array of field-effect transistors (110); and / or wherein theplurality of distributed on-chip metal electrodes are a multiple, equal in number, or a divisor of the field-effect transistors of the on-chip array of (110).4.- The biosensing system (200) according to any one of the previous claims, wherein the electrodes pathway configurator (260) is configured to: operate at least one of said plurality of distributed on-chip metal electrodes as one of said one or more sense electrodes, and to operate at least one of said plurality of distributed on-chip metal electrodes as one of said one or more drive electrodes.5.- The biosensing system (200) according to any one of the previous claims, further comprising:- a first off-chip reference electrode configured to be or being in contact with the liquid sample; and wherein the electrodes pathway configurator (260) is configured to operate the first off-chip reference electrode either as one of said one or more sense electrodes (160) or as one of said one or more drive electrodes (150); preferably the first off-chip reference electrode being an Ag / AgCI electrode.6.- The biosensing system (200) according to the previous claim, further comprising:- a second off-chip reference electrode configured to be or being in contact with the liquid sample; and wherein the electrodes pathway configurator (260) is configured to operate one of the first and second off-chip reference electrode as one of said one or more sense electrodes (160) and to operate the other of the first and second off-chip reference electrode as one of said one or more drive electrodes (150); preferably the second off-chip reference electrode being an Ag / AgCI electrode.7.- The biosensing system (200) according to any one of the previous claims, wherein: said one of said one or more sense electrodes (130,160) comprises a plurality of electrodes, and wherein the feedback control system (140) is configured to use a processed feedback signal being a mathematical combination and / or a statistic inference of said feedback signals8. The biosensing system (200) according to the previous claim, wherein the control device (210) is configured to determine a first characteristic of a first selected subset of the field-effect transistors (110) of said on-chip array (290) of field-effect transistors (110); and wherein the gate of each field-effect transistors of the first selected subset is functionalized to interact with the substance so as to be sensitive to said substance.9.- The biosensing system (200) according to the previous claim, wherein the control device (210) is configured to determine a second characteristic of a second selected subset of the field-effect transistors (110) of said on-chip array (290) of field-effect transistors; preferably the second selected subset being distinct from the first selected subset.10.- The biosensing system (200) according to the previous claim, wherein the gate of each field-effect transistor (110) of the second selected subset is not functionalized so as to be insensitive to said substance; and wherein the control device (210) is configured to determine said characteristic based on said first and second characteristic.11.- The biosensing system (200) according to the claim 9, wherein the gate (112) of each field-effect transistors (110) of the second selected subset is functionalized to a different substance so as to be sensitive to said different substance, preferably said another substance being alternatively or complementarily requested in the given application; and wherein the control device (210) is further configured to detect a presence and / or a concentration of said different substance in the liquid sample based on said second characteristic.

12. The biosensing system (200) according to any one of the previous claims wherein each field-effect transistor (110) of the on-chip array (290) of field-effect transistors (110) comprises a source (111) and a drain (113) for biasing the field-effect transistor; and wherein the control device is able to collectively operate a group of field-effect transistors, preferably by managing and / or using and / or measuring, an electrical quantity at the sources and / or at the drains of the group of field-effect transistors, and preferably, when dependent on claims 8or 9, of the first and / or second subset of the array for determine said characteristic and / or said first and / or second characteristic; or preferably to individually operate each field-effect transistor, for example by managing and / or using and / or measuring, an electrical quantity at the source and / or at the drain of each field-effect transistor of the array for determining said characteristic, and / or said first and / or said second characteristic.13.- The biosensing system (200) according to any one of the previous claims, wherein the control device (210) is configured to: detect a flawed field-effect transistor within the on-chip array, and when dependent on claims 8 or 9, preferably within said first or second selected subset of the field-effect transistors, and to exclude said flawed field effect transistor from the determination of the characteristic, and when dependent on claims 8 or 9, preferably of the first characteristic and / or of the second characteristic; preferably the on-chip control device is configured to detect said flawed field-effect transistor by measuring said electrical quantity at the source and / or at the drain of said flawed fieldeffect transistor and by comparing the measured electrical quantity with one or more of the followings:- a given threshold;- a prior electrical quantity being previously measured at the source and / or at the drain of said flawed field-effect transistor, notably during a calibration process;- a common electrical quantity based on electrical quantities measured at the sources and / or at the drains of others field-effect transistors of the array, notably of the subset.14.- The biosensing system (200) according to any of the previous claims, wherein each of the field-effect transistors (110) is configured such that a drain source current versus gate source voltage transfer function has a local minimum for a specific voltage, wherein said specific voltage of each field-effect transistor, having functionalized gate to interact with a substance, is sensitive to a presence and / or to a concentration of said substance; and wherein a characteristic of a group of field-effect transistors (110) of the on-chip array (290) is based on the specific voltage of one or more field-effect transistors of the group, and wherein preferably, when dependent on claim 8 or 9, the first subset and / or second subset are one of the groups.15.- The biosensing system (200) according to the previous claim, wherein the control device (210) is configurable to acquire the drain source current of each field-effect transistor of the array; preferably to selectively acquire the drain source current of one or more selected field-effect transistors of the array for determining said characteristic of each selected field-effect transistor or group of field effect transistors.16.- The biosensing system (200) according to the claim 14 or 15, wherein the control device (210) is configured to modify the desired voltage provided to the feedback control system so as to determine said specific voltage.17.- The biosensing system (200) according to the previous claim, wherein the control device (210) is configured to apply a following sequence on one or more field-effect transistors (110) of said on-chip array (290): modulate or alternate the desired voltage between two given values one being less and the other being greater than a current estimate of the specific voltage of the said one or more fieldeffect transistors; and to update the current estimate according to one or more measures of the drain source currents of said one or more field-effect transistors.18.- The biosensing system (200) according to the previous claim when depending on claim 9, wherein one of said two given values is less than a first current estimate of the specific voltage of the field-effect transistors of the first subset and a second current estimate of the specific voltage of the field-effect transistors of the second subset; and wherein the other of said two given values is greater than the first and the second current estimate; and wherein the control device (210) is configured to update: the first current estimate according to one or more measures of the drain source currents of the field-effect transistors of the first subset, andthe second current estimate according to one or more measures of the drain source currents of the field-effect transistors of the second subset.19.- The biosensing system (200) according any one of the previous claims, comprising a microfluidic cell arrangement for carrying the liquid sample to a first group of field-effect transistors of the on-chip array of field-effect transistors and to carry a second liquid sample to a second group of field-effect transistors of the on-chip array of field-effect transistors; preferably, when dependent on claim 8 or 9, the first group comprises the first subset of fieldeffect transistors and the second group comprises the second subset of field-effect transistors, or preferably the first group comprises a portion of the first subset of field-effect transistors and a portion of the second subset of field-effect transistors and the second group comprises another portion of the first subset of field-effect transistors and another portion of the second subset of field-effect transistors.20.- The biosensing system (200) according to any of the previous claims, further comprising an on-chip temperature sensor (280) for sensing a temperature of a portion of the biosensing system (200), preferably of the on-chip array of field-effect transistors; and wherein the control device (210) is configured to determine said characteristic of one or more of said field effect transistors (110) and / or the presence and / or the concentration of the substance in the liquid sample based on a temperature provided by said on-chip temperature sensor.21.- A method (300) for operating an on-chip array (290) of field-effect transistors (110), each field-effect transistor having a gate configured to receive a liquid sample and being individually functionable to a substance, wherein the on-chip array comprises a plurality of distributed on- chip metal electrodes, preferably the field-effect transistors being graphene field-effect transistors each being configured such that a drain source current versus gate source voltage transfer function has a local minimum for a specific voltage; the method comprising:- providing (305) one or more drive electrodes (120, 150) and one or more sense electrodes (130, 160) by selectively operating at least one, or even each of said plurality of distributed on- chip metal electrodes as one of said one or more sense electrodes and / or as one of said one or more drive electrodes, and bringing them in contact with the liquid sample;- applying (310) a drive voltage to the liquid sample to obtain a desired voltage at the gate of the field-effect transistor (110) using said one or more drive electrodes (120, 150),- measuring (320) a voltage of the gate with said one or more sense electrodes (130, 160) to obtain one or more feedback signals indicative of said measured voltage;- regulating (330) the applied voltage using a feedback control system (140) based on said one or more feedback signals.22.- The method (300) according to the previous claim, wherein said step of providing (305) one or more drive electrodes (120, 150) and one or more sense electrodes (130, 160) comprises:- providing a first reference electrode (150) to be in contact with the liquid sample; and- configuring the first reference electrode (150) to operate as one or more drive electrodes.23.- The method (300) according to any one of the claims 21 and 22, wherein said step of providing one or more drive electrodes (120, 150) and one or more sense electrodes (130. 160) comprises:- providing a second reference electrode (160) to be in contact with the liquid sample; and- configuring the second reference electrode (160) to operate as one or more sense electrodes.

24. The method (300) according to any one of the claims 21 to 23, wherein said step of regulating (330) comprises:- determining a processed feedback signal by mathematically combining and / or statistically inferring said one or more feedback signals, and- regulating the applied voltage using the processed feedback signal.

25. The method (300) according to any one of the claims 21 to 24, comprising: - functionalizing the gate of at least one field-effect transistor (110) of the on-chip array (290) to a substance;- determining a characteristic of said at least one field-effect transistor by applying the desired voltage at the gate of said at least one field-effect transistor and preferably by acquiring a drain source current of said at least one field-effect transistor; and- detecting a presence and / or a concentration of the substance in the liquid sample based on said characteristic.

26. The method (300) according to the previous claim, comprising: determining a first given value being lower than a current estimate of a specific voltage of said at least one field-effect transistor, wherein at the specific voltage a drain source current versus gate source voltage transfer function has a local minimum; determining a second given value being higher than said current estimate; modulating or alternating the desired voltage between the first and the second given value; and updating the current estimate according to one or more measures of the drain source currents of said at least one field-effect transistors.

27. The method according to any one of the claims 21 to 24, comprising:- functionalizing the gate of each field-effect transistor (110) of a first subset of the on-chip array (290) to a substance; while having the gate of each field-effect transistor (110) of a second subset of the on-chip array not functionalized, the second subset being distinct from the first subset;- wherein the step of applying (310) a drive voltage implies applying the desired voltage at the gate of the field-effect transistors of the first and of the second subset;- wherein determining a characteristic implies determining a first characteristic of the fieldeffect transistors of the first subset by acquiring a drain source current of the field-effect transistors of the first subset and determining a second characteristic of the field-effect transistor of the second subset by acquiring a drain source current of the field-effect transistors of the second subset;- and wherein detecting a presence and / or a concentration of the substance in the liquid sample is done based on the first and the second characteristic, preferably based on a difference between the first and the second characteristic.

28. The method (300) according to the previous claim, comprising: determining a first given value being lower than a first current estimate of a first specific voltage of the field-effect transistors of the first subset, wherein at the first specific voltage a drain source current versus gate source voltage transfer function of the field-effect transistors of the first subset has a local minimum, and lower than a second current estimate of a second specific voltage, wherein at the second specific voltage a drain source current versus gatesource voltage transfer function of the field-effect transistors of the second subset has a local minimum; determining a second given value being higher than the first and the second current estimate; modulating or alternating the desired voltage between the first and the second given value; updating the first current estimate according to one or more measures of the drain source currents of the field-effect transistors of the first subset, and updating the second current estimate according to the drain source currents of the field-effect transistors of the second subset.

29. The method according to any one of the claims 21 to 24, comprising:- functionalizing the gate of each field-effect transistor (110) of a first subset of the on-chip array (290) to a substance;- functionalizing the gate of each field-effect transistor (110) of a second subset of the on-chip array (290) to a different substance, the second subset being distinct from the first subset;- while having the gate of each field-effect transistor (110) of a third subset of the on-chip array not functionalized, the third subset being distinct from the first and the second subset;- wherein the step of applying (310) a drive voltage implies applying the desired voltage at the gate of the field-effect transistors of the first, second and third subset;- wherein determining a characteristic implies determining a first characteristic of the fieldeffect transistors of the first subset by acquiring a drain source current of the field-effect transistors of the first subset;- and determining a second characteristic of the field-effect transistors of the second subset by acquiring a drain source current of the field-effect transistors of the second subset;- and determining a third characteristic of the field-effect transistors of the third subset by acquiring a drain source current of the field-effect transistors of the third subset- and wherein detecting a presence and / or a concentration of the substance in the liquid sample is done based on the first and third characteristic, preferably based on a difference between the first and the third characteristic;- and wherein detecting a presence and / or a concentration of said different substance in the liquid sample based on the second and third characteristic, preferably based on a difference between the second and the third characteristic.

30. The method (300) according to the previous claim, comprising:determining a first given value being: lower than a first current estimate of a first specific voltage of the field-effect transistors of the first subset, wherein at the first specific voltage a drain source current versus gate source voltage transfer function of the field-effect transistors of the first subset has a local minimum, and lower than a second current estimate of a second specific voltage of the field-effect transistors of the second subset, wherein at the second specific voltage a drain source current versus gate source voltage transfer function of the field-effect transistors of the second subset has a local minimum, and lower than a third current estimate of a third specific voltage of the field-effect transistors of the third subset, wherein at the second specific voltage a drain source current versus gate source voltage transfer function of the field-effect transistors of the second subset has a local minimum; determining a second given value being higher than the first, the second and the third current estimate; modulating or alternating the desired voltage between the first and the second given value; updating the first current estimate according to one or more measures of the drain source currents of the field-effect transistors of the first subset, updating the second current estimate according to the drain source currents of the field-effect transistors of the second subset, and updating the third current estimate according to the drain source currents of the field-effect transistors of the third subset.

31. The method according to claim 30, comprising: detecting a flawed field-effect transistor within said first or second or third selected subset of the field-effect transistors, wherein said step of determining said first characteristic and / or said second characteristic comprises excluding said flawed field effect transistor from said first or second or third selected subset of the field-effect transistors.

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