CHARGE SENSING DEVICE WITH GATE VOLTAGE SELECTED TO OPERATE AROUND THE CHARGE NEUTRALITY POINT AND TUNE THE QUANTUM CAPACITANCE

Abstract

The present invention relates to a system comprising an electronic apparatus which comprises:—an electronic device comprising:—a gate electrode (G, BE);—a dielectric (D) arranged over the gate electrode (G, BE); and—a charge sensing structure (CE) with a 2-dimensional charge sensing layer to provide a gate capacitance (C.sub.g) between the charge sensing structure (CE) and the gate electrode structure (G, BE) and a quantum capacitance (C.sub.q) resulting in a total capacitance (C.sub.tot);—a voltage detector to detect an output voltage (V.sub.o) stored in the total capacitance (C.sub.tot). The system further comprises means to apply a gate voltage (V.sub.g) to the gate electrode structure (G, BE) selected to:—make the device operate around most sensitive point of fermi level of the charge sensing structure (CE); and—tune the quantum capacitance (C.sub.q). The present invention also relates to an electronic apparatus adapted to allow the tuning of its quantum capacitance.

Claims

1. A system comprising an electronic apparatus, wherein the electronic apparatus comprises: an electronic device comprising: a gate electrode structure; a dielectric structure arranged over said gate electrode structure; and a charge sensing structure comprising at least one 2-dimensional charge sensing layer configured to sense at least one of electrical charges and electrical charge density changes induced by an external physical quantity, and that is configured and arranged over said dielectric structure to provide a gate capacitance between the charge sensing structure and the gate electrode structure; wherein said charge sensing structure shows a quantum capacitance in series with said gate capacitance resulting in a total capacitance between the charge sensing structure and the gate electrode structure; and a voltage detector electrically connected to the charge sensing structure or to the gate electrode structure, to detect an output voltage that is representative of said sensed electrical charges stored in said total capacitance; wherein the system further comprises a mechanism configured and arranged to apply a gate voltage to said gate electrode structure, wherein said gate voltage is selected to, both: make the electronic device operate around the most sensitive point of fermi level of the charge sensing structure; and tune the quantum capacitance to modify the sensitivity and dynamic range of the electronic device.

2. The system according to claim 1, wherein said mechanism comprises a voltage source that generates said gate voltage.

3. The system according to claim 1, wherein said mechanism comprises a control unit configured and arranged to apply said gate voltage to said gate electrode structure, and to perform said selection of the gate voltage.

4. The system according to claim 3, wherein said gate voltage is a DC voltage, an AC voltage, or a combination of DC and AC voltages, and wherein the control unit is configured to select the properties of said gate voltage, at least regarding its magnitude.

5. The system according to claim 3, wherein the control unit comprises a selection input to receive selection signals regarding operation modes, and wherein the control unit is configured to select and apply said gate voltage to said gate electrode structure in response to a selection signal received through said selection input, to make the apparatus operate according to the selected operating mode.

6. The system according to claim 5, wherein the control unit is configured not to apply said gate voltage to said gate electrode structure also in response to a selection signal received through said selection input.

7. The system according to claim 5, wherein said operation modes include at least the following modes: a high sensitive mode, in which the control unit does not apply said gate voltage to the gate electrode structure or selects and applies a gate voltage with an absolute magnitude below (0.9*V.sub.t−V.sub.cnp) volts, where V.sub.t=q.sub.e.Math.n*.Math.A/C.sub.g, where q.sub.e is the electron charge, n* the residual charge carrier density, A the area and C.sub.g the capacitance of the gate and V.sub.cnp the voltage at which the quantum capacitance is lowest, to reduce, not to increase or increase just a percentage below 35% said quantum capacitance; a high dynamic range mode, in which the control unit selects and applies to the gate electrode structure a gate voltage with an absolute magnitude above (1.1*V.sub.t−V.sub.cnp) volts, to increase to a percentage above 45% said quantum capacitance; and a trade-off mode, in which the control unit selects and applies to the gate electrode structure a gate voltage with an absolute magnitude between 0.9−(1.1*V.sub.t−V.sub.cnp) volts range, to increase said quantum capacitance to a percentage ranging between 35 and 45%.

8. The system according to claim 3, wherein the control unit further comprises an adjustment input connected to an output of said voltage detector or of a read-out circuit operatively connected thereto, and is configured to implement a closed-loop adjustment process to adjust the gate voltage based on a detected output voltage or read-out signal received through said adjustment input.

9. The system according to claim 7, wherein the control unit further comprises an adjustment input connected to an output of said voltage detector or of a read-out circuit operatively connected thereto, and is configured to implement a closed-loop adjustment process to adjust the gate voltage based on a detected output voltage or read-out signal received through said adjustment input, and wherein the control unit is configured to implement said closed-loop adjustment process also based on the selected operation mode.

10. The system according to claim 3, wherein said voltage detector includes a reset circuit to discharge the total capacitance under the control of the control unit, and wherein the apparatus further comprises a read-out circuit operatively connected to the out of the voltage detector to provide a read-out signal based on the detected output voltage.

11. The system according to claim 1, wherein the electronic device further comprises a sensitizing or functionalizing structure arranged over said charge sensing structure, wherein said sensitizing or functionalizing structure is configured to at least one of induce said electrical charge carriers and modify the charge carrier density therein induced by said external physical quantity, wherein the sensitizing or functionalizing structure is only sensitive to said external physical quantity.

12. The system according to claim 11, wherein said sensitizing or functionalizing structure is a photoactive structure configured and arranged to, upon illumination, generate electron-hole pairs which, due to a field created by either a Schottky junction between the charge sensing structure and the photoactive structure or a topgate electrode on top of the photoactive structure or an interlayer between the charge sensing structure and the photoactive structure, are separated and either the electrons or holes gets transported, as said induced electrical charge carriers, to the charge sensing structure.

13. The system according to claim 12, implementing an image sensor comprising an array of pixels, wherein the electronic apparatus comprises a plurality of said electronic devices each constituting one pixel of said array of pixels.

14. The system according to claim 1, wherein the electronic device is absent of any sensitizing or functionalizing structure arranged over said charge sensing structure, the charge sensing structure being configured to at least one of induce itself said electrical charge carriers and modify the charge carrier density therein induced by said external physical quantity.

15. An electronic apparatus, comprising: an electronic device comprising: a gate electrode structure; a dielectric structure arranged over said gate electrode structure; and a charge sensing structure comprising at least one 2-dimensional charge sensing layer configured to sense at least one of electrical charges and electrical charge density changes induced by an external physical quantity, and that is configured and arranged over said dielectric structure to provide a gate capacitance between the charge sensing structure and the gate electrode structure, wherein said charge sensing structure shows a quantum capacitance in series with said gate capacitance resulting in a total capacitance between the charge sensing structure and the gate electrode structure; and a voltage detector electrically connected to the charge sensing structure or the gate electrode structure, to detect an output voltage stored in said total capacitance and that is representative of said sensed electrical charges; wherein the electronic apparatus further comprises at least an input terminal electrically connected to said gate electrode structure and that is accessible to apply thereto a gate voltage selected to, both: make the electronic device operate around the most sensitive point of fermi level of the charge sensing structure; and tune the quantum capacitance to modify the sensitivity and dynamic range of the electronic device.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0077] In the following some preferred embodiments of the invention will be described with reference to the enclosed figures. They are provided only for illustration purposes without however limiting the scope of the invention.

[0078] FIG. 1 schematically shows the system of the first aspect of the present invention, for an embodiment;

[0079] FIG. 2 is a schematic side view of the structure of the electronic device of the electronic apparatus of the second aspect of the invention and of the electronic apparatus of the system of the first aspect, for an embodiment, with electrical connections indicated as round circles: CE=charge sensing layer electrode and BE=bottom electrode.

[0080] FIG. 3 is a schematic side view of the of the electronic device of the electronic apparatus of the second aspect of the invention and of the electronic apparatus of the system, for an embodiment for which the electronic device comprises a photoactive structure for, upon illumination, generate electron-hole pairs which are separated and one of them gets transported to the charge sensing structure (CE), as indicated by the charge flow illustrated.

[0081] FIG. 4 is a plot of the capacitance for a conventional parallel plate capacitor with two metal plates (MIM: “Metal-Insulator-Metal”) and the total capacitance (including quantum capacitance) for a parallel plate capacitor of which one plate is a layer of 2D material (MI2D: “Metal-Insulator-2D material”).

[0082] FIG. 5 is a plot of the capacitance of the electronic device of the electronic apparatus of the second aspect of the invention and of the electronic apparatus of the system of the first aspect of the present invention, as a function of the applied gate voltage V.sub.g with respect to the charge neutrality point (d=10 nm, ε.sub.r=6, n*=7.Math.10.sup.10 cm.sup.−2).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] FIG. 1 shows an embodiment of the system of the first aspect of the present invention, for which the system comprises an electronic apparatus which comprises the components depicted within a dotted-line square, i.e. an electronic device comprising: [0084] a gate electrode structure G; [0085] a dielectric structure D arranged over the gate electrode structure G; and [0086] a charge sensing structure CE comprising a 2-dimensional charge sensing layer configured to sense electrical charges and/or electrical charge density changes induced by an external physical quantity, and that is configured and arranged over the dielectric structure D to provide a gate capacitance C.sub.g between the charge sensing structure CE and the gate electrode structure G.

[0087] The charge sensing structure CE has a density of states low enough to provide a quantum capacitance C.sub.q in series with the gate capacitance C.sub.g resulting in a total capacitance C.sub.tot in value between C.sub.q and C.sub.g (C.sub.tot=1/(1/C.sub.q+1/C.sub.g) when measured between the charge sensing structure CE and the gate electrode structure G.

[0088] As shown in FIG. 1, also within the dotted-line square, the electronic apparatus further comprises a voltage detector, formed by an amplifier A which input is electrically connected to the charge sensing structure CE, to detect an output voltage V.sub.o that is representative of the sensed electrical charges stored in the total capacitance C.sub.tot.

[0089] The system of the first aspect of the present invention further comprises means which for the illustrated embodiment comprise a control unit CU configured and arranged to apply a gate voltage V.sub.g to the gate electrode structure G, wherein the gate voltage V.sub.g is selected by the control unit CU to, both:

[0090] make the electronic device operate around the most sensitive point of fermi level of the charge sensing structure CE, i.e. around the charge neutrality point when the 2-dimensional material is graphene; and

[0091] tune the quantum capacitance C.sub.q to modify the sensitivity and dynamic range of the electronic device.

[0092] As shown in FIG. 1, the voltage detector includes a reset circuit, formed by a transistor F, to discharge the total capacitance C.sub.tot under the control of the control unit CU (by closing the transistor F so as to connect C.sub.tot to the gate electrode structure G), and the apparatus further comprises a read-out circuit R operatively connected to the out of the voltage detector to provide a read-out signal S.sub.o based on the detected output voltage V.sub.o.

[0093] For the illustrated embodiment, the voltage detector includes an amplifier A, which needs to have a low input capacitance and thus a very high input impedance, although other kind of known voltage detectors are also covered by the present invention.

[0094] The read sequence is as follows: [0095] 1. Close Reset transistor F [0096] 2. Apply V.sub.g [0097] 3. Read S.sub.o [0098] 4. Open reset transistor F to drain charges

[0099] FIG. 1 also shows an embodiment of the electronic apparatus of the second aspect of the present invention which comprises the components depicted within or in contact with the contour of the dotted-line square, i.e. the components of the electronic apparatus of the system of the first aspect of the present invention and further an input terminal TV.sub.g electrically connected to the gate electrode structure G and that is accessible to apply thereto a gate voltage V.sub.g selected to, both:

[0100] make the electronic device operate around the most sensitive point of fermi level of the charge sensing structure CE, i.e. around the charge neutrality point when the 2-dimensional material is graphene; and

[0101] tune the quantum capacitance to modify the sensitivity and dynamic range of the electronic device.

[0102] For an implementation of that embodiment, the components of the electronic apparatus are embedded in an integrated circuit chip, which has an input pin for terminals TV.sub.g, a further input pin to connect to the illustrated reset terminal T.sub.Reset and also an output pin connected to terminal TS.sub.o, so that a control unit CE can be connected to those input pins to provide gate voltage V.sub.g and Reset signal, while S.sub.o goes out through output terminal TS.sub.o.

[0103] In FIG. 2, an embodiment of the system and electronic apparatus of the present invention is shown, for which the electronic device is a photodetector which comprises a substrate S, a bottom electrode structure BE (as the above mentioned gate structure), and a sensitizing or functionalizing structure PS constituted by a photoactive structure PS (formed by colloidal quantum dots, III-V semiconductor, perovskites, 2D material, etc.) arranged over the charge sensing structure CE (for example, formed by a single layer or few layer graphene, black phosphorus, MoS2, WS2, WSe2 etc.) configured and arranged to, upon illumination, generate electron-hole pairs which, due to a built-in field created by a Schottky junction between the charge sensing structure CE and the photoactive structure PS, are separated and either the electrons or holes (depending on the type of Schottky junction) gets transported to the charge sensing structure CE. A voltage now builds up on the gate capacitor C.sub.g. In case of a photosensitive layer it is the total photogenerated charge: Q.sub.ph=EQE*q.sub.e*τ.sub.tr A/E.sub.p I, (EQE is the external quantum efficiency, q.sub.e the electron charge, τ.sub.tr the trapping time of the photogenerated charges and I the irradiance, A the area of the device and E.sub.p the photon energy). This process is illustrated in FIG. 3.

[0104] FIG. 4 plots the total capacitance of a conventional parallel plate capacitor with two metal plates (MIM) and the total capacitance (including quantum capacitance) for a parallel plate capacitor of which one plate is a layer of 2D material exhibiting quantum capacitance effects (MI2D). A typical gate dielectric thickness of 10 nm made of Al.sub.2O.sub.3 (εr=6) and the minimum quantum capacitance for a high electronic quality graphene layer in a capacitor with the same dielectric at room temperature (n*=7.Math.10.sup.10 cm.sup.−2): 0.0012 F/m.sup.2 were taken. For a typical gate dielectric thickness of 10 nm made of Al.sub.2O.sub.3 the normal capacitance is 0.0053 F/m2. In this case the signal will be enhanced by a factor 5.

[0105] For the present invention, particularly when a large detector sensitivity is not required, the electronic device can be tuned to the classical regime by applying a different V.sub.g to allow for more photogenerated charges (or charges generated by other means, for those embodiments not including a photosensitizing structure) to be stored and thus enable a larger dynamic range. This effect is illustrated in FIG. 5 with the results obtained from a simulation of the present invention for the arrangement of FIGS. 2 and 3. As shown in that Figure, applying a gate voltage of 3V with respect to the charge neutrality point gives a capacitance that is 3× enhanced.

[0106] A person skilled in the art could introduce changes and modifications in the embodiments described without departing from the scope of the invention as it is defined in the attached claims.