EP4014260A1 - Sensor for detecting photons incident on the surface thereof and/or foreign substances accumulating on the surface thereof - Google Patents

Abstract

The sensor for detecting photons incident on the surface thereof and/or foreign substances accumulating on the surface thereof has a) a diode having a two-dimensional barrier layer based on a layer arrangement composed of a metal electrode (20), a dielectric barrier (22) and a graphene layer (24), and b) a surface layer (26) which is located above and on the graphene layer (24), reacts electrically to photons and/or accumulated foreign substances and forms the surface of the sensor.

Description

Sensor for the detection of photons incident on its surface and / or foreign substances that accumulate on its surface

The invention is based on a previously known sensor which has a vertical diode with a two-dimensional, two-dimensional transition and based on a layer arrangement of a metal electrode, a dielectric barrier and a graphene layer.

In addition to sensors based on semiconductors, graphene phototransistors and photodetectors are known which have a double-layer heterostructure, see for example US 8 344 358 B2, US 2014/0264275 A1. These sensors provide a very short response time and a higher sensitivity compared to conventional, semiconductor-based sensors.

From Nat. Nanotechnol, 7, 2012, 363, a graphene FET with an electrically reactive surface layer in the form of quantum dots is known. It is only sensitive to photons and has shown a response sensitivity of 108 A / W at 25% external quantum efficiency.

The content of these three prior publications is fully part of the disclosure content of the present application.

Because of the transparency and flexibility of graphene, such sensors are ideal for application to any surface, such as curved surfaces such as skin and the like, to detect light. They are well suited for healthcare applications.

A disadvantage of the known sensors is that they have high dark currents in the range of pA and high noise levels. The high noise levels limit the specific sensitivity and the signal / noise ratio.

The object of the invention is to further develop a sensor of the previously known type in such a way that it is sensitive to light and / or accumulating and adsorbed foreign substances, is easy to manufacture, has a low dark current and exhibits high sensitivity with a quick response time. This object is achieved by a sensor for detecting photons incident on its surface and / or foreign matter deposited / deposited on its surface, the sensor a) being a diode with a two-dimensional barrier layer based on a layer arrangement of a metal electrode, egg ner dielectric barrier and a graphene layer, and b) a surface layer which is located above and on the graphene layer and electrically reacts to photons and / or deposited / deposited foreign substances and which forms the surface of the sensor.

Furthermore, the object is achieved by a method for detecting photons and / or foreign substances that accumulate and / or are accumulated, with the sensor according to the previous paragraph, by measuring the change in resistance and / or capacitance between the two Connections of the diode.

Further developments can be found in the subclaims.

This sensor can be easily manufactured, for example, using thin-film technology. It has a high sensitivity with low self-noise. The dark currents are very low. This enables use with low power requirements and high specific sensitivity. A sensitivity of up to 103 A / W for light with a wavelength of 633 nm with currents in the nA range was achieved, using a surface layer with PbS colloidal quantum dots.

The sensor can be used for optical communication systems, for image recording and also for photovoltaic systems.

Photons are preferably understood to mean photons in the visible spectral range, in the near UV and in the infrared range. For the absorption of photons, one or more photoactive layers, in particular quantum dots, J-aggregates and / or chalcogenides such as HgS (Zin nober), CdS (cadmium yellow), CdSe and especially transition metal dichalcogenides, are used for the surface layer. The graphene layer can be used as the surface layer, in particular a top layer of the multilayer graphene layer. The The surface layer can also be formed by modified or functionalized graphene.

The surface layers specified in the previous paragraph for the absorption of photons can be used to detect foreign substances. In addition, linker biomolecules can be used as a surface layer. Foreign substances are typically atoms or molecules. In particular, they reach the surface by themselves, without solvents or the like. For example, it can be micro-dust, fine dust, gas. The foreign substances can also enter into chemical reactions with the surface layer or with another partner. They are preferably adsorbed, that is, kept on the surface via so-called Van der Waals forces. The foreign substances can be chemically and / or bioactive.

In the case of a surface layer that reacts electrically to deposited foreign matter, it is advantageous that cleaning methods or means are provided in order to detach the foreign matter from the surface layer again after accumulation has taken place. For example, neural signals can also be recorded. One application is in the area of direct detection of in vivo electrical signals, another application is in the area of implemented biosensors that use chemically bound linker molecules that increase the selectivity of specific biomolecules. When a molecule to be detected docks or binds to the linker, it transfers a charge into the graphene layer or induces an electric field in it, so that the charge distribution in the graphene layer is influenced.

The graphene layer preferably has dimensions in the range from 1 × 1 to 15 × 15 μm, for example approximately 10 × 10 μm. The area of the barrier is preferably between 1 pm2 and 400 pm2, preferably in the range below 120 pm2. The graphene layer preferably has n = 1 to 15, in particular n = 1 to 10 and particularly preferably n = 1 to 5 monolayers of graphene. The material of the barrier can be an insulator or a semiconductor. For example, SiO 2, Al 2 O 3, hBN, SiN, MoS 2 or the like are possible. The diode has a two-dimensional barrier layer. When illuminated, the surface layer absorbs light. If the surface layer has quantum dots, for example, electron-hole pairs are generated in the quantum dots, depending on the quantum dots used. The electron or the hole is transferred to the graphene and changes the charge distribution and / or doping there. This can be read out electrically, for example by measuring the resistance or capacitance of the diode.

Corresponding processes take place when a chemoactive or bioactive graphene diode is used. You can follow an adsorption process during the adsorption process. Due to foreign substances that increasingly reach the surface, a charge shift takes place, which leads to a change in the resistance and the capacity of the diode. This change can be verified using suitable measuring methods. For example, the resistance can be measured. The diode can also be connected to an inductance, so that an oscillating circuit is formed which has a resonant frequency which changes when the capacitance of the diode changes.

Further features and advantages of the invention emerge from the remaining claims and from the following description of an embodiment of the invention, which is not to be understood as limiting. For this purpose, reference is made to the drawing in which it shows

Figure 1: a basic sectional view across the barrier layer through the sensor and with a detection device, and

FIG. 2 shows a sectional view like FIG. 1, but now with a surface layer formed by at least one top layer of a graphene layer.

The diode of the sensor has a metal electrode 20, a barrier 22 and a Gra phenschicht 24. This arrangement is also referred to as MIG (metal-insulator-graphene). It forms a two-dimensional transition. On the side of the graphene layer 24 facing away from the barrier 22 there is a surface layer 26. In an alternative, it can also be located between the barrier 22 and the graphene layer 24. It is specially designed for the event to which the sensor is sensitive, i.e. light and / or foreign matter. As photosensitive Surface layer 26 are in particular photoactive materials, for example quantum dots, J-aggregates, in particular in the form of dye molecules (for example merocyanines, rhodamine) and chalcogenides, in particular metal chalcogenides and here preferably transition metal chalcogenides. The task of the surface layer is to give the sensor a light sensitivity and / or sensitivity for the adsorption of foreign substances. When light is absorbed or a foreign substance is adsorbed, free charge carriers are released from the surface layer into the graphene layer 24 and / or the charge distribution in the surface layer changes, for example due to the dipole moments. This leads to a change in the charge distribution in the graphene layer 24, for example the doping and / or the distribution of the charge carriers. This changes the resistance and capacitance of the MIG diode.

Any metal can be used as the metal for the metal electrode 20, for example Al, Ti, Au or a ferromagnetic material such as Ni, Fe, Co. the metal electrode has a thickness of typically 1 nm to a few millimeters, for example 3 mm. The barrier 22 is made of insulating or semiconducting material. It typically has a thickness of 1 to 15 nm.

The metal electrode 20 can be arranged on a substrate (not shown) in order to fix it mechanically. This substrate does not add functionality. It can be rigid or flexible. It is preferably very thin, in particular a film a few μm thick or a rigid carrier.

The diode is connected in a known manner by means of contacts on the graph layer 24 and on the metal electrode 20. In each of the two figures, a detection device is also shown that uses these contacts. It has a voltage source 28 and an ammeter 30. The ohmic resistance of the diode is measured in each case. For this purpose, the voltage source 28 is connected to the metal electrode 20. The voltage source 28 is in turn connected to the current measuring device 30, which in turn is connected to the graphene layer 24.

In the embodiment according to FIG. 1, light falls from above onto the surface layer 26 and is absorbed there. In the embodiment of Figure 2 is the Surface layer 26 formed by one or more uppermost layers of the multilayer graphene layer 24. The adsorption of a gas molecule is indicated by an arrow 32.

The sensor for detecting photons incident on its surface and / or foreign matter accumulating on its surface has a) a diode with a two-dimensional barrier layer based on a layer arrangement of a metal electrode 20, a dielectric barrier 22 and a graphene layer 24, and b) a via the surface layer 26 located under the graphene layer 24, which reacts electrically to photons and / or accumulated foreign substances and which forms the surface of the sensor.

Terms such as essentially, preferably and the like, as well as information that is possibly to be understood as imprecise, are to be understood in such a way that a deviation of plus or minus 5%, preferably plus or minus 2% and in particular plus or minus one percent from the normal value is possible. The applicant reserves the right to combine any features and sub-features from the claims and / or any features and also partial features from a set of the description in any way with other features, sub-features or partial features, including outside the features of independent claims. The applicant continues to reserve the right to delete any features and also partial features.

Reference to funding

The project that led to this application was financed under grant agreement No. 649953 and the corresponding sub-projects from the European Union's "Horizon 2020" research and innovation program. Reference symbol metal electrode barrier graphene layer surface layer voltage source ammeter arrow

Claims

1 claims 1. Sensor for the detection of photons incident on its surface and / or foreign matter accumulating on its surface, the sensor a) being a diode with a two-dimensional barrier layer based on a layer arrangement of a metal electrode (20), an electrical barrier (22) and a graphene layer (24), and b) a surface layer (26) which is located above and on the graphene layer (24) and reacts electrically to photons and / or the deposited foreign matter and which forms the surface of the sensor. 2. Sensor according to claim 1, characterized in that the surface layer (26) reacts with the absorption of photons and / or the accumulation of a foreign substance with a shift of electrical charge carriers, in particular emits free charge carriers in the graphene layer (24). 3. Sensor according to one of the preceding claims, characterized in that the sensor detects photons, and that the Oberflä chenschicht (26) quantum dots, J-aggregates, in particular special J-aggregates in the form of organic dye molecules, and / or chalcogenides. 4. Sensor according to one of the preceding claims, characterized in that the barrier (22) is made of an insulating or semiconducting material. 5. Sensor according to one of the preceding claims, characterized in that the barrier (22) has a thickness of greater than zero and less than 20 nm, in particular 1 to 15 nm. 6. Sensor according to one of the preceding claims, characterized in that the area of the barrier (22) is between 1 and 400 pm2, in particular 4 to 120 pm2, and particularly preferably less than 100 pm2. 2 7. Sensor according to one of the preceding claims, characterized in that the graphene layer (24) has n = 1 to 20, in particular n = 1 to 10 monolayers of graphene. 8. A method for the detection of photons and / or accumulating or accumulating foreign substances with a sensor according to one of the preceding claims, characterized by measuring the change in resistance and / or capacitance between the terminals of the diode. 9. The method according to claim 8, characterized in that a zero measurement is carried out before the sensor is irradiated with photons and / or before foreign substances accumulate on the surface of the sensor, and that at least one further measurement is then carried out. 10. The method according to any one of the preceding method claims, characterized in that a measurement is carried out while the sensor is irradiated with photons and / or while foreign substances accumulate on the surface of the sensor. 11. The method according to any one of the preceding method claims, characterized in that after an adsorption of foreign substances and carried out measurement, the surface of the sensor is cleaned of the foreign substances.