Barristor device

Abstract

A barristor device is disclosed. The barristor device comprises: a substrate; a doped region formed by doping the substrate with impurities; a graphene layer laminated on the doped region; a first electrode connected to the doped region; and a second electrode connected to the graphene layer. The work function of the graphene layer changes according to the concentration of the doped region, and the doping concentration of the doped region is 1016 / ㎤ to 5*1018 / ㎤.

Description

Varistor element

[0001] An embodiment of the present invention relates to a baristor element.

[0002] Graphene is being actively researched as a new material that could replace semiconductors. Graphene has a two-dimensional planar crystal structure with a hexagonal honeycomb pattern. Its thinness, light weight, durability, and excellent conductivity make it a versatile material for a wide range of applications. Recently, a new barristor device utilizing graphene has emerged, functionally similar to a transistor but structurally closer to a diode.

[0003] Varistors are devices that control the current flowing through them by controlling the height of the Schottky junction formed at the junction between graphene and a semiconductor. Varistors can be used as switching devices or as various sensors. For example, varistors can be used in biosensors that detect DNA and various viruses, and gas sensors that measure gas concentrations (e.g., NO2).

[0004] The technical problem to be solved by the embodiment of the present invention is to provide a varistor element with improved sensitivity.

[0005] In order to achieve the above technical task, an example of a varistor device according to an embodiment of the present invention includes: a substrate; a doping region formed by doping an impurity into the substrate; a graphene layer stacked on the doping region; a first electrode connected to the doping region; and a second electrode connected to the graphene layer; wherein the work function of the graphene layer changes depending on the concentration of the doping region, and the doping concentration of the doping region is 10 16 / ㎤ ~ 5*10 18 / ㎤.

[0006] According to an embodiment of the present invention, the sensitivity of a varistor element can be improved by doping at an optimal doping concentration. When the varistor element of this embodiment is used as a sensor, changes in the concentration of a sample can be detected more accurately than with conventional sensors.

[0007] FIG. 1 is a drawing showing an example of a varistor element according to an embodiment of the present invention;

[0008] Fig. 2 is a diagram showing an example of an equivalent circuit of the varistor element of Fig. 1.

[0009] FIG. 3 is a diagram illustrating a change in the graphene work function according to the doping concentration of a varistor element according to an embodiment of the present invention.

[0010] FIG. 4 is a table showing the change in the graphene work function according to the doping concentration of a baristor element according to an embodiment of the present invention.

[0011] Figures 5 to 7 are drawings showing experimental examples of current change according to time or drain voltage of a varistor element according to an embodiment of the present invention.

[0012] FIG. 8 is a drawing showing another example of a varistor element according to an embodiment of the present invention, and

[0013] FIG. 9 is a drawing illustrating another example of a varistor element according to an embodiment of the present invention.

[0014] Hereinafter, a varistor element according to an embodiment of the present invention will be described in detail with reference to the attached drawings.

[0015] FIG. 1 is a drawing illustrating an example of a varistor element according to an embodiment of the present invention.

[0016] Referring to FIG. 1, the baristor element (100) includes a substrate (110), a graphene layer (130), a first electrode (151), a second electrode (152), and a third electrode (170).

[0017] The substrate (110) can be implemented with silicon, etc. The substrate (110) has a doping region (111, 112) doped with an n-type or p-type impurity. This embodiment illustrates a case where a p-type impurity is doped. In one embodiment, the doping regions (111, 112) can be formed as a first doping region (111) and a second doping region (112) having different doping concentrations. For example, in order to improve the sensitivity of the varistor element, the first doping region (111) can have a first concentration (e.g., 10 16 / ㎤~5*10 18 / cm3), and the second doping region (112) has a second concentration (>=first concentration) (e.g., 10 19 / cm3 or more). In another embodiment, the entire doping region (111, 112) may be doped with the same first concentration. The area and depth of each doping region (111, 112) may be variously modified depending on the embodiment. In another embodiment, the doping concentration of the substrate (110) may be doped with the same first concentration as the entire doping region (111, 112). The process of deriving the optimal value of each doping region (111, 112) will be reviewed again in FIG. 2 and below.

[0018] A graphene layer (130) is stacked on top of the first doped region (111). The first doped region (111) is connected to the graphene layer (130), and the second doped region (112) is connected to the first electrode (151). That is, the first electrode (151) and the graphene layer (130) are not directly connected to each other, but are connected through the doped regions (111, 112). The second electrode (152) is connected to the graphene layer (130). The third electrode (i.e., gate electrode) (170) exists on the graphene layer (130) with the insulating layer (160) interposed therebetween. In addition, an insulating layer (120) exists for insulation between each component.

[0019] This embodiment is only one example to help understanding of the varistor element (100), and the connection structure of the first electrode (151) - doped region (111, 112) - graphene layer (130) - second electrode (152) can be implemented in various forms. In one embodiment, the varistor element (100) can be implemented as a switch element using the third electrode (170). In another embodiment, the varistor element (100) can be implemented as a sensor by stacking a reaction layer (880 in FIG. 8) on the graphene layer (130) instead of the gate electrode (170), and an example of this is illustrated in FIG. 8.

[0020] Fig. 2 is a diagram showing an example of an equivalent circuit of the varistor element of Fig. 1.

[0021] Referring to FIGS. 1 and 2 together, the first electrode (151) acts as a drain electrode, and the second electrode (152) acts as a source electrode. The capacitance of the varistor element (100) includes the capacitance (C) between the gate electrode (170) and the graphene layer (130). GATE ), capacitance (C) accumulated in the graphene layer (130) Q ), capacitance (C) between the doping region (111) and the graphene layer (130) DEP ) etc. exist.

[0022] C GATE Wow C DEP Assuming that the intermediate electrodes are connected in series and the amount of charge accumulated in the intermediate electrode is Q, the potential of the intermediate electrode (V M ) is expressed by the following mathematical formula.

[0023]

[0024] Here, V G is the potential of the gate electrode (170), V D represents the potential of the drain electrode (151).

[0025] The potentials of the gate electrode (170) and the drain electrode (151) are both positive (i.e., V G>0, V D >0), if the intermediate electrode is replaced by a grounded graphene layer (130), the charge (Q) accumulated in the graphene layer (130) is composed of electrons and can be expressed as follows.

[0026]

[0027] Here, e represents the charge of an electron, is the work function of graphene, (h is Planck's constant), represents the Fermi velocity.

[0028] If the work functions of the gate electrode (170) and the drain electrode (151) are the same from the Dirac point, the potential V of the intermediate electrode M The graphene work function for charge Q is ) can be set to be the same as . In this case, the graphene work function ( ) can be determined by the following mathematical formula.

[0029]

[0030] Mathematical expression 3 is the graphene work function ( ) can be summarized as follows.

[0031]

[0032] The capacitance per unit area (C / A) accumulated at the junction between a semiconductor (P-type or N-type) and graphene is expressed by the following mathematical equation.

[0033]

[0034] C represents capacitance, A represents area, V represents voltage applied to the semiconductor-graphene junction, and V0 represents contact potential generated in the depletion region at the semiconductor-graphene junction.

[0035] The capacitance (C) of mathematical expression 5 is C of this embodiment DEP The capacitance between the graphene layer (130) and the doped region (111) can be obtained by substituting C using mathematical expression 5. DEP Applying to Equation 4, C DEP Graphene work function according to ( ) can be obtained.

[0036] FIG. 3 is a diagram illustrating a change in the graphene work function according to the doping concentration of a varistor element according to an embodiment of the present invention.

[0037] Referring to Figure 3, when the doping concentration of the doping region (111) decreases, the capacitance (C) between the graphene layer (130) and the doping region (111) DEP ) decreases and the graphene work function ( according to Equations 4 and 5) ) also increases. The graph on the right (310) of Fig. 3 is a graph that expresses the graph on the left (300) in a log scale.

[0038] As an example, when a voltage is applied to the third electrode (170) in the varistor element (100) of FIG. 1 or a sample is applied to the reaction layer (880) of the varistor element of FIG. 8, the graphene work function ( ) changes, and accordingly the height (φ) of the Schottky barrier between the graphene layer (130) and the doping region (111) SBH ) changes. The graphene work function ( ) can be used to obtain the concentration of the sample. At this time, in order to improve the sensitivity of the baristor element (100), the graphene work function ( ) change, that is, the slope of the graph in Figure 3 should be large.

[0039] Graphene work function ( ) The slope of the change varies depending on the doping concentration of the doping region (111). In the left graph (300) of Fig. 3, as the doping concentration of the doping region (111) decreases, the graphene work function ( ) can be seen to have a greater change in slope.

[0040] The height (φ) of the Schoffky barrier between the graphene layer (130) and the doping region (111) SBH ) generates a thermionic emission current in the varistor element (100). The current density (J) flowing in the varistor element (100) TE ) is expressed as the following mathematical formula.

[0041]

[0042] Here, A * represents the graphene version of the Richardson constant, T is the absolute temperature, k B is the Dirac constant, φ SBH represents the height of the Schottky barrier between the graphene layer (130) and the doped region (111), and V represents the voltage applied to the varistor element (100).

[0043] Referring to mathematical expression 6, the height (φ) of the Schottky barrier when a constant voltage is applied SBH ) can be seen to vary the current of the baristor element (100). When the same amount of charge is collected in the graphene layer (130), the height of the Schottky barrier (φ SBH ) is the change in the graphene work function ( ) is the same as the change in capacitance (C) between the graphene layer (130) and the doping region (111). DEP ) depends on the height (φ) of the Schottky barrier between the graphene layer (130) and the doping region (111). SBH ) can improve the sensitivity of the baristor element (100).

[0044] This embodiment determines the optimal doping concentration within the doping region (111) as a method for improving the sensitivity of the varistor element (100). The change in current density of the varistor element (100) according to the doping concentration within the doping region (111) of the varistor element (100) can be expressed by the following mathematical equation.

[0045]

[0046] Here, J TE represents the initial current density of the varistor element (100), and J TE ' represents the current density when voltage is applied to the gate electrode (170) of the varistor element (100) of FIG. 1 or when a sample is applied to the reaction layer (880) of the varistor element of FIG. 8. Here, the initial current density means the current density when no voltage or material is applied to the gate electrode (170) or the reaction layer (880).

[0047] Figure 4 shows the amount of trace charges (1 to 10*10) induced in the graphene layer according to an embodiment of the present invention. 10 This is a table showing the change in the graphene work function according to the doping concentration in the doping region ( / ㎠).

[0048] Referring to Fig. 4, the change in current density according to the doping concentration is shown when measuring NO2 using the varistor element of Fig. 8. The doping region within the substrate is doped as n-type.

[0049] First, let us examine the case where NO20.2 ppm is applied to the reaction layer (880) of the varistor element of Fig. 8. The doping concentration of the first doping region (850) of the varistor element is 10 20 In this case, the change in current density (R) is 2%. In other words, it can be seen that the difference between the current density when NO2 is not applied and the current density when NO2 is applied to the reaction layer (880) is minimal at 2%. The doping concentration of the first doping region (850) of the varistor element is 10 19When lowered to , the change in current density (R) increases to 7%. The doping concentration of the first doping region (850) is 10 18 When lowered, the change in current density (R) increases significantly by 20%. As the doping concentration of the first doping region (850) is lowered, the change in current density (R) increases.

[0050] Next, when applying 1 ppm of NO2 to the reaction layer (880) of the varistor element of Fig. 8, the change in current density is greater than when applying 0.2 ppm of NO2. In other words, it can be seen that the greater the concentration of the reactant in the reaction layer (880), the greater the change in current density. In addition, when the doping concentration is 10 19 10 in 18 It can be seen that when the current change amount (R) of the varistor element changes to a significant size, even when NO22ppm is applied, the current density change amount (R) of the varistor element changes to a significant size when the doping concentration is 10. 19 10 in 18 You can see that there is a big change between them.

[0051] Therefore, in order to improve the sensitivity of the varistor element, the doping concentration of the first doping region (850) of the varistor element is 10 18 ~10 15 It can be set to a value between 10 and 10. More preferably, a large change in the current density change (R) of the varistor element is achieved when the doping concentration is 10. 19 10 in 18 Since it occurs between, the doping concentration is 5*10 18 ~ 10 15 You can set it between.

[0052] Fig. 5 is a diagram illustrating an experimental example of current change over time in a varistor element according to an embodiment of the present invention. Figs. 6 and 7 are diagrams illustrating an experimental example of current change over drain voltage in a varistor element according to an embodiment of the present invention.

[0053] Referring to Figure 5, the horizontal axis represents time and the vertical axis represents the current density change (R) of Equation 7. In this embodiment, the doping concentration of the doping region is 2.05*10 19 This is a case where 1 μM DNA sample is applied to the reaction layer of a varistor element of / ㎤. The change in current density (R) increases with the passage of time after application of the sample, but the change is approximately 0 to 30%.

[0054] Referring to Fig. 6, the horizontal axis represents the drain voltage and the vertical axis represents the current density change (R). In this embodiment, the doping concentration of the doping region is 4.14*10 18 / ㎤~1.19*10 18 This is the case where 1 μM DNA as a sample is applied to a varistor element of / cm3. That is, Fig. 6 is different from Fig. 5 only in the doping concentration, and the structure of the varistor element and the concentration of the sample are all the same. The change in current density (R) is -100% to 300%, which is a difference of more than 10 times compared to 30% in Fig. 5. In other words, it can be seen that lowering the doping concentration can greatly improve the sensitivity to the sample.

[0055] Referring to Fig. 7, the doping concentration of the doping region is 4*10 14 / ㎤~4*10 15 / cm3. The varistor structure and sample of this embodiment are the same as those of FIGS. 5 and 6, with only the doping concentration being different. In the examples of FIGS. 5 and 6, it can be seen that lowering the doping concentration improves the sensitivity. However, when the doping concentration is lowered below a certain level as in this embodiment, the current induced to the sample (i.e., drain current) becomes very low, at the pA level, making it difficult to use as a sensor.

[0056] Therefore, in order to improve the sensitivity of the varistor element, the doping concentration of the doping region is 10 19 / ㎤ or less (preferably 5*10 18 / ㎤ or less). However, if the doping concentration is too low, the current intensity becomes too weak, so the doping concentration is 1016 / ㎤ or more is preferable.

[0057] FIG. 8 is a drawing illustrating another example of a varistor element according to an embodiment of the present invention.

[0058] Referring to FIG. 8, a baristor element used as a graphene-based sensor includes a substrate (800), an insulator layer (810), a graphene layer (820), a first electrode (830), a second electrode (840), and a doped region (860).

[0059] A doping region (860) formed by doping an impurity exists in the substrate (800). In one embodiment, the substrate may be a semiconductor layer composed of a general semiconductor material such as silicon, germanium, or a compound semiconductor, rather than a two-dimensional material. The doping region (860) may be doped as an n-type or a p-type. In one embodiment, the doping region (860) may be formed of two regions (850, 855) having different doping concentrations. For example, the doping region (860) may have a first concentration (e.g., 10 16 / ㎤~5*10 18 / cm3) and a first doping region (850) doped with a second concentration (>=first concentration) (e.g., 10 19 / cm3 or more) may be doped. In another embodiment, the entire doped region (860) may be doped with the same first concentration. The area and depth of the doped region (860) may vary depending on the embodiment. In another embodiment, the doping concentration of the substrate (800) may be doped with the same first concentration as the entire doped region (860).

[0060] The insulator layer (810) is formed on the substrate (800) except for a portion of the doped region (860). For example, the insulator layer (810) is not present on a portion or the entire upper portion of the first doped region (850) and is exposed on the substrate (800). In one embodiment, the insulator layer (810) may be composed of various oxides such as silicon oxide, hafnium oxide, and aluminum oxide. In one embodiment, the insulator layer (810) may be composed of various nitrides such as silicon nitride and boron nitride.

[0061] A graphene layer (820) composed of graphene is laminated on a doped region (860) that is not covered by the insulator layer (810) among the doped regions (860). For example, the graphene layer (820) may have a structure in which it is laminated across the insulator layer (810) and the doped region (860).

[0062] The first electrode (840) is connected to the doped region (860) under the substrate (800). The second electrode (830) is connected to the graphene layer (820). In another embodiment, the upper surface of the substrate (800) may further include a via electrode (870) connected to the first electrode (840) on the lower surface of the substrate. The via electrode (870) may penetrate the insulating layer (810) and the substrate (800) and be connected to the first electrode (840) under the substrate (800). The connection structure of the second electrode (830) and the first electrode (840) in this embodiment is only one example to help understanding of the present invention, and is not limited to this embodiment.

[0063] The graphene layer (820) may further include a reaction layer (880) formed of a material that reacts with a sample or a structure that detects pressure on the surface. The type of material constituting the reaction layer may vary depending on the type of sample (e.g., light, biomaterial, gas, etc.). For example, the reaction layer (880) may be formed by applying a biomaterial (e.g., DNA, antigen, antibody, enzyme, etc.), quantum dots (e.g., lead sulfide quantum dots), or polymer film to the graphene layer (820), or a reaction layer (880) composed of a structure that measures pressure may be laminated on the graphene layer (820). In another embodiment, the reaction layer (880) may be composed of multiple materials or multiple layers. Depending on the type of material of the reaction layer (880) located on the surface of the graphene layer (820), the graphene-based sensor of the present embodiment may be used in various forms, such as an optical sensor that detects light, a biosensor that detects biomaterials, and an environmental sensor that detects gas, temperature, humidity, etc.

[0064] FIG. 9 is a drawing illustrating another example of a varistor element according to an embodiment of the present invention.

[0065] Referring to FIG. 9, a baristor element (900) used as a graphene-based sensor includes a first doped region (910), a second doped region (920), a graphene layer (930), a first electrode (950), and a second electrode (940). An insulating layer (960) made of SiO2 or the like may be further included between the second electrode (940) and the first doped region (910). A reaction layer (not shown) may be present on the graphene layer (930).

[0066] In one embodiment, a first doped region (910) and a second doped region (920) can be formed by doping an entire substrate with impurities. The doped regions (910, 920) can be doped with an n-type or a p-type. The first doped region (910) can have a first concentration (e.g., 10 16 / ㎤~5*10 18 / cm3), and the second doping region (920) has a second concentration (>=first concentration) (e.g., 10 19 / cm3 or more). In another embodiment, the entire doping region (910, 920) may be doped with the same first concentration. The area and depth of each doping region (910, 920) may be varied depending on the embodiment.

[0067] The present invention has been described above, focusing on preferred embodiments thereof. Those skilled in the art will appreciate that the present invention can be implemented in modified forms without departing from its essential characteristics. Therefore, the disclosed embodiments should be considered illustrative rather than limiting. The scope of the present invention is set forth in the claims, not the foregoing description, and all differences within the scope equivalent thereto should be construed as being encompassed by the present invention.

Claims

1. Substrate; A doped region formed by doping impurities into the above substrate; A graphene layer laminated in the above doped region; A first electrode connected to the above doping region; A second electrode connected to the graphene layer; The work function of the above graphene layer changes depending on the concentration of the doping region, The doping concentration of the above doping region is 10 16 / ㎤ ~ 5*10 18 A varistor element characterized by having a / cm3.

2. In paragraph 1, A varistor device further comprising a reaction layer positioned on the graphene layer and including a material that induces a charge in the graphene layer.

3. In paragraph 1, An insulating layer laminated on the above graphene layer; and A varistor element further comprising a third electrode connected to the insulating layer.

4. In paragraph 1, The above doping region is, 10 16 / ㎤ ~ 5*10 18 A first doped region doped with a concentration of / cm3; and 10 19 / ㎤ or more of a second doped region doped with a concentration; The above first doping region is connected to the graphene layer, A varistor element characterized in that the second doped region is connected to the first electrode.

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