KR20130006990A - Switching device comprising redox protein with multi-layer and method of manufacturing the same - Google Patents

Abstract

PURPOSE: A switching device including redox protein with a multilayer and a manufacturing method thereof are provided to improve a memory property using a redox protein thin film. CONSTITUTION: An active layer is formed on a bottom electrode. A top electrode is formed on the active layer and is composed of a multilayer thin film obtained by alternatively laminating a material layer. The material layer includes one or more proteins and is composed of a positive charge material layer and a negative charge material layer.

Description

Switching device comprising redox protein as a multilayer thin film and a method for manufacturing the same {SWITCHING DEVICE COMPRISING REDOX PROTEIN WITH MULTI-LAYER AND METHOD OF MANUFACTURING THE SAME}

The present invention relates to a switching device including a multilayer thin film disposed between an upper electrode and a lower electrode, and a method of manufacturing the same. More particularly, the multilayer thin film alternates between a positively charged material layer and a negatively charged material layer. The material layer comprises at least one protein, wherein the multilayer thin film causes a reversible current change through a redox reaction in a solution, and applies an external voltage to the multilayer thin film containing the protein. Thus, the present invention relates to a switching device including a multilayer thin film interposed between an upper electrode and a lower electrode causing reversible resistance change through charge capture / release of a heme Fe III / Fe II redox pair, and a method of manufacturing the same.

The electrochemical properties of redox proteins, which can cause reversible current changes through redox reactions in solution, are important for bioelectrochemical applications. These redox properties are often dependent on the chemical activity of transition metal ions, which act as cofactors in the active site of the enzyme. The redox protein has attracted interest in the field of bioelectronics such as sensor devices and biofuel cells because it can control various biochemical reactions with high specificity under mild conditions. Such biochemical reactions are often due to the redox active site which is responsible for the effective charge transport through direct electron exchange between the redox protein and the electrode in the electrolyte solution. For example, catalase (CAT), an enzyme commonly found in almost all living things, has heme FeIII / FeII redox pairs. Since the redox reaction is closely related to the emission (oxidation) and the capture (reduction) of the electrons, the redox protein may have a resistance switching property causing a reversible resistance change by the application of an external voltage. This possibility is significant in that various natural biomaterials exhibiting redox reactions can be used as active materials in resistive switching nonvolatile memory (RSNM) devices that can be applied to portable electronic devices such as MP3 players, digital cameras and mobile phones. Have

Furthermore, according to a number of techniques for existing biomemory devices, these devices utilize electrochemical reactions of redox proteins, measured by cyclic voltammetry, in a buffered aqueous solution, and are electrically separated to form a memory. There are problems such as requiring two positions.

In the present invention, a positively charged material layer and a negatively charged material layer are alternately stacked between the upper electrode and the lower electrode, and the material layer includes a multilayer thin film including at least one protein. The present invention provides a switching device capable of inducing a reversible resistance change through charge capture / release of a heme Fe III / Fe II redox pair and a method of manufacturing the device.

In addition, the switching device according to the present invention provides an electronic device having a nanosecond-level fast switching speed, high ON / OFF current ratio, long-term stability, and appropriate processability, and thus, resistance switching for the development of next-generation nonvolatile memory devices. A nonvolatile memory device and a method of manufacturing the same are provided.

In order to solve the above problems, the present invention is applied between the upper electrode and the lower electrode that can induce a reversible resistance change through charge trapping / emission of the heme Fe III / Fe II redox pair by applying an external voltage to the device Provided is a switching device including a multilayer thin film and a method of manufacturing the same.

According to a preferred embodiment of the present invention,

Lower electrode;

An active layer formed on the lower electrode; And

An upper electrode formed on the active layer,

The active layer is a multilayer thin film in which a positively charged material layer and a negatively charged material layer are alternately stacked, and the material layer may include at least one protein.

According to another preferred embodiment of the present invention, the active layer may be formed by alternately stacking 2-100 positively charged material layers and 2-100 negatively charged material layers alternately.

According to another preferred embodiment of the present invention, the active layer may be laminated by a layer-by-layer self-assembly method.

According to another preferred embodiment of the present invention, the positively charged material layer and the negatively charged material layer are each independently (i) a protein whose surface charge varies depending on pH conditions, and (ii) a polymer having an electrostatic charge. Can be selected from.

According to another preferred embodiment of the present invention, the protein is at least one selected from catalase, hemoglobin and myoglobin, and the polymer is selected from poly (allylaminehydrochloride), poly (styrenesulfonate) and poly (ethyleneimine). One or more may be selected.

According to another preferred embodiment of the present invention,

Switching element according to the invention

Lower electrode;

An active layer formed on the lower electrode; And

An upper electrode formed on the active layer,

The active layer may be a multilayer thin film in which 2-100 catalase and 2-100 poly (allylamine hydrochloric acid) are alternately stacked.

According to another preferred embodiment of the present invention,

In the manufacturing method of the switching device according to the present invention in a method for manufacturing a switching device by laminating a multilayer thin film on a substrate,

(1) depositing a charging material of a second charge opposite to the first charge on a substrate charged with a first charge;

(2) stacking a charge material of a first charge on the charge material of the second charge; And

(3) repeating two to 100 steps of alternately stacking the charged material of the second charge and the charged material of the first charge; and at least one of the charged materials of the first and second charges. May comprise one or more proteins.

According to another preferred embodiment of the present invention, the charged material of the first charge and the charged material of the second charge are each independently (i) a protein whose surface charge varies depending on pH conditions and (ii) a polymer having a static charge Can be selected from.

According to another preferred embodiment of the present invention, the multilayer thin film formed by alternately stacking the charged material of the first charge and the charged material of the second charge is a layer-by-layer self-assembly method. Can be laminated by.

According to another preferred embodiment of the invention, the transistor according to the invention may comprise a switching element.

A positively charged material layer and a negatively charged material layer are alternately stacked between the upper electrode and the lower electrode according to the present invention, and the material layer includes an active layer of a multilayer thin film including one or more protein layers. The switching device comprising can induce a reversible resistance change through charge capture / release of the heme FeIII / FeII redox pair by applying an external voltage to the device, and this novel electrical switching property of the redox protein It can be applied to bio-based electronic devices such as next-generation nonvolatile memory devices.

In addition, in the present invention, a biomaterial such as a redox protein may be used as a resistance switching active material of a nonvolatile memory device in the semiconductor industry, and this switching property may be attributed to a reversible redox site inside the protein.

In addition, the bio-based electronic device according to the present invention is distinguished by the direct use of natural biomaterials instead of artificial materials (eg, metal nanoparticles or conjugated polymers) or transition metal oxides. On the Pt-coated substrate, a multilayer thin film composed of anionic poly (allylamine hydrochloride) (CAT) and cationic polyelectrolyte (PE) may be formed. Electrostatic Multilayer (LbL) fabrication, which enables the formation of thin films with controlled thickness, composition and functionality on substrates of various sizes and shapes, extends to transistor memories through charge capture / release from redox sites in CAT Can be.

Therefore, the switching device according to the present invention has an advantage that the various proteins extracted from biological tissues such as liver (catalase), blood (hemoglobin) or muscle (myoglobin) can be directly applied to the memory industry.

According to a number of techniques for existing biomemory devices, these devices utilize electrochemical reactions of redox proteins, measured by cyclic voltammetry, in buffered aqueous solutions, which are electrically separated to form a memory. In contrast to the need for two positions, the electronic device including the switching device according to the present invention is intended for the development of a next generation nonvolatile memory device having a fast switching speed, high ON / OFF current ratio, long-term stability, and appropriate machinability at the nanosecond level, The fabrication method of the resistive switching nonvolatile memory device (except for the rapid production of an electroactive thin film by LbL-assembled redox protein) and the electrical operation mechanism were applied. Therefore, the electronic device including the switching element according to the present invention has a completely different characteristic from the conventional biomemory elements in the structure, the operation mechanism, and the physical characteristics of the device.

Therefore, the switching device using the biomaterial according to the present invention can be applied to RSNM and OFETM devices having high memory characteristics by using a redox protein thin film, and in particular, the nonvolatile memory of the redox protein can be easily manipulated through electrical manipulation. It has an effect that can be obtained.

1 is a graph showing the electrochemical properties and thickness of PAH / CAT multilayer thin film.
FIG. 1A is a graph showing a cyclic current voltage curve (pH 7.0 PBS, scan rate = 0.05 V · S ⁻¹ ) of a multilayer thin film coated electrode of (PAH / CAT) ₁₀ . The redox reaction by redox of the FII / FeIII pair in the compound is shown.
1B is a graph showing QCM data of a PAH / CAT multilayer thin film according to the number of layers.
FIG. 1C shows the thin film thickness of (PAH / CAT) _n = 5, 10 and 15 multilayer thin films before and after annealing at 150 ° C. for 2 hours, measured from SEM cross-sectional images.
1C is an SEM cross-sectional image after annealing of 15 bilayer thin films.
FIG. 1D shows the cyclic current voltage curve (pH 7.0 PBS with 21 mM H ₂ O ₂ , scan rate = 0.05 V × s ⁻¹ ) of the uncoated gold electrode and (PAH / CAT) ₁₅ multilayer thin film coated electrode. It is a graph.
2 is a diagram illustrating nonvolatile memory characteristics of a PAH / CAT multilayer thin film.
Figure 2a is a graph showing the IV curve of the (PAH / CAT) _n multilayer thin film device measured while increasing the number n of bilayers from 5 to 15.
FIG. 2B is a graph showing cycling test results for a device consisting of 15 double layers measured at a switching speed of 100 ns.
Figure 2c is a graph showing the residence time of the device consisting of 15 double layers, measured in 0.1V units while increasing the measurement temperature from 25 ℃ to 150 ℃.
Figure 2d is a graph showing the IV curve of (PAH / CAT) ₁₅ multilayer thin film without annealing.
FIG. 2E is a graph illustrating a linear fit of a log-log scale IV curve of a 15 bilayer device during a negative voltage sweep SET process.
3 is a graph illustrating a transistor memory device using a PAH / CAT multilayer thin film and an OFETM device using a multilayer thin film of (PAH / CAT) ₄₀ .
FIG. 3A is a diagram illustrating a drain current ID-drain voltage VD output curve measured while sweeping from 0 V to −10 V. FIG.
3B is a graph showing a drain current-gate voltage (ID-VG) transition curve obtained by repeating ten times.
3c is a graph showing the results of experiments with residence time.
FIG. 4 is a diagram showing the structure of a transistor fabricated by a nonvolatile memory cell and an LbL method. FIG. 4A is a PAH / CAT multilayer RSNM, and FIG. 4B is a schematic diagram of an organic field effect transistor memory (OFETM) device.
5 is a SEM image of an upper electrode stacked on a PAH / CAT multilayer.
FIG. 6 shows the electrical switching characteristics of the multilayer thin film of (PAH / CAT) ₁₅ measured for 100 samples. About 20 samples in the red line showed poor switching characteristics. Thus, the output performance of the device was about 80%.
7A shows a CS-AFM image of a (PAH / CAT) ₅ multilayer thin film in an ON state.
7B is a diagram showing a CS-AFM image of a (PAH / CAT) ₅ multilayer thin film in an OFF state.
8 is a measurement using a tungsten tip electrode, the current-voltage of (a) (hemoglobin / PSS) ₁₅ (Example 3) and (b) (myoglobin / PSS) ₁₅ multilayer thin film (Example 4) annealed This is a graph measured by applying a pulse voltage of 1 μs in a curved atmospheric condition.

Switching element according to the invention

Lower electrode;

An active layer formed on the lower electrode; And

An upper electrode formed on the active layer,

The active layer is a multilayer thin film in which a positively charged material layer and a negatively charged material layer are alternately stacked, and the material layer includes at least one protein.

In the active layer of the switching device according to the present invention, it is preferable that 2-100 positively charged material layers and 2-100 negatively charged material layers are alternately stacked to form a multilayer thin film. More preferably, the band-like material layer and the 5-80 negatively charged material layer are alternately stacked to form a multilayer thin film, and the 5-50 positively charged material layer and the 5-50 negatively charged material. It is most preferable to form a multilayer thin film by alternately stacking layers. If the thickness is less than 2, the film thickness is so thin that a large amount of leakage current is generated due to the tunneling current. It is not desirable to rise anymore because there is economic loss. In particular, in the case of 5-50 individuals, it is preferable because the electrical stability in the ON / OFF state is very excellent in the electrical switching characteristics.

Therefore, limiting the number of positively charged material layers and negatively charged material layers within the above range is most preferable in view of synergistically improving the effect of the desired electrical switching characteristics.

The active layer may be deposited by layer-by-layer self-assembly.

In the active layer of the switching device according to the present invention, the positively charged material layer and the negatively charged material layer are each independently (i) a protein whose surface charge varies depending on pH conditions and (ii) a polymer having an electrostatic charge. Can be selected from.

The protein is not particularly limited as long as the protein contains a metal ion and redox is possible, and may be selected from catalase, hemoglobin, myoglobin and the like. The polymer is not particularly limited as long as it is a polymer having an electrostatic charge, and the polymer may be at least one selected from poly (allylamine hydrochloride), poly (styrenesulfonate), and poly (ethyleneimine).

According to one preferred embodiment of the invention, the catalase (CAT) is composed of four polypeptide chains each consisting of 500 or more amino acids, pI (isoelectric point) is about 5.6. The CAT has a property of changing the surface charge according to the pH change. Thus, CAT is positively charged at pH <5.6 and negatively charged at pH> 5.6. Poly (allylamine hydrochloric acid) (PAH) has a pKa (pH value when 50% of the functional groups of the polymer are ionized) in the bulk solution, so that CAT and PAH can be used as negative charge species and positive charge species at pH> 5.6, respectively. Can be. Based on this electrostatic property, which depends on pH, LbL assembly of cationic PAH and anionic CAT can be carried out on gold electrodes at pH 9.

Therefore, the switching element according to the present invention

Lower electrode;

An active layer formed on the lower electrode; And

An upper electrode formed on the active layer,

The active layer may be a multilayer thin film in which 2-100 catalase and 2-100 poly (allylamine hydrochloric acid) are alternately stacked.

As described above, in the active layer of the switching device according to the present invention, a positively charged material layer and a negatively charged material layer are alternately stacked by LbL assembling, and thus the multilayer is formed of a multilayer thin film. By including, electrochemical redox characteristic is shown. This is due to the oxidation and reduction of the heme FeIII / FeII redox pair in the protein layer, which can induce a reversible resistance change through charge capture / release of the heme FeIII / FeII redox pair by applying external electrolysis to the active layer. have.

The redox reaction of the PAH / CAT multilayer thin film can be expressed as follows.

(1) CAT-Fe ^III + H ₂ O ₂ → [CAT-Fe ^IV = O] ^* + H ₂ O

(2) [CAT-Fe ^IV = O] ^* + H ₂ O ₂ → CAT-Fe ^III + O ₂ + H ₂ O

According to still another preferred embodiment of the present invention, a cation-charged material layer of a second charge opposite to the first charge is stacked on a substrate on which an anion is charged as a first charge, and a cation that is the second charge is deposited. On the charged material layer, a material layer in which an anion as a first charge is charged is stacked. Herein, the cation-charged material layer or the anion-charged material layer is selected from one or more kinds of polymers having different surface charges and polymers having static charges according to pH conditions as described above. In the above, the protein is charged with a cation using a pH condition of 5.6 or less. As such, any protein capable of having an anion or a cation and a polymer having an electrostatic charge may be used in the active layer of the multilayer thin film according to the present invention, which is within the scope of the present invention.

The layer of material having the surface charge of the cation is deposited on the substrate of the anion by electrical attraction. As long as the first and second charges generate mutual attraction, the first charge may be changed to a cation and a second charge to an anion as necessary, which is also within the scope of the present invention.

The manufacturing method of the switching element according to the present invention

In the method of manufacturing a switching device by laminating a multilayer thin film on a substrate,

(1) depositing a charging material of a second charge opposite to the first charge on a substrate charged with a first charge;

(2) stacking a charge material of a first charge on the charge material of the second charge; And

(3) repeating two to 100 steps of alternately stacking the charged material of the second charge and the charged material of the first charge; and at least one of the charged materials of the first and second charges. Is characterized in that it comprises one or more proteins.

In the present invention, the charged material of the first charge and the charged material of the second charge may be independently selected from (i) a protein having a surface charge that varies according to pH conditions and (ii) a polymer having a static charge.

The protein is not particularly limited as long as the protein contains a metal ion and redox is possible, and may be selected from catalase, hemoglobin, myoglobin and the like. The polymer is not particularly limited as long as it is a polymer having an electrostatic charge, and the polymer may be at least one selected from poly (allylamine hydrochloride), poly (styrenesulfonate), and poly (ethyleneimine).

In the present invention, when the positively charged material layer and the negatively charged material layer are alternately stacked to form a multilayer thin film, the positively charged material layer may be laminated by a layer-by-layer self-assembly method. .

The transistor according to the invention is characterized in that it comprises a switching element according to the invention.

Hereinafter, the present invention will be described in more detail with reference to examples and the like, but the scope and contents of the present invention are not limited or interpreted by the following examples. Moreover, it is clear that a person skilled in the art can easily carry out the present invention, in which no experimental results are specifically presented, based on the disclosure of the present invention including the following examples.

Example  And Comparative example

Example  One

Catalase (CAT) (extracted from bovine liver, Aldrich) and PAH (Mw = 70 000, Aldrich) were prepared, and the concentrations of the catalase and PAH in the solution were all 1 mg · mL −1. The pH of the CAT and PAH solutions was adjusted to 9. The zeta potential values of PAH and CAT measured at pH 9 were about +25 mV and -40 mV, respectively. CAT was used as anionic component at pH 9. The Pt coated Si substrate was treated with UV light to have an anionic surface. The treated substrate was first immersed in a cationic PAH solution (containing 0.5 M NaCl) for 10 minutes, immersed in water for 1 minute twice, and then air dried under a gentle nitrogen stream. Then, after the same adsorption, washing and drying, the anionic CAT was laminated on the PAH coated substrate, and then the above procedure was performed nine more times to form a multilayer thin film of (PAH / CAT) ₁₀ . Was annealed at 150 ° C. for 2 hours under air conditions.

The formed multilayer thin film of (PAH / CAT) ₁₀ showed electrochemical redox characteristics by CAT in pH 7.0 phosphate buffer (PBS) (FIG. 1A). In the voltage range of -0.6 V to 1.0 V, the oxidation peak was observed at about + 0.12 V and the reduction peak was at about -0.13 V, which is the oxidation / reduction peak of oxidation and reduction of the FeIII / FeII redox pair in the CAT layer. It can be seen that.

Example  2

(PAH / CAT) It was manufactured in the same manner as in Example 1 except that a multilayer thin film of ₄₀ was formed.

Example  3

Hemoglobin (extracted from human body, Aldrich) and PSS (Mw = 70000, Aldrich) were prepared, and the concentrations in the solution of both hemoglobin and PSS were 1 mg · mL −1. The pH of hemoglobin and PSS solution was adjusted to 5.5. PSS is anionic regardless of pH range and hemoglobin was used as cationic component at pH 5.5. The Pt coated Si substrate was treated with UV light to have an anionic surface. The treated substrate was first immersed in a cationic hemoglobin solution (containing 0.5 M NaCl) for 10 minutes, immersed in water for 1 minute twice, and then air dried under a gentle nitrogen stream. Subsequently, after the same adsorption, washing and drying process, anionic PSS was deposited on the hemoglobin-coated substrate, and the above procedure was performed 14 times to form a multilayer thin film of (hemoglobin / PSS) ₁₅ . Annealed at 150 ° C. for 2 hours under air conditions.

Example  4

It was prepared in the same manner as in Example 3 except for replacing the hemoglobin with myoglobin.

Comparative example  One

Electrodes not coated with any material were prepared and the electrochemical redox properties were measured. However, Comparative Example 1 did not show a current response in the voltage range of -0.6 to 1.0 V. Therefore, it can be seen that Comparative Example 1 does not cause a redox reaction.

Comparative example  2

₁₀ multilayer thin films (PAH / poly (styrenesulfonate)), which is an insulating polymer electrolyte multilayer thin film, were prepared, and after the electrode was modified using the multilayer thin film, electrochemical redox characteristics were measured. However, Comparative Example 2 did not show a current response in the voltage range of -0.6 to 1.0 V. Therefore, it can be seen that Comparative Example 2 does not cause a redox reaction.

Example  5

It was manufactured in the same manner as in Example 1 except that the multilayer thin film of (PAH / CAT) ₅ was formed.

Example  6

It was prepared in the same manner as in Example 1 except that a multilayer thin film of (PAH / CAT) ₁₅ was formed.

Example  7

(PAH / CAT) It was manufactured in the same manner as in Example 1 except that a multilayer thin film of ₃₀ was formed.

Fabrication of Resistive Switching Memory Devices

All samples were formed on a Si substrate (2 cm × 2 cm) with a SiO ₂ layer about 100 nm thick. Subsequently, a Ti layer having a thickness of 20 nm was stacked on the substrate, and the lower electrode Pt was stacked using a DC magnetron sputtering apparatus. Subsequently, the multilayer thin films of Examples 1-3 were each formed on a Pt-coated Si substrate. The resulting multilayer thin film was annealed at 150 ° C. for 2 hours under air conditions. As a result, an upper electrode having a diameter of 100 μm was stacked on the nanocomposite film (FIG. 5).

In order to investigate the resistance switching characteristics of the LbL multilayer device, the current-voltage (IV) was measured under air conditions using a semiconductor parameter analyzer (SPA, Agilent 4155B). The dependence on the pulse voltage duration of the high current and low current states was investigated using a semiconductor parameter analyzer (HP 4155A) and a pulse generator (Agilent 81104A). Ag electrodes were used as the top electrodes of the device, but similar switching characteristics were observed when Au, Pt or tungsten were used. This indicates that the Ag electrode has little effect on the resistance switching characteristics of the LbL (PE / enzyme or hemoglobin) _n multilayer.

In order to measure the resistance switching memory characteristics of the device, more than 50 samples were made and tested. Each sample was made with hundreds of electrodes. Electrical switching characteristics were confirmed from about 100 samples, with a good switching rate of about 80% (FIG. 6).

Fabrication of Memory Transistors

A pentacene organic field effect transistor memory having a double insulator top contact structure composed of a 200 nm thick SiO ₂ layer and 40 PAH / CAT bilayers (Example 2) was grown on a Si substrate. First, the SiO ₂ substrate was washed with acetone and isopropyl alcohol for 10 minutes, and then rinsed with distilled water and dried with nitrogen. 40 PAH / CAT bilayers were then formed on the SiO ₂ insulating layer via LbL assembly. Pentacene was thermally deposited using a shadow mask in a vacuum chamber (pressure ˜3 × 10 ⁻⁶ Torr, thickness 500 Pa, deposition rate 0.5 Pa / s). Subsequently, gold and drain electrodes were deposited by thermal evaporation using a shadow mask having a width / length (W / L) ratio of 1000/100 μm in a vacuum chamber (pressure ˜3 × 10 ⁻⁶ Torr, thickness 1000 Pa, deposition). Speed 5 Å / s). Current-voltage characteristics were measured using an Agilent 4155B semiconductor parameter analyzer. All measurements were made in the dark at atmospheric conditions.

Zeta Potential  Measure

Zeta potential of catalase was measured using an electrophoretic light scattering spectrophotometer (ELS-8000) when the micelles were alternately adsorbed onto silica particles having a diameter of 600 nm.

(PAH / CAT) ₂ coated silica particles were prepared as follows.

0.5 mL of PAH (1 mg · mL ^-1 at pH9) was added to the negatively charged 600 nm silica particles. After 20 minutes, excess catalase was removed via three centrifugation (7000 g, 5 minutes) / wash cycles. CAT (1 mg · mL ⁻¹ at pH9) was then laminated to the catalase coated PS particles under the same conditions. This process was repeated until four layers were laminated, and then the zeta potential of the resulting colloid was measured with increasing pH from 0 to 4.

QCM  Measure

Using a QCM instrument (QCM200, SRS), the mass of the material deposited after each adsorption step was measured. The resonance frequency of the QCM electrode was about 5 MHz. Adsorption mass △ m of PAH, PSS and biological material is the change amount of QCM frequency △ F , sourbray equation [△ F (Hz) = -56.6xΔ m _A , where Δ m _A per unit area of the quartz crystal Mass change amount (μg · cm ⁻² )].

Surface Morphology Analysis

The shape and roughness of the enzyme multilayer formed on the Si substrates were measured in tapping mode using atomic force microscopy (AFM, SPA400, SEIKO).

Current sensing Atomic force ( atom force A) microscopic measurement

A local current map of the nanoscale was measured using a current sensing atomic force microscope (CS-AFM, e-sweep, SEIKO). In the CS-AFM measurement, a CS-AFM tip (Pt tip) having a diameter of about 7 μm was used as the upper electrode instead of the Ag electrode.

Quantitative growth of multilayer thin films was observed through quartz crystal microgravimetric analysis (QCM). Figure 1b shows the change in frequency with increasing number of layers -Δ F and the mass change of adsorbed PAH and catalase. Mass change was calculated from frequency change. This change in QCM frequency (or mass) means that multilayer thin films grow regularly when PAH and catalase are assembled LbL from solution. PAH and CAT were alternately stacked, and-△ F of each layer was 30 ± 2 (△ m = ~ 533.6 ng · cm ^-2 ) and 83.8 ± 4 Hz (△ m = ~ 1480.6 ng · cm ^-2 ). LbL assembly enabled precise control of the layer thickness and the amount of water-soluble CAT adsorbed. After the LbL lamination, the multilayer thin film formed to completely remove water remaining in the thin film and form a dense structure was annealed at 150 ° C. for 2 hours (FIG. 1C).

In this process, the thickness of the (PAH / CAT) ₁₅ multilayer thin film was reduced from 52 nm to 49 nm. The biological redox activity of the PAH / CAT multilayer thin film measured through catalytic activity on H ₂ O ₂ decreased after annealing, but the multilayer thin film still showed unique catalytic properties (FIG. 1D).

Referring to FIG. 1, the CAT used in the present invention utilizes charge trapping / emission by transition metal ions (FeIII / FeII) present in CAT, rather than the inherent biological properties of CAT.

Based on the above results, a nonvolatile memory device based on the (PAH / CAT) _n multilayer thin film according to the present invention was fabricated (FIGS. 4A and 4B). The fixed CAT thin film produced by the LbL assembly method effectively exhibits electrical switching characteristics due to the relatively thick and dense thin film. Other chemical methods, such as self-assembled monolayer (SAM) or simply forming a single layer by spin coating, have also been tried, but the film thickness is too thin (<10 nm) resulting in a large amount of leakage current due to tunneling current.

In addition, a memory device and a transistor including a (PAH / CAT) _n (where n is 5, 10, 15, and 30) multilayer thin films were manufactured to measure the experimental results.

First, the electrical characteristics of the nonvolatile memory cell were measured while applying a voltage in air. Pt and Ag were used as the lower and upper electrodes, respectively. The voltage was swept from -1.8 V to +1.8 V and back to -1.8 V for bipolar switching measurements. The current was limited to a maximum of 100 mA. After the initial electroforming step (conducting passages in the multilayer film), after a high current state (scan range ± 1.8 V or more), a multilayer thin film of (PAH / CAT) _n (where n = 5,10,15) When the polarity of the voltage applied to the device changed, it suddenly switched to the low current state at + 1.8V. In addition, as the number of bilayers increased (i.e., the thickness of the multilayer thin film increased), the current, especially the OFF current, was considerably lowered because the thickness of the thin film increased (Fig. 2A). As a result, the ON / OFF current ratio of these devices increased up to 10 ² or more. Cycling and residence time of 15 bilayer PAH / CAT thin film devices were measured in units of +0.1 V to evaluate electrical stability in the ON and OFF states (FIGS. 2B and 2C). The ON and OFF states continued to remain stable during the 10 ⁴ cycles of cycling test in air. In particular, the multilayer thin film devices showed thermally stable memory reliability even when the measurement temperature was increased from 25 ° C. to 150 ° C. (FIG. 2C). In addition, CAT devices were able to operate repeatedly at switching speeds of 100 nanoseconds to 1 microsecond (FIG. 2B), and this reversible switching characteristic was maintained for more than one year. Thus, excellent electrical stability and fast switching speed have been demonstrated. Recently, it can be seen that the solid electrolyte or the transition metal oxide interposed between the Ag electrode and the inactive electrode having electrochemical activity exhibits resistance switching characteristics due to the electrochemical redox reaction caused by the high mobility of Ag ions. In the present invention, the Ag electrode is used as the upper electrode, but similar switching characteristics are observed even when Au, Pt or tungsten (W) which is electrochemically inactive is used as the upper electrode. In particular, the (PAH / CAT) ₃₀ multilayer thin film interposed between the Pt (bottom) electrode and the Au (upper) electrode showed an ON / OFF ratio of 10 ² or more when measured in +0.1 V units. This fact means that the electrically active Ag electrode by itself does not significantly affect the resistance switching characteristics of the PAH / CAT multilayer thin film device. In addition, since water molecules remaining in the thin film are completely removed, there is no possibility that the electrical switching characteristics are thereby improved. In fact, in the PAH / CAT multilayer thin film in which water molecules remain without annealing, very low ON / OFF current ratio (<1) and poor switching characteristics were shown (FIG. 2D). On the other hand, the conventional polyelectrolyte multilayer thin film composed of cationic PAH and anionic poly (acrylic acid) exhibited insulation characteristics when annealed at the same temperature, and showed no switching memory characteristics.

To understand the conduction characteristics of CAT multilayer thin films, 15 bilayers Thin film ((PAH / CAT) ₁₅ ), IV characteristics in negative voltage sweep region are shown on log-log scale (FIG. 2E). In the ON state, the IV graph clearly shows the resistive conduction characteristic with a slope of ~ 1.0, indicating that a conductive passage was formed in the device during the SET process (switching from low current (OFF) to high current (ON)). On the other hand, the conduction characteristics in the OFF state are much more complicated. The fitting result in the high resistance state shows charge transport characteristics consistent with the space charge limiting conductivity (SCLC). At this time, the space is composed of three different conduction areas: low negative voltage resistance area (1VV), resistance area to transition to SCLC transport area (I1VV2), and current rapidly increasing to be. As a result, different conduction characteristics in the ON and OFF states mean that the ON / OFF switching of the CAT memory device is determined by the SCLC conduction and the local conduction path. Also, if the current curve of Fig. 2C is redrawn as logR _OFF vs. temperature (K) and logR _ON vs. temperature (K) curves, conduction is conducted from the temperature dependence of the resistance of the ON state (R _ON ) and the OFF state (R _OFF ). The mechanism is easier to understand. That is, R _ON decreases linearly with increasing ambient temperature, indicating that the conductive passage is in a metallic state (ie, a resistive state). On the other hand, the temperature dependence of R _OFF of the device showed semiconductor characteristics.

The formation of the conductive passage was also confirmed through the observation of current sensing atomic force microscope (CS-AFM) (FIG. 7). Pt tips were used as upper electrodes instead of Ag electrodes. When V _SET is 5 V, a local conductive channel is randomly formed and disappears when V _RESET is -5 V. Thus, randomly distributed in the "RESET" process (switching from the high current (ON) state to the low current (OFF) state) and the "SET" process (switching from the low current (OFF) state to the high current (ON) state) Formation and destruction of conductive passages were observed. This suggests that the current density between the top and bottom electrodes is not uniform but is concentrated in the local conductive path and turned on and off during the switching process. In addition, V _RESET and V _SET in FIG. 2A were higher than those observed in CS-AFM at ± 1.8 V. It can be seen that contamination of the conductive AFM surface acts as an energy barrier, increasing the threshold voltage values for set and reset. In addition, it may not be excluded that the electric field applied to the multilayer from the conductive AFM tip was uneven. This non-uniform electric field can increase the voltage applied for resistance switching.

1.5 V)에서 전도성이 급격히 증가하여, 터널링 확률이 높아지는(SET 과정) 것으로 생각된다.Various switching mechanisms have been reported for resistive switching memory devices (e.g., membrane models, fuse-fuse-type filament conduction models, or charge transfer between active devices with different energies), but the high current and low current of switching devices according to the present invention have been reported. The memory effect in the current state is due to the accumulation of charge (high resistance) and release (low resistance) in the charge trapping region. In the device including the multilayer thin film according to the present invention, the redox active portion in the multilayer acts as a charge trapping element, which can significantly affect the switching mechanism. First, after the first electroforming, in the course of the device being negatively swept from −1.8 V to 0 V (area 1 in FIG. 2A), electrons are released at the redox site, leading to a high conductivity state. This ON state is maintained until electrons are partially introduced into the redox site ((2)), trapped in the redox site and the polarity of the voltage is changed ((2) → (3)). However, if the polarity of the voltage is changed, the conductive passage in the CAT multilayer is broken, leading to a decrease in conductivity, which corresponds to a RESET process (switching from a high current (ON) state to a low current (OFF) state). This OFF state is maintained up to about -1.5 V (area 4). However, if the external electric field for releasing electrons trapped within the redox site increases (area (4)), the SET voltage (VSET)

It is thought that the conductivity sharply increases at 1.5 V), thereby increasing the tunneling probability (SET process).

In order to better understand the switching mechanism by the heme FeIII / FeII redox pair in CAT, a non-volatile memory device was fabricated using a simple molecular phthalocyanine-based material (phthalocyanine-Fe) containing Fe ions instead of CAT. . Electrical switching measurements were the same as for PAH / CAT multilayers, and PAH / phthalocyanine-transition metal ions (eg Fe or Ni ions) multilayers showed distinct resistance switching characteristics. These results indicate that the main resistive switching active site in CAT is a heme FeIII / FeII redox pair. Resistance switching nonvolatile memory characteristics were also observed in hemoglobin and myoglobin having heme groups (FIG. 8). The LbL multilayer thin film was easily and quickly manufactured through the LbL assembly process by using a spin coating method currently applied to semiconductor devices.

In order to further confirm the switching mechanism through the capture and release of the charge, the present invention has fabricated a pentacene-based organic field effect transistor memory (OFETM) device including (PAH / CAT) ₄₀ multilayer and SiO ₂ as a double layer as an insulating layer. . It is well known that the memory function of OFETM (organic field-effect transistor memory) is due to the control of the field effect of the charge stored in the filling insulating material from the polymer to the inorganic nanoparticles. First, as shown in the ID-VD output curve of FIG. 3A, the OFETM device showed relatively excellent transistor characteristics. The measured OFETM variables, ie mobility, threshold voltage and ON / OFF ratio, were 0.065 cm ² · V ⁻¹ · S ⁻¹ , 1.4 V, and 2.4 × 10 ⁴ , respectively. As shown in FIG. 3B, distinct memory hysteresis intervals were repeatedly measured below V _D = -40 V. At this time, the PAH / CAT multilayer acted as a cause of the memory effect of the insulator. More specifically, the redox active site of CAT captures electrons under forward bias and releases under reverse bias (FIG. 3B). When a negative voltage is applied to the gate electrode in the forward process ('region 1'), the transport channel in pentacene expands, and then the drain current increases. Saturation of the channel promotes electron accumulation in the upper layer of the insulator by the bias, and the accumulated electrons partially affect the reduction of redox sites in CAT. In the reverse process (region 2), since the reduced form of the redox active element of CAT is lower in polarity than the oxidized form, the drain current is drastically reduced in the reverse gate bias.

When a positive voltage is applied to the gate electrode, the forward bias of the gate promotes the accumulation of holes in the upper layer (PAH / CAT multilayer) of the insulator and changes the redox active element in the CAT to its own oxidation state. After the forward gate bias is applied, the insulation characteristics and polarity are restored, so the dependence of the drain current on the gate bias in the forward process increases again, which is greater than in the reverse process. In addition, during the test period of 10 ⁵ seconds under atmospheric conditions, the ON and OFF states could be kept continuously stable (Fig. 3c). Considering that the memory function of the OFETM device is mainly due to the redox reaction of the redox active portion in the CAT, it can be seen that the electrical switching characteristics of the CAT RSNM device are due to the charge trapping mechanism of the redox portion in the CAT.

Claims (10)

Lower electrode;
An active layer formed on the lower electrode; And
An upper electrode formed on the active layer,
The active layer is a multilayer thin film in which a positively charged material layer and a negatively charged material layer are alternately stacked, and the material layer comprises at least one protein. The switching device according to claim 1, wherein the active layer is formed by alternately stacking 2-100 positively charged material layers and 2-100 negatively charged material layers alternately. The switching device of claim 1, wherein the active layer is laminated by a layer-by-layer self-assembly method. The method of claim 1, wherein the positively charged material layer and the negatively charged material layer are each independently selected from (i) a protein whose surface charge varies depending on pH conditions and (ii) a polymer having a static charge Switching element. The method of claim 4, wherein the protein is at least one selected from catalase, hemoglobin and myoglobin, and the polymer is at least one selected from poly (allylaminehydrochloride), poly (styrenesulfonate) and poly (ethyleneimine). Switching element, characterized in that. Lower electrode;
An active layer formed on the lower electrode; And
An upper electrode formed on the active layer,
The active layer is a switching device, characterized in that the multi-layer thin film of 2-100 catalase and 2-100 poly (allylamine hydrochloric acid) alternately stacked. In the method of manufacturing a switching device by laminating a multilayer thin film on a substrate,
(1) depositing a charging material of a second charge opposite to the first charge on a substrate charged with a first charge;
(2) stacking a charge material of a first charge on the charge material of the second charge; And
(3) repeating two to 100 steps of alternately stacking the charged material of the second charge and the charged material of the first charge; and at least one of the charged materials of the first and second charges. The manufacturing method of the switching device comprising at least one protein. The method of claim 7, wherein the charge material of the first charge and the charge material of the second charge are each independently selected from (i) a protein whose surface charge varies depending on pH conditions and (ii) a polymer having a static charge The manufacturing method of the switching element made into. 8. The method of claim 7, wherein the multilayer thin film in which the charged material of the first charge and the charged material of the second charge are alternately stacked is laminated by a layer-by-layer self-assembly method. A method for manufacturing a switching element, characterized in that. A transistor comprising the switching element according to any one of claims 1 to 6.

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