Electric double layer transistor

Abstract

To control Weil fermion in electrical conduction and magnetic resistance after production of Weil semimetal such as SrRuO3.SOLUTION: An electric double-layer transistor comprises: a thin film 101 formed from a substance comprising Sr1-XAXRu1-YBYO3 (A is an alkali metal or an alkali-earth metal other than Sr, 0≤X≤0.05, and B is a transition metal and 0≤Y≤0.05), and exhibiting a Weil fermion transport phenomenon, of which the requirement for development of the phenomenon is the ratio of a resistivity at 300 K and a resistivity at 4 K is 21 or larger; a source electrode 102 and a drain electrode 103, which are formed on a surface of the thin film 101 so as to be separated from each other; and a carrier-introduction layer 104 formed on the thin film 101 between the source electrode 102 and the drain electrode 103, into which carriers are introduced.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electric double layer transistor. [Background technology]

[0002] SrRuO 3 (Perovskite structure) has a Curie temperature (T C ) is a ferromagnetic metal with a maximum temperature of 160K. 3 has high chemical stability, high electrical conductivity, and is SrTiO 3 These features make it possible to develop a highly compatible perovskite oxide, SrRuO 3 is a promising material for electronics applications such as oxide-based MOSFETs and LEDs (Non-Patent Document 1).

[0003] SrRuO, also known as a Weyl semimetal 3 Among them, massless Weyl fermions with linear band dispersion have high mobility as a transport property (Non-Patent Document 2). 3 is expected to be applied to devices such as transistors that operate at high speed and low power consumption, and is also promising as a highly sensitive magnetic field sensor that utilizes the giant positive magnetoresistance effect and the chiral anomalous magnetoresistance, which is a large negative magnetoresistance effect. Here, the positive and negative magnetoresistance can be controlled by the angle between the direction of the applied magnetic field and the direction of the applied electric field. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] HY Hwang et al., "Emergent phenomena at oxide interfaces", Nature Materials, vol. 11, pp. 103-113, 2012. [Non-Patent Document 2] K. Takiguchi et al., "Quantum transport evidence of Weyl fermions in an epitaxial ferromagnetic oxide", Nature Communications, vol. 11, Article number: 4969, 2020. [Non-Patent Document 3] S. Shimizu et al., "Gate tuning of anomalous Hall effect in ferromagnetic metal SrRuO3", Applied Physics Letters, vol. 105, 163509, 2014. Summary of the Invention [Problem to be solved by the invention]

[0005] SrRuO 3 Weyl fermions at 10000 cm 2 / Vs. However, due to the following reasons, 3 There is no technology to control the electrical conductivity and magnetoresistance of Weyl fermions after their creation.

[0006] First, the residual resistance ratio RRR ≡ ρ(300K) / ρ(4K) is 10 or less for general-quality SrRuO 3 This is because the electrical conduction and magnetoresistance of Weyl fermions have not been realized in gate voltage application elements using thin films (Non-Patent Document 3). 3 This is because the structure and technology to control the electrical conductivity and magnetoresistance of Weyl fermions using gate voltage have not yet been established.

[0007] As mentioned above, SrRuO 3 However, the problem with Weyl semimetals such as these is that there is no established technology to control the electrical conductivity and magnetoresistance of Weyl fermions after their creation.

[0008] The present invention has been made to solve the above problems, and 3 The aim is to create Weyl semimetals such as these and then control the electrical conductivity and magnetoresistance of Weyl fermions. [Means for solving the problem]

[0009] The electric double layer transistor according to the present invention is made of Sr 1-X A X Ru 1-Y B Y O 3 The device comprises a thin film made of a material that exhibits the transport phenomenon of Weyl fermions, the phenomenon being characterized by a ratio of the resistivity at 300 K to the resistivity at 4 K of 21 or greater (where A is an alkali metal or an alkaline earth metal other than Sr, 0≦X≦0.05, and B is a transition metal, 0≦Y≦0.05), a source electrode and a drain electrode formed and spaced apart from each other on the surface of the thin film, a carrier introduction layer formed in the thin film between the source electrode and the drain electrode and into which carriers have been introduced, an ionic liquid disposed in contact with the surface of the thin film, and a gate electrode spaced from the source electrode, the drain electrode, and the thin film and in contact with the ionic liquid. Effect of the Invention

[0010] As described above, according to the present invention, Sr 1-X A X Ru 1-Y B Y O 3 was used as the material for the thin film on which the carrier introduction layer of the electric double layer transistor is formed, so SrRuO 3 After creating a Weyl semimetal such as this, the electrical conductivity and magnetoresistance of the Weyl fermions can be controlled. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of an electric double layer transistor according to an embodiment of the present invention. [Diagram 2]FIG. 2 is a perspective view showing the crystal structure of SrRuO3. [Diagram 3] FIG. 3 is a cross-sectional view showing a state in which a thin film 101 made of SrRuO3 is formed on a growth substrate 201 made of SrTiO3 with a major surface having a plane orientation of (001). [Figure 4] FIG. 4 is a characteristic diagram showing the temperature dependence of resistivity measured between the source electrode 102 and the drain electrode 103 formed on the thin film 101. As shown in FIG. [Diagram 5] FIG. 5 is a characteristic diagram showing the change in magnetoresistance measured between the source electrode 102 and the drain electrode 103 when a magnetic field and an electric field are applied perpendicular to the plane of the thin film 101. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An electric double layer transistor according to an embodiment of the present invention will be described below with reference to Fig. 1. This electric double layer transistor includes a thin film 101, a source electrode 102 and a drain electrode 103 formed on the surface of the thin film 101 and spaced apart from each other, and a carrier introduction layer 104 formed on the thin film 101 between the source electrode 102 and the drain electrode 103 and into which carriers are introduced.

[0013] Thin film 101 is Sr 1-X A X Ru 1-Y B Y O 3 (A is an alkali metal or an alkaline earth metal other than Sr, 0≦X≦0.05, B is a transition metal, 0≦Y≦0.05), and is made of a material that exhibits the transport phenomenon of Weyl fermions, the condition for which is that the ratio of the resistivity at 300 K to the resistivity at 4 K is 21 or more. Typically, the thin film 101 is SrRuO 3 It can be composed of Sr 1-X A X Ru 1-Y B Y O 3 can be said to be a Weyl semimetal. SrRuO with X=0 and Y=0 3Since substitution of elements A and B is not required, it can be prepared more easily.

[0014] The electric double layer transistor also includes an ionic liquid 105 and a gate electrode 106. The ionic liquid 105 is disposed in contact with the surface of the thin film 101 between the source electrode 102 and the drain electrode 103. The ionic liquid 105 can be composed of, for example, N,N-Diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoro methanesulfonyl)imide (DEME-TFSI). The ionic liquid 105 can be, for example, an imidazolium-based ionic liquid, a pyridinium-based ionic liquid, an aliphatic ionic liquid, a phosphonate-based ionic liquid, or an iodine-based ionic liquid. In this example, the ionic liquid 105 is also in contact with the source electrode 102 and the drain electrode 103.

[0015] The gate electrode 106 is spaced apart from the source electrode 102 , the drain electrode 103 and the thin film 101 and is in contact with the ionic liquid 105 .

[0016] In this electric double layer transistor, when a gate voltage is applied to the gate electrode 106, the electrical conduction and magnetoresistance ratio of the Weyl fermions in the carrier introduction layer 104 between the source electrode 102 and the drain electrode 103 are modulated. The carrier introduction layer 104 shown in FIG. 1 shows an approximate state, and the formation region of the carrier introduction layer 104 is not limited to the state shown in FIG. 1. As will be described later, the carrier introduction layer 104 is formed by introducing carriers into the thin film 101 from a portion in contact with the ionic liquid 105 by applying a gate voltage. Therefore, for example, the carrier introduction layer 104 may be formed in a position deeper in the thickness direction of the thin film 101 than the state shown in FIG. 1. It is also possible that the carrier introduction layer 104 is formed by spreading to the region directly under the source electrode 102 or the drain electrode 103 of the thin film 101.

[0017] Here, SrRuO 3 The composition of each element can be made 21 or more if it is within ±5%. 2 / Vs and the transport phenomena of Weyl fermions exhibiting chiral anomalous magnetoresistance with a magnetoresistance ratio exceeding -10%.

[0018] The thin film 101 can be made of a material in which a part of Sr is replaced by an alkali metal atom or an alkaline earth metal atom (A). 1-X A X RuO 3 In this case, if the range is 0≦X≦0.05, then 1000 cm 2 / Vs and the transport phenomena of Weyl fermions exhibiting chiral anomalous magnetoresistance with a magnetoresistance ratio exceeding -10%.

[0019] The thin film 101 can be made of Sr, which is a transition metal atom (B) that replaces part of Ru. 1-X A X Ru 1-Y B Y O 3 If the range is 0≦Y≦0.05, then 1000 cm 2 / Vs and the transport phenomena of Weyl fermions exhibiting chiral anomalous magnetoresistance with a magnetoresistance ratio exceeding -10%.

[0020] SrRuO 3 As shown in Figure 2, SrRuO has a pseudocubic crystal structure in which strontium atoms (Sr), ruthenium atoms (Ru), and oxygen atoms (O) are arranged at the lattice points. 3 If the material is fabricated under conditions where the residual resistivity ratio RRR ≡ ρ(300K) / ρ(4K), which is the ratio of the resistivity at 300 K ρ(300K) to the resistivity at 4 K ρ(4K), is 21 or greater, transport phenomena of Weyl fermions can be realized.

[0021] Sr that can be used to form thin film 101 1-X AX Ru 1-Y B Y O 3 has a perovskite structure, TaAs (reference 1), NbP (reference 2), Co 3 Sn 2 S 2 Compared to conventional materials that exhibit Weyl fermion transport phenomena without a perovskite structure, such as (Reference 3), it also has the advantage of being easier to incorporate into oxide epitaxial heterostructures.

[0022] For example, SrRuO 3 can be used by forming it as a thin film on a predetermined substrate. 3 The residual resistivity ratio RRR ≡ ρ(300K) / ρ(4K), which is the ratio of resistivity ρ(300K) at room temperature (300K) to resistivity ρ(4K) at 4K, is widely used as an index of thin film quality.

[0023] Ru deficiency and RuO 2 High-quality SrRuO with few precipitates 3 The thinner the film, the smaller ρ(4K) and the larger the RRR. 3 In order to realize the high mobility and chiral anomalous magnetoresistance, which are the transport properties of Weyl fermions, the crystal growth conditions must be such that the RRR is 21 or more. 3 It is important to fabricate SrRuO with an RRR of 21 or more. 3 If this is the case, then the transport of Weyl fermions can be realized regardless of the growth method.

[0024] The above-mentioned SrRuO 3 As a growth method of SrTiO 3 , for example, the well-known molecular beam epitaxy method is known. For example, as shown in FIG. 3, SrTiO 3 , whose main surface has a plane orientation of (001), is 3 On the growth substrate 201 made of SrRuO 3 Grow SrRuO 3 The thin film 101 made of MgO(001), (La 0.3 Sr 0.7)(Al 0.65 Ta 0.35 )O 3 It can be made of materials such as (001).

[0025] In addition, growth methods other than molecular beam epitaxy, such as sputtering and pulsed laser ablation, have been used to grow SrRuO, which can transport Weyl fermions. 3 It is possible to fabricate SrRuO 3 The shape of the material is not limited to a thin film formed on a substrate, but may also be a powder or bulk shape obtained by bulk synthesis techniques.

[0026] The method for manufacturing an electric double layer transistor is described below. First, SrTiO 3 On the growth substrate consisting of (001), SrRuO 3 is grown to form a thin film 101.

[0027] For example, a growth substrate is carried into a growth chamber of a molecular beam epitaxy apparatus, the growth chamber is made ultra-high vacuum, the substrate temperature condition is set to 780° C., and atomic beams of an alkaline earth metal Sr and a 4d transition metal Ru are introduced at 10 -6 The active oxygen is supplied to the growth substrate under an atmosphere of about Torr. 3 The thin film 101 can be grown to a thickness of, for example, 10 nm.

[0028] SrRuO 3 In order to realize the high mobility and positive magnetoresistance ratio, which are the transport properties of Weyl fermions, the crystal growth conditions must be such that the RRR is 21 or more. 3 It is necessary to prepare SrRuO with RRR of 21 or more. 3 If this is the case, transport phenomena of Weyl fermions can be observed regardless of the growth method (Reference 4).

[0029] Next, a source electrode 102 and a drain electrode 103 are provided spaced apart from each other on the surface of the formed thin film 101. For example, the source electrode 102 and the drain electrode 103 can be formed by patterning a metal film that will become the electrodes, which is deposited by a well-known metal deposition technique, by known lithography and ion milling techniques.

[0030] Next, an ionic liquid 105 is placed in contact with the surface of the thin film 101. Next, a gate electrode 106 is provided in contact with the ionic liquid 105, separated from the source electrode 102, the drain electrode 103, and the thin film 101. The source electrode 102, the drain electrode 103, and the gate electrode 106 can be made of Ag. These electrodes can also be made of single-element metals such as Au and Cr, or Nb-doped SrTiO 3 The conductive material may be a conductive material such as

[0031] Here, the characteristics of the thin film 101 will be described. First, the temperature dependence of the resistivity measured between the source electrode 102 and the drain electrode 103 is shown in Figure 4. The RRR value of the thin film 101 is 21. A bend in the electrical resistance indicating the transition from paramagnetism to ferromagnetism is observed at 150K, and the Curie temperature is 150K.

[0032] Next, FIG. 5 shows the change in magnetoresistance measured between the source electrode 102 and the drain electrode 103 when a magnetic field and an electric field are applied perpendicular to the plane of the thin film 101 at 2K. A linear positive magnetoresistance ratio exceeding 10% is observed, along with quantum oscillations corresponding to the oscillation period of the Weyl fermions, indicating that transport of Weyl fermions has been realized. The mobility of Weyl fermions in the thin film 101 estimated from these quantum oscillations is 10,000 cm 2 / Vs, which is a very high value.

[0033] A gate voltage is applied to the gate electrode 106 of the thin film 101 having the above-mentioned characteristics to form the carrier introduction layer 104. By applying this gate voltage, carriers are introduced into the thin film 101 in contact with the ionic liquid 105, and the carrier introduction layer 104 is formed.

[0034] For example, a carrier introduction layer 104 is formed from the surface of the thin film 101 between the source electrode 102 and the drain electrode 103 to a predetermined depth. In this process, a gate voltage is applied while measuring the resistance value between the source electrode 102 and the drain electrode 103. Also, in this process, the application of the gate voltage is controlled in accordance with the resistance value between the source electrode 102 and the drain electrode 103, thereby controlling the carrier concentration in the carrier introduction layer 104.

[0035] For example, when a gate voltage of 4 V is applied, the sheet carrier density becomes 2×10 15 cm -2 of electron doped, 2 x 10 at -4V 15 cm -2 hole doping is obtained for the thin film 101 (Reference 5). These sheet carrier densities can be grasped by measuring the sheet resistance between the source electrode 102 and the drain electrode 103, or the like.

[0036] SrRuO formed to a thickness of 10 nm 3 The sheet carrier density in the state where the carrier introduction layer 104 is formed on the thin film 101 made of 16 cm -2and the resistivity and magnetoresistance ratio between the source electrode 102 and the drain electrode 103 can be modulated by about 5%. Moreover, by making the thin film 101 thinner, the amount of modulation can be increased. For example, if the thin film 101 is formed to a thickness of 1 nm, about 50% modulation is possible. Moreover, if the thin film 101 is formed to a thickness of 0.5 nm, about 100% modulation is possible. This modulation amount is also proportional to the gate voltage, and for example, if 8V is applied, the modulation amount is double that of if 4V is applied. In this way, it is possible to freely control the modulation amount of the resistivity and magnetoresistance ratio between the source electrode 102 and the drain electrode 103 by designing the gate voltage and the thickness of the thin film 101.

[0037] In the electric double layer transistor according to the embodiment, an ionic liquid 105 is disposed between a thin film 101 on which a carrier introduction layer 104 is formed and a gate electrode 106. In contrast, a large modulation amount cannot be obtained with a structure using silicon oxide or aluminum oxide, which are used as a gate insulating film in a general transistor structure, instead of the ionic liquid.

[0038] As described above, according to the present invention, Sr 1-X A X Ru 1-Y B Y O 3 was used as the material for the thin film on which the carrier introduction layer of the electric double layer transistor is formed, so SrRuO 3 After preparing a Weyl semimetal such as Sr, it becomes possible to control the electrical conductivity and magnetoresistance of the Weyl fermions. According to the present invention, gate voltage control of the transport of Weyl fermions is realized, enabling device applications that utilize the high mobility and large magnetoresistance ratio of Weyl fermions. 1-X A X Ru 1-Y B Y O 3 Since it can be grown as a single crystal epitaxially on a substrate such as an oxide, it is possible to realize a gate voltage control device for the transport of Weyl fermions, which is highly compatible with oxide electronics.

[0039] It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0040] [Reference 1] X. Huang et al., "Observation of the Chiral-Anomaly-Induced Negative Magnetoresistance in 3D Weyl Semimetal TaAs", Physical Review X, vol. 5, no. 3, 031023, 2015. [Reference 2] C. Shekhar et al., "Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal candidate NbP", Nature Physics, vol. 11, no. 645-649, 2015. [Reference 3] DF Liu et al., "Magnetic Weyl semimetal phase in a Kagome crystal", Science, vol. 365, pp. 1282-1285, 2019. [Reference 4] SK Takada et al., "Thickness-dependent quantum transport of Weyl fermions in ultra-high-quality SrRuO3 films", Applied Physics Letters, vol. 118, 092408, 2021. [Reference 5] K. Ueno et al., "Field-Induced Superconductivity in Electric Double Layer Transistors", Journal of the Physical Society of Japan, vol. 83, 032001, 2014. [Explanation of symbols]

[0041] 101...thin film, 102...source electrode, 103...drain electrode, 104...carrier introduction layer, 105...ionic liquid, 106...gate electrode.

Claims

1. Sr 1-X A X Ru 1-Y B Y O 3 (A is an alkali metal or an alkaline earth metal other than Sr, 0≦X≦0.05, B is a transition metal, 0≦Y≦0.05) and a thin film made of a material that exhibits the transport phenomenon of Weyl fermions, the condition for which is that the ratio of the resistivity at 300K to the resistivity at 4K is 21 or more; a source electrode and a drain electrode formed on a surface of the thin film and spaced apart from each other; a carrier introduction layer formed on the thin film between the source electrode and the drain electrode and having carriers introduced therein; an ionic liquid disposed in contact with a surface of the thin film; a gate electrode spaced apart from the source electrode, the drain electrode, and the thin film and in contact with the ionic liquid; Equipped with The thin film is made of SrRuO 3 and has a thickness of 1 nm or less.

2. 2. The electric double layer transistor according to claim 1, The electric double layer transistor is characterized in that the ionic liquid is composed of N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide.

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