WO2016175251A1

WO2016175251A1 - Oscillation element and oscillation device

Info

Publication number: WO2016175251A1
Application number: PCT/JP2016/063239
Authority: WO
Inventors: 公一芦澤
Original assignee: 株式会社Uacj
Priority date: 2015-04-28
Filing date: 2016-04-27
Publication date: 2016-11-03
Also published as: JP2018107153A

Abstract

An oscillation element (1) provided with a first metal layer (2), a tunneling-exhibiting tunnel insulation layer (3) in Schottky contact with the first metal layer (2), and a second metal layer (4) for applying a voltage between the first metal layer (2) and the tunnel insulation layer (3). Current oscillation is brought about by applying the voltage and establishing no more than a predetermined high current density, the voltage being applied in the direction in which the first metal layer (2) is reverse-biased with respect to the second metal layer (4).

Description

Oscillation element and oscillation device

The present invention relates to an oscillation element and an oscillation device using a Schottky barrier diode.

A barrier generated at the junction of a metal and a semiconductor is called a Schottky barrier, and a diode using this Schottky barrier is a Schottky barrier diode. When the semiconductor is p-type, the Schottky barrier diode exhibits a rectifying action in which a large amount of current flows from the semiconductor to the metal in the forward bias, and a small amount of current flows from the metal to the semiconductor in the reverse bias. In the case of the mold, the forward bias shows a rectifying action in which a large amount of current flows from the metal to the semiconductor, and the reverse bias causes a small amount of current to flow from the semiconductor to the metal.

Such a Schottky barrier includes a metal and an oxide film, a hydroxide film or a mixed film formed on the surface thereof (hereinafter, these three films are collectively referred to as “metal oxide film”). It also occurs in joining. This is because the metal oxide film is an oxygen-deficient or oxygen-rich semiconductor, or a metal-rich or metal-deficient semiconductor. In general, it is said that if the metal oxide film is an oxygen-deficient type or a metal-excess type, it is an n-type semiconductor, and if it is an oxygen-excess type or a metal-deficient type, it is a p-type semiconductor.

By the way, since the metal oxide film is an insulating film, normally, a large amount of current does not flow directly through the metal oxide film, but as the film thickness is changed from thicker to thinner, As the thickness of the depletion layer, which is an insulating layer in the film, is changed from thicker to thinner, a phenomenon in which a large amount of current flows directly in the metal oxide film, that is, a tunnel phenomenon starts to occur. Due to this tunnel phenomenon, a current based on the tunnel phenomenon flows in addition to the current based on the rectifying action described above at the junction between the metal and the metal oxide film.

Japanese Patent Publication “Japanese Laid-Open Patent Publication No. 2004-297092 (Released on October 21, 2004)” Japanese Patent Gazette “Japanese Patent Laid-Open Publication No. 2007-48613 (published February 22, 2007)” Japanese Patent Publication “JP 2013-12755 Publication (January 17, 2013)”

The present inventor has found that in such a junction between a metal and a metal oxide film in which two kinds of currents flow, oscillation is observed in the current flowing through the junction, and this current oscillation is below a predetermined high current density. The expression was confirmed.

Up to now, although there is a prior art document (see Patent Documents 1 to 3) that has been studied to investigate the current-voltage characteristic representing the current characteristic regarding the characteristic of the current flowing through the junction between the metal and the metal oxide film, There is no report that the above-described current oscillation has occurred in this document.

The present invention has been completed on the basis of the above knowledge by the present inventor, and an object thereof is to provide an oscillation element that oscillates with a simple element structure.

An oscillation element according to the present invention includes a metal layer, a tunnel insulating layer that is Schottky-bonded to the metal layer and causes a tunnel phenomenon, and an electrode for applying a voltage between the metal layer and the tunnel insulating layer A current flowing through the Schottky junction by applying a voltage in a direction in which the metal layer is reverse-biased with respect to the electrode to reduce a current flowing through the Schottky junction to a predetermined high current density or less. Oscillate.

The present invention has the effect of oscillating current with a simple element structure.

It is sectional drawing which shows typically the principal part structure of the oscillation element which concerns on embodiment of this invention. It is a schematic block diagram of the power control unit used for an electric vehicle using the said oscillation element. It is sectional drawing which shows the structure of the sample element used for evaluation. It is a schematic diagram of the apparatus which produces and evaluates the sample element of Example 1. It is a figure which shows the current-voltage characteristic of the said sample element. (A) is a figure which shows the reverse bias voltage applied to the said sample element, (b) is a figure which shows the electric current which flowed through the said sample element. (A) is a figure which shows the reverse bias voltage applied to the said sample element, (b) is a figure which shows the electric current which flowed through the said sample element. (A) is a figure which shows the reverse bias voltage applied to the said sample element, (b) is a figure which shows the electric current which flowed through the said sample element. It is a schematic diagram which shows the depletion area | region and carrier area which arise in the tunnel insulating layer of the said oscillation element. It is a schematic diagram which shows the depletion area | region and carrier area which arise in the tunnel insulating layer of the said oscillation element. It is a schematic diagram which shows the depletion area | region and carrier area which arise in the tunnel insulating layer of the said oscillation element. FIG. 6 is a diagram showing current-voltage characteristics of the sample element of Example 2. It is a figure which shows the electric current which flowed through the said sample element. (A) is a diagram showing a circuit in which a lithium ion battery and a load resistor are connected, (b) is a diagram showing a circuit in which a current oscillator is added to the circuit shown in (a), and (c) is a current diagram. The figure which shows the structure of an oscillator, (d) is a figure which shows the inverter circuit using the current oscillator shown in (c).

Hereinafter, embodiments of the present invention will be described in detail. Note that the same or similar parts are denoted by the same or similar reference numerals, and those having the same or similar reference numerals in the drawings may be omitted. In addition, the dimensions, materials, shapes, relative arrangements, processing methods, and the like of the configurations described in the present embodiment are merely one embodiment, and the scope of the present invention should not be construed as being limited thereto. Further, the drawings are schematic, and the ratio and shape of dimensions are different from actual ones.

[Structure of oscillation element 1]
FIG. 1 is a cross-sectional view schematically showing a main structure of an oscillation element 1 according to an embodiment of the present invention. As shown in FIG. 1, the oscillation element 1 includes a first metal layer (metal layer) 2, a tunnel insulating layer 3, and a second metal layer (electrode) 4. The first metal layer 2, the tunnel insulating layer 3, and the second metal layer 4 are stacked in this order.

The first metal layer 2 and the tunnel insulating layer 3 form a Schottky barrier at the junction. That is, the first metal layer 2 and the tunnel insulating layer 3 are in Schottky junction. Due to this Schottky junction, the oscillation element 1 exhibits the rectifying action described in the background art.

On the other hand, the tunnel insulating layer 3 and the second metal layer 4 are in ohmic junction without forming a Schottky barrier at the junction. By this ohmic junction, the second metal layer 4 functions as an electrode attached to the tunnel insulating layer 3. The second metal layer 4 only needs to function as an electrode of the tunnel insulating layer 3. For this reason, in the oscillation element 1, the above-described second metal layer 4 is laminated with the first metal layer 2 and the tunnel insulating layer 3. It is not limited to the structure. In short, the second metal layer 4 only needs to have a structure capable of applying a voltage between the first metal layer 2 and the tunnel insulating layer 3.

In addition, the second metal layer 4 is generally made of a metal such as platinum. However, the second metal layer 4 only needs to be able to form an ohmic junction with the tunnel insulating layer 3. A conductive material can also be used.

Note that whether the junction between the metal layer and the insulating layer is a Schottky junction or an ohmic junction depends on the height of the barrier generated in the energy band structure between the metal layer and the insulating layer. For this reason, each material is selected so that the 1st metal layer 2 and the tunnel insulating layer 3 may carry out a Schottky junction. For the selection, for example, each work function or electron affinity that determines the height of the barrier of the energy band structure is used. The same applies to the ohmic junction between the tunnel insulating layer 3 and the second metal layer 4.

Furthermore, the tunnel insulating layer 3 causes the tunnel phenomenon described in the background art. Due to this tunnel phenomenon, a tunnel current also flows through the Schottky junction between the first metal layer 2 and the tunnel insulating layer 3. The current based on the rectifying action described above flows beyond the Schottky barrier, whereas the tunnel current passes through the Schottky barrier, that is, tunnels quantum mechanically.

Thus, the oscillation element 1 uses the first metal layer 2 and the second metal layer 4 as two electrodes, and outputs a current I12 when a voltage V11 is applied between the two electrodes.

Hereinafter, a case where the tunnel insulating layer 3 is a p-type semiconductor will be described as an example. If the tunnel insulating layer 3 is an n-type semiconductor, the sign of the bias voltage applied between the first metal layer 2 and the second metal layer 4 is different from the case of a p-type semiconductor described below. The reverse relationship.

[Operation of Oscillating Element 1]
Next, the operation of the oscillation element 1 in which the tunnel insulating layer 3 is a p-type semiconductor will be described. As shown in FIG. 1, the voltage V <b> 11 is applied between the first metal layer 2 and the second metal layer 4, which are two electrodes, in the oscillation element 1. The application direction of the voltage V11 includes a case where a negative voltage (hereinafter referred to as “forward bias voltage”) V11 is applied to the first metal layer 2 with respect to the second metal layer 4, and the second metal layer 4 is In some cases, a positive voltage (hereinafter referred to as “reverse bias voltage”) V11 is applied to the first metal layer 2 as a reference. That is, if the forward bias voltage V11 is applied to the first metal layer 2 with the second metal layer 4 as a reference, the voltage in the direction in which the first metal layer 2 becomes forward biased with respect to the second metal layer 4 is applied. Is applied, and a reverse bias voltage is applied to the first metal layer 2 with reference to the second metal layer 4, the first metal layer 2 is reversely biased with respect to the second metal layer 4. A voltage is applied.

First, the case where the forward bias voltage V11 is applied will be described. When a forward bias voltage is applied between the first metal layer 2 and the second metal layer 4, each of a current based on the above-described rectification characteristics (hereinafter simply referred to as “rectification characteristic current”) and a tunnel current are generated. Flowing.

By applying a forward bias voltage, the height of the Schottky barrier is reduced with respect to carriers (electrons or holes) flowing from the tunnel insulating layer 3 side to the first metal layer 2 side. On the other hand, the height of the Schottky barrier from the first metal layer 2 side to the tunnel insulating layer 3 side remains the same. Therefore, carriers can be easily moved only from the tunnel insulating layer 3 side to the first metal layer 2 side. That is, a large amount of rectification characteristic current (hereinafter referred to as “forward current”) flows from the tunnel insulating layer 3 side to the first metal layer 2 side.

As described above, the tunnel current passes through the Schottky barrier and flows from the tunnel insulating layer 3 side to the first metal layer 2 side.

As described above, when the forward bias voltage V11 is applied to the oscillation element 1, the current I12 obtained by adding the tunnel current and the forward current flows from the tunnel insulating layer 3 side to the first metal layer 2 side.

Next, the case where the reverse bias voltage V11 is applied will be described. Even when the reverse bias voltage V11 is applied, each of the rectification characteristic current and the tunnel current basically flows as in the case where the forward bias voltage V11 is applied.

Application of the reverse bias voltage V11 raises the height of the Schottky barrier against carriers (electrons or holes) flowing from the tunnel insulating layer 3 side to the first metal layer 2 side. On the other hand, the height of the Schottky barrier from the first metal layer 2 side to the tunnel insulating layer 3 side remains the same. Accordingly, it becomes difficult to move carriers from the tunnel insulating layer 3 side to the first metal layer 2 side. That is, a very small amount of rectification characteristic current (hereinafter referred to as “reverse current”) flows from the first metal layer 2 side to the tunnel insulating layer 3 side.

As described above, the tunnel current passes through the Schottky barrier and flows from the first metal layer 2 side to the tunnel insulating layer 3 side.

As described above, when the reverse bias voltage V11 is applied to the oscillation element 1, the current I12 obtained by adding the tunnel current and the reverse current flows from the first metal layer 2 side to the tunnel insulating layer 3 side.

Here, the feature of the present invention is that, when the reverse bias voltage V11 is applied, the current I12 flowing from the first metal layer 2 side to the tunnel insulating layer 3 side oscillates in a predetermined high current density region.

In the oscillation element 1, by applying the reverse bias voltage V11 and setting it to a predetermined high current density or less, output of a current I12 oscillating at a high frequency, that is, an alternating current is realized. Further, this current oscillation is realized by a simple laminated structure as described above without using a complicated circuit configuration by using a principle that has not been known so far. Furthermore, if the oscillation element 1 is used, it is expected that an extremely downsized oscillation device can be made.

Next, two application examples of the oscillation element 1 will be considered. It should be noted that the following two application examples consider the practical application of the oscillation element 1 based on the knowledge obtained through research and evaluation by the present inventors.

[Application example of oscillation element 1]
(Application 1)
An application example 1 of the oscillation element 1 will be described. FIG. 2 is a schematic configuration diagram of a power control unit 100 used in an electric vehicle. The oscillation element 1 is built in an inverter 103 that converts a direct current into an alternating current.

The power control unit 100 includes a battery 101, a DC / DC converter 102, an inverter 103, a control circuit 104, a motor 105, and a TG (output shaft torque) 106. The DC / DC converter 102 converts the output voltage of the battery 101 as necessary, and the inverter 103 converts a direct current into an alternating current. The oscillation element 1 can take the process of converting this direct current into alternating current.

The motor 105 rotates using the alternating current output from the inverter 103. The control circuit 104 detects the output voltage of the DC / DC converter 102 and the output voltage of the inverter 103, and controls the conversion process of the inverter 103 by detecting the speed and position of the motor 105 using the TG 106.

Here, the DC / DC converter 102 is a power supply device that applies a voltage to the oscillation element 1. A positive voltage, that is, a reverse bias voltage, is applied to the first metal layer 2 with respect to the second metal layer 4 due to the output voltage of the DC / DC converter 102. By applying the reverse bias voltage, the current flowing through the oscillation element 1 oscillates. The motor 105 may be selected so that it can rotate according to the frequency of the alternating current output from the oscillation element 1, or the frequency of the alternating current output from the oscillation element 1 is converted to a frequency that can be used by the motor 105. A conversion circuit may be provided.

In the battery 101, the DC voltage can be increased by increasing the number of batteries in series. As a result, the battery 101 can be directly connected to the inverter 103 in which the oscillation element 1 is built in without boosting the voltage of the battery 101 using the DC / DC converter 102. Therefore, the DC / DC converter 102 becomes unnecessary, and the number of parts of the power control unit 100 can be reduced.

In addition to the inverter described above, the oscillation element 1 includes an electronic component that oscillates at a specific frequency, for example, a clock signal source in a digital circuit such as a microprocessor, other televisions, videos, electrical equipment, telephones, copiers, cameras, Use in timing circuits in a wide range of fields such as speech synthesizers and communication equipment is also expected.

(Application example 2)
An application example 2 of the oscillation element 1 will be described. FIG. 14 is a diagram for explaining an inverter circuit that converts a direct current of a battery into an alternating current.

For example, consider the case where the oscillation element 1 is used in a circuit in which the lithium ion battery 201 and the load resistor 202 shown in FIG. In the circuit shown in FIG. 14A, the current flowing through the load resistor 202 is a direct current. If this direct current can be converted into an alternating current, the alternating current will flow through the load resistor 202.

FIG. 14B is a circuit in which a current oscillator 1A composed of two oscillation elements 1 having the same characteristics is added to the circuit shown in FIG. In the current oscillator 1A, as shown in FIG. 14C, the oscillating element 1A-1 and the oscillating element 1A-2 are directly connected at the anodes, and this connection configuration allows the positive and negative directions of the alternating current to flow. Can be used without being affected by the rectifying property of the oscillation element 1. Of course, the oscillation element 1A-1 and the oscillation element 1A-2 may be directly connected to each other at the cathodes. If each of the oscillation element 1A-1 and the oscillation element 1A-2 has a structure in which a single aluminum oxide film is sandwiched between two platinum layers, the respective frequencies and phases are equal to each other. Can be realized.

However, in the circuit shown in FIG. 14B, an alternating current can flow through the load resistor 202, but the effective value of the AC voltage is the same value as the DC voltage of the circuit shown in FIG. It is.

Next, FIG. 14 (d) shows an inverter circuit capable of boosting the DC voltage of the circuit shown in FIG. 14 (a). As shown in FIG. 14D, the lithium ion battery 201 and the current oscillator 1 </ b> A are directly connected to the primary side of the transformer 203. On the other hand, various loads can be connected to the secondary side of the transformer 203, but here the load resistance 204 is used. The alternating voltage generated at both ends of the primary side can be freely boosted and lowered by the turns ratio of the primary side and the secondary side of the transformer 203.

Here, in the inverter circuit shown in FIG. 14D, the output voltage of the lithium ion battery 201 is 3.5 V, the battery capacity is 1 Ah, the maximum current amplitude (peak) of the oscillation element 1A-1 and the oscillation element 1A-2. A simulation was performed for a case where the toe peak) was 2200 A, the oscillation frequency was 2.5 kHz, the turns ratio of the transformer 203 was 1:10, and the load resistance 204 was 400Ω. According to the simulation results, the effective value of the alternating voltage applied to the load resistor 204 was 34 V, the effective value of the alternating current was 0.085 A, and the effective value of the alternating current power was 2.9 W.

On the other hand, as a comparative example, in the circuit shown in FIG. 14A, a simulation was also performed for a case where a load resistance 202 of 4Ω was connected to the lithium ion battery 201. According to the simulation results, the DC voltage applied to the load resistor 202 was 3.5 V, the DC current was 0.85 A, and the DC power at the load resistor 202 was 3.0 W.

When comparing the two, the power consumption in the load resistor 202 was almost the same, but the voltage applied to the load resistor 202 was 10 times, although there was a difference between DC and AC.

Further, the fact that the voltage on the secondary side of the transformer 203 can be changed by changing the turns ratio of the transformer 203 is also a feature of the inverter circuit shown in FIG.

Furthermore, since the oscillation frequency of the oscillation element 1A-1 and the oscillation element 1A-2 is 2.5 kHz, the volume of the transformer 203 is much higher than the volume of the transformer for 50 Hz and 60 Hz which are Japanese commercial power supply frequencies. The feature of the inverter circuit is that it can be made smaller.

Thus, it is considered that by using the oscillation element 1, it is possible to realize an inverter circuit that converts direct current to alternating current with a very simple circuit.

Hereinafter, the present invention will be described in more detail by two examples, but the present invention is not limited to the examples.

<Example 1>
(Production of sample element)
A sample of an oscillation element used for evaluation was produced. FIG. 3 is a cross-sectional view showing the structure of the sample element used for the evaluation. As shown in FIG. 3, there is an aluminum oxide film 6 formed by anodic oxidation treatment on the surface of an aluminum plate (Al) 5, and a platinum plating layer 7 is laminated on the surface of the aluminum oxide film 6. Sample element 8 was produced.

The details of each layer of the sample element 8 are as follows.

Aluminum plate 5 (first metal layer 2): The material is 1085 (Al is 99.85%, mainly containing Fe and Si as other elements), the size is 50 mm × 50 mm, and the thickness is about 0.1 mm.

As shown in FIG. 4, the sample element 8 was manufactured and evaluated in an AFM (Atomic Force Microscope) contacting mode using a scanning probe microscope, model number JSPM-5200, manufactured by JEOL. The cantilever 18 with the tip of the probe 17 is made by Budgetsensors, model number Tap190E-G, the tip diameter is about 25 nm, 5 μm thick chrome plating, and the surface of the chrome plating is further plated with 10 μm thick platinum. . The resonance frequency was 190 kHz. Since the tip diameter of the platinum plating layer 7 at the tip of the probe 17 in the sample element 8 is in contact with the aluminum oxide film 6 is about 25 nm, the contact area between the aluminum oxide film 6 and the platinum plating layer 7 is about 450 nm ^2. Met.

Aluminum oxide film 6 (tunnel insulating layer 3): A voltage of +5 to +10 V is applied to the aluminum plate 5 for 1 minute in the atmosphere to the platinum plating layer 7 (second metal layer 4) at the tip of the probe 17 to anodic oxidation By the treatment, an aluminum oxide film 6 was grown on the surface of the aluminum plate 5. Since several nanometers to several tens of nanometers of water adhere to the surface of the aluminum plate 5 in the atmosphere, the aluminum oxide film 6 can be grown by this treatment. The thickness of the aluminum oxide film 6 was 10 nm or less. If the aluminum oxide film 6 is a natural oxide film, the aluminum oxide film 6 has a thickness of at least 0.5 nm.

(Sample element evaluation method)
Sample element 8 was evaluated as follows. The sample element 8 was evaluated in the atmosphere at room temperature. FIG. 4 is a sample production apparatus and an evaluation apparatus for evaluating the sample element 8 as described above, and a schematic diagram thereof is shown. As shown in FIG. 4, the sample element 8 is arranged on a stage 16 installed on a support base 15 of the evaluation apparatus. The back surface of the aluminum plate 5 of the sample element 8 is in contact with the stage 16, and the platinum plating layer 7 at the tip of the probe 17 is in contact with the aluminum oxide film 6 disposed on the aluminum plate 5.

Between the cantilever 18 and the stage 16, a power supply device 19 capable of applying a forward bias voltage and a reverse bias voltage to the sample element 8 and an ammeter 20 are connected in series. On the other hand, a voltmeter 21 is connected between the cantilever 18 and the stage 16. A current I12 (see FIG. 1) flowing through the sample element 8 can be measured using the ammeter 20, and a voltage V11 (see FIG. 1) applied to the sample element 8 can be measured using the voltmeter 21. . The internal resistance of the ammeter 20 is sufficiently low with respect to the measurement system, and the internal resistance of the voltmeter 21 is sufficiently high with respect to the measurement system.

(Evaluation results)
FIG. 5 shows the result of evaluating the sample element 8 using the evaluation apparatus shown in FIG. The horizontal axis in FIG. 5 indicates the bias voltage (V) applied to the sample element 8, and the vertical axis indicates the current (nA) flowing through the sample element 8.

As shown in FIG. 5, when a forward bias voltage was applied to the sample element 8 (minus side of the horizontal axis), the current flowing through the sample element 8 increased substantially linearly (linearly) with the forward bias voltage. On the other hand, when a reverse bias voltage is applied to the sample element 8 (the positive side of the horizontal axis), a large oscillation is observed in the current flowing through the sample element 8 when the reverse bias voltage is 0.012 V to 0.078 V. It was done. The current generation amplitude was in a wide range of −0.1 μA to 0.45 μA. In the range where the reverse bias voltage is not 0.012 V to 0.078 V, it increases almost linearly with the reverse bias voltage, as in the case of applying the forward bias voltage.

Here, the average current density of the current flowing through the sample element 8 when the reverse bias voltage was 0.012 V to 0.078 V was calculated. As described above, since the contact area between the platinum plating layer 7 and the aluminum oxide film 6 at the tip of the probe 17 was about 450 nm ² , the contact area was set to 450 nm ² . From FIG. 5, it can be read that when the reverse bias voltage is 0.2 V, the current flowing through the sample element 8 is 0.88 × 10 ⁻⁶ A. Therefore, the platinum plating layer 7 and the aluminum plate at the tip of the probe 17 The resistance of the aluminum oxide film 6 between 5 and 5 was 2.3 × 10 ⁵ Ω, and the sheet resistance was 1.0 × 10 ⁻⁶ Ωcm ² . From this, when the reverse bias voltage was 0.2 V, the current density of the current flowing through the sample element 8 was calculated to be 2.0 × 10 ⁵ Acm ⁻² . On the other hand, when applying the reverse bias voltage in which current oscillation was observed, for example, when the reverse bias voltage was 0.05 V, the average current of the oscillating current flowing through the sample element 8 was calculated from the value read from FIG. The density was 4.0 × 10 ⁴ Acm ⁻² . The current density of 40 kA per square cm is extremely large, and it is expected that the current density can be applied to a power device that handles a large current.

Similarly, when the average current density of the current flowing through the sample element 8 when the reverse bias voltage is 0.012 V to 0.078 V is calculated, the average current density range is 1.2 × 10 ⁴ Acm ^−2. It was ˜7.8 × 10 ⁴ Acm ⁻² .

(Observation of current oscillation)
Next, the reverse bias voltage applied to the sample element 8 and the oscillation current flowing through the sample element 8 were observed using an oscilloscope (manufactured by Tektronix). FIG. 6 shows the observation results when the evaluation apparatus shown in FIG. 4 is used for evaluation, FIG. 7 shows the observation results after the evaluation using the evaluation apparatus shown in FIG. 4, and FIG. This is an observation result when the platinum plating layer 7 at the tip of the probe 17 is separated from the aluminum oxide film 6. 6A to 8A show the reverse bias voltage, and FIG. 6B shows the current flowing through the sample element 8. In (a) of each figure, the horizontal axis is 50 μS per square, and the vertical axis is 0.1 nA per square. Also, in (b) of each figure, the horizontal axis is 250 μS per square, and the vertical axis is 0.1 μA per square. In addition, (b) of each figure shows the electric current which flowed through the sample element 8, as mentioned above.

In each figure (a), an alternating current or peak waveform of about 20 kHz is measured, but this waveform is noise caused by the measurement system or measuring apparatus used in this evaluation, and is actually a sample element. The bias voltage value (direct current) applied to 8 can be read from the average value of the measured alternating current waveform. It was confirmed that this noise did not affect the current measurement results.

In FIG. 6, it was observed that the current flowing through the sample element 8 oscillated as shown in (b) when a reverse bias voltage of 0.032 V was applied as shown in (a). The oscillation frequency was about 2.5 kHz. Also in FIG. 7, it was observed that the current flowing through the sample element 8 oscillated as shown in (b) when a reverse bias voltage of 0.032 V was applied as shown in (a). . The oscillation frequency was about 2.5 kHz. FIG. 8 shows an observation result in a state where the platinum plating layer 7 at the tip of the probe 17 is separated from the aluminum oxide film 6, but no current flowing through the sample element 8 was observed.

In order to further research, the present inventor evaluated the following Example 2 following the evaluation of Example 1 described above.

<Example 2>
(Production of sample element)
A sample of an oscillation element used for evaluation was produced. FIG. 3 is a cross-sectional view showing the structure of the sample element used for the evaluation. As shown in FIG. 3, there is an aluminum oxide film 6 formed by anodic oxidation treatment on the surface of an aluminum plate (Al) 5, and a platinum plating layer 7 is laminated on the surface of the aluminum oxide film 6. Sample element 8 was produced.

The details of each layer of the sample element 8 are as follows.

Aluminum plate 5 (first metal layer 2): The material is 1085 (Al is 99.85%, mainly containing Fe and Si as other elements), the size is 50 mm × 50 mm, and the thickness is about 0.1 mm. As a pretreatment of the aluminum plate 5, the material surface was smoothed by electrolytic polishing.

As shown in FIG. 4, the sample element 8 was manufactured and evaluated in an AFM (Atomic Force Microscope) contacting mode using a scanning probe microscope, model number JSPM-5200, manufactured by JEOL. The cantilever 18 with the probe 17 attached to the tip was manufactured by Budgetsensors, model No. Tap190E-G, the tip diameter was about 25 nm, 5 μm thick chromium plating, and the surface of the chromium plating was further plated with 10 μm thick platinum. The resonance frequency was 190 kHz. In the sample element 8, the tip diameter at which the platinum plating layer 7 at the tip of the probe 17 contacts the aluminum oxide film 6 is about 25 nm, but not only the tip of the probe 17 but also the probe peripheral portion near the tip is oxidized with aluminum. The film 6 grew and the contact area between the platinum plating layer 7 and the aluminum oxide film 6 increased. As a result, the contact area between the aluminum oxide film 6 and the platinum plating layer 7 became about 730 nm ² .

Aluminum oxide film 6 (tunnel insulating layer 3): A voltage of +5 to +60 V is applied to the aluminum plate 5 in the atmosphere against the platinum plating layer 7 (second metal layer 4) at the tip of the probe 17 for 5 to 300 seconds. An aluminum oxide film 6 was grown on the surface of the aluminum plate 5 by anodic oxidation treatment. Since several nanometers to several tens of nanometers of water adhere to the surface of the aluminum plate 5 in the atmosphere, the aluminum oxide film 6 can be grown by this treatment. By changing the conditions of anodic oxidation, aluminum oxide, aluminum hydroxide, or a mixture thereof grows on the surface of the aluminum plate 5, and is collectively referred to as aluminum oxide here. In this embodiment, the aluminum oxide film 6 formed by anodic oxidation is a p-type semiconductor.

The thickness of the aluminum oxide film 6 was 100 nm or less. If the aluminum oxide film 6 is a natural oxide film, the aluminum oxide film 6 has a thickness of at least 0.5 nm. The electrode area of the aluminum plate (first metal layer 2) varies depending on the thickness of the aluminum oxide film 6, but is reduced or enlarged to 0.6 to 200 times the tip area of the probe 17.

When the aluminum oxide film 6 is an n-type semiconductor, the following method was used. 100 ml of an electrolytic solution of 0.5 mol / dm ³ boric acid and 0.5 mol / dm ³ sodium hydroxide (pH 8.95) was prepared, and a drop was dropped on the aluminum plate 5 in contact with the tip of the probe 17 with a dropper. It was.

Aluminum oxide film 6 (tunnel insulating layer 3): A voltage of +5 to +60 V is applied to the aluminum plate 5 in the atmosphere for 5 to 300 seconds to the platinum plating layer 7 at the tip of the probe 17, and the aluminum plate is subjected to anodic oxidation treatment. An aluminum oxide film 6 was grown on the surface of 5. After the aluminum oxide film was formed, the electrolyte was removed with distilled water and dried.

In this case, the platinum plating layer 7 becomes the first metal layer 2 of the oscillation element 1, the aluminum plate 5 becomes the second metal layer 4 of the oscillation element, and the aluminum oxide film 6 formed by the anodic oxidation treatment is an n-type semiconductor. became. The characteristics of the oscillation element 1 obtained here were almost the same as those of the p-type semiconductor oscillation element 1.

(Evaluation results)
FIG. 12 shows the result of evaluating the sample element 8 using the evaluation apparatus shown in FIG. The horizontal axis of FIG. 12 indicates the bias voltage (V) applied to the sample element 8, and the vertical axis indicates the current (nA) flowing through the sample element 8.

As shown in FIG. 12, when a forward bias voltage was applied to the sample element 8 (minus side of the horizontal axis), the current flowing through the sample element 8 increased substantially linearly (linearly) with the forward bias voltage. On the other hand, when a reverse bias voltage is applied to the sample element 8 (the positive side of the horizontal axis), a large oscillation is observed in the current flowing through the sample element 8 when the reverse bias voltage is about 0 V to about 0.08 V. It was done. The current generation amplitude was in a wide range of −0.8 μA to 1.1 μA. In the range where the reverse bias voltage is not between about 0 V and about 0.08 V, it increased almost linearly with the reverse bias voltage, as in the case of applying the forward bias voltage.

Here, the average current density of the current flowing through the sample element 8 when the reverse bias voltage is about 0 V to about 0.08 V was calculated. As described above, the contact area between the platinum plating layer 7 and the aluminum oxide film 6 at the tip of the probe 17 is about 730 nm ² , the thickness of the aluminum oxide film 6 is 50 nm, and the electrode expansion ratio of the aluminum plate is about 25 times. Therefore, the contact area was set to 18,000 nm ² .

From FIG. 12, it can be read that when the reverse bias voltage is 0.2 V, the current flowing through the sample element 8 is 0.6 × 10 ⁻⁶ A, so the platinum plating layer 7 and the aluminum plate at the tip of the probe 17 The resistance of the aluminum oxide film 6 between 5 and 5 was 3.3 × 10 ⁵ Ω, and the sheet resistance of the aluminum plate side electrode was 5.9 × 10 ⁻⁵ Ωcm ² . This value can be referred to as the internal resistance of the oscillation element 1. Further, the current density of the current flowing through the sample element 8 when the reverse bias voltage was 0.2 V was calculated to be 3.3 × 10 ³ Acm ⁻² .

On the other hand, when the reverse bias voltage in which current oscillation is observed is applied, for example, when the reverse bias voltage is in the range of about 0 V to about 0.08 V, the flow into the sample element 8 is calculated from the value read from FIG. The effective value of the oscillation current was almost constant 3.2 × 10 ³ Acm ⁻² regardless of the value of the reverse bias voltage. In this bias voltage range, the amplitude of the current is constant regardless of the internal resistance of the element. This is an extremely advantageous characteristic for the application of the inverter, and the current density of 3.2 kA per square cm is extremely large and large. It is expected that the present invention can be applied to power devices that handle current.

The basis for the effective value (3.2 × 10 ³ Acm ⁻² ) of the oscillating current flowing through the sample element 8 is as follows.

In FIG. 12, the peak-to-peak amplitude of the oscillation current is 1.6 μA (−0.8 to 0.8 μA), and its effective value is 1.6 / 2 / √2 = 0.567 μA. Since the contact area is 18,000 nm ² , the current density is 0.567 × 10 ⁻⁶ / 18,000 × 10 ⁻¹⁴ = 3.2 × 10 ³ A / cm ² .

(Observation of current oscillation)
Next, the reverse bias voltage applied to the sample element 8 and the oscillation current flowing through the sample element 8 were observed using an oscilloscope (manufactured by Tektronix). FIG. 13 shows an observation result in a state where an evaluation is performed using the evaluation apparatus shown in FIG. FIG. 13 shows the current flowing through the sample element 8. In FIG. 13, the horizontal axis is 250 μS per square, and the vertical axis is 0.5 μA per square.

In FIG. 13, it was observed that the current flowing through the sample element 8 oscillated in the state where a reverse bias voltage of about 0 V to about 0.08 V was applied. The oscillation frequency was 2 kHz to 3 kHz. In the state where the platinum plating layer 7 at the tip of the probe 17 was separated from the aluminum oxide film 6, no current flowing through the sample element 8 was observed.

<Consideration of current oscillation mechanism>
Next, the mechanism of current oscillation of the oscillation element 1 will be considered. The following mechanism is only a hypothesis, and in order to elucidate the whole mechanism, further research is needed in the future.

First, before entering into consideration of the mechanism of current oscillation, the inventor's knowledge regarding the characteristics of the Schottky junction described above will be described.

When the first metal layer 2 and the tunnel insulating layer 3 are joined, of the holes in the tunnel insulating layer 3 (here, the tunnel insulating layer 3 is a p-type semiconductor), the holes near the junction are the first metal. It diffuses to the layer 2 side, recombines with the electrons of the first metal layer 2, and disappears. For this reason, the hole density of the tunnel insulating layer 3 is remarkably reduced in the vicinity of the junction. As a result, as shown in FIG. 9, a depletion region A in which holes are depleted is generated in the tunnel insulating layer 3. On the other hand, holes still exist in the carrier region B excluding the depletion region A. In FIG. 9, since the switch 13 is off, the forward bias voltage and the reverse bias voltage are applied between the first metal layer 2 and the second metal layer 4 of the oscillation element 1 from the power supply device 14. It is not in a state.

As shown in FIG. 10, when a forward bias voltage is applied from the power supply device 14 between the first metal layer 2 and the second metal layer 4 by turning on the switch 13, tunnel insulation is performed from the first metal layer 2 side. While electrons flow to the layer 3 side, holes flow from the tunnel insulating layer 3 side to the first metal layer 2 side, and the electrons and holes recombine in the vicinity of the junction, whereby a current flows to the oscillation element 1. . By applying a forward bias voltage, electrons are supplied from the first metal layer 2 and holes are supplied from the tunnel insulating layer 3 in the vicinity of the junction, so that the depletion region A shrinks and its thickness decreases or almost disappears. To do.

Actually, in addition to the current of the Schottky junction by the forward bias voltage application of the tunneling current J _t flowing in the same direction is the current of the whole are added.

On the other hand, when a reverse bias voltage is applied from the power supply device 14 between the first metal layer 2 and the second metal layer 4 by turning on the switch 13, as shown in FIG. Are pulled toward the power supply device 14, while holes in the tunnel insulating layer 3 are pulled toward the second metal layer 4. That is, both electrons and holes flow in the opposite direction from the case where the forward bias voltage shown in FIG. 10 is applied. As a result, the recombination of electrons and holes decreases near the junction, so that the current flowing through the oscillation element 1 decreases. Further, since holes are swept out from the vicinity of the junction, the depletion region A is expanded. This depletion region A becomes an insulator due to hole depletion. Further, a small amount of donor (negative charge) is left behind in the depletion region A due to hole depletion, and negative charge accumulates on the second metal layer 4 side of the depletion region A. Further, positive charges accumulate in the first metal layer 2 due to electron deficiency. Thereby, a capacitor in which positive charges and negative charges are accumulated on both sides of the depletion region A is formed.

As described in (Evaluation result) of <Example 2> above, the current oscillation of the sample element 8 was stopped when the reverse bias voltage reached about 0.08V. This stop is thought to be caused by the breakdown phenomenon of the Schottky junction. The breakdown voltage of the Schottky junction is about 0.08 V, which is the voltage at which this breakdown phenomenon occurs. There are two types of breakdown phenomena in Schottky junctions, one is avalanche breakdown and the other is Zener breakdown. The former occurs when the carrier density of the junction is low, and the latter occurs when the carrier density is high. The stop of the current oscillation of the sample element 8 is considered to be caused by avalanche breakdown.

When a reverse bias voltage is applied, at about 0.08V or more of the reverse bias voltage in the example of FIG. 12, only flows tunnel current J _t is.

Next, the mechanism of current oscillation considered by the present inventor will be described.

As described above, when the thickness of the tunnel insulating layer 3 becomes thinner than about 10 nm, a tunnel current flows through the tunnel insulating layer 3. The tunnel current J _t (A) includes the voltage V (V) between the first metal layer 2 and the second metal layer 4, the tunnel resistance R _t (Ω), the tunnel barrier width d (m), and the tunnel barrier height φ ( If eV) is used, the following approximate expression holds.
J _t = V / R _t (1)
However,

Where q is the charge of the electron (1.602 × 10 ⁻¹⁹ C), m is the mass of the electron (9.109 × 10 ⁻³¹ kg), and h is the Planck's constant (6.626 × 10 ⁻³⁴ J · s). ).

As shown in FIGS. 9 to 11, in the oscillation element 1, the aluminum oxide film 6 is divided into two regions, a depletion region A and a carrier region B. If the resistance of the depletion region A is R _dep and the resistance of the carrier region B is R _car ,
R _t = R _dep + R _car (3)
It becomes.

In the depletion region A, since the carrier concentration is low and the tunnel barrier φ is high, R _dep is a large value according to the above equation (2). However, in the carrier region B, since the carrier concentration is high and the tunnel barrier φ is low, the above (2) From the equation, R _car is considered to be a small value. That is,
R _dep >> R _car (4)
It is.

Therefore, the above equation (3) is
R _t _{≈R dep} (5)
It can be. Hereinafter, based on the above equation (5), description will be made using R _dep as the tunnel resistance.

When a forward bias voltage is applied to the oscillation element 1, as described above, the current I12 obtained by adding the tunnel current and the forward current flows from the tunnel insulating layer 3 side to the first metal layer 2 side.

On the other hand, when a reverse bias voltage was applied to the oscillation element 1, current oscillation occurred. The reason was estimated as follows. When the tunnel current J _t passes through the depletion region A, the voltage generated at both ends of the depletion region A is V _dep .
J _t = V _dep / R _dep (6)
Further, when the width of the depletion region A is d _dep , the following can be said.
(A) When a reverse bias voltage is applied to the oscillation element 1, d _dep becomes thick as shown in FIG. As d _dep becomes thicker, V _dep increases and R _dep increases.
(B) When R _dep increases, J _t decreases from the above equation (1).
(C) When J _t decreases, V _dep decreases.
(D) When V _dep decreases, d _dep decreases and R _dep decreases.
(E) When R _dep decreases, J _t increases from the above equation (1).

_That, _{J t} decreases with increase in _{V _dep,} _{J t} is increased by decreasing the _{V dep,} steps are repeated such, it is believed that current oscillation occurs.

<Oscillation frequency>
The oscillation frequency obtained by this evaluation was about 2.5 kHz. The reason for this frequency was estimated, and the oscillation frequency was calculated based on the estimation.

The oscillation frequency f is considered to be f = 1 / τ, which is the reciprocal of the time constant τ = CR.

The capacity of the depletion region A C, when the specific resistance ρ of volume resistivity R _v of the depletion region A,
C = ε ₀ ε _r S / d _dep (7)
R _v = ρd _dep / S (8)
So
f = 1 / C / R _v = 1 / ε ₀ / ε _r /ρ=2.66×10 ³ [Hz] (9)
It was almost the same as the measured value of 2.5 kHz.

Here, ε ₀ is the dielectric constant of vacuum (8.854 × 10 ⁻¹² [F / m]), ε _r is the relative dielectric constant of the aluminum oxide film (estimated as 8.5), and ρ = 5.0 × 10 ⁶ [Ωm] (estimated value of the specific resistance of the aluminum oxide film produced by the anodic oxidation treatment).

The capacity C of the depletion region A is
C = ε ₀ ε _r S / d _dep = 5.4 × 10 ⁻¹⁶ [F]
It becomes. However, d _dep was 2.5 × 10 ⁻⁹ [m] and S = 1.8 × 10 ⁻¹⁴ [m ² ].

There are two ways of thinking about the resistance in the depletion region A. One is the tunnel resistance R _dep and the other is the volume resistivity R _v in the depletion region A.

R _dep is R _dep = 3.3 × 10 ⁵ [Ω] based on an actual measurement value obtained from the slope of the IV measurement straight line shown in FIG. Thus, f is calculated as follows.
f = 1 / C / R _dep = 5.6 × 10 ⁹ [Hz] (10)
For R _v , R _v = ρd _dep / S, so ρ = 5.0 × 10 ⁶ [Ωm], d _dep is 2.5 × 10 ⁻⁹ [m], S = 1.8 × 10 ^{− If 14} [m ² ], then R _v = 6.94 × 10 ¹¹ [Ω]. The calculated value of f is as shown in the above equation (9).

There is a difference of 6 digits between R _dep and R _v, and f calculated by the above equations (9) and (10) is also different by 6 digits. Therefore, the actual oscillation frequency is considered to be determined at R _v. Because determination, substantially coincident with that from the frequencies f calculated using the R _v is measured, and as can be seen from equation (2), the tunnel resistance R _dep is a tunnel barrier width d and the tunnel barrier height φ This is because the value is not affected by ρ.

The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope shown in the claims, and the present invention is also applied to an embodiment obtained by appropriately combining technical means disclosed in the embodiment. It is included in the technical scope of the invention.

The present invention can also be expressed as follows. That is, the oscillation element according to the present invention applies a voltage between the metal layer, the tunnel insulating layer that is Schottky-bonded to the metal layer, and causes a tunnel phenomenon, and the metal layer and the tunnel insulating layer. And applying a voltage in a direction in which the metal layer is reverse-biased with respect to the electrode to reduce a current flowing through the Schottky junction to a predetermined high current density or less, thereby reducing the Schottky junction. Oscillates the flowing current.

According to the above configuration, the oscillation element can be oscillated by setting the current flowing through the Schottky junction between the metal layer and the tunnel insulating layer to a predetermined high current density or less.

Therefore, it is possible to realize an oscillation element that oscillates with a simple element structure including a metal layer, a tunnel insulating layer, and an electrode.

Note that the predetermined high current density is a current density region where the oscillation occurs, which is determined by the configuration of the oscillation element, that is, the material of each of the metal layer and the tunnel insulating layer and the thickness of the tunnel insulating layer. This current density region is a region having a current density much higher than the current density of a current flowing through a general Schottky diode or the like. The current density region can be specified by observing the presence or absence of oscillation while passing a current through the oscillation element and changing the current density.

The tunnel insulating layer is preferably an anodic oxide film formed on the metal layer by an anodic oxidation treatment, an anodic hydroxide film, or a mixed film of an anodic oxide film and an anodic hydroxide film.

The metal layer is an aluminum layer, and the tunnel insulating layer is either an aluminum oxide film covering the surface of the aluminum layer, an aluminum hydroxide film, or a mixed film of an aluminum oxide film and an aluminum hydroxide film. Preferably there is.

The metal layer is a platinum layer, the electrode is an aluminum layer, and the tunnel insulating layer is an aluminum oxide film, an aluminum hydroxide film, or an aluminum oxide film and an aluminum hydroxide film covering the surface of the aluminum layer. It is preferable that it is either a mixed film with a film.

The average current density range of the current region where the current flowing through the Schottky junction oscillates is preferably 7.8 × 10 ⁴ Acm ⁻² or less.

The thickness of the tunnel insulating layer is preferably 0.5 nm or more and 100 nm or less.

The frequency at which the current flowing through the Schottky junction oscillates is preferably 2 kHz or more and 3 kHz or less.

The oscillation device according to the present invention includes the oscillation element and a power supply device that applies a voltage in a direction in which the metal layer is reverse-biased with respect to the electrode.

According to the above configuration, an oscillation device using an oscillation element that oscillates with a simple element structure can be realized.

The present invention relates to an inverter that converts a direct current into an alternating current, an electronic component that oscillates at a specific frequency, for example, a clock signal source in a digital circuit such as a microprocessor, other televisions, videos, electrical equipment, telephones, and copying machines. It is also expected to be used in timing circuits in a wide range of fields such as cameras, speech synthesizers, and communication equipment.

DESCRIPTION OF SYMBOLS 1 Oscillation element 2 1st metal layer 3 Tunnel insulating layer 4 2nd metal layer 5 Aluminum plate 6 Aluminum oxide film 7 Platinum plating layer

Claims

A metal layer,
A tunnel insulating layer that is Schottky-bonded to the metal layer and exhibits a tunnel phenomenon;
An electrode for applying a voltage between the metal layer and the tunnel insulating layer;
Applying a voltage in the direction in which the metal layer is reverse-biased with respect to the electrode to oscillate the current flowing through the Schottky junction by setting the current flowing through the Schottky junction to a predetermined high current density or less An oscillation element characterized by the above.
The tunnel insulating layer is any one of an anodic oxide film, an anodic hydroxide film, or a mixed film of an anodic oxide film and an anodic hydroxide film formed on the metal layer by anodic oxidation. The oscillating device according to claim 1.
The metal layer is an aluminum layer,
3. The tunnel insulating layer is any one of an aluminum oxide film, an aluminum hydroxide film, or a mixed film of an aluminum oxide film and an aluminum hydroxide film covering the surface of the aluminum layer. The oscillation element described.
The metal layer is a platinum layer, the electrode is an aluminum layer,
The tunnel insulating layer is any one of an aluminum oxide film, an aluminum hydroxide film, or a mixed film of an aluminum oxide film and an aluminum hydroxide film covering the surface of the aluminum layer. The oscillation element described.
The oscillation according to any one of claims 1 to 4, wherein an average current density range of a current region in which a current flowing through the Schottky junction oscillates is 7.8 x 10 4 Acm -2 or less. element.
6. The oscillation element according to claim 1, wherein a thickness of the tunnel insulating layer is not less than 0.5 nm and not more than 100 nm.
The oscillation element according to any one of claims 1 to 6, wherein a frequency at which the current flowing through the Schottky junction oscillates is 2 kHz or more and 3 kHz or less.
The oscillation element according to any one of claims 1 to 7,
An oscillation device comprising: a power supply device that applies a voltage in a direction in which the metal layer is reverse-biased with respect to the electrode.