Current sensor and power conversion circuit

Abstract

The present disclosure provides a current sensor and a power conversion circuit. A current sensor includes: an element that is in a high-resistance state when an absolute value of a current flowing between a first terminal and a second terminal is within a first range, and that changes to a low-resistance state having a resistance value lower than the resistance value in the high-resistance state when the absolute value of the current exceeds the first range; and a circuit that supplies a current to be measured to the element and senses a value of the current to be measured based on a voltage of the first terminal and / or the second terminal.

Description

Technical Field

[0001] The present invention relates to a current sensor and a power conversion circuit. Background Art

[0002] A current sensor that senses current by sensing both ends of a resistor through which current flows is known (for example, Non-Patent Document 1). In a detector that detects current using the on-resistance of a field effect transistor (FET), it is known to switch the measurement range by switching the voltage applied to the FET gate (for example, Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-300677

[0006] Non-Patent Documents

[0007] Non-Patent Document 1: Extended Abstracts of the 2019 International Conference on Solid State Devices and Materials, 2019, pp707-708 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] Non-Patent Document 1 is an example, and generally, a current sensor that senses the current flowing through a resistor using a detection value such as a voltage drop between both ends of the resistor is used. In such a current sensor, a resistor with a low resistance is used to reduce the voltage drop and loss when current flows. However, when the resistance is low, the value of the voltage drop becomes small, making it difficult to improve the detection accuracy. In addition, in Patent Document 1, a circuit that switches the voltage applied to the FET gate to switch the measurement range is used, making it difficult to miniaturize the current sensor.

[0010] The present invention has been made in view of the above problems, and a first object thereof is to provide a current sensor that can be miniaturized, reduce losses, and have high detection accuracy.

[0011] A second object of the present invention is to provide a power conversion circuit using the above current sensor.

[0012] Means for Solving the Problem

[0013] According to a specific embodiment of the present invention, a current sensor includes: an element that is in a high-resistance state when the absolute value of the current flowing between a first terminal and a second terminal is within a first range, and that changes to a low-resistance state when the absolute value of the current exceeds the first range, and in the low-resistance state, the resistance value is lower than the resistance value in the high-resistance state; and a circuit that supplies a current to be measured to the element and senses the value of the current to be measured based on at least one of the voltages of the first terminal and the second terminal.

[0014] In the above configuration, the circuit may sense the value of the current based on the difference between the voltages of the first terminal and the second terminal.

[0015] In the above configuration, the circuit may sense the value of the current based on the voltage of the first terminal and a provided reference voltage.

[0016] In the above configuration, the element is a two-terminal element including a resistance element connected between the first terminal and the second terminal.

[0017] In the above configuration, the resistance element may be a resistance element that is in the high-resistance state when the temperature of the resistance element is within a first temperature range, and that changes to the low-resistance state when the temperature of the resistance element is higher than the first temperature range.

[0018] In the above configuration, the resistance element may include VO 2 , NbO 2 or Ti 2 O 3 .

[0019] In the above configuration, the element may include a first element and a second element connected in parallel between the first end and the second end. When the current flowing from the first end to the second end is equal to or less than a threshold current, each of the first element and the second element enters the high-resistance state without external control, and when the current flowing from the first end to the second end is greater than the threshold current, each of the first element and the second element enters the low-resistance state without external control. The first end of the first element may be connected to the first terminal, the second end of the first element may be connected to the second terminal, the first end of the second element may be connected to the second terminal, and the second end of the second element may be connected to the first terminal.

[0020] According to a specific embodiment of the present invention, a current sensor includes: an element or circuit that enters a high-resistance state without external control when the absolute value of the current flowing between a first terminal and a second terminal is within a first range, and enters a low-resistance state without external control when the absolute value of the current is within a second range higher than the first range, and in the low-resistance state, the resistance value is lower than that in the high-resistance state, wherein the current sensor senses the current.

[0021] According to a specific embodiment of the present invention, a power conversion circuit includes: a switching unit; and a control unit that controls the turning on and off of the switching unit based on the output of the above current sensor.

[0022] In the above configuration, the switching unit may include: a first switching unit connected between a first terminal and a second terminal, a second switching unit connected between a third terminal and a fourth terminal, a third switching unit connected between the first terminal and the fourth terminal, and a fourth switching unit connected between the second terminal and the third terminal, and the element may be coupled to one of the following positions: between the first terminal and the first and third switching units, and between the second terminal and the first and fourth switching units, and the control unit may change the first and second switching units from off to on and change the third and fourth switching units from on to off based on the change in the sign of the current, and may change the first and second switching units from on to off and change the third and fourth switching units from off to on based on the next change in the sign of the current.

[0023] Effects of the present invention

[0024] The present invention can provide a current sensor that can be miniaturized, reduce losses, and has high detection accuracy. In addition, a power conversion circuit using the above current sensor can be provided. Description of the drawings

[0025] Figure 1 Figure 1 (a) is a graph of the electrical conductivity of vanadium dioxide versus temperature, Figure 1 (b) illustrates an element using vanadium dioxide as a resistive element, Figure 1 (c) is a graph of voltage V versus current I (logarithmic representation) in an element using vanadium dioxide;

[0026] Figure 2 ​​​​Figure 2 FIG. (a) is a plan view of an element according to the first embodiment; Figure 2 FIG. (b) is a sectional view taken along line A-A in Figure 2 FIG. (a);

[0027] Figure 3 Figure 3 is a graph of voltage versus current in the element under test;

[0028] Figure 4 Figure 4 FIG. (a) and Figure 4 FIG. (b) are circuit diagrams of a current sensor according to the first embodiment;

[0029] Figure 5 Figure 5 is a timing diagram of the current sensor according to the first embodiment;

[0030] Figure 6 Figure 6 FIG. (a) is a circuit diagram of a current sensor according to the first comparative example; Figure 6 FIG. (b) is a schematic diagram illustrating the voltage difference ΔV with respect to the current Iin in the first embodiment and the first comparative example;

[0031] Figure 7 Figure 7 FIG. (a) and Figure 7 FIG. (b) are circuit diagrams of a current sensor according to the first modification of the first embodiment;

[0032] Figure 8 Figure 8 is a timing diagram of the current sensor according to the first modification of the first embodiment;

[0033] Figure 9 Figure 9 is a circuit diagram of a current sensor according to the second modification of the first embodiment;

[0034] Figure 10 Figure 10 is a timing diagram of the current sensor according to the second modification of the first embodiment;

[0035] Figure 11 Figure 11 is a circuit diagram illustrating a synchronous rectifier circuit according to the second embodiment;

[0036] Figure 12 Figure 12 is a timing diagram of the synchronous rectifier circuit according to the second embodiment;

[0037] Figure 13 Figure 13 ​​​​​​​​​​​​​​​​​​​​​​Is the circuit diagram of the synchronous rectifier circuit according to the first variant of the second embodiment;

[0038] Figure 14 Figure 14 Is the timing diagram of the synchronous rectifier circuit according to the first variant of the second embodiment;

[0039] Figure 15 Figure 15 of (a) to Figure 15 of (c) schematically illustrates the buck circuit in the second variant of the second embodiment;

[0040] Figure 16 Figure 16 of (a) is the circuit diagram of the buck circuit in the second variant of the second embodiment, Figure 16 of (b) illustrates the flip-flop circuit;

[0041] Figure 17 Figure 17 Is the timing diagram of the voltage and current of each node of the buck circuit in the second variant of the second embodiment;

[0042] Figure 18 Figure 18 of (a) to Figure 18 of (d) is an example of a cross-sectional view of a method of manufacturing the components illustrated in Figure 2 of (a) and Figure 2 of (b);

[0043] Figure 19 Figure 19 Is a plan view illustrating the transistor used in the third embodiment;

[0044] Figure 20 Figure 20 of (a) is a circuit diagram illustrating an example of the connection of the transistor in the third embodiment, and Figure 20 of (b) schematically illustrates the current with respect to the voltage;

[0045] Figure 21 Figure 21 of (a) illustrates the structure of the component 30 used in the third embodiment, Figure 21 of (b) schematically illustrates the current with respect to the voltage; and

[0046] Figure 22 Figure 22 Is a block diagram of a system of a power conversion circuit using the second embodiment and its variants. Detailed Description

[0047] Hereinafter, embodiments will be described with reference to the drawings.​​​​​​​​​​​​​​​​​​

[0048] The first embodiment

[0049] Vanadium dioxide (VO 2 ) will be described as an example of an element used in the first embodiment. Figure 1 FIG. (a) is a graph showing the relationship between the conductivity of vanadium dioxide and temperature.

[0050] As Figure 1 illustrated in FIG. (a), as the temperature increases, the conductivity of vanadium dioxide increases. In Figure 1 the example of FIG. (a), when the temperature exceeds 30 °C, the conductivity increases rapidly. At 30 °C or below 30 °C, the conductivity is low. This is because vanadium dioxide is in a tetragonal metal phase at high temperatures but in a monoclinic insulator phase at low temperatures.

[0051] Figure 1 FIG. (b) illustrates an element using vanadium dioxide as a resistance element. In element 10, resistance element 14 is connected between electrodes 16a and 16b. The current flowing through resistance element 14 is represented by I, and the voltage V between electrodes 16a and 16b is represented by V.

[0052] Figure 1 FIG. (c) is a graph of voltage V against current I (logarithmic representation) in an element using vanadium dioxide. As Figure 1 illustrated in FIG. (c), in the range 50 where the current I is less than the threshold current Ith, the temperature of resistance element 14 is low, and vanadium dioxide is in the insulator phase. Therefore, resistance element 14 is in a high-resistance state, where resistance element 14 has a high resistance. Thus, when the current I increases, the voltage V increases. When the current I increases, the temperature of resistance element 14 increases. When the current I becomes the threshold current Ith, the temperature of vanadium dioxide becomes the temperature at which a phase change from the insulator phase to the metal phase occurs. Therefore, in the range 52 where the current I is equal to or greater than the threshold current Ith, resistance element 14 is in a low-resistance state. Thus, even when the current increases, the voltage is approximately 0. A resistance element having a hysteresis characteristic in the current-voltage characteristics can be used. That is, the threshold current Ith when the current I increases and the threshold current Ith when the current I decreases can be different.

[0053] Figure 2 FIG. (a) is a plan view of an element according to the first embodiment, Figure 2 FIG. (b) is a cross-sectional view taken along line A-A in Figure 2 FIG. (a). As Figure 2 illustrated in FIGS. (a) and Figure 2As illustrated in (b) of, element 10 includes a substrate 12, a resistive element 14, and electrodes 16a and 16b. A thin film 15 made of the resistive element 14 is formed on the substrate 12. Electrodes 16a and 16b are formed on respective ends of the resistive element 14. The resistive element 14 includes an active portion 14a and lead portions 14b. The length of the active portion 14a in the current flow direction is represented by L, and the width is represented by W. The lead portions 14b electrically connect the active portion 14a to the respective electrodes 16a and 16b. The width of each lead portion 14b gradually increases from the active portion 14a toward the electrodes 16a and 16b. The voltage between the electrodes 16a and 16b is mainly concentrated in the active portion 14a. Therefore, the resistance change of the element 10 is mainly the resistance change of the active portion 14a.

[0054] The substrate 12 is an insulating substrate, such as a silicon (Si) substrate having silicon oxide (SiO 2 ) provided on its upper surface, a titanium oxide (TiO 2 ) substrate, or an aluminum oxide (Al 2 O 3 ) substrate. The substrate 12 can be any substrate as long as it can form the resistive element 14 with desired characteristics. The resistive element 14 is a vanadium dioxide (VO 2 ) thin film. The electrodes 16 are formed of a metal, such as a gold (Au) layer, a copper (Cu) layer, or an aluminum (Al) layer.

[0055] To prevent heat from being released from the resistive element 14 to the substrate 12, a low thermal conductivity layer having a lower thermal conductivity than the substrate 12 can be provided between the substrate 12 and the resistive element 14. For example, an amorphous layer (such as amorphous SiO 2 ) or a porous layer is used as the low thermal conductivity layer. By appropriately designing the materials of the substrate 12 and the low thermal conductivity layer and the length L, width W, and thickness T of the active portion 14a, the threshold current Ith can be adjusted to a desired value.

[0056] Element 10 is manufactured to measure the current-voltage characteristics. The substrate 12 is a single crystal TiO 2 substrate having (101) as the main surface. The resistive element 14 is a VO 2 film formed using a pulsed laser deposition method. The length L, width W, and thickness T of the active portion 14a are adjusted to 10 μm, 40 μm, and 90 nm, respectively. The electrodes 16a and 16b are gold layers.

[0057] Figure 3 is a graph of voltage versus current in the element under test. The current I is increased, and the voltage V is measured. As Figure 3As illustrated, in the range 50 of a minute current where the current I is equal to or less than the threshold current Ith, the element 10 is in a high-resistance state, and as the current I increases, the voltage V increases. In the range 52 where the current I is equal to or greater than the threshold current Ith, the voltage V is low, and the element 10 is in a low-resistance state. As can be seen from the above, the same current-voltage characteristics as those in Figure 1 (c) are obtained in the manufactured element 10. Additionally, the threshold current Ith can be made 1 μA or less. At a minute current where the current I is 1 μA or less, the voltage V can be made several volts. The threshold current Ith and the value of the voltage V at the threshold current Ith can be adjusted by changing the length L and the width W of the above-described active portion 14a.

[0058] Figure 4 (a) and Figure 4 (b) of are circuit diagrams of a current sensor according to the first embodiment. As Figure 4 illustrated in (a), the element 10 is connected between the terminals T1 and T2. The current Iin flows in the terminal T1. The detector 20 detects the current Iin based on the voltage of the node N1 between the electrode 16a of the element 10 and the terminal T1 and the voltage of the node N2 between the electrode 16b of the element 10 and the terminal T2. The detector 20 is, for example, a differential amplifier circuit, and outputs the voltage difference ΔV between the nodes N1 and N2 as information Inf regarding the current Iin. The voltage difference ΔV is substantially proportional to the current Iin.

[0059] As Figure 4 illustrated in (b), the detector 20 can be a comparator 22. The comparator 22 outputs a high level when the voltage of the node N1 is higher than the voltage of the node N2, and outputs a low level when the voltage of the node N1 is lower than the voltage of the node N2.

[0060] Figure 5 is a timing diagram of a current sensor according to the first embodiment. The current Iin represents the value of the current input to the terminal T1. The resistance state R represents the low-resistance state RL and the high-resistance state RH of the element 10. The voltage difference ΔV represents Figure 4 the input voltage difference of the detector 20 in (a). The voltage Vout represents Figure 4 the output of the comparator 22 in (b). It is assumed that there is no hysteresis in the threshold current Ith, and it is assumed that the absolute value of the threshold current Ith when the current Iin is positive and the absolute value of the threshold current -Ith when the current Iin is negative are the same. The range between the threshold current Ith and -Ith corresponds to the range 50, and the range above the threshold current Ith and the range below the threshold current -Ith correspond to the range 52.

[0061] As Figure 5As illustrated, before time t1, the current Iin is negative and less than the threshold current - Ith. The element 10 is in the low-resistance state RL, the voltage difference ΔV is negative and approximately equal to 0V, and the voltage Vout is at a low level. When the current Iin becomes the threshold current - Ith at time t1, the resistance state R switches to the high-resistance state RH. The voltage difference ΔV becomes a negative value corresponding to the current Iin. Since the voltage of node N1 is lower than the voltage of node N2, the voltage Vout remains at the low level.

[0062] As the current Iin increases in the period from time t1 to time t2, ΔV increases. The voltage Vout remains at the low level. At time t2, the current Iin becomes 0 and the voltage difference ΔV becomes 0. After time t2, the voltage Vout switches from the low level to the high level.

[0063] As the current Iin increases in the period from time t2 to time t3, the voltage difference ΔV increases and the voltage Vout remains at the high level. When the current Iin becomes the threshold current Ith at time t3, the resistance state R switches to the low-resistance state RL. The voltage difference ΔV becomes a positive value approximately equal to 0V. The voltage Vout remains at the high level.

[0064] At time t4, the current Iin switches from increasing to decreasing. In the period from time t3 to time t5, the current Iin is greater than the threshold current Ith, the resistance state R is the low-resistance state RL, the voltage difference ΔV is approximately 0V (a small positive value), slightly increases with time in the period from time t3 to time t4, and slightly decreases with time in the period from time t4 to time t5.

[0065] At time t5, the current Iin becomes the threshold current Ith, at time t6, the current Iin becomes 0, and at time t7, the current Iin becomes the threshold current - Ith. In the period from time t5 to time t6, the resistance state R is the high-resistance state RH, the voltage difference ΔV is a positive value corresponding to the current Iin, and the voltage Vout is at the high level. In the period from time t6 to time t7, the resistance state R is the high-resistance state RH, the voltage difference ΔV is a negative value corresponding to the current Iin, and the voltage Vout is at the low level. At and after time t7, the resistance state R is the low-resistance state RL, the voltage difference ΔV is a negative value approximately equal to 0V, and the voltage Vout remains at the low level.

[0066] The current sensor of the first embodiment senses the current Iin within the range 50 where the current Iin flowing through the element 10 is approximately 0. In the range 52, the element 10 enters the low-resistance state and does not sense the current.

[0067] [First Comparative Example]

[0068] Figure 6 (a) is a circuit diagram of a current sensor according to a first comparative example. As Figure 6 illustrated in (a), the difference between the first comparative example and the Figure 4 elements of the first embodiment illustrated in (a) is that a resistor 11 is connected between terminals T1 and T2 instead of element 10. Other structures are the same as those of the first embodiment, and thus their descriptions are omitted.

[0069] Figure 6 (b) schematically illustrates the voltage difference with respect to current in the first embodiment and the first comparative example. As Figure 6 illustrated in (b), in the first comparative example, the resistance value of the resistor 11 is set low. This is because when the resistance value of the resistor 11 is high, in the range 52 where the current Iin is large, the voltage drop caused by the resistor 11 becomes large, and the loss caused by Joule heat and the like becomes large. However, in the range 50 where the current is small, the voltage difference ΔV between nodes N1 and N2 is small. This reduces the detection accuracy of the detector 20. To improve the detection accuracy, it is conceivable to use an amplifier circuit that amplifies the voltage difference ΔV between nodes N1 and N2. However, providing an amplifier circuit increases the size and cost of the current sensor. In addition, the power consumption of the current sensor increases.

[0070] In the case of sensing a minute current but not requiring sensing of a large current, the use of the current sensor of the first comparative example makes it difficult to achieve improvement in the detection accuracy of the minute current and reduction of the loss of the large current.

[0071] In the first embodiment, a circuit including the detector 20 or the comparator 22 supplies the current Iin to be measured to the element 10 to sense the value of the current Iin to be measured. When the absolute value of the current Iin (the value of the current) flowing between the electrode 16a (the first end) and the electrode 16b (the second end) is within the range 50 (the first range) (the absolute value of the current Iin is less than the threshold current Ith), the element 10 enters a high-resistance state without being controlled from the outside (for example, an external circuit). For example, when the absolute value of the current Iin is below the threshold current Ith, the element 10 enters a high-resistance state. Thereby, the voltage difference ΔV increases within the range 50. Therefore, the current Iin can be detected with high accuracy without using an amplifier circuit. For example, in Figure 3 , when the current I is 10 nA, the voltage V is approximately 0.1 V, and the current can be detected with high accuracy. For example, the power consumption of the comparator 22 is generally less than that of an amplifier circuit. Therefore, the power consumption of the current sensor can be reduced.

[0072] When the absolute value of the current Iin is within a range 52 (second range) greater than the range 50, the element 10 is in a low-resistance state where the resistance value is lower than the resistance value in the high-resistance state without external control. More specifically, when the absolute value of the current Iin reaches the range 52 (second range) exceeding the range 50, the element 10 changes to a low-resistance state where the resistance value is lower than the resistance value in the high-resistance state. Therefore, in the range 52, the voltage drop caused by the element 10 can be reduced, and the loss caused by Joule heat or the like can be reduced. For example, in Figure 3 when a current I greater than the threshold current Ith flows, the voltage is approximately 1V, and the loss can be reduced. The resistance value of the element 10 in the high-resistance state is preferably equal to or greater than 10 times the resistance value of the element 10 in the low-resistance state, and more preferably equal to or greater than 100 times the resistance value of the element 10 in the low-resistance state. In addition, different from Patent Document 1, since a circuit for switching the resistance state is not required, the current sensor can be miniaturized.

[0073] [First Variant Example of the First Embodiment]

[0074] Figure 7 of (a) and Figure 7 of (b) are circuit diagrams of a current sensor according to the first variant example of the first embodiment. As Figure 7 illustrated in (a) of, the element 10 is connected between the terminal T1 and the ground. The current Iin flows in the terminal T1. The detector 20 detects the current Iin based on the voltage at the node N1 between the electrode 16a of the element 10 and the terminal T1 and the reference voltage Vref. The detector 20 is, for example, a differential amplifier circuit, and outputs the voltage difference ΔV between the voltage at the node N1 and the voltage of the reference voltage Vref as the information Inf of the current Iin.

[0075] As Figure 7 illustrated in (b) of, the detector 20 can be a comparator 22. The comparator 22 outputs a high level when the voltage at the node N1 is higher than the reference voltage Vref, and outputs a low level when the voltage at the node N1 is lower than the reference voltage Vref.

[0076] Figure 8 is a timing diagram of a current sensor according to the first variant example of the first embodiment. The voltage difference ΔV represents Figure 7 the output voltage of the detector 20 in (a) of. The voltage Vout represents Figure 7 the output of the comparator 22 in (b) of. As Figure 8As illustrated, at time t11, the current Iin is 0, the element 10 is in the high-resistance state RH, the voltage difference ΔV is approximately 0V, and the voltage Vout is at a low level. In the period from time t11 to time t12, the current Iin increases and the voltage difference ΔV rises. When the voltage difference ΔV becomes the reference voltage Vref at time t12, the voltage Vout becomes a high level. The current Iin at this time is the reference current Iref.

[0077] As the current Iin increases in the period between time t12 and time t13, the voltage difference ΔV increases. When the current Iin becomes the threshold current Ith at time t13, the resistance state R switches to the low-resistance state RL. The voltage difference ΔV becomes a positive value approximately 0V. The voltage Vout remains at a high level.

[0078] At time t14, the current Iin switches from increasing to decreasing. In the period between time t13 and time t15, the current Iin is greater than the threshold current Ith, the resistance state R is the low-resistance state RL, the voltage difference ΔV is approximately 0V (a small positive value), slightly increases with time in the period from time t13 to time t14, and slightly decreases with time in the period from time t14 to time t15.

[0079] At time t15, the current Iin becomes the threshold current Ith, at time t16, the voltage difference ΔV becomes the reference voltage Vref, and at time t17, the current Iin becomes 0. In the period from time t15 to time t16, the resistance state R is the high-resistance state RH, the voltage difference ΔV is a value corresponding to the current Iin, and the voltage Vout is at a high level. In the period between time t16 and time t17, the resistance state R is the high-resistance state RH, the voltage difference ΔV is a value corresponding to the current Iin, and the voltage Vout is at a low level.

[0080] The current sensor of the first modification of the first embodiment detects the current Iin in the current sensor detection range 50 (where the current Iin flowing through the element 10 is approximately 0). In the range 52, the element 10 enters the low-resistance state and the current is not detected. Therefore, the current can be sensed with high precision within the range 50, while losses are reduced within the range 52. In addition, in Figure 7 the current sensor illustrated in (b) of, it is possible to determine whether the current Iin is above or below the reference current Iref.

[0081] As in the first embodiment, the detector 20 can sense the current Iin based on the voltage difference ΔV between the electrodes 16a and 16b. As in the first variant of the first embodiment, the detector 20 can sense the current Iin based on the voltage of the electrode 16a and the provided reference voltage Vref. As described above, the detector 20 senses the current Iin based on the voltage value of at least one of the electrodes 16a and 16b. In addition, the sensing of the current Iin includes, for example, measuring the current Iin and determining whether the current Iin is above or below the desired current value.

[0082] [Second Variant of the First Embodiment]

[0083] The second variant of the first embodiment is an example of a current sensor that converts the current flowing through the element 10 into the period (frequency) of a pulse signal. Figure 9 is a circuit diagram of a current sensor according to the second variant of the first embodiment. As Figure 9 illustrated, the element 10 is connected between the terminal T1 and the ground. The circuit described in Non-Patent Document 1 is used as the detector 20a. The detector 20a includes resistors R1 and R2, switches S1 and S2, a differential integration circuit 24, and a hysteresis determination device 26. The node N1 between the terminal T1 and the electrode 16a of the element 10 is connected to the node N3 through the switch S1, and the node N2 between the ground and the electrode 16b of the element 10 is connected to the node N3 through the switch S2. Between the nodes N1 and N2, the resistors R1 and R2 are connected in parallel with the element 10. The voltage of the node N4 is the voltage obtained by dividing the voltage between the nodes N1 and N2 by the resistors R1 and R2.

[0084] The differential integration circuit 24 integrates the difference between the voltage of the node N3 and the voltage of the node N4, and outputs the voltage Vo. When the voltage Vo becomes above the reference voltage VrefH, the hysteresis determination device 26 sets the control signals FC1 and FC2 to low level and high level, respectively, and holds the control signals FC1 and FC2 until the voltage Vo becomes below the reference voltage VrefL. When the voltage Vo becomes below the reference voltage VrefL, the hysteresis determination device 26 sets the control signals FC1 and FC2 to high level and low level, respectively, and holds FC1 and FC2 until the voltage Vo becomes above the reference voltage VrefH. The control signals FC1 and FC2 are signals for controlling the switches S1 and S2, respectively. During the period when the control signals FC1 and FC2 are at high level, the switches S1 and S2 are on, and during the period when the control signals FC1 and FC2 are at low level, the switches S1 and S2 are off.

[0085] A description will be given of the case where the current Iin is small and the element 10 is in a high-resistance state. Figure 10This is the timing diagram of the current sensor in the second variant of the first embodiment. Before time t21, the control signals FC1 and FC2 are at high level and low level respectively, and the switches S1 and S2 are on and off respectively. Node N3 is connected to node N1 but is disconnected from node N2. As a result, the voltage difference between nodes N3 and N4 becomes positive, and the voltage Vo increases.

[0086] When the voltage Vo becomes the reference voltage VrefH at time t21, FC1 and FC2 become low level and high level respectively. The switches S1 and S2 are turned off and on respectively. Node N3 is disconnected from node N1 and connected to node N2. As a result, the voltage difference between nodes N3 and N4 becomes negative, and the voltage Vo decreases.

[0087] When the voltage Vo becomes the reference voltage VrefL at time t22, FC1 and FC2 become high level and low level respectively, and the voltage Vo increases. Thereafter, the above steps are repeated.

[0088] When the voltage difference between nodes N1 and N2 is small, the period P of the control signals FC1 and FC2 becomes longer, and when the voltage difference between nodes N1 and N2 is large, the period P of the control signals FC1 and FC2 becomes shorter. When the element 10 is in the high-resistance state, the detector 20a outputs the amplitude of the current Iin as the period (frequency) of the control signal FC1.

[0089] When the current Iin is equal to or greater than the threshold current Ith, the element 10 enters the low-resistance state. Therefore, the voltage difference between nodes N1 and N2 becomes substantially 0V, and the period P of the control signals FC1 and FC2 becomes very long.

[0090] As can be seen from the above, in the range of small currents, the current can be converted into a period with high precision and output, while in the range of large currents, the loss can be reduced. As in the second variant of the first embodiment, the detector 20a can output the current Iin instead of the voltage as information. The current sensing of the current sensor includes the case where the current Iin is output as information instead of the voltage.

[0091] The first embodiment and its variants use the resistive element 14 that undergoes a phase change, such that when the temperature of the resistive element 14 is within the first temperature range, the element 10 enters the high-resistance state, and when the temperature of the resistive element 14 is within the second temperature range higher than the first temperature range, the element 10 enters the low-resistance state. Instead of vanadium dioxide (VO 2 ), it is niobium oxide (NbO 2 ) or titanium oxide (Ti 2 O 3) can be used as such a resistance element 14. In vanadium dioxide, the phase transition temperature during the switching between the high-resistance state and the low-resistance state is about 30°C to 70°C. In niobium oxide, the phase transition temperature is about 840°C. In titanium oxide, the phase transition temperature is about 130°C to 330°C. The resistance element 14 can be made of a material different from the above materials. In addition, impurities can be added to the above materials. For example, adding W to VO 2 lowers the phase transition temperature, while adding Al, Cr, or Ge raises the phase transition temperature. The addition of Ti little changes the phase transition temperature.

[0092] The resistance element 14 can switch between the high-resistance state and the low-resistance state through a mechanism different from temperature phase transition. For example, when an electrochemical filament is formed between the electrodes, the resistance element 14 can enter the low-resistance state, and when the filament is cut off, the resistance element 14 can enter the high-resistance state. The resistance element 14 can be a copper compound, a chalcogenide, tungsten oxide, or an amorphous oxide. The current-voltage characteristics of the element 10 can have hysteresis, but when the absolute value of the current is 0, the element 10 enters the high-resistance state.

[0093] Second Embodiment

[0094] The second embodiment and its modified examples are examples in which a current sensor according to any one of the first embodiment and its modified examples is used in a power conversion circuit. The second embodiment and its first modified example are exemplary synchronous rectifier circuits, and the second modified example of the second embodiment is an exemplary buck circuit (DC-DC converter). For example, in an energy harvesting device such as vibration power generation that uses the vibration energy of a bridge to generate electricity, a small amount of power is generated.

[0095] The current sensor used in a power conversion circuit for converting the power generated by such a generator needs to be able to detect a minute current. It is also necessary to reduce the loss caused by the current sensor.

[0096] Figure 11 is a circuit diagram of the synchronous rectifier circuit according to the second embodiment. As Figure 11 illustrated, the switch SW1 (first switch unit) is connected between the terminal T01 (first terminal) and T02 (second terminal), the switch SW2 (second switch unit) is connected between the terminal T03 (third terminal) and T04 (fourth terminal), the switch SW3 (third switch unit) is connected between the terminal T01 and the terminal T04, and the switch SW4 (fourth switch unit) is connected between the terminal T03 and the terminal T02. The switch SW1 and SW3 are connected at the node NO1, the switch SW1 and SW4 are connected at the node NO2, the switch SW2 and SW4 are connected at the node NO3, and the switch SW2 and SW3 are connected at the node NO4.

[0097] The current sensor 21 includes an element 10 and a detector 20. The element 10 is connected between a terminal T01 and a node N01. The node between the terminal T01 and the electrode 16a of the element 10 is the node N1, and the node between the node N01 and the electrode 16b of the element 10 is the node N2. The detector 20 outputs the voltage difference ΔV between the nodes N1 and N2. The control unit 28 outputs a control signal CT1 to the switches SW1 and SW2 based on the voltage difference ΔV, and outputs a control signal CT2 to the switches SW3 and SW4.

[0098] Figure 12 is a timing diagram of the synchronous rectifier circuit according to the second embodiment. The current input to the terminal T01 is represented by the current Iin, and the current output from the terminal T02 is represented by the current Iout. A current equal to the current Iin is output from the terminal T03, and a current equal to the current Iout is output to the terminal T04. An alternating current is input between the terminal T01 and the terminal T03, and a rectified current is output between the terminals T02 and T04. The current Iin corresponds to, for example, the electric power generated by an energy harvesting device.

[0099] In energy harvesting, the waveform of the current is not always a trigonometric function, but in Figure 12 for the sake of convenience, the waveform of the current Iin is described as a trigonometric function. As Figure 12 illustrated, before the time t31, the current Iin is negative and the current Iin is less than the threshold current -Ith. The element 10 is in a low resistance state, and the voltage difference ΔV is approximately 0V. The switches SW1 and SW2 are off, and the switches SW3 and SW4 are on. The terminal T01 is connected to the terminal T04, and the terminal T03 is connected to the terminal T02. The current input to the terminal T01 is output from the terminal T04. The sign of the current Iout output from the terminal T02 is opposite to the sign of the current Iin, that is, positive.

[0100] At the time t31, the current Iin becomes greater than the threshold current -Ith. The element 10 enters a high resistance state, and the voltage difference ΔV becomes a value corresponding to the current Iin. At the time t32, the current Iin becomes 0. The voltage difference ΔV becomes 0V. The current Iout becomes substantially 0. At the time t34, the current Iin becomes greater than the threshold current Ith. The element 10 enters a low resistance state, and the voltage difference ΔV becomes substantially 0V.

[0101] The control unit 28 determines that the voltage difference ΔV changes from negative to positive at a certain point between the time t31 and the time t34. At Figure 12In this case, the control unit 28 determines that the voltage difference ΔV changes from negative to positive at time t33, switches the switches SW1 and SW2 from off to on, and switches the switches SW3 and SW4 from on to off. The terminal T01 is connected to the terminal T02, and the terminal T03 is connected to the terminal T04. The current input to the terminal T01 is output from the terminal T02. The sign of the current Iout output from the terminal T02 is the same as the sign of the current Iin, that is, positive.

[0102] In the period between time t34 and time t35, the current Iin is greater than the threshold current Ith. Therefore, the voltage difference ΔV is approximately 0 V (a small positive value), slightly increases with time, and then slightly decreases with time. The switches SW1 and SW2 remain in the on state, while the switches SW3 and SW4 remain in the off state. The current Iout is positive.

[0103] At time t35, the current Iin becomes less than the threshold current Ith. The element 10 enters the high-resistance state, and the voltage difference ΔV becomes a value corresponding to the current Iin. At time t36, the current Iin becomes 0, and at time t38, the current Iin becomes less than the threshold current -Ith. The element 10 enters the low-resistance state, and the voltage difference ΔV becomes substantially 0 V.

[0104] The control unit 28 determines that the voltage difference ΔV changes from positive to negative at some point between time t35 and time t38. In Figure 12 this case, the control unit 28 determines that the voltage difference ΔV changes from positive to negative at time t37, switches the switches SW1 and SW2 from on to off, and switches the switches SW3 and SW4 from off to on. The terminal T01 is connected to the terminal T04, and the terminal T03 is connected to the terminal T02. The current input to the terminal T01 is output from the terminal T04. The sign of the current Iout output from the terminal T04 is opposite to the sign of the current Iin, that is, positive. As described above, the current Iin input from the terminal T01 is half-wave rectified and then output from the terminal T02.

[0105] In the second embodiment, the control unit 28 changes the switches SW1 and SW2 from off to on and the switches SW3 and SW4 from on to off based on the change of the current Iin from negative to positive, and changes the switches SW1 and SW2 from on to off and the switches SW3 and SW4 from off to on based on the change of the current Iin from positive to negative. As described above, the switching of the sign of the current Iin is determined to switch the switches SW1 to SW4, so as to substantially maintain the state where the current Iout is positive. In other words, the control unit 28 and the switches SW1 to SW4 function as a rectifier. The current sensor can sense the current Iin with high precision in the range 50 where the absolute value of the current Iin is small. In the range 52 where the absolute value of the current Iin is large, the element 10 enters the low-resistance state, so that the loss caused by the element 10 can be reduced.

[0106] [First Variant Example of the Second Embodiment]

[0107] Figure 13 is a circuit diagram of a synchronous rectification circuit according to the first variant example of the second embodiment. As Figure 13 illustrated, the current sensor 21 is connected between the node NO2 and the terminal TO2. In the second embodiment, the current sensor 21 senses the current Iin before rectification, while in the first variant example of the second embodiment, the current sensor 21 senses the current Iin after rectification. The other structures are the same as those of the second embodiment Figure 11 illustrated, so the description thereof is omitted.

[0108] Figure 14 is a timing diagram of the synchronous rectification circuit according to the first variant example of the second embodiment. As Figure 14 illustrated, before the time t31, the switches SW1 and SW2 are off, the switches SW3 and SW4 are on, and the sign of the current Iout is opposite to that of the current Iin. When the current Iout becomes the threshold current Ith at the time t31, the element 10 enters the high-resistance state. The voltage difference ΔV becomes a positive value corresponding to the current Iout. At the time t32, the current Iout becomes 0 and ΔV becomes 0. The control unit 28 determines that the voltage difference ΔV changes from positive to negative at the time t33, switches the switches SW1 and SW2 from off to on, and switches the switches SW3 and SW4 from on to off. As a result, the sign of the current Iout is the same as the sign of the current Iin, and the voltage difference ΔV changes from negative to positive. At the time t34, the current Iout becomes the threshold current Ith, and the element 10 enters the low-resistance state.

[0109] The period from the time t35 to the time t38 is the same as the period from the time t31 to the time t34. The control unit 28 determines that the voltage difference ΔV changes from positive to negative at the time t37, switches the switches SW1 and SW2 from on to off, and switches the switches SW3 and SW4 from off to on. As a result, the sign of the current Iout is opposite to the sign of the current Iin, and the voltage difference ΔV changes from negative to positive. The other timings are the same as those of the second embodiment Figure 12 illustrated, so the description thereof is omitted.

[0110] In the first modification of the second embodiment, the current sensor 21 senses the rectified current Iout. In this case, the control unit 28 changes the switches SW1 and SW2 from off to on and the switches SW3 and SW4 from on to off based on the change of the current Iout from positive to negative, and changes the switches SW1 and SW2 from on to off and the switches SW3 and SW4 from off to on based on the next change of the current Iout from positive to negative. As described above, the switching of the sign of the current Iout is determined to switch the switches SW1 to SW4. This allows the current sensor 21 to sense the current Iout with high precision in the range 50 where the absolute value of the current Iout is small. In the range 52 where the absolute value of the current Iout is large, the element 10 enters the low-resistance state, so that the loss caused by the element 10 can be reduced.

[0111] As in the second embodiment and its first modification, it is only required that the element 10 be connected to one of the following positions: between the terminal T1 and the switches SW1 and SW3, and between the terminal T2 and the switches SW1 and SW4. In addition, it is only necessary for the control unit 28 to change the switches SW1 and SW2 from off to on and the switches SW3 and SW4 from on to off based on the change of the sign of the current Iin or Iout, and change the switches SW1 and SW2 from on to off and the switches SW3 and SW4 from off to on based on the next change of the sign of the current Iin or Iout.

[0112] [Second modification of the second embodiment]

[0113] Figure 15 of (a) to Figure 15 of (c) are schematic diagrams of the step-down circuit according to the second modification of the second embodiment. As Figure 15 illustrated in (a) of, the current I1 is input to the node A. The capacitor C1 and the PFET (field effect transistor) M4 are connected between the node A and the ground. The capacitor C1 is the primary capacitor. The PFET M4 is a switch. The inductor L1 and the capacitor C4 are connected in series between the node A and the ground. The capacitor C4 is the secondary capacitor. The NFET M3 is connected as a switch between the inductor L1 and the capacitor C4. The NFET M2 is connected as a switch between the node between the capacitor C1 and the inductor L1 and the ground.

[0114] The capacitance values of the capacitors C1 and C4 are adjusted to 100 pF and 10 nF respectively, and the inductance of the inductor L1 is adjusted to 0.3 nH. These values are set so that the voltage drop of the on-resistance (e.g., 10 kΩ) of the NFET M4 can be ignored. These values can be set freely.

[0115] During the operation of the step-down circuit, the NFET M3 is on, the PFET M4 is on, and the NFET M2 is off. As a result, as Figure 15As illustrated in (b), the charge accumulated in capacitor C1 flows as current Ia through inductor L1 and charges capacitor C4. At this time, magnetic flux energy is stored in inductor L1.

[0116] When the charge in capacitor C1 decreases, PFET M4 turns off and NFET M2 turns on. As Figure 15 illustrated in (c), the magnetic flux energy of inductor L1 causes current Ib to flow and is stored in capacitor C4. As a result, the magnetic flux energy of inductor L1 is restored to capacitor C4.

[0117] For example, when the voltages used to charge capacitors C1 and C4 are set to 10V and 1V respectively, a charge that is 10 times the charge transferred from capacitor C1 is stored in capacitor C4. In Figure 15 (b), a part of the charge stored in capacitor C1 charges capacitor C4. At this time, energy is stored as the magnetic flux energy of inductor L1. In Figure 15 (c), the energy stored as magnetic flux energy is converted into current Ib to charge capacitor C4. This allows a charge approximately 10 times the charge transferred from capacitor C1 to be stored in capacitor C4.

[0118] Figure 16 (a) is a circuit diagram of a step-down circuit in the second modification of the second embodiment, Figure 16 (b) illustrates a flip-flop circuit. In the step-down circuit of the second modification of the second embodiment, a current sensor 21 is connected between NFET M2 and ground and detects the current flowing through NFET M2. Current sensor 21 includes element 10 and comparator 22.

[0119] The operation of flip-flop (FF) circuits X1 to X4 in Figure 16 (a) will be described. As Figure 16 (b) illustrates, flip-flop (FF) circuit 25 includes input terminals 25a and 25b, and output terminals 25c and 25d. When a high-level signal is input to input terminal 25a, FF circuit 25 outputs a low level to output terminal 25c and a high level to output terminal 25d. Then, FF circuit 25 holds output terminal 25c at a low level and output terminal 25d at a high level until the next high-level signal is input to input terminal 25b. When a high-level signal is input to input terminal 25b, FF circuit 25 outputs a high level to output terminal 25c and a low level to output terminal 25d, and holds output terminal 25c at a high level and output terminal 25d at a low level until the next high-level signal is input to input terminal 25a.

[0120] When the voltage at node A becomes 8V or more, Figure 16The spike generation circuit X5 in (a) outputs a positive spike signal to the FF circuit X1 and the FF circuit X4 through the node B. When the node C goes high, the spike generation circuit X8 outputs a positive spike signal to the node E after 1 μs. The voltage of the node A where the spike generation circuit X5 outputs the spike signal and the time when the spike generation circuit X8 outputs the spike signal to the node E after the node C goes high can be freely set.

[0121] Figure 17 is a timing diagram of the voltages and currents of the respective nodes of the buck circuit in the second variant of the second embodiment. The node A corresponds to the input voltage of the buck circuit, and the node P corresponds to the output voltage of the buck circuit. As Figure 16 in (a) and Figure 17 illustrated, the current I1 is supplied from the current source X6 to the node A. The current source X6 is a generator, such as an energy harvesting device. During the period between the time t41 and the time t42, since the current I1 flows into the node A, the voltage of the node A gradually increases from 7V to 8V. Since the increase rate of the voltage of the node A is small, the voltage of the node A appears to be constant during the period between the time t41 and the time t42 in Figure 17 . Before the time t42, the voltage of the node A does not reach 8V. During this period, the node B is at a low level. The FF circuit X4 holds the node Q at a low level. When the node Q is at a low level, the NFET M3 is off, and when the node Q is at a high level, the NFET M3 is on. Therefore, during the period between the time t41 and the time t42, the NFET M3 is off. The current IL flowing through the inductor L1 in the right direction is 0. The current I1 charges the capacitor C1, and the voltage of the node A increases.

[0122] The operation of the NFET M3 will be described. The threshold voltages of the NFET M3 and M7 are set to 0.4V. The NFET M7 is used as a diode, and its forward direction is from the node Q to the node P. When the node Q is at a low level, the gate voltage of the NFET M3 is approximately -0.3V lower than the voltage of the node P which is the first end of the capacitor C4, which corresponds to the forward voltage of the diode. Therefore, the NFET M3 is off.

[0123] The voltage of the node A increases, and when the voltage of the node A exceeds 8V at the time t42, the spike generation circuit X5 outputs a spike signal 29a to the node B. The FF circuit X4 outputs a high level to the node Q. The gate voltage of the NFET M3 becomes approximately +0.7V higher than the voltage of the node P, and the NFET M3 turns on. As a result, the current IL starts to flow in the inductor L1.

[0124] In addition, at time t42, a spike signal 29a is input from node B to the FF circuit X1. The FF circuit X1 outputs a high level to node C and outputs a low level to the first terminal of the capacitor C2. The spike generation circuit X8 outputs a spike signal 29b to node E at time t43, where time t43 is 1 μs after time t42 when node C enters the high level. This causes the FF circuit X1 to output a low level to node C and a high level to the first terminal of the capacitor C2 at time t43. As a result, node C is at a high level during a 1-μs period between time t42 and time t43 and is at a low level during other periods.

[0125] Node D is connected to ground through the NFET M6 that acts as a diode. The voltage of node D is a negative voltage during the period between time t42 and time t43 and is 0 V during other periods (including the period after time t43). As a result, the PFET M4 (whose gate is connected to node D) conducts during the period between time t42 and time t43. Since the NFET M3 remains conducting, the connection relationship illustrated in (b) of Figure 15 is established. A part of the charge stored in the capacitor C1 flows as a current IC in node A. The current IC becomes a current IL that charges the capacitor C4 through the inductor L1. The voltage of node A decreases. Magnetic flux energy is stored in the inductor L1.

[0126] Before time t43, node F is at a low level and the NFET M2 is off. The current IR flowing through the element 10 is 0, and the resistance state R of the element 10 is a high-resistance state RH. Since the voltage difference between nodes N1 and N2 is substantially 0 V, the voltage of node G is substantially 0 V. The comparator 22 outputs a low level to node H.

[0127] At time t43, when the spike signal 29b is input from node E to the FF circuit X3, the FF circuit X3 places node F at a high level. The NFET M2 turns on. As described above, at time t43, the PFET M4 turns off. As a result, the connection relationship illustrated in (c) of Figure 15 is established. The current IR flows from ground into node A. The current IR is greater than the threshold current Ith. Therefore, the resistance state R changes to a low-resistance state RL. The voltage difference between nodes N1 and N2 is very small, and the voltage of node G is a small negative value. The comparator 22 keeps node H at a low level.

[0128] After time t43, the currents IR and IL flow out from the magnetic flux energy stored in the inductor L1 to charge the capacitor C4. As a result, the voltage of node P increases. The currents IL and IR of the inductor L1 decrease with time. The voltage of node G approaches 0 V with time.

[0129] When the current IR of element 10 becomes the threshold current Ith at time t44, the resistance state R of element 10 changes to the high-resistance state RH. The voltage difference ΔV between nodes N1 and N2 becomes negative, and the voltage of node G becomes negative. Since the voltage of node G is negative, comparator 22 holds node H at a low level.

[0130] At time t45, when the current IR of element 10 becomes 0, the voltage of node G becomes 0V. Thereafter, current IL becomes negative and current IR becomes negative. After time t45, the voltage of node P switches from increasing to decreasing. At time t46, comparator 22 determines that the voltage of node G has become higher than 0V and places node H at a high level. FF circuit X4 places node Q at a low level. As a result, NFET M3 turns off. FF circuit X3 places node F at a low level. As a result, NFET M2 turns off. Currents IL and IR become 0. Since the voltage of node G has become 0V, node H returns to a low level. This completes the step-down operation.

[0131] In the second variant of the second embodiment, when the absolute value of current IR is small as in the period from time t44 to time t46, element 10 is in the high-resistance state RH, and comparator 22 can accurately determine that current IR has become substantially 0. Since element 10 is in the low-resistance state RL when the absolute value of current IR is large as in the period from time t43 to time t44, the resistance loss caused by element 10 can be reduced.

[0132] In the second embodiment and its first variant, control unit 28 controls the turning on and off of switches SW1 to SW4 based on the output of current sensor 21. In the second variant of the second embodiment, FF circuits X3 and X4 (control unit) control NFETs M2 and M3 (switch unit) based on the output of current sensor 21. This allows current sensor 21 to accurately sense the minute current flowing through element 10 and reduce losses when the current flowing through element 10 is large.

[0133] In the second embodiment and its variants, the synchronous rectifier circuit and the step-down circuit are described as power conversion circuits using the current sensor according to any one of the first embodiment and its variants, but the power conversion circuit can be a step-down circuit, a boost circuit, a DC-AC power conversion circuit, or an AC-DC power conversion circuit having other circuit configurations. In the power conversion circuit, current sensing is performed to control the switch unit. Current sensing is generally performed in the range where the absolute value of the current is small. Therefore, using the current sensor according to any one of the first embodiment and its variants can accurately sense minute currents and reduce losses in the large-current range. The current sensor of the first embodiment and its variants can also be used in circuits and electronic circuits other than power conversion circuits.

[0134] [Manufacturing method of component 10]

[0135] The manufacturing method of the component used in the first embodiment and the second embodiment will be described Figure 2 in (a) of Figure 2 and its variant examples of the manufacturing method of component 10 in (b) of Figure 18 from (a) to Figure 18 in (d) of Figure 2 are cross-sectional views illustrating the manufacturing method of the component exemplified in (a) of Figure 2 and (b) of Figure 18 As exemplified in (a) of 2 , a thin film 15 is formed on a substrate 12. The substrate 12 is, for example, a single crystal TiO 2 substrate, and the thin film 15 is, for example, a VO 2 film. The VO

[0136] film is formed using sputtering or pulsed laser deposition technology. For example, the film is formed under the conditions that the temperature of the substrate 12 is 300 °C and the oxygen partial pressure is 1 Pa. Figure 18 As exemplified in (b) of

[0137] , a masking layer 40 having holes 41 is formed on the thin film 15. The masking layer 40 is, for example, a photoresist. By applying a photoresist and exposing and developing it, a masking layer 40 having holes 41 is formed. Figure 18 As exemplified in (c) of

[0138] , the thin film 15 is removed using the masking layer 40 as a mask. The thin film 15 is removed using, for example, wet etching or dry etching technology. By removing the masking layer 40, the thin film 15 is patterned to form a resistance element 14. Figure 18 As exemplified in (d) of Figure 2 , a masking layer 42 having holes 43 is formed on the substrate 12 and the resistance element 14. The masking layer 42 is, for example, a photoresist. By applying a photoresist and exposing and developing it, a masking layer 42 having holes 43 is formed. Thereafter, a metal film serving as an electrode is formed using, for example, vacuum evaporation technology. By removing the masking layer 42, the metal film on the masking layer 42 is peeled off. This forms

[0139] Third Embodiment

[0140] The third embodiment uses the PN-body tied SOI-FET described in S. Momose et. Al., "Gate Controlled Diode Characteristics of Super Steep Subthreshold Slope PN-Body Tied SOI-FET for High Efficiency RF Energy Harvesting", 2017 IEEE SOI-3D-Subthreshold Microelectronics Technology Unified Conference, as the element 10 used in the first embodiment and its variants.

[0141] Figure 19 is a plan view of the transistor used in the third embodiment. The transistor 54 is formed on a semiconductor-on-insulator (SOI) substrate. The sections 44 to 48 are formed in a semiconductor layer (e.g., a silicon layer) formed on the insulating layer of the SOI. The section 44 (first semiconductor section) and 46 (second semiconductor section) are n + sections (first conductivity type sections), the section 45 (third semiconductor section) is a p-section (second conductivity type section), the section 47 (fourth semiconductor section) is an n - section, and the section 48 (fifth semiconductor section) is a p + section. The source terminal S is connected to the section 45, the drain terminal D is connected to the section 46, and the body terminal B is connected to the section 48. The gate terminal G is connected to the section 45 through the gate insulating film 49. The drain terminal D and the gate terminal G are electrically connected and short-circuited.

[0142] Figure 20 (a) of is a circuit diagram illustrating an example of the connection of the transistor in the third embodiment, and Figure 20 (b) of schematically illustrates the current with respect to the voltage. As Figure 20 illustrated in (a) of, the source terminal S of the transistor 54 is connected to the ground, and the drain terminal D is connected to the terminal T1. A constant voltage Vb is applied from the voltage supply circuit to the body terminal B. The voltage Vb is, for example, 1V. The preferred voltage of the voltage Vb depends on the doping amount of each of the sections 44 to 48 and is, for example, 1V or more. In order to avoid using a boost circuit, the voltage Vb is preferably equal to or less than the power supply voltage using the current sensor. That is, the voltage supply circuit generates the voltage Vb, for example, by dividing the power supply voltage with a resistor. The voltage applied to the terminal T1 is represented by Vin, and the current flowing from the terminal T1 to the ground is represented by Iin.

[0143] In Figure 20In (b), the vertical axis represents the logarithm of the absolute value of the current Iin, denoted as log|Iin|. In the range where the voltage Vin is negative, the absolute value |Iin| of the current Iin is very small. In the range where the voltage Vin is positive, |Iin| is small when the voltage Vin is approximately 0. When the voltage Vin exceeds the threshold voltage Vth, |Iin| increases rapidly. In other words, when the value of the current Iin exceeds a predetermined range, the resistance state changes to a low-resistance state with a resistance value lower than that of the high-resistance state. The threshold voltage Vth is, for example, 0.05V.

[0144] Figure 21 Example (a) illustrates the details of the element 30 used in the third embodiment. Figure 21 Example (b) schematically illustrates the current with respect to the voltage. As Figure 21 illustrated in example (a), the element 30 includes two transistors 54a and 54b. The first terminal 31 (first terminal) and the second terminal 32 (second terminal) of the element 30 are connected to the terminal T1 and the ground, respectively. The transistors 54a (first element) and 54b (second element) are connected in parallel between the first terminal 31 and the second terminal 32. The source terminal S of the transistor 54a is connected to the second terminal 32, and the drain terminal D is connected to the first terminal 31. The source terminal S of the transistor 54b is connected to the first terminal 31, and the drain terminal D is connected to the second terminal 32. A constant voltage Vb is applied to the body terminals B of the transistors 54a and 54b. The current flowing through the transistor 54a from the first terminal 31 to the second terminal 32 is denoted as Ia, and the current flowing through the transistor 54b from the first terminal 31 to the second terminal 32 is denoted as Ib. The current Iin = Ia + Ib.

[0145] In Figure 21 Example (b), the vertical axis represents the logarithm of the absolute value of the current, denoted as log|Iin|, log|Ia|, and log|Ib|. The log|Iin| with respect to the voltage Vin is the same as the log|Iin| in Figure 20 Example (b). When the voltage Vin becomes greater than the positive threshold voltage Vth, |Ia| increases rapidly. By Figure 20The log|Iin| in (b) is inverted with respect to the voltage Vin to obtain log|Ib| with respect to the voltage Vin. When the voltage Vin becomes less than the negative threshold voltage -Vth, |Ib| rapidly increases. In the range 50 where the absolute value of the voltage Vin is equal to or less than the threshold voltage Vth (i.e., the absolute value of the current Iin is equal to or less than the threshold current Ith), |Iin| is small. That is, the resistance between the terminal T1 and the ground in the element 30 becomes low. In the range 52 where the absolute value of the voltage Vin is greater than the threshold voltage Vth (i.e., the absolute value of the current Iin is greater than the threshold current Ith), |Iin| is large. That is, the resistance between the terminal T1 and the ground in the element 30 becomes high. That is, when the absolute value of the current exceeds a predetermined range, Figure 21 the element 30 illustrated in (a) becomes a low-resistance state with a resistance value lower than the resistance value in the high-resistance state.

[0146] The element or circuit used in the first embodiment, the second embodiment, and their modified examples may be a two-terminal element. When the absolute value of the current Iin is within the range 50 that is lower than the range 52, the two-terminal element enters a high-resistance state without external control, and when the absolute value of the current Iin is within the range 52, the two-terminal element enters a low-resistance state without external control, as Figure 1 the element 10 in (c). The use of the two-terminal element eliminates the need to use a circuit for switching the resistance state. Therefore, a current sensor with a small circuit size can be realized.

[0147] As in the third embodiment, the element may be two elements: as Figure 21 the element 30 in (a), the first element and the second element are connected in parallel. This configuration has an I-V characteristic similar to that of the element 10, as Figure 21 illustrated in (b). Therefore, the element 30 can be used instead of the element 10 in the first embodiment, the second embodiment, and their modified examples. In the element 10 of the first embodiment, materials that are not often used in semiconductor processes, such as VO 2 are used. On the other hand, the element 30 using the transistor 54 can be formed using a normal semiconductor process.

[0148] In the element 30, the gate terminal G other than the terminals through which the currents Ia and Ib flow is short-circuited to the drain terminal D, and a fixed bias voltage is applied to the body terminal B, as Figure 21 illustrated in (a). This structure enables switching of the resistance state according to the magnitudes of the currents Ia and Ib without applying a control voltage from an external circuit. Therefore, it is not necessary to use a circuit for switching the resistance state, and thus the current sensor can be miniaturized.

[0149] [Example of a System Using a Power Conversion Circuit]

[0150] Figure 22 is a block diagram of a system that illustrates a power conversion circuit using the second embodiment and its modified examples. As Figure 22 illustrated, the system includes a power generation unit 60, rectifier circuits 61 and 62, a matching circuit 63, a voltage conversion circuit 64, a charge management circuit 65, a power storage device 66, a cold start circuit 67, and a boost circuit 68.

[0151] The power generation unit 60 is, for example, an energy harvesting element and is a vibration power generation unit such as a microelectromechanical system (MEMS). The power generation unit 60 generates AC power with a small current. The rectifier circuit 61 is, for example, a diode bridge, and the rectifier circuit 62 is, for example, a synchronous rectifier circuit. The matching circuit 63 matches the output impedance of the rectifier circuits 61 and 62 with the input impedance of the voltage conversion circuit 64. The voltage conversion circuit 64 is, for example, a DC (direct current)-DC converter. The charge management circuit 65 stores the power in one of the appropriate power storage devices 66. The power storage device 66 is, for example, a capacitor. The charge management circuit 65 monitors the voltage across each power storage device 66 and stores the generated power in an appropriate power storage device. When the power storage device 66 is hardly charged, the cold start circuit 67 stores the output current of the rectifier circuit 61 in the power storage device 66. The boost circuit 68 is, for example, a charge pump and generates the voltage used in the rectifier circuit 62 and the voltage conversion circuit 64.

[0152] The operation of the system will be described. In a state where the power storage device 66 is hardly charged, when the power generation unit 60 generates small power, the rectifier circuit 61 rectifies the small power. The rectifier circuit 61 can perform rectification without an external power source (such as a diode bridge). The current rectified by the rectifier circuit 61 reaches the charge management circuit 65 through the cold start circuit 67 to be stored in the power storage device 66. When the power storage device 66 is charged to a sufficient voltage, the boost circuit 68 boosts the voltage of the power storage device 66 to the voltage used in the rectifier circuit 62 and the voltage conversion circuit 64. The voltage of the power storage device 66 is, for example, 1V, and the output voltage of the boost circuit 68 is, for example, 2V. When the rectifier circuit 62 and the voltage conversion circuit 64 operate using the voltage of the power storage device 66, the boost circuit 68 can be omitted.

[0153] The matching circuit 63 changes the input voltages of the rectifying circuits 61 and 62 according to the power generation amount of the power generation unit 60. Thereby, the output impedance of the power generation unit 60 is matched with the input impedances of the rectifying circuits 61 and 62. The matching circuit 63 switches the rectifying circuits 61 and 62 according to the input voltage. For example, in the case where the rectifying circuits 61 and 62 are a diode bridge and a synchronous rectifying circuit, respectively, when the input voltage becomes 1 V or less, the loss due to the voltage drop of the diode increases. Therefore, the rectifying circuit 62 is used. When the input voltage is 1 V or more, the rectifying circuit 61 is used.

[0154] The voltage conversion circuit 64 converts the input voltage set by the matching circuit 63 into a voltage for charging the power storage device 66. The voltage of the power storage device 66 is, for example, 1 V or 3.3 V. The charge management circuit 65 monitors the voltage of the power storage device 66 and stores the generated power in the appropriate power storage device 66.

[0155] A system adopting the power generation unit 60 that generates such a minute current needs to reduce losses. Therefore, the synchronous rectifying circuit according to any one of the second embodiment and its first modification is used as the rectifying circuit 62, and the step-down circuit according to the second modification of the second embodiment is used as the voltage conversion circuit. This can reduce the loss of the current sensor and reduce the losses in the system.

[0156] Although the preferred embodiments of the present invention have been described so far, the present invention is not limited to these specific embodiments, and various changes and modifications can be made within the scope of the present invention claimed herein.

[0157] Description of Reference Numerals

[0158] 10, 30 Elements

[0159] 12 Substrate

[0160] 14 Resistance Element

[0161] 14a Active Portion

[0162] 14b Lead-Out Portion

[0163] 16a, 16b Electrodes

[0164] 20, 20a Detectors

[0165] 21 Current Sensor

[0166] 22 Comparator

[0167] 24 Differential Integration Circuit

[0168] 26 Hysteresis Determination Device

[0169] 28 Control Unit

[0170] Transistors 54, 54a, 54b

Claims

1. A current sensor, the current sensor comprises: an element including a resistive element which is in a high-resistance state when the absolute value of the current flowing between a first terminal and a second terminal is within a first range, and which changes to a low-resistance state by a phase change from an insulator phase to a metal phase when the absolute value of the current exceeds the first range, and in the low-resistance state, the resistance value is lower than the resistance value in the high-resistance state; and a circuit which supplies a current to be measured to the element and senses the value of the current to be measured based on at least one of the voltages of the first terminal and the second terminal.

2. The current sensor according to claim 1, wherein the circuit senses the value of the current based on the difference between the voltages of the first terminal and the second terminal.

3. The current sensor according to claim 1, wherein the circuit senses the value of the current based on the voltage of the first terminal and a provided reference voltage.

4. The current sensor according to claim 1, wherein the element is a two-terminal element in which the resistive element is connected between the first terminal and the second terminal.

5. The current sensor according to claim 4, wherein the resistive element is a resistive element which is in the high-resistance state when the temperature of the resistive element is within a first temperature range, and which changes to the low-resistance state when the temperature of the resistive element is higher than the first temperature range.

6. The current sensor according to claim 4 or 5, wherein The resistance element includes VO 2 , NbO 2 or Ti 2 O 3 .

7. The current sensor according to any one of claims 1 to 3, wherein the element includes a first element and a second element connected in parallel between the first terminal and the second terminal, and each of the first element and the second element enters the high-resistance state without external control when the current flowing from a first end to a second end is equal to or less than a threshold current, and each of the first element and the second element enters the low-resistance state without external control when the current flowing from the first end to the second end is greater than the threshold current, and wherein the first end of the first element is connected to the first terminal, the second end of the first element is connected to the second terminal, the first end of the second element is connected to the second terminal, and the second end of the second element is connected to the first terminal.

8. A current sensor, the current sensor comprises: An element or circuit including a resistive element, when the absolute value of the current flowing between a first terminal and a second terminal is within a first range, the resistive element enters a high-resistance state without external control through a phase change from a metallic phase to an insulating phase, and when the absolute value of the current is within a second range higher than the first range, the resistive element enters a low-resistance state without external control through a phase change from the insulating phase to the metallic phase, and in the low-resistance state, the resistance value is lower than the resistance value in the high-resistance state. Wherein, the current sensor senses the current.

9. A power conversion circuit, the power conversion circuit comprises: a switching unit; and a control unit that controls the turning on and off of the switching unit based on the output of the current sensor according to any one of claims 1 to 5 and claim 8.

10. The power conversion circuit according to claim 9, wherein, the switching unit comprises: a first switching unit connected between a first terminal and a second terminal, a second switching unit connected between a third terminal and a fourth terminal, a third switching unit connected between the first terminal and the fourth terminal, and a fourth switching unit connected between the second terminal and the third terminal, wherein the element is coupled to one of the following positions: between the first terminal and the first and third switching units, and between the second terminal and the first and fourth switching units, and wherein the control unit changes the first and second switching units from off to on and changes the third and fourth switching units from on to off based on a change in the sign of the current, and changes the first and second switching units from on to off and changes the third and fourth switching units from off to on based on the next change in the sign of the current.

11. A current sensor, the current sensor comprises: an element including a resistive element that is in a high-resistance state when the absolute value of the current flowing between a first terminal and a second terminal is within a first range, and becomes a low-resistance state when the absolute value of the current exceeds the first range, and in the low-resistance state, the resistance value is lower than the resistance value in the high-resistance state; and a circuit that supplies a current to be measured to the element and senses the value of the current to be measured based on at least one of the voltages of the first terminal and the second terminal, wherein the resistive element is connected between the first terminal and the second terminal, and is in the high-resistance state when the temperature of the resistive element is within a first temperature range, and becomes the low-resistance state when the temperature of the resistive element is higher than the first temperature range.

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