JP2018128414A - Semiconductor device and design method of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device capable of improving the measurement sensitivity while preventing damages on the semiconductor base plate, a laminated body on the semiconductor base plate or peeling from a housing when disposed on a measuring object, and a design method of semiconductor device.SOLUTION: The semiconductor device includes: a semiconductor base plate 12; a first electrode 20-1 formed on the semiconductor base plate 12, which outputs input measuring signal as an input signal; and a second electrode 20-2 formed on the semiconductor base plate 12, to which an input signal output from the first electrode 20-1 is input and which outputs the input signal as an output signal. Each of the first electrode 20-1 and the second electrode 20-2 has a second side which faces a first side and forms an acute angle between the first side and the second side.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a semiconductor device and a semiconductor device design method.

  As an example of a semiconductor device, a sensor (hereinafter referred to as “EC sensor”) that measures the amount of water in soil from the electrical conductivity (EC) of the soil that is the measurement target is known. The EC sensor applies an AC signal between two electrodes brought into contact with soil, and measures the amount of water in the soil from, for example, a change in impedance and a change in phase between the two electrodes.

  As a prior art of a semiconductor device having a function as an EC sensor, Patent Document 1 discloses a pH measurement unit that comes into contact with a solution and measures a pH value, and an electric current that detects the electrical conductivity of a portion immediately above the pH measurement unit. PH which detects the pH value of a solution based on the measured pH value, electrical conductivity and temperature, comprising a conductivity measuring unit (equivalent to an EC sensor) and a temperature measuring unit for detecting the temperature in the vicinity of the pH measuring unit There is disclosed a detection device, a pH detection device in which a pH measurement unit, an electrical conductivity measurement unit, and a temperature measurement unit are arranged on the same semiconductor substrate.

  In patent document 1, the electrode pair of EC sensor is arrange | positioned in the position which pinches | interposes a pH measurement part from both sides. Thus, in the pH detection device according to Patent Document 1, since the solution on the pH measurement unit is surely in contact with the electrode pair of the electrical conductivity measurement unit, the pH measurement unit is obtained from the output of the electrical conductivity measurement unit. It can be determined whether or not the liquid is in contact with the droplet, and as a result, the measurement accuracy of the pH detector is improved.

JP 2008-39523 A

  However, a semiconductor substrate of a semiconductor device or a semiconductor laminate formed on the semiconductor substrate is extremely fragile. For this reason, for example, when the EC sensor is embedded in the soil, the semiconductor substrate may be cracked or chipped. Moreover, when the laminated body formed on a semiconductor substrate is damaged, there is a possibility that the function of the EC sensor may not be performed sufficiently. Further, there may be a problem that the semiconductor itself is peeled off from the housing. Therefore, in a semiconductor device as an EC sensor, it is important to consider an electrode (hereinafter referred to as a “sensor electrode”) that is in direct contact with soil when measuring electrical conductivity. In the pH detection device according to Patent Document 1, such a point is not particularly studied, so that there is a possibility that damage may occur when the device is placed in contact with the measurement target.

  On the other hand, the shape and size of the sensor electrode can be a factor that determines the measurement sensitivity of the EC sensor. Therefore, when examining the electrodes of the EC sensor, it is necessary to consider the maintenance and improvement of measurement sensitivity.

  Furthermore, when examining the sensor electrode, it is necessary to consider the problem of the electric double layer. The electric double layer generally refers to a layer of positive and negative charges formed at the interface between a solid and a liquid in a system composed of a liquid sandwiched between solids. Even in the EC sensor, when measuring the electrical conductivity of the liquid, an electric double layer is formed at the interface between the electrode and the liquid to be measured, although there is a difference in degree. Since this electric double layer functions as a capacitor, in measuring the electrical conductivity of the liquid, it may affect the measurement frequency and the like, leading to a decrease in measurement accuracy.

  The present invention has been made in view of the above problems, and suppresses damage to the semiconductor substrate and the laminate on the semiconductor substrate, or damage such as peeling from the housing, in the case of arranging the measurement object. An object of the present invention is to provide a semiconductor device and a semiconductor device design method capable of improving measurement sensitivity.

  The semiconductor device according to the present invention is provided on the semiconductor substrate, the first electrode for outputting the input measurement signal as an input signal, the first electrode provided on the semiconductor substrate, and the first electrode. A second electrode that receives the input signal output from one electrode and outputs the input signal as an output signal, and each of the first electrode and the second electrode includes The second side is opposed to the first side and forms an acute angle with the first side.

  A semiconductor device according to another aspect of the present invention includes a semiconductor substrate, a first electrode that is provided on the semiconductor substrate, and that outputs an input measurement signal as an input signal, and the semiconductor substrate. And a second electrode that receives the input signal output from the first electrode and outputs the input signal as an output signal, and includes the first electrode and the second electrode. Each of the first side and the second side parallel to each of the two sides of the semiconductor substrate intersecting at a predetermined angle, and the first side and the second side parallel to each of the first side and the second side, respectively. With 3 sides and 4th side

  On the other hand, the method for designing a semiconductor device according to the present invention includes a step of determining a direction in which a sensor equipped with a semiconductor device is embedded in soil, a first side parallel to the direction of embedding, and an acute angle with respect to the direction of embedding. Laying out a sensor electrode having a second side forming the following.

  According to the present invention, it is possible to suppress damage to the semiconductor substrate and the stacked body on the semiconductor substrate, or damage such as peeling from the housing, and improve measurement sensitivity when arranged on the measurement target. The semiconductor device and the method for designing the semiconductor device are provided.

(A) is an overview of the EC sensor according to the present embodiment, (b) is a plan view of the semiconductor device according to the present embodiment, and (c) is a cross-sectional view. (A) is a general-view figure explaining the effect | action of the EC sensor which concerns on this Embodiment, (b) is sectional drawing explaining the effect | action of the semiconductor device which concerns on this Embodiment, (c) is a top view. It is a top view which shows the modification of the semiconductor device which concerns on embodiment. It is a top view which shows the variation of the semiconductor device which concerns on embodiment. (A), (c)-(e) is a top view which shows an example of a structure of EC electrode of the semiconductor device which concerns on embodiment, (b) is a cross section explaining the effect | action of EC electrode which concerns on this Embodiment FIG. It is a graph explaining the effect of the EC electrode which concerns on this Embodiment. (A) is an overview of an EC sensor according to a comparative example, (b) is a plan view of a semiconductor device according to the comparative example, and (c) is a cross-sectional view. (A) is a general-view figure explaining the effect | action of the EC sensor which concerns on a comparative example, (b) is sectional drawing explaining the effect | action of the semiconductor device which concerns on a comparative example, (c) is a top view. (A) And (b) is a figure explaining the sensor electrode peeling of the EC sensor which concerns on a comparative example, (c) And (d) is a figure explaining a protective layer defect | deletion.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  With reference to FIGS. 1 to 6, a semiconductor device and a method for designing the semiconductor device according to the present embodiment will be described. Hereinafter, soil will be exemplified and described as a measurement target of electrical conductivity.

  First, an EC sensor, a semiconductor device as an EC sensor chip, and a semiconductor device design method according to the present embodiment will be described with reference to FIG. 1A is an overview of the EC sensor 1 according to the present embodiment, FIG. 1B is a plan view of the semiconductor device 10 according to the present embodiment, and FIG. 1C is FIG. It is sectional drawing of the semiconductor device 10 cut | disconnected by the AA line shown.

  As shown in FIG. 1A, the EC sensor 1 includes a housing 2 and a semiconductor device 10. The semiconductor device 10 is mounted on a mounting substrate (not shown) disposed in the housing, and is disposed so as to be exposed from a window (opening) provided in a part of the housing 2. Then, when measuring the electrical conductivity of the soil using the EC sensor 1, a part of the housing 2 including the semiconductor device 10 is embedded in the soil.

  As shown in FIG. 1B, the semiconductor device 10 includes a pair of sensor electrodes 20-1 and 20-2 (hereinafter collectively referred to as “sensor electrode 20”), a pH sensor 22, and a temperature sensor 24. I have.

  The sensor electrode 20 is an electrode for measuring electrical conductivity, and in the measurement, each of the pair of sensor electrodes 20-1 and 20-2 is brought into contact with a different part of the soil, so that the sensor electrodes 20-1 and 20- For example, the impedance of the soil is measured via 2. In the present embodiment, each of the pair of sensor electrodes 20 has a substantially right triangle shape, and is arranged at opposite vertices of the substrate 12 of the semiconductor device 10 so as to have opposite sides.

  The pH sensor 22 is a part that measures the pH in the vicinity of the soil in contact with the sensor electrode 20. The temperature sensor 24 is a part that measures the temperature in the vicinity of the soil in contact with the sensor electrode 20. In the present embodiment, two sets of pH sensors 22 and temperature sensors 24 are used, and each of the two sets of pH sensors 22 and temperature sensors 24 is arranged at the position of the other opposite vertex of the substrate 12. On the other hand, each of the two sets of the pH sensor 22 and the temperature sensor 24 is not disposed in a region between the sensor electrode 20-1 and the sensor electrode 20-2. The reason why two sets of the pH sensor 22 and the temperature sensor 24 are used is mainly to increase the measurement accuracy.

  On the other hand, when viewed in cross section, the semiconductor device 10 includes a substrate 12, an insulating layer 14 formed on the substrate 12, a sensor electrode wiring 16 formed on the insulating layer 14, and a sensor, as shown in FIG. Sensor electrode 20 formed on electrode wiring 16 (sensor electrode 20-1 is visible in FIG. 1C), surface protective film formed on insulating layer 14 and covering part of sensor electrode wiring 16 18 is comprised. The sensor electrode wiring 16 is a wiring layer for connecting between the sensor electrode 20 and a pad (not shown) for connecting the sensor electrode 20 to the outside (measurement system such as an AC signal source and an ammeter). It is.

In the semiconductor device 10 according to the present embodiment, for example, silicon (Si) is used as the substrate 12. As the insulating layer 14, for example, a silicon oxide film (SiO ₂ film) formed by thermally oxidizing the substrate 12 made of Si is used.

  On the other hand, in the semiconductor device 10 according to the present embodiment, for example, aluminum (Al), AlCu (aluminum / copper), or AlSiCu (aluminum / silicon / copper) is used as the sensor electrode wiring 16. For example, platinum (Pt) is used. Further, a barrier metal (adhesion layer) 26-1 is provided between the insulating layer 14 and the sensor electrode wiring 16, and a barrier metal 26-2 is provided between the sensor electrode wiring 16 and the sensor electrode 20. Sometimes. For example, a titanium (Ti) film or a nitrogen titanium (TiN) film is used as the barrier metals 26-1 and 26-2.

  Here, with reference to FIG. 7 thru | or FIG. 9, the failure | damage of the EC sensor in the case of using the EC sensor which concerns on a comparative example is demonstrated.

  7A is an overview of the EC sensor 100 according to the comparative example, FIG. 7B is a plan view of the semiconductor device 110 according to the comparative example, and FIG. 7C is a cross-sectional view taken along line BB shown in FIG. It is sectional drawing of the semiconductor device 110 cut | disconnected by the line.

  As shown in FIG. 7A, the EC sensor 100 includes a housing 102 and a semiconductor device 110, and the appearance is the same as that of the EC sensor 1 according to the present embodiment.

  On the other hand, unlike the semiconductor device 10, the semiconductor device 110 according to the comparative example includes a pair of rectangular sensor electrodes 120 arranged in parallel with two opposite sides of the substrate 112 as shown in FIG. Yes.

  As shown in FIG. 7C, the cross-sectional structure of the semiconductor device 110 is the same as that of the semiconductor device 10. That is, the substrate 112, the insulating layer 114 formed on the substrate 112, the sensor electrode wiring 116 formed on the insulating layer 114, the sensor electrode 120 formed on the sensor electrode wiring 116, and the insulating layer 114 are formed. A surface protective film 118 covering a part of the sensor electrode wiring 116 is included.

  Next, with reference to FIG. 8, the effect | action at the time of measuring the electrical conductivity of soil of EC sensor 100 and the semiconductor device 110 is demonstrated. As shown in FIG. 8A, when measuring the electrical conductivity of the soil, the EC sensor 100 is inserted into the soil in a direction D1 indicated by a white arrow. The embedded area SA indicates a portion embedded when the EC sensor 100 is inserted. In this state, the sensor electrode 120 is brought into contact with the soil, and for example, the amount of water in the soil is measured.

  On the other hand, as 100 is embedded in the EC sensor, as shown in FIG. 8B, the semiconductor device 110 also enters the soil in the direction D1, so that the soil is relatively pushed from the direction D2. When this state is viewed from the plane direction, it is as shown in FIG. In other words, the region A1 which is one side in a direction orthogonal to the insertion direction D1 of the EC sensor 100 and the region S2 which is a side in a direction orthogonal to each direction D1 of the sensor electrode 120 of the substrate 112 are opposed to the soil S. To do. Since the substrate 112, the sensor electrode 120, and the surface protective film 118 of the semiconductor device 110, that is, the stacked body of the semiconductor device 110, have a step surface perpendicular to the direction D2, there is a possibility that the substrate 112 may be pressed against the soil S to be damaged.

  With reference to FIG. 9, the damage of the semiconductor device 110 will be described in more detail. Hereinafter, among the damage modes that can occur in the semiconductor device 110 according to the comparative example, three damage modes of sensor chip peeling, sensor electrode peeling, and protective layer loss will be described as an example.

  The sensor chip peeling is damage in which the semiconductor device 110 itself is peeled off from the mounting substrate disposed in the housing 102 when the end surface of the semiconductor device 110 is pressed against the soil S. The sensor chip peeling causes a problem in electrical connection between the semiconductor device 110 and the wiring of the mounting substrate, and the semiconductor device 110 may be detached from the housing 102 in some cases.

  As shown in FIG. 9A, the sensor electrode peeling refers to damage in which the sensor electrode 120 is subjected to pressure by the soil S to be pressed and peels off. If the sensor electrode 120 is peeled off, the measurement accuracy of the EC sensor 100 may be lowered. Further, as shown in FIG. 9B, corrosion G may occur when the sensor electrode wiring 116 that does not originally contact the soil S contacts the soil. Corrosion G may lead to a decrease in the reliability of the sensor chip over a long period of use.

  As shown in FIG. 9C, the protective layer defect is damage that causes a defect in a part of the surface protective film 118 due to the soil S that is pushed in. If a part of the surface protective film 118 is lost, the sensor electrode wiring 116 that does not originally contact the soil may contact the soil S and cause corrosion G as shown in FIG. Corrosion G may lead to a decrease in the reliability of the sensor chip over a long period of use. Further, when the sensor electrode 120 is peeled off due to the loss of the surface protective film 118, the measurement accuracy of the EC sensor 100 is lowered.

  Next, operations of the EC sensor 1 and the semiconductor device 10 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 2A, the EC sensor 1 is also inserted into the soil in the direction D1 with the semiconductor device 10 facing downward in the drawing. As shown in FIG. 2B, when the semiconductor device 10 is also made to enter the soil in the direction D1, the soil is pushed from the direction D2.

  FIG. 2C shows a state of contact between the soil S and the semiconductor device 10 when the EC sensor 1 is inserted into the soil S. Hereinafter, for ease of understanding, description will be made assuming that the outer shape of the semiconductor device 10 is a square. However, the external shape of the semiconductor device 10 is not limited to a square, and may be other external shapes, such as a rhombus and a polygon. Further, the shape of the sensor electrode 20 is not limited to a right triangle, and may be a triangle having an acute angle or an obtuse angle, for example.

  In the present embodiment, the insertion direction D1 of the semiconductor device 10 is the direction of a diagonal line connecting vertices where no pair of sensor electrodes 20 is arranged. In other words, the pair of sensor electrodes 20 is arranged at the corners at both ends of the diagonal line that is substantially orthogonal to the insertion direction D1. Each sensor electrode 20 forming a substantially right triangle has two sides (second sides) sandwiching the apex angle so that the apex angle is positioned in the vicinity of the apexes at both ends of the diagonal line substantially orthogonal to the insertion direction D1. It arrange | positions along the edge | side of the board | substrate 12 (it is parallel). Accordingly, two sides (second side) sandwiching the right angle of the sensor electrode 20 form an acute angle with the insertion direction D1, the oblique sides (first side) of the sensor electrode 20 face each other, and the four sides of the substrate 12 Make an angle of 45 °. In other words, the semiconductor device 10 according to the present embodiment is mounted on the housing 2 so that at least one side of the semiconductor device 10 forms an acute angle with the insertion direction D1.

  By arranging the semiconductor device 10 as described above, as shown in FIG. 2C, the soil S that rushes from the direction D <b> 2 is left and right (vertex P <b> 1) at an apex P <b> 1 of the semiconductor device 10 with a 45 ° front view. 2 directions). By the distribution of the soil S, the pressure exerted on the semiconductor device 10 by the soil S is dispersed, and the semiconductor device 10 itself is less likely to be peeled off (sensor chip peeling). Further, since the soil S travels along the side of the sensor electrode 20, the pressure exerted on the sensor electrode 20 by the soil S is relaxed, and the occurrence of sensor electrode peeling and protective layer loss is also suppressed.

  Moreover, according to the semiconductor device 10 according to the present embodiment, the pair of sensor electrodes 20 is arranged in a direction orthogonal to the insertion direction D1 into the soil S, that is, in a direction horizontal to the ground to be measured. Accurate measurement of moisture having a horizontal distribution with respect to the ground becomes possible. Further, since the area of the sensor electrode can be increased, an effect that the sensor sensitivity is further improved can be obtained. In addition, by arranging at the apex of the semiconductor substrate 12, the distance between the sensor electrode 20 and the sensor electrode 20 is also increased by about 1.4 (square root of 2) times compared to the semiconductor device 110 according to the comparative example. The measurement range can be expanded without changing the chip size.

<Modification>
A modification of the semiconductor device according to the present embodiment will be described with reference to FIG. FIG. 3 is a plan view of a semiconductor device 10a according to a modification.

  The semiconductor device 10a is obtained by changing the sensor electrode 20 to the sensor electrode 20a in the semiconductor device 10. In contrast to the sensor electrode 20 forming a substantially right triangle, the sensor electrode 20a has a shape in which a rectangle having a certain width is bent into an L shape. The vertex P2 of the L-shaped bending point is disposed in the vicinity of the position of one vertex of the substrate 12. Therefore, compared with the sensor electrode 20, the area where the distance between the sensor electrodes 20a becomes longer becomes larger. Therefore, the sensor electrode 20a according to this modification is an advantageous configuration when it is desired to increase the interval between the sensor electrodes. Also by the semiconductor device 10a having the sensor electrode 20a, it is possible to suppress the damage of the semiconductor device 10a when it is embedded in soil and measured on the same principle as the semiconductor device 10.

  In each of the above embodiments, the sensor electrodes 20 and 20a have been described as the shape of the sensor electrode. However, the present invention is not limited to this, and the shape shown in FIG. That is, the corner portions at both ends along the insertion direction D1 of the sensor electrodes 20 and 20a may be cut off to provide the flat portion F.

  FIG. 4A shows a semiconductor device 10b in which flat portions F are provided at both ends along the insertion direction D1 in the sensor electrode 20. FIG. FIG. 4B shows a semiconductor device 10c in which flat portions F are provided at both ends along the insertion direction D1 in the sensor electrode 20a. By providing the flat portion F, the concentration of the electric field when the power is applied to the sensor electrode is further relaxed.

  The pair of sensor electrodes 20 do not necessarily have the same shape. For example, in consideration of the layout of the sensor electrodes, the electrode shapes described in the above embodiments and modifications are combined to form separate shapes. Also good.

<Configuration example of sensor electrode>
Next, a configuration example of the sensor electrode according to the present embodiment will be described with reference to FIGS. 5 and 6. In this configuration example, the surface area of the sensor electrode is enlarged to cope with the problem of the electric double layer described above.

  First, an example of a measurement system for measuring electrical conductivity using the EC sensor 1 will be described. In measurement using the EC sensor 1, an AC signal source is connected to the sensor electrode 20-1 via a pad (not shown), and an ammeter is connected to the sensor electrode 20-2 via a pad (not shown). Of course, this connection relationship may be reversed, that is, an AC signal source may be connected to the sensor electrode 20-2 and an ammeter may be connected to the sensor electrode 20-1. The liquid whose electric conductivity is to be measured is placed in contact with the sensor electrodes 20-1 and 20-2.

  There is no particular limitation on the method for specifying the amount of water to be measured which is a dispersion system using the EC sensor 1. As an example, a method for specifying the amount of moisture by detecting the phase change θ of the electrical signal will be described. In the above measurement system, the output of the semiconductor device 10 is proportional to the amount of water and the ion concentration, and if the ion concentration is specified, the amount of water in the soil can be specified by the electrical conductivity.

  The AC signal source and ammeter in the measurement system constitute a part of a control unit (not shown), and the AC signal source and ammeter are controlled by the control unit. When measurement is started, the control unit controls the AC signal source and applies an AC signal (measurement signal) having a predetermined frequency as an input signal to the sensor electrode 20-1. The sensor electrode 20-1 outputs an input signal toward the measurement target. The AC signal output from the sensor electrode 20-1 is input to the sensor electrode 20-2 after passing through the measurement target. The control unit compares the phase of the AC signal input to the sensor electrode 20-1 with the phase of the AC signal output from the sensor electrode 20-2. The control unit performs the above measurement by sweeping the frequency of the AC signal source.

  A specific example of the comparison target is to detect and compare the phase difference (phase change θ) between the two. When the phase change θ is detected, the ion concentration is specified by the detected phase change θ. The phase change θ and the ion concentration are associated in advance. Furthermore, the moisture content of the soil can be specified by the measured electrical conductivity with the specified ion concentration as a reference.

  In the above measurement system, for example, when measuring the electrical conductivity of a liquid, the above-described electric double layer between the sensor electrode 20-1 and the liquid as the measurement object and between the sensor electrode 20-2 and the liquid. Formation is assumed. When the electric double layer is formed, it is equivalent to the case where a capacitor is connected in series between the sensor electrodes 20-1 and 20-2 due to the region where there is no electric charge that functions as an insulator. Become. Originally, the purpose of the above measurement system is to measure the resistance component of the liquid and calculate the electrical conductivity, so the capacitance caused by this electric double layer has a restriction on the measurement frequency when measuring the electrical conductivity of the liquid. Will affect the measurement accuracy.

  On the other hand, the sensor electrodes 20-1 and 20-2 form a capacitor having both of them as electrode plates. When this capacity is C including the capacity due to the electric double layer, the impedance due to the capacity C Is proportional to 1 / C. Therefore, by reducing 1 / C, that is, by increasing C, the influence of the capacitance C on the measured value of the impedance of the liquid can be ignored, and the resistance component can be dominant.

  FIG. 5A is a plan view of the semiconductor device 10 as viewed from above, schematically showing portions of the sensor electrode wiring 16, the sensor electrode 20, and the surface protective film 18 of the semiconductor device 10 according to the above embodiment. is there. In the electrode structure 30 shown in FIG. 5A, only the sensor electrode wiring 16 and the sensor electrode 20 are stacked, and the sensor electrode wiring 16 has a so-called solid shape, and is not particularly devised to increase the capacitance. In this example, as an example, the sensor electrode wiring 16 is Al, and the sensor electrode 20 is Pt.

  FIG. 5B shows an example of an electrode configuration for increasing the capacitance. In this example, the surface area of the electrode plate is increased to increase the capacity. In this example, as shown in FIG. 5 (b), unevenness is formed in the sensor electrode wiring 16 in the manufacturing process. Since the sensor electrode 20 is formed along the irregularities of the sensor electrode wiring 16, the surface area of the sensor electrode 20 can be increased as shown in FIG.

  In this example, the planar shape (pattern) of the sensor electrode wiring 16 for forming the irregularities is not particularly limited. FIG. 5C to FIG. 5E show an example of a planar pattern of the sensor electrode wiring 16 for forming irregularities. 5C to 5E, the surface protective film 18 is not shown.

  FIG. 5C shows an electrode structure 30a in which the pattern of the sensor electrode wiring 16 is a ladder pattern. FIG. 5D shows an electrode structure 30b in which the pattern of the sensor electrode wiring 16 is a mesh pattern. Further, FIG. 5E shows an electrode structure 30c in which the pattern of the sensor electrode wiring 16 is a dot pattern. The area of the sensor electrode 20 increases in the order of the electrode structures 30a, 30b, and 30c. In particular, according to the electrode structure 30 c, the surface area of the sensor electrode 20 can be about 1.5 times that of the electrode structure 30.

  With reference to FIG. 6, the effect at the time of using the electrode structure of this example is demonstrated. A curve C2 shown in FIG. 6 shows an example in which the impedance of the measurement target is actually measured using the conventional electrode structure (electrode structure 30). A measurement system in which a measurement target is arranged between sensor electrodes can be roughly represented by an equivalent circuit in which a resistance component of the measurement target and a capacitance component associated with the measurement system are connected in series. Therefore, the frequency characteristic of the impedance represented by the curve C2 gradually decreases as indicated by a region A2 as the frequency increases from a low frequency close to DC, and a certain frequency (a frequency indicated by reference sign f2 in FIG. 6). Hereinafter, the characteristic becomes substantially constant from “switching frequency”) as indicated by a region A1. As the impedance (resistance component) used when calculating the electrical conductivity, the impedance of the portion flattened in the frequency region above the switching frequency f2 is used as in the region A1 of the curve C2. In the actual measurement example using the conventional electrode structure shown by the curve C2, the frequency f2 is a relatively high frequency due to the influence of the capacitance of the electric double layer.

  When an electrode structure (electrode structures 30a, 30b, 30c) in which the surface area of the electrode is enlarged is used with respect to the curve C2, the impedance curve is downward (in the direction of low impedance) as shown by an arrow E1 in FIG. For example, and changes like a curve C1. With this shift, the switching frequency changes from the switching frequency f2 to the switching frequency f1 (<f2) as indicated by an arrow E2 in FIG. As the switching frequency changes, the region A1 in which the resistance component can be measured is also expanded.

  For example, a liquid having a salinity equivalent to seawater has a high electric conductivity (impedance is low), so that the switching frequency in the frequency characteristic of the impedance is shifted to a high frequency region. For this reason, although the measurement becomes lower as the measurement object has a lower electrical conductivity, the measurement can be easily performed even if the measurement object has a lower electrical conductivity by lowering the switching frequency as in this example.

  By lowering the switching frequency in the frequency characteristic of impedance, the following effects are also obtained. That is, the frequency of the above-mentioned AC signal source used in the electrical conductivity measurement system can be lowered. In general, a signal source with a higher frequency is more expensive and more difficult to handle, but if the measurement frequency can be lowered, there are effects such as cost reduction and simplification of handling.

DESCRIPTION OF SYMBOLS 1 EC sensor 2 Case 10, 10a, 10b, 10c Semiconductor device 12 Board | substrate 14 Insulating layer 16 Sensor electrode wiring 18 Surface protective film 20, 20-1, 20-2, 120 Sensor electrode 22 pH sensor 24 Temperature sensor 26- 1, 26-2 Barrier metal 30, 30a, 30b, 30c Electrode structure 100 EC sensor 102 Housing 110 Semiconductor device 112 Substrate 114 Insulating layer 116 Sensor electrode wiring 118 Surface protective film A1, A2 Regions D1, D2 Direction F Flat part G Corrosion P1, P2 Vertex S Soil SA Buried area

Claims (6)

A semiconductor substrate;
A first electrode that is provided on the semiconductor substrate and outputs the input measurement signal as an input signal;
A second electrode that is provided on the semiconductor substrate and that receives the input signal output from the first electrode and outputs the input signal as an output signal;
Each of the first electrode and the second electrode includes a second side that is opposed to a first side included in the first electrode and a second side that forms an acute angle with the first side. The semiconductor device according to claim 1, wherein the semiconductor substrate includes four sides, and the second side is parallel to any one of the four sides of the semiconductor substrate. The semiconductor device according to claim 1, wherein the semiconductor substrate includes four sides, and the first side forms an angle of 45 degrees with each of the four sides of the semiconductor substrate. The semiconductor device is mounted on the housing such that at least one side of the semiconductor device forms an acute angle with respect to an embedding direction when the housing including the semiconductor device is embedded in soil. The semiconductor device according to claim 3. A semiconductor substrate;
A first electrode that is provided on the semiconductor substrate and outputs the input measurement signal as an input signal;
A second electrode that is provided on the semiconductor substrate and that receives the input signal output from the first electrode and outputs the input signal as an output signal;
Each of the first electrode and the second electrode includes a first side and a second side parallel to each of two sides of the semiconductor substrate that intersect at a predetermined angle, and the first side. A semiconductor device comprising a third side and a fourth side parallel to each of the second sides. Determining the direction of embedding the sensor with the semiconductor device in the soil;
Laying out a sensor electrode having a first side parallel to the embedding direction and a second side making an acute angle with the embedding direction;
A method for designing a semiconductor device including: