Measuring device

Abstract

To provide a measuring device capable of increasing yield while suppressing the influence of noises.SOLUTION: The measuring device includes: a sensor unit 10 that measures a predetermined physical quantity; an amplification circuit 20 for amplifying signals output from the sensor unit 10; and a linear power supply 30 for supplying the electric power to the amplification circuit 20. The amplification circuit 20 includes a first amplifier 21 that has a first transistor using a SiC semiconductor. The linear power supply 30 includes a second amplifier 31 that has a second transistor using a SiC semiconductor. The noise characteristics of the first amplifier 21 are superior to the noise characteristics of the second amplifier 31.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a measuring instrument. [Background technology]

[0002] With regard to circuits of pressure transmission devices installed in nuclear power plants and the like, for example, the technology of Patent Document 1 is known. That is, Patent Document 1 describes a radiation-resistant circuit device including "a SiC semiconductor having a SiC integrated circuit mounted thereon, and a printed circuit board on which the SiC semiconductor is installed." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-28620 Summary of the Invention [Problem to be solved by the invention]

[0004] Problems with circuits containing SiC semiconductors include the high price of wafers produced in the manufacturing process and the large deviation in low-frequency noise (variation between products). For example, if circuits containing SiC semiconductors are selected based on low low-frequency noise, the product yield will decrease, resulting in increased manufacturing costs. Furthermore, if the above-mentioned selection is not performed, the deviation in low-frequency noise will increase, increasing the possibility that some products will have high low-frequency noise, resulting in a decrease in quality.

[0005] As described above, in circuits including SiC semiconductors, there is a trade-off between suppressing the influence of noise and improving yield. It is desirable to increase yield while suppressing the influence of noise in circuits including SiC semiconductors, but Patent Document 1 does not describe such a technique.

[0006] Therefore, an object of the present invention is to provide a measuring instrument that can suppress the influence of noise and increase yield. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the measuring instrument of the present invention includes a sensor unit that measures a predetermined physical quantity, an amplifier circuit that amplifies a signal output from the sensor unit, and a linear power supply that supplies power to the amplifier circuit, wherein the amplifier circuit includes a first amplifier having a first transistor that uses a SiC semiconductor, and the linear power supply includes a second amplifier having a second transistor that uses a SiC semiconductor, and the noise characteristics of the first amplifier are superior to the noise characteristics of the second amplifier. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a measuring instrument that can suppress the influence of noise and increase yield. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a configuration diagram of a measuring device according to a first embodiment. [Figure 2] FIG. 2 is a circuit diagram of a first amplifier included in the measuring instrument according to the first embodiment. [Figure 3] FIG. 2 is a circuit diagram of a linear power supply included in the measuring instrument according to the first embodiment. [Figure 4] 5 is an explanatory diagram relating to the amount of noise of a first amplifier and a second amplifier of the measuring instrument according to the first embodiment. FIG. [Figure 5] 3A and 3B are cross-sectional views of an n-type transistor and a p-type transistor used in a first amplifier and a second amplifier of the measuring instrument according to the first embodiment. [Figure 6A] 4 is an explanatory diagram showing a frequency distribution of the amount of noise in an n-type transistor included in the measuring device according to the first embodiment. FIG. [Figure 6B] 4 is an explanatory diagram showing a frequency distribution of the amount of noise in a p-type transistor included in the measuring device according to the first embodiment. FIG. [Figure 7] 10 is an explanatory diagram showing the relationship between the crystal defect density of SiC and the amount of noise at the intersection G1 in the measuring device according to the first embodiment. FIG. [Figure 8] 4 is an explanatory diagram showing the relationship between the depth from the top surface of the gate insulating film and the nitrogen concentration in the measuring device according to the first embodiment. FIG. [Figure 9] FIG. 10 is a configuration diagram of a measuring device according to a second embodiment. [Figure 10] FIG. 10 is a configuration diagram of a measuring device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] First Embodiment <Measurement equipment configuration> FIG. 1 is a diagram showing the configuration of a measuring device 100 according to the first embodiment. 1 is a device that measures a predetermined physical quantity (state quantity). In the first embodiment, a case will be described in which measuring instrument 100 is a pressure transmitter (pressure sensor) as an example, but the type of measuring instrument 100 is not limited to this.

[0011] As shown in FIG. 1, measuring instrument 100 includes a sensor unit 10, an amplifier circuit 20, and a linear power supply 30. Sensor unit 10 measures a predetermined physical quantity such as pressure. In the example of FIG. 1, sensor unit 10 includes resistance elements R1, R2, and R3, and a strain gauge R4. Strain gauge R4 is an element that outputs a strain amount caused by external pressure as a predetermined electrical signal. For example, a predetermined pressure may be applied to strain gauge R4 in response to the fluid pressure in a tube (not shown) connected to a diaphragm (not shown).

[0012] As shown in FIG. 1, resistor elements R1, R2, and R3 and strain gauge R4 are connected to form a bridge circuit (Wheatstone bridge). The output voltage of the bridge circuit is applied to the input side of amplifier circuit 20 via wires K1 and K2. The voltage applied to amplifier circuit 20 is amplified to a predetermined level by amplifier circuit 20, and the amplified voltage is output via output terminal T3. Although not shown in FIG. 1, the signal output from output terminal T3 (voltage indicating the pressure value) is converted into a digital signal by an A / D converter and further input to a display IC (Integrated Circuit). The configuration of sensor unit 10 shown in FIG. 1 is an example and is not limited to this.

[0013] The amplifier circuit 20 amplifies a signal (voltage) output from the sensor unit 10 via wires K1 and K2. As shown in FIG. 1, the amplifier circuit 20 includes a first amplifier 21. The first amplifier 21 amplifies a voltage applied between an inverting input terminal T1 and a non-inverting input terminal T2. In the example of FIG. 1, a wire K1 is connected to the inverting input terminal T1 of the first amplifier 21, and a wire K2 is connected to the non-inverting input terminal T2. The output side of the first amplifier 21 is connected to the output terminal T3 via a wire K3. A power supply wire K4 on the high-voltage side of the first amplifier 21 is connected to a linear power supply 30. A power supply wire K5 on the low-voltage side of the first amplifier 21 is grounded. The circuit configuration of the first amplifier 21 will be described later.

[0014] The linear power supply 30 is a power supply that supplies power to the amplifier circuit 20 and is connected to the first amplifier 21 via a power line K4. A "linear power supply" is a power supply that does not require switching operations using switching elements. As such, the linear power supply 30 has the advantage of being less susceptible to breakdowns even in a radiation environment, since it does not require switching operations. As shown in FIG. 1, the linear power supply 30 includes a second amplifier 31 and a transistor 32. The circuit configuration of the linear power supply 30 will be described later.

[0015] FIG. 2 is a circuit diagram of the first amplifier 21 provided in the measuring device. 2, the first amplifier 21 includes a differential circuit 211, a current control circuit 212, and an output stage 213. The differential circuit 211, the current control circuit 212, and the output stage 213 are each connected to a high-voltage power supply line L1 and a low-voltage power supply line L2. A voltage is applied between the power supply lines L1 and L2 from a linear power supply 30 (see FIG. 1).

[0016] The first amplifier 21 includes transistors M1 to M8 (first transistors) that use SiC semiconductors. In the example of Fig. 2, the transistors M1, M2, and M5 to M7 are n-channel MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), and the remaining transistors M3, M4, and M8 are p-channel MOSFETs. Hereinafter, "n-channel type" will be simply referred to as "n-type," and "p-channel type" will be simply referred to as "p-type."

[0017] Generally, semiconductor elements are susceptible to radiation (especially gamma rays), but SiC semiconductors, which are one type of wide bandgap semiconductor, are characterized by their excellent radiation resistance. Therefore, in the first embodiment, SiC semiconductors are used for the transistors M1 to M8 of the first amplifier 21, thereby improving the radiation resistance of the first amplifier 21. Each of the transistors M1 to M8 operates in the saturation region.

[0018] 2 is a circuit that amplifies the differential voltage between the inverting input terminal T1 and the non-inverting input terminal T2, and is configured to include transistors M1 to M4. The current control circuit 212 controls the idling current I of the transistors M5 etc. A The output stage 213 is a circuit for controlling the voltage amplified by the differential circuit 211, and is configured to include a resistor element R5 and transistors M5 to M7. The output stage 213 is a circuit for outputting the voltage amplified by the differential circuit 211, and is configured to include a transistor M8 and a capacitor C1.

[0019] 2, a high-voltage power supply line L1 is connected to a low-voltage power supply line L2 via a p-type transistor M3, an n-type transistor M1, and an n-type transistor M6 in this order. Similarly, a high-voltage power supply line L1 is connected to a low-voltage power supply line L2 via a p-type transistor M4, an n-type transistor M2, and an n-type transistor M6 in this order.

[0020] The gate of the n-type transistor M1 is connected to the inverting input terminal T1. The gate of the n-type transistor M2 is connected to the non-inverting input terminal T2. The gates of the p-type transistors M3 and M4 are connected to each other via wiring. The gates of the n-type transistors M5 to M7 are connected to each other to form a current mirror circuit. Therefore, in the current control circuit 212, the idling current I of the transistor M5 is A A current having a magnitude equal to or depending on the ratio of the gate widths of the transistor M5 also flows through the transistors M6 and M7.

[0021] An n-type transistor M5, which is a component of the current mirror circuit, is connected to the high-voltage power supply line L1 via a resistor R5. An n-type transistor M7, which is also a component of the current mirror circuit, is connected to the high-voltage power supply line L1 via a p-type transistor M8. The gate of transistor M8 is connected between transistors M2 and M4 and also connected to output terminal T3 via capacitor C1. The voltage between the inverting input terminal T1 and the non-inverting input terminal T2 is amplified to a predetermined level, and the amplified voltage is output via output terminal T3. The configuration of first amplifier 21 shown in FIG. 2 is merely an example and is not limiting.

[0022] FIG. 3 is a circuit diagram of a linear power supply 30 provided in the measuring device. As described above, the linear power supply 30 is a power supply that supplies power to the first amplifier 21 (see FIG. 1). As shown in FIG. 3, the linear power supply 30 includes a Zener diode Z1, a resistive element R6, a second amplifier 31, and transistors 32 and 33. The Zener diode Z1 is an element that maintains a substantially constant voltage across both ends regardless of changes in current when a predetermined Zener voltage (reverse voltage) is applied.

[0023] The anode of the Zener diode Z1 is connected to the low-voltage power supply line L4. The cathode of the Zener diode Z1 is connected to the non-inverting input terminal T5 of the second amplifier 31 and also to the high-voltage power supply line L3 via a resistor R6. By using such a Zener diode Z1, the input voltage V in Even if the voltage fluctuates, the potential of the non-inverting input terminal T5 of the second amplifier 31 is kept substantially constant.

[0024] The second amplifier 31 is a circuit that amplifies the voltage applied between the inverting input terminal T4 and the non-inverting input terminal T5, and has a second transistor (not shown) that uses a SiC semiconductor. The configuration of the second amplifier 31 may be the same as that of the first amplifier 21 (see FIG. 2) of the amplifier circuit 20 (see FIG. 1), or may be a different configuration from that of the first amplifier 21. In the first embodiment, a case will be described in which the circuit configuration of the second amplifier 31 is the same as that of the first amplifier 21 (see FIG. 2). If FIG. 2 is considered to be the circuit configuration of the second amplifier 31, the transistors M1 to M8 shown in FIG. 2 correspond to the "second transistor."

[0025] 3, the non-inverting input terminal T5 of the second amplifier 31 is connected between the Zener diode Z1 and the resistor R6 via a wiring K6. The inverting input terminal T4 of the second amplifier 31 is connected to the collector side of the transistor 33 on the high-voltage power supply line L3 via a wiring K7. The output side of the second amplifier 31 is connected to the base of the transistor 32 via a wiring K8.

[0026] The transistors 32 and 33 are bipolar transistors that amplify current in accordance with the output of the second amplifier 31. The base of the transistor 32 is connected to the output side of the second amplifier 31, the emitter is connected to the low-voltage power supply line L4, and the collector is connected to the base of the other transistor 33.

[0027] The emitter of the other transistor 33 is connected to the input side of the high-voltage power supply line L3. The collector of the transistor 33 is connected to the output side of the high-voltage power supply line L3 and is also connected to the inverting input terminal T4 of the second amplifier 31 via a wiring K7. These transistors 32 and 33 each operate in the saturation region. A substantially constant output voltage V OUT The configuration of the linear power supply 30 shown in Fig. 3 is an example, and the present invention is not limited to this.

[0028] FIG. 4 is an explanatory diagram relating to the amount of noise of the first amplifier and the second amplifier (also see FIG. 1 as appropriate). The horizontal axis of FIG. 4 represents the frequency of noise when a DC voltage is applied to the first amplifier 21 or the second amplifier 31. The vertical axis of FIG. 4 represents the amount of noise in the first amplifier 21 or the second amplifier 31. The S id [au] indicates that the amount of noise has been normalized by dividing it by the square of the drain current. As shown in Fig. 4, when compared at the same frequency (noise frequency), the amount of noise of the first amplifier 21 is smaller than the amount of noise of the second amplifier 31. In other words, the noise characteristics of the first amplifier 21 are superior to the noise characteristics of the second amplifier 31.

[0029] In the example of FIG. 4, when a DC voltage is applied to the first amplifier 21 and the second amplifier 31, the noise frequency is 1.00×10 0 [Hz]~1.00×10 4The amount of noise of the first amplifier 21 is smaller than the amount of noise of the second amplifier 31 within the range of [Hz]. Note that it is not particularly necessary for the amount of noise of the first amplifier 21 to be smaller than the amount of noise of the second amplifier 31 over the entire range of noise frequencies. For example, the amount of noise of the first amplifier 21 may be smaller than the amount of noise of the second amplifier 31 within a predetermined noise frequency range that is likely to occur when the first amplifier 21 or the second amplifier 31 is used. Even in such a case, the noise characteristics of the first amplifier 21 are considered to be superior to the noise characteristics of the second amplifier 31.

[0030] As described above, the SiC semiconductor used in each transistor of the first amplifier 21 and the second amplifier 31 has excellent radiation resistance. However, with conventional technology, a relatively high percentage of amplifiers failed the inspection stage due to crystal defects specific to SiC semiconductors, resulting in reduced product yields and increased manufacturing costs. While selecting amplifiers with low low-frequency noise during the inspection stage is effective in reducing the noise of the measuring instrument 100, this further reduces product yields and increases manufacturing costs. Therefore, in the first embodiment, the amount of noise of the amplifiers is measured during the inspection stage, and the amplifiers are classified into low-noise and high-noise amplifiers.

[0031] As described above, the first amplifier 21 and the second amplifier 31 can share a common circuit configuration. Therefore, after classifying a type of amplifier into low noise and high noise, a low-noise amplifier is used for the first amplifier 21 (see FIG. 1) that processes the signal from the sensor unit 10 (see FIG. 1). Furthermore, a high-noise amplifier is used for the second amplifier 31 (see FIG. 1) of the linear power supply 30 (see FIG. 1), which is less susceptible to noise. This, for example, can reduce the number of amplifiers that fail inspection due to high noise, thereby reducing the unit cost of the amplifier. Furthermore, noise can be suppressed by using a low-noise amplifier as the first amplifier 21 (see FIG. 1) of the amplifier circuit 20 (see FIG. 1), which is highly susceptible to noise.

[0032] FIG. 5 is a cross-sectional view of an n-type transistor 40n and a p-type transistor 40p used in the first amplifier and the second amplifier. The n-type transistor 40n shown in FIG. 5 is, for example, the transistors M1, M2, M5 to M7 (see FIG. 2) described above. The p-type transistor 40p shown in FIG. 5 is, for example, the transistors M3, M4, M8 (see FIG. 2) described above. Note that the second amplifier 31 (see FIG. 3) may have the same circuit configuration as the first amplifier 21 (see FIG. 2), and therefore uses the transistors M1 to M8. Although FIG. 5 shows a case where the n-type transistor 40n and the p-type transistor 40p are integrated, there is no particular need for them to be integrated.

[0033] 5, an n-type epitaxial layer 42 (semiconductor layer) is formed on an n-type semiconductor substrate 41 made of a compound semiconductor such as SiC (silicon carbide). Like the semiconductor substrate 41, the epitaxial layer 42 is made of a compound semiconductor such as SiC (silicon carbide). The impurity concentration of the epitaxial layer 42 is lower than the impurity concentration of the semiconductor substrate 41. A metal layer 43 is formed below the semiconductor substrate 41.

[0034] In the n-type transistor 40n, a p-type well region 44 is formed on the n-type epitaxial layer 42. In the p-type well region 44, n-type high-concentration impurity regions 45a and 45b, which have an impurity concentration higher than that of the semiconductor substrate 41, are formed. One of the high-concentration impurity regions 45a and 45b is the source of the transistor 40n, and the other is the drain of the transistor 40n. The p-type well region 44 is located between these high-concentration impurity regions 45a and 45b. A wiring 46a is connected to the n-type high-concentration impurity region 45a. Similarly, a wiring 46b is connected to the other high-concentration impurity region 45b.

[0035] A gate insulating film 47 is formed on the n-type high-concentration impurity regions 45a, 45b and the p-type well region 44. For example, a silicon oxide film is used as the gate insulating film 47. The gate insulating film 47 protrudes upward in the region including the n-type high-concentration impurity regions 45a, 45b, and a field oxide film 48 is provided below this protruding portion. For example, a silicon oxide film is used as the field oxide film 48. A gate electrode 49 is formed on the gate insulating film 47. For example, a polycrystalline silicon film into which n-type impurities are implanted is used as the gate electrode 49. Below the gate electrode 49, the well region 44 between the high-concentration impurity regions 45a, 45b functions as a channel region.

[0036] An interlayer insulating film 50 is formed so as to cover the gate insulating film 47 and the gate electrode 49 from above. For example, a silicon oxide film is used as the interlayer insulating film 50. The above-mentioned wiring 46a passes through the interlayer insulating film 50, the gate insulating film 47, and the field oxide film 48 in this order, and is connected to the high-concentration impurity region 45a (the same is true for the other wiring 46b).

[0037] 5 is similar to the n-type transistor 40n, except that the well region 44 is not provided and p-type impurities are implanted into the high-concentration impurity regions 45c and 45d. That is, in the p-type transistor 40p, the p-type high-concentration impurity regions 45c and 45d are formed on the n-type epitaxial layer 42.

[0038] FIG. 6A is an explanatory diagram showing a frequency distribution of the amount of noise in an n-type transistor. The horizontal axis of FIG. 6A represents the value obtained by normalizing the amount of noise by dividing it by the square of the drain current. The vertical axis of FIG. 6A represents the cumulative frequency expressed as a percentage. The measurement conditions for FIG. 6A were as follows: a constant voltage of 3 [V] was applied between the drain and source of n-type transistor 40n (see FIG. 5), and a predetermined voltage was applied between the gate and source so that the drain current was 0.1 [mA]; and the fluctuations in the drain current (noise) were measured with a spectrum analyzer (not shown). The measurement conditions for FIGS. 6B and 7, which will be described later, were the same.

[0039] As shown in FIG. 6A, the amount of noise in the n-type transistor 40n is approximately 1.00×10 -11 [ / Hz], and each point of the frequency distribution based on the magnitude of the noise amount is distributed along the line N1 (a line with a steep positive slope). Therefore, for a product with an n-type transistor 40n, the noise amount is approximately 1.00 × 10 -11 It can be treated as [ / Hz].

[0040] FIG. 6B is an explanatory diagram showing the frequency distribution of the amount of noise in a p-type transistor. The horizontal axis of FIG. 6B represents the value obtained by normalizing the amount of noise by dividing it by the square of the drain current. The vertical axis of FIG. 6B represents the cumulative frequency expressed as a percentage. As shown in FIG. 6B, the amount of noise in the p-type transistor 40p is approximately 1.00×10 -11 [ / Hz] are distributed along the line N2 (a line with a steep positive slope). However, the amount of noise is about 1.00 × 10 -11 If it exceeds [ / Hz], the frequency distribution will no longer follow the line N2, and the amount of noise will vary greatly.

[0041] FIG. 7 is an explanatory diagram showing the relationship between the crystal defect density of SiC and the amount of noise at the intersection G1. The horizontal axis of FIG. 7 represents the crystal defect density of the epitaxial layer 42 (see FIG. 5) made of SiC in the p-type transistor 40p (see FIG. 5). The vertical axis of FIG. 7 represents the amount of noise at the intersection G1 shown in FIG. 6B. That is, the amount of noise at the intersection G1 (see FIG. 6B) when the frequency distribution (see FIG. 6B) based on the amount of noise in the p-type transistor 40p (see FIG. 5) starts to deviate from the predetermined line N2 and begin to vary is the amount of noise. "E-11" included in the numerical values ​​on the vertical axis of FIG. 7 is 10 -11 Also, "E-12" means 10 -12 This means:

[0042] Incidentally, the frequency distribution of FIG. 6B is obtained when the crystal defect density of the epitaxial layer 42 (see FIG. 5) formed of SiC is about 100 cm -2 ] (corresponding to point H1 in FIG. 7) was used as the target. FIG. 7 plots data for various transistors 40p having different crystal defect densities in the epitaxial layer 42 (see FIG. 5). Note that in FIG. 7, the data for the transistors 40p having a crystal defect density of about 100 [cm -2 ] and point H1 when the crystal defect density is about 570 [cm -2 ] and point H2 in the case of , but in reality, many points are plotted along the line N4.

[0043] For example, when the crystal defect density is about 100 cm -2 ], the amount of noise is about 1.00 × 10 -11 (See point H1 in FIG. 7 and the noise amount at intersection G1 in FIG. 6B) In the range below this, the frequency distribution based on the noise amount hardly varies and is distributed along a predetermined line N2 (see FIG. 6B). Similarly, when the crystal defect density is about 570 cm -2 ], the amount of noise is approximately 1.08 × 10 -11 (See point H2 in FIG. 7) In the range below this point, the frequency distribution based on the amount of noise is distributed along a predetermined straight line (not shown).

[0044] As shown in FIG. 7, the value (intercept) of the line N4 when the crystal defect density of the epitaxial layer 42 (see FIG. 5) made of SiC becomes zero is 9.80×10 -12 Therefore, it is preferable to use the following noise characteristics for the "second transistor" of the second amplifier 31 (see FIG. 1), which has a larger amount of noise than the first amplifier 21 (see FIG. 1): That is, the normalized value obtained by dividing the amount of noise of the "second transistor" by the square of the drain current is 9.80×10 -12 It is preferable that it is greater than [ / Hz].

[0045] This makes it possible to suppress variations in the amount of noise in the p-type transistor 40p of the first amplifier 21, regardless of the magnitude of the crystal defect density of SiC. As a result, it becomes possible to treat the amount of noise in the entire system as low by regarding the amount of noise in the transistor 40p as being constant. In addition, the method described below can also be used to suppress variations in the amount of noise itself.

[0046] FIG. 8 is an explanatory diagram showing the relationship between the depth from the top surface of the gate insulating film and the nitrogen concentration (also see FIG. 5 as appropriate). 8, the horizontal axis represents the depth from the top surface of the gate insulating film 47, and the vertical axis represents the nitrogen concentration. Regarding the expression "p-well or epitaxial layer" in FIG. 8, "p-well" corresponds to the n-type transistor 40n (n-type MOSFET). In other words, in FIG. 8, the depth of the interface between the well region 44 (p-well) of the n-type transistor 40n and the gate insulating film 47 is the value D1. Furthermore, the "epitaxial layer" in FIG. 8 corresponds to the p-type transistor 40p (p-type MOSFET). In other words, in FIG. 8, the depth of the interface between the epitaxial layer 42 of the p-type transistor 40p and the gate insulating film 47 is the value D1.

[0047] 8, in the n-type transistor 40n (n-type MOSFET), the nitrogen concentration increases toward the interface (depth value D1) between the gate insulating film 47 and the well region 44. In addition, in the p-type transistor 40n (p-type MOSFET), the nitrogen concentration increases toward the interface (depth value D1) between the gate insulating film 47 and the epitaxial layer 42.

[0048] In an n-type transistor 40n using a SiC semiconductor, an oxynitriding treatment (NO annealing) is usually performed on the interface between the gate insulating film 47 and the well region 44. The same is true for a p-type transistor 40p using a SiC semiconductor. However, in the p-type transistor 40p, due to the presence of nitrogen at the interface between the gate insulating film 47 and the epitaxial layer 42, carriers are more likely to be trapped in defects near the interface, which is presumably why noise deviation (variation between products) increases. In the example of FIG. 6B, the amount of noise is approximately 1.00×10 -11 The frequency distribution based on the amount of noise varies in the range exceeding [ / Hz].

[0049] Therefore, the inventors have found that noise variation can be reduced by making the nitrogen concentration at the interface between the gate insulating film 47 and the epitaxial layer 42 in a p-type transistor 40p (p-type MOSFET) lower than the nitrogen concentration at the interface between the gate insulating film 47 and the well region 44 in an n-type transistor 40n (n-type MOSFET).

[0050] 8, the nitrogen concentration near the interface of the gate insulating film 47 of the p-type transistor 40p is lower than that of the n-type transistor 40n. This reduces the variation in noise presumably caused by nitrogen. Note that the magnitude relationship of the nitrogen concentration at the interface described above can be said to be the same for each transistor of the second amplifier 31 as well as for each transistor M1 to M8 of the first amplifier 21 (see FIG. 2).

[0051] Furthermore, it is preferable that the gate capacitance of the p-type transistor 40p is larger than the gate capacitance of the n-type transistor 40n. For example, among the transistors M1 to M4 (first transistors) of the first amplifier 21 (see FIG. 2), the gate capacitance of the p-type transistors M3 and M4 (p-type MOSFETs) should be larger than the gate capacitance of the n-type transistors M1 and M2 (n-type MOSFETs).

[0052] Furthermore, the gate capacitances of the p-type transistors M3, M4, and M8, including the remaining transistors M5 to M7, may be made larger than the gate capacitances of the n-type transistors M1, M2, and M5 to M7. In this way, increasing the gate capacitances of the p-type transistors M3, M4, and M8 makes it easier to absorb noise. The same applies to the second amplifier 31 (see FIG. 1) as well as the first amplifier 21 (see FIG. 1).

[0053] In addition, the nitrogen concentration (1 cm 3 ) at the interface between the gate insulating film 47 and the epitaxial layer 42 in the p-type transistors M3, M4, and M8 (p-type MOSFETs) of the first amplifier 21 (see FIG. 2) 2 The number of nitrogen molecules per 10 [cm -2 ] or more, and 10 14 [cm -2 ] or less. By suppressing the nitrogen concentration at the interface as described above, defects at the interface are reduced, making it difficult for carrier traps to occur near the interface. As a result, noise in the first amplifier 21 is suppressed. The same can be said for each p-type transistor of the second amplifier 31 (see FIG. 3).

[0054] <Effects> In the first embodiment, the first amplifier 21 that processes the signal from the sensor unit 10 has better noise characteristics than the second amplifier 31 used in the linear power supply 30. This makes it possible to suppress the effects of noise in the measuring device 100. Furthermore, a high-noise amplifier (i.e., an amplifier with poor noise characteristics) that would previously have been rejected during testing can be used as the second amplifier 31 of the linear power supply 30. This makes it possible to improve yield and reduce the unit cost of the first amplifier 21 and the second amplifier 31. As a result, the manufacturing cost of the measuring device 100 can be reduced. In this way, according to the first embodiment, it is possible to achieve both suppression of the effects of noise in the measuring device 100 and improvement of yield.

[0055] Second Embodiment The second embodiment differs from the first embodiment in that the measuring device 100A (see FIG. 9) includes a pressure sensor 10a (see FIG. 9) and a temperature sensor 10b (see FIG. 9) as the sensor unit 10A. The second embodiment also differs from the first embodiment in that a first amplifier 21a (see FIG. 9) is connected to the pressure sensor 10a, and another first amplifier 21b (see FIG. 9) is connected to the temperature sensor 10b. The rest of the second embodiment is similar to the first embodiment. Therefore, only the parts that differ from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0056] FIG. 9 is a diagram showing the configuration of a measuring device 100A according to the second embodiment. As shown in FIG. 9, measuring instrument 100A includes sensor unit 10A, amplifier circuit 20A, and linear power supply 30. Sensor unit 10A includes pressure sensor 10a and temperature sensor 10b (another sensor). Pressure sensor 10a is a sensor that detects pressure (a predetermined physical quantity). The configuration of pressure sensor 10a is similar to that of sensor unit 10 (see FIG. 1) described in the first embodiment, and therefore a detailed description thereof will be omitted. Temperature sensor 10b is a sensor that detects temperature (a predetermined physical quantity). The configuration of temperature sensor 10b is well known, and therefore a detailed description thereof will be omitted.

[0057] As shown in Fig. 9, the amplifier circuit 20A includes first amplifiers 21a and 21b. The first amplifier 21a amplifies a signal output from the pressure sensor 10a and is connected to the pressure sensor 10a via a wire K11. For simplification, Fig. 9 shows a single wire as the wire K11 connecting the pressure sensor 10a and the first amplifier 21a, but in reality, the pressure sensor 10a and the first amplifier 21a are connected via two wires (the same applies to the temperature sensor 10b). A predetermined signal is output via the output terminal T6 of the first amplifier 21a.

[0058] The first amplifier 21b (another first amplifier) ​​amplifies the signal output from the temperature sensor 10b and is connected to the temperature sensor 10b via a wire K12, and outputs a predetermined signal via an output terminal T7 of the first amplifier 21b.

[0059] 9, the first amplifier 21a is connected to the linear power supply 30 via a high-voltage power supply line K13 and is grounded via a low-voltage power supply line K14. Similarly, the other first amplifier 21 is connected to the linear power supply 30 via a high-voltage power supply line K15 and a part of the power supply line K13 in that order and is grounded via a low-voltage power supply line K16. In this way, supplying power to the first amplifiers 21a and 21b from a common linear power supply 30 simplifies the configuration and reduces the manufacturing costs of the measuring instrument 100A.

[0060] For example, in nuclear power plants and radiation utilization facilities, pressure sensor 10a often requires higher detection accuracy than temperature sensor 10b. In such cases, it is preferable to ensure that the noise characteristics of first amplifier 21a connected to pressure sensor 10a are superior to the noise characteristics of first amplifier 21b (another first amplifier) ​​connected to temperature sensor 10b (another sensor). For example, the amount of noise of the amplifiers may be measured during an inspection and classified into three levels: low noise, medium noise, and high noise. A low-noise amplifier may be used as first amplifier 21a connected to pressure sensor 10a, a medium-noise amplifier may be used as first amplifier 21b connected to temperature sensor 10b, and a high-noise amplifier may be used as second amplifier 31 of linear power supply 30. This reduces the effects of noise while reducing the manufacturing cost of measuring instrument 100A.

[0061] <Effects> According to the second embodiment, a common linear power supply 30 is used as a power supply to supply power to the first amplifier 21a connected to the pressure sensor 10a and the first amplifier 21b connected to the temperature sensor 10b. This simplifies the circuit configuration of the measuring instrument 100A and reduces manufacturing costs. Furthermore, the first amplifier 21a connected to the pressure sensor 10a has better noise characteristics than the first amplifier 21b connected to the temperature sensor 10b. This allows, for example, in a nuclear power plant, to detect the pressure of cooling water with high accuracy and also detect the temperature with accuracy within an acceptable range.

[0062] Third Embodiment The third embodiment differs from the first embodiment in that the amplifier circuit 20B (see FIG. 10) includes two first amplifiers 21c and 21d (see FIG. 10). The third embodiment also differs from the first embodiment in that a linear power supply 30 (see FIG. 10) is connected to the high-voltage side of the two first amplifiers 21c and 21d (see FIG. 10) and another linear power supply 30B (see FIG. 10) is connected to the low-voltage side. The rest of the third embodiment is the same as the first embodiment. Therefore, only the parts that differ from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0063] FIG. 10 is a diagram showing the configuration of a measuring device 100B according to the third embodiment. As shown in FIG. 10, measuring instrument 100B includes sensor unit 10, amplifier circuit 20B, and linear power supplies 30 and 30B. Amplifier circuit 20B amplifies a signal from sensor unit 10 and includes first amplifiers 21c and 21d. One of the first amplifiers 21c is connected to sensor unit 10 via wiring K1 and K2. The other first amplifier 21d is connected to the other first amplifier 21c via wiring K21. A predetermined signal is output via output terminal T8 of first amplifier 21d.

[0064] The linear power supplies 30 and 30B are power supplies that supply power to the first amplifiers 21c and 21d of the amplifier circuit 20B. As shown in Fig. 10, the linear power supply 30 (high-voltage side linear power supply) is connected to the first amplifier 21c via a high-voltage side power supply line K22 and to another first amplifier 21d via a high-voltage side power supply line K23. The other linear power supply 30B (low-voltage side linear power supply) is connected to the first amplifier 21c via a low-voltage side power supply line K24 and to another first amplifier 21d via a low-voltage side power supply line K25. The linear power supply 30B may have the same configuration as the other linear power supply 30, or may have a different configuration.

[0065] It is preferable that the noise characteristics of at least one of the first amplifiers 21c and 21d be superior to both the noise characteristics of the second amplifier 31 of the linear power supply 30 (high-voltage side linear power supply) and the noise characteristics of the second amplifier 31B of the linear power supply 30B (low-voltage side linear power supply). This makes it possible to increase the yield of each amplifier while suppressing the effects of noise.

[0066] <Effects> According to the third embodiment, by providing a plurality of first amplifiers 21c and 21d, it is possible to design an amplifier circuit 20B that meets predetermined specifications. Furthermore, the noise characteristics of at least one of the first amplifiers 21c and 21d are made superior to both the noise characteristics of the second amplifier 31 of the high-voltage linear power supply 30 and the noise characteristics of the second amplifier 31B of the low-voltage linear power supply 30B. This makes it possible to increase the yield of each amplifier while suppressing the effects of noise.

[0067] <<Variations>> Although the measuring device 100 and the like according to the present invention have been described in the above in relation to the various embodiments, the present invention is not limited to these descriptions and various modifications can be made. For example, in the first embodiment, the linear power supply 30 has been described as having the configuration shown in Fig. 3, but the present invention is not limited to this. That is, the linear power supply 30 may use an AC transformer (not shown) including an iron core and a coil to step up or step down the voltage. The same can be said for the second and third embodiments.

[0068] In the second embodiment, the sensor unit 10A (see FIG. 9) includes the pressure sensor 10a and the temperature sensor 10b, but the number and types of sensors in the sensor unit 10A can be changed as appropriate. Examples of physical quantities detected by the sensors include, but are not limited to, pressure and temperature, as well as mass, flow rate, illuminance, luminous intensity, volume, viscosity, current, and voltage. Furthermore, in a configuration in which the sensor unit 10A (see FIG. 9) includes the pressure sensor 10a and another sensor that measures a physical quantity other than pressure, it is preferable that the noise characteristics of the first amplifier 21a connected to the pressure sensor 10a be superior to the noise characteristics of another first amplifier connected to the other sensor. This allows pressure to be measured with high accuracy in a nuclear power plant or the like, and other physical quantities to be measured with accuracy within an acceptable range.

[0069] In the third embodiment, the amplifier circuit 20B (see FIG. 10) includes two first amplifiers 21c and 21d, and the linear power supplies 30 and 30B (see FIG. 10) each include one second amplifier. However, this is not limiting. For example, the amplifier circuit may include multiple first amplifiers, and the linear power supplies may include multiple second amplifiers. In such a configuration, it is preferable that the noise characteristics of at least one of the multiple first amplifiers be superior to the noise characteristics of any of the multiple second amplifiers. This configuration can also increase product yield while suppressing the effects of noise. Furthermore, the noise characteristics of each of the multiple first amplifiers may be superior to the noise characteristics of any of the multiple second amplifiers. This configuration can further reduce the effects of noise.

[0070] In addition, in a configuration in which the linear power supply includes a plurality of second amplifiers, a value obtained by dividing the amount of noise of a second transistor included in at least one of the plurality of second amplifiers by the square of the drain current is 9.80×10 -12 [ / Hz], which makes it possible to suppress noise variations regardless of the magnitude of the crystal defect density in the epitaxial layer 42 (see FIG. 5) made of SiC.

[0071] Furthermore, in each embodiment, the transistors M1 to M8 (see FIG. 2) are MOSFETs, but the present invention can also be applied to other types of transistors. Furthermore, in each embodiment, the first amplifier 21 and the second amplifier 31 are transimpedance amplifiers, but the present invention can also be applied to other types of amplifiers such as operational amplifiers.

[0072] In addition, in each embodiment, a case has been described in which a SiC semiconductor is used for each of the transistors M1 to M8 included in the first amplifier 21 (see FIG. 2) and a SiC semiconductor is used for each of the transistors (not shown) included in the second amplifier 31 (see FIG. 3), but this is not limiting. For example, the plurality of transistors included in the first amplifier 21 may include a mixture of transistors that do not contain a SiC semiconductor. Furthermore, the plurality of transistors included in the second amplifier 31 may include a mixture of transistors that do not contain a SiC semiconductor.

[0073] Furthermore, the respective embodiments can be combined as appropriate. For example, the second embodiment (see FIG. 9) and the third embodiment (see FIG. 10) may be combined so that in a configuration in which the sensor unit 10A includes the pressure sensor 10a and the temperature sensor 10b (second embodiment), the amplifier circuit that amplifies the signals from each sensor includes a plurality of first amplifiers (third embodiment).

[0074] Furthermore, in each embodiment, the case where measuring instrument 100 (see FIG. 1) is used in a nuclear power plant or a radiation utilization facility has been described, but the present invention is not limited to this. For example, measuring instrument 100 can be used in various plants such as oil refineries and chemical plants, as well as in research facilities.

[0075] Furthermore, each embodiment has been described in detail to clearly explain the present invention, and is not necessarily limited to having all of the configurations described. Furthermore, some of the configurations of each embodiment can be added to, deleted from, or replaced with other configurations.

[0076] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely realized in hardware, for example, by designing them as integrated circuits. Furthermore, the mechanisms and configurations shown are those considered necessary for the explanation, and do not necessarily represent all mechanisms and configurations in the product. Furthermore, the control lines and information lines shown are those considered necessary for the explanation, and do not necessarily represent all control lines and information lines in the product. In reality, it can be assumed that almost all components are interconnected. [Explanation of symbols]

[0077] 100, 100A, 100B measuring instrument 10,10A sensor part 10a Pressure sensor 10b Temperature sensor (another sensor) 20, 20A, 20B Amplification circuit 21, 21a, 21c, 21d 1st amplifier 21b Primary Amplifier (another primary amplifier) 30 Linear power supply (high voltage side linear power supply) 30B Linear Power Supply (Low Voltage Linear Power Supply) 31 Second amplifier 41 Semiconductor substrate 42 Epitaxial layer 43 Metal layer 44 well area 45a, 45b, 45c, 45d High concentration impurity region 46a, 46b wiring 47 Gate insulating film 48 Field Oxide 49 gate electrode 50 Interlayer insulating film K22, K23 Power line (high voltage side power line) K24, K25 Power line (low voltage side power line) M1, M2, M5, M6, M7 Transistors (first transistor, second transistor, n-type MOSFET) M3, M4, M8 transistors (first transistor, second transistor, p-type MOSFET)

Claims

1. a sensor unit for measuring a predetermined physical quantity; an amplifier circuit that amplifies a signal output from the sensor unit; a linear power supply for supplying power to the amplifier circuit; the amplifier circuit includes a first amplifier having a first transistor using a SiC semiconductor; the linear power supply includes a second amplifier having a second transistor using a SiC semiconductor; The noise characteristics of the first amplifier are superior to the noise characteristics of the second amplifier.

2. the amplifier circuit includes a plurality of the first amplifiers, the linear power supply includes a plurality of the second amplifiers; At least one of the plurality of first amplifiers has noise characteristics superior to any of the plurality of second amplifiers.

2. The measuring device according to claim 1, wherein:

3. The normalized value obtained by dividing the amount of noise of the second transistor by the square of the drain current is 9.80×10 －１２ [ / Hz] or greater 2. The measuring device according to claim 1, wherein:

4. the linear power supply includes a plurality of the second amplifiers; a normalized value obtained by dividing the amount of noise of the second transistor included in at least one of the plurality of second amplifiers by the square of the drain current is 9.80×10 －１２ [ / Hz] or greater 2. The measuring device according to claim 1, wherein:

5. the first amplifier includes, as the first transistor, an n-type MOSFET and also a p-type MOSFET; The gate capacitance of the p-type MOSFET is larger than the gate capacitance of the n-type MOSFET.

2. The measuring device according to claim 1, wherein:

6. the first amplifier includes, as the first transistor, an n-type MOSFET and also a p-type MOSFET; The nitrogen concentration at the interface between the gate insulating film and the epitaxial layer in the p-type MOSFET is lower than the nitrogen concentration at the interface between the gate insulating film and the well region in the n-type MOSFET.

2. The measuring device according to claim 1, wherein:

7. The nitrogen concentration at the interface between the gate insulating film and the epitaxial layer in the p-type MOSFET is 10 １０ [cm －２ ] or more, and １４ [cm －２ ] or less 7. The measuring device according to claim 6, wherein:

8. the sensor unit includes a pressure sensor and another sensor that measures a physical quantity different from pressure; The noise characteristics of the first amplifier connected to the pressure sensor are superior to the noise characteristics of another first amplifier connected to the other sensor.

2. The measuring device according to claim 1, wherein:

9. the linear power supply comprises a high-voltage side linear power supply connected to the first amplifier via a high-voltage side power supply line, and a low-voltage side linear power supply connected to the first amplifier via a low-voltage side power supply line, The noise characteristics of the first amplifier are superior to both the noise characteristics of the second amplifier of the high-voltage side linear power supply and the noise characteristics of the second amplifier of the low-voltage side linear power supply.

2. The measuring device according to claim 1, wherein:

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