Pressure sensor

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention comprises a metal stem housed in a metal housing and having a diaphragm for pressure detection, a sensor substrate made of a semiconductor fixed to the surface of the diaphragm via an insulating film, and a sensor substrate formed on the sensor substrate. The present invention relates to a pressure sensor provided with a strain gauge for converting diaphragm strain into an electrical signal.

【0002】

[Conventional technology]

The general overall configuration of a conventional pressure sensor of this type is shown in FIG. 11 as a schematic cross section. This is applicable to, for example, a sensor for high pressure detection that detects a high pressure (fuel pressure) in a fuel pipe in a fuel injection system (for example, a common rail) of an automobile.

【0003】

A metal stem 10 having a diaphragm 11 for pressure detection is housed in a metal housing 10. The metal stem 10 is fixed to the housing 30 by a screw member 20 or the like, and the diaphragm 11 is distorted by the pressure introduced from the pressure introduction passage 32 of the housing 30.

【0004】

Here, FIG. 12 is a schematic cross-sectional view showing an enlarged configuration of the vicinity of the diaphragm 11 in the pressure sensor shown in FIG. 11, and the distortion of the diaphragm 11 is used as an electric signal on the surface of the diaphragm 11 of the metal stem 10. A sensor substrate J40 made of a semiconductor for conversion is fixed via an insulating film 50 made of low melting point glass (silicon oxide or the like) or the like.

【0005】

The sensor substrate chip J40 has a distortion gauge J41 for converting the distortion of the diaphragm 11 into an electric signal (see FIG. 12). In the sensor substrate J40 shown in FIG. 12, a P-shaped region formed on the surface of the N-type silicon substrate is formed as a strain gauge J41.

【0006】

Further, a circuit board 60 is arranged around the sensor board J40, and the sensor board J40 and the circuit board 60 are connected by a bonding wire 64 and electrically connected. Further, the circuit board 60 is electrically connected to the terminal 72 via the pin 66.

【0007】

In such a pressure sensor, the diaphragm 11 is distorted by the pressure introduced from the pressure introduction passage 32, and the distortion is converted into an electric signal via the strain gauge J41 of the sensor substrate chip J40, and this signal is converted into a wire 64 and a circuit board 60. , Pin 66, and terminal 72, output to an external circuit (such as an ECU of an automobile) to detect pressure.

【0008】

[Problems to be Solved by the Invention]

By the way, in the conventional pressure sensor, as shown in FIG. 12, the sensor substrate J40 is fixed to the surface of the diaphragm 11 of the metal stem 10 via the insulating film 50, so that the metal stem 10 A capacitor (parasitic capacitance) Cp having a metal stem 10 and a sensor substrate J40 as electrodes and an insulating film 50 as a dielectric is formed between the sensor substrate J40 and the sensor substrate J40.

【0009】

Therefore, when the pressure sensor is used in a noisy environment, the following problems occur. The noisy environment is, for example, an environment in which electromagnetic waves such as radio waves are generated. Noise currents due to such electromagnetic waves (for example, 1 MHz to 1000 MHz, several tens to 200 V) propagate in the path of the metal stem 10, the parasitic capacitance Cp, the sensor substrate J40, and the strain gauge J41 in this order from the housing 30.

【0010】

Then, a noise current is added to the electric signal output via the strain gauge J41, which is amplified by the subsequent processing circuit, leading to a decrease in the S / N ratio at the sensor output and the occurrence of malfunction. Problems occur.

【0011】

In view of the above problems, the present invention accommodates a metal stem having a diaphragm for pressure detection in a metal housing, and fixes a sensor substrate made of a semiconductor on which a strain gauge is formed to the surface of the diaphragm via an insulating film. The purpose of the pressure sensor is to suppress the influence of external noise on the sensor output.

【0012】

[Means for solving problems]

In order to achieve the above object, in the invention according to claim 1, a metal stem (10) and a strain gauge are provided at a portion between the strain gauge (41) and the insulating film (50) on the sensor substrate (40). It is characterized by providing a shield layer (44) that electrically blocks the air.

【0013】

According to the present invention, the shield layer (44) can electrically block external noise applied to the strain gauge (41) from the metal stem (10) via the housing (30) to the sensor output. The influence of external noise can be suppressed.

【0014】

Here, the invention according to claim 2 provides a specific configuration of a sensor substrate. That is, the sensor substrate (40) is made of a silicon semiconductor chip, and the first conductive layer (40a) and the second conductive layer (40b) are directed from the insulating film (50) side surface to the opposite surface. The shield layer (44) is composed of the first conductive type layer, and the strain gauge (41) is separated from the first conductive type layer and inside the second conductive type layer. It can be composed of a first conductive type region (40c) formed in.

【0015】

Further, the shield layer (44) may be grounded as in the invention of claim 3.

【0016】

Further, in the invention according to claim 4, the strain gauge (41) constitutes a bridge circuit (48) for converting a resistance value change according to the strain of the diaphragm (11) into an electric signal. The sensor board (40) is provided with a shield layer grounding pad (46) for grounding the shield layer (44) and a bridge circuit grounding pad (42b) for grounding the bridge circuit separately. The shield layer grounding pad and the bridge circuit grounding pad are connected to the grounding terminal (72) provided in the housing (30) by separate wiring. ..

【0017】

According to this, the external noise current is released through the shield layer grounding pad (46), which is grounded separately from the bridge circuit grounding pad (42b), so that the external noise to the sensor output is more reliably performed. The influence of can be suppressed.

【0018】

The reference numerals in parentheses of the above means are examples showing the correspondence with the specific means described in the embodiments described later.

【0019】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention shown in the drawings will be described. FIG. 1 shows the overall cross-sectional configuration of the pressure sensor S1 according to the embodiment of the present invention. Further, FIG. 2 is an enlarged perspective view showing an outline (cross section of the sensor chip and the metal stem) of the circled part A in FIG.

【0020】

In the present embodiment, the pressure sensor S1 is attached to a fuel pipe (not shown) in a fuel injection system (for example, a common rail) of an automobile, and a liquid as a pressure medium in the fuel pipe is attached. Alternatively, it will be described as detecting the pressure of the gas-liquid mixture.

【0021】

Reference numeral 10 denotes a metal stem having a hollow cylindrical shape, which is screwed and fixed to the housing 30 by a screw member 20. The metal stem 10 has a thin-walled diaphragm 11 as a closing portion on one end side and an opening 12 on the other end side. Further, on the other end side (opening 12 side) of the metal stem 10, a stepped portion 13 having a larger outer peripheral diameter than the one end side (diaphragm 11 side) is formed.

【0022】

As shown in FIG. 2, a sensor chip 40 made of a semiconductor (sensor substrate in the present invention) is joined and fixed to the surface of the diaphragm 11 of the metal stem 10 by an insulating film 50 made of low melting point glass or the like.

【0023】

The sensor chip 40 detects the distortion generated when the diaphragm 11 is deformed by the pressure of the pressure medium introduced into the metal stem 10 from the opening 12, and converts the distortion of the diaphragm 11 into an electric signal. It is equipped with a strain gauge 41 (see Fig. 3) for this purpose.

【0024】

The material of the metal stem 10 is required to have high strength because it receives ultra-high pressure, and to have a low coefficient of thermal expansion because the sensor chip 40 made of Si is joined by an insulating film 50 such as glass. Specifically, Fe, Ni, Co or Fe, Ni is the main component, and Ti, Nb, Al or Ti, Nb is added as the precipitation strengthening material, and the material is formed by pressing, cutting, cold forging, etc. it can.

【0025】

The housing 30 is directly attached to the fuel pipe as an attached body, and a screw 31 for the attachment is formed on the outer peripheral surface thereof. Further, inside the housing 30, a pressure introduction passage 32 communicating with the opening 12 of the metal stem 10 is formed. The pressure introduction passage 32 communicates with the inside of the fuel pipe in a state where the housing 30 is attached to the fuel pipe, and introduces the pressure medium into the metal stem 10.

【0026】

The screw member (screw) 20 has a cylindrical shape that covers the outer periphery of the metal stem 10, and a male threaded portion 21 is formed on the outer peripheral surface thereof. A female threaded portion 33 having a shape corresponding to the threaded portion 21 is formed.

【0027】

Then, due to the screw connection of both screw portions 21 and 33, the pressing force from the screw member 20 is applied to the stepped portion 13 in the metal stem 10, so that the metal stem 10 is pressed and fixed to the housing 30 and further. By this pressing force, the communication portion between the opening 12 and the pressure introduction passage 32, that is, the boundary portion K between the opening 12 side of the metal stem 10 and the pressure introduction passage 32 side of the housing 30 is sealed.

【0028】

In this way, the housing 30 has the functions of fixing to the fuel pipe (ultra-high pressure seal and mechanical holding) and fixing using the screw member 20 of the metal stem 10 (ultra-high pressure sealing and mechanical holding). Furthermore, it has a function of fixing (sealing and mechanically holding) the connector case 80, which will be described later. Therefore, the required quality of the housing 30 includes corrosion resistance from the pressure medium and the actual vehicle environment, and screw strength for maintaining the axial force that generates a high sealing surface pressure at the boundary portion K.

【0029】

Based on these required qualities, the housing 30 is made of carbon steel (for example, S15C) that has both corrosion resistance and high strength with Zn plating to improve corrosion resistance, and XM7, SUS430, SUS304, which have corrosion resistance. SUS630 etc. can be adopted.

【0030】

Further, the screw member 20 is required to have high strength in order to fix the metal stem 10 to the housing 30 and maintain the axial force that generates a high sealing surface pressure. However, the screw member 20 is a package composed of the housing 30 and the connector case 80. Since it is stored inside, unlike the housing 30, it does not require corrosion resistance, and carbon steel or the like can be used.

【0031】

Reference numeral 60 denotes a ceramic substrate as a circuit board, which is arranged around the sensor chip 40 in the housing 30 by being adhered and fixed to the screw member 20. An amplifier (Amp) IC chip 62 and a characteristic adjustment IC chip 62 that amplify the output of the sensor chip 40 are fixed to the substrate 60 with an adhesive. Although not shown in FIG. 1, each IC chip 62 and the ceramic substrate 60 are electrically connected by bonding wires.

【0032】

Here, the ceramic substrate 60 and the sensor chip 40 are connected by a bonding wire 64, which is a thin wire such as Al (aluminum) formed by ultrasonic wire bonding, and are electrically connected. Further, a pin 66 for electrical connection to the connector terminal 70 is joined to the ceramic substrate 60 with silver wax.

【0033】

The connector terminal 70 is an assembly in which the terminal 72 is formed by insert molding into the resin 74. The terminal 72 and the ceramic substrate 60 are joined to the pin 66 by laser welding. As a result, the output from the sensor chip 40 can be transmitted from the bonding wire 64 to the terminal 72 via the pin 66.

【0034】

Further, the connector terminal 70 is fixedly held to the connector case 80 by the adhesive 76, and the terminal 72 can be electrically connected to the ECU of an automobile or the like via a wiring member.

【0035】

Although two terminals 72 are shown in FIG. 1, at least three terminals 72 are provided for input / output, output, and grounding for inputting / outputting voltage to / from the sensor chip 40 via the amplifier IC chip 62. There is.

【0036】

The connector case 80 forms the outer shape of the connector terminal 70, and is integrated with the housing 30 assembled via the O-ring 90 to form a package, and the sensor chip 40, various ICs, and electrical connections inside the package are formed. It protects the part from moisture and mechanical external force. As the material of the connector case 80, PPS (polyphenylene sulfide) or the like having high hydrolyzability can be adopted.

【0037】

Next, a more detailed configuration of the sensor chip 40 will be described with reference to FIGS. 3 and 4. FIG. 3 is a diagram schematically showing a planar configuration of the sensor chip 40 when viewed from a surface (hereinafter referred to as the front surface) opposite to the surface of the sensor chip 40 on the insulating film 50 side (hereinafter referred to as the back surface), and FIG. It is a figure which shows typically the cross-sectional structure of 40.

【0038】

The hatching shown in FIG. 3 does not show a cross section, but is provided for convenience in order to identify each conductive type region appearing on the surface of the sensor chip 40. The hatched region is P. The type area and the white area without diagonal hatching indicate the N type area.

【0039】

In the present embodiment, four strain gauges 41 are formed, and as shown in FIG. 3, these four strain gauges 41 are deformed by being electrically connected to each other by wiring 43 to deform the diaphragm 11. It constitutes a bridge circuit 48 for converting a change in resistance value according to an electric signal into an electric signal. The bridge circuit 48 is a Wheatstone bridge (see FIG. 6 described later) connected at points a, b, c, and d in FIG.

【0040】

The sensor chip 40 of the present embodiment is made of a silicon semiconductor chip, and as shown in FIG. 4, the P-shaped layer (first conductive material) is formed from the back surface side (lower side in the figure) to the front surface (upper side in the figure). The mold layer) 40a and the N-type layer (second conductive mold layer) 40b are sequentially laminated.

【0041】

Here, the strain gauge 41 is formed as a P-type region (first conductive type region) 40c which is formed in the N-type layer 40b separately from the P-type layer 40a and has a different impurity concentration from the P-type layer 40a. ing. Further, in the sensor chip 40, the P-type layer 40a located on the back surface (the surface on the insulating film 50 side) constitutes the shield layer 44 referred to in the present invention.

【0042】

That is, a shield layer 44 that electrically shields the metal stem 10 and the strain gauge 41 is provided at a portion of the sensor chip 40 between the strain gauge 41 and the insulating film 50.

【0043】

In addition, an electrically insulating oxide film 45 is formed on the surface of the sensor chip 40 (see FIG. 4). A gauge pad 42 and a wiring 43 are formed on the oxide film 45 by vapor deposition of Al (aluminum) or the like. Further, the strain gauge 41 and the wiring 43 are electrically connected to each other through an opening formed at a desired portion of the oxide film 45.

【0044】

Then, as shown in FIG. 3, the four strain gauges 41 are electrically connected to each other by the wiring 43 and electrically connected to each gauge pad 42. Since these pads 42 are wire-bonded parts, the oxide film 45 under the gauge pad 42 may be damaged during bonding, and the isolation (electrical separation) of the pad 42 may be broken. Therefore, in this example, as shown in FIG. 4, isolation is ensured by surrounding the N-type layer 40b directly below the gauge pad 42 with the P-type region 40d.

【0045】

Further, as shown in FIG. 4, a shield layer grounding pad 46 for grounding the shield layer 44 is formed on the P-type region 40d, and the pad 46, the P-type region 40d, and the shield layer 44 are formed. Are electrically connected via an opening formed in the oxide film 45.

【0046】

Here, the pads 42 and 46 and the ceramic substrate 60 are connected via a bonding wire 64, whereby the pads 42 and 46 are input, output and grounded according to their respective applications. It is electrically connected to each terminal 72 for.

【0047】

That is, the four gauge pads 42 constituting the bridge circuit 48 are an input pad that is electrically connected to an input terminal 72 for inputting a voltage, and an output terminal for outputting a signal. The applications are shared as an output pad that is electrically connected to the 72 and a bridge circuit grounding pad that is electrically connected to the grounding terminal 72 to ground the bridge circuit 48.

【0048】

The shield layer grounding pad 46 provided separately from the bridge circuit grounding pad is connected to the grounding terminal 72 by separate wiring. Therefore, the shield layer 44 can be grounded by the grounding terminal 72 via the P-shaped region 40d and the shield layer grounding pad 46.

【0049】

In the sensor chip 40 of the present embodiment, each conductive layer and each conductive type region 40a to 40d are formed by an ion implantation method, heat diffusion, or the like, or wiring 43, pads 42, and 46 are formed by a vapor deposition method. It can be manufactured by using a well-known semiconductor manufacturing technique such as forming.

【0050】

A method of assembling the pressure sensor S1 having such a configuration will be described. First, the metal stem 10 to which the sensor chip 40 is joined by the insulating film 50 is screwed to the housing 30 via the screw member 20, and the metal stem 10 is fixed to the housing 30. Next, the ceramic substrate 60 is adhered to the screw member 20, and the ceramic substrate 60 and the sensor chip 40 are connected by wire bonding and electrically connected.

【0051】

Next, the connector terminal 70 and the pin 66 are joined by laser welding (YAG laser welding, etc.). Next, the connector case 80 is assembled to the groove portion of the housing 30 via the O-ring 90, and the connector case 80 and the housing 30 are fixed by crimping the groove portion. In this way, the pressure sensor S1 shown in FIG. 1 is completed.

【0052】

The pressure sensor S1 is connected and fixed to the fuel pipe by directly connecting and attaching the screw 31 of the housing 30 to the screw portion formed on the fuel pipe (not shown above).

【0053】

Then, when the fuel pressure in the fuel pipe is introduced into the inside of the metal stem 10 from the opening 12 of the metal stem 10 through the pressure introduction passage 32, the diaphragm 11 is distorted and deformed by the pressure, and this deformation is detected by the sensor. It is converted into an electric signal by the chip 40, and this signal is processed by the ceramic substrate 60 or the like constituting the processing circuit portion of the sensor to detect the pressure. Then, based on the detected pressure (fuel pressure), fuel injection control is performed by the above-mentioned ECU or the like.

【0054】

The conversion of the diaphragm deformation into an electric signal by the sensor chip 40 can be performed in detail as follows. For example, in FIG. 4, if the gauge pad 42 closest to the shield layer grounding pad 46 is the bridge circuit grounding pad 42b, the gauge pad 42 diagonally located to the bridge circuit grounding pad 42b is input. Pads 42a and the remaining two gauge pads 42 are output pads 42c and 42d.

【0055】

When the usage of each gauge pad 42a to 42d is divided in this way, the pad 42a is connected from the input terminal 72, the amplifier IC chip 62, the wiring on the ceramic substrate 60 (see Fig. 6), and the bonding wire 64. A voltage (input voltage) is applied between abs in the bridge circuit 48 via the bridge circuit 48.

【0056】

Also was, terminal 72 for grounding, the wiring on the ceramic substrate 60 (see FIG. 6), the bonding wire 64, the bridge circuit 48 via the pad 42b is grounded. Further, as described above, the shield layer 44 is also grounded by the grounding terminal 72 via the wiring on the P-shaped region 40d, the shield layer grounding pad 46, the bonding wire 64, and the ceramic substrate 60.

【0057】

When the diaphragm 11 is distorted in this state, the resistance value of the strain gauge 41 changes due to the strain stress. This resistance value change is output as a voltage (output voltage) between cds in the bridge circuit 48, and this output voltage is transmitted from the wiring on the bonding wire 64 and the ceramic substrate 60 to the amplifier IC chip 62 via the pads 42c and 42d. It is sent, and processing such as amplification and differential is performed there, and it is output as sensor output from the output terminal 72 to the outside.

【0058】

By the way, in the present embodiment, as shown in FIG. 4, a shield that electrically shields the metal stem 10 and the strain gauge 41 at a portion between the strain gauge 41 and the insulating film 50 in the sensor chip 40. The main feature is that layer 44 is provided.

【0059】

According to this, even when the pressure sensor S1 is used in a noisy environment, the shield layer 44 can electrically block external noise applied to the strain gauge 41 from the metal stem 10 via the housing 30. Therefore, the influence of external noise on the sensor output can be suppressed.

【0060】

That is, in the present embodiment, as shown in FIG. 5, the parasitic capacitance Cp formed between the sensor chip 40 and the metal stem 10 is formed between the grounded shield layer 44 and the metal stem 10. ..

【0061】

Therefore, in the present embodiment, the path of the noise current (see FIG. 12 above) that has conventionally flowed in the order of the housing 30, the metal stem 10, the parasitic capacitance Cp, the sensor substrate J40, and the strain gauge J41 is the housing 30 and the metal stem 10. , The parasitic capacitance Cp, the shield layer 44 of the sensor chip 40, the P-type region 40d, the shield layer grounding pad 46, and GND (grounding) flow in this order (see Fig. 5), and do not flow to the strain gauge 41.

【0062】

Therefore, according to the present embodiment, the shield layer 44 can electrically cut off the noise current applied to the strain gauge 41 from the housing 30 and the metal stem via the parasitic capacitance before the strain gauge 41. , The influence of external noise on the sensor output can be suppressed.

【0063】

Further, in the present embodiment, the sensor chip 40 is separately provided with the shield layer grounding pad 46 and the bridge circuit grounding pad (for example, 42b in FIG. 4), and these two grounding pads 42b and 46 are provided separately. Another feature is that it is connected to the grounding terminal 72 provided in the housing 30 via the connector case 80 by separate wiring.

【0064】

Here, the shield layer grounding pad and the bridge circuit grounding pad are the same one pad. For example, the bridge circuit grounding pad 42b may also be used as the shield layer grounding pad, but for both grounding. If the pads 42b and 46 are provided separately and grounded with separate wiring systems, the influence of external noise on the sensor output can be suppressed more reliably.

【0065】

The effectiveness of the configuration in which the two grounding pads 42b and 46 are separately provided and grounded by different wiring systems will be specifically described with reference to FIGS. 6 and 7. FIG. 6 shows a block diagram of the detection methods when both grounding pads are separated and grounded by a separate wiring system, and FIG. 7 shows the detection methods when both grounding pads are the same one pad. It is explanatory drawing.

【0066】

First, FIG. 6 shows a sensor chip 40 when the gauge pad 42 closest to the shield layer grounding pad 46 is used as the bridge circuit grounding pad 42b. The thick wires in FIG. 6 are the pads 42a to 42d and 46 of the sensor chip 40 and the pads 62a to 62d of the amplifier IC chip 62, and the pads 60a to 60d, 60g and 61a to 61d on the ceramic substrate 60. The bonding wire for connecting the above is shown.

【0067】

The input pad 42a of the sensor chip 40 is electrically connected to the input pad 62a of the amplifier IC chip 62 via the bonding wire 64, the pad 60a on the ceramic substrate 60, the wiring La, the pad 61a, and the bonding wire. There is. The input pad 62a of the amplifier IC chip 62 is electrically connected to the connection portion T3 of the input terminal 72 by a wiring or the like (not shown) formed on the ceramic substrate 60.

【0068】

The bridge circuit grounding pad 42b of the sensor chip 40 is electrically connected to the grounding terminal 72 connection T1 via the bonding wire 64, the pad 60b on the ceramic substrate 60, the wiring Lb1, and the wiring LG1. ..

【0069】

One output pad 42c of the sensor chip 40 is electrically connected to one output pad 62c of the amplifier IC chip 62 via the bonding wire 64, the pad 60c on the ceramic substrate 60, the wiring Lc, the pad 61c, and the bonding wire. It is connected to the.

【0070】

The other output pad 42d of the sensor chip 40 is electrically connected to the other output pad 62d of the amplifier IC chip 62 via the bonding wire 64, the pad 60d on the ceramic substrate 60, the wiring Ld, the pad 61d, and the bonding wire. It is connected to the.

【0071】

Further, in the amplifier IC chip 62, the signals of the first operational amplifier 63c and the second operational amplifier 63d electrically connected corresponding to the output pads 62c and 62d and the signals of these operational amplifiers 63c and 63d are differentially processed. A differential amplifier 63 is provided. Further, the output from the differential amplifier 63 is sent to the connection portion T2 of the terminal 72 for output by a wiring or the like (not shown) formed on the ceramic substrate 60.

【0072】

Further, the grounding pad 62b of the amplifier IC chip 62 is electrically connected to the connection portion T1 of the grounding terminal 72 via the bonding wire, the pad 61b on the ceramic substrate 60, the wiring Lb2, and the wiring LG1. ..

【0073】

Further, the shield layer grounding pad 46 of the sensor chip 40 is electrically connected to the connection portion T1 of the grounding terminal 72 via the bonding wire 64, the pad 60g on the ceramic substrate 60, and the wiring LG2.

【0074】

In this way, the shield layer grounding pad 46 is a grounding terminal via a wiring LG2 that is different from the wiring Lb1 and the wiring LG1 that connect the bridge circuit grounding pad 42b and the connection portion T1 of the grounding terminal 72. It is connected to 72. The wiring LG2 is thicker than other wiring.

【0075】

Although there are some overlaps, the pressure detection method of the present embodiment will be described with reference to FIG. Here, the reference potential in the operation of the bridge circuit 48 and the amplifier IC chip 62 is the potential Vh of the wiring connection portion Lb3 of the wiring LG1, the wiring Lb1 and the wiring Lb2. This is because the grounding by the grounding terminal 72 is stable, and the potential Vg of the connection portion T1 and the potential Vh of the wiring connection portion Lb3 are substantially equal.

【0076】

First, the detection operation in an environment without external noise will be described. A voltage Vcc is applied between abs of the bridge circuit 48 via the amplifier IC chip 62. At this time, the potential of the pad 60a of the ceramic substrate 60 is Vcc, the potential of the pad 60b is (Vh + ZS · iS), where the impedance of the wiring Lb1 is ZS and the current flowing through the bridge circuit 48 is iS.

【0077】

Further, the potential of the pad 61b of the ceramic substrate 60 is (Vh + ZB · iB) when the impedance of the wiring Lb2 is ZB and the current flowing through the bridge circuit 48 is iB. The potentials Vg and Vh and the impedances ZS and ZB are shown in parentheses after the corresponding constituent codes in FIG.

【0078】

In this way, with the voltage Vcc applied between the abs of the bridge circuit 48, the resistance value change according to the distortion of the diaphragm 11 due to the pressure is output as the voltage between the cds of the bridge circuit 48.

【0079】

Specifically, the output voltage (VS1 + Vh) sent to one output pad 62c of the amplifier IC chip 62 is amplified by the first operational amplifier 63c and sent to the other output pad 62d of the amplifier IC chip 62. The sent output voltage (VS2 + Vh) is amplified by the second operational amplifier 63d, the difference between them is taken by the differential amplifier 63, and the trowel is used as the sensor output and output to the output terminal 72.

【0080】

Consider the case where external noise is added in the detection operation shown in FIG. The noise current transmitted from the housing 30, the metal stem 10, and the parasitic capacitance Cp to the sensor chip 40 is the shield layer 44 of the sensor chip 40, the P-shaped area 40d, the shield layer grounding pad 46, the pad 60g on the ceramic substrate 40, and the wiring LG2. , The wiring system in which the noise current flows from the terminal 72 for grounding to GND is separate from the wiring system involved in the detection operation.

【0081】

In addition to this, the grounding by the grounding terminal 72 is stable, and the potential Vh of the connection part Lb3, which is the reference potential for the detection operation, may be stable, so an external noise current enters. Also, the potential Vcc of the pad 60a of the ceramic substrate 60, the potential of the pad 60b (Vh + ZS iS), the potential of the pad 61b (Vh + ZB iB), and the output pads 62c and 62d of the amplifier IC chip 62 The potential (VS1 + Vh) and (VS2 + Vh) do not change.

【0082】

Therefore, if the shield layer grounding pad 46 and the bridge circuit grounding pad 42b are separated from each other and grounded by different wiring systems, the influence of external noise on the sensor output is almost completely suppressed. be able to.

【0083】

On the other hand, the case where both grounding pads are the same one pad will be described with reference to FIG. 7. In FIG. 7, as compared with FIG. 6, the shield layer grounding pad is eliminated, and the circuit grounding pad for the bridge circuit also serves as the shield layer grounding pad-the shield layer grounding pad 47 is provided, and accordingly. The difference is that the pad 60g on the ceramic substrate 60 and the wiring LG2 are eliminated, and the others are the same.

【0084】

The circuit-shield layer grounding pad 47 of the sensor chip 40 is, for example, electrically connected to the shield layer 44 via the P-shaped region 40d. Then, in FIG. 7, this circuit-shield layer grounding pad 47 is electrically connected to the connection portion T1 of the grounding terminal 72 via the bonding wire 64, the pad 60b on the ceramic substrate 60, the wiring Lb1, and the wiring LG1. Is connected.

【0085】

The detection operation in the environment without external noise in FIG. 7 is the same as the detection operation in FIG. 6 above. That is, in an environment without external noise, the potential of the pad 60a of the ceramic substrate 60 is Vcc, the potential of the pad 60b is (Vh + ZS iS), the potential of the pad 61b is (Vh + ZB iB), and the amplifier. The potentials of the output pads 62c and 62d of the IC chip 62 are (VS1 + Vh) and (VS2 + Vh).

【0086】

Here, when external noise is added, the noise current transmitted to the sensor chip 40 is the shield layer 44 of the sensor chip 40, the P-shaped region 40d, the circuit-shield layer grounding pad 47, the pad 60b on the ceramic substrate 60, and the wiring. Since Lb1, wiring LG1, and ground terminal 72 are released to GND, the inflow of noise current into the strain gauge 41, that is, the bridge circuit 48 can be cut off.

【0087】

However, strictly speaking, the influence of the noise current described below occurs. Circuit-Assuming that the noise current escaped from the shield layer grounding pad 47 is iN, the potential of pad 60a of the ceramic substrate 60 described above is Vcc, and the potential of pad 61b is the same as (Vh + ZB iB), but the bridge circuit The potential of the pad 60b, which is the ground potential of 48, is (Vh + ZS / iS + ZS / iN), and the potential change ZS / iN due to the noise current is added.

【0088】

Therefore, the potentials of the output pads 62c and 62d of the amplifier IC chip 62 are also (VS1 + Vh + ZS iN) and (VS2 + Vh + ZS iN), respectively.

【0089】

Here, each of the operational amplifiers 63c and 63d has the frequency characteristics as shown in FIG. 8, and in the high frequency region, the characteristics of both operational amplifiers 63c and 63d usually do not match.

【0090】

Therefore, noise (ZS / iN) can be canceled by taking a differential if the operational amplifier's operating frequency (for example, several kHz) is used, but when the frequency of the noise current becomes high (for example, MHz region), noise (ZS / iN) is not canceled even if differential is taken because the characteristics of both operational amplifiers 63c and 63d are different, and noise is added to the sensor output.

【0091】

Therefore, as in the present embodiment, it is better to separate the shield layer grounding pad 46 and the bridge circuit grounding pad 42b and ground them with different wiring systems as described above. It is also effective against the noise of. Actually, the results of noise tests conducted by the present inventors on a configuration in which both grounding pads are separated (configuration shown in FIG. 6) and a configuration in which both grounding pads are separated (configuration shown in FIG. 7) are shown in FIG. Shown in.

【0092】

Figure 9 shows the relationship between the frequency (MHz) of this electromagnetic wave and the amount of fluctuation in the sensor output from the initial stage (no noise) by applying an electromagnetic wave of 200 V / m as external noise to the pressure sensor S1. It is a thing. FIG. 9 (a) shows a conventional product without a shield layer (shown by a broken line) and a configuration in which both grounding pads are integrated (shown by a solid line), and FIG. 9 (b) shows both grounding. The configuration in which the pad is separated is shown.

【0093】

As can be seen from Fig. 9 (a), in the configuration where both ground pads are integrated, the noise in the low frequency region (several tens of MHz) that appeared in the conventional product is suppressed, and the external noise to the sensor output is suppressed in the normal use region. However, the influence of noise appears in the high frequency region (several hundred MHz).

【0094】

On the other hand, as can be seen from Fig. 9 (b), in the configuration where both ground pads are separated, noise is suppressed from the low frequency region to the entire high frequency region, even in a severe noise environment. We have realized a pressure sensor that can surely suppress the influence of external noise on the sensor output.

【0095】

(Other Embodiment) As the sensor chip 40, instead of the configuration shown in FIG. 4 above, as another example, an integrated chip as shown in FIG. 10 may be used. The P-type region (P-type isolation region) 40d forms a signal processing circuit element region 40e isolated from the region in which the strain gauge (gauge region) 40c is formed.

【0096】

In this integrated chip, the N-type epitaxial region (N epi region) 40f has a low concentration for circuit formation, and the depletion layer tends to spread, so the depletion layer becomes the P-type layer (P substrate) 40a. High concentration (1 x 10) so as not to reach¹⁸/cm^-3) Embedded N + region 40g is formed.

【0097】

Further, the sensor substrate may have a configuration in which the first conductive type is N type and the second conductive type is P type, contrary to the above embodiment.

【0098】

In addition to the sensor substrate made of a silicon semiconductor chip, a silicon oxide film and a silicon semiconductor film are vapor-deposited on the diaphragm of a metal stem to form a silicon oxide film as an insulating film and a silicon semiconductor film as a sensor substrate. It can also be applied to the configured pressure sensor.

[Simple explanation of drawings]

[Figure 1]

It is schematic cross-sectional view which shows the whole structure of the pressure sensor which concerns on embodiment of this invention.

[Figure 2]

It is a perspective view which shows the outline of the circled part A in FIG. 1 in an enlarged manner.

[Fig. 3]

It is a figure which shows the schematic plane structure when the sensor chip is seen from the surface.

[Fig. 4]

It is a figure which shows the schematic cross-sectional structure of the sensor chip 40.

[Fig. 5]

It is explanatory drawing of the effect by a shield layer.

[Fig. 6]

It is explanatory drawing which shows the detection method when the shield layer grounding pad and the bridge circuit grounding pad are separated, and grounded by another wiring system.

[Fig. 7]

It is explanatory drawing which shows the detection method when the shield layer grounding pad and the bridge circuit grounding pad are the same one pad.

[Fig. 8]

It is a figure which shows typically the frequency characteristic of the 1st operational amplifier and the 2nd operational amplifier.

[Fig. 9]

It is a figure which shows concretely the noise suppression effect of this invention.

[Fig. 10]

It is a schematic cross-sectional block diagram which shows another example of a sensor chip.

[Fig. 11]

It is the schematic sectional drawing which shows the general whole structure of the conventional pressure sensor.

[Fig. 12]

It is a schematic cross-sectional view which shows the structure in the vicinity of the diaphragm in FIG. 11 in an enlarged manner.

[Explanation of symbols]

10 ... metal stem, 11 ... diaphragm, 30 ... housing, 40 ... sensor chip (sensor substrate), 40a ... P-type layer (first conductive type layer), 40b ... N-type layer (second conductive type layer), 40c ... P-type region (first conductive type region), 41 ... strain gauge, 42b ... bridge circuit grounding pad, 44 ... shield Layers, 46 ... Shield Layer Grounding Pads, 48 ... Bridge Circuits, 50 ... Insulations, 72 ... Terminals.