JP5002468B2 - Semiconductor pressure sensor - Google Patents

Description

  The present invention relates to a semiconductor pressure sensor that detects a pressure applied to a diaphragm portion using a bridge circuit composed of a plurality of piezoresistive elements.

Conventionally, by arranging piezoresistive elements at a plurality of spaced positions on the surface of the diaphragm part, and forming a bridge circuit with this piezoresistive element, the resistance value of the piezoresistive element is caused by the bending that occurs in the diaphragm part under pressure. 2. Description of the Related Art A semiconductor pressure sensor that detects a change in the output voltage of a bridge circuit with respect to an applied bias accompanying a change in voltage is known. In such a semiconductor pressure sensor, a phenomenon occurs in which the offset voltage (the output voltage value of the bridge circuit when no pressure is applied to the sensor) fluctuates when power is supplied to the bridge circuit. A possible cause of this phenomenon is that the resistance value of the piezoresistive element changes due to the movement of mobile ions present on the sensor surface on the surface of the piezoresistive element after the power is turned on. From such a background, a conductive film is formed on the surface of the piezoresistive element through an insulating film, and this conductive film is connected to the lowest potential portion of the bridge circuit, so that a so-called electric shield is provided to provide the movable ion. There has been proposed a method for suppressing a change in the resistance value of the piezoresistive element due to (see Patent Document 1).
JP 2001-281085 A

  However, according to the conventional semiconductor pressure sensor, when the film thickness of the insulating film is as large as micron, the fluctuation of the offset voltage after power-on can be suppressed, but the film thickness of the insulating film is compared with several thousand mm. When it becomes smaller, the fluctuation of the offset voltage cannot be suppressed. For this reason, according to the conventional semiconductor pressure sensor, it has been difficult to reduce the thickness of the insulating film while suppressing the fluctuation of the offset voltage after the power is turned on, thereby realizing the downsizing of the sensor.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide a semiconductor pressure sensor that can be miniaturized while suppressing fluctuations in offset voltage after power-on.

A semiconductor pressure sensor according to the present invention includes a semiconductor substrate having a diaphragm portion, a plurality of piezoresistive elements that are formed on the surface of the diaphragm portion and detect pressure applied to the diaphragm portion as a change in resistance value, and formed on the surface of the semiconductor substrate. A diffusion wiring that connects a plurality of piezoresistive elements to form a bridge circuit, an insulating film that covers the surface of the semiconductor substrate including the surfaces of the piezoresistive elements and the diffusion wiring, and a conductor formed on the surface of the insulating film In the semiconductor pressure sensor having a layer, a conductor layer is connected to the highest potential portion of the bridge circuit, and among the diffusion wirings, a piezoresistance element between a pair of diffusion wirings spaced apart with the piezoresistance element interposed therebetween The conductor layer is not formed on the surface of the insulating film corresponding to a region where no intervening layer is present.

  According to the semiconductor pressure sensor of the present invention, it is possible to reduce the size while suppressing the fluctuation of the offset voltage after the power is turned on.

  Hereinafter, a semiconductor pressure sensor according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIGS. 1A and 1B, a semiconductor pressure sensor 1 according to an embodiment of the present invention includes an SOI semiconductor substrate 3 on which a rectangular diaphragm portion 2 is formed, and the center of each side of the diaphragm portion 2. Piezoresistive elements R1 to R8 formed in the surface region of the SOI semiconductor substrate 3 near the inside. Adjacent piezoresistive elements R1, R2 are connected via a diffusion line L1. The piezoresistive element R1 is connected to the ground terminal GND serving as the lowest potential portion via the diffusion line L2 and the thin film metal line 4a, and the piezoresistive element R2 is connected to the voltage output terminal Vout + via the diffusion line L3 and the thin film metal line 4b. Has been. Adjacent piezoresistive elements R3 and R4 are connected via a diffusion line L4. The piezoresistive element R3 is connected to the voltage output terminal Vout + via the diffusion line L5 and the thin film metal line 4c, and the piezoresistive element R4 is a bias voltage application terminal that becomes the highest potential portion via the diffusion line L6 and the thin film metal line 4d. Connected to Vdd.

  Adjacent piezoresistive elements R5 and R6 are connected via a diffusion line L7. The piezoresistive element R5 is connected to the bias voltage application terminal Vdd via the diffusion line L8 and the thin film metal line 4e, and the piezoresistive element R6 is connected to the voltage output terminal Vout− via the diffusion line L9 and the thin film metal line 4f. ing. Adjacent piezoresistive elements R7 and R8 are connected via a diffusion line L10. The piezoresistive element R7 is connected to the voltage output terminal Vout− via the diffusion line L11 and the thin film metal line 4g, and the piezoresistive element R8 is connected to the ground terminal GND via the diffusion line L12 and the thin film metal line 4h. The diffusion lines L1 to L12 are formed by implanting and diffusing impurity ions on the surface of the SOI semiconductor substrate 3. The thin film metal wirings 4a to 4h are formed on the surface of an insulating film 5 described later, and are connected to the diffusion wirings L1 to L12 through through holes formed in the insulating film 5.

  In the semiconductor pressure sensor 1 having such a configuration, the piezoresistive elements R1 to R8 form a bridge circuit as shown in FIG. That is, the piezoresistive elements R1 and R2, the piezoresistive elements R5 and R6, the piezoresistive elements R3 and R4, and the piezoresistive elements R7 and R8 are paired and arranged on the bridge circuit. In the semiconductor pressure sensor 1 having such a configuration, when pressure is applied to one surface of the diaphragm portion 2, a differential pressure is generated between the upper surface and the lower surface of the diaphragm portion 2, so that the diaphragm portion 2 is bent, Due to this bending, the crystals forming the piezoresistive elements R1 to R8 are distorted and the resistance value changes. Then, changes in the resistance values of the piezoresistive elements R1 to R8 are detected from the output terminals Vout + and Vout− as voltage changes with respect to the bias voltage Bias applied to the bias voltage application terminal Vdd using a bridge circuit.

  In this semiconductor pressure sensor 1, an insulating film 5 is formed on the surface of the SOI semiconductor substrate 3 including the surfaces of the piezoresistive elements R1 to R8 and the diffusion lead wires L1 to L12, and further the surface of the diaphragm portion 2 and the surfaces of the diffusion wirings L1 to L12. A conductor film 6 is formed on the surface of the insulating film 5 corresponding to. The conductor film 6 is connected to a bias voltage application terminal Vdd that is the highest potential portion in the region X. Here, when the film thickness of the insulating film 5 is on the order of several thousand Å, the conductor film 6 is connected to the bypass voltage application terminal Vdd that is the highest potential part and the ground film GND that is the lowest potential part. As a result of simulating the fluctuation of the offset voltage after power-on, when the conductor film 6 is connected to the lowest potential portion, the fluctuation amount of the offset voltage was 1.7%, whereas the conductor film 6 was the highest potential. In the case of being connected to the part, the variation amount of the offset voltage was 0.2%.

  Therefore, according to the semiconductor pressure sensor 1 according to the embodiment of the present invention, it is possible to reduce the size of the sensor while suppressing the fluctuation of the offset voltage after the power is turned on. In the present embodiment, the conductor film 6 is formed on the entire surface of the diaphragm portion 2 and has a line-symmetric shape with respect to the central axis of the diaphragm portion 2, so that the conductor film 6 has a non-local and asymmetric shape. Compared with the case where it forms, it can make the stress balance of the diaphragm part 2 surface favorable, and can suppress that an offset voltage generate | occur | produces by breaking a stress balance.

  In this embodiment, the conductor film 6 is formed on the entire surface of the diaphragm portion 2. However, as shown in FIGS. 2A and 2B, the diffusion wirings L1 to L12 are spaced apart from each other with the piezoresistive element interposed therebetween. Diffusion line pairs (specifically, diffusion lines L1 and L2, diffusion lines L1 and L3, diffusion lines L4 and L5, diffusion lines L4 and L6, diffusion lines L7 and L8, diffusion lines L7 and L9, diffusion line L10) , L11, diffusion wirings L10, L12) (for example, region S2 shown in FIG. 2B) corresponding to the region where no piezoresistive element is interposed (for example, region Y shown in FIG. 2A). In the region S 1, the surface of the insulating film 5 corresponding to the region where the piezoresistive element is interposed) is preferably not formed by, for example, making the shape of the conductor layer 6 into a ring shape. .

  According to such a configuration, it is possible to suppress the leakage current from flowing between the diffusion wirings without using the piezoresistive element, and to further suppress the fluctuation of the offset voltage. Moreover, when the shape of the conductor layer 6 is a ring shape, the stress balance on the surface of the diaphragm portion 2 can be improved, and the occurrence of an offset voltage can be suppressed. In addition, the area of the conductor layer 6 is reduced, and the stress balance design in the surface of the diaphragm portion 2 which is difficult in the three-layer structure of the SOI semiconductor substrate 3, the insulating film 5, and the conductor film 6 becomes unnecessary, and the stress design is reduced. It becomes easy.

  In the present embodiment, the conductor film 6 is formed on the entire surface of the diaphragm portion 2, but as shown in FIG. 3, adjacent piezoresistive elements (specifically, piezoresistive elements R1, R2, piezoresistive elements R3, R4). It is desirable that the conductor layer 6 is not formed on the surface of the insulating film 5 corresponding to the space between the piezoresistive elements R5 and R6 and the piezoresistive elements R7 and R8 (for example, the region Z shown in FIG. 2A). . According to such a configuration, it is possible to suppress the leakage current from flowing between adjacent piezoresistive elements and further suppress the fluctuation of the offset voltage.

  As mentioned above, although embodiment which applied the invention made by the present inventors was described, this invention is not limited by description and drawing which make a part of indication of this invention by this embodiment. That is, it is needless to say that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above-described embodiments are all included in the scope of the present invention.

It is a circuit diagram which shows the structure of the bridge circuit comprised by (a) top view and (b) sectional drawing which show the structure of the semiconductor pressure sensor used as embodiment of this invention, and (b) piezoresistive element. It is sectional drawing which shows the structure of the modification of the semiconductor pressure sensor shown in FIG. It is sectional drawing which shows the structure of the modification of the semiconductor pressure sensor shown in FIG.

Explanation of symbols

1: Semiconductor pressure sensor 2: Diaphragm part 3: SOI semiconductor substrates 4a-4h: Thin film metal wiring 5: Insulating film 6: Conductor film GND: Ground terminals L1-L12: Diffusion wirings R1-R8: Piezoresistive element Vdd: Bias Voltage application terminals Vout +, Vout-: Output terminals

Claims (3)

A semiconductor substrate having a diaphragm portion; a plurality of piezoresistive elements formed on the surface of the diaphragm portion for detecting pressure applied to the diaphragm portion as a change in resistance; and a plurality of piezoresistors formed on the surface of the semiconductor substrate. Diffusion wiring that connects elements to form a bridge circuit, an insulating film that covers the surface of the semiconductor substrate including the surface of the piezoresistive element and the diffusion wiring, and a conductor layer formed on the surface of the insulating film; In the semiconductor pressure sensor, the conductor layer is connected to the highest potential portion of the bridge circuit, and the piezoresistive element between the pair of diffusion wirings that are spaced apart from each other with the piezoresistive element being sandwiched among the diffusion wirings A semiconductor pressure sensor characterized in that the conductor layer is not formed on the surface of the insulating film corresponding to a region where no intervening material is present . 2. The semiconductor pressure sensor according to claim 1 , wherein the conductor layer is not formed on the surface of the insulating film corresponding to adjacent piezoresistive elements among the plurality of piezoresistive elements. Semiconductor pressure sensor. 2. The semiconductor pressure sensor according to claim 1 , wherein the conductor layer has a ring shape.

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