JP5081071B2 - Semiconductor pressure sensor - Google Patents

Description

  The present invention relates to a semiconductor pressure sensor that measures pressure such as atmospheric pressure.

  Conventionally, a diaphragm type semiconductor pressure sensor is known as a semiconductor pressure sensor for measuring a tire pressure of an automobile (Patent Documents 1 and 2).

  A planar structure of a conventional semiconductor pressure sensor is shown in FIG. In this conventional semiconductor pressure sensor, four piezo elements 103 and 104 formed so as to cover the center of each side (contour) 102 of a diaphragm 101 having a rectangular shape in plan view are connected so as to form a bridge circuit. Yes. Thus, the midpoint voltage of the bridge circuit is output as a pressure measurement voltage. When pressure is applied to the diaphragm 101, a force in the compression direction acts on the pair of piezo elements 103, and a force in the tension direction acts on the pair of piezo elements 104.

In these conventional semiconductor pressure sensors, the shape of the four piezoelectric elements is the same (Patent Document 1), or the width of the piezoelectric element 104 in the direction perpendicular to the longitudinal direction of the diaphragm 101 is parallel to the longitudinal direction. The resistance value is made smaller than the width of the element 103.
JP 56-133877 A JP 58-148467 A

  However, conventionally, it has been difficult to accurately form the diaphragm alignment (the relative position of the piezo elements 103 and 104 and the diaphragm 101 (its contour 102)), resulting in variations. For this reason, there is a problem that the balance of the bridge circuit is lost when the pressure changes. In particular, the influence of the diaphragm misalignment is that when the piezoelectric element 103 in the direction parallel to the contour 102 of the diaphragm 101 is displaced in the orthogonal direction, the piezoelectric element 104 whose longitudinal direction is orthogonal is displaced in the longitudinal direction. There was also a prominent problem.

  In view of the problems of the prior art, an object of the present invention is to obtain a semiconductor pressure sensor that is less affected by the relative displacement between the diaphragm and the piezo element.

The present invention for achieving such an object is a semiconductor pressure sensor having a diaphragm formed on a silicon substrate and a plurality of piezo elements whose resistance values change according to the distortion of the diaphragm, and each piezo element includes a plurality of piezo elements. The planar elongated elements are connected in series, and each of the planar elongated elements constituting the piezoelectric element acting in the compression direction and the piezoelectric element acting in the tension direction are formed in parallel in one direction. Te, among the elements of the plurality of plan view an elongated shape of the compression direction, the element in plan view elongated across the contour of the diaphragm, the area of the plan view wider than the area in plan view of the elements of the other in plan view elongated And the aspect ratio in plan view is the same as the aspect ratio in plan view of other elongated elements in plan view .

Preferably, the diaphragm is formed in a square shape in a plan view, and the piezoelectric element in the compression direction is configured such that each elongated element in a plan view is formed in parallel with the contour line of the diaphragm, and the contour line of the diaphragm is formed. the element in plan view elongated across the area of the short-side direction is formed across the contour of the diaphragm, and a plan view of the element area in plan view of another plan view slender portion located on the diaphragm Are formed identically.

  According to the present invention having the above configuration, the area of the piezo element that is displaced on the diaphragm is set to be the same for the piezo element in the tensile direction and the piezo element in the compression direction, so that four piezo elements are bridged. Bridge balance deviation when connected is corrected.

The best mode for carrying out the present invention will be described with reference to the accompanying drawings. FIG. 1 is a plan view of a pressure sensor used for absolute pressure detection, gauge pressure detection, and the like, and FIG. 2 is a cross-sectional view taken along the section line II-II in FIG. The pressure sensor 1 is formed using an SOI (Silicon on Insulator) substrate 10. This SOI substrate 10 has a laminated structure in which a first silicon substrate 11 and a second silicon substrate 13 are bonded together via a silicon oxide film (SiO ₂ ) 12 that is an oxide film. A silicon oxide film 14 is formed as an oxide film on the circuit surface (upper side surface) of the first silicon substrate 11, and a bridge circuit is formed under the silicon oxide film 14 so as to form a first resistive resistor element. The first piezo element A, the second piezo element B, the third piezo element C, and the fourth piezo element D are electrically connected to the first to fourth pads 24A to 24D, and the piezo elements A to D are connected to the first to fourth pads 24. A wiring 23 is formed. Further, a passivation film 15 made of silicon nitride Si ₃ N ₄ or the like for insulating and protecting the surfaces of the first to fourth piezo elements A to D, the wiring 23 and the first silicon substrate 11 is formed. Note that the surfaces of the first to fourth pads 24 </ b> A to 24 </ b> D are exposed from the passivation film 15.

  In the SOI substrate 10, a cavity (concave portion) 20 is formed on the second silicon substrate 13 from the surface side (lower surface in FIG. 2), and the silicon oxide film 12 constituting the upper surface of the cavity 20, the first silicon A diaphragm 21 is formed by the substrate 11, the silicon oxide film 14, and the passivation film 15. The diaphragm 21 is a rectangle (square) in plan view (FIG. 1).

  Part of the first to fourth piezo elements A to D is formed at positions corresponding to the outline of the square diaphragm 21 or the diaphragm outline 21a corresponding to each side. In other words, most of the first to fourth piezo elements A to D are present on the diaphragm 21 above the cavity 20, and a part of the outer periphery of the cavity 20 (no distortion occurs even when pressure is applied). It is formed so as to be located in the fixed region 22). The diaphragm outline 21 a corresponds to an extension of the cavity inner surface of the second silicon substrate 13 that regulates the cavity 20.

  A base substrate 31 made of a glass substrate or an Si substrate is bonded to the surface (lower surface) of the second silicon substrate 13 of the SOI substrate 10 configured as described above, and the cavity 20 between the diaphragm 21 and the base substrate 31 is sealed. The The inside of the cavity 20 is evacuated.

  When the diaphragm 21 is distorted (displaced) according to the pressure applied from the outside of the cavity 20, the resistance values of the first to fourth piezo elements A to D change according to the distortion, and the first to fourth are changed. The midpoint potential of the bridge circuit formed by the piezo elements A to D changes. The displacement when the pressure is applied to the diaphragm 21 acts on the pair of first and fourth piezo elements A and D in the compression direction so that the resistance value becomes small, so that the pair of second, The third piezo elements B and C act in the pulling direction so as to increase the resistance value.

  Thus, the midpoint potential that is displaced by the resistance value that is changed by the force in the compression direction and the tension direction acting on the first to fourth piezoelectric elements A to D is output as a sensor output to a known measuring device. The first piezo element A and the second piezo element B are connected in series via the first pad 24A, and the third piezo element C and the fourth piezo element D are connected in series via the second pad 24B. The piezo element A and the third piezo element C are connected to the input voltage via the third pad 24C, and the second piezo element 24B and the fourth piezo element 24D are connected to the ground terminal via the fourth pad 24D. Thus, the midpoint potential is output from the first and second pads 24A and 24B. The first to fourth pads 24 </ b> A to 24 </ b> B are all formed in the fixed region 22 on the outer periphery of the diaphragm 21.

  The first to fourth pads 24A to 24B and the connection wiring 23 extending from each pad are formed of a plated layer or sputtered layer of a good conductor such as Al or Au.

  Details of the first to fourth piezo elements A to D will be described with reference to FIGS. The first to fourth piezo elements A to D are formed with a P-type semiconductor layer on the front side of the diaphragm 21. In this embodiment, the first to fourth piezo elements A to D are first to third element portions A1 to A3, B1 to B3, C1 to C1, which are elongated in plan view, each consisting of three P-type semiconductor layers. C3 and D1 to D3 are connected in series. The first to third element portions A1 to A3, B1 to B3, C1 to C3, and D1 to D3 of the first to fourth piezo elements A to D that are elongated in plan view are parallel to each other with a predetermined interval. The first to third element portions A1 to A3, B1 to B3, C1 to C3, and D1 to D3 have a meander shape connected in series by a connection portion E made of a P-type semiconductor layer. ing. As shown in FIG. 1, both ends of each of the first to fourth piezo elements A to D formed in a meander shape are connected to a wiring 23 to form a bridge circuit.

  The first to third element portions A1 to A3 and D1 to D of the first and fourth piezoelectric elements A and D are compressed in the longitudinal direction when the diaphragm 21 is distorted by pressure (downward in FIG. 2). Directional force is applied to reduce the resistance value, and the first to third element portions B1 to B3 and C1 to C3 of the second and third piezo elements B and C have the diaphragm 21 exerting pressure. When it is received and distorted (downward in FIG. 2), the tensile force acts in the longitudinal direction of each of the element portions B1 to B3 and C1 to C3 to increase the resistance value.

  More specifically, in the first and fourth piezoelectric elements A and D, the third element portions A3 and D3 straddle the diaphragm contour 21a in the short direction (the diaphragm contour 21a is the third element portion A3). The first and second element portions A 1, A 2, D 1, and D 2 are disposed on the diaphragm 21. On the other hand, the second and third piezo elements B and C all extend from the first to third element portions B1 to B3 and D1 to D3 across the diaphragm contour 21a (the diaphragm contour 21a is short). Are arranged on the diaphragm 21 so as to cross the hand direction).

  Thus, in this embodiment, the third element portions A3 and D3 straddling the diaphragm outlines 21a of the first and fourth piezoelectric elements A and D are replaced with the aspect ratios of the other element portions A1, A2, D1, and D2. While maintaining the same aspect ratio, the line magnification is enlarged by about 1.35 times. FIG. 3 shows an enlarged view of the first piezo element A and the second piezo element B. Except for the third element portion A3 of the first piezo element A, each element portion is formed such that the length L in the longitudinal direction is 40 μm and the length (width) W in the short direction is 8 μm. The third element portion A3 has the same aspect ratio and a linear magnification of 1.35 times, that is, the length L1 in the longitudinal direction is 54 μm and the length (width) W1 in the short direction is 10.8 μm.

  Since the third element portion A3 is enlarged while maintaining the aspect ratio (the aspect ratio of the first and second element portions A1 and A2), the resistance value does not change regardless of the enlargement ratio. Therefore, the resistance values of the first and second piezoelectric elements A and B in the unstrained (no load) state are equal. Although not shown in FIG. 3, as shown in FIG. 1, the third piezo element C is formed symmetrically with the second piezo element B, and the fourth piezo element D is formed symmetrically with the first piezo element A. Yes.

Further, the third element portion A3 is formed so that the area of the portion located on the diaphragm 21 is equivalent to the first and second element portions A1 and A2. That is, in the illustrated embodiment, the third element portion A3 is set to be positioned at 4.8 μm on the outer periphery (fixed region 22) of the diaphragm 21. As a result, the area of the third element portion A3 on the diaphragm 21 is 54 × (10.8−4.8) = 324 (× 10 ⁻¹² m ² ), and the first and second element portions A1, A2 (40 × 8 = 320 (× 10 ⁻¹² m ² )).

  Since the areas of the first to fourth element portions A1 to A3 and D1 to D3 of the first and fourth piezo elements A in the compression direction are substantially equal in area, the diaphragm 21 has a substantially equal area. Even if the applied pressure changes, the bridge balance is kept constant.

  In FIG. 4, as a comparative example, a third element portion A3 ′ corresponding to the third element portion A3 of the first piezo element A has the same size as the first and second element portions A1 and A2. A piezo element A ′ is shown. The second piezo element B of this comparative example has the same specifications as the second piezo element B of the embodiment of FIG. 3, and each element portion A1, A2, A3 'of the first piezo element A is the same as that of the second piezo element B. It is the same as each element part B1 thru | or B3. That is, the length L2 of each element portion B1 to B3, A1, A2, and A3 ′ is 40 (μm), and the width W2 is 6 (μm).

In this comparative example, the third element portion A3 ′ is set so that the lateral direction straddles the diaphragm outline 21a and is positioned at 2.0 μm on the outer periphery (fixed region 22) of the diaphragm 21. Therefore, the area of the third element portion A3 ′ located on the diaphragm 21 is 40 × 6 = 240 (× 10 ⁻¹² m ² ), which is based on the first and second element portions A1 and A2. Is too narrow. Therefore, in this comparative example, the bridge balance is lost when the pressure acting on the diaphragm 21 changes.

  Further, when the alignment of the diaphragm 21 and the first to fourth piezo elements A to D is lost during the manufacture of the semiconductor pressure sensor, the bridge balance is affected by deviation from the design value. For example, in FIGS. 3 and 4, it is assumed that the alignment is shifted by 1 μm in the X-axis direction. When shifted in the Y-axis direction, there is almost no effect on the first piezo elements A and A ′, but when shifted in the X-axis direction, the first piezo elements A and A ′ are affected.

  In the case of the present embodiment, the area of the portion where the third element portions A3 and A3 ′ are located on the diaphragm 21 is changed by 1 / 10.8 in the third element portion A3, whereas the area of the comparative example is 3 element part A3 'changes 1/8. That is, the area change rate is smaller in the present embodiment than in the comparative example. Here, since the rate of change in area is the rate of change in resistance, the rate of change in resistance is smaller in this embodiment than in the comparative example, and the influence of the diaphragm alignment error is reduced.

  As described above, according to the present embodiment, the third element portions A3 and C3 of the first and third piezoelectric elements A and C that receive a force in the compression direction are enlarged while maintaining the aspect ratio, and the area on the diaphragm 21 is increased. Is set to be equivalent to the first and second element portions A1, A2, C1, and C2, so that the deviation of the bridge balance when the diaphragm 21 is displaced is reduced. Moreover, even if the diaphragm alignment in the direction orthogonal to the longitudinal direction of the third element portions A3 and C3 is shifted, the influence is small, and the generated error is small.

  3 and 4, when the diaphragm alignment is shifted by 1 μm in the Y-axis direction, the areas of the first to third element portions B1 to B3 on the diaphragm 21 change by 1/38. This area change rate is smaller than the area change rate of the third element portions A3 and C3 when the diaphragm alignment is shifted to 1 μm in the X-axis direction, so that the influence of the diaphragm alignment shift is small.

  The embodiment in which the present invention is applied to a meander-shaped piezo element has been described above, but the present invention is not limited to a three-row meander shape, and the aspect ratio is not limited.

  The above embodiment is an absolute pressure sensor in which the cavity 20 is evacuated, but the present invention provides a differential pressure or gauge pressure sensor in which a pressure introduction port is formed in the base substrate 31 and the cavity 20 communicates with the outside. Is also applicable.

It is a top view which shows the principal part of the semiconductor pressure sensor to which this invention is applied. It is sectional drawing shown along the cutting line II-II of FIG. It is a top view which expands and shows the piezoelectric element part of the semiconductor pressure sensor. It is a top view which expands and shows the comparative example of the piezoelectric element part of a semiconductor pressure sensor. It is a top view which shows the outline | summary of the conventional semiconductor pressure sensor.

Explanation of symbols

10 SOI substrate 11 First silicon substrate (the other silicon substrate)
12 Silicon oxide film (oxide film)
13 Second silicon substrate (one silicon substrate)
14 Silicon oxide film 15 Passivation film 20 Cavity 21 Diaphragm 21a Diaphragm outline 22 Piezo element (sensitive resistance element)
23 Wiring 31 Base substrate A First piezo element (piezo element in compression direction)
A1 A2 A3 First, second and third element portions B Second piezo element (piezo element in the tensile direction)
B1 B2 B3 First, second and third element portions C Third piezo element (piezo element in the tensile direction)
C1 C2 C3 First, second and third element portions D Fourth piezo element (piezo element in compression direction)
D1 D2 D3 First, second and third element parts

Claims (2)

A semiconductor pressure sensor having a diaphragm formed on a silicon substrate and a plurality of piezo elements whose resistance values change according to strain of the diaphragm,
Each piezo element has a plurality of elongated elements in plan view connected in series,
Each of the plurality of elongated elements in a plan view constituting the piezoelectric element acting in the compression direction and the piezoelectric element acting in the tension direction is formed in parallel in one direction,
Among elements of the plurality of plan view an elongated shape of the compression direction, the element in plan view elongated across the contour of the diaphragm, the area of the plan view wider than the area in plan view of the elements of the other in plan view elongated, and the semiconductor pressure sensor that the aspect ratio of the plan view is formed in the same aspect ratio in plan view of the elements of the other in plan view elongated, characterized by. 2. The semiconductor pressure sensor according to claim 1, wherein the diaphragm is formed in a square shape in a plan view, and the piezoelectric elements in the compression direction are formed so that each elongated element in a plan view is formed in parallel with the contour line of the diaphragm. element in plan view elongated across the contour of the diaphragm, the lateral direction to be formed across the contour of the diaphragm, and the area of the plan view of the portion located on diaphragm other in plan view elongated A semiconductor pressure sensor formed to have the same area as a planar view of a shaped element.

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