JPH0473631B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field to Which the Invention Pertains] This invention relates to a pressure sensor that uses a strain gauge to detect a force applied to a pressure receiving surface, and particularly to a pressure sensor that detects a force that is applied to a pressure receiving surface. This invention relates to a small pressure sensor suitable for detecting the distribution of

[Prior Art and its Problems] Fig. 1 shows a conventionally used sensor (octagonal stress ring) that detects three-directional components of force. This sensor has strain gauges 41 to 41 on six outer peripheral surfaces of a metal octagonal ring 1 excluding the pressure receiving surface 2 and the substrate surface 3, and on both side surfaces and the inner peripheral surface.
44, 51 to 54, and 61 to 64 are pasted, and the three directional components are separated from each other and detected depending on the pasting position. The above-mentioned strain gauges 41 to 44 are attached to the outer peripheral surface of the octagonal ring perpendicular to the pressure receiving surface 2 and to the inner peripheral surface of the ring, and detect the force component Fz perpendicular to the pressure receiving surface 2. Further, the strain gauges 51 to 54 are attached to four oblique outer peripheral surfaces of the octagonal ring, and detect the x-direction component Fx of the horizontal force component applied to the pressure receiving surface 2. Furthermore, the strain gauges 61 to 64 are attached to both sides of the ring at the same angle as the diagonal surface of the octagonal ring and approximately at the center of the wall thickness of the ring, so that the strain gauges 61 to 64 are affixed to both sides of the ring at the same angle as the diagonal surface of the octagonal ring and approximately at the center of the wall thickness of the ring. Detect the component Fy in the y direction.

In this way, the three-direction force sensor shown in the figure separates the force into a basic rectangular coordinate system and detects it as three-direction component forces, so by combining these three component forces using an arithmetic expression, , the magnitude and direction of force can be determined. Furthermore, force in any direction can be determined.

The ability to easily separate and combine forces in this way is a major feature of the three-directional force sensor.

However, although the conventional octagonal stress ring shown in the figure is well-known as a sensor for detecting force components in three directions, it has the following drawbacks, especially when arranged in a planar array. It is inappropriate to detect the load distribution of a load distributed over a surface. The drawbacks are listed below.

Since it has a structure in which a large number of strain gauges are attached in each direction of the ring body, it is difficult to downsize it.

Since the strain gauge is attached, creep occurs due to the attached layer, resulting in poor safety.

Depending on where the strain gauge is attached, a large interference output is generated.

It is relatively difficult to manufacture. In particular, it is difficult to attach the strain gauge to the inner peripheral surface of the ring.

It is not suitable for mass production and is expensive.

On the other hand, in order to realize a robot hand with an advanced pressure sensing function as close as possible to the pressure sensing function of the human palm, the pressure sensor must have the function of a three-directional force sensor, and a large number of such sensors must be used. Arranged in a high-density surface array, the distribution state of the applied force and the center of force (center of gravity)
It is necessary to be able to accurately determine the resultant force acting on it. Therefore, such a pressure sensor is required to be able to accurately separate and accurately detect the component forces of a load without mutual interference, and to be able to minimize dimensions and integrate at a high density. It is desirable that the size be several mm square, preferably less than 1 mm square.

FIG. 2 shows an example of a silicon planar pressure sensor which is the object of the present invention and has been proposed for the purpose of eliminating the drawbacks of the above-mentioned prior art. A plurality of diffusion type strain gauges 101 to 10 are installed at predetermined positions on a plane 13 perpendicular to the pressure receiving surface 8 of the pressure sensitive structure 7.
104, 111 to 114, and 121 to 124 are formed by planar technology. The strain gauges 101 to 104 described above detect the force component Fz perpendicular to the pressure receiving surface 8, and the strain gauges 111 to
114 detects one component Fx of the force parallel to the pressure receiving surface 8, and furthermore, strain gauges 121 to 124 detect another component Fz of the force parallel to the pressure receiving surface 8. As will be described later, these strain gauges are arranged in locations that are highly sensitive and are theoretically unaffected by component forces in other two directions. Furthermore, if the diffusion type strain gauge 1 is formed on a {111} plane in which the gauge factor (piezoresistance coefficient) does not depend on the crystal direction, a pressure sensor with very small variation in characteristics can be obtained.

The pressure-sensitive structure 7 is fixed on a substrate (not shown) at a substrate surface 9 and receives the force applied to the pressure-receiving surface 8 .
The above-mentioned strain gauge groups that detect each component of this force are each connected to a bridge, as shown in FIGS. 3A to C, for example, and output electric signals Ez, Ex, and Ey according to the force component. do. In addition, the second
In the figure, wiring for bridge connection is omitted to avoid complexity.

FIG. 4 shows a gauge arrangement and a line of wiring on the strain gauge 1 forming surface (plane) 13 of FIG. 2. FIG.
This row is based on the conventional wiring method, but as shown in the figure, strain gauges 101 to 1 for Fz detection are connected.
A total of four 04 are arranged on the line A-A' that passes through the center of the pressure-sensitive structure 7 and is parallel to the upper pressure-receiving surface 8 on the strain gauge forming surface 13 near the left and right outer edges and inner edge, and the wiring Bridge connected at 141,
Input and output are performed through the bonding pad section 15 connected to this wiring 141. In addition, the strain gauges 111 to 114 for Fz detection are connected to the line A-
A total of four pieces are arranged on the strain gauge 1 forming surface 13 near the outer edge on two lines inclined at an angle α° in both the upper and lower directions from A′, and are bridge-connected with wiring 142,
Input and output are performed through the bonding pad section 15 connected to this wiring 142. Furthermore, the strain gauges 121 to 124 for Fy detection are connected to the line A described above.
A total of four strain gauges are arranged on the strain gauge forming surface 13 at a position on the material mechanical neutral axis near the center of the ring on a line tilted at an angle α° in both the vertical and vertical directions from −A', and are bridge-connected with wiring 143. Wiring 143
Input/output is performed through a bonding pad section 15 connected to. The above-mentioned angle α° is selected at a position that does not cause distortion when only a force perpendicular to the pressure receiving surface 8 is applied to the pressure receiving surface. For example, in the case of a circular ring as shown in the figure, the angle α° is 50.4 Become a neighborhood.
That is, in the case of a circular ring, the strain gauge is preferably arranged on a line passing through the center point parallel to the pressure receiving surface 8 and on a line having an inclination of about 50 degrees with this line.

In such a silicon planar pressure sensor, a major factor that determines its reliability is the reliability of the wiring. In other words, as described above, strain gauges are formed near the surface of the silicon that constitutes the pressure-sensitive structure, and connections between the strain gauges and wiring for input/output are formed on the surface of the silicon. The strain that occurs in the pressure-sensitive structure also extends to the wiring section. If this distortion causes a resistance change or disconnection in the wiring section, reliability will be greatly reduced. In the case of a pressure sensor that detects three components of force, the wiring is complicated, and in the configuration of the wiring 24 made of a normal metal thin film as shown in FIG. 5, a considerable number of wiring 24- 1,24-2 crossover is required. (Note that here, 2
2 is SiO ₂ formed on an N-type silicon substrate 21
The film 26 is two wirings 24-1 on the SiO ₂ film 22,
24-2 is a covering insulating layer that separates both wires at the crossover position, 21 is an N-type silicon substrate, 25
is the bonding opad section. ) For example, in the case of a single-sided three-component power supply safety independent type pressure sensor unit cell in which the three-component force detection power supply is wired completely independently for each three-component force detection strain gauge group as shown in Figure 4 above. In this case, 39 wiring crossovers would be required. X ₃ in the figure,
X ₄ , Y ₃ , Y ₄ , Z ₃ , and Z ₄ are positive or negative power terminals. In addition, as shown in Figure 7, a single-sided three-component power supply is an incompletely independent type in which one side of the power supply is common (earth terminal G) and the other is an independent positive terminal (V _X , V _Y , V _Z ). So, the wiring will have 35 crossovers. Furthermore, even in the case of a single-sided three-component power supply type in which the power supply is common to each bridge (positive side terminal V, negative side terminal V) as shown in Figure 8, there are 31 wiring crossovers. is also required. In such a crossover, when the strain generated in the silicon pressure-sensitive structure reaches the crossover portion, resistance change or disconnection of the wiring portion 24 is likely to occur, greatly reducing reliability.

Therefore, if the wiring crossovers are placed at the left and right locations and at the bottom of the pressure sensor unit cell, and the left and right locations are placed at the center between the two strain gauges for vertical component force Fz detection,
The left and right parts can be set as areas where distortion is relatively small, and the influence on crossover reliability there is almost eliminated, but on the other hand, the lower position is the area where distortion is relatively the largest, so The lower crossover is prone to resistance changes and disconnections, which poses reliability problems.

[Objective of the Invention] The object of the present invention is to overcome the drawbacks of the above-mentioned prior art, to provide a compact and high-density integration system that is highly stable and capable of accurate detection of three-direction components of force. The object of the present invention is to provide a pressure sensor that can be easily mass-produced, is manufactured at low cost, and has little interference between three-directional components of force, and in particular reduces the number of wiring crossovers that are problematic in terms of reliability. The object of the present invention is to provide a highly reliable pressure sensor by reducing the number of crossovers at the lower position of the pressure sensor unit cell and, if possible, eliminating the crossovers.

[Summary of the Invention] This invention uses single crystal silicon, which has excellent properties as an elastic body, as a pressure-sensitive structure, and uses a diffusion type strain gauge group formed by planar technology on a plane perpendicular to the pressure-receiving surface. In a silicon planar pressure sensor that detects three-directional components of force applied to a pressure-receiving surface by changes in resistance,
Since there are two surfaces that can form a strain gauge, the front and back surfaces share the component of the force to be detected.
Furthermore, by penetrating the epitaxial layer and connecting the substrate part and surface wiring with a diffusion layer, and replacing part of the wiring, especially part of the power supply wiring, from metal wiring,
This reduces crossovers and reduces the wiring density on the surface.

[Embodiments of the Invention] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 9 shows an enlarged cross-section of a main part of an embodiment of the present invention, where 36 is a single crystal silicon substrate of a silicon planar pressure sensor unit cell as shown in FIG. This single crystal silicon substrate 3
Epitaxial layers 37 and 3 are formed on the front and back surfaces of 6.
7, and epitaxial layers 37,
Diffusion type strain gauges 23, 2 near the surface of 37
3 and further these epitaxial layers 3
Through-diffusion layers 38 and 38 are formed to reach the substrate 36 by penetrating through the layers 7 and 37. These penetration diffusion layers 38
The diffusion type strain gauge 23 and the metal thin film wiring 24 of the bonding pad portion 25 are connected to the silicon substrate 36 via the silicon substrate 36, and the diffusion type strain gauge 23 and the silicon substrate 36 are directly connected.

As a result, the double-sided diffused strain gauge 2
3, 23 and the bonding pad portion 25 on one side are electrically connected through the three through diffusion layers 38, 38, 38 and a common silicon substrate 36. Note that, of course, the number of wiring lines is further reduced when the diffusion type strain gauge 23 and the silicon substrate 36 are directly connected via the through-diffusion layer 38.

In order to electrically connect in this manner, the silicon substrate 36, the through diffusion layer 38, and the diffusion type strain gauge 23 are all made of the same conductivity type (for example, P type), and an epitaxial layer 37 serving as an insulating layer is formed.
should be of the opposite conduction type (for example, N type). In this way, a portion of the wiring is replaced by the above-described through diffusion layer 38 and silicon substrate 36, so that the number of wiring crossovers can be significantly reduced. That is, since the metal thin film wiring 24 connected to the through diffusion layer 38 can be made very short,
For example, as described later, this wiring etc. 2
If lines 4, 36, and 38 are used, at least this wiring will not cross over with wiring such as other detection signal lines.

Although it is possible to form the N-type diffused strain gauge 23 in the P-type epitaxial layer 37, it is better to form the P-type diffused strain gauge 23 in the N-type epitaxial layer 37 for better sensitivity. A high value can be obtained. Furthermore, as the P-type single crystal silicon substrate 36 is used as a part of wiring, it is preferable to use silicon having a specific resistance of 1 Ω·cm or less.

Furthermore, to briefly explain an example of the manufacturing process, after growing an N-type epitaxial layer 37 on both surfaces of a P-type single crystal silicon substrate 36 by vapor phase growth, SiO ₂ oxidation is applied on this epitaxial layer 37. The film 22 is formed by thermal oxidation or the like. Next, using photoetching technology on the formed oxide film 22,
A diffusion hole is provided in a portion where selective diffusion is performed. Then,
A P-type diffusion type strain gauge 23 and a P-type through diffusion layer 38 are formed in the epitaxial layer 37 by selectively diffusing highly concentrated P-type impurities using ion implantation technology. At that time, P type diffusion type strain gauge 2
3 is formed near the surface of the epitaxial layer 37,
The P-type through diffusion layer 38 is formed to penetrate the epitaxial layer 37. Subsequently, an aluminum thin film is deposited on the SiO ₂ oxide film 22 using a vapor deposition technique, and a metal thin film wiring 24 is further formed using a photoetching technique. A bonding pad 25 is fixed to a predetermined portion of this wiring 24.

FIGS. 10A and 10B show examples of wiring of the pressure sensor unit cell according to the present invention. However, FIG. 10A represents the front surface, and FIG. 10B represents the back surface. The invention shown in FIG. 9 is applied to the part indicated by 〓 in the figure. Further, G in the figure is a negative power terminal (earth terminal). As shown in the figure, this corresponds to a case where one of the power supply wirings is used in common for the double-sided diffusion type strain gauge, and the power supply for two components is common among the other power supply wirings. Detect Fz on the surface,
Detect Fx and Fy on the back side. Even if the front and back sides are reversed, they are exactly the same. By applying this invention, the crossover is reduced to one location, which is also located near the center of the middle portion of the left side strain gauge where the strain is least.

Next, an example of a method for manufacturing the pressure sensor configured as described above will be briefly described with reference to FIGS. 11A and 11B. First, a given thickness (e.g. 0.6mm)
{1
11} of the epitaxial layer of the opposite conduction type (for example, N type) formed on both sides of the surface, the diffusion type strain gauges 101 to 101 are arranged as shown in FIGS. IC manufacturing technology (planar technology) such as maskless ion beam processing and Al evaporation for 124 groups and metal wiring
formed by According to this IC manufacturing method,
A large number of pressure sensor unit cells can be fabricated in the epitaxial layer of one wafer 16. Pressure sensor unit cells are cut out from this wafer 16 by mechanical processing such as wire saw cutting, laser processing, or etching cutting, resulting in small size (for example, a few mm to
A planar pressure sensor unit cell with a diameter of 1 mm) is obtained. Although the above description has been made regarding a ring-shaped pressure sensor, it goes without saying that the planar structure of the present invention can also be applied to pressure sensors other than ring-shaped.

Note that the pressure sensor unit cell of this example can be made extremely small, so as shown in FIG. If the pressure sensor unit cells 202 are vertically arranged and fixed in a planar array, and a pressure receiving plate 205 is fixed to the top of the pressure sensor unit cells 202 to form a pressure sensor array 206, the load distribution of the load distributed in a planar manner can be accurately detected. be able to. At that time, the pressure sensor unit cell 202 is
When a unit of pressure-receiving micro-modules is formed by one unit or a set of two pressure-receiving micro-modules, each of the pressure-receiving micro-modules can be integrated into an array at a density of about 25 to 100 ^per cm2. By attaching it to the gripping surface of a robot hand, etc., it is possible to perform various types of highly accurate control.

[Effects of the Invention] As explained above, according to the present invention, two of the three components of force are detected on one side, and the other component is detected on the opposite side. Since the strain gauge is formed on both sides, and part of the wiring of the diffusion type strain gauge is replaced with a through-diffusion layer and a silicon substrate, the wiring density is significantly lowered, making the wiring easier and achieving the highest reliability. The number of cross-overs that affect the performance can be significantly reduced to just one, and the wiring for this can be located in the area with the least distortion, so reliability is dramatically improved.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing a pressure sensor (octagonal stress ring) according to the prior art, Fig. 2 is a perspective view showing an example of a pressure sensor to which the present invention is applied, and Figs.
C is a circuit diagram showing the connection state of the strain gauge of the pressure sensor in Fig. 2, Fig. 4 is a schematic diagram showing an example of the wiring arrangement of the pressure sensor wired using the conventional technology, and Figs. 5 and 6. are cross-sectional views showing the configuration of the wiring part of the pressure sensor shown in FIG. 4, and FIGS. 7 and 8.
Figure 9 is a schematic diagram of an example of the wiring arrangement of a pressure sensor wired using the conventional technology, Figure 9 is a sectional view showing an example of the configuration of the wiring part of a pressure sensor according to the present invention, and Figure 10 is A and B. A schematic diagram showing an example of the wiring arrangement of a pressure sensor wired according to the present invention, FIG. 11A is an explanatory diagram of the method for manufacturing a pressure sensor unit cell according to the present invention, and FIG. 11B is an enlarged view of part A. FIG. 12 is a perspective view showing an example of a pressure sensor array formed by arranging pressure sensor unit cells in a planar array according to the present invention. DESCRIPTION OF SYMBOLS 1... Metal octagonal ring, 7... Silicon pressure sensitive structure, 2, 28... Pressure receiving surface, 3, 9... Substrate surface, 13... Strain gauge forming surface, 15... Bonding pad part, 16...Silicon wafer,
17... Area equivalent to pressure sensor unit cell, 21...
(N type) silicon substrate, 22... SiO ₂ film, 23...
...(P type) diffusion type strain gauge, 24...metal thin film wiring, 24-1, 24-2...first and second metal thin film wiring, 25...bonding pad portion, 2
8... Covering insulating layer, 36... (P type) silicon substrate, 37... (N type) epitaxial layer, 38...
...(P type) penetration diffusion layer, 101 to 104, 111
~114, 121-124... Diffusion type strain gauge, 141-143... Wiring.

Claims (1)

[Claims] 1. A pressure sensitive structure made of single crystal silicon, a plurality of diffusion type strain gauges formed on a surface perpendicular to the pressure receiving surface of the pressure sensitive structure, and a resistance value of the strain gauges. In a pressure sensor that detects three components of force applied to the pressure-receiving surface due to changes, the epitaxial layer provided on both surfaces of the single-crystal silicon substrate portion has a strain formed on the surface of the epitaxial layer. and a diffusion layer formed by penetrating the epitaxial layer to the surface of the substrate portion, and the epitaxial layer has a conductivity type opposite to that of the substrate portion, the diffusion layer, and the strain gauge. The diffusion layer and the substrate section are configured as part of the wiring to the strain gauge, and one surface of the substrate section of the strain gauge formed on the surface of the epitaxial layer on both surfaces of the substrate section. The strain gauge on the surface of the epitaxial layer formed on the other surface of the substrate portion is for detecting two of the three components of force, and the strain gauge on the surface of the epitaxial layer formed on the other surface of the substrate portion is for detecting two of the three components of force. A pressure sensor characterized in that it is used to detect one remaining component. 2. In the pressure sensor according to claim 1, P-type silicon is used as the substrate portion of the single crystal silicon, N-type silicon is used as the epitaxial layer, and a P-type diffusion layer is used as the diffusion type strain gauge. A pressure sensor characterized by using 3. The pressure sensor according to claim 1 or 2, wherein silicon having a specific resistance of 1 Ω·cm or less is used as the single-crystal silicon substrate.