JPH0473630B2 - - 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. 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 4 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.
4, 51 to 54, and 61 to 64 are pasted, and the three directional components are separated from each other and detected respectively 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 the inner peripheral surface of the ring to train 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 decomposes force into the basic orthogonal coordinate system and detects it as three-direction component forces, so by combining these three component forces using an arithmetic expression, You can find the magnitude and direction of force. Furthermore, force in any direction can be determined.

A major feature of the three-directional force sensor is that force can be easily decomposed and combined in this way.

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 plane. 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 stability.

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.

In order to realize a robot hand with 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 to determine the distribution of applied force and the center of force (center of gravity)
It must be possible to accurately determine the resultant force acting on it. Therefore, such a pressure sensor is required to be able to accurately separate the component forces of the load without mutual interference, and to be able to minimize dimensions and integrate at 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 above-mentioned strain gauges 101 to 104 measure the force component perpendicular to the pressure receiving surface.
Fz is detected, and strain gauges 111 to 1
14 detects one component Fx of the force parallel to the pressure receiving surface 8,
Furthermore, the strain gauges 121 to 124 detect a force component Fy 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 other bidirectional forces. Furthermore, if the diffusion type strain gauge is formed on the {111} plane in which the gauge factor (piezoresistance coefficient) does not depend on the crystal orientation, 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 an example of the gauge arrangement and wiring on the strain gauge forming surface (plane) 13 of FIG. 2. FIG.
This example is based on the conventional wiring method, but as shown in the figure, strain gauges 101 to 101 for Fz detection are used.
104 is a line A-A' that passes through the center of the pressure-sensitive structure 7 and is parallel to the upper pressure-receiving surface 8, and a total of 4
They are arranged and bridge-connected by a wiring 141, and input/output is performed by a bonding pad section 15 connected to this wiring 141. In addition, the strain gauges 111 to 114 for Fx detection are connected to the line A mentioned above.
A total of four strain gauges are arranged on the strain gauge forming surface 13 near the outer edge on two lines tilted at an angle α° both upward and downward 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. That is, as described above, the strain gauges are formed near the surface of the silicon that constitutes the pressure sensitive structure, and the connections between the strain gauges and the wiring for input and output are formed on the surface of the silicon. The strain that occurs in the silicon 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, 22
is SiO ₂ formed on the 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 pad part. ) For example, in the case of a single-sided three-component power supply completely 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 Fig. 4 above. In this case, 39 wiring crossovers would be required. In the figure, X ₃ ,
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 installed 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 the reliability of the crossover there is almost eliminated.On the other hand, the lower position is the area where the distortion is relatively large, 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 reduce the number of crossovers at the lower position of a pressure sensor unit cell, and if possible, eliminate the crossovers altogether, thereby providing a highly reliable pressure sensor.

[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. A planar pressure sensor made of silicon that detects three-directional components of force applied to a pressure-receiving surface by changes in the resistance value of
The epitaxial layer provided on the surface of the single crystal silicon substrate has a strain gauge formed on the surface of this epitaxial layer and a diffusion layer formed on or through this epitaxial layer. and the epitaxial layer has a conductivity type opposite to that of the substrate portion, the diffusion layer, and the strain gauge, and the diffusion layer and the substrate portion are configured as part of wiring to the strain gauge. This reduces the number of wiring crossovers by replacing part of the wiring from the metal wiring on the surface to the internal silicon substrate.

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

FIG. 9 shows a cross section of a main part of an embodiment of the present invention applied to a silicon planar pressure sensor unit cell as shown in FIG. , a diffusion type strain gauge 23 is formed near the surface of this epitaxial layer 37, and
The metal thin film wiring 24 and the silicon substrate 36 are connected by the through diffusion layer 38 penetrated through the metal thin film wiring 24 and the two short metal thin film wiring 24 and the two through diffusion layers. 38 and a common silicon substrate 36 .

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 wires 4, 26, and 38 are used, at least this wire will not cross over with wires for other detection signals, etc.

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 resistivity 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 the entire surface of a P-type single crystal silicon substrate 36 by a vapor phase growth method,
A SiO ₂ oxide film 22 is formed on this epitaxial layer 37.
is formed by thermal oxidation etc. Next, a photoetching technique is used in the formed oxide film 22 to provide a diffusion hole in a portion where selective diffusion is to be performed. Next, selective diffusion of highly concentrated P-type impurities is performed using ion implantation technology to form a P-type diffusion type strain gauge 23 and a P-type through diffusion layer 38 in the epitaxial layer 37. At this time, the P type diffusion type strain gauge 23 is formed near the surface of the epitaxial layer 37, and the P type through diffusion layer 38 is formed so as to penetrate the epitaxial layer 37. Next, an aluminum thin film is deposited on the SiO ₂ oxide film 22 by vapor deposition technology,
Furthermore, using photoetching technology, metal thin film wiring 2
form 4. A bonding pad 25 is fixed to a predetermined portion of this wiring 24.

FIG. 10 shows a cross section of a main part of another embodiment of the present invention, in which the penetration diffusion layer 38 on the strain gauge side is shown.
penetrates the epitaxial layer 37 and directly connects the diffusion type strain gauge 23 and the silicon substrate 36 . This eliminates the metal thin film wiring 24 that connects the strain gauge 23 and the through-diffusion layer 38, so the number of wiring can be further reduced and reliability can be further improved.

FIGS. 11 and 12 show examples of wiring of the pressure sensor unit L according to the present invention. The present invention shown in FIGS. 9 and 10 is applied to the area shown by 〓 in the figure. Note that G in the figure is a negative power terminal (earth terminal). By applying this invention, for example, in the case of the single-sided epitaxial type and three-component power supply type shown in Fig. 11, the crossover is reduced to approximately 1/3.
The number of locations can be reduced to 13, and in the case of the single-sided epitaxial type and three-component power supply type shown in Figure 12, the crossover is approximately 1/3.
It is possible to reduce the number of crossovers to 12 or 10 locations, and furthermore, the number of crossovers at the bottom position, which poses the greatest problem in reliability, can be reduced to 1 to 0 locations.

In this example, the case of a pressure sensor unit cell in which a diffusion type strain gauge is formed on only one predetermined side of a single crystal silicon pressure sensitive structure has been described. It is also suitable for forming a diffusion type strain gauge that detects each of the three components of force, and it goes without saying that a silicon substrate can be used as part of the wiring of the strain gauges on both sides.

Next, an example of a method for manufacturing the pressure sensor configured as described above will be briefly described with reference to FIGS. 13A and 13B. First, a given thickness (e.g. 0.6mm)
has. A conductivity type opposite to that formed on the {111} plane of the single-crystal silicon wafer 16 having a predetermined conductivity type (e.g., P type) and specific resistance (e.g., 1 Ω cm or less) and crystal orientation in a predetermined direction. A group of diffusion strain gauges 101 to 124 arranged as shown in FIG. 11 or FIG. 12 and metal wiring are formed in a region 17 corresponding to a pressure sensor unit cell of a (for example, N-type) epitaxial layer by maskless ion beam processing. IC manufacturing technology such as Al deposition (planar technology)
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. By accurately cutting out pressure sensor unit cells from this wafer 16 by wire saw cutting, laser processing, or machining such as etching cutting, pressure sensor unit cells can be cut into small pieces with well-matched characteristics (for example, from a few mm to
A planar pressure sensor unit cell of 1 mm) is obtained. In the above description, a ring-shaped pressure sensor has been described, but it goes without saying that the planar type manufacturing of the present invention can be applied to pressure sensors other than ring-shaped pressure sensors.

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. I can do it. At this time, when one or two pressure sensor unit cells 202 are used to form a unit of pressure-receiving micro-modules, each of the pressure-sensing micro-modules is arranged in an array at a density of about 25 to 100 cells ^per 1 cm2. They can be integrated into one body, and by attaching them to the gripping surface of a robot hand or the like, it becomes possible to perform various types of highly accurate control.

[Effects of the Invention] As explained above, according to the present invention, a part of the wiring of a diffusion type strain gauge is replaced with a through diffusion layer and a silicon substrate, so that the number of wiring crossovers is greatly reduced. Moreover, as a result, most of the crossover can be limited to the small strain region, making it possible to almost eliminate crossovers that tend to change resistance or disconnect, dramatically increasing the reliability of the pressure sensor. improves.

[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 of an example of the pressure sensor to which the present invention is applied, and FIGS. 3A to 3C are the pressure sensors shown in FIG. Fig. 4 is a schematic diagram showing an example of the wiring arrangement of the pressure sensor wired using the conventional technology, and Figs. 7 and 8 are schematic diagrams of examples of the wiring arrangement of a pressure sensor wired using the conventional technology, and FIG. 9 is a wiring portion of a pressure sensor according to the present invention. 10th cross-sectional view showing a configuration example of
The figure is a sectional view showing another embodiment of the present invention, No. 11.
12 and 12 are schematic diagrams showing examples of wire arrangement of a pressure sensor wired according to the present invention, FIG. 13A is an explanatory diagram of a method for manufacturing a pressure sensor unit cell according to the present invention, and FIG. 13B 14 is a perspective view showing an example in which pressure sensor unit cells according to the present invention are arranged in a planar array to form a pressure sensor array. DESCRIPTION OF SYMBOLS 1... Metal octagonal ring, 7... Silicon pressure sensitive structure, 2, 8... Pressure receiving surface, 3, 9... Substrate surface, 13... Strain gauge forming surface, 15... Bonding pad portion, 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
6... Covering insulating layer, 26... (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 the surface of the single-crystal silicon substrate has a strain gauge formed on the surface of the epitaxial layer. , a diffusion layer formed 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. . A pressure sensor, wherein the diffusion layer and the substrate portion are configured as part of wiring to the strain gauge. 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.