JPS60153176A - Sense of contact force sensor - Google Patents

Abstract

PURPOSE:To simplify the wiring by marked reduction of wiring density, and thus to contrive the improvement of reliability by enabling marked reduction of the number of cross-over only to one, by a method wherein diffused type strain gauges are formed on both surfaces, and a part of the strain gauges is replaced by a through-diffused layer and an Si substrate. CONSTITUTION:Epitaxial layers 37 and 37 are formed on two surfaces front and back of the single crystal Si substrate 36, and the diffused type strain gauges 23 and 23 are formed in the neighborhood of the surfaces of the layers 37 and 37 of both the surfaces; further, through diffused layers 38 and 38 reaching the substrate 36 by penetrating through these layers 37 and 37 are formed. A diffused strain gauge 23 or a metallic thin film wiring 24 of a bonding pad 25 is connected to the Si substrate 36 via these through-diffused layers 38, and the strain gauge 23 is directly connected to the substrate 36. Thereby, diffused type strain gauges 23 and 23 on both surfaces are electrically connected to the bonding pad 25 on one surface through three through-diffused layers 38, 38, and 38 and the common Si substrate 36.

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] A sensor (hexagonal stress ring) that detects three-directional components of force, which has been conventionally used in Ml[ffl, is shown. This sensor consists of a pressure receiving surface 2 of a metal rectangular ring 1 and a substrate surface 3.
Strain gauges 41-44.
is 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. Moreover, the strain gauges 51 to 54 are four of the octagonal rings.
It is attached to two oblique outer circumferential surfaces, and detects the component FX in the X direction of the horizontal force component applied to the pressure receiving surface 2.

Furthermore, the strain gauges 1 to 64 are affixed to both sides of the ring, at a rotation angle with the diagonal surface of the octagonal ring, and approximately at the center of the ring's wall thickness, so that the horizontal force applied to the pressure receiving surface 2 is reduced. Among the components, the component FW in the y direction is detected.

In this way, the three-direction force sensor shown in the figure decomposes the force into the basic orthogonal coordinate system and detects it as three-direction component force, so by combining these three component forces using an arithmetic expression, the force can be calculated. You can determine the size and direction. Furthermore, force in any direction can be measured.

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

However, although the conventional hexagonal stress ring shown in the figure is well-known as a sensor that detects 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.

■ It is difficult to downsize the ring body because it has a structure in which many strain gauges are attached in each direction.

■ In order to attach the strain gauge, creep occurs due to the attachment layer, resulting in poor stability (l/).

■ A large interference output is generated depending on the strain gauge's knot position.

■ 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 I hand that has an advanced pressure sensing function as close as possible to the pressure sensing function of the human palm, the pressure sensor must have a three-directional force sensor function, and this sensor must also be It must be possible to accurately determine the distribution of applied force, the center of force (center of gravity), and the resultant force acting on it by arranging a large number of them in a high-density planar array. 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 high density. It is desirable that the size be several milliliters and 11 squares, preferably no more than IIIIII square.

FIG. 2 shows an example of a silicon planar pressure sensor, which is the object of the present invention and was proposed to eliminate the drawbacks of the prior art described above. A plurality of diffusion type strain gauges lot~104°ut -114,121-1,!
4 is formed using planar technology. The above-mentioned strain gauges 101 to 104 have a force component F perpendicular to the pressure receiving surface 8.
In addition, the strain gauges 111 to 114 detect one component Fx of the force parallel to the pressure receiving surface 8, and furthermore, the strain gauges 121 to 124 detect another component FW of the force parallel to the pressure receiving surface 8. do. 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 is formed in the 1111 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 8,
It receives the force applied to the pressure receiving surface 8.

The above-mentioned strain gauge group that detects each component of this force is
For example, as shown in Fig. 3 (A) to (C), each wire is connected to a bridge and an electric signal Ez corresponding to the force component is transmitted.
, Ex and EV are output. Note that in FIG. 2, 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, the strain gauges 101 to 104 for Fz detection are connected to 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. 'A total of four strain gauges are arranged on the strain gauge forming surface 13 near the left and right outer edges and inner edges, and are bridge-connected with wiring 141,
Input/output is performed through the bonding pad section 15 connected to this wiring 141. In addition, a total of four strain gauges 111 to 114 for FX detection are arranged on the strain gauge forming surface 13 near the outer edge on two lines tilted at an angle α0 in both the up and down directions from the above-mentioned line AA', and are connected to the wiring 142. A bridge connection is made, and input and output are performed through the bonding pad section 15 connected to this wiring 142. Furthermore, the strain gauges 121 to 124 for FW detection are connected to the line A-A mentioned above.
A total of four strain gauges are placed on the strain gauge formation blood 13 at a position on the material mechanical neutral axis near the center of the ring on a line tilted at an angle α0 in both the vertical and vertical directions from A human output is provided by the connected bonding pad section 15. The above-mentioned angle α0 is calculated when only a force perpendicular to the pressure-receiving surface 8 is applied to the pressure-receiving surface.
The angle is selected at a position that does not cause distortion, and for example, in the case of a circular ring as shown in the figure, it is around 50.4°. 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 Brenna type 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 human output are formed on the surface of the silicon. The strain generated in the pressure-sensitive structure reaches as much as 1°■ in the wiring, and if this strain causes a change in resistance or disconnection in the wiring, reliability will be greatly reduced. In the case of a pressure sensor that detects three components of force, the wiring is complicated, and the configuration of the wiring 24 made of a normal metal thin film as shown in FIG. 5 requires a considerable number of wires Mi 24 as shown in FIG. -1.24-2 crossover is required. (Here, 22 is a 5102 film formed on the N-type silicon substrate 21, and 26 is a coating that separates the two wires 24-1 and 24-2 on the 5iOz11 layer 22 at the cross-over/toward position. 21 is an N-type silicon plate, and 25 is an insulating layer.) For example, a power source for detecting three components of force as shown in FIG. In the case of a single-sided three-component power supply completely independent type pressure sensor unit cell in which each group is wired completely independently, 38 wiring crossovers are required. ×3゜X4 +Y3'+Y4 +23 +
24 is a bluff or negative power terminal. Also, as shown in Figure 7, one of the power supplies is common (earth terminal G), and the other is an independent positive terminal (Vll, V
In a single-sided, three-component power supply incompletely independent type with a power supply voltage of 100% (Y, Vz), there are 35 wiring crossovers. moreover,
As shown in Figure 8, 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), there are 31 wiring cross-overs. It becomes necessary. This is how Rosso/Hiki goes,
If the strain occurring in the silicon pressure-sensitive structure extends to the crossover portion, resistance changes or disconnections in the wiring portion 24 are likely to occur.
This will greatly reduce the 1δ 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 detecting the vertical component force t2, it is possible to The left and right parts can be made into areas where comparative image distortion occurs, and the influence on the reliability of the cross-over there will be almost eliminated. The crossover at the bottom 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 highly integrated technology with good stability and accurate detection of three-directional components of force. The purpose of the present invention is to provide a pressure sensor that can be mass-produced at a low cost, has low interference between three-way components of force, and reduces the number of wiring crossovers, which are problematic in terms of reliability. However, it is an object of the present invention to provide a highly reliable pressure sensor by reducing the number of talosopers at the lower position of the pressure sensor unit cell and, if possible, eliminating the crossover.

[Summary of the Invention] This invention uses single-crystal silicon, which has excellent characteristics as an elastic body, as a pressure-sensitive structure, and uses a diffused strain gauge group resistor formed by planar technology on a plane perpendicular to the pressure-receiving surface. In a silicon planar pressure sensor that detects the three-directional components of force applied to the pressure-receiving surface by changes in value, there are two surfaces on which strain gauges can be formed, the front and back, so the force components detected on the front and back surfaces are Furthermore, the substrate part and the surface wiring are connected by a diffusion layer through the epitaxial layer, and part of the wiring, especially a part of the power supply wiring, is made of gold 7.
i! By replacing the wiring, the cross-over/to is made easier, and the arrangement on the surface is improved! M′& degree is reduced.

[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 38 is a single crystal silicon substrate of a silicon planar pressure sensor unit cell as shown in FIG.

Epitaxial layers 37, 3? A diffusion type strain gauge 2 is formed near the surface of the epitaxial layer 37 on both sides.
3 and 23, and further these epitaxial layers 3
7.37 to reach the substrate 38 through diffusion layer 38.
form 38. Through these penetration diffusion layers 38, the diffusion type strain gauge 23 and the metal thin film distribution 124 of the bonding pad portion 25 are connected to the silicon substrate 36, and the diffusion type strain gauge 23 and the silicon substrate 36 are directly connected. let

As a result, the diffusion type strain gauges 23° 23 on both sides and the bonding pad portion 25 on one side f1 are electrically connected through the three through diffusion layers 38, 38, 38 and the 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 make electrical connections in this way, a silicon substrate 36
, the through diffusion layer 38 and the diffusion type strain gauge 23 are all of the same conductivity type (eg, P type), and the epitaxial layer 37, which serves as an insulating layer, is of the opposite conductivity type (eg, N type). In this way, a part of the wiring is replaced with the above-mentioned through diffusion layer 3B and silicon substrate 38, so
The number of interconnections to/from cross-overs 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, if this wiring 24, 38, 38 is used as a power supply wiring as described later, at least this wiring can be connected to other detection signal lines. There will be no crossover with other wiring.

Although it is possible to form the N-type diffused strain gauge 23 in the P-type epitaxial layer 37, it is more convenient to form the P-type diffused strain gauge 23 in the N-type epitaxial layer 37. You can get something expensive. Also,
As the P-type single crystal silicon substrate 36, it is preferable to use silicon having a resistivity of 1 Ωecm or less since it is used as a part of wiring.

Furthermore, to briefly explain an example of the manufacturing process, an N-type epitaxial layer 37 is grown on the entire surface of both surfaces of a P-type single crystal silicon substrate 36 by a vapor phase growth method, and then a 5102 oxide film 22 is formed on this epitaxial layer 37. 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 high-concentration P-type impurities is performed using ion implantation technology to form a P-expanded 1t&-type strain gauge 23 and a P-type through diffusion layer 38 in the epitaxial layer 37. At that time, the P expansion and expansion type strain gauge 23 is formed near the surface of the epitaxial layer 37, and the P type through diffusion layer 38 is formed near the surface of the epitaxial layer 37.
is formed so as to penetrate the epitaxial layer 37. Subsequently, an aluminum thin film is deposited on the 5i02 oxide film 22 using a metal 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. 10(A) and 1(B) show examples of wiring of the pressure sensor unit cell according to the present invention. However, FIG. 1O (A) represents the front surface, and FIG. 1θ (B) represents the back surface. The invention shown in FIG. 8 is applied to the parts shown 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. Fz is detected on the surface, and FW and jY are detected on the surface. It is exactly the same whether it is front or back or reversed. By applying this invention, cross-over/
The strain gauge has been reduced to one location, and it is located near the center between the left strain gauges, where strain is the least.

Next, an example of a method for manufacturing the pressure sensor configured as described above will be briefly described with reference to FIGS. 11(A) and 11(B). First, it has a predetermined thickness (for example, 0.8 mm),
A predetermined conductivity type (e.g. P type) and specific resistance (e.g. lΩ・C
m or less) and having a crystal orientation in a predetermined direction, an area corresponding to a pressure sensor unit cell of an epitaxial layer of an opposite conductivity type (for example, N type) formed on both sides of the (1111 plane) of a single crystal silicon wafer 16 having a crystal orientation in a predetermined direction. Figure 17 (A)
, a diffusion type strain gauge 101- arranged as shown in (B).
124 groups and metal wiring are formed by IC manufacturing technology (planar technology) such as maskless ion beam processing and An evaporation. According to this IC manufacturing method, a large number of pressure sensor unit cells 8 can be fabricated in the epitaxial layer of one wafer 18. By accurately cutting out pressure sensor unit cells from this wafer 16 by wire saw cutting, laser processing, or machining such as etch cutting, a small (for example, several mm to 1 cm) planar pressure sensor with well-matched characteristics is produced. A unit cell 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 since the pressure sensor unit cell of this example can be made extremely small, the pressure sensor unit cell 2 as shown in FIG.
02 are fitted into the grooves 204 on the lower common substrate 203, and a large number of them are fixed vertically in a plane array in the x+Y direction, and the pressure receiving plate 205 is fixed to the second part of the pressure sensor unit cell 202. By forming the pressure sensor array 206 using the pressure sensor array 206, it is possible to accurately detect the load distribution of the load distributed in a planar manner. At that time, when a unit of pressure-receiving micro-modules is formed by using one or two pressure sensor unit cells 202 as one set, each of the pressure-sensing micro-modules is integrated in an array at a density of about 25 to 100 pieces per 1 cm2. By attaching these to the gripping surface of a robot hand, etc., it becomes 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. By forming strain gauges on both sides and replacing part of the wiring of the diffusion type strain gauge with a through diffusion layer and a silicon substrate,
The wiring density has been significantly lowered, making wiring easier, and the number of crossovers, which affect reliability the most, can be significantly reduced to just one, and the placement position is also in the area with the least distortion, which increases reliability. Sexuality improves dramatically.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing a pressure sensor (hexagonal 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. 2 is a circuit diagram showing the connection state of the strain gauge of the pressure sensor, 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 11 examples of the wiring arrangement of a pressure sensor wired using both conventional techniques. FIG. 101K (A) and (B) are schematic diagrams showing an example of the wiring arrangement of a pressure sensor wired according to the present invention; FIG. 11 (A) 11(B) is an enlarged view of part A of the manufacturing method of the pressure sensor unit cell according to the present invention, and FIG. 12 is an explanatory diagram showing the method of manufacturing the pressure sensor unit cell according to the present invention in a planar array. FIG. 3 is a perspective view showing an example in which a pressure sensor array is formed by using the pressure sensor array. l... Metal square ring, 7... Silicon pressure sensitive structure, 2.8... Pressure receiving surface, 3.8... Substrate surface, 13... Strain gauge forming surface, 15...・Pounding pad portion, 16... Silicon wafer, 17... Area corresponding to pressure sensor unit cell, 21... (
N type) silicon substrate. 22... Si02 film, 23... (P type) diffusion type strain gauge, 24...
Metal thin film wiring, 24-1.24-2... 1st. 2nd metal thin H-body wiring, 25... Bonding pad portion, 26... Covering insulating layer, 36... (P type) silicon substrate, 37... (N type) epitaxial layer, 3 days... ...(P
form) tribute diffusion layer, 101-104. lit~114,121 N124・
...Diffusion type strain gauge, 141-143...Wiring. Patent applicant: Fuji Electric Research Institute Co., Ltd. Figure 1/"z Figure 2 FZ Figure 3 (A> (B) (C) Figure 4 Figure 5 Figure 7 Figure 15" Figure S Figure 8 24 26 Figure 1O Figure 11 Part A

Claims (1)

[Claims] l) Single crystal silicon is used as a pressure-sensitive structure, a plurality of meters of diffused Stref cages are formed on a surface perpendicular to the pressure-receiving surface of the pressure-sensitive structure, and the resistance value of these Stref cages is changed. In the pressure sensor that detects the three components of force applied to the pressure receiving surface, an epitaxial layer having a conductivity type opposite to that of the substrate is formed on the single crystal silicon substrate, and the epitaxial layers on both sides are forming the stretch cage, and forming a diffusion layer having a conductivity type opposite to that of the epitaxial layers on both sides, penetrating the epitaxial layers on both sides until reaching the +iFj substrate section, and forming the diffusion layer and the substrate section. A pressure sensor configured as part of wiring to the Stref cage. 2. In the pressure sensor according to claim 1,
P-type silicon is used for the single-crystal silicon substrate portion and L2, and N-type silicon is used for the epitaxial layer;
A pressure sensor characterized in that a P-swelled diffusion layer is used as the diffusion type storage cage. 3) A pressure sensor according to claim 1 or 2, wherein silicon having a specific resistance of 1Ω·am or less is used as the single-crystal silicon substrate portion. (Margin below)