JPH0719975A - Pressure sensor chip, tactile sensor and manufacture of tactile sensor - Google Patents

Abstract

PURPOSE:To provide a two-dimensional array-shaped three-axis tactile sensor excellent in quantity production property and capable of being manufactured in the lump by arranging many sensor chips on a flexible printed board. CONSTITUTION:A rectangular mesa 14 having a trapezoidal cross section is formed on the surface of an element made of silicon, detecting electrodes 20 are provided on the slope portions 16 of the rectangular mesa 14, and a piezoelectric material thin film layer 18 having a piezoelectric effect is formed on the surface of the element in contact with the electrodes 20 as a pressure sensor chip 10. One or multiple rectangular mesas having a trapezoidal cross section are formed on the surfaces of multiple elements made of silicon and arranged and connected into a matrix shape on a flexible printed board, detecting electrodes are provided on the slope portions of the rectangular mesas, impedance converting elements electrically connected to the detecting electrodes are provided, a piezoelectric material thin film layer having a piezoelectric effect is formed on the surfaces of the elements in contact with the detecting electrodes, and it is covered with a ground electrode layer, a disturbance shielding layer, and a protective layer to form a tactile sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor chip, a tactile sensor, and a method for manufacturing the tactile sensor, and more particularly, to a pressure sensor having a structure suitable for being applied to a distributed tactile sensor for giving a tactile sensation to a robot arm. The present invention relates to a sensor chip, a tactile sensor, and a method for manufacturing a tactile sensor.

[0002]

2. Description of the Related Art Conventionally, a robot arm is generally operated by visual feedback, but if a fine operation is performed at a position away from a visual sensor, the operator will be burdened with a great burden. Therefore, from the viewpoint of improving operability and reducing operator fatigue, various sensors other than visual sensors that are input devices for feedback control are required,
In particular, realization of a tactile sensor is desired.

Conventionally, most of the pressure sensors used for this kind of tactile sensor and the like are of a relatively large size and of a one-axis detection type. In addition, the two-dimensional array type has many one-axis detection types, and the three-axis detection type is rare, and at the same time, the manufacturing process is significantly complicated. Furthermore, since many array sensors have a rigid structure, a distributed tactile sensor having a flexible structure is hardly found.

FIG. 5 shows an example of a conventional three-axis tactile sensor. This sensor is a matrix tactile sensor that was prototyped using anisotropic etching technology.
Pressure is detected by a semiconductor strain gauge. In this example, 4 × 4 elements are arranged in a matrix at a pitch of 1 mm, and an IC circuit is built under the sensing layer to form one chip. The tactile sensor element used here is called a triaxial 1 mm sensor in which the detection capability and the arrangement pitch are combined. FIG. 6 is a configuration diagram of the sensor, (1) shows a basic portion of a triaxial sensor, a black portion is an external force acting portion, a shaded portion is a sensing element, and (2) 4 of a to d in FIG. Semiconductor strain gauges are formed in some places. (3) is the sensing element side, and (5) is the back side on which the IC circuit is formed.

In the tactile sensor as described above, rectangular holes are punched in a silicon wafer at a predetermined pitch by an electric discharge machining method, and then the holes of the tactile sensor are rectangularly shaped in a vertical and horizontal direction by a diamond grindstone on the surface of the tactile sensor. Process the groove on the cross section. 1 by alternating the depth of this groove
3-axis 1 with 6 fixed beams on both ends alternately arranged in x and y directions
mm tactile sensor is formed. Then, the prepared sensing unit is directly soldered to a separate IC substrate to join the electrodes.

It has been argued that such a tactile sensor can be miniaturized, that it is a completely elastic body and has no hysteresis, and that it is strong and can be integrated with an electronic (IC) circuit. There is.

[0007]

However, as is clear from the above-mentioned manufacturing process, it is largely dependent on the conventional machining technology, and precise positioning is required, and at the same time, fine processing is difficult. is there. For this reason, there are drawbacks that mass productivity is poor, batch manufacturing is not possible, and the processing cost as a sensor becomes extremely high.

An object of the present invention is to provide a large number of small 3-axis pressure transducers manufactured by semiconductor manufacturing technology on a flexible printed circuit board to form a 2-axis array 3-axis tactile sensor, which is excellent in mass productivity. The present invention provides a pressure sensor chip, a tactile sensor, and a method of manufacturing the tactile sensor that can be manufactured in a batch.

[0009]

In order to achieve the above object, a pressure sensor chip according to the present invention has a trapezoidal cross-section rectangular mesa formed on a surface of an element made of silicon, and a sloped portion of the rectangular mesa. Is provided with a detection electrode, and a piezoelectric material thin film layer having a piezoelectric effect is formed on the surface of the element in contact with the detection electrode.

In the tactile sensor according to the present invention, one or more rectangular mesas having a trapezoidal cross section are formed on the surface of an element made of silicon arranged and connected in a matrix on a flexible printed circuit board, and the sloped surface of each rectangular mesa is formed. A detection electrode is provided on the portion, an impedance conversion element electrically connected to the detection electrode is provided, and a piezoelectric material thin film layer having a piezoelectric effect is formed on the surface of the element in contact with the detection electrode. It is covered.

Further, the method for manufacturing a tactile sensor of the present invention comprises:
After forming one or more rectangular mesas having a trapezoidal cross section on the surface of the silicon element by anisotropic etching and forming a MOS-FET in which at least a gate electrode is set on the slope of the mesa on the surface of the silicon element, a flexible printed circuit board is formed. , And the back surface of the silicon is separated for each element, a thin film layer of piezoelectric material having a piezoelectric effect is formed on the surface of the silicon element on the mesa side, and a ground electrode layer and a disturbance shield are formed on the outer surface. The layer and the protective layer were coated.

[0012]

According to the structure of the distributed pressure sensor chip,
The amount of electric charge generated in the piezoelectric material thin film layer by the external force acting on the surface of the mesa is detected by the detection electrode provided on the slope of the mesa. Since the mesa has a trapezoidal cross section and a rectangular shape in plan view, the normal and tangential forces are detected by the electrodes on each inclined surface, and the acting forces in the orthogonal triaxial directions can be detected.

Further, since a plurality of the above chips are arranged in a matrix and connected to the flexible printed circuit board, the sensor main body can be relatively flexibly deformed, and the restrictions on the shape of the mounting location are lessened, and it acts on each chip. Since the magnitude of the applied pressure and the acting direction are detected at multiple locations, the distribution of the applied pressure in the contact area of the sensor body can be detected, and the recognition data for grasping the surface texture and contact state of the target object as a tactile sensor. Can be applied to a robot arm that requires.

Further, in the manufacturing method of the present invention, the etching process, the coating of the thin film layer and the like are also included in the basic manufacturing process, and there is no assembly process which requires positioning in the machining process and the manufacturing process. Since it can be created and handling and manufacturing are extremely easy, it is excellent in mass productivity.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of a pressure sensor chip, a tactile sensor, and a method of manufacturing a tactile sensor according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a plan view and a sectional view of a pressure sensor chip of the embodiment. In this chip 10, a rectangular mesa 14 having a trapezoidal cross section is formed on the surface of a silicon substrate 12. This is a rectangular frame-shaped mesa in which a frame-shaped SiO2 mask is provided on the surface of the silicon substrate 12 so as to have a square opening in the center and anisotropic etching is performed so that a portion corresponding to the mask portion has a trapezoidal cross section. 14 are configured.
As a result, the surfaces located on the four sides of the inner peripheral portion of the mesa 14 are inclined surfaces 16.

On the silicon substrate 12 having such a rectangular mesa 14, thin film layers of piezoelectric material having a piezo effect are laminated. As a piezoelectric material having a piezoelectric effect, polyvinylidene fluoride (hereinafter referred to as PV
DF) is used, and this film is heated, pressure-transferred in vacuum, and bonded to the mesa 14 of the silicon substrate 12. There are piezoelectric ceramics and piezoelectric polymers as piezoelectric materials, and both can be used. However, since the dielectric constant of the piezoelectric polymers is small, applying the same stress to both causes a voltage about 10 times larger than that of the piezoelectric ceramics. , Piezoelectric polymer has an advantage. In addition, in a tactile sensor that makes mechanical contact with an object, a flexible sensing material is desirable, so a piezoelectric polymer is advantageous. Further, the piezoelectric polymer includes a polymer alone represented by PVDF and a composite material in which piezoelectric ceramic powder is mixed in PVDF or silicone rubber for the purpose of improving piezoelectric performance. The latter is ceramic powder. If is not evenly dispersed in the matrix polymer, there is a drawback that the piezoelectric characteristics tend to become non-uniform depending on the location. Therefore, the former simple substance polymer is desirable from the viewpoint of the stability of the material.

Since the mesa 14 is formed on the silicon substrate 12 and the PVDF thin film layer 18 is provided on the surface of the mesa 14, when the mesa 14 contacts the object through the PVDF layer 18, the magnitude of the contact pressure is increased. Accordingly, a voltage is generated in the PVDF layer 18 by the piezo effect. In order to detect this, a detection electrode 20 is provided on each of the four inclined surfaces 16 on the inner surface side of the mesa 14, which is particularly surrounded by a rectangle. That is, the PVDF layer 1 is formed on the surface of the silicon substrate 12.
Before stacking 8 layers, the detection electrodes 20 are formed in advance on each of the inclined surfaces 16 in a chip base state as shown in FIG. The detection electrode 20 is simultaneously connected to the gate electrode of a MOS-FET 22 as an impedance conversion element. The MOS-FET 22 detects a pressure sensitive signal from the PVDF layer 18 as a gate voltage signal and amplifies the detected signal, and is formed in the vicinity of the inclined surface 16 of the mesa 14. In the example shown in FIG. 2, this is arranged on the upper end surface of the mesa 14, and the MOS-FET 22 is formed in the surface of the silicon substrate 12 by implanting impurities or the like. An output electrode 24 connected to the drain electrode of the MOS-FET 22 and a power supply electrode 26 connected to the source electrode are provided around the mesa 14 so as to serve as connection terminals to the circuit of the flexible printed board 28. It is arranged. The MOS-FET 22 is provided corresponding to each detection electrode 20, and is provided at four places in the sensor chip 10 of the embodiment. These MOS-FET22
After forming the electrodes 20, 24 and 26 connected thereto, the flexible printed board 28 is connected so that the detection signal is taken into the circuit in the board and a predetermined sensing output is performed.

Thus, after the detection electrode 20 and the MOS-FET 22 are formed after the etching of the mesa 14 and at the same time, the flexible printed board 28 is connected,
The PVDF layer 18, which is a pressure sensitive element, is formed.
The surface of the VDF layer 18 is coated with an aluminum layer 30 that also serves as a ground electrode and serves as a disturbance shield, and further, a silicone rubber layer 32 is sequentially coated on the outermost surface portion to improve wear resistance.

The pressure sensor chip 1 thus constructed
According to 0, electric charges are generated in the PVDF layer 18 by the external force acting through the protective layers 30 and 32, and this is generated by the MOS.
-The voltage is converted by the FET 22 and the magnitude of the applied pressure can be detected by detecting the generated voltage. The applied pressure is applied to the upper surface of the mesa 14, but the detection electrode 20 is set on the inclined surface of the rectangular mesa 14, and the force in the normal direction and the tangential direction to the mesa surface can be detected. Function. That is, when the force acts only in the normal direction of the sensor chip, the voltages converted from the charges generated in the pair of PVDF layers 18 provided on the facing mesa inclined surfaces 16 become equal, and the voltage in the normal direction at this time becomes equal. The output voltage Vn becomes 1/2 of the sum of the output voltages from the PVDF layers 18 facing each other. Similarly, when the force acts only in the tangential direction of the sensor chip, the opposite mesa inclined surface 16
Since one of the pair of PVDF layers 18 provided in 1 is subjected to compression and the other is subjected to tension, the output voltages of the two have different polarities, and the tangential output is obtained by taking the difference between the two voltages. Therefore, the magnitude of the normal component can be detected by the average value of the output voltages obtained from the facing PVDF layers 18, the magnitude of the tangential component can be detected by obtaining the difference, and the action direction of the force for obtaining the polarity can be detected. This allows
It is possible to detect each component of the applied stress in the three axis directions.

Here, since the pressure distribution information can be detected by arranging the above-described sensor chips 10 in a matrix at the same time, the sensor chip 10 can be used as the tactile sensor 34. As shown in FIG. 3, the sensor chip 10 is formed by arranging the sensor chip 10 on the flexible printed board 28 vertically and horizontally at regular intervals. A manufacturing process of such a tactile sensor 34 will be described with reference to FIG.

First, in the first step, as shown in FIG. 4A, the mesa 14 having a predetermined height is formed on the surface of the silicon substrate 12 by anisotropic etching. SiO 2 is used as a mask for etching the mesa 14. The mesas 14 are formed in a 2 × 2 matrix in the illustrated example.

Then, as shown in FIG. 4B, a MOS-FET 22 for impedance conversion is formed in the engraved surface of the silicon substrate 12 as a second step. The diffusion of impurities may be performed by ion implantation. In this example, the MOS-FET 22 is formed on the upper surface of the mesa 14, but the flatness of the silicon substrate 12 is sufficient and the FET
If the characteristics do not become uneven, the electrodes 20, 24, 26
You may comprise in arbitrary positions other than. This MOS-FE
To insulate the gate electrode of T22 from the PVDF film 18, the gate surface is coated with a resist film.

The third step is the flexible printed circuit board 28.
This is a bonding step with the flexible printed board 28 through the electrode pads (output electrode 24, power supply electrode 26) around the sensor chip 10 (FIG. 4C). For this purpose, bumps may be printed on the board-side pads with a conductive paste, and then the joints may be positioned and joined. The mesa 14 is formed by etching according to the thickness of the printed board 28.

After connecting the flexible printed circuit board 28, the fourth step of separating the sensor chip 10 is performed (FIG. 4).
(4)). This is to separate the back surface of the silicon substrate 12 opposite to the surface on which the mesas 14 are formed into each chip 10 of each mesa 14 by anisotropic etching. As a result, the plurality of sensor chips 10 are arranged in a matrix and mounted on the flexible printed board 28.

Next, the fifth step of laminating the PVDF film 18 as a pressure sensitive element by pressure bonding is performed (FIG. 4 (5)). The surface shape of the silicon substrate 12 is transferred to the PVDF film 18 by pressing with a pad made of a slightly soft silicone rubber while being heated so that the surface of the silicon substrate 12 is bonded to the surface of the silicon substrate 12 at the same time. Pressurization in vacuum is desirable for cleaning and defoaming the bonding interface. Here, it is desirable that the silicon substrate 12 and the PVDF film 18 be directly bonded. However, if the bonding is not possible with both of them, a paste-like thermosetting is used by using a mask having a shape suitable for the unevenness of the surface of the silicon substrate 12. The resin is applied to the surface of the silicon substrate 12 by screen printing or the like. Then, after positioning, the PVDF film 18 and the silicon substrate 12 are bonded.

After the PVDF film 18 is laminated, a layer for protecting it is formed. As shown in FIG. 4 (6), this is an aluminum layer 30 on the entire surface of the PVDF film 18.
Then, the outer surface side is coated with a silicone rubber layer 32 to improve wear resistance (FIG. 4 (7)). The former is a disturbance shielding coating that also serves as a ground electrode. The reflectance of the aluminum coating layer 30 exhibits a high reflectance in a wide wavelength range from infrared rays to ultraviolet rays, and thus has a great effect of suppressing disturbance.

In the tactile sensor 34 manufactured by such a method, the tactile sensing chip 10 in which the structure made by silicon anisotropic etching and the PVDF film 18 as a pressure converting element are combined is a flexible printed circuit board. A large number of matrix sensors are arranged on the 28, and the following effects can be obtained. In other words, in terms of functionality, the sensor is a triaxial sensor that can detect forces in the normal and tangential directions with respect to the upper surface of the sensing chip, and since there is little leakage of generated charge, quasi-static pressure detection is also possible. ing. Further, the miniaturized matrix sensor has a high resolution, and this resolution can also be arbitrarily set by adjusting the interval between the sensor chips 10.

Further, in terms of structure, since it is formed on the flexible printed circuit board 28, there are few restrictions due to the shape of the mounting location. Moreover, since the sensing chip 10 is made of silicon, it has high strength, and an electronic (processing) circuit can be formed around the chip 10. In addition, in terms of manufacturing, it can be manufactured by a batch process, a sensor with a relatively high density can be manufactured, and there is no assembly process that requires positioning in the manufacturing process, so that handling and manufacturing are easy.

[0030]

As described above, according to the present invention,
It has a rectangular mesa with a trapezoidal cross section formed on the surface of the element made of silicon, a detection electrode is provided on the slope of this rectangular mesa, and a piezoelectric material thin film layer having a piezo effect is formed on the surface of the element in contact with the electrode. Since it is the pressure sensor chip, it is possible to detect the force in the normal line and the tangential direction and obtain the effect that the force can be detected in the three axis directions.

Further, in the tactile sensor of the present invention, a rectangular mesa having a trapezoidal cross section is formed on the surface of an element made of silicon arranged and connected in a matrix form on a flexible printed circuit board.
Or a plurality of piezoelectric materials, each of which is provided with an impedance conversion element electrically connected to the detection electrode and provided with a detection electrode on the inclined surface of each rectangular mesa, and which has a piezoelectric effect on the element surface in contact with the detection electrode. Since a thin film layer is formed and covered with a protective layer, there is no restriction on the attachment location, it can be detected with high resolution, and it can be attached to a robot arm etc. to easily grasp the pressure distribution and perform feedback control. There is an effect that extremely effective sensing can be performed as an input means.

Further, according to the manufacturing method of the present invention, one or more rectangular mesas having a trapezoidal cross section are formed in an array on the surface of the silicon element by anisotropic etching, and at least the gate electrode is set on the slope of the mesa. After the MOS-FET is formed on the surface of the silicon element, a thin film of a piezoelectric material having a piezo effect on the surface of the silicon element on the mesa side is formed by connecting the flexible printed circuit board and separating the back surface of the silicon for each element. A layer is formed, and the outer surface is coated with a ground electrode layer, a disturbance shielding layer, and a protective layer.Therefore, there are no positioning elements and there is no drilling process, so batch manufacturing is possible, and tactile sensor The effect that the manufacturing cost can be significantly reduced is obtained.

[Brief description of drawings]

FIG. 1 is a plan view and a cross-sectional view of a pressure sensor chip according to an embodiment.

FIG. 2 is an explanatory diagram of an electrode array of the sensor chip.

FIG. 3 is a plan view and a side view of a tactile sensor.

FIG. 4 is an explanatory diagram of a manufacturing process of the tactile sensor.

FIG. 5 is an explanatory diagram of a conventional tactile sensor.

[Explanation of symbols]

 10 Pressure Sensor Chip 12 Silicon Substrate 14 Rectangular Mesa 16 Slope 18 PVDF Film 20 Detection Electrode 22 MOS-FET 24 Output Electrode 26 Power Supply Electrode 28 Flexible Printed Board 30 Aluminum Coating Layer 32 Silicone Rubber Layer 34 Tactile Sensor

Claims (3)

[Claims] 1. A piezoelectric material having a trapezoidal cross-section rectangular mesa formed on a surface of an element made of silicon, a detection electrode being provided on a slope portion of the rectangular mesa, and having a piezoelectric effect on the surface of the element in contact with the detection electrode. A pressure sensor chip comprising a thin film layer. 2. One or a plurality of rectangular mesas having a trapezoidal cross section are formed on a surface of an element made of silicon arrayed and connected in a matrix on a flexible printed circuit board, and a detection electrode is provided on a slope portion of each rectangular mesa. A tactile sensation characterized in that an impedance conversion element electrically connected to the detection electrode is provided, a piezoelectric material thin film layer having a piezoelectric effect is formed on the surface of the element in contact with the detection electrode, and the piezoelectric material thin film layer is covered with a protective layer. Sensor. 3. A MOS in which one or more rectangular mesas having a trapezoidal cross section are formed on the surface of a silicon element by anisotropic etching, and at least a gate electrode is set on a sloped portion of the mesa.
A piezoelectric material thin film layer having a piezo effect on the surface of the silicon element on the mesa side while forming the FET on the surface of the silicon element and then connecting to the flexible printed circuit board to separate the back surface portion of the silicon for each element. And forming a ground electrode layer, a disturbance shielding layer, and a protective layer on the outer surface thereof, and manufacturing the tactile sensor.