JP3356401B2 - Surface shape recognition sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface shape recognition sensor for recognizing a surface shape having minute irregularities such as a human fingerprint or an animal nose.

[0002]

2. Description of the Related Art With the progress of the information society, interest in confidentiality technology is increasing in modern society. For example,
In order to construct a system such as electronic cash, personal authentication technology is an important key. In addition, research and development of authentication technologies to protect against theft and unauthorized use of cards are being actively conducted. Various authentication methods such as those using fingerprints and voice prints have been proposed. . Above all, many technologies have been developed for fingerprint authentication technology.

[0003] Various fingerprint authentication systems that have been developed in the past will be described below. First, the conventional fingerprint authentication method is roughly classified into a method of optically reading the unevenness of the fingerprint,
The method is classified into a method of reading the pressure difference of a fingerprint, a method of detecting unevenness of a fingerprint using electric characteristics of a human, and the like. First, in the optical reading method, the reflected optical image of the fingerprint is
This is a method in which the image is captured by an image sensor such as a CD and collated with a fingerprint pattern prepared in advance.

In the method of reading the pressure difference of a fingerprint,
The pressure difference of the fingerprint of the finger is read using a piezoelectric thin film. Further, in a method using human electrical characteristics, a fingerprint is detected by using a pressure-sensitive sheet to replace a change in electrical characteristics caused by skin contact with a distribution of electrical signals. In this method, a fingerprint pattern is recognized based on a resistance change amount or a capacitance change amount.

However, there are various problems in the above-mentioned conventional techniques. For example, in the system using light, miniaturization and versatility are difficult, for example, a light source, an optical system, and an optical image processing means are required. There is a problem that applications are limited. Also, in the method of detecting the unevenness of the finger using a pressure-sensitive sheet or the like, it is difficult to practically use the material such as the pressure-sensitive sheet because of its specialty and its workability, and the reliability is poor. There is also a problem. In order to solve such a problem, a capacitive fingerprint sensor using an LSI manufacturing technique has been newly proposed. This is a method of detecting the capacitance of small sensor elements arranged two-dimensionally on an LSI chip and detecting the uneven pattern of the skin.

[0006] This has a structure in which a capacitance sensor element composed of a deformable upper electrode and a lower electrode arranged on a semiconductor substrate is two-dimensionally arranged on an LSI chip. The upper electrode is configured to be deformed according to the unevenness of the skin of the touched finger. Here, since the capacitance value between the upper electrode and the lower electrode changes due to the deformation of the upper electrode, the unevenness of the fingerprint can be sensed by detecting the capacitance difference.

Such a conventional capacitive surface shape recognition sensor will be described in more detail with reference to FIG.
As shown in the cross-sectional view of FIG. 3A, a support member 503 made of a conductive material is formed in a grid pattern on a semiconductor substrate 501 with an insulating layer 502 interposed therebetween. Then, the supporting member 50
A lower electrode 504 is formed on the insulating layer 502 at the center of each lattice surrounded by 3 and separated from the support member 503. An upper electrode 505 is formed on the support member 503. The upper electrode 505 is connected to the lower electrode 50.
4 are formed at a predetermined distance from each other, and the lower electrode 504 and the upper electrode 505 form a capacitance Cf.

In this surface shape recognition sensor, a protective film 506 having a projection 506a is formed on the upper electrode 505. Further, the protrusion 506a is formed so as to be arranged in a region on the lower electrode 504. Then, the capacitance between the upper electrode 505 and the lower electrode 504 is detected by the sensor circuit 510. An equivalent circuit of the capacitance and the sensor circuit 510 is as shown in FIG. As shown in FIG. 6, the support members 503 are formed in a lattice shape, and the lower electrodes 504 are formed in the respective central portions of the cells and arranged in a matrix.
That is, the surface shape recognition sensor is provided with the lower electrode 50.
4 and a plurality of sensor elements including an upper electrode 505 on the upper side.

Then, for example, one lower electrode 504
Is provided with one sensor circuit 510. In some cases, one sensor circuit 510 is provided for a plurality of lower electrodes 504. Note that the sensor circuit 510 may be integrated and formed below the insulating layer 502 over the semiconductor substrate 501.
1, it may be formed in a region where the sensor element is not arranged. In addition, the sensor circuit 510 may be prepared other than the semiconductor substrate 501.

The operation of the surface shape recognition sensor composed of the plurality of sensor elements will be described below. Protrusion 50
When the protective film 506 is deformed due to the 6a touching the target, the upper electrode 505 is also deformed at the same time. As a result, the distance between the lower electrode 504 and the upper electrode 505 changes, and the capacitance Cf therebetween also changes. Then, the sensor circuit 510 detects the change in capacitance as an electric signal, and when the value becomes equal to or larger than the threshold value, the protrusion 506a can be detected as being deformed, and as a result, the unevenness of the object can be detected. Can be.

Here, since the fingerprint of the fingertip is formed by the unevenness of the skin, when the finger is brought into contact with the protective film 506, when the projection 506a touches the protrusion forming the fingerprint, and when the finger is in contact with the concave portion. When the protrusion 506a touches, the protrusion 50
The amount of deformation of the portion 6a is different. This difference in the amount of deformation results in a difference in the distance between the lower electrode 504 and the upper electrode 505, and as a result, the difference is detected as a difference in capacitance. Therefore, if the distribution of different capacities of each of the plurality of arrayed sensor elements is determined and detected using the threshold as a boundary, it becomes the shape of the protrusion of the fingerprint. That is, the capacitive surface shape recognizing sensor can detect the fine unevenness of the skin.

[0012]

However, in the above-mentioned conventional surface shape recognition sensor, the initial capacitance value of the sensor element may be manufactured differently from the design value due to manufacturing variations. In particular, the support member 503 shown in FIG.
Of the lower electrode 504 and the upper electrode 505 when they are not deformed may be significantly different from the design value. As described above, when the distance between the lower electrode 504 and the upper electrode 505 at the time of no deformation is different from the design value, the capacitance change is set even if the upper electrode 505 is deformed due to contact with an object. If the threshold value is not exceeded, the output of the sensor circuit 510 may detect that the upper electrode 505 is not deformed. In this case, the shape of the object is erroneously recognized.

[0013] Since the surface shape is recognized by a large number of sensor elements, it is necessary to suppress variations in the sensor elements. In particular, when detecting minute unevenness such as a fingerprint, the difference in the amount of deformation of the upper electrode 505 is small.
The capacity difference that can be detected is also small. Therefore, if the variation between the sensor elements is large, even if the deformation amount of the upper electrode 505 is the same, the capacitance change does not exceed the threshold value for a certain sensor element, and the capacitance change does not exceed the threshold value for a certain sensor element. In some cases, it will exceed. In this case, the detection accuracy of the fingerprint pattern is reduced, and in some cases, the fingerprint pattern cannot be detected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to enable the detection of minute irregularities such as fingerprints with high accuracy.

[0015]

According to the present invention, there is provided a sensor for recognizing a surface shape, comprising: a plurality of lower electrodes, each of which is insulated and separated on the same plane on a substrate; An upper electrode disposed on the substrate, a lower electrode disposed on the substrate for each lower electrode, a supporting member for supporting the upper electrode, and a lower electrode disposed on the substrate for each lower electrode between the lower electrode and the supporting member. The electrode and the support member are spaced apart from each other by a reference electrode arranged for each lower electrode, and a first capacitor formed on the substrate, between the upper electrode and the lower electrode, and a first capacitor between the upper electrode and the reference electrode. A sensor circuit for detecting a difference from the capacitance of the second electrode, one sensor circuit is provided for a pair of the lower electrode and the reference electrode, and the upper electrode is provided on a support member on each of the lower electrodes, is deformably formed in the electrode direction also, the lower electrode It is arranged through an insulating layer on a substrate
The sensor circuit is integrated and formed on the substrate under the insulating layer
It was in the state that has been. That is, when the upper electrode is deformed, the first capacitance greatly changes as compared with the second capacitance. In addition, the lower electrode and the reference electrode are formed so that the area of the surface facing the upper electrode is the same. As a result, the change in the first capacitance due to the deformation of the upper electrode and the change in the second capacitance
Have the same initial value of the change in capacitance. Further, the reference electrode was formed so as to surround the lower electrode. As a result, it is easy to make the areas of the lower electrode and the reference electrode the same. In addition, since a plurality of lower electrodes are arranged in a matrix, the shape can be recognized in a planar manner. Further, since the support member is formed in a lattice shape and the lower electrode is arranged at the center of the mass, the support of the upper electrode is stabilized .

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a partial configuration of a surface shape recognition sensor according to an embodiment of the present invention, and an equivalent circuit. As shown in FIG. 1, a sensor for surface shape recognition according to this embodiment
A support member 103 made of a conductive material is formed in a lattice shape with an insulating layer 102 interposed therebetween. The insulating layer 1 at the center of each grid (mass) surrounded by the support member 103
On lower surface 02, lower electrode 104 is formed apart from support member 103. An upper electrode 105 is formed on the support member 103.

The upper electrode 105 is formed at a predetermined distance from the lower electrode 104, and the lower electrode 104 and the upper electrode 105 form a capacitance Cf. And
In this surface shape recognition sensor, a protective film 106 having a protrusion 106 a is formed on the upper electrode 105. Further, the protrusion 106a is formed so as to be arranged in a region on the lower electrode 104. In this embodiment, the lower electrode 104 and the supporting member 103 are separated from each other so as to surround the periphery of the lower electrode 104.
The reference electrode 104a is arranged on the second electrode.

In this embodiment, the upper electrode 10
5 and the capacitance Cf between the lower electrode 104 and the upper electrode 1
05 and the reference electrode 104a,
The detection is performed by the sensor circuit 110. FIG. 1B shows an equivalent circuit of the capacitance and the sensor circuit 110. Further, as shown in FIG.
Are formed in a lattice shape, and a lower electrode 104 and a reference electrode 104a are formed at respective central portions of the cells, and are arranged in a matrix. That is, the surface shape recognition sensor is composed of the lower electrode 104 and the reference electrode 104a.
, And an upper electrode 105 on the sensor element.

Then, for example, one lower electrode 104
And one sensor circuit 11 for the reference electrode 104a.
0 is provided. Also, one sensor circuit 11 is provided for the plurality of lower electrodes 104 and the reference electrode 104a.
0 may be provided. The sensor circuit 11
0 may be integrated and formed below the insulating layer 102 on the semiconductor substrate 101.
It may be formed in a region where the sensor element is not arranged . Contact name is not shown in FIG. 1, the wiring structure for such connection between the electrodes and the sensor circuit, the semiconductor substrate 10
1.

The operation of the surface shape recognition sensor including a plurality of sensor elements according to this embodiment will be described below. As shown in FIG. 3, when the protective film 106 is deformed by the protrusion 106a touching the object, the upper electrode 105 is simultaneously deformed. As a result, the distance between the lower electrode 104 and the upper electrode 105 changes, and the capacitance Cf therebetween changes. At the same time, the distance between the reference electrode 104a and the upper electrode 105 changes, and the capacitance Cr between them also changes. At this time,
As is clear from FIG. 3, the change amount of the upper electrode 105 is small near the support member 103. That is, the lower electrode 1
The change in the distance between the reference electrode 104a and the upper electrode 105 is smaller than the change in the distance between the reference electrode 104a and the upper electrode 105.

Therefore, the amount of movement of the portion of the upper electrode 105 below the protrusion 106a (the center of the upper electrode) in the direction of the lower electrode 104 when the protrusion 106a touches the object is:
The capacitance Cf and the capacitance Cr change as shown in FIG. Then, the surface area of the reference electrode 104 a is
If the surface area is the same as that of the surface area No. 04, as shown in FIG.
The initial values of the capacitance Cf and the capacitance Cr can be made equal. Here, the relationship between the change in the capacitance Cf and the change in the capacitance Cr shown in FIG. 4 does not depend on the height (thickness) of the support member 103. Therefore, if the difference is detected by the sensor circuit 110, the detection result becomes constant even if the height of the support member 103 changes. In other words, if the magnitude of the capacitance Cf is detected based on the capacitance Cr, the change in the absolute value does not affect the detection result of the sensor circuit 110.

As described above, the sensor circuit 110 detects the difference in the capacitance change as an electric signal, and when the value exceeds the threshold value, it is possible to detect that the projection 106a is deformed. Irregularities of the object can be detected. Here, since the fingerprint of the fingertip is formed by the unevenness of the skin, when the finger contacts the protective film 106, the protrusion 106a touches the protrusion forming the fingerprint, and the protrusion 106a When touched, protrusion 10
The amount of deformation of the portion 6a is different. Then, the difference in the amount of deformation is detected as the difference in the above-described difference in capacitance change.

Therefore, if the distribution of the different detection results of each of the plurality of arrayed sensor elements is detected and determined, for example, using the threshold as a boundary, it indicates the shape of the projection of the fingerprint. That is, the capacitance type surface shape recognition sensor according to the present embodiment can detect the fine unevenness of the skin. According to the surface shape recognizing sensor of this embodiment, even if there is a manufacturing variation in the height of the support member, it does not affect the detection result of the sensor circuit 110, so that the shape of the object is erroneously recognized. I won't. In addition, since the detection results of the plurality of sensor elements can be made to have almost no variation, for example, in the case of fingerprint detection, the accuracy of fingerprint pattern detection can be improved.

By the way, in the above embodiment, in one sensor element, the reference electrode has a ring-shaped integral structure surrounding the lower electrode, but is not limited to this. In one sensor element, a plurality of divided reference electrodes may be arranged around the lower electrode.
This is the same as the above embodiment. Further, even if one rectangular reference electrode is disposed at one position between the support member and the lower electrode in one sensor element, the same as in the above-described embodiment. In this case, a plurality of reference electrodes may be provided for each lower electrode, and a plurality of capacitances between the upper electrode and the plurality of reference electrodes may be compared with the capacitances of the upper electrode and the lower electrode. Further, in the above embodiment, the protective film having the protrusion is arranged on the upper electrode, but the present invention is not limited to this. A flat protective film may be arranged on the upper electrode. Further, if a metal material having corrosion resistance is used for the upper electrode, it is not necessary to dispose a protective film on the upper electrode.

[0025]

As described above, according to the present invention, a plurality of lower electrodes, each of which is insulated and separated on the same plane on the substrate, and the upper electrode, which is spaced apart and opposed on the lower electrode, is provided. An electrode, and a supporting member that is disposed separately from the lower electrode for each lower electrode on the substrate and supports the upper electrode;
A reference electrode disposed between the lower electrode and the support member on the substrate for each lower electrode, with the lower electrode and the support member being separated from each other; a first capacitor between the upper electrode and the lower electrode; A sensor circuit for detecting a difference between the reference electrode and the second capacitor, wherein the upper electrode is formed on each of the lower electrodes so as to be deformable in the direction of the lower electrode with a support member serving as a fulcrum. And

That is, when the upper electrode is deformed, the first
Of the first capacitor greatly changes as compared with the second capacitor. As a result, according to the present invention, since the difference between them is detected by the sensor circuit, the detection result is constant even if the height of the support member changes, and the detection results by the plurality of lower electrodes are It can be obtained with good reproducibility and almost no variation. As a result, according to the present invention, minute irregularities such as fingerprints can be detected with higher accuracy. Further, in addition to the above, the lower electrode and the reference electrode have the same area on the surface facing the upper electrode. As a result, the initial values of the change in capacitance between the lower electrode and the upper electrode and the change in capacitance between the reference electrode and the upper electrode due to the deformation of the upper electrode become the same, and the difference between the first capacitance and the second capacitance. Differences can be more easily detected.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a partial configuration of a surface shape recognition sensor according to an embodiment of the present invention, and an equivalent circuit.

FIG. 2 is a plan view showing a partial configuration of the surface shape recognition sensor according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a partial configuration when the surface shape recognition sensor according to the embodiment of the present invention is deformed.

FIG. 4 is a characteristic diagram showing each of a capacitance Cf and a capacitance Cr.

FIG. 5 is a cross-sectional view showing a partial configuration of a conventional capacitive surface shape recognition sensor and an equivalent circuit.

FIG. 6 is a plan view showing a partial configuration of a conventional capacitive surface shape recognition sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 101 ... Semiconductor substrate, 102 ... Insulating layer, 103 ... Support member, 104 ... Lower electrode, 104a ... Reference electrode, 105 ...
Upper electrode, 106 ... Protective film, 106a ... Protrusion, 110 ...
Sensor circuit.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-11403 (JP, A) JP-A-5-215625 (JP, A) JP-A-9-257618 (JP, A) JP-A-6-257618 288851 (JP, A) JP-A-9-126918 (JP, A) JP-A-58-55732 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 7/28 A61B 5 / 117

Claims (5)

(57) [Claims] 1. A plurality of lower electrodes, each of which is insulated and separated on the same plane on a substrate, a plurality of lower electrodes, an upper electrode spaced apart and opposed on the lower electrode, and the lower electrode on the substrate. A support member that is disposed apart from the lower electrode for each electrode and supports the upper electrode; and the lower electrode and the support on the substrate for each lower electrode between the lower electrode and the support member. A reference electrode disposed for each of the lower electrodes separated from the member; a first capacitor formed on the substrate, between the upper electrode and the lower electrode; and a first capacitor between the upper electrode and the reference electrode. A sensor circuit for detecting a difference between the second electrode and the second capacitor, wherein one sensor circuit is provided for a pair of the lower electrode and the reference electrode, and the upper electrode is provided on each of the lower electrodes. With the support member as a fulcrum It is deformably formed on the lower electrode direction
The lower electrode is disposed on the substrate via an insulating layer.
The sensor circuit is integrated on a substrate below the insulating layer.
A sensor for surface shape recognition characterized by being formed . 2. The surface shape recognition sensor according to claim 1, wherein the lower electrode and the reference electrode have the same surface area facing the upper electrode. For sensors. 3. The surface shape recognition sensor according to claim 1, wherein the reference electrode is formed so as to surround a periphery of the lower electrode. 4. The surface shape recognition sensor according to claim 1, wherein a plurality of the lower electrodes are arranged in a matrix. 5. The sensor for recognizing a surface shape according to claim 1, wherein the support member is formed in a lattice shape, and the lower electrode is arranged at a central portion of the mass. Sensor for surface shape recognition.