JP2012150062A - Electrostatic capacitance detecting type fingerprint reading sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an effect of static electricity on a capacitance detecting circuit or the like of a sensor interior, improve the reliability of the sensor, and stably detect the fingerprint coming into contact with the surface of the sensor at a high sensitivity in the electrostatic capacitance detecting type fingerprint reading sensor configured by disposing a plurality of sensor electrodes on an insulating layer, wrapping the upper face and the side faces of the plurality of sensor electrodes with a passivation film, and further surrounding the four sides of each sensor electrode with a discharge layer comprising a metal pattern.SOLUTION: In the electrostatic capacitance detecting type fingerprint reading sensor, the passivation film is formed into by accumulating silicone oxynitride a thick film by a PECVD method, a discharge layer is formed on the upper face of the passivation film, and a concentrated part of the electric field distribution is formed on one or two sets of discharge layers aligned in an opposed state out of discharge layers surrounding the four sides of the sensor electrodes.

Description

  The present invention relates to a capacitance detection type fingerprint reading sensor.

  In recent years, an IC card equipped with an IC (integrated circuit) chip has been rapidly spread for reasons such as an increase in information capacity and an improvement in security as compared with a magnetic stripe card. In particular, a so-called contactless IC card of a type that transmits and receives data using electromagnetic waves has been introduced into public transportation means such as trains, and its convenience is remarkably improved.

Such an IC card must be as close as possible to the card size (85.6mm in length, 54mm in width, 0.76mm in thickness) conforming to the ISO international standards, from the viewpoint of card holding and convenience of carrying. . On the other hand, there is a high interest in the identity verification function based on fingerprint authentication as a defense against unauthorized use of IC cards such as theft, counterfeiting and alteration. A fingerprint reading sensor that can be mounted on an IC card is indispensable to satisfy the restrictions on the size of the IC card without impairing convenience and to prevent unauthorized use. As a fingerprint reading sensor that can be mounted on an IC card, a sensor electrode (metal plate) is formed on a semiconductor substrate, a passivation film layer is formed on the sensor electrode, and the static electricity between the skin and the sensor is interposed via the passivation film. A so-called capacitance detection type semiconductor fingerprint sensor (hereinafter referred to as FPIC) that detects the capacitance and detects the unevenness of the fingerprint has been developed (Patent Document 1). Among the various types of semiconductor fingerprint sensors using monolithic IC chips developed using LSI manufacturing technology, it is static considering the point that it can be formed at the lowest cost considering low power consumption, compactness, and small number of components. A capacitance detection type fingerprint sensor (hereinafter referred to as FPIC) is considered to be most effective.

  In the FPIC, as shown in FIG. 1, a plurality of sensor electrodes 1 generally composed of an array array of metal plates are arranged in a vertical and horizontal direction in a fingerprint sensing area, and each sensor electrode 1 is a fingerprint to be collected. Corresponds to the pixel that is the smallest unit of the image.

Each sensor electrode 1 is connected to the capacitance sensing circuit 2 in the lower layer, and at the same time, the capacitance according to the unevenness of the fingerprint between each sensor electrode 1 when a part of the finger touches the FPIC. It is covered with a passivation film layer 4 that is electrically insulated so as to be detected.

FIG. 2A is an enlarged cross-sectional view of the partial area 3 when a part of the finger touches the fingerprint sensing area of the FPIC. As shown in FIG. 2 (b), the skin (finger ridge) touching the passivation film layer 4 functions as a second electrode, and a capacitance is formed between the sensor electrode 1 and the sensor electrode 1 according to the distance d _0. The surface of the skin functions as a second plate, as in the region that hits the valley of the fingerprint, and is isolated by an insulating layer made of air, and the capacitance of both the air gap layer and the passivation film layer are connected in series. in the case where the capacitance C _S which are formed Te is formed, significantly former capacitance increases.

The depth of the adult valley line is about 150 μm, but this value is much larger than the thickness of the passivation film layer 4 (insulating layer) in contact with the finger surface, and the dielectric constant of air is that of the insulating layer. Less than dielectric constant. (Capacitance ∝ area of metal pair / distance between metal pairs, the proportionality constant of this proportional expression represents the dielectric constant specific to the dielectric between the metal pairs)

As a result, the capacity at the valley line is only a few percent of the capacity formed at the ridge line. Furthermore, since the pitch between valleys and ridges of an adult fingerprint is about 600 μm, the information on the unevenness of the fingerprint can be read sufficiently by the arrangement of sensor electrodes 1 arranged at a pitch of 50 μm (corresponding to a resolution of 508 dpi). It becomes.

Patent 3426565 Patent 4198239 US Patent 6,900,644 B2 Patent 4261127

  On the other hand, the excellent characteristics of the FPIC as described above are that, while sensing the fingerprint, the static electricity accumulated on the surface of the fingertip is discharged through the sensor electrode 1 when the fingertip directly touches the surface of the FPIC to the detection circuit 2. As a result, there is a possibility that the sensor device itself may be electrostatically damaged (hereinafter referred to as ESD).

Although it is known that this kind of static electricity discharge reaches about 20 kV, an ESD test method for electronic devices by air discharge is also standardized in “IEC61000-4-2”.
For FPIC that detects capacitance, this ESD protection measure is indispensable for commercialization, and many methods have been reported.

On the other hand, when a thick dielectric layer is laminated on the surface of the IC, the wafer itself is distorted by the residual stress of the dielectric layer, so that it is impossible to proceed to a wafer manufacturing process such as a subsequent photolithography process. become. Therefore, the thickness of the dielectric layer is about 3 to 5 μm at the maximum.

As the passivation film layer, a well-known polyimide (dielectric constant: about 4.0) is laminated to a thickness of 3 μm. However, as the static electricity generation source gets closer to the surface of the device, the earth for ESD protection becomes closer. Since the ESD protection capability of the electrode 11 depends on the dielectric strength characteristics of the passivation film layer, the ESD protection capability of the device for detecting the capacitance of the passivation film layer as described above is “IEC61000-4-2”. It must be said that it is difficult to satisfy the standard value.

On the other hand, in Patent Document 1, a plurality of sensor electrodes are arranged on an insulating layer, the upper surfaces and side surfaces of the plurality of sensor electrodes are covered with a passivation film, and the four sides of each sensor electrode are surrounded by a discharge wall made of a metal pattern. Such an FPIC has been proposed.

As shown in FIG. 3, the FPIC is provided with ground electrodes 11 in a lattice shape so as to surround the sensor electrode 1 on the surface of the device, and a human finger charged with static electricity contacts the surface of the device. The current generated in the current flows from the columnar earth electrode 11 to the ground side via the wiring 13 without flowing into the device, thereby suppressing the influence of static electricity on the capacitance detection circuit 2 and the like inside the device.

On the other hand, in this FPIC, a parasitic capacitance C _PX 12 generated between the sensor electrode 1 and the columnar earth electrode 11 is generated. The parasitic capacitance 12 is added to the C _S is detected by the sensor electrode 1 as a parallel-connected capacitor capacitance C _S is described where measurement occurs between the surface to be measured finger, resulting in measurement volume Increasing the value offset and apparently reducing the dynamic range of the sensor device results in a loss of grayscale information in the fingerprint image to be collected.

In Patent Document 2, in order to reduce the parasitic capacitance of the ground electrode 11 in Patent Document 1, the sensor electrode 1 is surrounded by a grid-like metal pattern (corresponding to the ground electrode 11) installed at zero potential. Proposed FPIC. That is, the ground electrode 11 in FIG. 3 is disposed only in a layer (area of thickness d ₀ ) above the sensor electrode 1 as a metal pattern for ESD protection.

However, there is no mention of the passivation film layer made of a dielectric covering the cell and the thickness and material of the lattice-like metal pattern, and as described above, the dielectric layer is usually thin (d ₀ ). The effect due to the difference in height between the two metal layers (sensor electrode and metal pattern) cannot be expected.

  Therefore, in order to form a very thick dielectric layer for expecting a sufficient effect of ESD protection of the sensing electrode, it is necessary to select a dielectric material having a low stress. Of course, the material having a small residual stress is selected in consideration of the strength against physical external force such as scratching and impact at the same time, considering that the sensor device is mounted on the IC card. Must be present (Patent Document 4).

In Patent Document 3, several percent of normal sensing pixels are replaced with “sacrificial devices” that are susceptible to electrostatic discharge, and a metal mesh at the same level as the sensor plate is placed in the discharge path to ground. Proposed structure. This method necessarily degrades the quality of the fingerprint image collected due to the presence of “sacrificial ESD pixels”.

  Accordingly, the inventors of the present invention form a very thick dielectric layer, reduce the parasitic capacitance between the ground electrode and the sensor electrode, and at the same time detect the electrostatic capacitance easily by the ground electrode. As a result of earnest research for the purpose of developing a fingerprint reading sensor, the present invention as described below has been completed.

In the present invention, a plurality of sensor electrodes are arranged on the insulating layer, the upper and side surfaces of the plurality of sensor electrodes are covered with a passivation film, and the four sides of each sensor electrode are surrounded by a discharge layer made of a metal pattern. In the capacitance detection type fingerprint reading sensor, the pasipeversion film is formed to have a film thickness by depositing silicon oxynitride by PECVD, and the discharge layer is provided on the upper surface of the passivation film, and the four sides of the sensor electrode are further formed. An electrostatic capacitance detection type fingerprint reading sensor is proposed in which a concentrated portion of an electric field distribution is formed in one or two sets of discharge layers arranged in opposition to each other.

That is, according to the study by the present inventors, this silicon oxynitride has various characteristics corresponding to a refractive index of 1.65 to 1.75, a dielectric constant of 6.4 to 6.8, and a hardness equivalent to H8, and silicon oxynitride is deposited by PECVD. Passivation film layer can be formed by this, and the ESD protection ability of this passivation film layer exceeds the performance of 15KV of “IEC61000-4-2” which is the ESD standard of electronic devices by air discharge. Achieved.

Further, by providing a discharge layer on the upper surface of the passivation film having a thickness, the distance (d) between the discharge layer and the sensor electrode is increased, and the parasitic capacitance between the discharge layer and the sensor electrode can be reduced.

In addition, the parasitic capacitance between a discharge layer and a sensor electrode can be reduced by arrange | positioning the discharge layer and sensor electrode which are arrange | positioned up and down so that it may not overlap.

Furthermore, by forming a concentrated portion of the electric field distribution in the discharge layer, the highest electric field is realized in the region surrounding one sensor electrode 1, and the place where the possibility of causing discharge is the highest is realized. As a result, the discharge layer This induces discharge in the concentrated portion of the electric field distribution.

The electric field distribution concentration portion in the discharge layer is formed by forming a recess in one or two pairs of discharge layers arranged in a confronting manner among the discharge layers surrounding the four sides of the sensor electrode, and forming a protrusion on the opposing surface of the recess. Can be provided.

That is, by forming a recess in one or two sets of discharge layers that are arranged opposite to each other in the discharge layer surrounding the sensor electrode and forming a protrusion on the opposite surface of the recess, the electric field is distorted around the protrusion in the recess. The concentration of the electric field distribution occurs, resulting in the highest electric field in the region surrounding one sensor electrode 1 and realizing the place most likely to cause discharge.

Further, the concentrated portion of the electric field distribution in the discharge layer is formed by forming a recess in a pair of discharge layers arranged in a face-to-face manner among the discharge layers surrounding the four sides of the sensor electrode, and forming a protrusion on the opposing surface of the recess. It can be provided by forming protrusions on the surface of the discharge layers arranged in a pair of opposed shapes.

That is, even in such a configuration, the same electric field is also distorted in the periphery of the protrusion formed on the surface of the other discharge layer arranged in the opposite direction, the electric field distribution is concentrated, and the place most likely to cause discharge Is realized.

The edge of the ESD protection discharge layer is wired so that it is connected to the ground outside the area where the sensor electrode is disposed, including the outside of the fingerprint reading sensor device, and when static electricity is discharged on it. The current is connected to flow into the ground line of the fingerprint sensor device.

  As described above, according to the present invention, it is possible to suppress the influence of static electricity on the capacitance detection circuit or the like inside the device, and thus the reliability of the device is improved, and the fingerprint of the finger touching the device surface can be detected stably and with high sensitivity. .

Schematic of capacitance detection type fingerprint reading sensor (A) State figure where a finger is placed on the capacitance detection type fingerprint reading sensor, (b) An enlarged cross section of region 3 in (a) and a diagram showing the principle of capacitance detection. The figure which shows the parasitic capacitance produced between a sensor electrode and earth electrodes. (A) AA sectional drawing of the electrostatic capacitance detection type fingerprint sensor by this invention, (b) The enlarged view of the surface of the electrostatic capacitance detection type fingerprint sensor by this invention. The enlarged view of the surface of the electrostatic capacitance detection type fingerprint sensor which shows other examples of the present invention. Configuration diagram of simulation experiment Diagram showing each observation layer in simulation experiment The figure which shows the result of the simulation which showed the intensity distribution of the electric field with the contour line supposing a simple grid-like metal line for ESD protection The figure which showed the result of the simulation which showed the intensity distribution of an electric field with the contour line supposing the metal arrangement | sequence for ESD protection which arranged the shape 21 and the shape 30

  Capacitance detection type in which a plurality of sensor electrodes are arranged on an insulating layer, the upper and side surfaces of the plurality of sensor electrodes are covered with a passivation film, and the four sides of each sensor electrode are surrounded by a discharge layer made of a metal pattern. In the fingerprint reading sensor, the passivation film is formed by depositing silicon oxynitride by PECVD to have a film thickness, the discharge layer is provided on the upper surface of the passivation film, and the discharge layers surrounding the four sides of the sensor electrode are opposed to each other. An electrostatic capacitance detection type fingerprint reading sensor in which a concentrated portion of electric field distribution is formed in one or two sets of discharge layers arranged in a line.

Hereinafter, a method for implementing a semiconductor fingerprint sensor according to the present invention will be described with reference to the drawings.
FIG. 4A is an enlarged view of a part of the cross section of the capacitance detection type fingerprint sensor FPIC according to the present invention. As shown in this figure, the passivation film layer (hereinafter referred to as IMD layer 4) is formed to have a film thickness by depositing silicon oxynitride by PECVD.

On the surface of the IMD layer 4, metal wires 20 constituting a discharge layer are arranged in a grid shape for ESD protection. The pitch of the parallel metal wires 20 is the same as that of the sensor electrode 1 and is arranged between two adjacent sensor electrodes 1. The width of the metal line 20 is designed not to overlap the sensor electrode 1 in order to minimize the parasitic capacitance between the line and the sensor electrode 1, and is considered not to cause an offset that impairs the sensitivity of the capacitance.

22 is a coating layer that is in direct contact with the finger, 23 is an interlayer insulating film, 24 is a capacitance detection circuit, and a silicon substrate is disposed below the coating.

  As shown in FIG. 4B, the metal wire 20 for ESD protection has a shape 21 in which a recess is formed on a lateral wiring extending in the left and right directions, and a protrusion is provided on the opposite surface of the recess. That is, the shape 21 has a structure in which a metal such as the tip of a nail is faced from the left and right facing surfaces of the recess and the ends thereof are connected by a thinner metal wire.

Further, the width of the metal wire 20 is arranged so as not to overlap the sensor electrode 1 in order to minimize the parasitic capacitance between the metal wire 20 and the pitch between the metal wires 20 is the same as that of the sensor electrode 1. To do.

The shape 21 causes the electric field to have a sharp curvature at the tip of the protrusions facing each other in the region of the gap 21, and a distribution that ends in a concentrated manner at the tip. As a result, the sharp nail tip produces the highest electric field in the periphery.

The highest part of the electric field means that it is most susceptible to electrostatic discharge compared to its surroundings. In other words, if a discharge occurs around the sensor electrode 1 and its surroundings, the shape 21 selectively becomes a discharge position.

The ends of all the ESD protection metal wires 20 are connected to a common earth electrode (not shown) at the edge of the fingerprint sensing area, and are connected to the ground of the FPIC device for bypassing the discharge current. The cross section of AA shown in FIG. 4B corresponds to FIG.

FIG. 5 shows another embodiment in which the electric field distribution concentrated portion is formed on the metal line 20, and the shape 21 is formed on the metal line 20 arranged in the horizontal direction in the same manner as described above, and arranged in the vertical direction. The metal wire 20 has a shape 30 provided with a protrusion at the center of the surface adjacent to the sensor electrode 1. By adopting the shape 30, the distribution is such that, by the same principle as described in the shape 21, a sharp curvature is exhibited at the tip of the protrusions facing each other in the gap area of the shape 30, and the concentration ends at the tip. Produce. The result is the highest electric field around it. Contributes greatly as an ESD protection measure.

According to the above-described invention, a high-density electric field distribution (protection point) against discharge is realized by surrounding the sensor electrode 1 on the fingerprint reading sensor FPIC of the type detecting capacitance.

  As described above, the effect of providing the above-described shapes 21 and 30 for the metal wire 20 for ESD protection has been analyzed by using a simulation for breaking the electric field distribution.

  The simulation was performed with the configuration shown in FIG. 6 compliant with the ESD protection test “IEC61000-4-2”.

  That is, 15 KV is applied to the probe 40 with the tip of the hemisphere having a radius of 4 mm (R4) 5 mm away from the sensor device surface, and each of the four observation layers of the sensor device shown in FIG. The electric field strength (V / cm) on the (layer) plane was calculated and analyzed. Detailed description of parameters (thickness, dielectric constant, conductivity, etc.) used for each component of the sensor device will be omitted.

FIG. 8 shows a simulation result in which the intensity distribution of the electric field in the second observation layer is expressed by contour lines when a simple grid-like ESD protection metal wire array having no shapes 21 and 30 is assumed.

  Similarly, FIG. 9 shows the result of expressing the intensity distribution of the electric field in the second observation layer with contour lines when the ESD protection metal wire array having the shapes 21 and 30 is assumed.

The numerical values written in FIG. 8 and FIG. 9 indicate the local maximum values of the electric field intensity distribution in the vicinity thereof.

Comparing the two figures, the intensity of the electric field at the center of the grid on which the sensor electrode 1 is arranged hardly changes, but the values in the vicinity of the shapes 21 and 30 provided on the metal wire for ESD protection are remarkably large. It turns out that it is high.

Table 1 shows the electric field strengths at positions closely related to ESD protection in each observation layer. Similar to the second observation layer corresponding to the surface of the passivation film layer 4 from this table, the shape 21 and the shape 30 were provided on the sensor surface and the surface of the sensor electrode 1 at the center of the lattice (center of the sensor electrode 1). On the other hand, on the metal lines of the grid, the electric field strength increases by about 150%, and the electric field becomes denser.

In other words, it was found that the ESD protection effect is increased 1.5 times by using the ESD protection metal wire having the shape 21 and the shape 30.

  According to the present invention, a capacitance detection type fingerprint sensor that can be formed at the lowest cost with low power consumption is mounted on a widespread and convenient device such as an IC card, so that reliable and stable identity verification is possible. Means can be realized and provided.

1 is a sensor electrode 2 is a capacitance detection circuit 3 is an enlarged region 4 in FIG. 2b is a passivation film layer (IMD layer)
11 is a ground electrode 12, a parasitic capacitance 13, a ground wire 20 is a metal wire cross-section 21 for ESD protection, and a shape 22 is applied to a metal wire arranged in a horizontal direction 22 is a coating layer 23, an interlayer insulation layer 24 is a silicon substrate 30 The shape 40 applied to the metal wires arranged in the vertical direction is the probe 41 used for the ESD test, the first observation layer 42 of the electric field distribution by simulation is the second observation layer 43 of the electric field distribution by simulation, and the electric field distribution by the simulation The third observation layer 44 is a fourth observation layer of electric field distribution by simulation.

Claims (4)

  Capacitance detection type in which a plurality of sensor electrodes are arranged on an insulating layer, the upper and side surfaces of the plurality of sensor electrodes are covered with a passivation film, and the four sides of each sensor electrode are surrounded by a discharge layer made of a metal pattern. In the fingerprint reading sensor, the passivation film is formed by depositing silicon oxynitride by PECVD to have a film thickness, the discharge layer is provided on the upper surface of the passivation film, and the discharge layers surrounding the four sides of the sensor electrode are opposed to each other. An electrostatic capacitance detection type fingerprint reading sensor in which a concentrated portion of electric field distribution is formed in one or two sets of discharge layers arranged in a line. 2. A concave portion is formed in one or two sets of discharge layers arranged in a confronting manner among the discharge layers surrounding the four sides of the sensor electrode, and a projection is formed on the opposing surface of the concave portion to form a concentrated portion of electric field distribution. Electrostatic capacitance detection type fingerprint reading sensor. Concave portions are formed in a pair of discharge layers arranged oppositely in the discharge layers surrounding the four sides of the sensor electrode, protrusions are formed on the opposite surface of the recesses, and protrusions are formed on the surface of the other discharge layer arranged in the opposite direction. The electrostatic capacitance detection type fingerprint reading sensor according to claim 1, wherein a concentration portion of the electric field distribution is formed by forming a portion. 2. The electrostatic capacitance detection type fingerprint reading sensor according to claim 1, wherein the discharge layer is connected to the ground outside the region where the sensor electrode is installed.

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