JP2001056204A - Capacitive fingerprint sensor - Google Patents

Abstract

(57) Abstract: A capacitance type fingerprint sensor capable of suppressing electrostatic breakdown due to discharge from a finger or the like of a capacitance detection cell constituting a capacitance type fingerprint sensor, and its manufacture. Provide a way. The system includes a plurality of capacitance detection cells for electrically detecting capacitance that changes according to a distance from a fingerprint, and detects a fingerprint based on a detection result of each of the capacitance detection cells. In the capacitance type fingerprint sensor 1 for recognizing a fingerprint, a wire 11 as a conductive wire material for giving a reference potential to a fingerprint is stretched across a detection surface 2a provided with a capacitance detection cell 3. Have been.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a capacitance type fingerprint sensor for specifying a fingerprint and a method of manufacturing the same.

[0002]

2. Description of the Related Art For example, a fingerprint collation system used for entry / exit management has begun to be applied as a personal authentication tool for a security system on a computer network, a portable terminal, an IC card, and the like. In the above fingerprint collation system, a capacitance type fingerprint sensor has been developed as a fingerprint sensor for recognizing a fingerprint. The capacitance type fingerprint sensor gives a reference potential to a finger and electrically detects a capacitance formed between the reference potential and an electrode in the fingerprint sensor. The distance between the reference potential and the electrode changes according to the unevenness of the fingerprint, and the capacitance changes. A change in capacitance corresponding to the unevenness of the fingerprint is electrically extracted to specify a fingerprint pattern.

[0003]

Here, FIG. 10 is a plan view showing an example of the structure of the above-mentioned capacitance type fingerprint sensor, and FIG. 11 shows an example of the structure of the above-mentioned capacitance type fingerprint sensor. FIG. As shown in FIG. 10, the capacitance type fingerprint sensor 101 has a plurality of capacitance detection electrodes 102 arranged in a matrix. A cell is configured. In addition, on the capacitance detecting electrode 102, FIG.
As shown in FIG. 7, an insulating protective film 103 is covered. In the capacitance-type fingerprint sensor 101 having the above structure, since the finger is used as a reference potential for recognizing a fingerprint, for example, as shown in FIG. The potential electrode 105 is provided and the finger F
Is given a reference potential. However, the human body is easily charged with static electricity, and before the finger F is applied with the reference potential by the reference potential electrode 105, the finger F and the capacitance type fingerprint sensor 1
In some cases, a discharge occurs between the protection film 103 and the protection film 103 of the capacitance detection cell of the capacitance type fingerprint sensor 101.

The present invention has been made in view of the above-described problem, and suppresses electrostatic breakdown of a capacitance detection cell constituting a capacitance type fingerprint sensor due to, for example, discharge from a finger or the like. It is an object to provide a possible capacitive fingerprint sensor.

[0005]

SUMMARY OF THE INVENTION The present invention has a plurality of capacitance detecting cells for electrically detecting a capacitance which varies according to a distance from a fingerprint. A capacitive wire sensor for recognizing the fingerprint based on the detection result of the cell for use, wherein the conductive wire for providing a reference potential to the fingerprint is provided with the plurality of cells for capacitance detection. It is stretched across the detection surface.

The wire is in contact with the detection surface.

The wire is separated from the detection surface.

A semiconductor chip having the plurality of capacitance detecting cells formed thereon, a conductive holding member for holding the semiconductor chip, and a semiconductor chip having a detection surface of the semiconductor chip exposed; And a package member for covering and fixing the holding member, and both ends of the wire are fixed to the semiconductor chip by the package member.

The package member is made of a resin material.

The wire is electrically connected to the holding member through the inside of the package member.

[0011] A reference potential electrode connected to a reference potential is provided on the package member so as to partially protrude from the package member.
It is connected to the holding member by a conductive material.

On the detection surface side of the chip, a spacer member for holding the wire at a predetermined distance from the detection surface is provided, and the wire is mounted on the spacer member by the package. It is fixed by a member.

The spacer member is made of the same material as the package member.

The wire is made of carbon fiber.

The capacitance detecting cell has a detecting electrode and an insulating protective film having a predetermined thickness and covering the detecting electrode.

[0016] A signal processing circuit for processing the detection signal of the capacitance detecting cell to specify the fingerprint is further provided, wherein the signal processing circuit crosses the wire or passes the wire in the vicinity. The detection signal of the capacitance detection cell is specifically processed.

In the present invention, a conductive wire for applying a reference potential to the fingerprint is stretched across the inspection surface for detecting the fingerprint. When the finger is pressed against the inspection surface, the finger surely comes into contact with the wire, so that even if a discharge occurs from the finger, static electricity escapes through the wire. For this reason, breakage of the capacitance detection cell due to the discharge is suppressed.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a cross-sectional view showing a structure of an embodiment of a capacitance type fingerprint sensor of the present invention, FIG. 2 is a cross-sectional view showing a structure of a capacitance detection cell, and FIG. It is a top view which shows the structure of the detection surface side of a semiconductor chip. As shown in FIGS.
The capacitance-type fingerprint sensor 1 according to the present embodiment includes a semiconductor chip 2, a die pad 41, a package member 31,
It has a wire 11 and a ground electrode 45.

As shown in FIG. 3, the semiconductor chip 2 has a plurality of capacitance detecting cells 3 for detecting a fingerprint formed in a matrix. The semiconductor chip 2 has, for example, an area of about several cm ² , and the capacitance detection cell 2 is formed within this area, for example, in the order of tens of thousands to hundreds of thousands, For example, several μm to several tens μm
Are arranged at intervals. As shown in FIG. 3, the capacitance detecting cell 3 has electrodes 21 made of a conductive material formed on an insulating layer 20, and these electrodes 21 are covered with a protective film 22 made of a dielectric. Have been. Note that the outermost surface of the protective film 22 is the detection surface 2a. The electrode 21 of the capacitance detection cell 3 is formed of, for example, a metal material such as aluminum, and the length of one side is, for example, several tens of μm. The protective film 22 is, for example, a film having a thickness of several μm and made of SiN or SiO ₂ as a base material.

The method of forming the capacitance detecting cell 3 is, for example, a method of forming a CVD (Chemical Vapor Depos) on a semiconductor substrate such as a silicon substrate via at least an insulating layer.
forming a conductive layer made of a metal material using a method or the like,
An electrode 21 is formed by patterning using a normal photolithography technique, and a protective film 22 is deposited to a predetermined thickness so as to cover the electrode 21.

The die pad 41 holds the semiconductor chip 2 via, for example, an adhesive. Die pad 41
Is a plate material made of a conductive metal material such as copper and aluminum.

The package member 31 is formed so as to cover the semiconductor chip 2 and the die pad 4, and fixes the semiconductor chip 2 and the die pad 4. Also,
The package member 31 is formed of, for example, a resin material used for a normal package of a semiconductor device.
The package member 31 has an opening 3a such that the detection surface 2a of the semiconductor chip 2 is exposed.

The wire 11 is a wire having electrical conductivity. For example, a wire such as a stainless steel wire can be used. In this embodiment, carbon fiber is used from the viewpoint of strength. The wire 11 is stretched across the detection surface 2a in contact with the detection surface 2a of the semiconductor chip 2, and for example, as shown in FIG. 3, electrostatic wires arranged in the same direction as shown by hatching It is provided so as to cross the capacitance detection cell 3. Also, for example, FIG.
As shown in (1), it may be provided so as to cross between the capacitance detecting cells 3 arranged in the same direction. Wire 11
1 are integrally fixed to the semiconductor chip 2 in the package member 31 as shown in FIG.

One end 11a of the wire 11 is connected to the surface of the die pad 41, and the wire 11 and the die pad 41 are electrically connected.

The ground electrode 45 is fixed inside the package member 31 and is provided so as to partially project from the package member 31. The ground electrode 45 is, for example, a gold wire,
It is electrically connected to the die pad 41 by a conductive member 43 such as an aluminum wire. Conductive member 43
Exist in the package member 31.

FIG. 5 is a schematic diagram showing an electrical configuration of the capacitance type fingerprint sensor 1 according to the present embodiment. As shown in FIG. 5, the electrode 21 of each capacitance detection cell 3 is connected to a signal processing circuit 51 via a transistor 40 functioning as a switch. Of the capacitance detection cells 3 arranged in a matrix, the gates of the transistors 40 connected to the capacitance detection cells 3 arranged in the same row are connected to the selection line WL. The signal processing circuit 51 detects the finger F based on the detection signal detected by each capacitance detection cell 3.
Is a circuit for specifying an image of a fingerprint.

Here, the principle of detecting a fingerprint by the capacitance type fingerprint sensor 1 will be described. As shown in FIG. 6, the electrode 21 of each capacitance detecting cell 4 is connected to a selection line BL in the column direction via a transistor 40, and the transistor 40
Are connected to the selection line WL in the row direction. When the finger F to which the reference potential is applied is positioned at a distance d from the electrode 21, the capacitance Cs between the electrode 21 and the finger F is expressed by the following equation (1). Here, ε ₀ is the permittivity of air, ε is the permittivity of the protective film 22 on the electrode 21, and S
Is the area of the electrode 21.

Cs = ε · ε ₀ · S / d (1)

Therefore, when the finger F is not opposed to the electrode 21 of the capacitance type fingerprint sensor 1, the electrode 21 and the finger F
Is infinite and the capacitance Cs on the electrode 21 is
Becomes 0.

As shown in FIG. 7, when the reference potential E is applied to the finger F and the finger 21 is brought close to the electrode 21 of the capacitance type fingerprint sensor 1, the fingerprint 21
The distance d between a and 21b and the finger F is different like d1 and d2, respectively. At this time, the selection line BL is set to the predetermined voltage Vcc.
When the transistor 40 is turned on by applying a voltage to the selection line WL, charges corresponding to the capacitance Cs determined by the distances d1 and d2 are accumulated in each of the electrodes 21a and 21b. Changes the potential of the selection line BL. The potential change amount ΔV of the selection line BL is represented by the following equation (2), where Cb is the parasitic capacitance of the selection line BL.

ΔV = {Cs / (Cb + Cs)} Vcc (2)

The potential change amount ΔV is an amount corresponding to the capacitance Cs determined by the distance d between the electrode 21 and the finger F, and is the potential change amount ΔV of the selection line BL in each capacitance detection cell 2. Is read out to the above-described signal processing circuit 51, the unevenness state of the fingerprint of the finger F can be specified.

Next, the capacitance type fingerprint sensor 1 having the above configuration
An example of the fingerprint detection operation will be described. For example, a case is considered in which the finger F to be brought into contact with the capacitance type fingerprint sensor 1 is charged, and the finger F discharges toward the capacitance type fingerprint sensor 1 before applying the reference potential E to the finger F. It is assumed that the ground electrode 45 of the capacitance type fingerprint sensor 1 is grounded. As shown in FIG.
Is in contact with the detection surface 2a, the finger 11 surely contacts the wire 11 because the wire 11 crosses the detection surface 2a. Thus, the ground potential, which is the reference potential, is applied to the finger F. The finger F is moved to the detection surface 2a of the semiconductor chip 2.
When the human body is charged and discharged from the finger F when approached, the discharge current flows to the wire 11 and is guided to the ground electrode 45 grounded through the die pad 41 and the conductive member 43. For this reason, the discharge current does not flow directly to the capacitance detection cell 3, and for example, the dielectric breakdown of the protective film 22 or the like included in the capacitance detection cell 3 due to the discharge is suppressed. As described above, according to the present embodiment, the detection surface 2 on which the plurality of capacitance detection cells 3 are formed
By providing the conductive wire 11 on “a”, the capacitance detection cell 3 is less likely to be destroyed even if a discharge occurs from the finger F.

Here, as shown in FIG. 8, when the finger F is in contact with the detection surface 2a of the semiconductor chip 2, the finger F contacts the wire 11, so that the finger F is deformed in this contact area. . For this reason, in an area where the finger F is deformed, a dead area R where the fingerprint cannot be detected occurs. For example, as shown in FIG. 3, when the wires 11 are provided so as to cross the capacitance detection cells 3 arranged in the same direction, each of the capacitance detection cells arranged in a row indicated by hatching in FIG. The use cell 3 is located in the dead area R. In addition, as shown in FIG. 4, when the wires 11 are provided between the capacitance detecting cells 3 arranged in the same direction, the two adjacent rows of the capacitance detection cells shown by hatching in FIG. The use cell 3 is located in the dead area R.

The capacitance detection cell 3 located in the dead area R is specified in advance in accordance with the arrangement of the wires 11 at the stage of assembling the capacitance type fingerprint sensor 1. For this reason, in the present embodiment, for example, the signal processing circuit 51 specifically processes a detection signal of the capacitance detection cell 3 located in the insensitive region R. Specifically, for example, the signal processing circuit 51 includes the capacitance detection cell 3 located in the insensitive region R.
Can be configured not to use the detection signal for the identification of the fingerprint. In this case, the finger F is brought into contact with the detection surface 2a of the semiconductor chip 2 at different positions a plurality of times, and data obtained by the plurality of detections is combined to specify the entire image of the fingerprint. it can. Alternatively, an algorithm for specially processing the detection signal of the capacitance detection cell 3 located in the dead area R is prepared in advance, and the detection signal of the capacitance detection cell 3 located in the dead area R is prepared by this algorithm. By complementing, it is also possible to specify the entire image of the fingerprint.

Second Embodiment FIG. 9 is a sectional view showing the structure of an embodiment of the capacitance type fingerprint sensor of the present invention. Note that among the components of the capacitance fingerprint sensor 201 shown in FIG. 9, the same components as those in the above-described first embodiment are denoted by the same reference numerals. The difference between the capacitive fingerprint sensor 201 according to the present embodiment and the capacitive fingerprint sensor 1 according to the first embodiment is that
Is separated from the detection surface 2a of the semiconductor chip 2 by a predetermined distance δ.

That is, in the capacitance type fingerprint sensor 201, the plurality of spacer members 4 having a height δ are formed on the semiconductor chip 2.
6 is provided, and the wire 11 is stretched over the spacer member 46 and fixed integrally with the package member 31. The spacer member 46 is, for example, a package member 3
1 can be formed of the same resin material.

In the present embodiment, with such a configuration, when the finger F approaches the detection surface 2a of the semiconductor chip 2, the wire 1
1 is closer to the finger F, the discharge current is reliably guided to the wire 11 even if the finger F is discharged, and the electrostatic discharge of the capacitance detecting cell formed on the semiconductor chip 2 can be reliably prevented. it can.

[0039]

According to the present invention, by providing a wire for applying a reference potential across the detection surface of the capacitance type fingerprint sensor, the capacitance detection cell can be used even if there is a discharge from the finger. Electrostatic damage can be reliably prevented, and a reference potential can be applied to a finger.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an embodiment of a capacitance type fingerprint sensor according to the present invention.

FIG. 2 is a cross-sectional view illustrating a structure of a capacitance detection cell.

FIG. 3 is a plan view showing a structure on a detection surface side of a semiconductor chip.

FIG. 4 is a plan view showing another example of the structure of the semiconductor chip on the detection surface side.

FIG. 5 is a schematic diagram showing an electrical configuration of the capacitance type fingerprint sensor 1.

FIG. 6 is a plan view showing an example of the structure of a capacitance type fingerprint sensor.

FIG. 7 is a diagram for explaining a detection principle of a capacitance type fingerprint sensor.

FIG. 8 is a diagram showing a state in which a finger F is brought close to a detection surface 2a of a semiconductor chip 2 of the capacitance type fingerprint sensor 1; It is sectional drawing which shows an example of a structure of a capacitance type fingerprint sensor.

FIG. 9 is a cross-sectional view illustrating the configuration of another embodiment of the capacitive fingerprint sensor according to the present invention.

FIG. 10 is a plan view showing an example of the structure of a capacitance type fingerprint sensor.

11 is a sectional view showing an example of the structure of the capacitance type fingerprint sensor of FIG.

FIG. 12 is a diagram illustrating a state in which a reference potential is applied to a finger when the finger is brought into contact with the capacitance-type fingerprint sensor.

[Explanation of symbols]

1. Capacitive fingerprint sensor, 2. Semiconductor chip, 2a ...
Detection surface, 3 ... cell for capacitance detection, 11 ... wire, 31
... package member, 43 ... conductive member, 45 ... ground electrode, 21 ... electrode, 22 ... protective film, 41 ... die pad.

Claims (12)

[Claims] A plurality of capacitance detection cells for electrically detecting a capacitance that varies according to a distance from a fingerprint, based on a detection result of each of the capacitance detection cells; An electrostatic capacitance type fingerprint sensor that recognizes the fingerprint, wherein a conductive wire that gives a reference potential to the fingerprint is stretched across a detection surface provided with the plurality of capacitance detection cells. Capacitive fingerprint sensor. 2. The capacitance type fingerprint sensor according to claim 1, wherein the wire is in contact with the detection surface. 3. The capacitance type fingerprint sensor according to claim 1, wherein the wire is separated from the detection surface. 4. A semiconductor chip on which the plurality of capacitance detecting cells are formed, a conductive holding member for holding the semiconductor chip, and the semiconductor with a detection surface of the semiconductor chip exposed. 2. The electrostatic capacitance type according to claim 1, further comprising: a package member that covers and fixes the chip and the holding member, and both ends of the wire are fixed to the semiconductor chip by the package member. 3. Fingerprint sensor. 5. The capacitance type fingerprint sensor according to claim 3, wherein said package member is made of a resin material. 6. The capacitance type fingerprint sensor according to claim 4, wherein the wire is electrically connected to the holding member through the inside of the package member. 7. A reference potential electrode connected to a reference potential provided on the package member so as to partially protrude from the package member, wherein the reference potential electrode is made of a conductive material. The capacitance type fingerprint sensor according to claim 6, which is connected to a holding member. 8. A spacer member for holding the wire at a predetermined distance from the detection surface is provided on a detection surface side of the semiconductor chip, and the wire is provided on the spacer member. The capacitance type fingerprint sensor according to claim 4, wherein the capacitance type fingerprint sensor is fixed by the package member. 9. The capacitance type fingerprint sensor according to claim 7, wherein said spacer member is made of the same material as said package member. 10. The capacitance type fingerprint sensor according to claim 1, wherein said wire is made of carbon fiber. 11. The capacitance-type fingerprint sensor according to claim 1, wherein the capacitance detection cell has a detection electrode and an insulating protective film having a predetermined thickness covering the detection electrode. . 12. A signal processing circuit for processing a detection signal of the capacitance detecting cell to specify the fingerprint, wherein the signal processing circuit crosses the wire or detects the vicinity of the wire. The capacitance type fingerprint sensor according to claim 1, wherein a detection signal of the passing capacitance detection cell is specifically processed.