JP3787565B2 - Fingerprint sensor, fingerprint reader and personal authentication system - Google Patents

Description

  The present invention relates to a fingerprint sensor, a fingerprint reading device, and a personal authentication system that receive light from an adjacent finger and detect a fingerprint pattern of the finger.

  In an imaging apparatus that captures an image, one factor of noise received by a sensor is electromagnetic induction noise due to radiation from a device that is used in combination with a CPU or imaging apparatus that is driven at a high frequency. As countermeasures against this electromagnetic induction noise, conventionally, a high-permeability object (usually a metal body) is placed between the combined device and the sensor, or unnecessary radiation is suppressed by bundling long cables. It was. In JP-A-07-38789 (Patent Document 1), an electromagnetic shield layer is provided between a sensor and a combination device that is a noise source, and the electromagnetic shield layer reduces incident light to the sensor. It is disclosed that it has been optimized so that there is no such thing.

  On the other hand, noise that the sensor receives from the outside includes noise due to electrostatic induction in addition to electromagnetic induction noise. This electrostatic induction noise propagates through the capacitance Cp between the detection unit of the sensor and the noise source. The larger the capacitance amount, the larger the noise propagation amount. By the way, the magnitude of capacitance between a substance A and a substance B is proportional to the dielectric constant of the substance filling the gap between the substance A, the substance B, and the substance AB from the theory of electromagnetics, and the distance between the substances AB. Inversely proportional. For this reason, when there is a sufficient distance between the sensor and the object as in a general detection device, and the material filling the space is air with a low dielectric constant, the influence of noise due to electrostatic induction Was so small that it could be ignored, and no action was required.

Japanese Patent Application Laid-Open No. 07-38789 JP 2003-6627 A

  However, in recent years, in a fingerprint sensor, the necessity of which has been attracting attention in the security field, it is necessary to bring a finger close to the sensor. There may be a problem that the performance is remarkably deteriorated. Actually, the finger (human body) is likely to have a state of electrical noise of about several tens of mV to several tens of V due to the influence of electric equipment such as a PC monitor.

  As an example of a fingerprint sensor that captures a fingerprint pattern by bringing a finger close to the image, for example, there is a fingerprint input device disclosed in Japanese Patent Laid-Open No. 2003-6627 (Patent Document 2). In this fingerprint sensor, in order to capture a fingerprint pattern with high contrast without using an optical member such as a lens, a prism, or an optical fiber, a refractive index of 1.4 or more is used as a design guideline for a thin plate placed on the sensor. Hereinafter, the thickness is set to 100 μm or less. In the case of Patent Document 2, the thickness of the thin plate is infinitely close to 0, which is superior in terms of contrast. However, it is clear from the above explanation that the thickness of the thin plate is more susceptible to electrostatic induction. In addition, from the theory of electromagnetics, the refractive index n of a material is given by the following [Equation 1]. Therefore, when a thin plate member is selected by paying attention only to the refractive index, a material having a high relative dielectric constant is selected. In some cases, the system may be more susceptible to electrostatic induction.

  In addition, as a method for reducing induction noise, there is a method in which a signal transmission path and a pair of signal transmission paths are arranged in parallel on the same plane. By arranging the two signal transmission paths in this manner, almost equal noise components are superimposed on each other. Therefore, it is possible to remove only the noise components by taking the difference between them with a differential amplifier.

  However, although the above-described method works effectively against electromagnetic induction noise, there is a problem that the method is not effective when a noise source is close to the electromagnetic induction. The electromagnetic induction noise is generated when electromagnetic noise of a certain combination device propagates through the space and is superimposed on the signal transmission path, and there is a certain distance between the combination device that is a noise source and the sensor. Therefore, it can be considered that the distance between the two signal transmission lines patterned in parallel and the noise source is almost equal and the influence of noise is also equal, so that only the noise component can be removed by the differential amplifier. On the other hand, electrostatic induction noise is noise that becomes a problem when the noise source is close to the signal transmission path as described above. Thus, when the noise source is present near the signal transmission path, the distance between the noise source and each signal transmission path cannot be considered to be substantially equal. For this reason, the degree of noise superposition changes between signal transmission paths, and noise cannot be canceled by the differential amplifier.

  The present invention has been made to solve the above-described problems. When a finger is brought close to the finger and the fingerprint pattern of the finger is detected by the fingerprint sensor, the performance of the fingerprint sensor is reduced due to electrostatic induction noise from the finger. The purpose is to avoid this.

  The fingerprint sensor of the present invention is a fingerprint sensor that detects a fingerprint by bringing a finger close to the fingerprint sensor, the area on the upper surface of the fingerprint sensor on which the finger is placed, the pixel signal transmission path provided below the area, A reference voltage transmission line paired with the pixel signal transmission line, and the distance to the pixel signal transmission line and the distance to the reference voltage transmission line are spatially equidistant with respect to the region. It is arranged to be.

  Another aspect of the fingerprint sensor according to the present invention is a fingerprint sensor for detecting a fingerprint by bringing a finger close to the fingerprint sensor, and an area on the upper surface of the fingerprint sensor on which the finger is placed and pixel signal transmission provided below the area. And a reference voltage transmission line paired with the pixel signal transmission line, and the two transmission lines are formed in a twisted line shape.

  In another aspect of the fingerprint sensor according to the present invention, the fingerprint sensor includes a plurality of photoelectric conversion elements.

  In another aspect of the fingerprint sensor according to the present invention, the fingerprint sensor includes a plurality of capacitance detection elements.

  According to another aspect of the fingerprint sensor of the present invention, the fingerprint sensor includes a plurality of piezoelectric elements.

  In another aspect of the fingerprint sensor according to the present invention, the fingerprint sensor includes a plurality of temperature detection elements.

  The fingerprint reading apparatus of the present invention includes the above-described fingerprint sensor and light irradiation means for irradiating light to a finger placed in a predetermined area on the upper surface of the fingerprint sensor.

  The personal authentication system according to the present invention includes the fingerprint reading device described above, a fingerprint registration unit that registers a fingerprint image of a subject to be personally authenticated in advance, a fingerprint image read by the fingerprint reading device, and the fingerprint registration unit. Fingerprint matching means for collating whether or not the registered fingerprint image matches, and outputting the collation result as a personal authentication signal.

  ADVANTAGE OF THE INVENTION According to this invention, when making a finger | toe close and detecting the fingerprint pattern of a finger with a fingerprint sensor, it can suppress that the electrostatic induction noise from a finger (human body) propagates to a fingerprint sensor. The output signal at can have a good S / N. Thereby, a high-quality fingerprint pattern can be detected.

  Hereinafter, embodiments of a fingerprint sensor, a fingerprint reading device, and a personal authentication system according to the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic sectional view of a fingerprint sensor according to the first embodiment of the present invention. A two-dimensional image sensor 10 as a fingerprint sensor is an XY address type CMOS image sensor having an amplifying element in a pixel portion.
In FIG. 1, 1 is a semiconductor substrate, 11 is a photoelectric conversion unit in which an N-type layer is formed in a P-type well, 12 is a gate electrode for transferring a charge signal, and 13 is a first signal for transmitting a photoelectrically converted signal. Reference numeral 14 denotes a second signal transmission line such as a vertical signal line, 15 denotes a dielectric noise shield layer, and 16 denotes a first signal electrically separating the first signal transmission line 13 and the second signal transmission line 14. 17 is a second insulating layer that electrically separates the second signal transmission line 14 and the dielectric noise shield layer 15, 18 is a passivation film that planarizes the surface of the image sensor 10, and 19 is an element isolation portion. It is. Here, the dielectric noise shield layer 15 is conductive and connected to the ground or a fixed potential with a low impedance. The signal transmission path is not limited to the pixel signal transmission path, and includes a bias line, a clock line, an analog signal line, and the like of the two-dimensional image sensor 10.

  When the two-dimensional image sensor 10 shown in FIG. 1 is used in a fingerprint reading apparatus, a finger is brought into close contact with a predetermined area on the two-dimensional image sensor 10, and light is irradiated to the finger by a light irradiation unit provided separately. The light scattered from the inside of the finger is received by the two-dimensional image sensor 10. The light incident on the two-dimensional image sensor 10 passes through the passivation film 18 and reaches the photoelectric conversion unit 11 where it becomes an electron-hole pair and is converted into an electric signal. This charge signal is transferred to the first signal transmission path 13 by a pulse applied to the gate electrode 12. When the two-dimensional image sensor 10 is a CMOS sensor, the charge signal is converted into a voltage signal by an amplifying element in the pixel, and is transferred from the second signal transmission path 14 to a line memory CDS circuit, a clamp circuit, an amplifier circuit, etc. Is transmitted.

  By the way, as described above, the potential of the human body constantly fluctuates depending on the surrounding environment, and the finger that is in close contact with the two-dimensional image sensor 10 also contains very large noise. On the other hand, the second signal transmission path 14 is a wiring pattern used in common by a plurality of pixels such as a vertical signal line and a horizontal signal line, and is a relatively long wiring pattern. For this reason, the area is increased, and parasitic capacitance is easily generated between the finger and the noise source. Therefore, when there is no means for blocking electrostatic induction noise between the second signal transmission path 14 and the finger, the noise of the finger (human body) is propagated by capacitive coupling and is two-dimensional. The S / N of the output signal in the image sensor 10 is significantly reduced.

  In contrast, in the two-dimensional image sensor 10 according to the present embodiment, the dielectric noise shield layer 15 connected to the ground or a fixed potential with a low impedance is provided between the second signal transmission path 14 and the finger. Since the noise of the finger (human body) can be blocked from entering the inside of the two-dimensional image sensor 10, it is possible to avoid the S / N of the output signal from the two-dimensional image sensor 10 from being significantly reduced. Is possible.

  As the material of the induction noise shield layer 15, aluminum, which can easily use a semiconductor process, is preferable from the viewpoint of manufacturing cost. In addition, by using a metal such as aluminum, light from an unintended location can be reflected, and it is also possible to serve as a light shield as a smear countermeasure or the like.

  In addition, although the induction noise shielding method in the signal transmission path around the pixel portion of the two-dimensional image sensor 10 has been described here, the place where noise shielding is performed is not limited to the periphery of the pixel portion. For example, if electrostatic induction noise is superimposed on a horizontal signal line or a clamp circuit, it is obvious that the quality (S / N) of the output signal of the two-dimensional image sensor 10 has a significant influence on the pixel signal. The circuit wiring should be shielded as well.

(Second Embodiment)
FIG. 2 is an equivalent circuit diagram of a general CMOS image sensor.
One pixel includes a photodiode 21, a photodiode reset switch 22, a pixel selection switch 23, and an amplification source follower 24. The output of each pixel is amplified through a vertical signal line 25 and a horizontal signal line 26 and a difference from a certain reference voltage 28 is amplified in a subsequent differential amplifier circuit 27. The reference voltage may be an output signal of a dark pixel provided separately or noise at reset of each pixel that outputs a signal. The same applies to the second embodiment of the present invention. At this time, the pattern of the reference voltage line 29 is wired so as to follow the horizontal signal line 26 as shown in FIG. Thus, by patterning the wiring pattern connected to the differential amplifier circuit 27 almost equally, as described above, the magnitude and phase of the electromagnetic induction noise jumping from the outside becomes almost equal in each wiring. The electromagnetic induction noise can be removed.

  However, for example, in the case of electrostatic induction noise, which is a problem in a fingerprint sensor or the like, since the finger as a noise source is placed close to the wiring pattern, the electrostatic induction also occurs between signal lines patterned in parallel. The propagation amount of noise is different, and even when the differential amplifier 27 is used, the electrostatic induction noise cannot be completely removed. This is schematically shown in FIG.

FIG. 3 is an equivalent circuit diagram of a general fingerprint sensor.
The pixels 31 are arranged in a 4 × 4 matrix, and the output of each pixel is selectively read out to the pixel signal transmission path 35 by the vertical shift register 32 and the horizontal shift register 33. The read pixel output is amplified by a differential amplifier 37 with a certain gain from the reference voltage 34. At this time, if the center of the finger 38 indicated by the broken line in FIG. 3 is placed at the center of the pixel array, the pixel signal transmission path 35 is hidden under the finger 38, but is paired with the pixel signal transmission path. The reference voltage transmission line 36 that is a signal line is not hidden under the finger 38. Therefore, the distance between the finger, which is a noise source, and each signal transmission path is not equal, and the noise superimposed on the signal transmission path is also different.

  As in the conventional wiring pattern described above (see FIG. 4), by simply patterning the two signal transmission paths (35, 36) in parallel, when noise sources are close to each other like electrostatic induction noise, Even if the differential amplifier circuit 37 is used without maintaining the spatial identity of the noise source and the signal transmission path, the electrostatic induction noise cannot be removed.

Therefore, the present inventors conceived the form of the fingerprint sensor shown below.
FIG. 5 is an equivalent circuit diagram of the fingerprint sensor according to the second embodiment of the present invention.
As shown in FIG. 5, the fingerprint sensor according to the present embodiment includes a pixel signal transmission path 55 that transmits an output signal from each pixel, and a reference voltage transmission path 56 that is a signal line paired with the pixel signal transmission path. Is formed in a twisted line shape. By forming in this way, the distance between the finger, which is a noise source, and each signal transmission path (55, 56) can be kept substantially equal, so electrostatic induction superimposed on each signal transmission path (55, 56). The amount of noise is also equal, and the noise removal by the differential amplifier 37 becomes possible. In order to form the pixel signal transmission path 55 and the reference voltage transmission path 56 in an actual semiconductor process, as shown in FIG. 6, two aluminum wiring layers are respectively subjected to predetermined patterning, and the aluminum wiring layers are formed. Are connected by through holes to form each transmission line in a twisted line shape. By forming in this way, a twist line can be formed without complicating the manufacturing process.

(Third embodiment)
Next, an embodiment of a fingerprint reader having the above-described fingerprint sensor and a personal authentication system including the fingerprint reader will be described with reference to FIGS.

FIG. 7 is a schematic configuration diagram of a personal authentication system according to the third embodiment of the present invention. FIG. 8 is a schematic configuration diagram of the fingerprint reading apparatus 100 constituting the personal authentication system in the third embodiment.
The personal authentication system shown in FIG. 7 includes a fingerprint sensor 101 including a plurality of photoelectric conversion elements, a peripheral circuit unit 102 thereof, and an LED (light) that irradiates light on a finger placed on the fingerprint sensor 101. And a fingerprint collation device 200 that is connected to the fingerprint reading device 100 and performs fingerprint collation.

  The peripheral circuit unit 102 is formed on, for example, the semiconductor substrate 1 shown in FIG. 1, and is output from the fingerprint sensor 101 and a control circuit (drive circuit) 1021 that controls the operation of the fingerprint sensor 101 as shown in FIG. An A / D converter 1023 that converts an analog image signal corresponding to an image related to a fingerprint of a finger from an analog signal to a digital signal via a clamp circuit 1022, and a digital signal converted by the A / D converter 1023 Are supplied from a communication control circuit 1024 for data communication to an external device (such as an interface) and a register 1025 connected thereto, an LED control circuit 1026 for controlling light emission of the LED 103, and an external oscillator 1027. Control the operation timing of the circuits 1021 to 1026 described above based on the reference pulse Is constructed and a timing generator 1028 for generating control pulses that. The circuit including the peripheral circuit unit 102 is not limited to the one described above, and may include another type of circuit. Moreover, you may comprise one part of the circuit mentioned above as another chip | tip.

  The fingerprint collation apparatus 200 includes an input interface 111 for inputting communication data output from the communication control unit 1024 of the peripheral circuit unit 102, an image processing unit (fingerprint collation unit) 112 connected to the input interface 111, and the image. A fingerprint image database (fingerprint registration means) 113 and an output interface 114 connected to the processing unit 112 are provided. The output interface 114 is connected to an electronic device (including software) that requires personal authentication in order to ensure security during use or login.

  Here, in the fingerprint image database 113, a fingerprint image of the finger of the subject to be personally authenticated is registered in advance. The target person here may be one person or plural persons. The fingerprint image of the target person is input in advance as the personal authentication information of the target person from the fingerprint reading apparatus 100 via the input interface 111 at the time of initial setting or when the target person is added.

  The image processing unit 112 inputs the fingerprint image read by the fingerprint reading device 100 via the input interface 111, and determines whether or not the image matches the registered image in the fingerprint image database 113 based on a known fingerprint matching image processing algorithm. The collation is performed, and the collation result (fingerprint match or mismatch) is output via the output interface 114 as a personal authentication signal.

  In the present embodiment, the fingerprint reading device 100 and the fingerprint collation device 200 are configured as separate devices. However, the present invention is not limited to this, and at least a part of the functions of the fingerprint collation device 200 is performed as necessary. The peripheral circuit unit 102 of the reading device 100 may be integrated. In addition, the personal authentication system of the present embodiment may be configured integrally with an electronic device that requires personal authentication, or may be configured separately from the electronic device.

  In the embodiment of the present invention, a two-dimensional image sensor provided with a plurality of photoelectric conversion elements, which are subject information detection elements, has been described as a fingerprint sensor. Capacitance detection elements, multiple piezoelectric elements, multiple temperature detection elements, etc. are applied to the fingerprint sensor in the same way as the photoelectric conversion elements described above, and these outputs are converted into electrical signals and superimposed on the wiring path after electrostatic induction noise A mode in which the quality of the output signal of the fingerprint sensor is improved by shielding the image sensor is also included in the present invention. Further, with the aid of a semiconductor process, the dielectric noise shield layer 15 is formed directly on the fingerprint sensor, or the pixel signal transmission path 55 for transmitting the output signal from the fingerprint sensor and the signal line paired with the pixel signal transmission path. By forming the reference voltage transmission line 56 that is a twisted line shape, it is possible to reduce electrostatic induction noise at low cost without complicating the manufacturing process.

It is a schematic sectional drawing of the fingerprint sensor in the 1st Embodiment of this invention. It is an equivalent circuit diagram of a general CMOS image sensor. It is an equivalent circuit diagram of a general fingerprint sensor. It is a schematic diagram of a general wiring pattern. It is the equivalent circuit schematic of the fingerprint sensor in the 2nd Embodiment of this invention. It is a schematic diagram of the wiring pattern of the fingerprint sensor in the 2nd Embodiment of this invention. It is a schematic block diagram of the personal authentication system in the 3rd Embodiment of this invention. It is a schematic block diagram of the fingerprint reader which comprises the personal authentication system in the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 10 Two-dimensional image sensor 11 Photoelectric conversion part 12 Gate electrode 13 1st signal transmission path 14 2nd signal transmission path 15 Dielectric noise shield layer 16 1st insulating layer 17 2nd insulating layer 18 Passivation film 19 Element separation unit 21 Photodiode 22 Photodiode reset switch 23 Pixel selection unit switch 24 Amplification source follower 25 Vertical signal line 26 Horizontal signal line 27 Differential amplification circuit 28 Reference voltage 29 Reference voltage line 31 Pixel 32 Vertical shift register 33 Horizontal shift register 34 Reference voltage 35 Pixel signal transmission path 36 Reference voltage transmission path 37 Differential amplifier 38 Finger 55 Pixel signal transmission path 56 Reference voltage transmission path

Claims (8)

A fingerprint sensor that detects a fingerprint by bringing a finger close to it,
A region of the upper surface of the fingerprint sensor on which the finger is placed, a pixel signal transmission path provided below the region, a reference voltage transmission path paired with the pixel signal transmission path,
Have
A fingerprint sensor, wherein the distance to the pixel signal transmission path and the distance to the reference voltage transmission path are spatially equidistant with respect to the region. A fingerprint sensor that detects a fingerprint by bringing a finger close to it,
A region of the upper surface of the fingerprint sensor on which the finger is placed, a pixel signal transmission path provided below the region, a reference voltage transmission path paired with the pixel signal transmission path,
Have
A fingerprint sensor characterized in that the two transmission paths are formed in a twisted line shape.   The fingerprint sensor according to claim 1, wherein the fingerprint sensor includes a plurality of photoelectric conversion elements.   The fingerprint sensor according to claim 1, wherein the fingerprint sensor includes a plurality of capacitance detection elements.   The fingerprint sensor according to claim 1, wherein the fingerprint sensor includes a plurality of piezoelectric elements.   The fingerprint sensor according to claim 1, wherein the fingerprint sensor includes a plurality of temperature detection elements. A fingerprint sensor according to claim 3;
And a light irradiating means for irradiating light on a finger placed on a predetermined area of the upper surface of the fingerprint sensor. A fingerprint reader according to claim 7;
Fingerprint registration means for registering a fingerprint image of a subject to be personally authenticated in advance;
Fingerprint collation means for collating whether or not the fingerprint image read by the fingerprint reading device matches the fingerprint image registered in the fingerprint registration means, and outputting the collation result as a personal authentication signal. A personal authentication system.

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