JP5344639B2 - Fingerprint reader - Google Patents

Description

  The present invention relates to a fingerprint reading sensor having an area for determining the authenticity of a finger or the state of a finger (wetting or dryness, etc.) at a position other than the sensor area that actually reads the irregularities of the fingerprint.

There has been a problem that the fingerprint reading conditions of the fingerprint reading sensor are always fixed, including finger perspiration, ambient temperature and humidity, and the physical condition of the collator (subject). In addition, since the fingerprint pattern reading conditions are fixed to the general finger conditions, it may be difficult for some subjects to read the fingerprint pattern itself. In optical fingerprint readers, proposals have been made to adjust the contrast by controlling the shutter speed of the CCD camera and controlling the amount of light that is totally reflected by the prism surface and incident on the camera. (Patent Document 1).

In the case of a semiconductor sensor, a method using software that analyzes a collected fingerprint image and corrects a fingerprint pattern using an image processing technique is widely used because of the ease of mounting. However, the image processing method using software not only increases the processing time, but also disturbs the information that the actual fingerprint pattern should have in its details, and hinders the risk of preventing the correct authentication result from being derived. It is.

On the other hand, when a fingerprint is used as the identity verification means, the existence of a crime using a fake fingerprint (pseudo-fingerprint) has been pointed out as one of the problems to be overcome in the future (Non-Patent Document 1). In recent years, introduction systems such as criminal records by fingerprints for foreign visitors have also been introduced at airports in Japan, but a woman with a film that copied another person's fingerprint on her finger easily passed through the customs at the airport. The news was widely introduced overseas. As a countermeasure against this problem, many “biological detection methods” have been proposed in which it is determined whether or not a subject is a living organism when it is placed on a reading device as a “finger” when reading a fingerprint.

Patent Document 4 discloses a living body detection device using a heat conduction sensor. However, because of the method of detecting the difference between the environmental temperature and the body temperature, the function of living body detection is broken if the fake finger is adjusted to an appropriate temperature. .

Patent Document 6 proposes a method for detecting a living body by reading a pulse, but it is difficult to adopt in a case of an apparatus using a semiconductor fingerprint sensor aiming at miniaturization and thinning.

On the other hand, according to Patent Literature 2, a living body detection device that detects whether a finger is a human finger using the capacitance of the finger has been proposed. In this living body detection device, a square pulse is generated by a CR oscillator corresponding to a time constant (frequency) determined from a capacitance value of a finger and a predetermined resistance value, and the frequency of the pulse is measured and set in advance. Compared with the threshold value, it is detected whether the finger is a living body.

This method only compares the measured value with a pre-set threshold, so if a counterfeit finger made of a material with the same capacitance as the finger is used, it will be distinguished I can't. That is, if only a material having a capacitance equivalent to that of a finger is obtained, it is relatively easy to create a forged finger that is recognized as a living body, which is a serious defect in safety measures.

Further, the transmission circuit including the Schmitt inverter used in this method is greatly affected by temperature changes, and also frequently occurs depending on the setting of the applied voltage and the resistance value, and adjustment at each time is required. That is, it is greatly affected by not only body temperature but also non-constant environmental temperature, and is unstable. As a result, mounting on a monolithic fingerprint reading sensor device is not practical.

In Patent Document 5 disclosed as a solution when a forged finger made of a material having a capacitance equivalent to that of a finger is used, a plurality of applied signals having different frequencies are applied to the subject finger, Disclosed is a living body determination method for determining whether or not a finger to be tested is a living body based on response signals relating to the finger to be tested with respect to a plurality of applied signals, but two or more different frequencies from the voltage application unit Since two or more oscillators are required in the voltage application unit and the biometric determination needs to be performed in response to output voltages of different frequencies, an increase in the number of parts, impedance of the finger It is difficult to reduce the size and cost because of the increase in the processing time of complicated calculation for calculating, and the feasibility is low.

Therefore, the present invention has been made in view of the above-described problems, and its purpose is to determine whether or not the subject is a living body with high accuracy, and the state of the subject finger submitted for identity verification. It is an object of the present invention to provide a small-sized and low-cost semiconductor fingerprint reading sensor that automatically adjusts fingerprint collection conditions according to the conditions and collects fingerprint images at high speed under optimum conditions.

JP 08-287219 A JP-A-10-165382 Special Table 2002-530680 " JP2003-290177 JP-A-2005-143804 JP 2005-46234 A

Masashi Une and Tsutomu Matsumoto, “Vulnerability in Biometric Authentication Systems: Focusing on Vulnerability in Counterfeiting Physical Features”, “Financial Studies” Vol. 24, No. 2, Bank of Japan, 35-84 2005 July "Test environment construction with fingerprint authentication device and resistance test against counterfeit fingerprints" www.cac.co.jp/softechs/pdf/st2601.10.pdf

  Therefore, the present invention is a semiconductor fingerprint reading device that is mounted on a fingerprint reading sensor and is small in size, low in cost, and fast in processing time. When reading a fingerprint provided for identity verification, the finger (subject) is Whether it is a living body or not is determined with high accuracy, and after the subject is recognized as a finger, the sampling conditions are automatically adjusted according to the state of the finger (wet or dry, etc.) so It is an object of the present invention to provide a semiconductor fingerprint reading device having a reading mechanism.

In the present application, in view of the above circumstances, in a fingerprint reading sensor device, a resistance value sensor (hereinafter referred to as an R sensor) that detects an electrical resistance value of a finger when the finger is placed on the fingerprint sensor device during fingerprint collection. And a capacitance detection sensor (hereinafter referred to as C sensor) for detecting the capacitance value of the finger, and a ground pad that is paired with these two pads in a monolithic manner, and a resistance detection circuit attached to the R sensor The electrical resistance value (R _X ) of the finger that is in contact with the pad of the R sensor is measured, and the finger that is in contact with the pad of the C sensor is measured by the capacitance detection circuit attached to the C sensor attached to the C sensor. The capacitance (C _X ) of the subject is measured, and the true / false of the subject finger or the state of the finger is determined based on the measured electric resistance value (R _X ) and the measured capacitance (C _X ) value. Realm It is intended to place in a position other than the sensor area to read the irregularities of fingerprint.

Next, the principle of determining the authenticity of the finger as the subject or the state of the finger from the measured values of the electric resistance value (R _X ) and the capacitance (C _X ) will be described. (1) Electric resistance value (R _X ) and capacitance (C _X ) are within the allowable range of the inherent electrical resistance value (several mega ohms) and capacitance value (several picofarads) of the human body, (2) between the two values And (3) electric resistance value (R _X ) and capacitance value (Cx) that there is no contradiction that does not fit the reason that “the resistance value is large and the capacitance value is large or the resistance value is small and the capacitance value is small”. If (1), (2), and (3) are confirmed that there is a gradual change, the provided subject is correctly determined as a finger of a living body.

On the contrary, when a result inconsistent with (1), (2), (3) is obtained, for example, when the resistance value is large and the capacitance value is large, or the resistance value is small and the capacitance value is small, the subject is artificial. Represents that it is made of various materials.

Therefore, the present invention reads the values output from the R sensor and the C sensor in a state where the subject is placed as a finger on the sensor device, and the electrical resistance value and capacitance value of the finger are values that the human body should have. Or whether the measured values output from both sensors are consistent with each other when viewed as values that the surface of the specimen should be in a "wet" or "dry" state Or a fingerprint reading sensor having a function of judging whether a placed subject is a part of a living body by judging whether a resistance value and a capacitance value are not constant values but fluctuating. It is.

Note that the electric resistance value (R _X ) and the capacitance value (C _X ) obtained by analog signals can be judged or compared by digitizing them, and in the present invention, therefore, provided in the sensor device. The resistance value sensor or the capacitance value sensor is activated by sending an externally determined command signal to the designated register, and the output from them is converted from analog to digital and stored in the storage element. A semiconductor fingerprint reading sensor having a function of reading a detection value in response to an output request from the outside is provided.

In the present invention, even when the sensor device is in the standby state of the low power mode, the R sensor is kept in the active state, the fluctuation of the detection value output in response to the output request from the outside is monitored, and the finger is placed The present invention provides a semiconductor fingerprint reading sensor having a function of starting the sensor device in an operating state after confirming that the detected value fluctuates.

On the other hand, even when the subject is determined to be a living finger, the wetness (or dryness) of the test finger can be determined from the results of the electrical resistance value (R _X ) and the capacitance value (C _X ). That is, if the electrical resistance value (R _X ) is small and the capacitance value (C _X ) is large, it can be determined as “wetting”, and vice versa.

Also, with optical fingerprint reading sensors and capacitance detection type reading sensors, the density level of the fingerprint image is usually dark when the finger to be examined is wet, and the density level is light when the finger is dry. The density condition of the collected fingerprint image can be appropriately adjusted according to the electric resistance value (R _X ) and the capacitance value (C _X ). At the time of this adjustment, a part or all of the fingerprint image can be collected and the density information of the image can be comprehensively judged and adjusted.

Therefore, in the present invention, the magnitude of the value output from the R sensor and the magnitude of the value output from the capacitance sensor are determined after it is determined that the subject is a living body finger while the subject is placed on the sensor device. Read to determine the “wetness” or “dryness” of the finger surface, feed back the results, and the density information of the collected fingerprint image is extremely dark (typically when the finger is wet), or When thin (generally the finger is dry), the gain and loss of the signal amplification circuit and the upper and lower limits (offset) of the analog / digital conversion circuit of the finger unevenness information provided on each pixel that constitutes the sensor that reads the unevenness of the fingerprint ) A fingerprint reading sensor having a function of automatically adjusting a characteristic value of a control circuit to an optimum value.

  When performing identity verification using a fingerprint, the subject placed on the fingerprint reading sensor is definitely a living finger, or if it is a living finger, the finger status such as the wetness is determined with high accuracy. At the same time, by automatically adjusting the reading conditions of the fingerprint image according to the state of the finger of the subject, it is possible to always obtain the fingerprint image under the optimum conditions.

Schematic diagram of the situation where a fingerprint is collected by placing a finger on the semiconductor fingerprint reading sensor Enlarged view of the components of the R and C sensors in region 1 of FIG. Sectional view along plane AA in FIG. Electrical resistance detection circuit diagram Capacitance detection circuit diagram

In a fingerprint reading sensor device, when a finger is placed on the fingerprint sensor device during fingerprint collection, an R sensor that detects the electrical resistance value of the finger, a C sensor that detects the capacitance value of the finger, and the two A ground pad paired with a pad is monolithically arranged, and a resistance detection circuit attached to the R sensor measures an electrical resistance value (R _X ) of a finger in contact with the pad of the R sensor, and the C sensor The capacitance detection circuit attached to the sensor measures the capacitance (C _X ) of the finger in contact with the pad of the C sensor, and the measured electric resistance (R _X ) and capacitance (C _X ) A semiconductor fingerprint reading sensor comprising: a region for determining the authenticity of a finger as a specimen or a state of a finger at a position other than a sensor region that actually reads the unevenness of a fingerprint.

Hereinafter, a method for implementing a semiconductor fingerprint sensor according to the present invention will be described with reference to the drawings.
FIG. 1 schematically shows a situation in which a fingerprint is collected by placing a finger on the semiconductor fingerprint reading sensor 3. In the example of FIG. 1, there is a region 1 in which an array of a plurality of R sensors and C sensors is provided outside and above the fingerprint reading region 2 of the semiconductor fingerprint reading sensor 3.

In this figure, reference numeral 4 denotes a control circuit portion of the semiconductor fingerprint reading sensor 3, and there is a connection terminal row 5 for signals to the outside of the sensor device.
The components 14 of the R sensor and C sensor in the region 1 are shown enlarged in FIG. FIG. 2 shows a pad 13 connected to the ground between a PAD / R 11 for detecting a resistance value and a PAD / C 12 for detecting a capacitance as sensitive pads for the R sensor and the C sensor on the finger side of the semiconductor fingerprint reading sensor 3. Are arranged side by side.

The resistance value R _X when the finger touches the PAD / R 11 and the ground 13 and the capacitance value C _X when the finger touches the PAD / C 12 and the ground 13 become the target values to be measured. .

Considering that the pitch of valleys and ridges of adult fingerprints is about 600 μm, the length L of each pad is about several millimeters so that one or more fingerprint ridges can be placed. The width H and the width between the pads are set to 200 μm, for example. However, this size is selected within the constraint that the parasitic capacitance described later is kept small. A plurality of components 14 having an arrangement as shown in FIG. 2 are arranged in the region 1.

A cross-sectional view of component 14 in region 1 is shown in FIG. It should be noted that in FIG. 2 and FIG. 3, the finger size is drawn larger than the actual size compared to the component for simplicity.

In FIG. 3, a resistance detection circuit 21 is connected to the lower layer of the PAD / R 11 that detects the resistance value, and a capacitance detection circuit 22 that measures the capacitance value is connected to the lower layer of the PAD / C 12 that detects the capacitance. Actually, a stray resistance exists between the PAD / R 11 and the resistance detection circuit, and a parasitic capacitance _CP exists between the PAD / C 12 and the capacitance detection circuit 22. In addition, in FIG. 3, each pad appears to be disposed on the surface of the passivation film layer 20, but actually, it may be disposed several μm below the surface of the passivation film layer 20.

Specific circuit diagrams of the resistance detection circuit 21 and the capacitance detection circuit 22 are shown in FIGS. 4 and 5, respectively.
Resistance detection circuit 21 is constituted by a voltage divider circuit having a known reference resistance R _S with respect to the resistance value R _X of the subject, placing the subject finger PAD / R11, as defined in the circuit 21 The applied voltage of the frequency is applied, the electric resistance value (R _X ) of the finger generated at that time is measured by _{dividing the divided} voltage with respect to the known reference resistance R _S , and the measured voltage value is inputted with the reference voltage value V _ref1. The signal is digitized by the AD converter 23 and output as a digital signal.

Next, the measurement principle of the capacitance detection circuit 22 will be described with reference to FIG.
The capacitance detection circuit 22 is configured by a voltage dividing circuit provided with a known reference capacitance Cs with respect to the capacitance (C _X ) of the subject. In this embodiment, the circuit 22 is provided with a capacitor Cc for initial charging, and three switching elements (SW1, SW2, SW3).

  Table 1 shows the operation of the circuit 22 when an on / off (open / close) switching step sequence of three switching elements (SW1, SW2, SW3), which is an example of use of the capacitance detection circuit 22, is performed. is there.

According to this table, in step 1, the switching element SW1 to which a voltage is applied is turned off (opened), and the remaining two switching elements SW2 and SW3 are turned on (closed), whereby the capacitance detection circuit 22 All the above capacitors are reset / cleared (discharged), and then in step 2, SW1 is turned on (closed), the charge is driven, and SW2 and SW3 are turned off (open). C _C is charged (charged). In step 3, the three switching elements are turned off (opened), whereby the charge charged in C _C moves and is stored according to the capacity of the two capacitors C _S and C _X. Since the values of the voltages V _S and V _X applied to both capacitors at this time are divided according to the capacitance, these values are measured. The charged charge is reset (discharged) in step 4. The measured voltage value is digitized by the AD converter 24 to which the reference voltage V _ref2 is input and is output as a digital signal.

The method of measuring the capacitance C _X by the on / off (open / close) switching step sequence (Table 1) of the capacitance detection circuit 22 shown in FIG. 5 is similar in that the capacitor C _C is used. It should be noted that this is different from the measurement method (for example, Patent Document 3). In other words, for the purpose of measuring a very slight change in capacitance according to the unevenness of the fingerprint, as described in Patent Document 3, directly applying a periodic voltage significantly reduces measurement accuracy. In the example, the capacitor Cc for initial charging is provided in the capacitance detection circuit 22 so as to improve the measurement accuracy. The capacitor C _C is in the present embodiment in which plays the role of a filter.

Further, in the capacitance detection circuit 22 of FIG. 5, the control circuit portion of the switching element is omitted for simplicity.
As can be seen from FIGS. 4 and 5 of the circuit, the components of this circuit are composed of only passive elements and are simple in construction, so that the mounting is easy, and even with respect to temperature changes. Since it uses a relative value with respect to the reference voltage, it is not easily affected, and stable operation and output are guaranteed.

Based on the output values R _X and C _X , it is determined whether or not the subject is a living body as follows.
For simplicity of explanation, the outputs from the AD converters 23 and 24 of both detection circuits are assumed to output 4 bits, that is, discrete values of 0 to 15, and the range of this value is classified into three types as follows. That is, [0 to 2] is called “very low value”, [13 to 15] is called “very high value”, and values in the range [3 to 12] are called “normal value”. The range of the “normal value” corresponds to a generally known biological characteristic value, and the parameter is adjusted so as to represent a range that can change according to environmental conditions.

The output values R _X and C _X are within this range and fluctuate without taking a constant value for a fixed time, for example, several hundred μs. If the value of R _X increases, the value of C _X The subject can be determined to be a living body when changes opposite to each other occur, such as “If the value of R _X decreases, the value of C _X increases”.
After it is concluded that the subject is a “biological finger”, the range of the above three digital output values is further subdivided, and the fingerprint collection conditions are automatically adjusted according to the state of the finger.

For a finger that is concluded that the subject is a “biological finger”, the range of “normal values” of the measured values R _X and C _X is [3-5], [6-10], If it is divided into three stages [10-12], Rx is [3-5], Cx is in the range [10-12], the finger is in a “moist” state, and Rx is [10-12], When Cx is in the range of [3-5], the finger is in a “dry” state.

  According to the density information of the fingerprint image collected by the so-called optical fingerprint reading sensor such as reflection, transmission or scattering of the light source by the finger or the capacitance and electric field detection type fingerprint reading sensor of the finger, When the finger is in the “dry” state, the tone level of the fingerprint image tends to be lighter.

  It is possible to adjust the density level of the fingerprint image by increasing or decreasing the sensitivity of the sensor for detecting the unevenness of the fingerprint provided in the fingerprint image sensing function. Specifically, in the case of an optical fingerprint reading sensor, the opening and closing of the light receiving unit or the adjustment of the shutter speed (Patent Document 1), and in the case of a capacitance detection type fingerprint reading sensor, the gain and capacitance offset of the amplifier circuit are set. Will be adjusted.

  Table 2 shows the density level of a fingerprint image when Rx is [3 to 5], Cx is [10 to 12], Rx is [10 to 12], and Cx is [3 to 5], and capacitance detection in this case This shows a countermeasure of the fingerprint reader sensor.

That is, when the measurement result of Table 2 is in the first row, it is determined as a “moist finger”. In this case, when the fingerprint image is actually collected, the shading level of the fingerprint image is “dark”. In order to improve the image quality of this image, the gain of the signal amplification circuit provided in each pixel constituting the sensor that reads the unevenness of the fingerprint is reduced, and the limit value of the offset control circuit of the analog / digital conversion circuit is increased. Thus, the overall image quality is alleviated normally.

In this case, in order to accurately check the transition of automatic adjustment, all or part of the actually collected fingerprint image data is used to automatically adjust the grayscale level data average and standard deviation values. You may use for. As an example of a specific method of automatic adjustment, the gain and offset values can be optimized by linear programming so as to minimize the standard deviation value of the gray level of the fingerprint image.

  As described above, according to the present invention, when performing identity verification by fingerprint, it is determined with high accuracy that the subject placed on the fingerprint reading sensor is definitely a finger of a living body, and the subject is examined. It is possible to provide a small-sized and low-cost semiconductor fingerprint reading sensor that always collects a fingerprint image under optimum conditions by automatically adjusting the reading conditions of the fingerprint image according to the state of the person's finger.

Reference numeral 1 is a finger resistance and capacitance sensor area on a semiconductor fingerprint reading sensor 2 is a sensor area 3 of a fingerprint irregularity on a semiconductor fingerprint reading sensor 3 is a semiconductor fingerprint reading sensor 4 is a control circuit section 5 of the semiconductor fingerprint reading sensor is a semiconductor fingerprint reading The connection terminal row 11 of the signal to the outside of the sensor is the R sensor pad 12, the C sensor pad 13 is the R sensor, and the C sensor ground pad 14 is the R sensor and the C sensor component 20 in the region 1. finger passivation film layer 21 is an electric resistance detection circuit 22 capacitance sensing circuit 23 analog-to-digital converter 24 of the electric resistance in contact with the analog-to-digital converter R _X is pad R sensor of the electrostatic capacitance value the capacitance Cc of the finger the electrical resistance R _S of a known reference resistance C _X in contact with the C sensor pad for the initial charge Capacitance SW1 of vignetting capacitor, SW2, SW3 are Suwinngu element capacitive sensing circuit

Claims (6)

In the fingerprint reading sensor device, when it was subject placed on the fingerprint sensor device at the time of fingerprinting, the value of capacitance detected and the resistance value sensor for detecting the electrical resistance value of the subject of the electrostatic capacitance value of the subject The sensor is arranged monolithically via a ground pad, and the resistance detection circuit attached to the resistance value sensor measures the electrical resistance value (Rx) of the subject in contact with the pad of the resistance value sensor. The capacitance detection circuit attached to the capacitance value sensor measures the capacitance (Cx) of the subject in contact with the capacitance value sensor pad, and the measured electrical resistance value (Rx) and capacitance ( Cx) is within the range of values that the human body should have, (2) there is no contradiction between the two values, and (3) the electrical resistance (Rx) and capacitance (Cx) are moderate There is a change, (1), 2), the semiconductor fingerprint reading sensor characterized with determining function that (3) If it is confirmed, a subject placed is part of a living body. The resistance detection circuit is constituted by a voltage dividing circuit provided with a known standard resistance value Rs with respect to the electrical resistance value (Rx) of the subject, and an applied voltage of a predetermined frequency is applied to the circuit to 2. The semiconductor fingerprint reading sensor according to claim 1, wherein the electrical resistance value (Rx) is measured as a divided voltage with respect to a known standard resistance value Rs. The capacitance detection circuit is constituted by a voltage dividing circuit provided with a known standard capacitance Cs with respect to the capacitance (Cx) of the subject, and an applied voltage of a predetermined frequency is applied to the circuit, In step 1, the switching elements SW1, SW2, and SW3 are turned off. In step 1, the switching elements SW1 to which voltage is applied are turned off, and SW2 and SW3 are turned on to clear the charges of all capacitors on the circuit. In step 2, the switching elements SW1 are switched. Is turned on and SW2 and SW3 are turned off, the capacitor Cc provided for charging in the circuit is charged. In step 3, the switching elements SW1, SW2 and SW3 are turned off, and the charge charged in the capacitor Cc is transferred to the capacitor Cc. In step 4, the electrostatic capacity (Cx) of the subject to be measured is measured as a divided voltage with respect to the known standard capacity Cs. Semiconductor fingerprint reading sensor according to claim 1, wherein which is adapted to reset the charged charges.   By sending an externally determined command signal to a register provided in the sensor device, the resistance value sensor or the capacitance value sensor becomes active, and the output from them is converted from analog to digital and stored in a storage element. 2. The semiconductor fingerprint reading sensor according to claim 1, wherein the sensor has a function of reading the detected value in response to an external output request. Even when the sensor device is in a low power mode standby state, the resistance value sensor is kept in an active state, the fluctuation of the detection value output in response to an output request from the outside is monitored, and the subject is placed. 2. The semiconductor fingerprint reading sensor according to claim 1 , further comprising a function of starting the sensor device in an operating state after confirming that the detected value fluctuates.

With the subject placed on the sensor device, the values output from the resistance value sensor and the capacitance value sensor are read, and the electrical resistance value (Rx) and the capacitance value (Cx) are values that the human body should have. checks the range, or both measurements object surface to be further outputted from the both sensors is, when viewed as a value should have the state "is dry", "wet" or not contradict each other determination, not more resistance and capacitance values is a constant value, it is determined whether the variation, respectively, a subject placed is characterized by having a function of determining to be a part of a living body The fingerprint reading sensor according to claim 1.

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