CN1221213C - Temperature sensor and fingerprint recognition chip using the temperature sensor - Google Patents

Abstract

The invention discloses a temperature sensor and a fingerprint identification wafer using the same, wherein the fingerprint identification wafer is formed by arranging a plurality of temperature sensors in a two-dimensional array mode. The sensor comprises a silicon substrate, a thermal insulation structure, a thermopile formed by connecting thermocouples in series, a hot contact area of the thermopile is positioned in the central part of the thermal insulation structure, a cold contact area of the thermopile is positioned on a thin oxide layer around the thermal insulation structure, and a heat conduction pipe. The fingerprint identification wafer uses the body temperature as the biological identification principle, a temperature gradient is caused by the contact of the fingerprint peaks of the finger and the sensor, and the temperature gradient is converted into an electric signal, so that the electric signal of the fingerprint peak profile can be obtained and output, and the purpose of fingerprint identification is achieved.

Description

Temperature sensor and fingerprint recognition chip using the temperature sensor

technical field

The invention relates to a design for identifying fingerprints, in particular to a temperature sensor based on the principle of thermoelectric temperature difference sensing and an integrated circuit manufacturing method and a fingerprint identification chip using the temperature sensor to read fingerprint thermal images, and The present invention is related to US Patent No. 6,300,554B1 (METHOD OF FABRTCATINTHERMOELECTRIC SENSOR ANDTHERMOELECTRIC SENSOR DEVICE), and US Patent No. 6,335,478B1 to the thermopile infrared sensor and thermopile Arrangement of infrared sensitive elements, and method of manufacturing the above device (THERMOPILE INFRARED SENSOR, THERMOPILE INFRARED SENSORS ARRAY AND METHOD OFMANUFACTURING THE SAME).

Background technique

In the traditional fingerprint identification method, the earliest method is to use ink to print the fingerprint on the paper, and then compare it optically or input it into a computer database by scanning for comparison, which is used as identity authentication. The biggest disadvantage of this traditional method is that it cannot achieve timely processing, that is to say, it cannot immediately identify the identity. Therefore, it cannot meet the needs of more and more real-time authentication, such as network authentication, e-commerce, portable electronic product security, IC card personal identity Authentication and security systems, etc.

So there are several methods that can be used as real-time fingerprint recognition, including: optical fingerprint recognition, see US Patent No. 4,053,228 and No. 4,340,300; electronic real-time fingerprint recognition systems are piezoelectric materials or electrical contact methods For details, see U.S. Patent No. 4,394,773, No. 5,503,029, No. 5,400,662 and No. 5,844,287, etc.; for fingerprint recognition that belongs to the electrostatic induction method of fingers, please refer to U.S. Patent No. 6,049,620; for fingerprint recognition with thermal induction method, please refer to U.S. Patent No. 6,061,464 .

Among them, the price of the optical system is relatively expensive, high power consumption (light source consumption) and large volume (limited by the size of optical components and the fixed distance required for optical imaging), making it unsuitable for many portable electronic products, such as notebooks Computers and mobile phones etc. As for the electronic system, although there is a considerable improvement in volume, it still consumes a lot of power (the electric contact sensor will have a current flow when the two electrodes are in contact), and it is not easy to combine with the integrated circuit process (the production of piezoelectric materials It is not easy to match with the integrated circuit technology). At the same time, electrostatic induction and capacitive induction methods are susceptible to dust, finger sweat, and electromagnetic interference, and complex analog circuits are required to read the tiny electrical signals of the sensor. In terms of manufacturing, although the electrostatic induction and capacitive induction methods can match the integrated circuit process, they require a high-level integrated circuit process (<0.35 μm) to obtain good results, thereby increasing the cost. The last heat dissipation sensing method, the basic structure of the sensor is a heating resistor and a temperature sensor. The heating resistor is used to make the temperature of the sensor higher than the body temperature of the human body, and part of the heat is taken away by the finger contact to cause a lower temperature. Through the The temperature sensor can obtain a temperature image corresponding to the fingerprint. The biggest disadvantage of this heat dissipation sensing method is that the power consumption is too high to be used in portable electronic products with limited electric power, and the manufacturing method cannot match the integrated circuit process.

Due to the above reasons, the current instant fingerprint reader made by traditional technology cannot simultaneously meet the requirements of thinness, lightness, ease of manufacture, high stability, low power consumption and low price. Therefore, how to overcome the above-mentioned shortcoming is where the creator's research motivation lies in the present invention. After many years of hard work and research, the temperature sensor and the fingerprint recognition chip using the temperature sensor are finally obtained in the present invention, so as to use as the best identity authentication (physiologically, everyone's fingerprints are different. ).

Contents of the invention

The temperature sensor and the fingerprint identification chip using the temperature sensor in the present invention are mainly to solve the requirements that various existing fingerprint readers cannot simultaneously meet the requirements of thinness, small size, easy manufacture, high stability, low power consumption and low price.

The temperature sensor in the present invention utilizes the body temperature of the human body as the principle of biometrics. It forms a temperature gradient through the contact between the fingerprint peak and the sensor, and then converts the temperature gradient into an electrical signal. The sensor includes:

a silicon substrate;

a field oxide layer or a trench insulation layer on the silicon substrate as a thermal insulation structure;

a thermopile composed of at least one thermocouple connected in series, the thermal contact of the thermopile is located in the center of the field oxide layer, and the cold contact area of the thermopile is located on the thin oxide layer around the field oxide layer; and

A heat pipe, the heat pipe at least includes a conductor connection layer and a through hole plug metal, the heat pipe is located in the center of the field oxide layer, and is located between the field oxide layer and the outermost protective layer.

In addition, the temperature sensor may also include a heating resistor, which is arranged above the thermal insulation structure, so as to facilitate heating at least a thermal contact area of a thermocouple to make its temperature higher than that of a finger.

In the present invention, a fingerprint identification chip using a temperature sensor is used to read fingerprint thermal images, and its design and manufacturing method fully matches the CMOS integrated circuit technology. The fingerprint identification chip includes: a plurality of fingerprints arranged in a two-dimensional array The temperature sensor, and the circuit for integrating and reading signals, the fingerprint identification chip uses human body temperature as the biometric principle, and creates a temperature gradient through the contact between the fingerprint peak of the finger and the temperature sensor, and then converts the temperature gradient into an electrical signal , and read the thermal image of the ripple peak when the finger touches it.

In addition, the fingerprint recognition chip also includes a thermoelectric cooler arranged under the fingerprint recognition chip, and the thermoelectric cooler is used to control and stabilize the temperature of the fingerprint recognition chip so that the temperature of the chip is higher or lower than that of the finger .

In addition, the manufacturing method of the temperature sensor has at least one layer of polysilicon and at least one CMOS integrated circuit technology from metal wiring layer metal, and the sensor includes the following components:

a silicon substrate;

a thermal insulation structure on the silicon substrate, the thermal insulation structure is a field oxide layer or a trench insulation layer;

a thin oxide layer surrounding the thermal isolation structure, and the thin oxide layer is a gate oxide layer;

At least one thermocouple, the thermocouple includes a first thermocouple material and a second thermocouple material, the thermal contact area of the thermocouple is located in the central part of the thermal insulation structure, and the cold contact area of the thermocouple is located in the thermal insulation structure on the surrounding thin oxide layer;

at least one contact plug metal, the contact plug metal connecting the first thermocouple material and the second thermocouple material; and

A heat conduction pipe includes at least one conductor layer and at least one plug metal. The heat conduction pipe is located at the central part of the heat insulation structure and between the heat insulation structure and the outermost protective layer.

The temperature sensor in the present invention and the fingerprint identification chip using the temperature sensor can achieve the functions of thinner and shorter, easy to manufacture, high stability, low power consumption and cheap price at the same time, so as to facilitate popularization and application, and serve as an effective method for identity authentication. Way.

Description of drawings

The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Fig. 1 is the schematic diagram when using the fingerprint identification chip of temperature sensor in the present invention to identify fingerprint;

Fig. 2 is a schematic diagram of the sensing principle of the fingerprint identification chip using the temperature sensor in the present invention;

Fig. 3 is a structural sectional view of a single temperature sensor in the present invention;

Fig. 4 is the analysis result schematic diagram of single temperature sensor temperature gradient shown in Fig. 3;

Figure 5a and Figure 5b are the corresponding diagrams of the temperature difference ΔT time of the fingerprint recognition chip in different ambient temperatures (30°C and 40°C) in the present invention;

Fig. 6 is a structural sectional view of another embodiment of the temperature sensor in the present invention;

FIG. 7 is a schematic diagram of a method for stabilizing the chip temperature of the fingerprint recognition chip using a temperature sensor in the present invention.

Detailed ways

As shown in Figure 1, the fingerprint identification chip 1 is used to read the thermal image of the fingerprint, and it includes a plurality of temperature sensors 10 arranged in a two-dimensional (2-D) array. When the finger 2 touches the chip 1, the finger 2 Ridges 20 with irregular shapes on the surface will come into contact with part of the sensor 10 and leave a thermal curve 20a corresponding to the ridges 20 on the surface of the wafer 1. By knowing the shape of the isothermal curve 20a, the fingerprint ridges 20 can be identified shape. Since the fingerprint identification chip 1 is an application of multiple sensors 10 , its technical principle is determined by the structure and characteristics of the sensors 10 .

As shown in FIG. 2 , each sensor 10 is manufactured using an integrated circuit process, especially a CMOS process. Wherein, the basic structure of the sensor 10 includes a silicon substrate 100, a field oxide layer (LOCOS) 101 as a thermal insulation structure, and a thermopile formed by connecting at least one thermocouple 102 in series. The thermal contact area 200 of the thermopile is located in the field The central part of the oxide layer 101, the cold contact region 300 of the thermopile is located on the thin oxide layer (ThinOxide) (not shown in the figure) around the field oxide layer 101, and a heat pipe (Heat Pipe) 400 includes at least one conductor The wiring layer (Metal Interconnect) and at least one via hole plug metal (Via Hole MetalPlug), the heat pipe 400 is arranged in the central part of the field oxide layer 101, and is located between the field oxide layer 101 and the outermost protective layer 106 (Passivation) .

Fingerprints include fingerprint peaks 20 and fingerprint valleys 21. When the finger 20 touches the sensor 10, heat (shown by double arrows in the figure) will be transferred between the fingerprint peaks 20 and the sensor 10 through a solid heat conduction mechanism. Wherein, most of the heat energy is conducted to the thermal contact region 200 on the field oxide layer 101 through the heat pipe 400, and then transferred to all directions through the thermal contact region 200, thus generating a gap between the thermal contact region 200 and the cold contact region 300. A temperature gradient (Temperature Gradient), thereby causing a temperature difference ΔT, the sensor 10 induces a voltage signal by means of the temperature difference ΔT, so as to determine whether it is in contact with the fingerprint peak 20 . The voltage signal produced by the sensor 10 can be expressed by the following formula:

V＝NαΔT (1)

Among them, N is the number of thermocouples connected in series, and α is the Seebeck coefficient (V/°C) of a single thermocouple.

In order to illustrate the internal structure of the sensor 10 shown in FIG. 2 more clearly, as shown in FIG. 3 , the sensor 10 is fabricated by a CMOS process using one layer of polysilicon and two layers of metal (1P2M). Since the CMOS integrated circuit technology is a traditional technology, its detailed manufacturing process will not be described in detail here, but only the structure and material properties of the sensor 10 are explained:

First, a thermal insulation structure 101 is defined on the silicon substrate 100. The thermal insulation structure 101 is made of a field oxide layer (Local Oxidation of Silicon) in a CMOS process, and the surrounding area around the thermal insulation structure 101 is defined as thin oxide Layer 101a, the thin oxide layer 101a is the gate oxide layer (Gate Oxide) in the CMOS process. Thermocouple 102 is made up of first thermocouple material 102a and second thermocouple material 102b, and this first thermocouple material 102a is gate polysilicon (Poly-Silicon Gate) material in CMOS technology, and second thermocouple material 102b is CMOS The first metal connecting wire (Metal#1) in the process is usually aluminum or aluminum alloy material. The first thermocouple material 102a and the second thermocouple material 102b are connected through a perforated plug metal 103a, and the perforated plug metal 103a is usually a tungsten (W) material, and the structure of the sensor 10 also includes an interconductor interlayer (Inter-Layer Dielectric, ILD) 103, inter-metal dielectric layer (Inter-Metal Dielectric, IMD) 104 and the most surface protection layer (Passivation) 106.

It is particularly worth mentioning that, in order to have the largest temperature gradient (temperature difference) between the hot contact region 200 and the cold contact region 300 of the thermocouple 102, the design of a heat pipe (Heat Pipe) 400 can enhance the effect of this temperature gradient. The heat pipe 400 is composed of at least one conductor wiring layer and at least one plug metal. In this process, the heat pipe 400 includes part of the polysilicon layer 102a, at least one contact hole plug metal 103a, at least one via hole plug metal 104a, part of the first A metal wiring layer 102 b and a part of the second metal wiring layer 105 .

As shown in Figure 4, each line in the curves 410-415 is an isothermal line, therefore, it can be found that the hot contact zone 200 and the cold contact zone 300 are indeed located in different temperature regions, resulting in a temperature difference ΔT, the temperature difference ΔT The analysis structure of is shown in Fig. 5a~5b.

Curve 1 represents the response curve of the temperature difference ΔT versus time when the sensor 10 is in contact with the fingerprint peak 20, and curve 2 represents the response curve of the temperature difference ΔT versus time when the sensor 10 is in contact with the fingerprint valley 21. The value of the lower curve 2 is closer to 0, which represents a relatively low voltage signal output (closer to 0), and even if the ambient temperature changes greatly, the absolute value of the curve 1 still has a relatively large temperature difference ΔT.

Take an actual specification as an example: a single sensor pixel (Pixel) has an area of 80 μm and contains 60 pairs of thermocouples. The Seebeck coefficient of the thermocouples is about 100 μV/°C. If the temperature difference ΔT is 1°C, it can be calculated by formula (1) The thermal electromotive force up to 6mV is obtained, which shows the superiority of the temperature difference induction principle of the present invention.

As shown in Figure 6, the biggest difference between another embodiment of the present invention and the embodiment shown in Figure 3 is that a heating resistor 700 is provided above the insulating structure 101, and the heating resistor 700 is made of polysilicon material to heat the thermoelectric The thermal contact area 200 of the pair 102 makes its temperature higher than that of the finger, so the temperature difference ΔT of the sensor 10 in contact with the peak of the fingerprint is small, while the temperature difference ΔT of the sensor 10 in contact with the valley of the fingerprint is relatively large. The purpose of this method It is to obtain a stable electrical signal output.

As shown in FIG. 7, the biggest difference between the embodiment shown in FIG. 7 and the embodiment shown in FIG. temperature, the method can be to make the temperature of the fingerprint recognition chip higher than the temperature of the finger, or make the temperature of the fingerprint recognition chip lower than the temperature of the finger. This method of using a thermoelectric cooler 800 to control and stabilize the temperature of the fingerprint recognition chip The biggest purpose is to get a stable electrical signal output.

The above-described embodiments are only to illustrate the technical ideas and characteristics of the present invention. The spirit disclosed by the present invention is modified or changed, such as the integrated circuit technology suitable for the temperature difference sensitive fingerprint recognition chip of the present invention, especially the CMOS technology, its basic requirement is to have at least one polysilicon layer and at least two metal wiring layers , and the integrated circuit technology with field oxide layer or trench insulation layer technology should still be considered to fall within the protection scope of the present invention.

Claims (6)

1. A kind of temperature sensor, utilizes human body body temperature as biometric principle, causes a temperature gradient by finger print pattern peak and sensor contact, and then temperature gradient is converted into electric signal, it is characterized in that: described sensor comprises: a silicon substrate; a field oxide layer or a trench insulation layer on the silicon substrate as a thermal insulation structure; a thermopile comprising at least one thermocouple connected in series, the thermal contact of the thermopile is located in the central portion of the field oxide layer, and the cold contact area of the thermopile is located on the thin oxide layer around the field oxide layer; and A heat pipe, the heat pipe at least includes a conductor connection layer and a through hole plug metal, the heat pipe is located in the center of the field oxide layer, and is located between the field oxide layer and the outermost protective layer. 2. The temperature sensor according to claim 1, characterized in that: the temperature sensor also includes a heating resistor, which is arranged above the thermal insulation structure, at least to facilitate heating the thermal contact area of a thermocouple , so that its temperature is higher than that of the finger. 3. The temperature sensor according to claim 1 or 2, wherein the thermocouple comprises a first thermocouple material and a second thermocouple material, and the first and second thermocouple materials are N-type and The P-type silicon conductor, or a silicon conductor and a metal conductor. 4. The temperature sensor according to claim 2, characterized in that: the heating resistor is made of N-type or P-type silicon conductor. 5. A fingerprint identification chip using a temperature sensor as claimed in claim 1, which is used to read fingerprint thermal images, and its design and manufacturing method fully matches the CMOS integrated circuit technology, characterized in that: the fingerprint identification chip includes have: A plurality of the temperature sensors arranged in a two-dimensional array, each of which includes a silicon substrate; a field oxide layer or a trench insulation layer on the silicon substrate as a thermal insulation structure; at least A thermopile composed of thermocouples connected in series, the thermal contact area of the thermopile is located in the central part of the field oxide layer, and the cold contact area of the thermopile is located on the thin oxide layer around the field oxide layer; and a heat conducting a tube, the heat tube at least includes a conductor connection layer and a via plug metal, the heat tube is located at the center of the field oxide layer, and is located between the field oxide layer and the outermost protective layer; and A circuit for integrating and reading signals. The fingerprint identification chip uses human body temperature as the principle of biometric identification. It creates a temperature gradient through the contact between the fingerprint peak of the finger and the temperature sensor, and then converts the temperature gradient into an electrical signal, and reads the finger contact. Ripple thermal image at time. 6. The temperature difference sensing fingerprint identification chip according to claim 5, characterized in that: it also includes a thermoelectric cooler arranged under the fingerprint identification chip, and the thermoelectric cooler is used to control the stability of the fingerprint identification chip. Temperature, make the wafer temperature higher or lower than the finger temperature.

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