Fingerprint sensor having ESD protection

A fingerprint sensor having ESD protection has a body and an ESD protection circuit. The body has a fingerprint sensing electrode array and an ESD protection electrode providing an ESD protection to the fingerprint sensing electrode array. The ESD protection circuit is connected respectively to the ESD protection electrode, a high electric potential terminal and a low electric potential terminal. The ESD protection circuit provides a first static electricity discharge path to the high electric potential terminal, and a second static electricity discharge path to the low electric potential terminal. The fingerprint sensor provides two static electricity discharge paths, so that the fingerprint sensor has a better ESD protection.

This application is based upon and claims priority under 35 U.S.C. 119 from Taiwan Patent Application No. 104124650 filed on Jul. 30, 2015, which is hereby specifically incorporated herein by this reference thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fingerprint sensor, especially to a fingerprint sensor with Electrostatic Discharge (ESD) protection.

2. Description of the Prior Arts

With reference toFIG. 12, a conventional fingerprint sensor50has multiple sensing electrodes51. To keep the sensing electrodes51from being damaged, an ESD protection electrode60is formed around the sensing electrodes51and is connected to a ground GND so that the static electricity charge is discharged to the ground GND.

Since the ESD protection electrode60is only connected to the ground GND, the positive and negative static electricity charges may not be discharged completely, and the sensing electrodes51and other electronic components may be damaged accordingly.

To overcome the shortcomings, the present invention provides a fingerprint sensor with ESD protection to mitigate or obviate the aforementioned problems.

SUMMARY OF THE INVENTION

To achieve the objective, the present invention provides a fingerprint sensor having ESD protection providing multiple discharging paths for the static electricity charges to discharge the positive and negative static electricity charges.

The fingerprint sensor having ESD protection comprises:

a body having a fingerprint sensing electrode array and an ESD protection electrode providing an ESD protection for the fingerprint sensing electrode array; and

an ESD protection circuit connected to the ESD protection electrode, a high electric potential terminal and a low electric potential terminal, wherein the ESD protection circuit provides a first static electricity discharge path to the high electric potential terminal and a second static electricity discharge path to the low electric potential terminal.

The ESD protection circuit provides the first static electricity discharge path to the high electric potential terminal and the second static electricity discharge path to the low electric potential terminal. Therefore, the positive and negative static electricity charges of the ESD protection electrode are rapidly discharged through the first and second static electricity discharge paths to keep the fingerprint sensing array and the interior circuit from damaging.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIGS. 1 and 2, a first embodiment of a fingerprint sensor with ESD protection in accordance with the present invention has a body10and an ESD protection circuit31.

The body10has a fingerprint sensing electrode array and an ESD protection electrode20. The fingerprint sensing electrode array has m*n sensing electrodes11arranged in m columns and n rows. The n rows are parallel to a first axis H1and the m columns are parallel to a second axis H2. The ESD protection electrode20provides ESD protection to the fingerprint sensing electrode array.

With reference toFIG. 2, the ESD protection circuit31is connected to the ESD electrode20, a high electric potential terminal VDD and a low electric potential terminal VSS (or ground) to provide a first static electricity discharge path to the high electric potential terminal VDD and to provide a second static electricity discharge path to the low electric potential terminal VSS. In this embodiment, the ESD protection circuit31has a connecting end310, a first discharging unit311and a second discharging unit312. The connecting end310is connected to the ESD protection electrode20. The first discharging unit311is coupled between the high electric potential terminal VDD and the connecting end310. The second discharging unit312is coupled between the low electric potential terminal VSS and the connecting end310.

With reference toFIGS. 3A and 3B, in one embodiment, the first discharging unit311may be a diode D1with an anode and a cathode. The anode of the diode D1is coupled to the connecting end310, and the cathode of the diode D1is coupled to the high electric potential terminal VDD. In another embodiment, the first discharging unit311may be a P-type Metal-Oxide-Semiconductor Field-Effect Transistor (PMOSFET) MP with a drain D, a gate G and a source G. The drain D of the PMOSFET MP is coupled to the connecting end310. The gate G of the PMOSFET MP is connected to the source S of the PMOSFET MP. The source S of the PMOSFET MP is coupled to the high electric potential terminal VDD.

In one embodiment, the second discharging unit312may be a diode D2with a cathode and an anode. The cathode of the diode D2is coupled to the connecting end310, and the anode of the diode D2is coupled to the low electric potential terminal VSS. In another embodiment, the second discharging unit312may be a N-type Metal-Oxide-Semiconductor Field-Effect Transistor (NMOSFET) MN with a drain D, a gate G and a source G. The drain D of the NMOSFET MN is coupled to the connecting end310. The gate G of the NMOSFET MN is connected to the source S of the NMOSFET MN. The source S of the NMOSFET MN is coupled to the low electric potential terminal VSS.

In another embodiment, the first and second discharging unit may be Silicon Controlled Rectifiers (SCRs).

With further reference toFIG. 4A, the first discharging unit311provides the first static electricity discharge path PH1to discharge the positive static charge+VESDto the high electric potential terminal VDD. With further reference toFIG. 4B, the second discharging unit312is coupled between the low electric potential terminal VSS and the connecting end310and provides the second static electricity discharge path PH2to discharge the negative static charge −VESDto the low electric potential terminal VSS.

The ESD protection electrode20may be arranged in different ways. With reference toFIG. 5A, in one embodiment, the ESD protection electrode20may have multiple first conductive lines201and two second conductive lines202. The first conductive lines201are parallel to the first axis H1and are arranged respectively on both sides of each column of the sensing electrodes11. The second conductive lines202are parallel to the second axis H2, are arranged respectively on two outer sides of the sensing electrode array and are electrically connected to the first conductive lines201. With reference toFIG. 5B, in another embodiment, the ESD protection electrode may have two first conductive lines201and multiple second conductive lines202. The first conductive lines201parallel to the first axis H1and are arranged respectively on two outer sides of the sensing electrode array. The second conductive lines202are parallel to the second axis H2, are arranged respectively on both sides of each row of the sensing electrodes11and are electrically connected to the first conductive lines201. In another embodiment as shown inFIG. 1, the ESD protection electrode20may have m+1 first conductive lines201and n+1 second conductive lines202. The first conductive lines201are parallel to the first axis H1and are arranged respectively on both sides of each rows of sensing electrode11. The second conductive lines202are parallel to the second axis H2, are arranged respectively on both sides of each column of sensing electrodes11and are electrically connected to the first conductive lines201. Each sensing electrode11is surrounded by the ESD protection electrode20.

In different embodiments, multiple ESD protection circuits may be arranged to connect to the ESD protection electrode20in the aforementioned embodiments. InFIGS. 6A and 6B, two arrangements of ESD protection circuits are respectively connect to the ESD protection electrodes shown inFIG. 5A. With reference toFIG. 6A, in one embodiment, one end of each first conductive line201may be connected to one ESD protection circuit31. With referenceFIG. 6B, in one embodiment, each of both ends of each first conductive line201may be connected to one ESD protection circuit31.

InFIGS. 6C and 6D, two arrangements of ESD protection circuits are respectively connect to the ESD protection electrodes shown inFIG. 5B. With reference toFIG. 6C, in one embodiment, one end of each second conductive line202may be connected to one ESD protection circuit31. With reference toFIG. 6D, in one embodiment, each of both ends of each second conductive line202may be connected to one ESD protection circuit31.

In embodiments shown inFIGS. 7A to 7J, multiple ESD protection circuits are arranged to connect to the ESD protection electrodes shown inFIG. 1. With reference toFIG. 7A, in one embodiment, one end of each first conductive line201may be connected to one ESD protection circuit31. With referenceFIG. 7B, in one embodiment, one end of each second conductive line201may be connected to one ESD protection circuit31.

With reference toFIG. 7C, in one embodiment, each of both ends of each first conductive line201may be connected to one ESD protection circuit31. With reference toFIG. 7D, in one embodiment, each of both ends of each second conductive line202may be connected to one ESD protection circuit31.

With referenceFIG. 7E, in one embodiment, each of both ends of each first conductive line201may be connected to one ESD protection circuit31and one end of each second conductive line202may be connected to one ESD protection circuit31. With referenceFIG. 7F, in one embodiment, one end of each first conductive line201may be connected to one ESD protection circuit31and each of both ends of each second conductive line202may be connected to one ESD protection circuit31.

With reference toFIG. 7G, in one embodiment, a middle part of an outermost one of the first conductive lines201is connected to multiple protection circuits31. With reference toFIG. 7H, in one embodiment, a middle part of an outermost one of the second conductive lines202is connected to multiple protection circuits31.

With reference toFIG. 7I, in one embodiment, each of both ends of each first conductive line201may be connected to one ESD protection circuit31and each of both ends of each second conductive line202may be connected to one ESD protection circuit31.

With reference toFIG. 7J, in one embodiment, one end of each first conductive line201may be connected to one ESD protection circuit31and one end of each second conductive line202may be connected to one ESD protection circuit31.

In the embodiments as shown inFIGS. 6A to 7J, each ESD protection circuit31may be connected to the first conductive lines201and to the second conductive lines202through the connecting end310.

The sensing electrodes11of the fingerprint sensing electrode array and the ESD protection electrode20may be located in the same layer or different layers in the semiconductor structure. Different arrangements are shown inFIGS. 8A to 9E.

With reference toFIG. 8A, in one embodiment, the sensing electrodes11and the ESD protection electrode20are formed in the same layer and are formed on a substrate101. A first dielectric layer102is covered on the sensing electrodes11and the ESD protection electrode20. A protecting layer104is covered on the first dielectric layer102.

With reference toFIG. 8B, in one embodiment, the sensing electrodes11and the ESD protection electrode20are formed in different layers and the layer with the ESD protection electrode20is formed above the layer with the sensing electrodes11. The first dielectric layer102is covered on the sensing electrodes11. The ESD protection electrode20is formed on an upper surface of the first dielectric layer102. A second dielectric layer103is covered on the ESD protection electrode20. The protecting layer104is covered on the second dielectric layer103.

With reference toFIG. 8C, in one embodiment, the sensing electrodes11and a first ESD protection electrode20aare formed in the same layer. The first dielectric layer102is covered on the sensing electrodes11and the first ESD protection electrode20a. A second ESD protection electrode20bis formed on the first dielectric layer102. The second ESD protection electrode20baligns with and is electrically connected to the first ESD protection electrode20a. The second dielectric layer103is covered on the second ESD protection electrode20b. The protecting layer104is covered on the second dielectric layer103.

With reference toFIG. 8D, in one embodiment, the sensing electrodes11and the first ESD protection electrode20aare formed in the same layer. The first dielectric layer102is covered on the sensing electrodes11and the first ESD protection electrode20a. The second ESD protection electrode20bis formed under the first ESD protection electrode20a. The second ESD protection electrode20baligns with and is electrically connected to the first ESD protection electrode20a. The second dielectric layer103is covered on the second ESD protection electrode20b. The protecting layer104is covered on the second dielectric layer102.

FIG. 8Eshows an embodiment modified from the embodiment shown inFIG. 8D, a third ESD protection electrode20cis formed on the first dielectric layer102and is covered by a third dielectric layer103′. The protecting layer104is covered on the second dielectric layer103′. The third ESD protection electrode20caligns with and is electrically connected to the first ESD protection electrode20a.

FIGS. 9A to 9E, show embodiments modified from the embodiments shown inFIGS. 8A to 8E. In theFIGS. 9A to 9E, multiple ground holes105are formed through the protecting layer104and may be connected to the uppermost ESD protection electrode of the ESD protection electrode20, the first ESD protection electrode20a, the second ESD protection electrode20bor the third ESD protection electrode20c.

The reference number101shown inFIGS. 8A to 9Erepresents a substrate. The substrate101is used for forming the ESD protection circuit31, the other electronic components for the fingerprint sensor, and the leading wires for transmitting signals.

With reference toFIG. 2, each ESD protection circuit31further has a driving circuit32to eliminate the parasitic capacitance CFASbetween the ESD protection electrode20and the sensing electrodes11. With further reference toFIG. 10, a detecting circuit40is coupled to one of the sensing electrodes11to be detected. The detecting circuit40has multiple switches including a first switch SW1A, a second switch SW2A, a third switch SW3Aand a fourth switch SW4Aand a differential circuit40a. The differential circuit40ahas a non-inverting input (+) coupled to the sensing electrode11to be detected. The first switch SW1Ais connected between a first voltage VR1and the sensing electrode11. The second switch SW2Ais connected between a second voltage VR2and the non-inverting input (+). The third switch SW3Ais connected between the sensing electrode11and the non-inverting input (+). The fourth switch SW4Ais connected between the second voltage VR2and an inverting input (−) of the differential circuit40a. A capacitor is coupled between the inverting input (−) and a ground. The ESD protection electrode20is connected to an ESD protection circuit31. A fifth switch SWSEis connected between a third voltage VR3and the ESD protection circuit31. A sixth switch SWSPis connected between a fourth voltage VR4and the ESD protection circuit31.

In a first phase, the first switch SW1A, the third switch SW3A, the fourth switch SW4Aand the fifth switch SWSEare turned on and the second switch SW2Aand the sixth switch SWSPare turned off. The first voltage VR1is supplied to the sensing electrode11to be detected. The non-inverting input (+) is connected to the second voltage VR2. The driving circuit32supplies the third voltage VR3to the ESD protection electrode20. The sensing electrode11to be detected is not connected to the differential circuit40a. The first voltage VR1minus the second voltage VR2leaves a non zero difference.

In a second phase, the first switch SW1A, the third switch SW3A, the fourth switch SW4Aand the fifth switch SWSEare turned off and the second switch SW2Aand the sixth switch SWSPare turned on. The driving circuit32supplies the fourth voltage VR4to the ESD protection electrode20. The sensing electrode11to be detected is not connected to the first voltage VR1and the non-inverting input (+) of the differential circuit40ais not connected to the second voltage VR2. The non-inverting input (+) of the differential circuit40ais connected to the sensing electrode11to be detected, so as to read out the sensing signal from the sensing electrode11to be detected. The third voltage VR3minus the fourth voltage VR4leaves a non zero difference. In one embodiment, the difference of the third voltage VR3minus the fourth voltage VR4is equal to the difference of the first voltage VR1minus the second voltage VR2(VR3−VR4=VR1−VR2). In one embodiment, the first voltage VR1is equal to the third voltage VR3, and second voltage VR2is equal to the fourth voltage VR4.

With reference toFIGS. 2 and 11, in one embodiment, the sensing circuit41has an operational amplifier OPA, a sensing capacitor Cfba, a first switch SW1A, a second switch SW2Aand a third switch SW3A. An inverting input (−) of the operational amplifier OPA is coupled to a sensing electrode11to be detected. The sensing capacitor Cfbais coupled between the inverting input (−) of the operational amplifier OPA and an output VOA. The first switch SW1Ais connected between a first voltage VR1and the sensing electrode11. The second switch SW2Ais connected between the sensing electrode11and the inverting input (−) of the operational amplifier OPA. The third switch SW3Ais connected to the sensing capacitor Cfbain parallel. A second voltage V is connected to a non-inverting input (+) of the operational amplifier OPA. The capacitances Cp1aand Cp2aare represented as parasitic capacitances. The ESD protection electrode20is connected to an ESD protection circuit31. A fifth switch SWSEis connected between a first voltage VR1and the ESD protection circuit31. A sixth switch SWSPis connected between a second voltage V and the ESD protection circuit31.

In the first phase, the first switch SW1A, the third switch SW3Aand the fifth switch SWSEare turned on and the second switch SW2Aand the sixth switch SWSPare turned off. The first voltage VR1is supplied to the sensing electrode11to be detected and to the ESD protection electrode20. The sensing electrode11to be detected is not connected to the operational amplifier OPA.

In the second phase, the first switch SW1A, the third switch SW3Aand the fifth switch SWSEare turned off and the second switch SW2Aand the sixth switch SWSPare turned on. The second voltage V is supplied to the ESD protection electrode20and the non-inverting input (+) of the operational amplifier OPA. The inverting input (−) of the operational amplifier OPA is connected to the sensing electrode11to be detected, so as to read out the sensing signal of the sensing electrode11to be detected.

In conclusion, the ESD protection circuit in accordance with the present invention provides a first static electricity discharge path to the high electric potential terminal and a second static electricity discharge path to the low electric potential terminal. Therefore, the positive and negative static electricity charges of the ESD protection electrode are discharged through the first and second static electricity discharge paths to keep the fingerprint sensing array from damaging. Further, the ESD protection circuit in accordance with the present invention supplies different voltages to the ESD protection electrode in different phases Thus parasitic capacitance between the ESD protection electrode and the sensing electrodes is reduce.