MANUFACTURING THE FINGERPRINT SENSING MODULE

Field of the Invention

The present invention relates to a biometric imaging device and to a method of manufacturing the biometric imaging device. In particular, the invention relates to a fingerprint sensor module comprising a thin-film- transistor (TFT) fingerprint sensor.

Background of the Invention

As the development of biometric imaging devices for identity verification, and in particular of fingerprint sensing devices, has led to devices which are made smaller, cheaper and more energy efficient, the range of applications for such devices is increasing.

In particular, capacitive fingerprint sensing devices have been adopted more and more in for example consumer electronic devices due to small form factor, relatively beneficial cost/performance factor and high user acceptance. There is also an increasing interest in using fingerprint sensors in smartcards to enable biometric identification in a card such as a bank card where other types of biometric systems are not applicable.

Capacitive fingerprint sensors can be manufactured in large numbers and at low cost using a thin film transistor (TFT) process. However, current TFT-circuits are often very thin, having a thickness of about 5 pm, and a total thickness of about 30 pm including a carrier substrate, which requires careful handling of the TFT-circuits during manufacturing of a fingerprint sensing module to prevent wrapping, cracking or other damages.

Previous solutions have included arranging the TFT-circuit on a thick substrate such as a flexible substrate or a glass substrate. However, such additional substrates increase the overall thickness of the sensing module, while in fingerprint sensing modules suitable for smartcard integration it is desirable to minimize the thickness. Moreover, in applications where fingerprint sensing takes place through the substrate, it is even more important to minimize the thickness of the substrate on which the TFT-circuit is arranged.

Furthermore, for a capacitive fingerprint sensor it is also desirable to place the capacitive sensing matrix as close to the finger as possible to get the strongest possible sensing signals.

Accordingly, it is desirable to provide improved manufacturing methods for fingerprint sensing modules comprising a capacitive fingerprint sensing device based on a TFT-process.

Summary

In view of above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide an improved biometric imaging device and a method for manufacturing a biometric imaging device based on thin-film transistor technology.

According to a first aspect of the invention, it is provided a fingerprint sensing module comprising: a substrate; a spacer arranged on the substrate, the spacer having a smaller area than an area of the substrate; and a flexible TFT-film comprising a fingerprint sensing matrix, the flexible TFT-film being partially arranged on the spacer, wherein a portion of the flexible TFT-film outside of the spacer is curved towards the substrate to form a mechanical contact with the substrate, a first electrically conductive contact arranged on an upper surface of the flexible TFT-film on the portion of the flexible TFT-film being in mechanical contact with the substrate, a second electrically conductive contact on an upper surface of the substrate, and an electrically conductive path between the first contact and the second contact.

The TFT-film should in the present context be seen as a thin layer of material or materials comprising TFT-circuitry and which is flexible. The TFT- film can thereby be provided as sheets or on a roll. Moreover, the fingerprint sensing matrix comprises active circuitry in the form of an array of capacitive plates connected to TFT-circuitry so that the fingerprint sensing matrix define an active sensing region of a capacitive fingerprint sensor. The present invention is based on the realization that when a TFT-film is used to form the active sensing matrix of a fingerprint sensing module, the flexibility of the TFT-film can be utilized to form a connection between the fingerprint sensing module and external circuitry which is located below the surface of the active sensing matrix of the TFT-film, thereby allowing the use of a spacer to ensure that the fingerprint sensing matrix is located higher, i.e. closer to a finger, than contact areas of the fingerprint sensing module. The distance between the fingerprint sensing matrix and a finger placed on an outer surface of the fingerprint sensing module can thereby be minimized while still allowing for convent formation of electrical connections to external circuitry. According to various embodiments of the present invention, a connection to external circuitry is facilitated by the curved portion of the TFT- film bending below the plane of the fingerprint sensing matrix to form a mechanical connection to the substrate on which the TFT-film is arranged.

The fingerprint sensing module further comprises a first electrically conductive contact arranged on an upper surface of the flexible TFT-film on the portion of the flexible TFT-film being in mechanical contact with the substrate. The electrically conductive contact can be assumed to be in connection with the fingerprint sensing matrix to thereby enable an electrical connection to be formed to external circuitry from the portion of the TFT-film being in mechanical contact with the substrates. Accordingly, electrically conductive paths are present also in the curved portion of the TFT-film.

The fingerprint sensing module further comprises a second electrically conductive contact on an upper surface of the substrate and an electrically conductive path between the first contact and the second contact. The electrically conductive path may for example comprise a bond wire arranged to form an electrical connection between the first contact and the second contact.

According to one embodiment of the invention, the electrically conductive path comprises an electrically conductive printed circuit board, PCB arranged to form an electrical connection between the first contact and the second contact. The PCB may for example be a flexible PCB, but it may also be a rigid PCB. The use of a PCB substrate provides fast and reliable bonding of the first electrically conductive contact to the second electrically conductive contact since an electrical connection can easily be formed through the PCB substrate. In particular, the PCB allow for multiple electrical connections to be formed simultaneously which may be advantageous in comparison to wire bonding in applications where a large number of electrical connections are required.

According to one embodiment of the invention, the fingerprint sensing module further comprises a PCB-substrate having a first conductive area located on a bottom side of the PCB-substrate and arranged in contact with the first electrically conductive contact of the flexible TFT-film and a second conductive area configured to be connected to external circuitry. An electrical connection can thereby be formed via the PCB-substrate directly to external circuitry without the need to provide an electrical contact on the substrate of the fingerprint sensing module.

According to one embodiment of the invention, a portion of the PCB- substrate is arranged to extend outside of the substrate, and wherein the second conductive area is located on the bottom side of the PCB-substrate on the portion of the PCB-substrate extending outside of the substrate. The fingerprint sensing module can thereby be connected to external circuitry via the PCB-substrate by means of the second conducive area which can be arranged in contact with an external device in which the fingerprint sensing module is arranged.

According to one embodiment of the invention, the substrate comprises an opening and wherein the PCB-substrate comprising an electrical component arranged on the bottom side of the PCB-substrate and, the component being at least partially arranged in the opening of the substrate. Thereby, additional components and circuitry for operating the fingerprint sensing module can more easily be integrated in the sensing module without adding to the total thickness of the module. The electrical component may for example be an integrated circuit comprising readout circuitry for the fingerprint sensing matrix. The opening in the substrate may be a recess, trench or the like which does not reach through the entire thickness of the substrate. However, the opening may also be a through-opening reaching trough the substrate.

According to one embodiment of the invention, a top surface of a portion of the TFT-film comprising the fingerprint sensing matrix is located above a top surface of the PCB-substrate, thereby making it possible to minimize the distance between the fingerprint sensing matrix and a finger placed on an external surface of the fingerprint sensing module. In particular, the portion of the TFT-film comprising the fingerprint sensing matrix may advantageously be the uppermost surface of the fingerprint sensing module.

According to one embodiment of the invention, at least an active portion of the sensing matrix is arranged in overlap with the spacer. The relatively thin fingerprint sensing matrix of the TFT-film is thereby mechanically supported by the spacer.

According to one embodiment of the invention, the fingerprint sensing module is integrated in a smartcard comprising a card body in which the fingerprint sensing module according to any one of the aforementioned embodiments is arranged; and a conductive layer electrically connected to contact pads of the fingerprint sensing module.

According to a second aspect of the invention, there is provided a method for manufacturing a fingerprint sensor module comprising: providing a substrate; arranging a spacer the substrate, the spacer having a smaller area than an area of the substrate; arranging a flexible TFT-film comprising a fingerprint sensing matrix so that the fingerprint sensing matrix overlaps the spacer; and bending a portion of the flexible TFT-film located outside of the spacer towards the substrate to form a mechanical contact between the flexible TFT-film and the substrate, and forming an electrically conductive path between a first electrically conductive contact arranged on an upper surface of the flexible TFT-film on the portion of the flexible TFT-film being in mechanical contact with the substrate and a second electrically conductive contact on an upper surface of the substrate. Further effects and features of the second aspect of the invention are largely analogous to those described above in connection with the first aspect of the invention.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

Brief Description of the Drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

Figs. 1 schematically illustrates a fingerprint sensing module according to an embodiment of the invention;

Figs. 2A-B schematically illustrate a fingerprint sensing module according to an embodiment of the invention;

Figs. 3A-C schematically illustrate fingerprint sensing modules according to embodiments of the invention;

Fig. 4 schematically illustrates a smartcard comprising a fingerprint sensing module according to an embodiment of the invention; and

Fig. 5 is a flow chart describing steps of a method of manufacturing a fingerprint sensing module according to an embodiment of the invention.

Detailed Description of Example Embodiments

In the present detailed description, various embodiments of a fingerprint sensing module and a method of manufacturing the fingerprint sensing module according to the present invention are mainly discussed with reference to a fingerprint sensing module comprising a capacitive fingerprint sensing device. However, the concepts described herein may also be applicable for other types of biometric imaging devices. Fig. 1 A is a schematic cross section view of a fingerprint sensing module 100 according to an example embodiment. The fingerprint sensing module 100 comprises a substrate 102 and a spacer 104 arranged on the substrate 102. The substrate 102 can be made from any solid material providing sufficient structural support for the fingerprint sensing module 100. The material can be selected to suit a particular implementation, and materials such as plastic or metal substrates may be used. The substrate 102 can also be a PCB substrate in applications where it is desirable to form electrical connections via the substate.

The spacer 104 has a smaller surface area than the area of the substrate 102 so that the substrate 102 extends outside of the spacer 104 on at least one side of the spacer 104. The fingerprint sensing module further comprises a flexible TFT-film 106 comprising a fingerprint sensing matrix 108. As can be seen in Fig. 1 , the flexible TFT-film 106 is partially arranged on the spacer 104, wherein a portion 110 of the flexible TFT-film extending outside of the spacer 104 is curved towards the substrate 102 to form a mechanical contact with the substrate 102.

Moreover, the fingerprint sensing module 100 comprises a first electrically conductive contact 112 arranged on an upper surface 114 of the flexible TFT-film 106 on the portion of the flexible TFT-film 106 being in mechanical contact with the substrate 102. A second electrically conductive contact 116 is arranged on an upper surface 118 of the substrate 102, where the upper surface 118 is defined as the surface facing in the same direction as the fingerprint sensing matrix 108. An electrically conductive path in the form of a bond wire 120 is arranged between the first contact 112 and the second contact 116 to electrically connect the TFT-film 106 to the substrate 102, thereby enabling connection of the fingerprint sensing module 100 to external circuitry (not shown). The bond wire 120 may be covered by an encapsulation layer to protect the bond wire 120 and the first and second contacts 112, 116.

The mechanical contact between the TFT-film 106 and the substrate

102 facilitates the wire bonding between the two. Moreover, the bond wire 120 is configured to be lower than the surface of the fingerprint sensing matrix 108 to not add to the total thickness of the fingerprint sensing module 100. Furthermore, the thickness of the TFT-film 106 is normally lower than the thickness of the spacer but this not an absolute requirement since the primary focus is that the fingerprint sensing matrix 108 is arranged as the uppermost surface of the fingerprint sensing module 100. The fingerprint sensing matrix 108 may however include protective layers, cover layers or the like.

Here, conventional TFT manufacturing processes are used and the steps of manufacturing a TFT-film 106 comprising a TFT-based fingerprint sensing matrix 108 as part of a fingerprint sensing module 100 are generally known and will not be described in further detail herein.

The fingerprint sensing matrix 108 comprises an array of electrically conductive sensing elements connected to thin-film transistors to forma capacitive fingerprint sensing device. A capacitive fingerprint sensing device should be understood to further comprise sensing circuitry connected to the sensing elements for reading a signal from the sensing elements. The sensing circuitry may in turn comprise internal readout circuitry or be connected to external readout circuitry for providing a result of the sensing elements to an external device for further processing, which in the present case may be included in the fingerprint sensing module.

Fig. 2A is a top view of a fingerprint sensing module 200 according to an example embodiment and Fig. 2B is a cross section view of the same module 200. The fingerprint sensing module 200 of Figs. 2A-B is largely similar the fingerprint sensing module 100 of Fig. 1 with the difference being that the electrically conductive path between the TFT-film 106 and the substrate 102 is formed by a flexible PCB-substrate 202. The flexible PCB- substrate 202 comprises a first electrically conductive area 206 arranged in contact with the first contact 112 of the TFT-film 104 and a second electrically conductive area 208 arranged in contact with the second contact 116. The first and second electrically conductive areas 206, 208 may be metal contacts located on or in a bottom side 210 of the PCB-substrate 202. In the present description, the “top side” of an object refers to the side facing in the direction of the fingerprint sensing matrix 108, and the bottom side refers to the side opposite the top side.

The flexible PCB-substrate 202 further comprises electrically conductive traces (not shown) forming an electrical connection between the first contact 112 and the second contact 116. Moreover, a top surface 204 of the flexible PCB-substrate 202 is located below a top surface of the fingerprint sensing matrix 108 so as to not add to the overall thickness of the fingerprint sensing module 200.

Figs. 3A-C schematically illustrate example embodiments of the fingerprint sensing module 300, 302 according to example embodiments of the invention. Fig. 3A is a top view and Figs 3B-C are cross section views of two different examples of fingerprint sensing modules 300, 302.

In Fig. 3A, it is illustrated that the substrate 102 comprises an opening 306 and in Figs. 3B-C it is shown that an electrical component 310 arranged on the bottom side 308 of the PCB-substrate is at least partially arranged in the opening 306 of the substrate 102. The opening 306 may be a through opening reaching through the substrate 102 or the opening 306 may be a recess in the substrate 102 and which to choose may for example depend on the size of the component in relation to the thickness of the substrate and other geometric dimensions of the fingerprint sensing module 300, 302.

Fig. 3B illustrates an embodiment where the connection element is a flexible PCB-substrate 202 and in Fig. 3C the connection element is a rigid PCB-substrate 304. In both cases, the PCB-substrate 202, 304 is attached to the substrate 102 using an adhesive 312. The thickness of the adhesive 312 can be selected to suit the properties of the particular PCB-substrate 202, 304 to be used.

A portion 314 of the PCB-substrate 202, 304 is arranged to extend outside of the substrate 102, and the second conductive area 208 is located on the bottom side 308 of the PCB-substrate 202, 304 on the portion 314 of the PCB-substrate 202, 304 extending outside of the substrate 102. The fingerprint sensing module 300, 302 can thereby be connected to external circuitry through the PCB-substrate 202, 304 and in particular by the second conductive area 208 of the PCB-substrate 202, 304 being located outside of the substrate 102.

Fig. 4 schematically illustrates a smartcard 400 comprising a card body 402 comprising a fingerprint sensing module 100, 200, 300, 302 according to any one the preceding examples arranged in the card body 402. The smartcard 400 is provided with means for wireless communication with a smartcard reader such as a point-of-sale (POS) terminal 406 and it is further provided with a contact plate 404 for communication via physical contact with the terminal 906.

Fig. 5 is a flow chart outlining steps of a method for manufacturing a fingerprint sensing module 100 according to various embodiments of the invention. The method comprises providing 502 a substrate 102, arranging 504 a spacer 104 on the substrate 102, the spacer 104 having a smaller area than an area of the substrate 102, arranging 506 a flexible TFT-film 106 comprising a fingerprint sensing matrix 108 on the spacer so that the fingerprint sensing matrix 108 overlaps the spacer 104. The flexible TFT-film 106 is thereby partially arranged on the spacer 104 with a portion 110 of the TFT-film 106 protruding outside of the spacer 104. The method further comprises bending 508 a portion 110 of the flexible TFT-film 106 located outside of the spacer 104 towards the substrate 104 to form a mechanical contact between the flexible TFT-film 106 and the substrate 102. Moreover, the mechanical contact between the flexible TFT-film 106 and the substrate 102 may comprise an adhesive, bonding or the like to permanently attach the flexible TFT-film 106 to the substrate 102. The method further comprises forming an electrically conductive path 120, 202 between a first electrically conductive contact 112 arranged on an upper surface 114 of the flexible TFT- film on the portion of the flexible TFT-film being in mechanical contact with the substrate and a second electrically conductive contact 116 on an upper surface 118 of the substrate.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Also, it should be noted that parts of the fingerprint sensing module may be omitted, interchanged or arranged in various ways, the biometric imaging device yet being able to perform the functionality of the present invention.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.