Thin film transistor type optical sensor

[0002] This application claims the benefit of Korean Patent Application No. 1999-01699, filed on Jan. 20, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.

[0003] 1. Field of the Invention

[0004] The present invention relates to an image detector and, more particularly, to a thin film transistor (TFT) type optical sensor with a conductive object or living object detection pattern.

[0005] 2. Discussion of the Related Art

[0006] Generally, a thin film transistor type optical sensor comprises a window for receiving light reflected from an object, a sensor TFT for generating an optical current in proportion to the intensity of the light, a storage capacitor for storing charges of the optical current transmitted from the sensor TFT as charged information, and a switching TFT for outputting the charged information stored in the storage capacitor in accordance with an external control signal.

[0007] FIG. 1 shows a conventional TFT type optical sensor.

[0008] A sensor S1 is coupled to a controller 2 whose output end is coupled to an input end of an electrical power source 4. An output end of the electrical source 4 is electrically coupled to both the sensing part 6 and a light source 8. The sensor S1 may be replaced with a mechanical switch or an infrared switch. In operation, when a signal is output from the sensor S1, the controller 2 transmits the signal to the sensing part 6 and the light source 8 through the electrical power source 4.

[0009] FIG. 2 shows another conventional TFT type optical sensor using a mechanical switch SW1 instead of the sensor S1.

[0010] One end of the switch SW1 is coupled to an input end of the electrical power source 4 and the other end to an input end of a controller 2. An output end of the controller 2 is coupled to an input end of the electrical power source 4 whose output end in turn is coupled to both a sensing part 6 and a light source 8.

[0011] In operation, when the switch SW1 is turned “ON” to operate the optical sensor, electrical power is supplied from the electrical power source 4 to the controller 2, then input to the electrical power source 4 as a predetermined control signal. Next, the electrical power source 4 transmits electrical power to the sensing part 6 and the light source 8.

[0012] The two above-described conventional TFT type optical sensors have the following drawbacks:

[0013] 1. When the switch is turned ON, since electrical power is always supplied, electrical power is unnecessarily consumed even when the sensor is not detecting an object.

[0014] 2. They have no means for recognizing whether an object is living or not. For example, the sensor may be a fingerprint detection device, In that case, it is important for the sensor to discriminate between a live human finger, and, for example, a photograph or photocopy of a human fingerprint. Otherwise, the fingerprint detection device may be spoofed.

[0015] Accordingly, the present invention is directed to an image detector that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

[0016] It is an objective of the present invention to provide a TFT type optical sensor that uses a minimal amount of electrical power and can recognize whether an object is living or not.

[0017] To achieve the above objective, in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a TFT type optical sensor with a conductive object detection pattern, having a backlight and a sensing part to which electrical power is supplied only when the detection of an object is carried out. By detecting whether and to what degree the object is conductive, the a TFT type optical sensor can detect a living object.

[0018] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

[0019] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

[0020] In the drawings:

[0021] FIG. 1 is a block diagram of a conventional optical sensor;

[0022] FIG. 2 is a block diagram of another conventional optical sensor;

[0023] FIG. 3 is a sectional view of a TFT type optical sensor according to a preferred embodiment of the present invention;

[0024] FIG. 4 is a schematic block diagram of a TFT type optical sensor according to a preferred embodiment of the present invention; and

[0025] FIGS. 5ato 5fare plan views of various conductive object detection patterns provide to a TFT type optical sensor according to a preferred embodiment of the present invention.

[0026] Reference will now be made in detail to a preferred embodiment of the present invention, an example of which is illustrated in the accompanying drawings.

[0027] FIG. 3 shows a sectional view of a TFT type optical sensor according to a preferred embodiment of the present invention.

[0028] A substrate 10 is divided into a window A, a sensor TFT area B, a storage area C, and a switching TFT area D. A conductive metal is deposited on the substrate 10, then patterned such that a sensor gate 12, a first storage electrode 14, and a switch gate 16 are respectively formed on the sensor TFT area B, the storage area C, and storage area C, and the switching TFT area D. An amorphous silicon is deposited on the substrate 10, and then patterned such that a sensor semiconductor layer 20aand a switch semiconductor layer 20bare formed on the first insulating layer 18 corresponding to sensor TFT area B and the switching TFT area D, respectively.

[0029] A conductive metal is further deposited on the first insulating layer 18, then patterned such that a sensor drain 22aand a sensor source 22bare formed covering an edge of the sensor semiconductor layer 20aand the switch semiconductor layer 20b. A second storage electrode 20cis formed on the first insulating layer 18 corresponding to the first storage electrode 14, and a switch drain 22dand a switch source 22eare formed on the first insulating layer 18 while covering an edge of the switch semiconductor layer 20b.

[0030] A second insulating layer 24 is deposited on the first insulating layer 18 while covering the semiconductor layers and the sensor drains and sources

[0031] A light blocking layer 25 is formed on the second insulating layer 24 corresponding to the switching TFT area D, then a protecting layer 26 is formed on the second insulating layer 24 and covering the light blocking layer 25.

[0032] A conductive object detection pattern (which may be a living object detection pattern) 28 is formed on the protecting layer 26. The conductive object detection pattern 28 (or living object detection pattern) comprises first and second electrodes 28aand 28bthat are spaced apart from each other. In a preferred embodiment, each of the first and second electrodes 28aand 28bare finger-shaped, fingers of the first and second electrodes 28aand 28bbeing alternately disposed. The controller 30 is coupled to the conductive object detection pattern 28 to supply an electrical signal to one of the first and second electrodes 28aand 28band to receive a predetermined electrical signal from the other of the first and second electrodes 28aand 28b. The distance between the first and second electrodes 28aand 28bis narrower than a width of a human finger so that when a user presses the conductive object detection pattern 28, the first and second electrodes 28aand 28bcan be electrically coupled to each other via a user's finger by virtue of the electrical conductivity of the human finger.

[0033] When the first and second electrodes 28aand 28bare electrically coupled to each other by the user's finger, the controller 30 receives the electrical signal from one of the electrodes 28aand 28b. The controller 30 then transmits an electrical control signal to the electrical power source 36, then the electrical power source 36 applies a predetermined voltage to the sensing part 32 and the light source 34. When the first and second electrodes 28aand 28bare electrically disconnected by the user removing his/her finger, the application of the voltage to the sensing part 32 and the light source 34 is discontinued. Preferably, the controller 30 may sense a current flowing between the first and second electrodes 28aand 28bto determine a conductivity between the first and second electrodes 28aand 28bto discriminate whether a living object is on the conductive object detection pattern 28. In one embodiment, the controller 30 may receive an electrical signal to be supplied to the conductive object detection pattern 28 from the electrical power source 36. Alternatively, the controller may produce the electrical signal to be supplied to the conductive object detection pattern 28.

[0034] Accordingly, since the TFT type optical sensor uses electrical power only when it is detecting the object, electrical power is saved. In addition, since the conductive object detection pattern is disposed on the outermost surface of the optical sensor, it should be made of a material that can effectively transmit light. Such a material may be selected from the group consisting of indium tin oxide, tin oxide and TiOx.

[0035] The shape of the conductive object detection pattern can be varied. FIGS. 5ato 5fshow various shapes of the conductive object detection pattern FIG. 5ashowing a fingershaped pattern which is shown in FIG. 4. In FIG. 5b, the first and second electrodes are parallel, having a P-shaped pattern. In FIG. 5c, the first and second electrodes are linearly disposed having a triangle-shaped pattern. In FIG. 5d, the first and second electrodes are parallel having a rail-shaped pattern. In FIG. 5e, the first electrode is disposed having a U-shaped pattern, and the second electrode is disposed having an I-shaped pattern. In FIG. 5f, the first and second electrodes are parallel, having a coil-shaped or spiral-shaped pattern.

[0036] It will be apparent to those skilled in the art that various modifications and variation can be made in the thin film transistor type optical sensor of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention, provided they come within the scope of the appended claims and their equivalents.