JP2009086565A - Display device incorporating optical sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To implement a low-cost and stable display device incorporating an optical sensor, which is free from malfunction due to external light and light of a backlight. <P>SOLUTION: A unit pixel on an array substrate of the display device incorporating the optical sensor includes a thin film transistor for switching and a thin film transistor for optical detection, which are formed on a glass substrate, and a pixel electrode 9 controlled by the thin film transistor for switching. Respective channel layers 4 of the thin film transistor for switching and the thin film transistor for optical detection comprise a microcrystalline silicon film having sensitivity in a wavelength band of near infrared light. Therefore, the thin film transistor for optical detection absorbs near-infrared light being auxiliary light for detection of a push with a finger or the like to detect the push with a finger or the like. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to, for example, a thin film transistor (TFT) array substrate incorporating a photosensor used in a liquid crystal display device or an EL (Electroluminescence) display device, and a display device using the same.

  FIG. 12 is a longitudinal sectional view of a two-dimensional photosensor array described in Patent Document 1 using an amorphous silicon thin film transistor (TFT) as an optical sensor. According to the description in Patent Document 1, the pixel of the liquid crystal display unit and the pixel of the photosensor unit are made to coincide, and the laminated structure of the gate insulating film / channel amorphous silicon of the liquid crystal driving TFT and the photoelectric conversion TFT A gate insulating film / channel amorphous silicon laminated structure is simultaneously formed. FIG. 13 and FIG. 14 are diagrams showing pixel configurations. According to FIGS. 13 and 14, there is provided a device for reading out a signal by forming a liquid crystal pixel driving TFT, a photoelectric conversion TFT, and a circuit having a storage capacitor in a unit pixel, and connecting an external circuit to the periphery. Are disclosed.

  FIG. 15 is a longitudinal sectional view showing the structure of a TFT array incorporating the photoelectric conversion element disclosed in Patent Document 2. A liquid crystal display device with a built-in optical sensor described in Patent Document 2 includes a low-temperature polysilicon thin film transistor (TFT) having a top gate structure in which an active layer lower portion is shielded by an amorphous silicon layer as a light shielding layer through an insulating film, The photosensor includes the amorphous silicon film as a photoelectric conversion layer. In FIG. 15, reference numeral 1 is a glass substrate as a transparent substrate, 3 is an amorphous silicon film, 12 is a scanning line, 25 is a pixel electrode, 27 is a switching thin film transistor for display, and 28 is a light receiving element as a photoelectric conversion element. Thin film transistor. Further, from the plan view of Patent Document 2, the unit pixel is composed of a switching TFT for liquid crystal driving and a holding capacitor, and a TFT for optical sensor and its holding capacitor, and the signal is formed in the peripheral portion of the panel. It is detected by a driving circuit consisting of a polycrystalline silicon TFT.

JP-A-5-121715 JP 10-90655 A

  As described above, in a conventional photosensor built-in display device, an amorphous silicon TFT is used as a photoelectric conversion element. Amorphous silicon TFTs have a problem that their characteristics are not stable, and their photosensitivity changes with time due to stress during operation. Further, in the display device with a built-in optical sensor when formed only with amorphous silicon TFT, since the mobility of TFT is small, it is necessary to connect all readout circuits as external circuits, and the circuit scale increases. There is also a problem that the manufacturing cost increases due to a decrease in yield due to the mounting process.

  On the other hand, in the display device with a built-in optical sensor described in Patent Document 2, since the readout circuit can be formed of a polycrystalline silicon TFT, problems of the mounting process and the circuit cost can be overcome. However, it is necessary to form an amorphous silicon film as a photoelectric conversion layer under the polycrystalline silicon switching TFT. Therefore, in the process of manufacturing a polycrystalline silicon TFT, there is a process of 400 ° C. or higher when forming the gate insulating film and the interlayer insulating film, so that hydrogen in the amorphous silicon film is released and the defect level increases. This causes a problem that the photosensitivity is lowered. In liquid crystal display devices, a color filter substrate is generally used as the substrate on the front side, and the TFT array substrate is often placed on the backlight side. In the case of a TFT for photoelectric conversion with a top gate structure, The TFT array substrate must be used as the substrate on the surface side, and the display characteristics deteriorate due to the reflected light of the external light on the wiring formed on the TFT array substrate or the metal wiring pattern of the TFT electrode Occurs.

  Furthermore, the use of an amorphous silicon layer for the photoelectric conversion layer has the advantage that it can effectively utilize high sensitivity to light of 550 nm to 600 nm, which is the center of visible light, but the influence of backlight light or external light. It also has a demerit that the S / N ratio of the optical sensor decreases due to the disturbance caused by.

  As described above, in a display device with a built-in optical sensor using an amorphous silicon TFT as a photoelectric conversion element, a TFT array substrate with a built-in photosensor having a low cost, a simple structure, and high sensitivity is formed. It was difficult. Moreover, the method using an amorphous silicon TFT as a photoelectric conversion element has excellent sensitivity to visible light, but it is difficult to avoid a malfunction due to external light or backlight light, and is a practical display device with a built-in optical sensor. Could not be configured.

  The present invention has been made to solve the above-described problems, and its main purpose is an optical sensor using an amorphous silicon TFT as a photoelectric conversion element without increasing the number of manufacturing steps. An object of the present invention is to overcome the disadvantages of the built-in display device and to obtain a photosensor built-in display device that is low in cost and has few malfunctions.

  The subject of the present invention is a display device with a built-in optical sensor comprising an array substrate in which unit pixels are arranged in a matrix, wherein the unit pixels are formed on a transparent substrate, a switching thin film transistor, and the transparent substrate. A thin film transistor for photodetection formed, and a pixel electrode controlled by the thin film transistor for switching, and each channel layer of the thin film transistor for switching and the thin film transistor for photodetection is made of a microcrystalline silicon film. It is characterized by that.

  Hereinafter, various embodiments of the subject of the present invention will be described in detail along with the effects and advantages thereof with reference to the accompanying drawings.

  According to the subject of the present invention, the channel layers of the thin film transistor for light detection and the thin film transistor for switching used in the display device with a built-in optical sensor are both microcrystalline silicon films formed in the same process, and the microcrystalline silicon film Is sensitive to a wide range from the visible light region to the near-infrared region, has a small threshold voltage shift, etc., and is highly reliable, so there are few malfunctions by using near-infrared light as an auxiliary light source. A display device incorporating a highly sensitive and stable optical sensor can be realized.

  Moreover, since the microcrystalline silicon TFT has a mobility several times that of the conventional amorphous silicon TFT, a part of the signal detection circuit of the optical sensor can be formed by the microcrystalline silicon TFT. As a result, the scale of the readout circuit connected to the outside can be reduced. As a result, the cost can be reduced as compared with the conventional display device with a built-in photosensor.

(Embodiment 1)
The feature of the display device with a built-in photosensor according to this embodiment is that both the channel layer of the pixel switching TFT and the channel layer of the photodetection TFT are formed of a microcrystalline silicon film. 1 and 2 showing the components included in each unit pixel arranged in a matrix, FIG. 3 and FIG. 4 showing a circuit block diagram and an overall configuration diagram of the optical sensor built-in display device of the present embodiment, respectively. In addition, the configuration and manufacturing method of the display device with a built-in photosensor according to the present embodiment will be described in detail with reference to other drawings (FIGS. 5 and 6).

  FIG. 2 is a plan view of the array substrate of the display device with a built-in optical sensor according to the present embodiment, and a longitudinal sectional view of the array substrate regarding A1-A2 in FIG. 2 corresponds to FIG. The array substrate according to the present embodiment is a substrate on the back side of the panel on which the backlight of the display device is arranged.

  In FIG. 1, reference numeral 1 is a transparent glass substrate, 2 is a gate electrode made of a metal film formed on the glass substrate 1, and 3 is a coating covering both gate electrodes 2. A gate insulating film made of a silicon nitride film or a silicon oxide film is shown. Reference numeral 4 denotes a TFT channel layer made of a microcrystalline silicon film, and 5 denotes an ohmic contact made of an n-type microcrystalline silicon film formed on both ends of the upper surface of the channel layer 4 and doped with phosphorus as an impurity. The contact layer, 6 is a TFT source electrode, 7 is a TFT drain electrode, 8 is a protective film that covers both the pixel TFT and the photosensor TFT, and 9 is a pixel TFT drain electrode 7. Reference numeral 16 denotes a pixel electrode controlled by the pixel TFT, and 16 denotes a common wiring having a region overlapping with the drain electrode 7 of the photosensor via the gate insulating film 2.

  FIG. 3 is a block diagram of an equivalent circuit of the display device with a built-in photosensor according to the first embodiment. The pixel portion with the built-in photosensor is provided with a photosensor charge storage capacitor 31 provided between the photosensor 19 according to the present embodiment and the common wiring 16, and is detected as a charge proportional to the photocurrent. To do. In FIG. 2, a region overlapping with the drain electrode 7 of the photosensor via the gate insulating film 2 is the charge holding capacitor 31 for the photosensor. Alternatively, the photosensor charge holding capacitor 31 may be omitted, and the photosensor and the common wiring may be connected through a contact hole and directly detected as a photocurrent. In FIG. 3, 12 is a pixel TFT, 13 is a charge storage capacitor provided for the purpose of holding the charge accumulated in the pixel electrode and preventing the voltage applied to the liquid crystal from decreasing, and 19 is the present invention. 14 is a data wiring, 15 is a gate wiring, 16 is a common wiring for supplying a voltage to the above-described charge retention capacitor, and 18 is a wiring for taking out a signal of the optical sensor. Photosensor signal wiring, 30 is a pixel portion liquid crystal capacitor, 31 is a photosensor charge storage capacitor, 35 is a vertical scanning circuit formed of a microcrystalline silicon TFT according to the present invention, 36 is an external horizontal scanning circuit, and 37 is An optical sensor circuit comprising a multiplexer circuit, etc., formed using the microcrystalline silicon TFT of the present invention formed between the external optical sensor circuit and an external optical sensor circuit comprising a charge and current detection circuit. so That. Reference numeral 39 denotes a pixel portion incorporating a photosensor.

  Furthermore, FIG. 4 shows a light source that emits near-infrared light in a wavelength band that can be absorbed by the microcrystalline silicon films constituting the channel layers of both TFTs as described later, for example, light having a wavelength of 700 nm to 1000 nm. It is a figure which shows the display apparatus arrange | positioned as one side of the light-guide plate of a backlight. In FIG. 4, 50 is a display backlight light source, 51 is a near infrared light source, 52 is a backlight light guide plate, 53 is a color filter substrate, 54 is a TFT array substrate, and 55 is a finger press. Showing a finger. That is, the near-infrared ray emitted from the auxiliary light source is transmitted through the gap between the gate electrodes 2 and propagates to the panel surface side, and is reflected on the fingertip of the person touching the touch panel. , And is absorbed by the channel layer 4 of the light detection TFT. It is also possible to perform detection based on the presence or absence of a shadow by pressing a finger by arranging a near-infrared auxiliary light source above the display device with a built-in photosensor according to the present invention.

  Here, FIG. 5 shows the wavelength dependence of the absorption coefficient of the microcrystalline silicon film. Further, FIG. 6 contrasts photoelectric conversion characteristics of the microcrystalline silicon film and the amorphous silicon film. As apparent from FIGS. 5 and 6, unlike the amorphous silicon film, the microcrystalline silicon film has sufficient sensitivity to near-infrared light belonging to a wavelength band from 700 nm to 850 nm. Here, it should be noted that the band gap decreases as the crystal size increases, but the absorption coefficient tends to decrease as the film thickness increases. From such a point of view, the microcrystalline silicon film exhibiting a sufficient absorption coefficient for near infrared light has a crystal size of 50 nm or less, in other words, the crystal grain size of the microcrystalline silicon film is 5 nm or more, It is suitable for the channel layer 4 of the TFT for optical sensors that the optical band gap is 100 nm or less and the optical band gap is in the vicinity of 1.4 eV with reference to FIG. Furthermore, it is preferable to use a microcrystalline silicon film having a signal intensity ratio (Ic / Ia) of Raman spectroscopy between the crystalline silicon phase and the amorphous phase of about 3 to 10. In other words, it is desirable that the ratio of the volume of the amorphous region to the volume of the crystal region of the microcrystalline silicon film is 1/10 to 1/5. Then, it is desirable to adjust the signal intensity ratio of the optical band gap and Raman spectroscopy in accordance with the spectral sensitivity characteristics required for the optical sensor.

  The same effect can be obtained by using a phosphorus-doped amorphous silicon film instead of the phosphorus-doped microcrystalline silicon film 5.

  Next, a method for manufacturing the array substrate for a display device with a built-in optical sensor shown in FIG. 1 will be described.

  First, after a metal film is formed on the glass substrate 1 by sputtering or the like, a gate electrode line 2 (reference numeral 15 in FIG. 3) for driving a pixel portion of the liquid crystal display device, a common electrode line (in FIG. 3) Reference numeral 16) and photodetection (photosensor) gate electrode line 2 are patterned by a photolithography process.

  Next, the silicon nitride film to be the gate insulating film 3 has a thickness in the range of 200 to 500 nm, the non-doped microcrystalline silicon film 4 has a thickness in the range of 100 to 500 nm, and the phosphorus-doped microcrystalline silicon film 5 has a thickness of 30 to 100 nm. The layers are sequentially formed by a plasma CVD apparatus with a thickness within the range of.

  Here, the microcrystalline silicon film 4 has a flow rate ratio of H2 gas to SiH4 gas of 10 or more in a parallel plate type plasma CVD apparatus, and pressure, input power, substrate temperature, and electrode-to-electrode conditions that are plasma discharge conditions. It can be obtained by adjusting the distance. In particular, a desired microcrystalline silicon film can be obtained by setting the flow rate ratio of H2 gas to SiH4 gas to 120, the pressure of 800 Pa, and the substrate temperature of 300.degree. Further, instead of H2 gas, Ar gas or SiF4 gas may be used instead of SiH4. In addition, a good microcrystalline silicon film can be produced by an inductively coupled plasma CVD apparatus instead of a parallel plate plasma CVD apparatus.

  Next, in order to form channel layers of the photodetection thin film transistor and the switching thin film transistor, the above-described stacked layers of the non-doped microcrystalline silicon film 4 and the phosphorus-doped microcrystalline silicon film 5 are patterned in an island shape. Further, a metal film is formed by sputtering or the like and patterned to form a source electrode line and a drain electrode line of the switching thin film transistor and an electrode line of the light detection thin film transistor.

  Thereafter, the phosphorus-doped microcrystalline silicon film 5 on the channel portion of the switching thin film transistor and between the electrodes of the light detection thin film transistor is removed by etching (back channel etch type). At this time, the upper surface of the channel layer 4 of the photodetection thin film transistor is damaged by the etching, so that the near infrared light absorption coefficient of the upper surface side portion of the non-doped microcrystalline silicon film constituting the channel layer 4 is slightly reduced. It should be noted that the third embodiment to be described later is to improve this point.

  Next, a protective film 8 composed of a silicon nitride film or a two-layer film of a silicon nitride film and a silicon oxide film is formed.

  Finally, a contact hole is formed on the electrode, and then a pixel electrode 9 made of a transparent electrode is formed, thereby completing a thin film transistor array substrate for a display device incorporating a photosensor made of a photodetection thin film transistor.

  As described above, according to this embodiment, a pixel switching thin film transistor and a photodetection thin film transistor (photosensor), both of which are channel layers made of a microcrystalline silicon film, can be manufactured on the same substrate in the same process. Without increasing the process, high-performance switching thin film transistor (the mobility of a thin film transistor using a microcrystalline silicon film as a channel layer is about 3 to 5 times the mobility of a thin film transistor using an amorphous silicon film as a channel layer) Therefore, the switching characteristics are further improved.) And a thin film transistor for photodetection having sensitivity up to the near-infrared light region can be formed on the same substrate. For this reason, as shown in FIG. 3, a part or all of the vertical scanning circuit and the optical sensor circuit can be formed inside the TFT array substrate by using the microcrystalline silicon TFT. A high-performance thin film transistor array substrate with a built-in photosensor can be realized. By using this thin film transistor array substrate to construct a liquid crystal display device, sensing with near infrared light that is not visible to humans is possible, so near infrared light is used as auxiliary light to assist detection of finger presses, etc. I can do it. For this reason, it is possible to reduce the influence of the scattered light and the external light of the backlight, which is visible light, and it is possible to realize a display device with a built-in photosensor that has fewer malfunctions than the prior art. Especially at night or in a dark room or in a car, the brightness of backlight and external light is low, so it is difficult to sense detection of finger presses using visible light. In the case of this embodiment using near-infrared light as auxiliary light for assisting detection of the above, such a problem does not occur, and in this respect also, the display device with a built-in photosensor of this embodiment It can be said that it is advantageous.

(Embodiment 2)
FIG. 7 is a vertical cross-sectional view of the array substrate of the photosensor built-in display device according to the present embodiment. In the figure, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

  In the first embodiment, the photosensor has a thin film transistor structure. However, as shown in FIG. 7, the photosensor according to the present embodiment has no gate electrode and is similar to the channel layer of the pixel switching thin film transistor. And used as a “photoconductive element” made of a microcrystalline silicon film. An auxiliary light source for detection such as finger pressing is a light source that can emit near-infrared light, and is disposed on the backlight side. Therefore, the photosensor is a photoconductive element based on a change in resistance value due to absorption of near-infrared light that is incident on the photoconductive element made of a microcrystalline silicon film after being reflected by a human finger or the like. A finger press or the like is detected according to a change in voltage between both electrodes 6 and 7 provided at both ends of the element.

  In particular, in the present embodiment, contrary to the normal arrangement, the array substrate of FIG. 7 is disposed on the surface side of the panel of the liquid crystal display device with a built-in optical sensor, and the array substrate is opposed to the array substrate. A counter substrate or a color filter substrate to be bonded to is provided on the back side of the panel of the display device. Therefore, the backlight and the near-infrared auxiliary light source are arranged behind the counter substrate, and a person views the image from the glass substrate 1 side of the array substrate in FIG.

  By adopting such a reverse arrangement of both the substrates, the near-infrared ray radiated from the auxiliary light source and reflected by a human finger or the like is transmitted through the glass substrate 1 on the panel surface and is made of a microcrystalline silicon film. Incident from the lower surface 4FS1 side of the photoconductive element 4 and absorbed by the microcrystalline silicon film. The lower surface 4FS1 of the photoconductive element 4 is a surface that has not been etched by back channel etching in manufacturing the photoconductive element 4, and has no damaged portion. In the case where there is a damaged portion of the microcrystalline silicon film due to such back channel etching, near-infrared light becomes difficult to be absorbed in the damaged portion, and it becomes difficult to extract it as a photocurrent. Accordingly, the near infrared light absorption rate at the surface portion of the lower surface 4FS1 is larger and more uniform than the surface portion of the upper surface etched by the back channel etching. Therefore, by adopting the structure of this embodiment mode, it is possible to improve the decrease in photosensitivity to near-infrared light due to the damage caused by the back channel etching in the manufacturing process described above. In addition, with this structure, near-infrared light to be detected is also incident and absorbed in the portion 4A of the microcrystalline silicon film corresponding to the layer immediately below the electrode portions 6 and 7 of the photoconductive element 4. Therefore, a larger photocurrent can be extracted from the electrode portions 6 and 7 of the photoconductive element 4.

  In the case of this structure, in order to prevent visible light from the backlight from entering the photoconductive element 4, the black matrix of the color filter substrate, which is the counter substrate disposed on the back side of the panel, is used. Shield from light.

(Embodiment 3)
FIG. 8 is a longitudinal sectional view of the array substrate of the display device with a built-in photosensor according to the present embodiment. In the figure, the same reference numerals as those in FIG. 1 denote the same or corresponding parts. The characteristic points will be described below with reference to the drawings.

  The present embodiment relates to the improvement of the first embodiment (see FIG. 1), and the feature thereof is that a channel in which a thin film transistor for light detection is formed on the upper surface of the channel layer 4 of the thin film transistor for light detection. The protective film 10 is provided. Similarly, the switching thin film transistor also includes a channel protective film 10 formed on the upper surface of the channel layer 4.

  Here, in the first embodiment, both the switching thin film transistor and the photodetection thin film transistor have the channel etching type structure.

  However, in this embodiment mode, as shown in FIG. 8, both the switching thin film transistor and the light detection thin film transistor are channel protective thin film transistors. That is, in the manufacturing process of the array substrate shown in FIG. 8, the channel protective film 10 is formed on the upper surface of each channel layer 4 of the switching thin film transistor and the photodetection thin film transistor, and then the phosphorus doped microcrystalline silicon film 5 is formed. Layers and layers of electrodes 6 and 7 are formed. Thereafter, as already described in the first embodiment, the upper surface of the channel protective film 10 is formed so that the phosphorus-doped microcrystalline silicon film 5 and the electrodes 6 and 7 after etching cover the both end portions of the channel protective film 10. Until exposed, the phosphorus-doped microcrystalline silicon film 5 on the channel portion of the switching thin film transistor and between the electrodes of the light detection thin film transistor is removed by etching (back channel etch). At this time, since the channel protective film 10 exists in the present embodiment, the situation that the upper surface side portion of the channel layer 4 of the photodetection thin film transistor is damaged by the etching does not occur.

  As described above, since the back channel etching is performed after the channel protective film 10 is provided in manufacturing the array substrate, the back channel side, that is, the interface side between the channel protective film 10 and the microcrystalline silicon film 4 is used. It is possible to reduce defects (decrease in the absorption coefficient of near-infrared light) in a partial silicon layer. For this reason, the thin film transistor array substrate with a built-in photosensor in FIG. 8 as a finished product can have a photosensor with higher sensitivity than the thin film transistor array substrate with a built-in photosensor shown in FIG.

(Embodiment 4)
The present embodiment relates to the improvement of the second embodiment (see FIG. 7), and the feature is that the unit pixel is formed immediately above the photoconductive element 4 made of a microcrystalline silicon film. And a visible light filter layer made of an amorphous silicon film. Hereinafter, feature points will be described in detail with reference to the drawings.

  Here, FIG. 9 is a longitudinal sectional view of the array substrate of the photosensor built-in display device according to the present embodiment. In the figure, the same reference numerals as those in FIG. 7 denote the same or corresponding parts. The characteristic points will be described below with reference to the drawings.

  As shown in FIG. 9, an amorphous material having a film thickness in the range of 200 nm to 500 nm on the upper surface of the protective film 8 portion directly above the photoconductive element 4 of the second embodiment (see FIG. 7). A visible light filter 11 made of a silicon film is formed.

  As described above, by forming the amorphous silicon film as the visible light filter 11 immediately above the photoconductive element 4, the incident of visible light having a large energy to the photoconductive element 4 is cut, and the photoconductive element 4, only light having a long wavelength of about 650 nm or more (near infrared light or infrared light) reaches (see FIG. 5). Therefore, scattered light of backlight light in the photoconductive element 4 And malfunction due to external light (visible light) or the like can be further reduced.

(Embodiment 5)
The present embodiment relates to the improvement of the fourth embodiment (see FIG. 9). The feature of the present embodiment is that the visible light filter 11 includes each electrode and contact hole formed immediately below each of both ends thereof. It is electrically connected to the light source and functions as a visible light photoconductive element. Hereinafter, the feature points will be described in detail with reference to the drawings.

  Here, FIG. 10 is a longitudinal sectional view showing the configuration of the array substrate of the display device with a built-in optical sensor according to the present embodiment. In the figure, the same reference numerals as those in FIG. 9 denote the same or corresponding parts.

  As shown in FIG. 10, electrodes (not shown) are formed at both ends of the amorphous silicon film 11, and the upper surface portion of the gate insulating film 3 corresponding to the electrodes immediately below the amorphous silicon film 11. The electrodes E1 and E2 are formed on the top. Then, the electrode E1 or E2 corresponding to the electrode (not shown) at each end of the amorphous silicon film 11 is electrically connected by the contact hole 25 formed in the protective film 8. With this configuration, in addition to the near-infrared light photoconductive element formed of the microcrystalline silicon film 4, a visible light photoconductive element formed of the amorphous silicon film 11 is also formed.

  As described above, the photoconductive element of the amorphous silicon film 11 having high sensitivity to visible light and the photoconductive element of the microcrystalline silicon film 4 having high sensitivity to near infrared light are formed in a laminated structure. In addition, it is possible to realize a display device with a built-in optical sensor with fewer malfunctions. In particular, the present embodiment has an advantage that malfunction caused by sunlight can be prevented. That is, when detection by the photoconductive element of the amorphous silicon film 11 is obtained simultaneously with the detection of the microcrystalline silicon film 4 by the photoconductive element, it is not the detection of human fingering or the like, but the visible light and near It is determined that sunlight including infrared light is incident on the optical sensor of the display device with a built-in optical sensor as noise.

(Embodiment 6)
This embodiment is a modification of the above-described first and third embodiments, and the feature thereof is that a part of the signal readout circuit of the photodetection thin film transistor is a thin film transistor made of a microcrystalline silicon film. It is in the point.

  Because of this feature, the built-in photosensor with sensitivity to near-infrared light with a wavelength of 700 nm to 900 nm, which could not be detected by the display device with built-in photosensor that was made of amorphous silicon thin film transistor, was impossible. A display device can be realized. A thin film transistor made of a microcrystalline silicon film having a mobility several times larger than that of amorphous silicon and having a small threshold voltage fluctuation, and in the same process as the pixel switching thin film transistor, A part of the reading circuit can be formed, and the cost and size of the display device can be reduced. Hereinafter, the present embodiment will be described with reference to the drawings.

  FIG. 11 shows a circuit and a system configuration of a photosensor built-in liquid crystal display device incorporating the photosensor described in Embodiment Mode 1 or 3. This circuit and system is a known system, and has an advantage that a signal of an optical sensor can be easily extracted as a binarized signal. However, when a TFT whose channel layer is an amorphous silicon film is used, There is a problem that the sensitivity changes due to the shift of the threshold voltage of the TFT. In addition, the operation of a circuit built in the periphery is slow, and there is a problem that it is difficult to increase the size and the definition.

  In the present embodiment, the optical sensor TFT 19 and the switching pixel TFT 12 described in the first or third embodiment are adopted for this circuit and system. In addition, all the transistors 20 to 22 in the peripheral circuit shown in FIG. 11 are constituted by thin film transistors whose channel layer is made of a microcrystalline silicon film. For this reason, a part of the signal readout circuit of the optical sensor TFT 19 is fabricated on the same substrate as the built-in circuit together with the optical sensor TFT 19 and the switching pixel TFT 12, and the characteristics and reliability of the signal readout circuit of the optical sensor TFT 19 are improved.

(Appendix)
While the embodiments of the present invention have been disclosed and described in detail above, the above description exemplifies aspects to which the present invention can be applied, and the present invention is not limited thereto. In other words, various modifications and variations to the described aspects can be considered without departing from the scope of the present invention.

  For example, a light source capable of emitting near-infrared light in the above wavelength band may be disposed on the upper surface (front surface) side of the panel of the display device. In this case, the optical sensor described in each of the first to fifth embodiments determines whether or not a shadowed portion is generated by a human finger or the like, and the near-infrared light absorbed by entering the optical sensor. Detection is based on the presence or absence of a decrease in the amount of light.

It is a longitudinal cross-sectional view which shows the structure of the TFT array substrate with a built-in optical sensor which concerns on Embodiment 1 of this invention. It is a top view which shows the structure of the TFT array substrate with a built-in optical sensor which concerns on Embodiment 1 of this invention. It is a block diagram which shows the circuit structure of the display apparatus with a built-in optical sensor which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the display apparatus with a built-in optical sensor which concerns on Embodiment 1 of this invention. It is a figure which shows the absorption coefficient of a microcrystal silicon film. It is a figure which shows the spectral sensitivity characteristic of a microcrystal silicon optical sensor. It is a longitudinal cross-sectional view which shows the structure of the TFT array substrate with a built-in optical sensor which concerns on Embodiment 2 of this invention. It is a longitudinal cross-sectional view which shows the structure of the TFT array substrate with a built-in optical sensor which concerns on Embodiment 3 of this invention. It is a longitudinal cross-sectional view which shows the structure of the TFT array substrate with a built-in optical sensor which concerns on Embodiment 4 of this invention. It is a longitudinal cross-sectional view which shows the structure of the TFT array substrate with a built-in optical sensor which concerns on Embodiment 5 of this invention. It is a figure which shows the equivalent circuit of the unit pixel in the TFT array substrate with a built-in optical sensor which concerns on Embodiment 6 of this invention. 6 is a longitudinal sectional view showing a configuration of a photosensor built-in TFT array substrate described in Patent Document 1. FIG. It is a figure which shows the system configuration | structure of the display apparatus with a built-in optical sensor of patent document 1. FIG. It is a figure which shows the system configuration | structure of the display apparatus with a built-in optical sensor of patent document 1. FIG. 6 is a longitudinal sectional view showing a configuration of a photosensor built-in TFT array substrate described in Patent Document 2. FIG.

Explanation of symbols

  1 glass substrate, 2 gate electrode, 3 gate insulating film, 4 non-doped microcrystalline silicon film, 5 phosphorus-doped microcrystalline silicon film, 6 source electrode, 7 drain electrode, 8 protective film, 9 pixel electrode, 10 channel protective film, 11 non Crystalline silicon film visible light filter, 16 common wires, 25 contact holes.

Claims (8)

A display device with a built-in optical sensor comprising an array substrate in which unit pixels are arranged in a matrix,
The unit pixel is
A switching thin film transistor formed on a transparent substrate;
A thin film transistor for light detection formed on the transparent substrate;
A pixel electrode controlled by the switching thin film transistor,
The channel layers of the switching thin film transistor and the light detection thin film transistor are both made of a microcrystalline silicon film,
Photosensor built-in display device. The display device with a built-in optical sensor according to claim 1,
The thin film transistor for light detection is
It comprises a channel protective film formed on the upper surface of the channel layer of the photodetection thin film transistor,
Photosensor built-in display device. The display device with a built-in optical sensor according to claim 1 or 2,
A part of transistors of the signal readout circuit of the photodetection thin film transistor is a thin film transistor made of the microcrystalline silicon film,
Photosensor built-in display device. A display device with a built-in optical sensor comprising an array substrate in which unit pixels are arranged in a matrix,
The unit pixel is
A switching thin film transistor formed on a transparent substrate;
A photoconductive element formed on the transparent substrate;
A pixel electrode controlled by the switching thin film transistor,
The switching thin film transistor and the photoconductive element are both made of a microcrystalline silicon film,
Photosensor built-in display device. The display device with a built-in optical sensor according to claim 4,
The unit pixel is
Further comprising a visible light filter layer made of an amorphous silicon film formed directly above the photoconductive element,
Photosensor built-in display device. The display device with a built-in optical sensor according to claim 5,
The visible light filter layer is electrically connected to each electrode formed immediately below each of both ends thereof through a contact hole, and is used as a visible light photoconductive element,
Photosensor built-in display device. The display device with a built-in optical sensor according to claim 1,
The crystal grain size of the microcrystalline silicon film is 5 nm or more and 100 nm or less, and the ratio of the volume of the amorphous region to the volume of the crystal region of the microcrystalline silicon film is 1/10 to 1/5. To
Photosensor built-in display device. A display device with a built-in optical sensor according to claim 1,
It is provided with a light source including near infrared light disposed on one of the upper surface side and the back surface side of the display device,
Photosensor built-in display device.

Images