Semiconductor device

Abstract

To prevent the decrease in light reflection characteristic and the increase in electric resistance due to oxidation of silver in a semiconductor device including an optical sensor in which silver is used for a cathode of a photoconductive film.SOLUTION: A semiconductor device includes a thin film transistor formed on a substrate 100. An electrode connected electrically to the thin film transistor is formed of a silver film 128. A first indim tin oxide (ITO) film 129 is formed on the silver film. On the first ITO film 129, an alumina (AlOx) film 130 is formed.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a semiconductor device having an optical sensor using a photoelectric conversion element made of an organic material.

Background Art

[0002] Optical sensors using photoelectric conversion are used not only for image recognition but also in fields such as biometric authentication, and their applications are expanding. Photoelectric materials using organic materials are being developed because they can reduce dark current, improve photoelectric conversion efficiency, and add wavelength selectivity.

[0003] As an example of a description of an organic material used as a photoelectric conversion element, Patent Document 1 can be cited. Also, as an example of a description of a film configuration as a photoelectric conversion element using an organic material, Patent Document 2 can be cited.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] A sensor device using a photodiode using an organic photoconductive film (hereinafter, also referred to as an organic photoconductive film diode OPD: Organic Photo Diode) uses a reflective electrode to improve the utilization efficiency of external light. As the reflective electrode, silver with high reflectivity is used. And this silver is used as one electrode of the organic photoconductive film diode. Although a thin film of about 100 nm of silver is used, such a thin film has a high reducing action and binds to oxygen in the air and oxidizes immediately after film formation, resulting in high resistance.

[0006] On the one hand, since the organic photoconductive film material is vulnerable to moisture, it is necessary to block moisture from the atmosphere. Regarding moisture blocking, an aluminum oxide film (hereinafter also referred to as alumina (AlOx)) has excellent properties. Therefore, alumina (AlOx) is laminated and used with silver as the reflective electrode for moisture blocking.

[0007] However, alumina (AlOx) contains oxygen. Also, since alumina (AlOx) is often formed by reactive sputtering, it contains more oxygen. Therefore, silver laminated with alumina (AlOx) is more likely to be further oxidized by oxygen from alumina (AlOx). When silver is oxidized, it becomes highly resistive and not only fails to function as an electrode but also the oxidized silver turns black or transparent and loses its role as a reflective electrode.

[0008] The problem of the present invention is to address the defect caused by the oxidation of the silver film when a laminated film of a silver film and an alumina (AlOx) film is used for one of the electrodes of a photodiode. Note that such a problem is not limited to the case of a photodiode but is the same in, for example, an organic EL display device (OLED) using an organic material.

Means for Solving the Problem

[0009] The present invention solves the above problems, and the main specific means are as follows.

[0010] (1) A semiconductor device in which a thin-film transistor is formed on a substrate, wherein the electrode electrically connected to the thin-film transistor is formed of a silver film, a first ITO film is formed on the silver film, and an alumina (AlOx) film is formed on the first ITO film.

[0011] (2) The semiconductor device has an optical sensor, and the optical sensor includes a photodiode composed of an anode, a photoconductive film, and a cathode on an upper layer of the thin film transistor. The electrode is the anode of the photodiode. The semiconductor device according to (1).

[0012] (3) The semiconductor device according to (2), wherein the photoconductive film is an organic photoconductive film.

[0013] (4) The semiconductor device according to (3), wherein the thickness of the first ITO film is 5 nm to 20 nm.

[0014] (5) The semiconductor device according to (4), wherein the thickness of the silver film is 90 nm to 200 nm.

[0015] (6) The semiconductor device according to (5), wherein the thickness of the alumina (AlOx) film is 10 nm to 50 nm.

[0016] (7) The semiconductor device according to (6), wherein the first ITO film is amorphous.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 4C

Figure 4D

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0018] The content of the present invention will be described below using examples. In Example 1, a photosensor device when receiving light from the lower surface of the sensor array will be described, and in Example 2, a photosensor device when receiving light from the upper surface of the sensor array will be described. Further, the present invention can also be applied to an organic EL display device (OLED) using an organic material as a light-emitting element.

Examples

[0019] FIG. 1 is a plan view of a photosensor device to which the present invention is applied. In FIG. 1, sensor elements are formed in a matrix in the sensor region. The size of the sensor region is, for example, a horizontal diameter xx of 3 cm and a vertical diameter yy of 3 cm. In the sensor region, scanning lines 11 extend in the horizontal direction (x direction) and are arranged in the vertical direction (y direction). Detection lines 12 and power supply lines 13 extend in the vertical direction and are arranged in the horizontal direction. The region surrounded by the scanning line 11 and the detection line 12, or the scanning line 11 and the power supply line 13, is the sensor element. Inside each sensor element, a switching TFT 15 and an organic photoconductive film diode 10 are formed.

[0020] A scanning line driving circuit 20 is arranged laterally outside the sensor region, a power supply circuit 40 is arranged upward, and a detection circuit 30 is arranged downward. The scanning line driving circuit 20 and the detection circuit 30 are formed of TFTs. The scanning lines 11 are sequentially selected from above by a shift register in the scanning line driving circuit 20.

[0021] The power supply line 13 is connected to the anode of each photodiode and extends in the vertical direction, and is connected to the same power supply in the power supply circuit 40 above the sensor region. Then, the anode potential is supplied to the power supply line 13. The detection line 12 is connected to the drain of the switching TFT, and the source of the switching TFT is connected to the cathode of the photodiode 10. The detection line 12 extends downward from each sensor element, and the photocurrent is detected by the detection circuit 30. In FIG. 1, when the sensor element selected by the scanning line 11 is irradiated with light, a photocurrent is generated from the photodiode 10, and this photocurrent is detected by the detection circuit 30 through the detection line 12.

[0022] FIG. 2 is a plan view of each sensor element. In FIG. 2, some electrodes and the like are omitted in order not to complicate the figure. The size of each sensor element is, for example, 50 μm in the horizontal direction x1 and 50 μm in the vertical direction y1. In FIG. 2, the scanning lines 11 extend in the horizontal direction and are arranged in the vertical direction. Also, the power supply line 13 and the detection line 12 extend in the vertical direction and are arranged in the horizontal direction. The cathode 126 of the photodiode, the organic photoconductive film 127, the anode 128, etc. are formed in the region surrounded by the scanning line 11 and the power supply line 13, or the scanning line 11 and the detection line 12.

[0023] Also, the anode electrode 128 is integrally formed over the entire sensor region. That is, there is one anode electrode 128 over the entire sensor region, and a plurality of cathode electrodes 126 overlap this one anode electrode 128.

[0024] The semiconductor film 107 extends in the x direction from the detection line 12 through the through hole 135, bends, and passes under the scanning line 11. At this time, a TFT is formed. In this case, the scanning line 11 serves as the gate electrode of the TFT. The semiconductor film 107 extends in the y direction and is connected at the through hole 123 to the cathode 126 of the photodiode formed of ITO. As described with reference to FIG. 3, the through hole 123 is formed in the thick organic passivation film 122, and thus has a large diameter. An organic photoconductive film 127 is formed on the cathode 126, and an anode 128 is formed thereon by a silver film. Thereby, an organic photoconductive film diode is formed. Also, the organic photoconductive film 127 is integrally formed over the entire sensor region and is not formed in an island shape for each of a plurality of sensor elements in the sensor region. That is, there is one organic photoconductive film 127 over the entire sensor region, and one anode electrode 128 and a plurality of cathode electrodes 126 overlap the one organic photoconductive film 127.

[0025] In the configuration of FIG. 2, as described above, the organic photoconductive film 127 and the anode 128 are formed over the entire sensor region in common for each element. Therefore, in FIG. 2, only the shape of the cathode 126 is depicted within the sensor element, but the organic photoconductive film 127 and the anode 128 are laminated on the cathode 126. More specifically, the organic photoconductive film 127 and the anode electrode 128 are present even between adjacent cathode electrodes 126 in the first direction x and the second direction y, that is, in a region where no cathode electrode 126 is formed. The anode electrode 128 is formed of a silver film 128 having a thickness of about 100 nm, and since the film thickness is small, the resistance as a whole cathode is reduced by connecting to a plurality of power supply lines 13. The power supply line 13 may be laminated on the silver film 128 and extend as it is to the power supply circuit 40, or may extend through a through hole formed in the organic passivation film 122 on the way and extend in the same layer as the drain electrode or the source electrode of the TFT.

[0026] Figure 3 is a cross-sectional view of the optical sensor device of Figure 1. The optical sensor shown in Figure 3 is of a type where light is input from the side of the substrate 100. As shown in Figure 1, outside the sensor region, a driving circuit formed of TFTs is formed. Since polysilicon semiconductors have high mobility, it is advantageous to form the TFTs constituting the driving circuit from polysilicon semiconductors.

[0027] On the other hand, the switching TFTs formed in the sensor region are advantageously formed of an oxide semiconductor (sometimes referred to as OS: Oxide Semiconductor) with low leakage current. Therefore, in this embodiment, a hybrid-type array substrate using both polysilicon semiconductor TFTs and oxide semiconductor TFTs is used. In Figure 3, the left side is polysilicon TFTs for peripheral circuits, and the central part is an organic film photodiode and the switching TFTs therefor.

[0028] For the polysilicon, so-called low-temperature polysilicon obtained by polycrystallizing a-Si with an excimer laser is used. However, even so, since the annealing temperature of the polysilicon semiconductor exceeds the process temperature for forming the oxide semiconductor, first, the polysilicon semiconductor TFTs are formed, and then the oxide semiconductor TFTs are formed. Therefore, first, it is manufactured from the peripheral circuits.

[0029] In Figure 3, a base film 101 made of a laminated film of silicon nitride (SiN) and silicon oxide (SiO) is formed on the glass substrate 100. This is to prevent impurities from the glass substrate 100 from contaminating the polysilicon semiconductor 102 and the oxide semiconductor 107. The thickness of the SiO film is, for example, 200 nm, and the thickness of the SiN film is, for example, 20 nm.

[0030] On top of it, a polysilicon film 102 for the TFT is formed. The polysilicon film 102 is formed by first forming an a-Si film and then converting the a-Si to polysilicon by an excimer laser and patterning it. The thickness of the polysilicon film 102 is, for example, 50 nm. Note that the SiO film, SiN film, and a-Si film, which are the underlying films 101, can be continuously formed by CVD.

[0031] Thereafter, a first gate insulating film 103 is formed of SiO over the polysilicon semiconductor film 102. The thickness of the first gate insulating film 103 is, for example, 100 nm. A first gate electrode 104 is formed of a metal or an alloy on top of it. The first gate electrode 104 is formed of, for example, MoW. Incidentally, the peripheral circuit region and the sensor region are formed simultaneously. At the same time as forming the first gate electrode 104, a light-shielding film 105 made of the same material as the first gate electrode 104 is formed in the portion corresponding to the switching TFT in the sensor region. This light-shielding film 105 can also be used as the bottom gate electrode of the oxide semiconductor TFT formed later.

[0032] A first interlayer insulating film 106 is formed of a laminated film of an SiO film and a SiN film over the first gate electrode 104 and the light-shielding film 105. The thickness of the SiN film is, for example, 300 nm, and the thickness of the SiO film is 200 nm. An oxide semiconductor film 107 is formed on the first interlayer insulating film 106. Examples of the oxide semiconductor include IGZO (Indium Gallium Zinc Oxide), ITZO (Indium Tin Zinc Oxide), ZnON (Zinc Oxide Nitride), IGO (Indium Gallium Oxide), etc. In this embodiment, IGZO is used as the oxide semiconductor.

[0033] Incidentally, in order to maintain the characteristics of the oxide semiconductor, it is important to maintain the amount of oxygen. Therefore, the upper layer of the first interlayer insulating film 106 needs to be an SiO film. This is because SiN supplies hydrogen and reduces the oxide semiconductor. If the SiO film is in contact with the oxide semiconductor film 107, oxygen can be supplied from the SiO film to the oxide semiconductor.

[0034] A drain protection electrode 108 is laminated on the drain region of the oxide semiconductor film 107, and a source protection electrode 109 is formed on the source region. The drain protection electrode 108 and the source protection electrode 109 are formed of metal, and when cleaning the through holes in the polysilicon TFT with hydrofluoric acid (HF), the oxide semiconductor film 107 is prevented from disappearing due to hydrofluoric acid (HF) at the through holes on the oxide semiconductor TFT side.

[0035] A second gate insulating film 110 is formed of an SiO film covering the oxide semiconductor film 107. The SiO film has a thickness of about 100 nm. A gate alumina film 111 is formed on the SiO film, and a second gate electrode 112 is formed thereon, for example, of a MoW alloy. The characteristics of the oxide semiconductor film 107 are stabilized by supplying oxygen to the oxide semiconductor film 107 from the second gate insulating film 110 formed of SiO and the gate alumina film 112.

[0036] A second interlayer insulating film 113 is formed of a laminated film of an SiO film and a SiN film covering the second gate electrode 112. The SiO film is, for example, 300 nm and the SiN film is 100 nm. The SiO film is often arranged closer to the lower side of the oxide semiconductor film 107. After forming the second interlayer insulating film 113, through holes 118 and 119 are simultaneously formed on the polysilicon TFT side of the peripheral circuit, and through holes 120 and 121 are formed on the oxide semiconductor TFT side of the sensor region side.

[0037] The through holes 118 and 119 on the polysilicon TFT side are cleaned with hydrofluoric acid (HF) to remove the oxide film. At this time, in order to prevent hydrofluoric acid (HF) from entering the through holes 120 and 121 on the oxide semiconductor TFT side and disappearing the oxide semiconductor film 107, the drain protection electrode 108 and the source protection metal film 109 are used.

[0038] Corresponding to the through-holes 118 and 119 on the polysilicon TFT side, the first drain electrode 114 and the first source electrode 115 are formed, and corresponding to the through-holes 120 and 121 on the oxide semiconductor TFT side, the second drain electrode 116 and the second source electrode 117 are formed. The second drain electrode 116 is connected to the detection line 12.

[0039] An organic passivation film 122 is formed, for example, of a resin such as acrylic, covering the second interlayer insulating film 113. Since the organic passivation film 122 also serves as a planarization film, it is formed thick to about 2 μm. A through-hole 123 for connecting the source electrode 117 and the cathode 126 of the photodiode is formed in the organic passivation film 122 corresponding to the source electrode 117 of the TFT. Due to the thick thickness of the organic passivation film 122, the diameter of the through-hole 123 becomes large.

[0040] An inorganic passivation film 124 is formed, for example, of SiN with a thickness of about 20 to 100 nm, covering the organic passivation film 122. This is to prevent impurities such as moisture from being released from the organic passivation film 122 and contaminating the organic photoconductive film 127 formed thereon.

[0041] On the inorganic passivation film 124, the cathode electrode 126 is formed of an ITO (Indim Tin Oxide) film, for example, with a thickness of about 50 nm. This ITO film is crystallized by annealing to reduce the electrical resistance. A through-hole 125 is formed in the inorganic passivation film 124 at the portion of the through-hole 123 of the organic passivation film 122 to connect the cathode electrode 126 and the source electrode 117. In the present invention, since ITO is also used on the upper electrode side which is the anode electrode 128 side, for the purpose of distinguishing this, the ITO as the cathode electrode 126 may also be referred to as cathode ITO126.

[0042] An organic photoconductive film 127 is formed on the cathode 126 with a thickness of 300 nm to 500 nm. The organic photoconductive film 127 is formed by sputtering or vacuum evaporation. Since the organic photoconductive film 127 has excellent photoconductive characteristics and can be given wavelength selectivity, it can be used as a so-called biometric sensor such as a vein image.

[0043] An anode electrode 128 is formed of a silver film on the upper side of the organic photoconductive film 127. Silver has excellent reflectivity when it is 90 nm or more. Also, its work function is suitable as the anode electrode 128, and its conductivity is excellent.

[0044] On the other hand, since the organic photoconductive film 127 is vulnerable to impurities such as moisture, it is necessary to block this from the outside. Therefore, an alumina (AlOx) film 130 with a thickness of about 30 nm is formed so as to cover the silver film 128 which is the anode electrode 128. The alumina (AlOx) film 130 is formed by sputtering, but since the film formation rate is very slow, it is formed by reactive sputtering. The alumina (AlOx) 130 formed by reactive sputtering contains a large amount of oxygen. For this purpose, the alumina (AlOx) film preferably has a range of 10 to 50 nm.

[0045] However, since silver has strong reducibility, it takes oxygen from this alumina (AlOx) film 130 and oxidizes. When the silver film 128 oxidizes, its electrical resistance increases and it blackens. And when the oxidation further progresses, it becomes transparent. Then, the silver film 128 loses its role as a reflective electrode.

[0046] The feature of the present invention is to prevent the oxidation of the silver film 128 by the alumina (AlOx) film 130 by forming an ITO film 129 between the silver film (or anode electrode) as the reflective electrode 128 and the alumina (AlOx) film 130 for moisture blocking. The thickness of the alumina (AlOx) film 130 may be a thin film of about 7 nm. When the thickness of the ITO film increases, crystallization progresses and irregularities become prominent on the surface of the ITO. Therefore, even when thickening, about 70 nm is preferable. The film thickness of the ITO film 129 for this purpose is, for example, from 5 nm to 70 nm, more preferably from 7 nm to 20 nm.

[0047] The ITO film 129 can be continuously sputtered without breaking the vacuum in the chamber where the silver film 128 is sputtered. Therefore, it is possible to prevent the silver film 128 from being oxidized by oxygen in the atmosphere. On the other hand, since the alumina (AlOx) film 130 is sputtered in a chamber different from that of the silver film 128, if the ITO film 129 does not exist, the silver film 128 will also be oxidized by oxygen in the atmosphere before the formation of the alumina (AlOx) 130. However, in this embodiment, since the silver film 128 is already covered by the ITO film 130, it is possible to prevent oxidation by oxygen in the atmosphere.

[0048] The ITO film 129 itself also contains oxygen. However, the amount of oxygen supplied from the ITO film 129 is much less than the amount of oxygen supplied from the alumina (AlOx) film 130. The ITO film 129 on the anode side is formed after the organic photoconductive film 127 is formed. Since the organic photoconductive film 127 is vulnerable to heat, the ITO film 129 on the anode side is formed at a low temperature, for example, while maintaining the substrate temperature at about 30 degrees. And since the film thickness is also as thin as about 7 nm, the ITO 129 on the anode side is formed in an amorphous state. It can be presumed that such an amorphous ITO thin film 129 does not supply enough oxygen to oxidize the silver film 128 which is the reflective electrode.

[0049] Note that since the ITO film 129 on the anode side is as thin as about 7 nm, it can also be formed by normal sputtering instead of reactive sputtering using oxygen. From this aspect as well, the amount of oxygen contained in the ITO film 129 can be suppressed more than usual.

[0050] In FIG. 3, an organic protective film 131 is formed of a resin such as acrylic for mechanical protection on the alumina (AlOx) film 130. This organic protective film 131 may be omitted depending on the product.

[0051] FIGS. 4A to 6 are diagrams showing the effects of this embodiment. In this embodiment, on the anode side, an ITO film 129 for preventing oxidation of the silver film 128 is formed between the silver film 128 as a reflective electrode and the alumina (AlOx) film 130 as a moisture block. In such a configuration, FIGS. 4A to 6 verify what kind of effects can be obtained when the ITO film 129 is formed to be about 7 nm, which is a thin film.

[0052] In FIGS. 4A to 4D, they are samples of various film configurations for confirming the effects. In FIGS. 4A to 4D, the film thickness of the ITO film 202 is 7 nm, and the film thickness of the alumina (AlOx) film is 30 nm. Samples with the film thickness of the silver film 201 changed as 100 nm, 200 nm, 300 nm, 400 nm, 500 nm were fabricated. All the films were formed by sputtering.

[0053] FIG. 4A is a cross-sectional view when only the silver film 201 is formed on the glass substrate 200. FIG. 4B is the case where alumina (AlOx) 203 is formed on the silver film 201. FIG. 4C is the case where the ITO film 202 is formed on the silver film 201. FIG. 4D is the case where the ITO film 202 is formed on the silver film 201 and the alumina (AlOx) film 203 is formed thereon, which is the film configuration in this embodiment.

[0054] Figure 5 shows the formation conditions of the ITO film 202 used for the sample. The ITO film 202 is formed to a thickness of 7 nm by sputtering, and the feature is that the sample substrate is maintained at 30 degrees. That is, it is considered in view of the heat-resistant temperature of the organic photoconductive film in Figure 3. Also, the oxygen flow rate is 0.05 sccm (standard cubic centimeter per minute), which is very small compared to the argon (Ar) flow rate of 140 sccm. The ITO film formed under such conditions is considered to be amorphous and have a small oxygen content.

[0055] In FIGS. 4B to 4D, the silver film 201 and the ITO film 202 are continuously formed in the same chamber, and the alumina (AlOx) film 203 is formed by sputtering the substrate 200 on which the ITO film has been formed once exposed to the atmosphere in another chamber. Since the oxidation state of the silver film 201 is significantly manifested in the electrical resistance, the oxidation state of the silver film 201 was measured by measuring the sheet resistance of the silver film 201.

[0056] After forming the films of FIGS. 4A to 4D, the sheet resistance of the silver film 201 was measured using Lowlesta (product name). Lowlesta measures the sheet resistance using four needles, and since the needles penetrate the alumina (AlOx) film 203 and the like, which are surface insulators, the sheet resistance of the silver film 201 can be measured. If the silver film 201 is oxidized, its sheet resistance becomes very large.

[0057] Figure 6 is a graph showing the evaluation results. In Figure 6, the horizontal axis is the film thickness of the silver film 201, and the vertical axis is the sheet resistance of the silver film 201. Since the resistance of the silver film 201 changes greatly due to oxidation, the vertical axis is on a logarithmic scale. For the cases where the film thickness of the silver film 201 is 100 nm, 200 nm, and 300 nm, all of the samples 4A to 4D were prepared and evaluated. For the cases where the film thickness of the silver film 201 is 400 nm and 500 nm, only the samples 4A and 4B were prepared and evaluated. The resistance values were measured immediately after film fabrication.

[0058] In FIG. 6, A corresponds to sample 4A, B corresponds to sample 4B, C corresponds to sample 4C, and D corresponds to sample 4D. When the film thickness of the silver film 201 is 100 nm, the resistance of sample B in which the alumina (AlOx) film 203 is laminated on the silver film 201 is 9×10 6 which is very large compared to other samples. That is, it can be seen that the silver film 201 has been oxidized by alumina (AlOx) throughout the layer thickness direction.

[0059] On the other hand, for sample A which is only the silver film 201, sample B in which the ITO film 202 is laminated on the silver film 201, and sample D in which the ITO film 202 and the alumina (AlOx) film 203 are laminated on the silver film 201, there is almost no difference in the resistance values. In particular, when focusing on sample B and sample D, it can be seen that just by having the ITO film 202 with a film thickness of 7 nm present between the silver film 201 and the alumina (AlOx) film 203, the influence of the alumina (AlOx) film 203 with a film thickness of 30 nm on the oxidation of the silver film 201 can be almost eliminated.

[0060] This tendency is the same when the film thickness of the silver film 201 is 200 nm. As shown in sample B, even when the film thickness of the silver film 201 is 200 nm, the sheet resistance is almost the same as when the film thickness is 100 nm. That is, it can be seen that the influence of the alumina (AlOx) film 203 extends to a film thickness of about 200 nm of the silver film 201 and oxidizes the silver.

[0061] On the other hand, when focusing on samples A, C, and D, when the thickness of the silver film 201 is 200 nm, the resistance of the silver film 201 has become almost half compared to when the thickness of the silver film 201 is 100 nm (the vertical axis in FIG. 6 is on a logarithmic scale). Therefore, it can be seen that samples A, C, and D are hardly oxidized.

[0062] When the silver film thickness reaches 300 nm, even in Sample B, the sheet resistance value of the silver film 201 has decreased to the same order as that of the other Samples A, C, and D. That is, it can be seen that the influence of the 30-nm-thick alumina (AlOx) film 203 does not reach up to about 300 nm of the silver film 201. Therefore, it can be seen that the influence of the 30-nm-thick alumina (AlOx) film 203 extends from the interface between the silver film 201 and the alumina (AlOx) film 203 to about 200 nm to 300 nm.

[0063] On the other hand, when comparing Sample C and Sample D, there is almost no difference in the sheet resistance of the silver film 201. That is, the presence of the ITO film 202 with a thickness of about 7 nm between the silver film 201 and the alumina (AlOx) film 203 can almost eliminate the influence of the alumina (AlOx) film 203 on the silver film 201.

[0064] When the film thickness of the silver film 203 is 400 nm and when the film thickness of the silver film 203 is 500 nm, only Samples A and B are measured. As the film thickness of the silver film 201 increases, the influence of the alumina (AlOx) film 203 laminated on the surface of the silver film 203 becomes smaller. However, in actual products, forming a silver film 201 with a thickness of 300 nm or more is disadvantageous in terms of cost. In actual products, the film thickness of the silver film 103 is 200 nm or less, and more preferably, it is used in the range of 90 nm or more and 120 nm or less.

[0065] In such a film thickness range of the silver film 202, forming the ITO film 202 between the silver film 201 and the alumina (AlOx) film 203 is very effective. With this configuration, it is possible to realize an optical sensor using an organic photoconductive film having excellent reflection characteristics and high reliability.

[0066] In the above description, the organic photoconductive film and the cathode, that is, the silver film are formed commonly over the entire sensor region. However, the same applies when the organic photoconductive film or the cathode is formed for each individual sensor element. Also, in the above description, the case where a thin film of ITO is disposed between the silver film and the alumina (AlOx) film has been described. However, the same effect can be obtained for transparent oxide conductive films such as AZO (Antimony Zinc Oxide) and IZO (Indium Zinc Oxide) in addition to ITO.

Example

[0067] The optical sensor of Example 1 is of the type in which light L is incident from the side of the substrate 100 in FIG. 3. On the other hand, there is also an optical sensor of the type in which light is incident from the opposite side of the substrate 100, that is, from the side of the upper electrode 128 of the photoconductive film 127. When light is incident from the side of the upper electrode 128, a reflective film is formed on the side of the lower electrode 126, and the upper electrode 128 becomes a transparent electrode. The configuration in which light is incident from the side of the upper electrode 128 is advantageous in terms of space because a switching TFT or a driving TFT can be formed between the lower electrode 126 and the substrate 100.

[0068] By the way, silver becomes transmissive to visible light when it forms a thin film with a film thickness of 50 nm or less, particularly 30 nm or less. By utilizing this property, it is possible to realize an optical sensor in which light is incident from the side of the upper electrode 128 (hereinafter also referred to as the upper light incident type) without changing the basic structure of the optical sensor described in Example 1.

[0069] Figure 7 is a cross-sectional view of the organic photodiode portion in Example 2. Since the configurations of the switching TFT and the driving TFT are the same as those described in FIG. 3, only the organic photodiode portion is shown in FIG. 7. In FIG. 7, an inorganic passivation film 124 is formed, for example, of a SiN film with a thickness of 100 nm on the organic passivation film 122. A reflective film 150 is formed of silver, aluminum, an aluminum alloy, or the like with a thickness of about 100 nm on the inorganic passivation film 124. A cathode 126 is formed of an ITO film with a thickness of about 50 nm thereon. The difference from FIG. 3 of Example 1 is that a reflective film 150 made of metal is formed under the cathode 126.

[0070] Similar to FIG. 3, an organic photoconductive film 127 is formed with a thickness of 300 nm to 500 nm on the cathode 126. An anode 128 is formed of a silver film on the organic photoconductive film 127. In FIG. 7, the silver film as the anode 128 does not act as a reflective electrode but needs to transmit light. Therefore, the film thickness of the silver film 128 is 50 nm or less, preferably 20 nm to 30 nm. When the silver film reaches this thickness, it has a transmittance comparable to or higher than that of ITO.

[0071] An ITO film 129 for preventing silver oxidation is formed with a thickness of about 7 nm on the anode 128 made of the silver film. The ITO film 129 is formed continuously with the silver film 128 by low-temperature sputtering. Similar to that described in Example 1, this ITO film 129 is an amorphous film. However, in the configuration of FIG. 7, in order to prevent light attenuation, the film thickness of this ITO film 129 is preferably kept small, and a more suitable film thickness is 5 nm to 20 nm.

[0072] Forming an alumina (AlOx) film 130, for example, about 10 nm to 50 nm thick on the ITO film 129 is the same as in Example 1. This is to prevent the organic photoconductive film from external moisture and the like. In the configuration of FIG. 7, since this alumina film 130 also does not attenuate light, a more suitable range is 10 nm to 30 nm. Since the oxygen from the alumina film 130 is blocked by the ITO film 129, it does not reach the cathode 128, and the silver film 128 is not oxidized and can maintain its conductivity.

[0073] Although the silver film 128 is thin, as shown in FIGS. 1 and 2, since the power line 13 extends in the longitudinal direction of the sensor region, the potential drop of the cathode 128 can be prevented. That is, the thin silver film 128 only needs to act as a conductive film only in each sensor element. Therefore, an increase in the resistance value due to thinning of the silver film 128 is not a substantial problem as long as the silver film 128 is not oxidized.

[0074] Thus, by forming the ITO thin film 129 between the silver film 128 as the anode and the alumina (AlOx) 130 for moisture blocking, oxidation of the silver thin film 128 can be prevented, and a photosensor having an upper surface incident light type organic photoconductive film can be realized.

[0075] In the above description, a photosensor using an organic photoconductive film has been described. However, the present invention is not limited to this, and can also be applied to other photosensors when silver is used as a cathode or an anode. Further, in the above, the present invention has been described for a photosensor using an organic photoconductive film. However, the present invention is not limited to this, and can also be used for an organic EL display device using an organic EL film and the like.

Explanation of Reference Numerals

[0076] 10… Organic photodiode, 11… Scanning line, 12… Detection line, 13… Power supply line, 15… TFT, 20… Scanning line drive circuit, 30… Detection circuit, 40… Power supply circuit, 100… Substrate, 101… Underlayer film, 102… Polysilicon semiconductor film, 103… First gate insulating film, 104… First gate electrode, 105… Light-shielding film, 106… First interlayer insulating film, 107… Oxide semiconductor film, 108… Drain protection electrode, 109… Source protection electrode, 110… Second gate insulating film, 111… Gate alumina film, 112… Second gate electrode, 113… Second interlayer insulating film, 114… First drain electrode, 115… First source electrode, 116… Second drain electrode, 117… Second source electrode, 118… First through-hole, 119… Second through-hole, 120… Third through-hole, 121… Fourth through-hole, 122… Organic passivation film, 123… Fifth through-hole, 124… Inorganic passivation film, 125… Sixth through-hole, 126… Cathode, 127… Organic photoconductive film, 128… Anode (silver film), 129… ITO film, 130… Alumina (AlOx) film, 131… Organic protective film, 135… Through-hole, 200… Sample substrate, 201… Sample silver (Ag) film, 202… Sample ITO film, 203… Sample alumina (AlOx) film, L… Light

Claims

1. A semiconductor device having a thin film transistor formed on a substrate, the semiconductor device has a photosensor, the optical sensor includes, above the thin film transistor, a photodiode configured of an upper electrode, a photoconductive film, a lower electrode, and a reflective film; the optical sensor detects light from the upper electrode side, the upper electrode is formed of a silver film, a first ITO film is formed on the silver film, and an alumina (AlOx) film is formed on the first ITO film; The thickness of the silver film is 50 nm or less, the lower electrode is formed of a second ITO film, The semiconductor device is characterized in that the reflective film is formed under the lower electrode.

2. 2. The semiconductor device according to claim 1, wherein the first ITO film has a thickness of 5 nm to 20 nm.

3. 2. The semiconductor device according to claim 1, wherein the thickness of the silver film is 20 nm to 30 nm.

4. 2. The semiconductor device according to claim 1, wherein the thickness of the alumina (AlOx) film is 10 nm to 50 nm.

5. 3. The semiconductor device according to claim 2, wherein the first ITO film is amorphous.

6. A semiconductor device having a thin film transistor formed on a substrate, the semiconductor device has a photosensor, the optical sensor includes, above the thin film transistor, a photodiode configured of an upper electrode, a photoconductive film, a lower electrode, and a reflective film; the optical sensor detects light from the upper electrode side, the upper electrode is formed of a silver film, and a first ITO film is formed on the silver film; The thickness of the silver film is 50 nm or less, the lower electrode is formed of a second ITO film, The semiconductor device is characterized in that the reflective film is formed under the lower electrode.

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