Patent ID: 12213329

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The contents of the present invention are described using embodiments below. In Embodiment 1, an optical sensor device for receiving light from a lower surface of a sensor array is described, and in Embodiment 2, an optical sensor device for receiving light from an upper surface of a sensor array is described. Further, the present invention is applicable to an organic EL display device (OLED) using an organic material as a light-emitting element.

Embodiment 1

FIG.1is a plan view of an optical sensor device to which the present invention is applied. InFIG.1, sensor elements are formed in a matrix in the sensor region. For example, the sensor area has a lateral diameter xx of 3 cm and a vertical diameter yy of 3 cm. In the sensor region, scanning lines11extend in the horizontal direction (x-direction) and are arranged in the vertical direction (y-direction). A detection line12and a power supply line13extend in the vertical direction and are arranged in the horizontal direction. A region surrounded by a scanning line11and a detection line12, or a region surrounded by a scanning line11and a power line13constitutes a sensor element. In each sensor element, a switching TFT15and an organic photoconductive film diode10are formed.

A scanning line driving circuit20is disposed in the lateral direction outside the sensor region, a power supply circuit40is disposed in the upward direction, and a detection circuit30is disposed in the downward direction. The scanning line driving circuit20and the detection circuit30are formed of TFTs. The scanning line11is sequentially selected from the upper direction by the shift register in the scanning line driving circuit20.

The power supply line13is connected to an anode of each photodiode, extends in the vertical direction, and is connected to the same power supply in the power supply circuit40above the sensor region. Then, an anode potential is supplied to the power supply line13. The detection line12is connected to the drain of the switching TFT, and the source of the switching TFT is connected to the cathode of the photodiode10. A detection line12extends downward from each sensor element, and a photocurrent is detected in the detection circuit30. InFIG.1, when light is applied to the sensor element selected by the scanning line11, a photocurrent is generated from the photodiode10, and this photocurrent is detected by the detection circuit30through the detection line12.

FIG.2is a plan view of each sensor element. In order not to complicate the drawing, some electrodes or the like are omitted fromFIG.2. The size of each sensor element is, for example, 50 μm in the lateral direction x1and 50 μm in the vertical direction y1. In FIG.2, the scanning lines11extend in the horizontal direction and are arranged in the vertical direction. Further, the power supply line13and the detection line12extend in the vertical direction and are arranged in the horizontal direction. A cathode126of a photodiode, an organic photoconductive film127, an anode128, and the like are formed in a region surrounded by a scanning line11, a power supply line13, or a scanning line11and a detection line12.

Further, the anode electrode128is integrally formed over the entire sensor region. In other words, one anode electrode128is provided over the entire sensor region, and a plurality of cathode electrodes126overlap the one anode electrode128.

The semiconductor film107extends in the x direction from the detection line12through the through hole135, then bends, and then passes under the scan line11. At this time, a TFT is formed. In this case, the scanning line11becomes the gate electrode of the TFT. The semiconductor film107extends in the y direction and is connected to the cathode126of the photodiode formed of ITO in the through hole123. As described inFIG.3, the through hole123is formed in the thick organic passivation film122, therefore the diameter of the through hole123is large. An organic photoconductive film127is formed on the cathode126, and an anode128is formed thereon by a silver film. Thus, an organic photoconductive film diode is formed. Also, the organic photoconductive film127is integrally formed on the entire surface of the sensor region, and is not formed in an island shape for each of the plurality of sensor elements in the sensor region. In other words, one organic photoconductive film127is provided on the entire sensor area, and one anode electrode128and a plurality of cathode electrodes126overlap the one organic photoconductive film127.

In the configuration shown inFIG.2, as described above, the organic photoconductive film127and the anode128are formed on the entire surface of the sensor region in common with the respective elements. Accordingly, inFIG.2, although only the shape of the cathode126is illustrated in the sensor element, the organic photoconductive film127and the anode128are stacked on the cathode126. More specifically, the organic photoconductive film127and the anode electrode128exist in the region between the cathode electrodes126adjacent to each other in the first direction x and the second direction y, that is, in the region where the cathode electrode126is not formed. Since the anode electrode128is formed of a silver film128of small thickness of about 100 nm, the resistance of the entire cathode is reduced by being connected to a plurality of power supply lines13. The power supply line13may be stacked on the silver film128and extend to the power supply circuit40as it is, or may extend in the same layer as the drain electrode or the source electrode of the TFT via a through hole formed in the organic passivation film122to the power supply circuit40.

FIG.3is a cross-sectional view of the optical sensor device ofFIG.1; In the optical sensor shown inFIG.3, light is input from the substrate100side. As shown inFIG.1, a driving circuit formed of a TFT is formed outside the sensor region. Since a polysilicon semiconductor has a large mobility, it is advantageous that the TFT constituting the drive circuit is formed of a polysilicon semiconductor.

On the other hand, it is advantageous that the switching TFT formed in the sensor region is formed of an oxide semiconductor (sometimes referred to as an OS: Oxide Semiconductor) having a small leakage current. Therefore, in this embodiment, a hybrid array substrate using both of a polysilicon semiconductor TFT and an oxide semiconductor TFT is used. InFIG.3, the left side is a polysilicon TFT for a peripheral circuit, and the central portion is an organic film photodiode and a switching TFT therefor.

Polysilicon is a so-called low-temperature polysilicon in which a-Si (amorphous Silicon) is poly-siliconized by an excimer laser. Nevertheless, since an annealing temperature of a polysilicon semiconductor exceeds a process temperature for forming an oxide semiconductor, a polysilicon semiconductor TFT is formed at first, and then an oxide semiconductor TFT is formed. Thus, a peripheral circuit is manufactured first.

InFIG.3, a base film101made of a laminated film of silicon nitride (SiN) and silicon oxide (SiO) is formed on a glass substrate100. This is for preventing impurities from the glass substrate100from contaminating the polysilicon semiconductor102and the oxide semiconductor107. The thickness of the SiO film is, for example, 200 nm, and the thickness of the SiN film is, for example, 20 nm.

On top of this, a polysilicon film102is formed. In the polysilicon film102, an a-Si film is first formed, and then a-Si is converted into polysilicon by an excimer laser and patterned. The thickness of the polysilicon film102is, for example, 50 nm. Note that the SiO film and the SiN film, serving as the base film101, and the a-Si film can be continuously formed by CVD.

Thereafter, the first gate insulating film103is formed of SiO covering the polysilicon semiconductor film102. A thickness of the first gate insulating film103is, for example, 100 nm. Then, a first gate electrode104is formed on the first gate insulating film103by metal or metal alloy. The first gate electrode104is formed of MoW, for example. Incidentally, the peripheral circuit region and the sensor region are formed simultaneously. At the same time as forming the first gate electrode104, a light shielding film105is formed of the same material as the first gate electrode104in a portion corresponding to the switching TFT in the sensor region. This light shielding film105can be used as a bottom gate electrode of an oxide semiconductor TFT to be formed later.

A first interlayer insulating film106is formed of a stacked film of an SiO film and an SiN film covering the first gate electrode104and the light shielding film105. For example, the SiN film has a thickness of 300 nm and the SiO film has a thickness of 200 nm. An oxide semiconductor film107is formed over the first interlayer insulating film106. Examples of the oxide semiconductor include IGZO (Indium Gallium Zinc Oxide), ITZO (Indium Tin Zinc Oxide), ZnON (Zinc Oxide Nitride), and IGO (Indium Gallium Oxide). In this embodiment, IGZO is used as an oxide semiconductor.

In order to maintain characteristics of an oxide semiconductor, it is important to maintain an oxygen amount. Therefore, the upper layer of the first interlayer insulating film106needs to be a SiO film. This is because SiN supplies hydrogen to reduce the oxide semiconductor. If the SiO film is in contact with the oxide semiconductor film107, oxygen can be supplied from the SiO film to the oxide semiconductor.

A drain protective electrode108is stacked on a drain region of the oxide semiconductor film107, and a source protective electrode109is formed on a source region thereof. The drain protection electrode108and the source protection electrode109are formed of a metal, and prevent the oxide semiconductor film107from being lost by hydrofluoric acid (HF) in the through holes on the oxide semiconductor TFT side when the through holes in the polysilicon TFT are cleaned with the hydrofluoric acid (HF).

A second gate insulating film110is formed of a SiO film covering the oxide semiconductor film107. The thickness of the SiO film is about 100 nm. A gate alumina film111is formed on the SiO film, on which a second gate electrode112is formed, for example, of a MoW alloy. By supplying oxygen to the oxide semiconductor film107from the second gate insulating film110formed of SiO and the gate alumina film112, the characteristics of the oxide semiconductor film107are stabilized.

A second interlayer insulating film113is formed of a stacked film of a SiO film and a SiN film covering the second gate electrode112. For example, the SiO film is 300 nm and the SiN film is 100 nm. In many cases, a SiO film is disposed on the lower side closer to the oxide semiconductor film107. After forming the second interlayer insulating film113, through holes118and119are formed on the polysilicon TFT side of the peripheral circuit, and through holes120and121are simultaneously formed on the oxide semiconductor TFT side on the sensor region side.

The through-holes118and119on the side of the polysilicon TFT are subjected to hydrofluoric acid (HF) cleaning in order to remove the oxide film. At this time, hydrofluoric acid (HF) is also introduced into the through holes120and121on the oxide semiconductor TFT side; to countermeasure the hydrofluoric acid (HF), the drain protective electrode108and the source protective electrode109, which are formed from metal, are used in order to prevent the oxide semiconductor film107from being lost.

A first drain electrode114and a first source electrode115are formed corresponding to the through holes118and119on the polysilicon TFT side; a second drain electrode116and a second source electrode117are formed corresponding to the through holes120and121on the oxide semiconductor TFT side. The second drain electrode116is connected to the detection line12.

An organic passivation film122is formed of, for example, acrylic resin covering the second interlayer insulating film113. Since the organic passivation film122also serves as a planarization film, it is formed to have a thickness of about 2 μm. Through hole123for connecting the source electrode117and the cathode126of the photodiode is formed in the organic passivation film122corresponding to the source electrode117of the TFT. Since the thickness of the organic passivation film122is large, the diameter of the through hole123is also large.

An inorganic passivation film124is formed to a thickness of about 20 to 100 nm, for example, with SiN covering the organic passivation film122. Impurities such as moisture are released from the organic passivation film122; the inorganic passivation film124prevents the organic photoconductive film127, formed on upper side, from being contaminated.

On the inorganic passivation film124, a cathode electrode126is formed by an ITO (Indium Tin Oxide) film to a thickness of, e.g., about 50 nm. The ITO film is crystallized by annealing to reduce electric resistance. Through holes125are formed in the inorganic passivation film124at the through holes123of the organic passivation film122to connect the cathode electrode126with the source electrode117. In the present invention, ITO is also used for the upper electrode side, which is the anode electrode128side; therefore, the ITO as the cathode electrode126is sometimes referred to as cathode ITO126in order to distinguish it from the anode side TFT.

An organic photoconductive film127is formed on the cathode126with a thickness of 300 to 500 nm. The organic photoconductive layer127is formed by sputtering or vacuum evaporation. Since the organic photoconductive film127has a wavelength selectivity as well as superior photoconductive characteristics, it can be used as a so-called bio-recognition sensor, e.g. for vein images.

An anode electrode128is formed of a silver film on the organic photoconductive film127. Silver has an excellent reflectivity when it becomes 90 nm or more. Also, the work function is suitable as the anode electrode128, and the conductivity is also excellent.

On the other hand, since the organic photoconductive film127is vulnerable to impurities such as moisture and the like, it is necessary to block it from outside, therefore, the alumina (AlOx) film130of a thickness of approximately 30 nm is formed to cover the silver film128which is an anode electrode128. The alumina (AlOx) film130is formed by sputtering, however, film formation rate is very low; thus, a reactive sputtering is used. Alumina (AlOx)130formed by reactive sputtering contains a large amount of oxygen. Incidentally, for the purpose of blocking moisture and the like, the alumina (AlOx) film preferably has a thickness of 10 to 50 nm.

However, since silver has strong reducibility, oxygen is removed from the alumina (AlOx) film130and the silver film128is oxidized. When the silver film128is oxidized, electric resistance increases and blackening occurs. Further, when the oxidation is further progressed, the silver film is made transparent. Then, the silver film128does not serve as a reflective electrode.

A feature of the present invention is to prevent oxidation of the silver film128by the alumina (AlOx) film130by forming an ITO film129between the silver film (or anode electrode) as the reflective electrode128and an alumina (AlOx) film130for moisture block. The thickness of the alumina (AlOx) film130may be about 7 nm. As the thickness of the ITO film increases, crystallization proceeds, and unevenness becomes conspicuous on the surface of ITO, and therefore, even when the thickness is increased, the thickness is preferably about 70 nm. The thickness of the ITO film129for this purpose is, for example, from 5 to 70 nm, and more preferably from 7 to 20 nm.

The ITO film129can be continuously sputtered without breaking the vacuum in a chamber in which the silver film128is sputtered. Therefore, it is possible to prevent the silver film128from being oxidized by oxygen in the atmosphere. On the other hand, since the alumina (AlOx) film130is sputtered in a separate chamber from the silver film128, if the ITO film129is not present, the silver film128is oxidized even by oxygen in the atmosphere before the formation of the alumina (AlOx)130. However, in this embodiment, since the silver film128is already covered with the ITO film130, oxidation due to oxygen in the atmosphere can be prevented.

The ITO film129itself also contains oxygen. However, the amount of oxygen supplied from the ITO film129is much smaller than that from the alumina (AlOx) film130. Note that the ITO film129on the anode side is formed after the organic photoconductive film127is formed. Since the organic photoconductive film127is vulnerable to heat, the ITO film129on the anode side is formed at a low temperature, e.g., at a substrate temperature of about 30 degrees Celsius. Since the film thickness is also as thin as about 7 nm, the ITO129on the anode side is formed in an amorphous state. It can be assumed that such an amorphous ITO thin film129does not supply oxygen which oxidizes the silver film128as a reflective electrode.

Since the ITO film129on the anode side has a thin film thickness of about 7 nm, it can be formed by ordinary sputtering rather than by reactive sputtering using oxygen. Also in this respect, the amount of oxygen contained in the ITO film129can be suppressed more than usual.

InFIG.3, an organic protective film131is formed of a resin such as acrylic for mechanical protection on an alumina (AlOx) film130. The organic protective film131may be omitted depending on a product.

FIGS.4A to6show the effects of the present embodiment. In this embodiment, an ITO film129for preventing the oxidation of the silver film128is formed between the silver film128as a reflective electrode and an alumina (AlOx) film130as a moisture block on the anode side. In such a configuration,FIG.4AtoFIG.6show how an effect can be obtained when the ITO film129is formed to have a thickness of about 7 nm.

FIGS.4A to4Dshow samples of various membrane configurations for confirming the effect. InFIGS.4A to4D, the film thickness of the ITO film202is 7 nm, and the thickness of the alumina (AlOx) film is 30 nm. As a film thickness of the silver film201, a sample whose thickness was changed like a 100 nm, 200 nm, 300 nm, 400 nm, 500 nm was prepared. All of the films are formed by sputtering.

FIG.4Ais a cross-sectional view of a case where only a silver film201is formed on a glass substrate200.FIG.4Bshows a case where alumina (AlOx) film203is formed on the silver film201.FIG.4Cshows a case where an ITO film202is formed on the silver film201.FIG.4Dshows a case where an ITO film202is formed on a silver film201and an alumina (AlOx) film203is formed thereon, which is the film structure according to embodiment 1.

FIG.5shows the condition for forming the ITO film202used for the sample. The ITO film202is formed to a thickness of 7 nm by sputtering, and the characteristic is that the sample substrate is maintained at 30 degrees Celsius. In other words, the temperature of the organic photoconductive film inFIG.3is taken into consideration. Further, the oxygen flow rate is 0.05 sccm (standard cubic centimeter per minute) and is very small compared with an argon (Ar) flow rate of 140 sccm. It is considered that the ITO film formed under such conditions is amorphous and has a small oxygen content.

InFIGS.4B to4D, the silver film201and the ITO film202are successively formed in the same chamber, however, the alumina (AlOx) film203was formed by exposing the substrate200on which an ITO film is formed to an atmosphere and then, sputtering the alumina (AlOx) in another chamber. Since the state of oxidation of the silver film201appears remarkably in electric resistance, the state of oxidation of the silver film201is measured by measuring the sheet resistance of the silver film201.

After forming the films ofFIGS.4A to4D, the sheet resistance of the silver film201was measured by Lowlesta (Product Name). A Lowlesta is used for measuring the sheet resistance using 4 needles, and an alumina (AlOx) film203, which is an insulating material on the surface, is penetrated by a needle. Thus, the sheet resistance of the silver film201can be measured. If the silver film201is oxidized, its sheet resistance becomes very large.

FIG.6is a graph showing an evaluation result. InFIG.6, the horizontal axis represents the thickness of the silver film201, and the vertical axis represents the sheet resistance of the silver film201. Since the resistance of the silver film201largely changes due to oxidation, the vertical axis is a log scale. In the case where the film thickness of the silver film201was 100 nm, 200 nm, 300 nm, all of the samples4A to4D were prepared and evaluated, and when the thickness of the silver film201was 400 nm and 500 nm, only samples4A and4B were prepared and evaluated. The resistance value was measured immediately after film fabrication.

InFIG.6, A corresponds to sample4A, B corresponds to sample4B, C corresponds to sample4C, and D corresponds to sample4D. When the thickness of the silver film201is 100 nm, a sample B in which an alumina (AlOx) film203is stacked on the silver film201has a resistance of 9×106, and is much larger than that of other samples. In other words, it is understood that the silver film201has been oxidized by alumina (AlOx) over the entire thickness direction.

On the other hand, there is only little difference in resistance among the sample A, which is only the silver film201, the sample B, in which the ITO film202is laminated on the silver film201, and the sample D, in which the ITO film202and the alumina (AlOx) film203are laminated on the silver film201. In particular, attention is given to Sample B and sample D, and it is understood that the effect of oxidation of the silver film201by the alumina (AlOx) film203having a thickness of 30 nm is almost eliminated only by disposing the ITO film202having a film thickness of 7 nm between the silver film201and the alumina (AlOx) film203.

This tendency is the same even when the thickness of the silver film201is 200 nm. As shown in Sample B, even when the film thickness of the silver film201is 200 nm, the sheet resistance is substantially the same as in the case where the film thickness is 100 nm. In other words, it is understood that the effect of the alumina (AlOx) film203to oxidize the silver reaches to a thickness of approximately 200 nm of the silver film201.

On the other hand, when attention is paid to the samples A, C, and D, when the thickness of the silver film201is 200 nm, the resistance of the silver film201is about half of that when the thickness of the silver film201is 100 nm (note the vertical axis ofFIG.6is a log scale). Thus, it can be seen that Samples A, C, and D are hardly oxidized.

When the film thickness of silver is 300 nm, the sheet resistance value of the silver film201decreases to almost the same level as that of the other samples A, C, and D even in Sample B. In other words, it is understood that the influence of the alumina (AlOx) film203having a thickness of 30 nm does not reach about 300 nm of the silver film201. Accordingly, it is understood that the influence of the alumina (AlOx) film203having a thickness of 30 nm extends from the interface between the silver film201and the alumina (AlOx) film203to about 200 to 300 nm.

On the other hand, when Sample C and Sample D are compared with each other, there is little difference in the sheet resistance of the silver film201. In other words, since an ITO film203of about 7 nm is present between the silver film201and the alumina (AlOx) film203, it is possible to almost eliminate the influence of the alumina (AlOx) film203on the silver film201.

When the thickness of the silver film203is 400 nm and the thickness of the silver film203is 500 nm, only the samples A and B are measured. As the thickness of the silver film201increases, the influence of the alumina (AlOx) film203stacked on the surface of the silver film203becomes small. However, in actual products, forming a silver film201of 300 nm or more is disadvantageous in terms of cost. In an actual product, the thickness of the silver film103is 200 nm or less, more preferably the thickness of the silver film103is between 90 and 120 nm.

In such a range of thickness of the silver film202, it is very effective to form an ITO film202between the silver film201and the alumina (AlOx) film203. With this configuration, it is possible to realize an optical sensor using an organic photoconductive film having excellent reflection characteristics and high reliability.

In the above description, the organic photoconductive film and the anode, i.e., the silver film, are commonly formed in the entire sensor region, but the same applies to the case where the organic photoconductive film or the anode is formed for each of the individual sensor elements. Further, in the above description, a case has been described in which a thin film of ITO is disposed between a silver film and an alumina (AlOx) film, but a similar effect can be obtained for a transparent oxide film such as AZO (Antimony Zinc Oxide) or IZO (Indium Zinc Oxide) instead of ITO.

Embodiment 2

In the optical sensor of Embodiment 1, light L is incident from the substrate100side inFIG.3. On the other hand, there is an optical sensor of a type in which light is incident on the opposite side of the substrate100, i.e., from the side of the upper electrode128of the photoconductive film127. When light is incident from the side of the upper electrode128, a reflective film is formed on the side of the lower electrode126, and the upper electrode128becomes a transparent electrode. In a configuration in which light is incident from the side of the upper electrode128, a switching TFT or a driving TFT can be formed between the lower electrode126and the substrate100, which is advantageous in terms of space.

Incidentally, when silver becomes a thin film having a film thickness of 50 nm or less, particularly 30 nm or less, it transmits visible light. By utilizing this property, it is possible to realize an optical sensor in which light is incident from the side of the upper electrode128without changing the basic structure of the optical sensor described in Embodiment 1 (hereinafter, also referred to as an upper light incident type).

FIG.7is a cross-sectional view of an organic photodiode portion in Embodiment 2. Since the configuration of the switching TFT and the driving TFT are the same as that described with reference toFIG.3, only the organic photodiode portion is shown inFIG.7. InFIG.7, an inorganic passivation film124is formed on an organic passivation film122, for example, by a SiN film having a thickness of 100 nm. On the inorganic passivation film124, a reflective film150made of silver, aluminum, an aluminum alloy or the like is formed to have a thickness of about 100 nm. A cathode126is formed from an ITO film of a thickness of about 50 nm thereon.FIG.7differs fromFIG.3of Embodiment 1 in that a reflecting film150made of metal is formed under the cathode126.

The organic photoconductive film127is formed on the cathode126with a thickness of 300 to 500 nm as shown inFIG.3. An anode128is formed of a silver film on an organic photoconductive film127. InFIG.7, the silver film as the anode128does not act as a reflective electrode, but rather needs to pass light. Therefore, the thickness of the silver film128is 50 nm or less, preferably 20 to 30 nm. When the thickness of silver film becomes equal to this level, a transmittance of the silver film becomes equal to or higher than that of ITO film.

An ITO film129for preventing the oxidation of silver is formed on the anode128by about 7 nm. The ITO film129is formed by low-temperature sputtering in succession to the silver film128. As described in Embodiment 1, the ITO film129is an amorphous film. However, in the configuration ofFIG.7, since the thickness of the ITO film129is preferably reduced in order to prevent the attenuation of light, a more preferable thickness is 5 to 20 nm.

On the ITO film129, an alumina (AlOx) film130having a thickness of, e.g., about 10 to 50 nm is formed, the same as Embodiment 1. This is for preventing an organic photoconductive film from being contaminated from external moisture or the like. In the configuration shown inFIG.7, in order not to attenuate the light, a more preferable range of the alumina film130is 10 to 30 nm. Since oxygen from the alumina film130is blocked by the ITO film129, it does not reach the anode128, and the silver film128is not oxidized, therefore the conductivity of the silver film128can be maintained.

Although the silver film128is thin, as shown inFIGS.1and2, since the power supply line13extends in the vertical direction, the potential drop of the anode128can be prevented. In other words, since the thin silver film128only needs to act as a conductive film only at each sensor element, an increase in the resistance value caused by thinning of the silver film128does not become a substantial problem unless the silver film128is oxidized.

As described above, by forming the ITO thin film129between the silver film128as the anode and the alumina (AlOx)130for the moisture block, it is possible to prevent the oxidation of the silver thin film128, and thus it is possible to realize an optical sensor having an organic photoconductive film of an upper surface incident type.

In the above description, a case in which an organic photoconductive film is used as an optical sensor has been described; however, the present invention is not limited to this, and the present invention can be applied to other optical sensors in the case where silver is used as a cathode or an anode. Further, while the present invention has been described with reference to an optical sensor using an organic photoconductive film, the present invention is not limited thereto and can be used in an organic EL display device using an organic EL film and so forth.