JP2013125782A - Oxide semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide semiconductor device having good characteristics and high reliability even when a flexible substrate is used.SOLUTION: An oxide semiconductor device has: a gate electrode 2; a gate insulating layer 3 provided on the gate electrode 2; a channel part provided on the gate electrode 2 via the gate insulating layer 3; and source-drain electrodes 6 electrically connected with the channel part. The channel part includes an oxide semiconductor layer 5 and a conductive layer 4. At least one of the source-drain electrodes 6 is connected to the conductive layer 4 via the oxide semiconductor layer 5.

Description

  The present invention relates to a thin film transistor (TFT) used for a flat panel display, RFID (Radio Frequency IDentification), and the like, and in particular, an oxide semiconductor device (TFT) using an oxide semiconductor in a channel portion. )

  The transition to terrestrial digital broadcasting and the spread of digital TV using FPD are rapidly progressing. With regard to these digital TVs, efforts are being made for higher definition in the future, and digital TVs will also change from the current full high-definition pixel count of 1920 × 1080 to 4k × 2k, or 8k, which is 16 times the current number of pixels. Progress to x4k is expected.

  However, in order to achieve high definition, the effects of increasing the area, miniaturizing the pixel electrode, increasing the number of wirings, etc. become obvious, so the current use of amorphous silicon (a-Si) for the channel layer Realization with an a-Si TFT is considered difficult. In particular, obtaining highly uniform film formation on a large area substrate and good on-characteristics are technically limited in a-Si using a chemical vapor phase method. Therefore, TFTs using amorphous oxides such as IGZO (indium gallium zinc composite oxide) are expected in recent years as TFTs for next-generation high-definition TVs. This oxide can realize a large area and highly uniform film formation by sputtering and has excellent on-characteristics compared to a-Si, so that it can be expected to have a high on-off ratio and high mobility. And as a pixel TFT for organic EL-TV.

On the other hand, with regard to this amorphous oxide, in recent years, light degradation (threshold shift) due to light irradiation at the time of negative bias has been regarded as a problem, and improvement of these reliability is indispensable for practical use. . The cause of this photodegradation is, for example, as described in Non-Patent Document 1, among the oxygen vacancies [V ₀ ] existing in the oxide from the time of film formation, a deep level near the valence band. It is supposed to form. Furthermore, by receiving light irradiation at the time of negative bias, holes generated by photoexcitation drift to the gate insulating layer side and are trapped by [V ₀ ] in the gate insulating layer, thereby causing a threshold fluctuation. It has been shown to be. At present, in order to solve these problems, it is important to reduce the initial [V ₀ ] formed at the time of forming the oxide layer. For example, high-temperature and high-pressure annealing as shown in Non-Patent Documents 1 to 4 Plasma treatment is effective. However, these annealing treatments themselves have an increase in the number of processes, and there are problems such as an increase in contact resistance due to electrode metal deterioration due to high temperature treatment, which may reduce process margin and increase costs. Has been pointed out. In addition, low-temperature film formation was originally possible including a sputtering process, and there was a possibility that the advantages of the oxide TFT, which was advantageous for the flexible substrate, could be impaired.

Byungki Ryu et al., Appl. Phys. Lett., 97, 022108 (2010) Jin-Seong Park et al, Appl. Phys. Lett., 90, 262106 (2007) Chen-Yi Wu et al, SID Digest 2010, P-20, 1298 (2010) Yutomo Kikuchi et al, Thin Solid Films, 518, 3017 (2010)

As described above, in a TFT based on an amorphous oxide, a threshold value due to oxygen vacancies [V ₀ ] caused by light incident upon application of a negative bias to the gate electrode by light incident on the oxide semiconductor thin film. Photodegradation called fluctuation occurs. In addition, high-temperature treatment for reducing the initial oxygen vacancies [V ₀ ] formed during the formation of the oxide layer may impair advantages such as adapting the oxide TFT to a flexible substrate.

  An object of the present invention is to provide an oxide semiconductor device having favorable characteristics and high reliability even when a flexible substrate is used.

  As one embodiment for achieving the above object, a gate electrode, a gate insulating layer provided on the gate electrode, a channel portion provided on the gate electrode via the gate insulating layer, and the channel In the oxide semiconductor device having a source electrode and a drain electrode electrically connected to a portion, the channel portion includes an oxide semiconductor layer and a conductive layer, and at least one of the source electrode and the drain electrode is the An oxide semiconductor device is connected to the conductive layer through an oxide semiconductor layer.

  In the oxide semiconductor device in which a current flowing between the source electrode and the drain electrode through the channel portion is controlled by the gate electrode, the channel portion has a switching function and a conductive function separated from each other. The oxide semiconductor device is as follows.

  According to the present invention, even when a flexible substrate is used, an oxide semiconductor device having favorable characteristics and high reliability can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure for demonstrating the oxide semiconductor device (oxide semiconductor TFT which has a function isolation | separation type channel part) which concerns on 1st Example of this invention, (a) is sectional drawing, (b) is a top view. is there. 2A and 2B are cross-sectional views for explaining another TFT structure that exhibits the same effect as the oxide semiconductor device shown in FIG. 1, wherein FIG. 1A is a top gate / bottom contact structure, FIG. 2B is a top gate / top contact structure, c) shows a bottom gate bottom contact structure. 2 is a cross-sectional view of a modification of the oxide semiconductor device shown in FIG. 1, wherein (a) and (b) are a stacked structure of a source electrode / semiconductor layer / conductive layer used for switching processing, the semiconductor layer being a source electrode, Alternatively, when formed on only one of the drain electrodes, (c) and (d) are a stacked structure of a drain electrode / semiconductor layer / conductive layer used for switching processing, and the semiconductor layer is a source electrode, or The case where it is formed on only one of the drain electrodes is shown. It is a flowchart for demonstrating the manufacturing process of the oxide semiconductor device (bottom gate top contact structure TFT) concerning the 1st Example of this invention. In the oxide semiconductor device (TFT) according to the first embodiment of the present invention, current-voltage characteristics and movement in the case where the channel portion configuration is the semiconductor layer IGZO (film thickness 20 nm) and the conductive layer ITO (film thickness 3 nm). It is a graph which shows an example of a degree-voltage characteristic. It is a graph which shows an example of the current-voltage characteristic and mobility-voltage characteristic in the case where the channel layer is an IGZO layer with a film thickness of 25 nm in a conventional oxide semiconductor TFT. Oxide semiconductor device (channel portion configuration: semiconductor layer IGZO (thickness 20 nm), conductive layer ITO (thickness 3 nm) TFT) according to the first embodiment of the present invention and conventional oxide semiconductor TFT (channel layer configuration: It is a graph which shows an example of the threshold value shift-light irradiation time characteristic for demonstrating the photodegradation (threshold value shift) under the negative bias stress of an IGZO layer (film thickness of 25 nm). 1 is a schematic plan view for explaining a configuration of an active matrix circuit to which an oxide semiconductor device according to a first embodiment of the present invention is applied. 1 is a bird's eye view for explaining the structure of an active matrix circuit and a thin film transistor to which an oxide semiconductor device according to a first embodiment of the present invention is applied. Other oxide semiconductor devices according to the first embodiment of the present invention (channel portion configuration is semiconductor layer ZTO (Zn composition 0.7, film thickness 20 nm), conductive layer ZTO (Zn composition 0.2, film thickness 5 nm) Is a graph showing an example of current-voltage characteristics and mobility-voltage characteristics. Other oxide semiconductor devices according to the first embodiment of the present invention (channel portion configuration: semiconductor layer ZTO (Zn composition 0.7, film thickness 20 nm), conductive layer ZTO (Zn composition 0.2, film thickness 5 nm) TFT) and conventional oxide semiconductor TFT (channel layer configuration: IGZO layer (film thickness 25 nm)) threshold shift-light irradiation time characteristics for explaining light degradation (threshold shift) under negative bias stress It is a graph which shows an example. It is sectional drawing for demonstrating the pixel basic composition of the organic electroluminescent display (top emission type) which applied the bottom gate top contact type oxide semiconductor TFT which has a function isolation | separation type channel part based on 2nd Example of this invention. is there. It is a circuit diagram for demonstrating the pixel drive circuit of the organic electroluminescent display which applied the oxide semiconductor TFT which has a function separation type channel part based on the 2nd Example of this invention. Sectional view for explaining a basic pixel configuration of an organic EL display (top emission type) using a top gate / bottom contact type oxide semiconductor TFT having a function-separated channel portion according to a second embodiment of the present invention. FIG. Sectional view for explaining a basic configuration of a pixel of an organic EL display (bottom emission type) using a top gate / bottom contact type oxide semiconductor TFT having a function-separated channel portion according to a second embodiment of the present invention. FIG. It is a schematic diagram for demonstrating the system configuration | structure of the RFID tag which applied the oxide semiconductor TFT which has a function separation type channel part based on the 3rd Example of this invention. It is a schematic sectional drawing of the RFID tag comprised from the oxide semiconductor TFT which has a function separation type channel part based on the 3rd Example of this invention. It is a circuit diagram for demonstrating the logic circuit of the RFID tag comprised from the oxide semiconductor TFT which has a function isolation | separation type channel part based on the 3rd Example of this invention. It is a graph of the reader output for demonstrating the UHF band (900 MHz band) radio | wireless response operation | movement of the RFID tag by the antenna integrated oxide semiconductor TFT circuit which has a function separation type channel part based on 3rd Example of this invention. .

In order to solve the above-described problem, a relatively high-resistance (resistivity: 10 ⁻² to 10 ³ Ωcm) oxide semiconductor layer that is in a range covered by an electric field from a gate electrode and that is independently in contact with at least a source electrode or a drain electrode The source and drain electrodes are connected by a conductive layer (resistivity: 10 ⁻³ Ωcm or less) in contact with the gate insulating layer through the relatively high resistance oxide semiconductor layer. Substantial switching due to gate bias is performed in the above-described relatively high-resistance oxide semiconductor layer, and the source and drain electrodes are connected by a conductive layer, so on-state characteristics such as higher mobility and improved on-off ratio are achieved. Improvement is also realized at the same time (channel function separation. A TFT having this structure is called a TFT having a function-separated channel portion). Further, considering the case of the top contact type TFT, if a metal material is used for the source / drain electrodes, the layered structure region where the switching is performed is shielded from light by the source / drain electrodes, and the probability of incidence of light is reduced. Therefore, a significant improvement in light degradation, which was a problem with conventional devices, can be expected. In addition, photo-degradation was said to be caused by holes being trapped on the gate insulating layer side near the interface, resulting in threshold fluctuations. In this structure, however, the amorphous oxide semiconductor with a relatively high resistance that switches with the gate insulating layer is used. Since the area where the layers are in contact with each other is very small, the structure is inherently resistant to light degradation. This eliminates the need for a process for improving reliability such as annealing, improves reliability such as photodegradation, and provides low-temperature formation, high mobility, and high characteristics that are characteristic of oxide TFTs. Features such as on / off ratio can be maintained. The above is the basic principle.

Hereinafter, a specific structure, manufacturing process, and the like of an oxide semiconductor device having a function-separated channel portion for realizing the above effects will be described. First, glass or a plastic film is used as the support substrate 1. A Mo layer or the like is formed as a gate electrode 2 on the substrate 1 with a film thickness of about 200 nm by vapor deposition or the like. Thereafter, the gate electrode 2 is processed using a photo process and the like, and an insulating layer material such as SiO ₂ or Al ₂ O _{3 having a} thickness of about 50 to 100 nm is formed thereon as a gate insulating layer 3 by vapor deposition, CVD, A film is formed by sputtering or the like. Further, a conductive layer 4 such as ITO (indium tin composite oxide), AZO (Al-doped zinc oxide), or ZTO (zinc tin composite oxide) is formed with a thickness of 5 nm or less by vapor deposition or sputtering. The conductive layer 4 is processed using an etching technique or the like so that contact with the source / drain electrodes is finally obtained. Thereafter, a relatively high-resistance oxide semiconductor layer 5 such as a-IGZO, a-ZTO, or a-IZO is formed with a film thickness of about 10 to 30 nm by sputtering or the like, and the conductive layer 4 is covered. It is processed using a photo process and etching technique. Thereafter, the source / drain electrode layer 6 is formed by vapor deposition or sputtering, and the source / drain electrode 6 is processed by a photo process and etching technique. Further, using the processed source / drain electrodes 6 as a mask, only the relatively high resistance amorphous oxide semiconductor layer 5 is removed using a selective processing technique or the like.

  FIGS. 1A and 1B show typical structural examples (cross-sectional views and plan views) of bottom gate top contact structure TFTs formed by this manufacturing method. FIGS. The top gate / bottom contact structure TFT, top gate / top contact type TFT, bottom gate / bottom contact structure TFT, etc., shown in FIG. 1, the gate electrode, the gate insulating layer, the channel portion (semiconductor layer and conductive layer), and the source / drain electrode positional relationship Similar effects can be expected with the same TFT structure. However, the top gate bottom contact structure TFT shown in FIG. 2A is easier to manufacture than other structures. The top gate top contact structure TFT of FIG. 2B is easily connected at the top and is suitable for TV.

  3A and 3B, the source electrode / semiconductor layer / conductive layer stacked structure used for the switching process, and the semiconductor layer is either the source electrode or the drain electrode. 3D, or as shown in FIGS. 3C and 3D, the drain electrode / semiconductor layer / conductive layer stacked structure used for the switching process, and the semiconductor layer is the source electrode, Or even if it forms only in any one of a drain electrode, there is no difference in the effect of this invention. However, the one having a switching function on the source electrode side shown in FIGS. 3A and 3B is more resistant to the applied voltage than the structure having a switching function on the drain electrode side shown in FIGS. Highly practical.

  As described above, by using the above-described TFT structure and manufacturing technology as an oxide semiconductor TFT, the high mobility and high on / off characteristics inherent in the oxide semiconductor are maintained without performing high-temperature annealing as in the conventional method. It is possible to suppress photodegradation at the time of negative bias stress and achieve both improvement in reliability and high on-state characteristics of the oxide semiconductor TFT. When applied to FPD, higher definition and lower power consumption can be realized compared to the conventional case. For high frequency applications such as RFID (Radio Frequency IDentification), improvement of the internal clock has been realized, resulting in higher frequency bands. Can be applied.

  In the following examples, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other. Some or all of the modifications, details, supplementary explanations, and the like are related.

  Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number. Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say. Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

  Further, in the drawings used in the following embodiments, hatching may be added to make the drawings easy to see even if they are plan views. In all the drawings for explaining the following embodiments, components having the same function are denoted by the same reference numerals in principle, and repeated description thereof is omitted. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  An example in which the oxide semiconductor device having a function-separated channel portion according to the first embodiment of the present invention is applied as an FPD pixel control TFT will be described with reference to FIGS. Here, FIGS. 1A and 1B and FIGS. 4A to 4E are bottom gate top contact type oxidations each having a function-separated channel portion in which the channel portion of this embodiment is made of IGZO and ITO. FIG. 5 and FIG. 6 are graphs and graphs showing current-voltage characteristics of an oxide semiconductor TFT having a function-separated channel portion and a conventional oxide semiconductor TFT, respectively, for explaining the structure and manufacturing process of the physical semiconductor TFT. 7 is a graph for explaining light deterioration (threshold shift) when an oxide semiconductor TFT having a function-separated channel portion is irradiated with light under a negative bias stress. FIGS. 8 and 9 are top views for explaining an active matrix pixel control circuit and a TFT array each using an oxide semiconductor TFT having a function-separated channel portion. FIG. 10 and FIG. 11 show current-voltage characteristics and negative bias stress of a bottom gate top contact type oxide semiconductor TFT having a rare-metal-free function-separated channel portion in which the channel portion is composed of a ZTO semiconductor layer and a ZTO conductive layer, respectively. It is a graph for demonstrating the light degradation (threshold shift) at the time of light irradiation below. In addition, the same code | symbol shows the same component.

A method for manufacturing an oxide semiconductor TFT having a function-separated channel portion of this example is as follows (FIGS. 4A to 4E). First, a Mo layer to be the gate electrode 2 is formed on the support substrate 1 such as a glass substrate by a vapor deposition method or the like, and processed into the gate electrode 2 using a photo process or the like. A flexible resin substrate can also be used as the support substrate 1. Next, a SiO ₂ gate insulating layer 3 having a thickness of about 100 nm is formed by a CVD process or the like. Thereafter, a transparent conductive layer 4 (film thickness: 3 nm) such as ITO is formed by DC magnetron sputtering (FIG. 4A). The film formation conditions were room temperature, sputtering gas Ar, film formation pressure 0.5 Pa, and discharge power 50 W. This is processed using a commercially available ITO etching solution or the like. This transparent conductive layer 4 shares the conductive function of the channel portion.

An oxide semiconductor layer 5 (film thickness 20 nm) such as IGZO is formed thereon by RF sputtering (FIG. 4B). The film formation conditions were room temperature, sputtering gas Ar (96%), O ₂ (4%), film formation pressure 0.5 Pa, discharge power RF (13.56 MHz) 40 W. Thereafter, the oxide semiconductor layer 5 is processed so as to cover the transparent conductive layer 4 by using a photo process and an etching technique (FIG. 4C). This oxide semiconductor layer 5 shares the switching function of the channel portion.

  Further, an Al electrode layer to be the source / drain electrode layer 6 is formed by vapor deposition (FIG. 4D), and the source / drain electrode 6 is formed by using a photo process and an etching technique. Using this source / drain electrode 6 as a mask, only the IGZO semiconductor layer 5 is removed by etching. Finally, a passivation layer 7 for surface protection is formed, and a desired oxide semiconductor TFT is completed (FIG. 4E). Note that when the present oxide semiconductor TFT is viewed from vertically above in the stacking direction of each layer, the gate electrode 2 and the oxide semiconductor layer 5 overlap each other as shown in FIG. Further, only the conductive layer 4 of the conductive layer 4 and the oxide semiconductor layer 5 is provided in the central region of the channel portion between the source / drain electrodes 6 (only when viewed from the source / drain electrode side). The same applies when viewed from the gate electrode side). The oxide semiconductor layer 5 is desirably disposed in the vicinity of the source / drain electrodes, and a situation where the oxide semiconductor layer 5 cannot be hidden behind the source / drain electrodes 6 is preferable. This structure is not limited to the bottom gate structure, and the same applies to the top gate structure.

FIG. 5 shows current-voltage characteristics of an oxide semiconductor TFT having a function-separated channel portion formed by the above method. Similar characteristics of a TFT using a conventional IGZO for the channel layer (film thickness 25 nm) are shown in FIG. 6. Compared with this, higher mobility and higher on-current are observed, and good TFT characteristics are obtained. You can see that Moreover, the measurement result of the light degradation at the time of negative bias application is shown in FIG. Measurement conditions were a gate-source bias potential V _GS of −20 V, a source-drain potential V _SD of 10 V, a light stress condition of a blue LED light source having a wavelength of ˜460 nm, light intensity of 0.07 mW / cm ² , light The flux density is 1.6 × 10 ¹⁴ cm ⁻² . In the case of a TFT using a single film IGZO as a channel layer (curve indicated by reference numeral 8), a threshold fluctuation of 7 V or more was observed by light irradiation of 10 ⁴ sec. By adopting a TFT having a channel portion (curve indicated by reference numeral 9), the threshold fluctuation can be significantly suppressed to about 1V. Using the oxide semiconductor TFT having the function-separated channel portion as a basic element, an active matrix TFT array as shown in FIGS. 8 and 9 is configured and applied as a pixel switch of a 4k × 2k next-generation liquid crystal TV. Good operation was confirmed. Reference numeral 10 is a support substrate (glass substrate, resin substrate, etc.), reference numeral 11 is a data line control circuit, reference numeral 12 is a gate line control circuit, reference numeral 13 is a gate line, reference numeral 14 is a data line, reference numeral 15 is a pixel electrode, Reference numeral 16 denotes an oxide semiconductor device (switching TFT).

In the above description, among the channels of the oxide semiconductor device (switching TFT) 16 having the function-separated channel portion, the oxide semiconductor layer includes IGZO, the conductive layer includes ITO and rare metals such as indium and gallium. However, by using ZTO as the oxide semiconductor layer 5 and AZO or ZTO as the conductive layer 4, a configuration in which a rare metal is not used can be used. For example, the oxide semiconductor layer 5 in the channel portion is ZTO having a Zn composition of 0.7, the conductive layer 4 is a ZTO conductive layer having a Zn composition of 0.2, and the function-separated channel portion having the configuration shown in FIG. 1 is provided. A bottom gate top contact type oxide semiconductor TFT was fabricated. FIG. 10 and FIG. 11 show the measurement results of the light deterioration when the light is irradiated under the current-voltage characteristics and the negative bias stress. Good current-voltage characteristics (mobility 73 cm ² / Vs, on / off ratio> 10 ¹⁰ ) and photodegradation after negative bias application after 10 ⁴ sec (conventional IGZO TFT (curve indicated by reference numeral 8) ΔV _th > In contrast to 7V, the TFT having the function-separated channel portion of this example (curve indicated by reference numeral 20) was also effectively suppressed by 0.2V). Regarding the above ZTO, the oxide semiconductor layer 5 is controlled to have a high resistance by adding 4 to 5% high-purity oxygen gas in the sputtering gas at the time of film formation by high-frequency sputtering. It is possible to control the resistance to a low level in a state in which moisture and oxygen mixed in the sputtering gas of high purity Ar by using a liquid nitrogen trap or the like are sufficiently removed during film formation. In addition, the conductive layer 4 side is difficult to etch compared to the oxide semiconductor layer 5 and has a relatively high Sn composition. By using a commercially available ITO etching solution or the like, the oxide semiconductor layer can be selectively used. There is also a manufacturing process advantage that it is easy to etch only.

  As described above, according to this embodiment, even when a flexible substrate is used by connecting at least one of the source and drain electrodes to the conductive layer through the oxide semiconductor layer constituting the channel portion. Thus, an oxide semiconductor device with favorable characteristics and high reliability can be provided. Further, it can be used as a pixel control TFT for FPD.

  A second embodiment of the present invention will be described with reference to FIGS. Note that the matters described in the first embodiment and not described in the present embodiment can be applied to the present embodiment as long as there is no special circumstances. In this embodiment, an example in which an oxide semiconductor TFT having a function-separated channel portion is applied to an organic EL display will be described. Here, FIG. 12 is a cross-sectional view showing a part of an organic EL display in which a bottom-gate top-contact type oxide semiconductor TFT having a function-separated channel portion is formed immediately below the top emission type organic EL element, and FIG. 13 is an organic EL element. FIG. 14 is a cross-sectional view showing the structure of a top gate bottom contact type oxide semiconductor TFT having a function-separated channel portion formed on a top emission type organic EL element. 15 is a cross-sectional view showing the structure of a top gate bottom contact type oxide semiconductor TFT having a function-separated channel portion formed on a bottom emission type organic EL element.

In the case of the top emission type organic EL element of FIG. 12, first, an oxide semiconductor device (current drive) having a function-separated channel portion which is pixel switching on a support substrate 30 such as a glass substrate by the method shown in the first embodiment. TFT) 31 is formed. A flexible resin substrate can be used as the support substrate 30. Thereafter, an organic EL element array of each of the three primary colors is formed through an interlayer insulating layer 32 that also serves as a passivation film. The organic EL element includes an anode electrode layer 33, a red light emitting element 34, a green light emitting element 35, a blue light emitting element 36, and a cathode electrode layer (transparent conductive layer) 37. Reference numeral 38 denotes a spacer layer that separates the light emitting element layers, and reference numeral 39 denotes a glass substrate that serves as a light emitting surface. In the oxide semiconductor TFT 31 described above, a TFT in which the semiconductor layer in the channel portion shown in Example 1 is ZTO (Zn composition 0.7) and the conductive layer is ZTO (Zn composition 0.2) (mobility 73 cm ² / Vs, on / off ratio> 10 ¹⁰ ) was employed. In the case of an organic EL display, actually, as shown in FIG. 13, a pixel switching TFT 42 and a TFT 44 for driving current to the organic EL element are necessary. Reference numeral 40 denotes a gate line, reference numeral 41 denotes a data line, reference numeral 43 denotes a capacitor, and reference numeral 45 denotes an organic EL element (p / n junction diode). Compared with a liquid crystal pixel switch, a large current is applied to the subsequent current driving TFT 44 in order to drive a large current. Therefore, the current driving TFT 44 is required to have high threshold stability. In addition, since the element structure easily receives light from the organic EL element, the stability of the threshold is a severe environment even for the oxide TFT. Using the oxide semiconductor TFT having the function-separated channel portion and driving the blue organic EL element to emit light by driving 9 V and 0.1 μA, the predicted ΔV _th after 3 × 10 ⁷ sec is 1.7 V. there were. It can be seen that the conventional structure IGZO TFT is very effective because the prediction ΔV _th > 8.2V. In addition, by using an oxide semiconductor TFT having a function-separated channel part, the mobility is also improved secondary, so that the power consumption of the organic EL display is reduced to about 1/3 compared with a TFT having a conventional structure. We were able to.

FIGS. 14 and 15 show examples in which top gate / bottom contact type oxide TFTs having function-separated channel portions formed on top emission type organic EL elements and bottom emission type organic EL elements are employed. In the channel portion, ZTO (Zn composition 0.7) with a thickness of 25 nm was used as the oxide semiconductor layer 52, and AZO (Al-doped ZnO) with a thickness of 3 nm was used as the conductive layer 53. In each film formation method, the semiconductor ZTO layer is formed by sputtering gas Ar (95%), O ₂ (0.5%), pressure 0.5 Pa, film formation temperature at room temperature, and RF (13.56 MHz) power 70 W. The RF sputtering and AZO conductive layer under the conditions are DC magnetron sputtering with the sputtering gas Ar, the pressure of 0.45 Pa, the film formation temperature at room temperature, and the DC power of 50 W as the film formation conditions. Reference numeral 50 denotes an organic EL element (p / n junction diode), reference numeral 51 denotes a source electrode (metal, transparent conductive layer), reference numeral 54 denotes a gate insulating layer, reference numeral 55 denotes a gate electrode (transparent conductive layer), and reference numeral 56 denotes a passivation layer. , 57 represents a gate electrode (metal), and 58 represents a drain electrode (metal). Even in the top gate bottom contact type oxide TFT having the function-separated channel portion, substantially the same results were obtained with respect to basic TFT characteristics and the effect of suppressing light degradation under negative bias stress. Although a transparent conductive layer can be used as the drain electrode 58, light from the organic EL element 50 to the oxide semiconductor layer can be blocked by using a metal.

In the case of the top emission type organic EL element shown in FIG. 14, the gate electrode 55 corresponding to the light emitting region is made of transparent material such as ITO, AZO, GZO (Ga doped ZnO), IZO (indium zinc composite oxide) in order to improve luminous efficiency. It is desirable to use a conductive layer.
Even when these oxide semiconductor TFTs having function-separated channel portions having different structures are used, it was confirmed that the effect when applied to an organic EL display can be obtained in the same manner.

  As described above, according to this embodiment, even when a flexible substrate is used by connecting at least one of the source and drain electrodes to the conductive layer through the oxide semiconductor layer constituting the channel portion. Thus, an oxide semiconductor device with favorable characteristics and high reliability can be provided. Further, it can be used as a pixel switch TFT or a current driving TFT of an organic EL element.

  A third embodiment of the present invention will be described with reference to FIGS. Note that the matters described in the first embodiment and not described in the present embodiment can be applied to the present embodiment as long as there is no special circumstances. In this embodiment, an example in which an oxide semiconductor TFT having a function-separated channel portion is applied to an RFID tag will be described.

  16 is a schematic diagram showing a circuit configuration of the RFID, FIG. 17 is a schematic cross-sectional view of an RFID tag including an oxide semiconductor TFT having a function-separated channel portion, and FIGS. 19 is a circuit diagram for explaining a basic logic circuit used in an RFID circuit, and FIG. 19 is a graph of a reader output showing a UHF band wireless response operation of an RFID tag manufactured using the oxide semiconductor TFT of the present invention.

In the case of an RFID tag, a radio wave output from an external device such as a reader or a writer is received by an attached antenna 60, and a direct current power source is driven by a rectifier circuit 61, thereby driving a subsequent logic circuit unit 70 and a memory area corresponding to an ID. The recording data (ROM data) 65 is taken out and sent back through the transmission circuit 68 and the antenna 60. Reference numeral 62 denotes a regulator circuit, reference numeral 63 denotes a reset circuit, reference numeral 64 denotes a clock generation circuit, reference numeral 66 denotes a ROM reading circuit, reference numeral 67 denotes an encoding circuit, and reference numeral 69 denotes a high-frequency circuit unit. Since oxide semiconductor TFTs exhibit n-type semiconductor characteristics in most cases, it is difficult to construct a CMOS circuit in an Si semiconductor, and it is necessary to construct a circuit using an n-type single channel. In particular, since the circuit scale of the logic circuit unit 70 becomes large, the power consumption increases when a commonly used saturated logic circuit is used, and the operation is performed with power supply power (about 300 μW) input from a reader / writer or the like. There are drawbacks that make it difficult. Therefore, power consumption can be reduced by using, for example, a logic circuit as shown in FIGS. 18A, 18B, and 18C in accordance with the characteristics of the oxide semiconductor TFT having the function-separated channel portion. is there. 18A is a basic circuit for performing a logical operation of NOT, FIG. 18B is a NOR circuit, and FIG. 18C is a NAND circuit. The NOT in FIG. 18A has two TFTs, a device is small, and power consumption is small. On the other hand, NOR and NAND in FIGS. 18B and 18C have good characteristics and are suitable for high-speed operation. The channel part configuration is a semiconductor layer ZTO (Zn composition 0.7) with a film thickness of 20 nm and a conductive layer ITO with a film thickness of 3 nm, and the drain electrode side as shown in FIG. In addition, an oxide semiconductor TFT having a function-separated channel portion which is connected to the conductive layer and has the same structure as that of the first embodiment is applied as a basic element of the circuit. The basic current-voltage characteristics of this oxide semiconductor TFT are as follows: mobility 95 cm ² / Vs, on / off ratio> 10 ¹⁰ , and photodegradation under negative bias as shown in FIGS. Good characteristics of ΔV _th = 0.8 V were exhibited after 10 ⁴ sec under the same measurement conditions. Using this oxide semiconductor TFT, an RFID tag having a structure as shown in FIG. 16 was constructed. FIG. 17 shows a schematic cross-sectional view. A circuit using an oxide semiconductor TFT 84 having a function-separated channel portion and a high-frequency antenna layer (metal) 83 can be integrally formed on the same surface. As a result, there is no need to mount the antenna, and the reliability of the antenna connection is greatly improved. In addition, when combined with a high-efficiency production system such as a large area or roll-to-roll process, the cost can be reduced. There is also an effect. Reference numeral 80 denotes a support substrate (thin film glass substrate, resin substrate), reference numeral 81 denotes an insulating layer, and reference numeral 82 denotes an antenna resonance capacity. FIG. 19 shows the result of examining the radio response spectrum of this RFID circuit (integrated antenna having an element length of about 160 mm) using a commercially available RFID reader with 900 MHz band output of 100 mW. The signal start and transfer speed setting (preamble 90) are performed by the input from the reader, and the ROM data 92 corresponding to the ID is output following the unique word 91 for signal separation. Has been. Only the initial portion of the ROM data 92 is displayed, but here, 128-bit output is confirmed. Further, the scale of the ROM using the thin film process can be freely increased or decreased depending on the device area.

By applying an oxide semiconductor TFT having a function-separated channel portion, high mobility and high on-state characteristics were also produced as secondary effects. Therefore, a conventional single film IGZO TFT (mobility 13 cm ² / Vs, on / Off ratio> 10 ⁸ ), the operable input frequency was ~ 25MHz and the internal clock 70Hz was improved to ~ 2.5GHz and 4.3kHz, respectively, and the operation in the UHF band became possible as described above. It was. In addition, the data transfer speed has improved by almost two digits. In addition, threshold fluctuations due to light irradiation under negative bias stress can be suppressed, and a sufficient value can be obtained in terms of reliability, and the manufacturing process can be lowered, so that it can be flexibly built into a film-like substrate. A simple circuit could also be realized.

  In addition, this invention is not limited to the said embodiment, It cannot be overemphasized that various changes can be made in the range which does not deviate from the summary, if a transparent conductive layer is required. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  The present invention relates to oxide semiconductor TFTs used in flat panel displays such as liquid crystal TVs and organic EL-TVs, RFIDs using these TFTs, flexible devices, and the like, and in particular, thresholds under negative bias stress. This is related to the improvement technology in terms of reliability, which was a major issue at the time of practical use of value fluctuation.

DESCRIPTION OF SYMBOLS 1 ... Support substrate (glass substrate, resin substrate etc.), 2 ... Gate electrode, 3 ... Gate insulating layer, 4 ... Conductive layer which comprises the channel part of this invention, 5 ... Oxide semiconductor which comprises the channel part of this invention Layer 6, source / drain electrode layer 7, passivation layer (protective layer), 8 Threshold fluctuation curve showing light degradation under negative bias stress of conventional oxide semiconductor TFT (IGZO TFT), 9. Threshold fluctuation curve showing photodegradation under negative bias stress of oxide semiconductor TFT (channel structure: semiconductor layer IGZO, conductive layer ITO) of the invention, 10 ... support substrate, 11 ... data line control circuit, 12 ... gate Line control circuit, 13 ... gate line, 14 ... data line, 15 ... pixel electrode, 16 ... oxide semiconductor device (switching TFT), 20 ... oxide semiconductor TFT of the present invention (channel configuration) Threshold fluctuation curve indicating photodegradation of semiconductor layer ZTO (Zn composition 0.7), conductive layer ZTO (Zn composition 0.2)) under negative bias stress, 30 ... support substrate (glass substrate, resin substrate, etc.) , 31... Oxide semiconductor TFT (for current driving), 32... Interlayer insulating layer, 33... Anode electrode layer, 34... Red organic EL element (p / n junction diode), 35. Junction diode), 36 ... Blue organic EL element (p / n junction diode), 37 ... Cathode electrode layer (transparent conductive layer), 38 ... Spacer layer, 39 ... Light emitting surface (glass substrate, resin substrate, etc.), 40 ... Gate 41, data line, 42 ... pixel switching TFT, 43 ... capacitance, 44 ... current drive TFT, 45 ... organic EL element (p / n junction diode), 50 ... organic EL element (p / n junction diode) ), 51... Source electrode layer (metal, transparent conductive layer), 52... Oxide semiconductor layer constituting the channel portion of the present invention, 53... Conductive layer constituting the channel portion of the present invention, 54. 55 ... Gate electrode (transparent conductive layer), 56 ... Passivation layer (protective layer), 57 ... Gate electrode (metal), 58 ... Drain electrode (metal), 60 ... Antenna (including resonance circuit), 61 ... Rectifier circuit, 62 ... Regulator circuit, 63 ... Reset circuit, 64 ... Clock generation circuit, 65 ... ROM data, 66 ... ROM read circuit, 67 ... Coding circuit, 68 ... Transmission circuit, 69 ... High frequency circuit section, 70 ... Logic circuit section, DESCRIPTION OF SYMBOLS 80 ... Support substrate (thin film glass substrate, resin substrate), 81 ... Insulating layer, 82 ... Antenna resonance capacity, 83 ... Antenna layer (metal), 84 ... Oxide semiconductor TFT of the present invention, 90 ... Amble, 91 ... unique word, 92 ... ROM data.

Claims (14)

A gate electrode; a gate insulating layer provided on the gate electrode; a channel portion provided on the gate electrode through the gate insulating layer; and a source electrode and a drain electrically connected to the channel portion In an oxide semiconductor device having an electrode,
The channel portion includes an oxide semiconductor layer and a conductive layer,
At least one of the source electrode and the drain electrode is connected to the conductive layer through the oxide semiconductor layer. The oxide semiconductor device according to claim 1,
The source electrode and the drain electrode are both connected to the conductive layer through the oxide semiconductor layer, respectively. The oxide semiconductor device according to claim 1,
The oxide semiconductor device according to claim 1, wherein the gate electrode and the oxide semiconductor layer have an overlapping portion when viewed from vertically above in the stacking direction. The oxide semiconductor device according to claim 1,
The source electrode and the drain electrode have a top contact structure,
Of the channel portion, a portion located between the source electrode and the drain electrode as viewed from above in the stacking direction of the gate electrode includes only the conductive layer among the oxide semiconductor layer and the conductive layer. An oxide semiconductor device is provided. The oxide semiconductor device according to claim 1,
The oxide semiconductor device, wherein the oxide semiconductor layer constituting the channel portion has a resistivity of 10 ⁻² to 10 ³ Ωcm. The oxide semiconductor device according to claim 1,
The oxide semiconductor device, wherein the resistivity of the conductive layer forming the channel portion is lower than 10 ⁻³ Ωcm. The oxide semiconductor device according to claim 1,
The oxide semiconductor layer constituting the channel portion includes zinc oxide, indium oxide, gallium oxide, tin oxide, zirconium oxide, hafnium oxide, vanadium oxide, molybdenum oxide, tungsten oxide, cadmium oxide, copper oxide, nickel oxide, and these An oxide semiconductor device characterized by being a composite oxide of The oxide semiconductor device according to claim 1,
The conductive layer constituting the channel portion is an indium tin composite oxide, indium zinc composite oxide, tin oxide, a transparent conductive layer in which boron, aluminum, or gallium is added to zinc oxide, and a metal or conductive organic film. An oxide semiconductor device, comprising: The oxide semiconductor device according to claim 1,
A combination of materials of the oxide semiconductor layer and the conductive layer forming the channel portion does not contain indium or gallium as a constituent element. The oxide semiconductor device according to claim 1,
One of the source electrode and the drain electrode is connected to the conductive layer through the oxide semiconductor layer, and the other is directly connected to the conductive layer. In an oxide semiconductor device that controls a current flowing between a source electrode and a drain electrode through a channel portion by a gate electrode,
In the oxide semiconductor device, the channel portion has a switching function and a conductive function separated from each other. The oxide semiconductor device according to claim 11,
The channel portion includes the oxide semiconductor layer and a conductive layer, the switching function is shared by the oxide semiconductor layer, and the conductive function is shared by the conductive layer. The oxide semiconductor device according to claim 12, wherein
The oxide semiconductor device, wherein the oxide semiconductor layer sharing the switching function is disposed between the source electrode and / or the drain electrode and the conductive layer. The oxide semiconductor device according to claim 13, wherein
In the central region of the channel portion between the source electrode and the drain electrode, only the conductive layer of the oxide semiconductor layer and the conductive layer is provided.

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