Double-active-layer indium gallium tin oxide thin film transistor and preparation method thereof
By adopting a dual active layer structure in the thin film transistor, the content of gallium and tin is regulated, and rare earth ions are incorporated into the second active layer, the problem of high mobility but negative threshold voltage and poor stability in the prior art is solved, and high mobility, positive threshold voltage and good stability performance are achieved.
Patent Information
- Application Number
- CN202510135667.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-07
- Publication Date
- 2025-05-13
AI Technical Summary
The existing metal oxide thin film transistors have high mobility but negative threshold voltage and poor stability, making it difficult to maintain a positive threshold voltage and good stability while improving mobility.
The dual active layer indium gallium oxide thin film transistor structure is adopted. The gallium content of the first active layer is smaller than that of the second active layer and the tin content of the first active layer is greater than that of the second active layer. The mobility, threshold voltage and stability of the thin film transistor are regulated through the gallium content. The second active layer may be doped with rare earth ions to improve the negative and positive bias light illumination stress stability.
High mobility, positive threshold voltage and good stability performance are achieved, which is significantly improved compared to the single-layer active layer structure.
Smart Images
Figure CN119997571A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of semiconductor thin film transistors, and in particular to a double-active-layer indium gallium tin oxide thin film transistor and a preparation method thereof. Background Art
[0002] As display technology develops towards large area, high refresh rate, high resolution, and flexible folding, thin film transistors (TFT) play a vital role as the core device in display technology.
[0003] In order to meet the development of display technology, TFT requires large mobility and good stability. According to the different semiconductor materials of the active layer, thin film transistors can be classified into hydrogenated amorphous silicon (α-Si), low temperature polycrystalline silicon (LTPS) and metal oxide (Metal Oxide). Among them, hydrogenated amorphous silicon and low temperature polycrystalline silicon have achieved large-scale industrialization. However, the mobility of hydrogenated amorphous silicon TFT is low (0.1~1cm 2 V -1 s -1 ), the preparation uniformity of low-temperature polysilicon is poor and the cost is high.
[0004] Compared with the other two materials, metal oxides have the advantages of higher mobility, better uniformity over a large area, lower preparation process temperature, and low-cost preparation. They provide technical support for new high-resolution, high refresh rate, low power consumption, flexible and other display technologies, and have received widespread attention at home and abroad.
[0005] However, the higher mobility of metal oxide thin film transistors usually leads to a more negative threshold voltage and poor stability, which has become a major challenge faced by metal oxide thin film transistors. Therefore, how to improve the mobility of metal oxide TFTs while maintaining a more positive threshold voltage and good stability has become a problem that needs to be solved urgently.
[0006] Therefore, in view of the shortcomings of the prior art, it is necessary to provide a double active layer InGaTnO thin film transistor and a preparation method thereof to overcome the shortcomings of the prior art. Summary of the invention
[0007] The object of the present invention is to avoid the shortcomings of the prior art and provide a double active layer indium gallium tin oxide thin film transistor and a preparation method thereof, wherein the obtained thin film transistor has high mobility, a relatively positive threshold voltage and good stability performance.
[0008] The purpose of the present invention is achieved through the following technical measures.
[0009] Provided is a double-active-layer indium gallium tin oxide thin-film transistor, comprising an indium gallium tin oxide double-layer active layer, wherein the second active layer is stacked and fixed on the first active layer, the gallium content in the first active layer is less than the gallium content in the second active layer, the tin content in the first active layer is greater than the tin content in the second active layer, and the indium content in the first active layer is greater than the indium content in the second active layer.
[0010] Preferably, in the above-mentioned dual-active-layer InGaTnO thin-film transistor, the mobility, threshold voltage and stability of the thin-film transistor are regulated by adjusting the gallium content of the first active layer and the second active layer.
[0011] Preferably, the second active layer is further doped with rare earth ions containing both trivalent and tetravalent ions, so that when negative bias light irradiation stress (NBIS) is applied, the photogenerated electrons move to the second active layer and are captured by the rare earth ions in the second active layer, which reduces the lifetime of the photogenerated electrons and improves the stability of the NBIS; while when positive bias light irradiation stress (PBIS) is applied, the electrons accumulate in the first active layer, which has no rare earth ions and has better PBIS stability. Therefore, the stability of both NBIS and PBIS can be improved at the same time.
[0012] Preferably, in the above-mentioned dual-active layer indium gallium tin oxide thin film transistor, the molar ratio of indium gallium elements in the first active layer is 100:10-30; and the molar ratio of indium gallium elements in the second active layer is 100:40-60.
[0013] Preferably, in the above dual active layer indium gallium tin oxide thin film transistor, the thickness of the first active layer is 0 to 10 nm, and the thickness of the first active layer is 10 nm to 20 nm. It should be noted that the thickness of the first active layer is 0 to 10 nm, and those skilled in the art should know that the case where the thickness of the first active layer is 0 is obviously excluded.
[0014] Preferably, the active layer of the dual-active-layer InGaSnO thin-film transistor is prepared by a co-deposition method, which may be a pulsed laser deposition method or a sputtering method.
[0015] Preferably, the active layer of the double active layer InGaTnO thin film transistor is prepared by a pulsed laser deposition method.
[0016] Furthermore, the preparation process of the active layer of the double active layer indium gallium tin oxide thin film transistor is as follows: -6The laser energy is below 250-450mJ, and the laser pulse ratio of ITO to Ga2O3 is 100:10-30 to deposit a 0-10nm IGTO film with a low Ga content as the first active layer, and then the laser pulse ratio of ITO to Ga2O3 is 100:40-60 to deposit a 10nm-20nm IGTO film with a high Ga content as the second active layer; the working pressure is 0-60mTorr, and the gas introduced is oxygen.
[0017] Furthermore, for the dual-active-layer InGaSnO thin-film transistor, the active layer annealing condition is: annealing for 1 hour in air at a temperature of 200-400°C.
[0018] The present invention also provides a method for preparing the above-mentioned double-active layer indium gallium tin oxide thin film transistor, wherein a first active layer and a second active layer are deposited in sequence to obtain a double-layer active layer structure, wherein the gallium content in the prepared first active layer is less than the gallium content in the second active layer, and the mobility, threshold voltage and stability of the thin film transistor are regulated by the gallium content in the first active layer and the second active layer.
[0019] Preferably, the method for preparing a dual active layer indium gallium tin oxide thin film transistor is performed at a background vacuum of 3×10 - 6 The laser energy is below 250-450mJ, and the laser pulse ratio of ITO to Ga2O3 is 100:10-30 to deposit a 0-10nm IGTO film with a low Ga content as the first active layer, and then the laser pulse ratio of ITO to Ga2O3 is 100:40-60 to deposit a 10nm-20nm IGTO film with a high Ga content as the second active layer; the working pressure is 0-60mTorr, and the gas introduced is oxygen.
[0020] The double active layer indium gallium tin oxide thin film transistor of the present invention and its preparation method are provided with a double active layer of indium gallium tin oxide, the second active layer is stacked and fixed on the top of the first active layer, the gallium content in the first active layer is less than the gallium content in the second active layer, the tin content in the first active layer is greater than the tin content in the second active layer, and the indium content in the first active layer is greater than the indium content in the second active layer. The present invention sets a double active layer, the component of the first active layer is an IGTO film with a low Ga content, which is conducive to forming a carrier transport channel, obtaining a larger current, and realizing high mobility of the thin film transistor; the second active layer adopts an IGTO film with a high Ga content, which is conducive to obtaining a more positive threshold voltage than the IGTO TFT with a low Ga content, and protects the first active layer from the influence of the external environment, and improves the electrical bias stability. Combining the two layers, a greater mobility can be obtained than the first active layer and the second active layer are used as active layers separately, and a more positive threshold voltage and good stability performance can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The present invention is further described with reference to the accompanying drawings, but the contents in the accompanying drawings do not constitute any limitation to the present invention.
[0022] Figure 1 It is a structural diagram of a double active layer indium gallium tin oxide thin film transistor of the present invention.
[0023] Figure 2 It is a flow chart of the method for preparing the thin film transistor of the present invention.
[0024] Figure 3 It is the transfer characteristic curve and mobility curve of the low Ga content single active layer thin film transistor prepared in comparative example 1 of the present invention.
[0025] Figure 4 These are the transfer characteristic curve and mobility curve of the high Ga content single active layer thin film transistor prepared in Comparative Example 2 of the present invention.
[0026] Figure 5 These are the transfer characteristic curve and mobility curve of the double active layer thin film transistor prepared in Example 2 of the present invention.
[0027] Figure 6 It is a comparison of the negative bias stress NBS stability of the single active layer IGTO thin film transistor prepared by comparative example 1 (a), comparative example 2 (b) and the double active layer IGTO thin film transistor prepared by embodiment 2 (c) of the present invention, and (d) the drift of the device threshold voltage with the stress action time. DETAILED DESCRIPTION
[0028] The present invention will be further described with reference to the following examples.
[0029] Example 1.
[0030] A double active layer indium gallium tin oxide thin film transistor, the structure of which is as follows Figure 1 As shown, there are provided: a substrate 10, a gate 11 located on the substrate 10, a gate insulating layer 12 located on the substrate 10 and the gate 11, an active layer 13 covering the upper surface of the gate insulating layer 12, and a source 14 and a drain 15 spaced apart from each other and electrically connected to the two ends of the active layer 13.
[0031] The substrate 10 may be one of substrate materials such as glass, a flexible polymer substrate, a silicon wafer, a metal foil, quartz, etc., and may further include a buffer layer or a water and oxygen barrier layer covering the substrate.
[0032] The material of the gate 11 can be a conductive material, such as metal, alloy, conductive metal oxide, doped silicon, conductive polymer, etc., or a superposition of two or more thin films composed of any combination of the above materials.
[0033] The gate insulating layer 12 can be an insulating material used for semiconductor devices, such as a single-layer film composed of silicon dioxide, silicon nitride, silicon oxynitride, aluminum oxide, aluminum oxide alloy, ytterbium oxide, titanium oxide, hafnium oxide, tantalum oxide, zirconium oxide, polymer insulating material, photoresist, etc., or a superposition of two or more thin films composed of any combination of the above materials.
[0034] The source electrode 14 and the drain electrode 15 may be made of a conductive material, such as a single-layer film of a metal, an alloy, a conductive metal oxide, a conductive polymer, etc., or a stack of two or more layers of films formed by any combination of the above materials.
[0035] The material of the channel layer 13 is an oxide semiconductor material. In the double active layer indium gallium tin oxide thin film transistor of this embodiment, the active layer 13 is set as a double active layer of indium gallium tin oxide (IGTO), the second active layer is stacked and fixed on the top of the first active layer, the gallium content in the first active layer is less than the gallium content in the second active layer, the tin content in the first active layer is greater than the tin content in the second active layer, and the indium content in the first active layer is greater than the indium content in the second active layer. The mobility, threshold voltage and stability of the thin film transistor are regulated by the gallium content of the first active layer and the second active layer. It should be noted that the upper and lower positions in this embodiment are described with the substrate as the bottom and the source and drain electrodes as the top.
[0036] By setting up a double-layer active layer, the materials of the first active layer and the second active layer are both IGTO thin films. The first active layer is composed of a low-Ga-content IGTO thin film, which is conducive to forming a carrier transport channel, obtaining a larger current, and realizing high mobility of the thin film transistor; the second active layer uses a high-Ga-content IGTO thin film, which is conducive to obtaining a more positive threshold voltage than the low-Ga-content IGTO TFT, and protects the first active layer from the external environment, improves stability, and can also improve device mobility.
[0037] As a preferred embodiment, the second active layer is further doped with trivalent and tetravalent rare earth ions, such as trivalent and tetravalent ions of cerium (Ce), praseodymium (Pr), samarium (Sm), europium (Eu), terbium (Tb) and dysprosium (Dy), with a content of 1-5 mol%. In this way, when negative bias light irradiation stress (NBIS) is applied, the photogenerated electrons move to the second active layer and are captured by the rare earth ions in the second active layer, which reduces the lifetime of the photogenerated electrons and improves the NBIS stability; while when positive bias light irradiation stress (PBIS) is applied, the electrons accumulate in the first active layer, which has no rare earth ions and has better PBIS stability. Therefore, the stability of NBIS and PBIS can be improved at the same time.
[0038] As a preferred method, the double active layer indium gallium tin oxide thin film transistor, the molar ratio of indium gallium element in the first active layer is 100:10-30; the molar ratio of indium gallium element in the second active layer is 100:40-60. The thickness of the first active layer is 0-10nm, and the thickness of the second active layer is 10nm-20nm. Under this parameter range, a double active layer indium gallium tin oxide thin film transistor with a threshold voltage value voltage drift in the range of -0.5V under 1H NBS test can be prepared.
[0039] The active layer can be prepared by a co-deposition method, which may be a pulsed laser deposition method or a sputtering method.
[0040] Preferably, the active layer is prepared by a pulsed laser deposition method. The preparation process of the active layer is: when the background vacuum is below 3×10-6mTorr, the laser energy is 250-450mJ, and a 0-10nm IGTO film with a low Ga content is deposited as the first active layer according to the laser pulse ratio of ITO to Ga2O3 of 100:10-30, and then a 10nm-20nm IGTO film with a high Ga content is deposited as the second active layer according to the laser pulse ratio of ITO to Ga2O3 of 100:40-60; the working pressure is 0-60mTorr, and the gas introduced is oxygen. The annealing conditions are: annealing for 1 hour in air at a temperature of 200-400°C.
[0041] The pulsed laser deposition method (PLD) has many advantages: (1) it can prepare thin films of various components, and the stoichiometric ratio of various components can be easily adjusted to study the role of each component; (2) the energy of the laser is very high, and the kinetic energy of the ablated particles is greater, so the quality of the thin film deposited on the substrate is also better; (3) the rate of thin film deposition is high; therefore, the present invention adopts pulsed laser deposition to prepare the active layer to improve the uniformity and density of the thin film covering the substrate.
[0042] The double active layer indium gallium tin oxide thin film transistor and its preparation method of the present invention are provided with an indium gallium tin oxide double active layer, the first active layer is composed of an IGTO thin film with a low Ga content, which is conducive to forming a carrier transport channel, obtaining a larger current, and realizing high mobility of the thin film transistor; the second active layer adopts an IGTO thin film with a high Ga content, which is conducive to obtaining a more positive threshold voltage than the IGTO TFT with a low Ga content, and protects the first active layer from the influence of the external environment, and improves the electrical bias stability. Combining the two layers can obtain a greater mobility than the first active layer and the second active layer as the active layer alone, and can obtain a more positive threshold voltage and good stability performance.
[0043] It should be noted that the characteristics of the double-layer active layer of the present invention are not only applicable to thin film transistor structures with bottom gate and top contact structures, but also applicable to thin film transistors with other structures such as top gate structures.
[0044] Example 2.
[0045] In this embodiment, a double active layer indium gallium tin oxide thin film transistor with a bottom gate top contact TFT device structure is prepared by a pulsed laser deposition co-deposition method. The prepared double active layer indium gallium tin oxide thin film transistor is used as a sample prepared by the method of Example 1.
[0046] The indium gallium tin oxide thin film transistor prepared by the method of this example includes: a substrate, a gate, a gate insulating layer, an active layer and a source-drain electrode arranged in sequence, such as Figure 1 As shown. Figure 2 As shown, the preparation method comprises the following steps:
[0047] Step S1: preparing a gate electrode and a gate insulating layer on the surface of a glass substrate;
[0048] Step S2: preparing an IGTO active layer by pulsed laser deposition and co-deposition;
[0049] Step S3: annealing the active layer prepared in step S2 in air;
[0050] Step S4: on the active layer, a conductive film is prepared as a source / drain electrode by DC magnetron sputtering deposition;
[0051] Step S5: annealing the device prepared in step S4 in air to obtain an IGTO thin film transistor prepared by pulsed laser deposition and co-deposition.
[0052] In step S1, Al:Nd metal prepared by magnetron DC sputtering method on the surface of glass substrate is used as gate with a thickness of 300nm, and a part of the gate is oxidized into AlO by anodization method. x :Nd, as the gate insulating layer. The unit area capacitance of the gate insulating layer is about 38nF / cm 2 , with a thickness of 200nm.
[0053] Step S2 is the key to the present invention. The double-layer active layer is made of indium gallium tin oxide active layer material prepared by pulsed laser deposition and co-deposition, and patterned by a mask. The preparation process of the active layer is: the background vacuum is 3×10 - 6mTorr; laser energy 450mJ; control the ratio of ITO and Ga2O3 laser pulses in each cycle to control the ratio of Ga in the IGTO film; the number of cycles is 3 to 30 to control the thickness of the active layer; the working pressure is 0 to 60mTorr, and the gas introduced is oxygen. According to the laser pulse ratio of ITO to Ga2O3 of 100:10 to 30, a 0 to 10nm IGTO film with a low Ga content is deposited as the first active layer, and then according to the laser pulse ratio of ITO to Ga2O3 of 100:40 to 60, a 10nm to 20nm IGTO film with a high Ga content is deposited as the second active layer.
[0054] The active layer material of the present invention is IGTO, and compared with the traditional active layer material IGZO, the Zn element is replaced by the Sn element; although the traditional IGZO has been widely used in commercial display technology, however, IGZO TFTs still face some challenges, such as poor gate bias stress stability, low carrier mobility (about 10cm 2 V -1 s -1 ) and other issues. Therefore, new AOS materials must be developed to meet the needs of science and technology; in this embodiment, IGTO is selected to replace IGZO AOS material. Since the s orbital overlap of In and Sn is greater than that of In and Zn, the permeation conduction path is enhanced, and a higher mobility can be achieved. In addition, Sn (528 kj mol -1 ) than Zn(250kj mol -1 ) has a stronger metal oxygen bond energy, which can reduce oxygen vacancies in the IGTO film, thereby improving the stability of the device. At the same time, the present invention adopts a co-deposition method to well control the Ga content in the IGTO to regulate the balance of mobility, threshold voltage and stability.
[0055] The active layer is an indium gallium tin oxide active layer material prepared by pulsed laser deposition (PLD) co-deposition. The proportion of gallium in the active layer is controlled by controlling the ratio of laser pulses hitting the ITO and Ga2O3 targets. A double-layer active layer is prepared, and the gallium content of the first active layer film is less than that of the second active layer, so as to regulate the mobility, threshold voltage and stability of the thin film transistor.
[0056] Step S3: anneal the active layer in air at a temperature of 200-400° C. for 1 hour.
[0057] Step S4, the preparation process of the source and drain electrodes is as follows: sputtering power 80W, working pressure 0.2-0.5Pa, sputtering gas is pure argon; electrode thickness is 200-300nm; source and drain electrodes are patterned through a mask.
[0058] Step S5, annealing conditions of source and drain electrodes are: in air, annealing temperature of ITO electrode is 200-400° C., annealing for 1 hour; annealing temperature of Mo / Al electrode is 100-300° C., annealing for 1 hour.
[0059] The double active layer indium gallium tin oxide thin film transistor was prepared through the above steps as the sample of Example 2.
[0060] In order to compare the results, comparative examples 1 and 2 were prepared.
[0061] Comparative Example 1:
[0062] Compared with Example 2, Comparative Example 1 is a single-layer oxide thin film transistor, that is, it does not contain a second active layer, which is a 10nm~20nm IGTO film with a low Ga content deposited in a ratio of 100:10~30. The components and preparation methods of the remaining structures are the same as those of Example 2.
[0063] Comparative Example 2:
[0064] Compared with Example 2, Comparative Example 2 is a single-layer oxide thin film transistor, that is, it does not contain the first active layer, which is a 10nm-20nm IGTO film with a high Ga content deposited in a ratio of 100:40-60. The components and preparation methods of the remaining structures are the same as those of Example 2.
[0065] The performance of the samples of Example 2, Comparative Example 1 and Comparative Example 2 were tested. Figure 3-5 The TFT performance test is further described in detail.
[0066] Figure 3 The transfer characteristic curve and mobility curve of comparative example 1, wherein the active layer is an IGTO film with a low Ga content deposited at a pulse ratio of ITO:Ga2O3 of 100:20, and the thickness is 13nm; the test conditions are V DS =15.1V, V G Sweep from -15V to 15V; its on-state current is 5.3×10 -4 A, the turn-on voltage is -8 V, and the saturation mobility is 18.3 cm 2 V -1 s -1 , subthreshold swing SS is 268mV / dec, on / off ratio is 10 8 .
[0067] Figure 4 The transfer characteristic curve and mobility curve of comparative example 2, the active layer of which is a high-Ga content IGTO film deposited with a pulse ratio of ITO:Ga2O3 of 100:50, and the thickness is 13nm. The test conditions are V DS=15.1V, V G Sweep from -15V to 15V; its on-state current is 1.6×10 -4 A, the turn-on voltage is 0 V, and the saturation mobility is 12 cm 2 V -1 s -1 , subthreshold swing SS is 102mV / dec, on / off ratio is 10 10 .
[0068] Figure 5 The transfer characteristic curve and mobility curve of the sample of Example 2, the active layer is first deposited with a 5nm IGTO film with a low Ga content at a ratio of 100:20, and then deposited with a 10nm IGTO film with a high Ga content at a ratio of 100:40, to obtain a double-layer IGTO active layer with different Ga contents; the test conditions are V DS =15.1V, V G Sweep from -15V to 15V; its on-state current is 3.1×10 -4 A, the turn-on voltage is -2V, and the saturation mobility is 20.3cm 2 V -1 s -1 , subthreshold swing SS is 131mV / dec, on / off ratio is 10 10 .
[0069] Figure 6 The NBS stability comparison of the samples of comparative example 1, comparative example 2 and embodiment 2 and the drift of the threshold voltage with the stress time. The test conditions of NBS stability are negative bias stress V G =-20V, V DS = 0V, and the stress is applied for 3600s (1h). It can be seen from the figure that the threshold voltage drift of the IGTO film with low Ga content in comparative example 1 is -1.6V under the 1h NBS stability test; the threshold voltage drift of the IGTO film with high Ga content in comparative example 2 is -0.4V under the 1h NBS stability test; and the threshold voltage drift of the IGTO film with double active layers in embodiment 1 is -0.8V under the 1h NBS stability test.
[0070] From the above results, it can be seen that the IGTO film with low Ga content in Example 1 has a large on-state current and a saturation mobility of 18.3 cm 2 V -1 s -1, but its turn-on voltage is very negative at -8V, and its subthreshold swing is large, which means that its interface defect state density is high, and the threshold voltage drift is -1.6V under the 1h NBS stability test, and the stability is poor. For the IGTO film with a high Ga content in Comparative Example 2, although its on-state current is much smaller, it can be turned on at around 0V, and the subthreshold swing is only 102mV / dec, which means that its interface defect state density is low, and the threshold voltage drift is only -0.4V under the 1h NBS stability test, and the stability performance is better. The sample of Example 2 uses a double active layer IGTO TFT, although its on-state current is lower than that of Comparative Example 1, its turn-on voltage becomes much more positive at -2.2V, and the mobility can be increased to 20.3cm 2 V - 1 s -1 , and can maintain a relatively low subthreshold swing of 131mV / dec, indicating that its interface defect state density is not high. In addition, under the 1h NBS stability test, the threshold voltage drift is -0.8V, which can be maintained within 1V. Compared with the comparative example 1, the threshold voltage drift is -1.6V, which has been significantly improved, and the stability performance is also better.
[0071] Example 3.
[0072] In this embodiment, a double active layer indium gallium tin oxide thin film transistor with a bottom gate top contact TFT device structure is prepared by a pulsed laser deposition co-deposition method, and the prepared double active layer indium gallium tin oxide thin film transistor is used as a sample prepared by the method of this embodiment.
[0073] The indium gallium tin oxide thin film transistor prepared by the method of this example includes: a substrate, a gate, a gate insulating layer, an active layer and a source-drain electrode arranged in sequence, and the specific steps are as follows.
[0074] Step S1: preparing a gate electrode and a gate insulating layer on the surface of a glass substrate;
[0075] Step S2: preparing an IGTO active layer by pulsed laser deposition and co-deposition;
[0076] Step S3: annealing the active layer prepared in step S2 in air;
[0077] Step S4: on the active layer, a conductive film is prepared as a source / drain electrode by DC magnetron sputtering deposition;
[0078] Step S5: annealing the device prepared in step S4 in air to obtain an IGTO thin film transistor prepared by pulsed laser deposition and co-deposition.
[0079] In step S1, Al:Nd metal prepared by magnetron DC sputtering method on the surface of glass substrate is used as gate with a thickness of 300nm, and a part of the gate is oxidized into AlO by anodization method. x :Nd, as the gate insulating layer. The unit area capacitance of the gate insulating layer is about 38nF / cm 2 , with a thickness of 200nm.
[0080] Step S2 is the key to the present invention. The double-layer active layer is made of indium gallium tin oxide active layer material prepared by pulsed laser deposition and co-deposition, and patterned by a mask. The preparation process of the active layer is: the background vacuum is 3×10 - 6 mTorr; laser energy 450mJ; control the ratio of ITO and Ga2O3 laser pulses in each cycle to control the ratio of Ga in the IGTO film; the number of cycles is 3 to 30 to control the thickness of the active layer; the working pressure is 0 to 60mTorr, and the gas introduced is oxygen. According to the laser pulse ratio of ITO to Ga2O3 of 100:10 to 30, a 0 to 10nm IGTO film with a low Ga content is deposited as the first active layer, and then according to the laser pulse ratio of ITO to Ga2O3 of 100:40 to 60, a 10nm to 20nm IGTO film with a high Ga content is deposited as the second active layer.
[0081] The active layer material of the present invention is IGTO, and compared with the traditional active layer material IGZO, the Zn element is replaced by the Sn element; although the traditional IGZO has been widely used in commercial display technology, however, IGZO TFTs still face some challenges, such as poor gate bias stress stability, low carrier mobility (about 10cm 2 V -1 s -1 ) and other issues. Therefore, new AOS materials must be developed to meet the needs of science and technology; in this embodiment, IGTO is selected to replace IGZO AOS material. Since the s orbital overlap of In and Sn is greater than that of In and Zn, the permeation conduction path is enhanced, and a higher mobility can be achieved. In addition, Sn (528 kj mol -1 ) than Zn(250kj mol -1 ) has a stronger metal oxygen bond energy, which can reduce oxygen vacancies in the IGTO film, thereby improving the stability of the device. At the same time, the present invention adopts a co-deposition method to well control the Ga content in the IGTO to regulate the balance of mobility, threshold voltage and stability.
[0082] The active layer is an indium gallium tin oxide active layer material prepared by pulsed laser deposition (PLD) co-deposition. The proportion of gallium in the active layer is controlled by controlling the ratio of laser pulses hitting the ITO and Ga2O3 targets. A double-layer active layer is prepared, and the gallium content of the first active layer film is less than that of the second active layer, so as to regulate the mobility, threshold voltage and stability of the thin film transistor.
[0083] Step S3: anneal the active layer in air at a temperature of 200-400° C. for 1 hour.
[0084] Step S4, the preparation process of the source and drain electrodes is as follows: sputtering power 80W, working pressure 0.2-0.5Pa, sputtering gas is pure argon; electrode thickness is 200-300nm; source and drain electrodes are patterned through a mask.
[0085] Step S5, annealing conditions of source and drain electrodes are: in air, annealing temperature of ITO electrode is 200-400° C., annealing for 1 hour; annealing temperature of Mo / Al electrode is 100-300° C., annealing for 1 hour.
[0086] Through the above steps, a dual active layer indium gallium tin oxide thin film transistor was prepared as a sample of Example 3. The threshold voltage drift of the device under PBIS was 0.5 V / h, and the threshold voltage drift under NBIS was -0.8 V / h. At the same time, it had good PBIS and NBIS stability.
[0087] Example 4.
[0088] A double active layer indium gallium tin oxide thin film transistor, the other features are the same as those of embodiment 2 or 3, except that the second active layer is doped with Pr 4+ and Pr 3+ Rare earth ions, content is 3 mol%.
[0089] The second active layer is further doped with both trivalent and tetravalent rare earth ions, so that when negative bias light irradiation stress (NBIS) is applied, the photogenerated electrons move to the second active layer and are captured by the rare earth ions in the second active layer, which reduces the lifetime of the photogenerated electrons and improves the stability of the NBIS; while when positive bias light irradiation stress (PBIS) is applied, the electrons accumulate in the first active layer, which has no rare earth ions and has better PBIS stability. Therefore, the stability of both NBIS and PBIS can be improved at the same time.
[0090] Example 5.
[0091] In this embodiment, a double active layer indium gallium tin oxide thin film transistor with a bottom gate top contact TFT device structure is prepared by a pulsed laser deposition co-deposition method. The prepared double active layer indium gallium tin oxide thin film transistor is used as a sample prepared by the method of Example 5.
[0092] The indium gallium tin oxide thin film transistor prepared by the method of this example includes: a substrate, a gate, a gate insulating layer, an active layer and a source-drain electrode arranged in sequence, and specifically includes the following steps.
[0093] Step S1: preparing a gate electrode and a gate insulating layer on the surface of a glass substrate;
[0094] Step S2: preparing an IGTO active layer by pulsed laser deposition and co-deposition;
[0095] Step S3: annealing the active layer prepared in step S2 in air;
[0096] Step S4: on the active layer, a conductive film is prepared as a source / drain electrode by DC magnetron sputtering deposition;
[0097] Step S5: annealing the device prepared in step S4 in air to obtain an IGTO thin film transistor prepared by pulsed laser deposition and co-deposition.
[0098] In step S1, Al:Nd metal prepared by magnetron DC sputtering method on the surface of glass substrate is used as gate with a thickness of 300nm, and a part of the gate is oxidized into AlO by anodization method. x :Nd, as the gate insulating layer. The unit area capacitance of the gate insulating layer is about 38nF / cm 2 , with a thickness of 200nm.
[0099] Step S2 is the key to the present invention. The double-layer active layer is made of indium gallium tin oxide active layer material prepared by pulsed laser deposition and co-deposition, and patterned by a mask. The preparation process of the active layer is: the background vacuum is 3×10 - 6 mTorr; laser energy 450mJ; control the ratio of ITO and Ga2O3 laser pulses in each cycle to control the ratio of Ga in the IGTO film; the number of cycles is 3 to 30 to control the thickness of the active layer; the working pressure is 0 to 60mTorr, and the gas introduced is oxygen. According to the laser pulse ratio of ITO to Ga2O3 of 100:10 to 30, a 0.1 to 10nm IGTO film with a low Ga content is deposited as the first active layer, and then according to the laser pulse ratio of ITO to Ga2O3 of 100:40 to 60, a 10nm to 20nm IGTO film with a high Ga content is deposited as the second active layer.
[0100] The active layer material of the present invention is IGTO, and compared with the traditional active layer material IGZO, the Zn element is replaced by the Sn element; although the traditional IGZO has been widely used in commercial display technology, however, IGZO TFTs still face some challenges, such as poor gate bias stress stability, low carrier mobility (about 10cm 2 V -1 s -1 ) and other issues. Therefore, new AOS materials must be developed to meet the needs of science and technology; in this embodiment, IGTO is selected to replace IGZO AOS material. Since the s orbital overlap of In and Sn is greater than that of In and Zn, the permeation conduction path is enhanced, and a higher mobility can be achieved. In addition, Sn (528 kj mol -1 ) than Zn(250kj mol -1 ) has a stronger metal oxygen bond energy, which can reduce oxygen vacancies in the IGTO film, thereby improving the stability of the device. At the same time, the present invention adopts a co-deposition method to well control the Ga content in the IGTO to regulate the balance of mobility, threshold voltage and stability.
[0101] The active layer is an indium gallium tin oxide active layer material prepared by pulsed laser deposition (PLD) co-deposition. The proportion of gallium in the active layer is controlled by controlling the ratio of laser pulses hitting the ITO and Ga2O3 targets. A double-layer active layer is prepared, and the gallium content of the first active layer film is less than that of the second active layer, so as to regulate the mobility, threshold voltage and stability of the thin film transistor.
[0102] Step S3: anneal the active layer in air at a temperature of 200-400° C. for 1 hour.
[0103] Step S4, the preparation process of the source and drain electrodes is as follows: sputtering power 80W, working pressure 0.2-0.5Pa, sputtering gas is pure argon; electrode thickness is 200-300nm; source and drain electrodes are patterned through a mask.
[0104] Step S5, annealing conditions of source and drain electrodes are: in air, annealing temperature of ITO electrode is 200-400° C., annealing for 1 hour; annealing temperature of Mo / Al electrode is 100-300° C., annealing for 1 hour.
[0105] Through the above steps, a dual active layer indium gallium tin oxide thin film transistor was prepared as a sample of Example 4. The threshold voltage drift of the device under PBIS was 0.3 V / h, and the threshold voltage drift under NBIS was -0.7 V / h. At the same time, it had good PBIS and NBIS stability.
[0106] Example 6.
[0107] A double active layer indium gallium tin oxide thin film transistor, the other features are the same as those of embodiment 5, except that the second active layer is doped with Pr 4+ and Pr 3+ Rare earth ions, content is 1 mol%.
[0108] The second active layer is further doped with both trivalent and tetravalent rare earth ions, so that when negative bias light irradiation stress (NBIS) is applied, the photogenerated electrons move to the second active layer and are captured by the rare earth ions in the second active layer, which reduces the lifetime of the photogenerated electrons and improves the stability of the NBIS; while when positive bias light irradiation stress (PBIS) is applied, the electrons accumulate in the first active layer, which has no rare earth ions and has better PBIS stability. Therefore, the stability of both NBIS and PBIS can be improved at the same time.
[0109] In summary, the present invention provides an indium gallium tin oxide thin film transistor prepared by pulsed laser deposition and co-deposition and a preparation method thereof, wherein a double-layer active layer is provided, wherein the first active layer is composed of an IGTO thin film with a low Ga content, which is conducive to forming a carrier transport channel, obtaining a larger current, and realizing high mobility of the thin film transistor; the second active layer uses an IGTO thin film with a high Ga content, which is conducive to obtaining a more positive threshold voltage than the IGTO TFT with a low Ga content, and protects the first active layer from the influence of the external environment, thereby improving the electrical bias stability. By combining the two layers, a greater mobility can be obtained than when the first active layer and the second active layer are used as active layers separately, and a more positive threshold voltage and good stability performance can be obtained.
[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.
Claims
1. A double active layer indium gallium tin oxide thin film transistor, characterized in that: An indium gallium tin oxide double-layer active layer is provided, the second active layer is stacked and fixed on the top of the first active layer, the gallium content in the first active layer is less than the gallium content in the second active layer, the tin content in the first active layer is greater than the tin content in the second active layer, and the indium content in the first active layer is greater than the indium content in the second active layer.
2. The double active layer InGaSnO thin film transistor according to claim 1, characterized in that: The mobility, threshold voltage and stability of the thin film transistor are regulated by adjusting the gallium content of the first active layer and the second active layer.
3. The double active layer InGaSnO thin film transistor according to claim 1, characterized in that: The second active layer is doped with both trivalent and tetravalent rare earth ions.
4. The double active layer InGaSnO thin film transistor according to claim 1, characterized in that: The molar ratio of the indium gallium element in the first active layer is 100:10-30; the molar ratio of the indium gallium element in the second active layer is 100:40-60.
5. The double active layer InGaSnO thin film transistor according to any one of claims 1 to 4, characterized in that: The thickness of the first active layer is 0-10 nm, and the thickness of the second active layer is 10 nm-20 nm; the active layer is prepared by a co-deposition method.
6. The double active layer InGaSnO thin film transistor according to claim 5, characterized in that: The active layer was prepared by pulsed laser deposition.
7. The double active layer InGaTnO thin film transistor according to claim 6, characterized in that: The preparation process of the active layer is as follows: the background vacuum is 3×10 -6 The laser energy is below 250-450mJ, and the laser pulse ratio of ITO to Ga2O3 is 100:10-30 to deposit a 0-10nm IGTO film with a low Ga content as the first active layer, and then the laser pulse ratio of ITO to Ga2O3 is 100:40-60 to deposit a 10nm-20nm IGTO film with a high Ga content as the second active layer; the working pressure is 0-60mTorr, and the gas introduced is oxygen.
8. The double active layer InGaTnO thin film transistor according to claim 7, characterized in that: The active layer annealing conditions are: annealing in air at a temperature of 200 to 400° C. for 1 hour.
9. A method for preparing a double active layer InGaSnO thin film transistor according to any one of claims 1 to 8, characterized in that: A first active layer and a second active layer are deposited in sequence to obtain a double-layer active layer structure, wherein the gallium content in the prepared first active layer is less than the gallium content in the second active layer, the tin content in the first active layer is greater than the tin content in the second active layer, and the indium content in the first active layer is greater than the indium content in the second active layer, and the mobility, threshold voltage and stability of the thin film transistor are regulated by the gallium content in the first active layer and the second active layer.
10. The method for preparing a double active layer indium gallium tin oxide thin film transistor according to claim 9, characterized in that: The background vacuum is 3×10 -6 The laser energy is below 250-450mJ, and the laser pulse ratio of ITO to Ga2O3 is 100:10-30 to deposit a 0-10nm IGTO film with a low Ga content as the first active layer, and then the laser pulse ratio of ITO to Ga2O3 is 100:40-60 to deposit a 10nm-20nm IGTO film with a high Ga content as the second active layer; the working pressure is 0-60mTorr, and the gas introduced is oxygen.