CN102226265A - A kind of amorphous oxide thin film and preparation method thereof - Google Patents

Abstract

The amorphous oxide thin film disclosed by the present invention has a chemical formula of In _x Al _y ZnO _2+1.5x+1.5y , 1≦x≦2, 0<y<2, and the resistivity of the film is 10 ^-4 ~10 ⁶ Ωcm, The average transmittance of visible light is greater than 85%, and the surface roughness is less than 1nm. It is prepared by magnetron sputtering or pulsed laser deposition. The In, Al and Zn elements in the thin film respectively play the role of increasing the mobility, controlling the carrier concentration and enhancing the stability of the amorphous state. The amorphous oxide thin film is suitable for use as a channel layer of a thin film transistor or as a transparent electrode.

Description

A kind of amorphous oxide thin film and preparation method thereof

technical field

The invention relates to an amorphous oxide film and a preparation method thereof.

Background technique

At present, the vast majority of flat panel display devices are active matrix display devices. The introduction of thin-film transistor (TFT) switching elements and storage capacitors in active matrix display devices can greatly improve the performance of display devices and achieve large-capacity, high-definition and full-color video display, which makes TFT the dominant force in today's flat-panel displays. technology. At present, amorphous silicon (α-Si) TFTs are mainly used in active matrix display devices, but α-Si-TFTs have low mobility (<1cm ² /Vs) and cannot drive large-scale high-definition displays, which is also the future of development. 3D display of maximum obstacles. At the same time, amorphous silicon TFT is opaque in the visible light range, and the pixel aperture ratio cannot reach 100%. In order to obtain sufficient brightness, it is necessary to increase the light intensity of the light source, thereby increasing power consumption; in addition, Si has strong photosensitivity in the visible light range and needs to be masked. Film layer (black matrix), these will increase the process complexity of TFT display, increase cost and reduce reliability.

Aiming at the problem of low mobility and opacity of amorphous silicon TFT, an effective solution is to use high mobility wide bandgap oxide semiconductor material instead of amorphous silicon as the channel layer. ZnO is one of the few oxides that can grow at a lower temperature or even at room temperature to obtain a film with good crystal quality and high mobility. At the same time, ZnO is also a wide bandgap semiconductor (the bandgap width at room temperature is 3.37eV), which has high transmittance in the visible light range, so there is no problem of light sensitivity of amorphous silicon. Therefore, in recent years, based on ZnO materials TFTs have been widely studied, but because the ZnO channel layer is a polycrystalline film, it is difficult to meet the requirements of large-area uniformity of flat panel display. Based on the above reasons, people have developed transparent amorphous oxides represented by InGaZnO. Compared with polycrystalline ZnO TFTs, InGaZnO is used as a channel layer in thin-film transistors to solve the problem of uniformity; compared with amorphous silicon TFTs, InGaZnO It has the advantages of high mobility, visible light transparency, and low-temperature process. Amorphous oxide will become the key material of the next generation of flat panel display, as well as the key material of flexible display and fully transparent display. However, InGaZnO also has shortcomings. For example, In and Ga are precious metals, and the cost of the device is high. At the same time, the InGaZnO channel layer and the source and drain electrodes are not easy to form a good ohmic contact, which affects the performance of the device.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and provide an amorphous oxide film that can be used as a channel layer of a thin film transistor or as a transparent electrode and a preparation method thereof.

The amorphous oxide thin film of the present invention has a chemical formula of In _x Al _y ZnO _2+1.5x+1.5y , 1≦ x ≦2, 0< y <2, the resistivity of the film is 10 ^-4 ~10 ⁶ Ωcm, and the migration The rate is greater than 10cm ² /Vs, the average transmittance of visible light is greater than 85%, and the surface roughness is less than 1nm.

The amorphous oxide thin film of the present invention can be prepared by magnetron sputtering or pulsed laser deposition, and the steps are as follows:

1) Sinter pure In ₂ O ₃ , pure Al ₂ O ₃ and pure ZnO according to the atomic ratio In:Al:Zn=x:y:1, 1≦ x ≦2, 0< y <2, and make ceramics target;

2) Using the magnetron sputtering method, a ceramic target is used as the target, and a layer of amorphous oxide film is deposited on the substrate. The sputtering conditions are: the distance between the target and the substrate is 5-10 cm, and the growth The vacuum degree of the chamber is at least 1×10 ^-3 Pa, the sputtering power is 50~300W, the working gas is a mixed gas of Ar and O ₂ , the oxygen partial pressure is 0~5%, and the total pressure is 0.6~1.2Pa; The temperature is from room temperature to 400°C;

Alternatively, a pulsed laser deposition method is used to deposit a layer of amorphous oxide film on the substrate with a ceramic target as the target. The deposition conditions are: the distance between the target and the substrate is 4-6 cm, and the vacuum degree of the growth chamber is Pumping to 1×10 ^-3 Pa, the growth chamber is fed with 0-100 SCCM of O ₂ , the total pressure is controlled to be 0.001-10 Pa, the substrate temperature is from room temperature to 400°C, and the laser energy is adjusted to 50-300 mJ.

The aforementioned substrate can be sapphire, quartz, glass, polyethylene phthalate (PET), polycarbonate (PC) or polyimide (PI).

The purity of the above-mentioned pure In ₂ O ₃ , pure Al ₂ O ₃ and pure ZnO is above 99.99%.

The thickness of the amorphous oxide thin film of the present invention is determined by the growth or deposition time, and can be used as a channel layer of a thin film transistor or as a transparent electrode according to different Al contents.

The beneficial effect that the present invention has compared with prior art is:

1) In _x Al _y ZnO _2+1.5x+1.5y (1≦ x ≦2, 0< y <2) is a transparent amorphous oxide semiconductor material, which is easy to prepare in large areas, with good uniformity and rough film surface Low density, compatible with large-area magnetron sputtering equipment commonly used in industry, suitable for mass production.

2) The In _x Al _y ZnO _2+1.5x+1.5y amorphous film has a low preparation temperature and can be deposited at a lower temperature or even at room temperature, so glass substrates and polymer flexible substrates can be used; at the same time, the amorphous film can be deposited at 500 The amorphous state can still be maintained well at ℃, so the subsequent processing temperature range of the device is wide.

3) The TFT with the amorphous In _x Al _y ZnO _2+1.5x+1.5y film as the channel layer has better performance than the amorphous silicon TFT. First of all, since In in the amorphous In _x Al _y ZnO _2+1.5x+1.5y has a spherically symmetrical 5S ² electron orbital with a large radius, the 5S ² electron orbitals of adjacent In atoms overlap to form an electron transport channel, so it is very The TFT with crystal In _x Al _y ZnO _2+1.5x+1.5y film as the channel layer has a large field effect mobility; secondly, In _x Al _y ZnO _2+1.5x+1.5y is an ionic bond semiconductor, relatively covalent Amorphous silicon of key semiconductors has a lower density of defect states, and thus has a smaller subthreshold swing and operating voltage than amorphous silicon TFTs.

4) TFT with amorphous In _x Al _y ZnO _2+1.5x+1.5y film as the channel layer has good uniformity. Compared with ZnO-TFT, the product yield rate is high and the stability is good.

5) In the amorphous In _x Al _y ZnO _2+1.5x+1.5y thin film, In, Al and Zn elements play the roles of improving the mobility, controlling the carrier concentration and enhancing the stability of the amorphous state, respectively. Compared with the InGaZnO-TFT that has been invented so far, Al has the same effect as Ga, and can also reduce the TFT off-state current. In the present invention, Al is cheaper and more environmentally friendly than Ga, and the product cost is low, and it is easy to be widely popularized and used.

6) Amorphous In _x Al _y ZnO _2+1.5x+1.5y film as channel layer TFT has the advantages of high field-effect mobility, sub-threshold swing, small working voltage, and good stability, and is suitable for large-area high-definition applications. Active Matrix Liquid Crystal Display (AMLCD) and Active Matrix Organic Light Emitting Diode Display (AMOLED) fields.

7) Amorphous In _x Al _y ZnO _2+1.5x+1.5y thin films are used as electrodes, which have low surface roughness, high visible light transmittance and good electrical properties, and are more suitable for optoelectronic devices electrode.

Description of drawings

Figure 1 is the ultraviolet-visible-infrared transmission spectrum of amorphous In _{x Aly} ZnO _2+1.5x+1.5y used as an electrode.

Detailed ways

Below in conjunction with accompanying drawing, the present invention will be further described:

Example 1:

1) Use In ₂ O ₃ , Al ₂ O ₃ and ZnO powders with a purity of 99.99% as source materials, weigh them according to the atomic ratio In:Al:Zn=2:1:1, and pour the weighed powders into In a ball mill jar equipped with agate balls and ethanol, mill on a ball mill for 48 hours to refine the powder and mix it evenly. Then the raw materials are separated and dried, added with a binder for grinding, and pressed into shape. Put the molded green body into a sintering furnace and sinter at 1300°C for 3 hours to obtain a ceramic target of In ₂ AlZnO _6.5 .

2) Fix the glass substrate on the sample tray after cleaning, and put it into the reaction vacuum chamber. Install the In ₂ AlZnO _6.5 ceramic target on the magnetron sputtering target head. Adjust the distance between the substrate and the target to 7 cm. The vacuum of the growth chamber was pumped to 1×10 ^-3 Pa, the growth chamber was fed with a mixed gas of Ar and O ₂ , the oxygen partial pressure was 1%, and the total pressure was 1 Pa. Deposit at room temperature, the deposition time was 10min, and the film thickness was 50nm. .

In ₂ AlZnO _6.5 film has high surface flatness and surface roughness less than 1nm. The resistivity is 10 ⁵ Ωcm, and the average transmittance of visible light is 90%.

The In ₂ AlZnO _6.5 film is used as the channel layer of the thin film transistor. The field effect mobility of the thin film transistor is 2 cm ² /Vs, the threshold voltage is 10V, and the on-off current ratio is greater than 10 ⁷ .

Example 2:

1) Use In ₂ O ₃ , Al ₂ O ₃ and ZnO powders with a purity of 99.99% as source materials, and weigh them according to the atomic ratio In:Al:Zn=1:0.1:1. Pour the weighed powder into a ball mill jar equipped with agate balls and ethanol, and mill it on a ball mill for 48 hours to refine the powder and mix it evenly. Then the raw materials are separated and dried, added with a binder for grinding, and pressed into shape. Put the formed green body into a sintering furnace and sinter at 1300°C for 3 hours to obtain a ceramic target of InAl _0.1 ZnO _2.55 .

2) Fix the glass substrate on the sample tray after cleaning, and put it into the reaction vacuum chamber. An InAl _0.1 ZnO _2.55 ceramic target was mounted on a pulsed laser deposition target head. Adjust the distance between the substrate and the target to 5.5 cm. The vacuum degree of the growth chamber was evacuated to 1×10 ^-3 Pa, the growth chamber was fed with 2.2 SCCM of O ₂ , the total pressure was controlled to 0.01Pa, the substrate temperature was raised to 350°C, the laser energy was adjusted to 300 mJ, and the deposition time was 30 min , film thickness 150nm.

InAl _0.1 ZnO _2.55 thin film has high surface flatness and surface roughness less than 1nm. It also has excellent electrical and optical properties, with a resistivity of 8×10 ^-4 Ωcm, a carrier concentration of 3×10 ²⁰ cm ^-3 , and a Hall mobility of 19 cm ² /Vs. The average transmittance in the visible light range is greater than 86%, see Figure 1.

Claims (3)

1. An amorphous oxide thin film, characterized in that the chemical formula is In _x Al _y ZnO _2+1.5x+1.5y , 1≦ x ≦2, 0< y <2, and the resistivity of the film is 10 ^-4 ~10 ⁶ Ωcm, the average transmittance of visible light is greater than 85%, and the surface roughness is less than 1 nm. 2. the preparation method of the described amorphous oxide film of claim 1 is characterized in that the steps are as follows: 1) Sinter pure In ₂ O ₃ , pure Al ₂ O ₃ and pure ZnO according to the atomic ratio In:Al:Zn=x:y:1, 1≦ x ≦2, 0< y <2, and make ceramics target; 2) Using the magnetron sputtering method, a ceramic target is used as the target, and a layer of amorphous oxide film is deposited on the substrate. The sputtering conditions are: the distance between the target and the substrate is 5-10 cm, and the growth The vacuum degree of the chamber is at least 1×10 ^-3 Pa, the sputtering power is 50~300W, the working gas is a mixed gas of Ar and O ₂ , the oxygen partial pressure is 0~5%, and the total pressure is 0.6~1.2Pa; The temperature is from room temperature to 400°C; Alternatively, a pulsed laser deposition method is used to deposit a layer of amorphous oxide film on the substrate with a ceramic target as the target. The deposition conditions are: the distance between the target and the substrate is 4-6 cm, and the vacuum degree of the growth chamber is Pumping to 1×10 ^-3 Pa, the growth chamber is fed with 0-100 SCCM of O ₂ , the total pressure is controlled to be 0.001-10 Pa, the substrate temperature is from room temperature to 400°C, and the laser energy is adjusted to 50-300 mJ. 3. by the preparation method of a kind of amorphous oxide film described in claim 2, it is characterized in that substrate is sapphire, quartz, glass, ethylene phthalate, polycarbonate or polyimide.

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