CN114481054B

CN114481054B - Oxide semiconductor target, thin film transistor and method for improving stability of oxide semiconductor target

Info

Publication number: CN114481054B
Application number: CN202210102412.0A
Authority: CN
Inventors: 兰林锋; 李潇; 彭俊彪
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2022-01-27
Filing date: 2022-01-27
Publication date: 2022-12-27
Anticipated expiration: 2042-01-27
Also published as: WO2023141967A1; CN114481054A

Abstract

An oxide semiconductor target, a thin film transistor and a method for improving the stability and mobility of the thin film transistor. Preparing a thin film material serving as a channel layer of the thin film transistor by using an oxide semiconductor target containing positive tetravalent lanthanide ions, and correspondingly preparing the thin film transistor. During illumination and negative grid voltage, the positive quadrivalent lanthanide series ion orbital hybrid transition absorbs blue light and even red and green light, and further down-converts the blue light and even the red and green light into low-energy light or a non-radiation form, so that the problems of increased conductivity and negative drift of threshold voltage caused by ionization of oxygen vacancies by blue light in backlight or self-luminescence are avoided, and the stability of NBIS is improved.

Description

Oxide semiconductor target, thin film transistor and method for improving stability of oxide semiconductor target

Technical Field

The invention belongs to the field of semiconductor materials and devices, and particularly relates to an oxide semiconductor target, a thin film transistor using the oxide semiconductor thin film as a channel layer, and a method for improving the stability and the mobility of the thin film transistor.

Background

In recent years, in the field of flat panel displays, particularly organic electroluminescent displays (OLEDs), thin-Film transistors (TFTs) based on oxide semiconductors have been gaining increasing attention.

TFTs, which are core components of display devices, are inevitably exposed to light in applications in the display field. For example: in liquid crystal display, the channel of the thin film transistor is irradiated by backlight; in OLED display, the channel of the thin film transistor is affected by self-luminescence of the OLED. Whether the backlight source or the OLED is self-luminous, the light emission is in a visible light range, and the largest photon energy is blue light emission. Oxide semiconductors (such as IZO and IGZO) are particularly sensitive to blue light because blue light ionizes oxygen vacancies of the oxide semiconductors and releases electrons into a conduction band to participate in conduction, thereby negatively drifting the threshold voltage of oxide semiconductor-based TFTs (referred to as oxide TFTs) and causing deterioration of display images.

Oxidation by oxygenNeutral oxygen vacancy (V) of the semiconductor under blue light irradiation _O ) Ionization to form positive divalent oxygen vacancy (V) _O ²⁺ ) Can cause lattice relaxation (e.g., V of ZnO) _O There will be 12% inward relaxation, and V after ionization _O ²⁺ There is 23% outward relaxation, with volume changes of up to 35% before and after ionization), so the ionization and recovery processes are slow, resulting in a continuous drift of the threshold voltage. Especially under negative gate bias and illumination, the energy band at the interface is tilted up and the valence band top is closer to the Fermi level, resulting in V _O ²⁺ The generation Energy (Formation Energy) of (V) is greatly reduced, when V is _O Will ionize more easily under light to form V _O ²⁺ Meanwhile, a large amount of photo-generated electrons are formed, and the threshold voltage drift phenomenon is serious. Therefore, not only is the stability of the oxide TFT under the influence of light improved, but also the problem of the stability of the threshold voltage of the oxide TFT under the influence of light plus Negative gate bias stress (NBIS) needs to be solved.

In the prior art, by adding a black matrix, the light-shielding treatment is performed on the channel layer of the thin film transistor, so that the light stability can be improved to a certain extent. However, this method merely solves the problem of stability under the influence of light irradiation, cannot solve the problem of light entering the oxide semiconductor layer by diffraction, and has a limited improvement in stability under long-term light irradiation conditions; moreover, the light shielding process is added, that is, the complexity of the preparation is increased, resulting in an increase in the manufacturing cost. Therefore, it is very important to improve the light stability of the oxide semiconductor itself.

Patent document 1 (CN 201710229199.9) discloses a rare earth oxide-doped oxide semiconductor thin film doped with praseodymium oxide, terbium oxide, dysprosium oxide, or ytterbium oxide. In the oxide doped in this patent, the rare earth element is trivalent, for example, praseodymium oxide is praseodymium trioxide, terbium oxide is also terbium trioxide, dysprosium oxide is dysprosium trioxide, and ytterbium oxide is ytterbium trioxide. According to the description of patent document 1, the principle of doping praseodymium oxide, terbium oxide, dysprosium oxide or ytterbium oxide is to replace original metal atoms with praseodymium, terbium, dysprosium and ytterbium atomsAnd the original M-M interaction is weakened, so that the valence band top is displaced, and the energy band structure of the original oxide semiconductor material is converted from a direct band gap to an indirect band gap. When incident light irradiates, valence band electrons of the indirect band gap need to interact with phonons to jump to a conduction band, so that contribution is made to transport characteristics, and the difficulty of increasing the generation of photo-generated electrons is increased. The material can reduce the threshold voltage shift of the device when the thin film transistor is irradiated by incident light, namely, the stability of illumination (without negative gate bias) is improved. However, the method of changing the energy band (top of valence band) structure by doping rare earth elements and increasing the difficulty of generating photo-generated electrons can only improve the stability of illumination (without adding negative gate bias), and cannot fundamentally solve the problem of poor stability under the more important stress of illumination plus negative gate bias (NBIS) faced by oxide TFTs. Because under negative gate bias, the energy band bends, the valence band at the interface warps upwards, the distance between the valence band top and the Fermi level is shortened, and oxygen vacancies (V) in positive and divalent states are generated _O ²⁺ ) The generated energy is greatly reduced; at this time, neutral oxygen vacancy (V) was observed under light irradiation _O ) More readily ionized, causing negative drift in the NBIS lower threshold voltage. That is, the method of reference 1 has much smaller effect on the change of the valence band top than the negative gate bias; therefore, the stability under illumination (without negative gate bias) can only be improved, and the problem of poor stability under illumination plus negative gate bias stress (NBIS), which is more important for oxide TFTs, cannot be fundamentally solved.

Non-patent document 1 (ACS appl. Mater. Interfaces 2019,11, 5232-5239) and non-patent document 2 (phys. Status Solidi a 2021,218, 2000812) disclose a Pr-doped oxide semiconductor material, in which Pr serves as a mediator, which can accelerate the recombination of electrons with positive divalent oxygen vacancies, reduce the lifetime of photogenerated electrons generated by ionization of oxygen vacancies, and improve the stability of light irradiation (without negative gate bias). However, ionization of neutral oxygen vacancy is not prevented in the mode, and Pr electrons are newly introduced to serve as electron traps, so that the electron traps can capture photo-generated electrons, and can also capture or scatter normal carriers, so that the mobility is reduced; meanwhile, because ionization of oxygen vacancies is not prevented, and only recombination is accelerated, rapid relaxation of crystal lattices can be caused, and under illumination plus negative bias stress (NBIS), because a large number of oxygen vacancies are ionized, the integral relaxation (expansion) of the crystal lattices is large, and the crystal lattices cannot be recovered quickly, the method can only improve the stability of illumination (without adding negative gate bias) and cannot thoroughly improve the stability under the illumination plus negative gate bias stress (NBIS). In addition, both the positive trivalent (containing 2 f electrons) and the positive quadrivalent (containing 1 f electron) contain less than full (or less than half full) f electrons, and the less than full or less than half full f electron structure is unstable and can be seriously influenced by a crystal field to form cleavage, so that a large number of defect state energy levels are caused, and the mobility and the subthreshold swing are seriously influenced. Therefore, in the oxide semiconductor material, the introduction of Pr ions cannot improve both mobility and NBIS stability.

Patent document 2 (CN 202011511468.9) discloses an oxide semiconductor doped with a trivalent positive rare earth compound, in which absorption of f-d transition is red-shifted by adjusting electronegativity of an anion. However, decreasing the electronegativity of the anion decreases the binding energy of the rare earth ion and the anion, so that impurities are decomposed to form during high-temperature sintering, thereby affecting the improvement of the performance.

Therefore, it is necessary to provide a solution that can essentially solve the stability problem of TFT devices under illumination plus negative gate voltage stress (NBIS), and that does not introduce new impurities or defect levels causing mobility degradation or process complexity increase.

Disclosure of Invention

The invention aims to essentially solve the problem of NBIS stability of an oxide TFT device, realize good device stability of the oxide TFT under illumination, particularly under NBIS, and avoid the additional performance, particularly the deterioration in mobility, caused by the complexity of a preparation process or the introduction of other impurities (or defect energy levels) due to a new scheme.

The above object of the present invention is achieved by the following technical means:

an oxide semiconductor target material is provided, which comprises a matrix oxide semiconductor material and a positive quadrivalent lanthanide ion, wherein the matrix oxide semiconductor material contains at least one of In, zn, sn, ga and Cd.

Oxidation of lanthanidesThe stable valence state of the lanthanide ion in the compound is usually trivalent and trivalent, such as lanthanum oxide, praseodymium oxide, neodymium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, etc. are usually the sesquioxide (Ln) ₂ O ₃ ) Only cerium oxide may be present in the form of CeO ₂ The form (2) exists stably. The f-d transition of the positive trivalent lanthanide ion is wide spectrum absorption, but the f-d transition energy gap of the positive trivalent rare earth ion is large, so that the positive trivalent rare earth ion only has strong wide spectrum absorption for ultraviolet or purple light generally, and cannot absorb a large amount of blue light, so that the problem of long-time threshold voltage stability under negative bias and visible light (LED backlight) irradiation (NBIS) cannot be solved. Ce ³⁺ The f-d absorption edge of the trivalent ion is the lowest and is positioned in a purple light area, and the f-d absorption edges of other trivalent ions are positioned in an ultraviolet light area. Tb ³⁺ The f-d transition of (a) requires a relatively high energy and the transition cannot be achieved by absorbing blue light, and thus, tb ³⁺ The broad spectrum of intense light emitted by the LED (blue portion) cannot be absorbed. Praseodymium (Pr) in the trivalent state ³⁺ ) Has weak band-shaped absorption in the blue light region of 450nm, which is Pr ³⁺ The f-f transition of (a) is absorbed, but the absorption is weaker because the f-f belongs to forbidden transition; in addition, the molar extinction absorption coefficient of the f-f transition is small, and the f-f transition absorption belongs to narrow spectrum absorption, so that the wide-spectrum intense light (blue light part) emitted by the LED cannot be completely absorbed. Therefore, doping with trivalent lanthanide ions has limited effect on improving photostability.

Part of lanthanide ions can have positive quadrivalence or positive bivalence under special conditions, and lanthanide ions with different valence states have channel hybridization charge transition absorption. In the process of orbital hybridization transition of positive tetravalent lanthanide ions, charge transition can absorb blue light or visible light, and relaxation of cations and anions can be mostly counteracted during orbital hybridization charge transition, so that large overall relaxation cannot be caused, therefore, orbital hybridization charge transition of lanthanide ions can more easily absorb photons than oxygen vacancies (the absorption of photons by oxygen vacancies is inhibited), and the lanthanide ions rapidly return to a ground state through nonradiative transition and other forms. The problem that ionization process and recovery process are slow due to severe lattice relaxation (expansion) caused by oxygen vacancy ionization is solved, and continuous threshold voltage drift is avoided.

Preferably, in the oxide semiconductor target, the positive lanthanide ion is Tb ⁴⁺ 。

Preferably, the oxide semiconductor target material, tb ⁴⁺ Ion number and Tb ³⁺ The ratio of the number of ions is greater than 0.1.

Preferably, the oxide semiconductor target material, tb ⁴⁺ Number of ions and Tb ³⁺ The ratio of the number of ions is greater than 1.

More preferably, the oxide semiconductor target material, tb ⁴⁺ Ion number and Tb ³⁺ The number of ions is greater than 2.

Most preferably, the oxide semiconductor target contains only Tb ⁴⁺ Does not contain Tb ³⁺ I.e. the matrix oxide semiconductor material is doped with positive quadrivalent terbium ion Tb only ⁴⁺ 。

In the prior art, the target needs to be sintered at high temperature, and even if the positive quadrivalent lanthanide ions exist in the raw materials, the lanthanide ions are easy to deoxidize and be reduced to positive trivalent ions in the high-temperature sintering process of the target due to the low redox potential. Thus, it is difficult to effectively incorporate a tetravalent lanthanide ion into the host oxide semiconductor material, with the lanthanide ion being substantially trivalent and trivalent in practical conventional target compositions. The solution method can form a tetravalent lanthanide ion in a special case, but the precursor and the solvent introduce a large amount of impurities, thereby reducing mobility. Oxide powder of lanthanide ions generally has a normal stable structure, and it is difficult to directly oxidize it into positive tetravalent oxide powder by a common method. Because the conventional oxide semiconductor target field has uncommon targets containing positive tetravalent lanthanide ions, the technical scheme of the oxide semiconductor target containing the positive tetravalent lanthanide ions cannot be set technically. Or, the person skilled in the art would not want to think in this direction. The method overcomes the technical bias, and selects the oxide semiconductor target material containing the positive tetravalent lanthanide ions as the technical scheme of the invention.

Further, the oxide semiconductor target material is prepared by the following method: firstly, oxide powder of lanthanide series element and matrix oxide semiconductor material powder are uniformly mixed, then are sintered in strong oxidizing atmosphere, are subjected to cold isostatic pressing or hot press molding after being subjected to secondary grinding and mixing, and are sintered in strong oxidizing atmosphere to obtain the oxide semiconductor target material. According to the method, terbium oxide powder and matrix oxide semiconductor material powder are mixed and sintered for multiple times, and when lanthanide ions and matrix oxide semiconductor material form a solid solution phase, trivalent lanthanide ions are easily oxidized into tetravalent lanthanide ions, so that the technical problem that tetravalent lanthanide ions are easily deoxidized to reduce trivalent positive ions and tetravalent positive lanthanide ions are not easily obtained when a target is sintered by a common method in the prior art is solved, and the proportion of tetravalent lanthanide ions in the target can be improved. It should be noted that the target material of the present invention is not limited to the preparation by this method.

The invention breaks through the limitation that the target material made of the conventional lanthanide is trivalent, and sets a new way for setting the oxide semiconductor target material containing the positive quadrivalent lanthanide ions, especially Tb ⁴⁺ The technical scheme of (1). Formation of a semiconductor material having positive tetravalent Tb using a host oxide semiconductor material ⁴⁺ For preparing a channel layer as a thin film transistor. Due to positive quadrivalence Tb ⁴⁺ When the thin film transistor is illuminated, blue light and even red light can be absorbed and further converted into a non-radiative form, so that the problems of increased conductance and negative drift of threshold voltage caused by ionization of oxygen vacancies by blue light in backlight or self-luminescence are avoided, and the illumination stability of the device is improved; under the condition of illumination plus negative grid voltage stress (NBIS), the problem of negative drift of the threshold voltage of the device can be solved; the problem of complicated preparation process is avoided, impurities or crystal field splitting energy level defects are not introduced, electron transportation is not influenced, and the TFT device with good NBIS stability and high mobility is realized.

The invention also provides an oxide semiconductor film which is prepared by a physical vapor deposition method, the thickness of the oxide semiconductor film is 3-200nm, and the target material used by the physical vapor deposition is the oxide semiconductor target material.

The present invention also provides a method of improving the stability of a thin film transistor,

preparing an oxide semiconductor target material, wherein the semiconductor target material comprises a matrix oxide semiconductor material and positive tetravalent lanthanide ions serving as functional ions, the functional ions can perform orbital hybridization, the energy required by orbital hybridization transition is not higher than that of blue light, and the functional ions are converted into a non-radiative form after orbital hybridization transition;

depositing an oxide semiconductor thin film for a channel layer of a thin film transistor through the oxide semiconductor target;

when the thin film transistor has illumination or illumination and negative grid bias voltage, the functional ions absorb blue light and even red and green light to realize orbital hybrid transition and convert the blue light and the red and green light into a non-radiative form; and the ionization of oxygen vacancies is prevented by absorbing illumination through the hybridization transition of functional ion orbitals, so that the serious lattice relaxation is avoided, and the threshold voltage drift is avoided.

Further, in the above method for improving stability and mobility of the thin film transistor, the positive tetravalent lanthanide ion is Tb ⁴ ⁺ ，Tb ⁴⁺ Ion number and Tb ³⁺ The ratio of the number of ions is greater than 0.1.

Preferably, the method for improving the stability of the thin film transistor is to deposit the oxide semiconductor thin film by a physical vapor deposition method.

The invention also provides a thin film transistor provided with a gate electrode, a channel layer, an insulating layer, and the like, the channel layer comprising one or more oxide semiconductor layers, wherein at least one of the oxide semiconductor layers is provided as the above-described oxide semiconductor thin film.

The thin film transistor is used for a driving back plate of display, and can also be used for an internal memory, a flash memory and a dynamic random access memory.

Compared with the prior art, the invention has the following advantages and beneficial effects:

the invention uses the oxide semiconductor target containing positive quadrivalent lanthanide series ion, especially positive quadrivalent terbium ion, to prepare the film material as the film transistor channel layer, and prepare the film transistor. Because the energy required by the orbital hybridization transition of the positive tetravalent terbium ion is lower, when the thin film transistor is illuminated, blue light and even red light can be absorbed and further converted into a non-radiation form, the problems of conductivity increase and threshold voltage negative drift caused by ionization of oxygen vacancies by the blue light in a backlight source or self-luminescence are avoided, and the illumination stability of the device is improved; under the condition of illumination and negative grid voltage stress (NBIS), the problem of negative drift of the threshold voltage of the device can be solved; the problem of complicated preparation process is avoided, impurities or crystal field splitting energy level defects are not introduced, electron transport is not influenced, and the TFT device with good NBIS stability and high mobility is realized.

Therefore, the oxide semiconductor target, the thin film and the transistor can keep the migration performance and improve the NBIS stability.

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings required to be used in some embodiments of the present invention will be briefly described below, and it is apparent that the drawings in the following description are only drawings of some embodiments of the present invention, and other drawings can be obtained by those skilled in the art according to these drawings. Furthermore, the drawings in the following description may be regarded as schematic diagrams, and do not limit the actual size of products, the actual flow of methods, the actual timing of signals, and the like, according to embodiments of the present invention.

FIG. 1 is a schematic diagram of a thin film transistor according to the present invention;

fig. 2 is a working schematic diagram of an address selection tube TFT1 and a driving tube TFT2 in the AMOLED display pixel driving;

FIG. 3 is a schematic illustration of the absorption energy levels of the f-d transition of a trivalent positive lanthanide ion in some experiments according to the present invention.

FIG. 4 is a schematic representation of the lowest energy required for the hybridization charge transitions of the positive trivalent and positive quadrivalent lanthanide ion orbitals in some experiments of the invention.

FIG. 5 shows different Tb's in example 5 of the present invention ⁴⁺ Reflectance spectrum of doped amount of target material.

FIG. 6 shows In utilization In example 6 of the present invention ₂ O ₃ Incorporation of Tb ⁴⁺ /Tb ³⁺ The Tb 4p peak spectrum of X-ray photoelectron spectroscopy (XPS) of the film prepared by sputtering the target material with the ratio of 1/1.

FIG. 7 shows pure In example 6 of the present invention ₂ O ₃ Transfer characteristics under NBIS of thin film transistors without Tb incorporation.

FIG. 8 shows In example 6 of the present invention ₂ O ₃ Incorporation of 3% of Tb, and Tb ⁴⁺ /Tb ³⁺ Transfer characteristic curve under NBIS of thin film transistor in case of = 1/0.

FIG. 9 shows In example 6 of the present invention ₂ O ₃ Incorporation of 3% of Tb, and Tb ⁴⁺ /Tb ³⁺ Transfer characteristic curve under NBIS of thin film transistor in case of =1/1

Fig. 10 is a schematic structural diagram of a thin film transistor in embodiment 9 of the present invention.

FIG. 11 shows the reflectance spectra of targets with different amounts of Pr doping in example 10 of the present invention.

FIG. 12 is a graph obtained by 3% Pr ⁴⁺ Transfer characteristics of the content of Thin Film Transistors (TFTs) under NBIS (white light illumination of the LED plus a gate bias of-20V).

FIG. 13 is a graph obtained by 7% Pr ⁴⁺ Transfer characteristic curves for Thin Film Transistors (TFT) under NBIS (white light illumination of LED plus-20V gate bias).

FIG. 14 shows a ratio of 3% based on Pr in example 11 of the present invention ⁴⁺ Content and same Tb ⁴⁺ The fluorescence spectra of the films in the contents were compared.

Detailed Description

The technical solutions in some embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present disclosure, and not all of the embodiments. The scope of the invention is not limited to the embodiments, and all other embodiments obtained by a person skilled in the art based on the embodiments provided by the disclosure belong to the scope of the disclosure.

Unless the context requires otherwise, throughout the description and the claims, the terms "comprise" (or include, contain, comprise) "and other forms thereof such as the third person's singular form" comprising "and the present participle form" comprising "are to be interpreted in an open, inclusive sense, i.e., as" including, but not limited to ". In the description of the specification, the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" and the like are intended to indicate that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. The schematic representations of the terms used above are not necessarily referring to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics may be included in any suitable manner in any one or more embodiments or examples.

Herein, a host oxide semiconductor material (e.g., in) ₂ O ₃ 、ZnO、InGaZnO ₄ Etc.) may be perfectly stoichiometrically matched, or non-stoichiometrically matched conditions such as oxygen vacancies, oxygen interstitials, cation vacancies, cation interstices, etc. may exist.

As used herein, "ion" is a representation of a chemical valence state, and is not limited to ionic compounds, but rather, elements of ionic compounds and covalent compounds may be referred to as "ions".

"at least one of A, B and C" has the same meaning as "at least one of A, B or C" and includes the following combinations of A, B and C: a alone, B alone, C alone, a combination of A and B, A and C in combination, B and C in combination, and A, B and C in combination.

"A and/or B" includes the following three combinations: a alone, B alone, and a combination of A and B.

The use of "adapted to" or "configured to" herein is meant to be an open and inclusive language that does not exclude devices adapted to or configured to perform additional tasks or steps.

Additionally, the use of "based on" means open and inclusive, as a process, step, calculation, or other action that is "based on" one or more stated conditions or values may in practice be based on additional conditions or values beyond those stated.

Example embodiments are described herein with reference to cross-sectional and/or plan views as idealized example figures. In the drawings, the thickness of layers and regions are exaggerated for clarity. Variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, the exemplary embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an etched region shown as a rectangle will typically have curved features. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the exemplary embodiments.

Some embodiments of the present disclosure provide a display device, which includes a display panel, and a driving circuit, such as a pixel driving circuit, a gate driving circuit, etc., disposed on the display panel.

Thin-Film transistors (TFTs) are important components constituting a pixel driving circuit, a gate driving circuit, and the like, and in the power-on process, the pixel driving circuit and the gate driving circuit are controlled to drive the display panel to display by controlling the on and off of the TFTs. It should be noted that the thin film transistor is one of the transistors, and the material, the manufacturing method and the device of the present invention are applicable to all types of transistors, and are not limited to thin film transistors; the application range is not limited to the display field, and other application fields of the transistor, such as a memory, a flash memory, a dynamic random access memory and the like, can also be included.

The Display device may be one of LCD (Liquid Crystal Display), OLED (Organic Light-Emitting Diode), QLED (Quantum Dot Light-Emitting Diode), micro led (Micro Light-Emitting Diode), miniLED (Mini Light-Emitting Diode), and the like.

The display device may be a mobile phone, a tablet computer, a notebook, a Personal Digital Assistant (PDA), a car computer, a laptop, a digital camera, etc.

The form of the display device is not limited, and rigid display, flexible display, stretchable display, display of any shape, and the like can be used.

The TFT mainly includes an amorphous silicon (e.g., hydrogenated amorphous silicon: a-Si: H) TFT, a Low Temperature Poly-silicon (LTPS) TFT, an oxide TFT, an organic TFT, and the like, depending on the material of the channel layer.

Wherein the oxide TFT is an oxide semiconductor (e.g. In) ₂ O ₃ ZnO, inZnO, inGaZnO, etc.) as a channel layer, much attention has been paid to the advantages of relatively high carrier mobility of an oxide semiconductor, low process temperature, low off-state current, good uniformity of devices, and the like. Meanwhile, the oxide TFT has some problems to be solved, for example, the stability of the oxide TFT under the negative gate voltage stress (NBIS) is still insufficient. Particularly, in the case of a TFT which is a display panel member, it is inevitably irradiated with light in the application to the display field. For example, as shown in fig. 1, in a liquid crystal display, the channel 131 of the TFT may be irradiated with backlight, and in an OLED display, the channel 131 of the TFT may be affected by self-luminescence of the OLED. Whether the backlight source or the self-luminous light source is adopted, the light emission is in a visible light range, and the light with the largest photon energy is blue light emission. Oxide semiconductors (such as IZO (Indium Zinc Oxide), IGZO (Indium Gallium Zinc Oxide), etc.) are particularly sensitive to blue light, because blue light ionizes oxygen vacancies in the Oxide semiconductor material and releases electrons into a conduction band to participate in conduction, thereby negatively drifting threshold voltage and causing deterioration of a display screen.

Here, as shown in fig. 2, in an AMOLED (Active-matrix organic light emitting diode) display pixel driving, at least two TFTs, which are respectively referred to as an address selection transistor TFT1 and a driving transistor TFT2, are included as an example,since oxide TFTs mostly only exhibit n-channel characteristics, they are turned on at positive gate voltages and turned off at negative gate voltages (when the oxide semiconductor carrier concentration is high, a normally-on state occurs, i.e., a negative gate voltage is required to turn them off completely). In each scanning period, the address transistor TFT1 is turned on only once, and is turned off in the rest of the time, so that the stability of the address transistor TFT1 under Negative Bias Stress (NBS) is very important. The source electrode of the driving tube TFT2 is directly connected with the OLED, and as long as the OLED emits light, a certain current flows through the source electrode and the drain electrode of the driving tube TFT2, so that the driving tube TFT2 is basically in an open state, the stability of the driving tube TFT under Positive Bias Stress (PBS) is important, and the oxide TFT shows a threshold voltage (V) under the gate Stress _th ) A drift phenomenon.

Hereinafter, the case of causing the threshold voltage shift under illumination will be described in detail. Neutral oxygen vacancy (V) under blue light irradiation _O ) Ionization to form positive divalent oxygen vacancy (V) _O ²⁺ ) Can cause lattice relaxation (e.g., V of ZnO) _O There will be 12% inward relaxation, and V after ionization _O ²⁺ There is 23% outward relaxation, with volume changes of up to 35% before and after ionization), so the ionization and recovery processes are slow, resulting in a continuous drift of the threshold voltage. Especially under negative grid bias and illumination, the energy band at the interface is tilted up, and the valence band top is closer to the Fermi level, resulting in V _O ²⁺ The generation Energy (Formation Energy) of (V) is greatly reduced _O Will ionize more easily under light to form V _O ²⁺ Meanwhile, a large amount of photo-generated electrons are formed, and the threshold voltage drift phenomenon is serious. Therefore, it is important to improve the threshold voltage stability of the oxide TFT under NBIS (Negative bias illumination stress).

Some embodiments of the present invention provide a transistor (or a thin film transistor) provided with a gate electrode, a channel layer provided as the above-described oxide semiconductor thin film including a host oxide semiconductor material and a positive tetravalent lanthanoid ion, an insulating layer, and the like. In some embodiments, the transistor comprises: the grid electrode, the channel layer, the insulating layer positioned between the grid electrode and the channel layer, and the source electrode and the drain electrode which are respectively and electrically connected with two ends of the channel layer; the electrical connection means that a conductive channel is arranged between the two, and the two can be in direct contact, and can further comprise a buffer layer and the like. It is to be noted that the specific structure of the transistor may adopt different structure types such as a bottom gate top contact, a bottom gate bottom contact, a top gate top contact, a top gate bottom contact, and the like, as long as the channel layer thereof is the above-mentioned oxide semiconductor thin film containing the host oxide semiconductor material and the positive tetravalent lanthanoid ion, which belong to the technique of the present invention.

In some embodiments, the channel layer may comprise one or more thin films, wherein at least one of the thin films is provided as the oxide semiconductor thin film comprising a host oxide semiconductor material and a positive tetravalent lanthanide ion described above. At this time, the thin films at different positions of the channel layer can be made of oxide semiconductor materials doped with different positive tetravalent lanthanide ions; or selecting the oxide semiconductor materials doped with the same positive tetravalent lanthanide ions and with different doping amounts; or any combination of thin films of oxide semiconductor material doped with positive tetravalent lanthanide ions and oxide semiconductor material not doped with positive tetravalent lanthanide ions. Here, the application position and the application doping ratio of the oxide semiconductor material doped with the positive tetravalent lanthanide ion in the channel layer are not particularly limited.

Hereinafter, the technical solution provided by the present invention will be exemplarily described in detail through specific experimental examples.

Example 1.

An oxide semiconductor target comprising a matrix oxide semiconductor material and a positive tetravalent lanthanide ion Tb ⁴⁺ . The matrix oxide semiconductor material is an oxide material and contains at least one of five elements including In, zn, sn, ga and Cd.

The matrix oxide semiconductor material is an oxide material, contains at least one of five elements of In, zn, sn, ga and Cd, and can further contain at least one of elements such as Al, B, sc, Y, zr, hf, ta, W and Mg.

The innovation point of the scheme is to form a target material containing positive quadrivalent lanthanide ions. The modifying substance being, in addition to the host oxide semiconductor material, a positive tetravalent lanthanide ion Tb ⁴⁺ Usually, tb is contained in a certain proportion due to factors such as preparation process ³⁺ . Except for Tb ⁴⁺ 、Tb ³⁺ In addition, other elemental substances are not treated as impurities for the target dopant substance, and ideally the target material does not contain impurities. The oxide semiconductor target material must contain a certain proportion of Tb ⁴⁺ Ions of other valency states, e.g. Tb ³⁺ Or other impurities are not required.

In the oxide semiconductor target material, the ratio of the number of terbium ions to the number of all cations is between 0.05% and 10%. It should be noted that, the ratio relationship between the substrate oxide semiconductor material and the modified substance in the target material can be flexibly selected by those skilled in the art according to actual needs, which is not a main research problem of the present invention.

In order to make the oxide semiconductor target meet the required performance, tb in the target is controlled and improved ⁴⁺ The content of ions is critical. Specifically, in the oxide semiconductor target, tb ⁴⁺ Number of ions and Tb ³⁺ The ratio of the number of ions is controlled to 0.1 or more, preferably 1 or more, and more preferably 2 or more. In the oxide semiconductor target material, the modified substance is Tb ⁴⁺ The performance is optimal.

In the prior art, an oxide semiconductor target containing positive quadrivalent lanthanide series ions is difficult to obtain and almost does not exist. The lanthanide ion is represented by Ln, since Ln ³⁺ —Ln ⁴⁺ Has a low redox potential and is difficult to remove from In ₂ O ₃ 、ZnO、SnO ₂ Oxygen is deprived from the oxide semiconductor to be oxidized into positive quadrivalence; in addition, the positive quadrivalent lanthanide series ions are easy to deoxidize and reduced into positive trivalent ions in the high-temperature sintering process of the target material. Therefore, it is difficult to effectively incorporate a positive tetravalent lanthanide ion in the host oxide semiconductor material. Solution processes can form the n-tetravalent lanthanide ion under special circumstances, but precursors and solventsImpurities are introduced to lower mobility. Oxide powder of lanthanide ions generally has a normal stable structure, and is difficult to be directly oxidized into positive tetravalent oxide powder by a common method; when the target is sintered at high temperature by a common method, the target is easy to deoxidize so that the positive quadrivalent lanthanide ions are reduced into positive trivalent ions. All the factors limit the prior art that the oxide semiconductor target containing the positive quadrivalent lanthanide ions is not easy to obtain. Thus, in the case where the raw material is not readily available, the skilled person would not consider the related art concept of improving the stability of the thin film transistor NBIS by a positive tetravalent lanthanide ion.

The invention breaks through the limitation that the target material made of the conventional lanthanide is trivalent, and overcomes the technical bias of setting a technical scheme that the oxide semiconductor target material contains positive quadrivalent lanthanide ions. The method of the invention utilizes a process to make tetravalent lanthanide ions and a matrix oxide semiconductor material form a solid solution phase, and the trivalent lanthanide ions are relatively easy to be further oxidized into tetravalent lanthanide ions, thereby improving the proportion of the tetravalent lanthanide ions in the target material.

The target material is prepared by the following method: the terbium oxide powder and the matrix oxide semiconductor material powder are uniformly mixed, then sintered in a strong oxidizing atmosphere, ground, mixed, formed by cold isostatic pressing or hot pressing, and sintered in the strong oxidizing atmosphere. By utilizing the preparation method of the target material, tb can be controlled to be improved ⁴⁺ Ion number and Tb ³⁺ The ratio of the number of ions.

Specifically, terbium oxide powder and matrix oxide semiconductor material powder are uniformly mixed, then sintered in a strong oxidizing atmosphere, ground, mixed, formed by cold isostatic pressing or hot pressing, and then sintered in a strong oxidizing atmosphere. Or the terbium oxide powder can be further oxidized into dioxide or into oxides or mixtures of positive quadrivalent and positive trivalent lanthanide series ions, the ground mixture is uniformly mixed with the matrix oxide semiconductor material powder, then the mixture is sintered in a strong oxidizing atmosphere, the mixture is ground and mixed for the second time, and then the mixture is sintered in the strong oxidizing atmosphere through cold isostatic pressing or hot pressing. It should be noted that the oxide semiconductor target material of the present invention is not limited to being prepared by the preparation method in the present embodiment, and other preparation methods are also applicable to the preparation of the oxide semiconductor target material of the present invention.

The stable valence state of the lanthanide ion in the lanthanide oxide is usually trivalent and trivalent, such as lanthanum oxide, praseodymium oxide, neodymium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, etc. are usually sesquioxide (Ln) ₂ O ₃ ) Exist in the form of (1). The f-d transition of the positive trivalent lanthanide ion is wide spectrum absorption, but the f-d transition energy gap of the positive trivalent rare earth ion is large, so that the positive trivalent rare earth ion only has strong wide spectrum absorption for ultraviolet or purple light generally, and cannot absorb a large amount of blue light, so that the problem of long-time threshold voltage stability under negative bias and visible light (LED backlight) irradiation (NBIS) cannot be solved. FIG. 3 shows the absorption edge of the f-d transition of a trivalent lanthanide cation, and it can be seen that Ce ³⁺ The f-d absorption edge of the trivalent ion is the lowest and is positioned in the purple light region, and the f-d absorption edges of other trivalent ions are positioned in the ultraviolet light region. Tb ³⁺ The f-d transition of (a) requires a relatively high energy and the transition cannot be achieved by absorbing blue light, and thus, tb ³⁺ The broad spectrum of intense light emitted by the LED (blue portion) cannot be absorbed. Praseodymium (Pr) in the trivalent state ³⁺ ) Has weak band-shaped absorption in the blue light region of 450nm, which is Pr ³⁺ The f-f transition of (a) is absorbed, but the absorption is weaker because the f-f belongs to forbidden transition; in addition, the molar extinction absorption coefficient of the f-f transition is small, and the f-f transition absorption belongs to narrow spectrum absorption, and cannot completely absorb the light (blue light part) with wide spectrum and strong intensity emitted by the LED. Therefore, doping with trivalent lanthanide ions has limited effect on improving photostability.

The most stable valence states of lanthanide ions are positive trivalent, part of lanthanide ions can have positive quadrivalent, and lanthanide ions with different valence states have channel hybridization charge transition absorption. In the process of positive tetravalent lanthanide ion orbital hybridization transition, the charge transition can absorb blue light or visible light, and the relaxation of cations and anions can be mostly counteracted during orbital hybridization charge transition, so that large overall relaxation cannot be caused, therefore, the orbital hybridization charge transition of lanthanide ions is easier to absorb photons than oxygen vacancies (the oxygen vacancies are inhibited from absorbing photons), and rapidly returns to the ground state through radiationless transition and the like. The problem that ionization process and recovery process are slow due to serious lattice relaxation (expansion) caused by oxygen vacancy ionization is solved, and continuous drift of threshold voltage is avoided.

Fig. 4 shows the lowest energy (absorption edge) required for the orbital hybrid charge transition for trivalent and tetravalent lanthanide ions in some experiments, and it can be seen that the absorption edges of trivalent lanthanide ions are both greater than 4.5eV and are located in the ultraviolet region. Compared with f-f transition and f-d transition, the positive quadrivalent lanthanide series ion orbital hybridization charge transition is allowed by selection law and is 10 more than the f-f transition in strength ⁶ Above, and with broad spectral absorption, the absorption spectrum is much wider than the f-f transition, and even wider than the f-d transition, so the orbital hybrid charge transition of lanthanide ions can absorb very strong broad spectrum light.

In the lanthanoid elements, ce, pr and Tb can have positive quadrivalent ions, wherein Ce ⁴⁺ Most stable, tb ⁴⁺ And Pr ⁴⁺ Unstable in the solid state. Nd and Dy have positive tetravalent ions in special cases, but are extremely unstable. Compared with Pr ⁴⁺ And Tb ⁴ ⁺ ，Ce ⁴⁺ Higher energy is required for orbital hybrid charge transition, so Ce ⁴⁺ The orbital hybridization transition of (1) can only absorb ultraviolet light, and is difficult to absorb blue light, so that Ce is doped into the oxide semiconductor ⁴⁺ The improvement of the photostability is limited. And Pr ⁴⁺ And Tb ⁴⁺ Compared to Ce ⁴⁺ The low-temperature-resistant oxide semiconductor material can absorb blue light, even red light and green light, and further down-convert the blue light and the green light into low-energy light or non-radiation light, so that the threshold voltage drift phenomenon caused by the fact that oxygen vacancies in the oxide semiconductor absorb blue light to ionize and release electrons is avoided. As shown in FIG. 4, ce ⁴⁺ Has an absorption edge of about 4.0eV and is also located in the UV region. Tb ⁴⁺ And Pr ⁴⁺ Is located in the blue region. And Nd ⁴⁺ And Dy ⁴⁺ Although visible light is also absorbed, it is very unstable.

In solids containing a tetravalent lanthanide ion, in general the same appliesWhen the lanthanide ions with the positive valence and the trivalent valence exist, the analysis shows that the lanthanide ions with the positive valence and the trivalent valence have little effect on the improvement of the NBIS stability, and can also influence the electron transportation and reduce the mobility. Furthermore, the positive trivalent lanthanide ion has a much larger radius than the positive tetravalent lanthanide ion, much larger than In the host oxide semiconductor material ³⁺ 、Zn ²⁺ 、Ga ³⁺ And Sn ⁴⁺ Radius (all are less than

) Therefore, the lattice relaxation of the host oxide semiconductor material doped with trivalent positive lanthanide ions is much more severe and the mobility is lower than the lattice relaxation of the host oxide semiconductor material doped with tetravalent positive lanthanide ions. Therefore, in the case where the amount of the lanthanide ion (including positive tetravalent and other valence states) to be incorporated is constant, the greater the ratio of the amount of the positive tetravalent lanthanide ion to the amount of the lanthanide ion in the other valence state, the more significant the effect of improving the light stability. Similarly, in the case of a certain amount of doped tetravalent lanthanide ions, the larger the ratio of the amount of positive tetravalent lanthanide ions to the amount of lanthanide ions in other valence states, the less the total amount of lanthanide ions (including positive tetravalent and other valence states) contained in the material, the smaller the scattering of electrons, and the higher the mobility.

In addition, due to concentration quenching, the positive trivalent lanthanide ion can affect the absorption of light by the positive tetravalent lanthanide ion. Thus, the ratio of the number of positive tetravalent lanthanide ions to the number of lanthanide ions in other valencies is greater than 0.1. More preferably, the ratio of the number of positive tetravalent lanthanide ions to the number of lanthanide ions in other valences is greater than 1. More preferably, the ratio of the number of positive tetravalent lanthanide ions to the number of lanthanide ions in other valences is greater than 2. Most preferably, all lanthanide ions are positive tetravalent.

The doping amount of the lanthanide ions required by the oxide semiconductor target material is less because the ratio of the number of the positive tetravalent lanthanide ions to the number of the lanthanide ions in other valence states is higher. Preferably, the ratio of the number of lanthanide ions to the number of all cations is between 0.05% and 10%. More preferably, the ratio of the number of lanthanide ions to the number of all cations is between 0.05% and 5%.

The invention breaks through the limit that the target material made of the conventional lanthanide element is trivalent, and develops a new technical scheme that the oxide semiconductor target material contains positive quadrivalent terbium ion. An oxide semiconductor target having a positive tetravalent lanthanide ion is formed using a host oxide semiconductor material for use in the preparation of a channel layer as a thin film transistor. Due to the characteristic of lower energy required by the orbital hybridization transition of the positive quadrivalent lanthanide ions, when the thin film transistor is illuminated, blue light and even red light can be absorbed and further converted into a non-radiative or low-energy light form, so that the problems of increased conductance and negative drift of threshold voltage caused by ionization of oxygen vacancies by the blue light in a backlight source or self-luminescence are avoided, and the illumination stability of the device is improved; under illumination plus negative gate voltage stress (NBIS), the problem of negative drift of the threshold voltage of the device can be solved, and the TFT has good stability under illumination, particularly under NBIS; the problem of complicated preparation process is avoided, impurities or crystal field splitting energy level defects are not introduced, electron transport is not influenced, and the TFT device with good NBIS stability and high mobility is realized.

Example 2.

An oxide semiconductor target material, which comprises a matrix oxide semiconductor material and positive terbium (Tb) ion ⁴⁺ 。

Incorporating only Tb in the host oxide semiconductor material ⁴⁺ The oxide semiconductor target material and the prepared thin film transistor have high electron mobility and NBIS performance stability. Experiments show that Tb is doped compared with other elements ⁴⁺ The performance of (2) is optimal.

Tb ⁴⁺ Contains 7 f electrons and is in a relatively stable half-full state, so Tb ⁴⁺ Can effectively avoid the influence of crystal field, namely different host oxide semiconductor material environments and oxygen vacancy environments on Tb ⁴⁺ The influence of the electronic structure is small. Thus, tb is doped in the host oxide semiconductor material ⁴⁺ Can improve the mobility and stability and widen the process window.

In addition to this, the present invention is,

has an ionic radius close to that in the host oxide semiconductor material

And

of the radius of (a). Thus, tb is doped in the host oxide semiconductor material ⁴⁺ The crystal lattice relaxation is small, the damage to the crystal lattice is small, and the mobility is high. Tb ⁴⁺ Absorbing blue light and converting the blue light into a non-radiation form without the influence of other stray light, so Tb ⁴⁺ The doping is more effective for improvement of photostability of the oxide semiconductor. Thus, the positive tetravalent lanthanide ion is Tb ⁴⁺ The oxide semiconductor target material has the best performance.

Example 3.

An oxide semiconductor thin film is prepared by a physical vapor deposition method, the thickness is 3-200nm, and the target material used in the physical vapor deposition is the oxide semiconductor target material comprising the matrix oxide semiconductor material and the positive tetravalent lanthanide ion in the

embodiment

1 or 2. Such physical vapor deposition includes, but is not limited to, sputtering (including dc sputtering, rf sputtering, or reactive sputtering), pulsed laser deposition, atomic layer deposition, and the like.

It is noted that the oxide semiconductor thin film may be prepared by preparing two or more targets, wherein at least one target comprises Tb ⁴⁺ And then the target materials are arranged on different target positions to obtain the oxide semiconductor film by a double-target or multi-target codeposition method.

The oxide semiconductor film prepared by the invention can absorb blue light and is used as a channel layer of a thin film transistor, so that the semiconductor thin film transistor has good device stability under illumination, particularly under NBIS, the good mobility and subthreshold performance of the thin film transistor are kept, the problem of complicated preparation process is avoided, impurities are not introduced, and the performance of the device can be ensured.

Example 4.

A transistor of a bottom-gate top-contact type in structure, as shown in fig. 1, provided with: the semiconductor device includes a substrate 10, a gate electrode 11 positioned on the substrate 10, an insulating layer 12 positioned on the substrate 10 and the gate electrode 11, a channel layer 13 covering an upper surface of the insulating layer 12 and corresponding to the gate electrode 11, and a source electrode 14a and a drain electrode 14b spaced apart from each other and electrically connected to both ends of the channel layer 13. Among them, the channel layer 13 is the oxide semiconductor thin film including the host oxide semiconductor material and the positive tetravalent lanthanoid ion in embodiment 2.

The substrate 10 may be one of substrate materials such as glass, flexible polymer substrate, silicon wafer, metal foil, quartz, etc., and may further include a buffer layer or a water-oxygen barrier layer, etc., which covers the substrate.

The material of the gate 11 may be a conductive material, such as a metal, an alloy, a conductive metal oxide, doped silicon, a conductive polymer, or a stack of two or more thin films made of any combination of the above materials.

The insulating layer 12 may be an insulating material used for a semiconductor device, such as a single-layer film formed of silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide alloy, ytterbium oxide, titanium oxide, hafnium oxide, tantalum oxide, zirconium oxide, a polymer insulating material, a photoresist, or a stack of two or more films formed of any combination of the above materials.

The material of the source electrode 14a and the drain electrode 14b may be a single-layer film of a conductive material, such as a metal, an alloy, a conductive metal oxide, a conductive polymer, or a stack of two or more layers of films made of any combination of the above materials.

The transistor of the present invention may be a closed structure including only a substrate, a gate electrode, an insulating layer, a channel layer, a source electrode, and a drain electrode, may further include an etch stopper layer, a passivation layer, a pixel definition layer, or the like, and may be integrated with other devices, or the like.

The transistor can be prepared by the following method:

(1) One or more layers of conductive films with the thickness of 100-500 nm are prepared by a sputtering method, and are patterned by a shielding mask or a photoetching method to obtain the grid electrode.

(2) Then the insulation layer is prepared by spin coating, drop coating, printing, anodic oxidation, thermal oxidation, physical vapor deposition or chemical vapor deposition, the thickness is 100-1000 nm, and the insulation layer is obtained by patterning through a shielding mask or photoetching method.

(3) The channel layer is prepared by a pulse laser deposition method, and is patterned by a mask UV irradiation method.

(4) One or more layers of conductive films are prepared by a vacuum evaporation or sputtering method, the thickness is 100-1000 nm, and a source electrode and a drain electrode are obtained simultaneously by patterning by a mask or photoetching method.

The transistor adopts the film containing the positive tetravalent terbium ions as the channel layer, and because the energy required by the orbital hybridization transition of the positive tetravalent terbium ions is lower, when the thin film transistor is illuminated, the thin film transistor can absorb blue light and even red and green light and further down convert the blue light and the red and green light into a non-radiation form, thereby avoiding the problems of increased conductance and negative drift of threshold voltage caused by ionization of oxygen vacancy by the blue light in a backlight source or self-luminescence, and improving the illumination stability of a device; under illumination and negative gate voltage stress (NBIS), the problem of negative drift of the threshold voltage of the device can be solved, and the TFT has good stability under illumination, particularly under NBIS; the problem of complicated preparation process is avoided, impurities or crystal field splitting energy level defects are not introduced, electron transport is not influenced, and the TFT device with good NBIS stability and high mobility is realized.

Therefore, the oxide semiconductor target, the thin film and the transistor can keep high mobility and improve NBIS stability.

Example 5.

An oxide semiconductor target comprising a matrix oxide semiconductor material and a positive tetravalent lanthanide ion. Wherein the matrix oxide semiconductor material is indium oxide (In) ₂ O ₃ ) With the positive lanthanide ion being Tb ⁴⁺ . Positive tetravalent lanthanide ions Tb ⁴ ⁺ The ratio of the amount to the amount of all cations was 3%.

The target material is prepared by the following method: the terbium oxide powder is further oxidized, is uniformly mixed with the matrix oxide semiconductor material powder after being ground, is sintered in an ozone atmosphere, is formed through cold isostatic pressing after being ground and mixed for the second time, and is sintered at the temperature of 1400 ℃ in a pure oxygen atmosphere. The total content of Tb in the target material with different valence states is 3%, and the Tb content of the target material with the Tb content of 3% is regulated by regulating the above-mentioned oxidation condition and sintering atmosphere ⁴⁺ /Tb ³⁺ Are controlled to be 1/1 and 1/0 respectively, i.e. Tb ⁴⁺ The contents of (A) are 1.5% and 3%, respectively.

FIG. 5 shows different Tb ⁴⁺ The reflection spectrum of the doped target shows that the target is not doped with Tb (pure In) ₂ O ₃ ) Strong reflection in the wavelength range of about 400-1000nm, indicating very weak absorption in this wavelength range (reflectance + absorptance =1 can be approximated because the target is opaque); and In ₂ O ₃ Incorporation 3% of Tb (Tb) ⁴⁺ /Tb ³⁺ = 1/0) the target material has very weak reflection in the range of 400-1000nm, which indicates that the absorption in the wavelength range is very strong; in ₂ O ₃ Incorporation 3% of Tb (Tb) ⁴⁺ /Tb ³⁺ Tb (Tb) was determined by adding 3% of the target material in the range of 400-1000nm in terms of reflectance ratio = 1/1) ⁴⁺ /Tb ³⁺ = 1/0) was increased, indicating Tb in the target material ⁴⁺ Plays a major role in absorption in the visible region.

Example 6.

A transistor, as shown in fig. 1, is prepared as follows: first, an Al — Nd alloy thin film with a thickness of 300nm is formed on a glass substrate by sputtering, and patterned by photolithography to obtain the gate electrode 11. The insulating layer 12 is then formed by anodization to form an alumina gate oxide layer. The channel layer 13 was prepared by sputtering, using the same target as in example 5, and the thickness of the channel layer 13 was 10nm. An Indium Tin Oxide (ITO) thin film with a thickness of 500nm is formed on the channel layer 13 by sputtering, and patterned by using a shadow mask, thereby obtaining a source electrode 14a and a drain electrode 14b.

FIG. 6 shows the utilization of In ₂ O ₃ Incorporation of Tb ⁴⁺ /Tb ³⁺ Tb 4p peak spectrum of X-ray photoelectron spectroscopy (XPS) of a thin film prepared by sputtering the target material with the ratio of 1/1 can be calculated ⁴⁺ And Tb ³⁺ The content ratio of (A) was 53.3%/46.7% (as shown in Table 1), which deviated from the composition of the target material, but was substantially the same. In is to be noted ₂ O ₃ The film is transparent in visible light, so that the absorption of the film with a small thickness (within 1000 nm) and a small Tb doping amount (within 10%) in the visible light region is much weaker than that of a corresponding target material, even weaker than the absorption fluctuation amount caused by the microcavity effect, which is a normal phenomenon.

Based on different Tb ⁴⁺ The transfer characteristics of the Thin Film Transistor (TFT) under NBIS (white light illumination of the LED plus a gate bias of-20V) are shown in FIGS. 7, 8 and 9. Wherein, FIG. 7 shows pure In ₂ O ₃ Transfer characteristic curve under NBIS of the thin film transistor without doping Tb; FIG. 8 shows In ₂ O ₃ Incorporation of 3% of Tb, and Tb ⁴⁺ /Tb ³⁺ =1/0 (i.e. only Tb is doped) ⁴⁺ ) Transfer characteristic curve under NBIS of the thin film transistor in the case; FIG. 9 shows In ₂ O ₃ Incorporation of 3% of Tb, and Tb ⁴⁺ /Tb ³⁺ Transfer characteristic curve under NBIS of thin film transistor in case of = 1/1. For comparison, only Tb was prepared by using the conventional target preparation method ³⁺ (i.e. not containing Tb) ⁴⁺ ) Doped In ₂ O ₃ Target (i.e. 3% Tb (Tb)) ⁴⁺ /Tb ³⁺ = 0/1)), based on different Tb ⁴⁺ The transfer properties of the Thin Film Transistors (TFTs) at NBIS (white light illumination of the LED plus a gate bias of-20V) are listed in Table one.

It can be seen that pure In ₂ O ₃ The mobility of TFT can reach 39.5cm ² Vs, but the amount of drift of the threshold voltage (Δ V) under NBIS _th ) But reaches-14.0V, the NBIS stability of the device is poor. When mixing 3% of Tb (Tb) ⁴⁺ /Tb ³⁺ = 1/0), the mobility is 38.1cm ² /Vs, whose NBIS lower threshold voltage hardly drifts (Δ V) _th only-0.01V). When mixingInto 3% Tb (Tb) ⁴⁺ /Tb ³⁺ = 1/1), the mobility decreases to 33.2cm ² /Vs, Δ V under NBIS _th is-0.06V. When incorporated 3% of Tb (Tb) ⁴⁺ /Tb ³⁺ = 0/1), the mobility decreases to 19.5cm ² /Vs, Δ V under NBIS _th It was-13.1V. This indicates that In is simple ₂ O ₃ The negative shift of the threshold voltage under NBIS of a TFT is severe. By adding Tb only ³⁺ The ions have little improvement effect on the negative drift of the threshold voltage of the NBIS device, and the mobility is greatly reduced, which cannot meet the requirements because of Tb ³⁺ The visible light cannot be absorbed, and the blue light cannot be down-converted; and Tb ³⁺ Contains 8 f electrons, is more than half full, is easy to be cleaved by the action of a crystal field to form a large number of defect energy levels, which causes the reduction of mobility. Therefore, only Tb ³⁺ The problem of negative drift of NBIS cannot be solved, and the mobility is low. Containing Tb ⁴⁺ The phenomenon of NBIS lower threshold voltage shift of the device is obviously improved, and especially only Tb is contained ⁴⁺ (not containing Tb) ³⁺ ) The NBIS lower threshold voltage of the device has little drift. Reduction of Tb ⁴⁺ /Tb ³⁺ The ratio of (a) will decrease mobility and NBIS stability.

Watch 1

It can be seen that Tb is adopted ⁴⁺ Doped In ₂ O ₃ The transistor as the channel layer can effectively improve the NBIS stability while maintaining high mobility.

Example 7.

An oxide semiconductor target comprising a matrix oxide semiconductor material and a positive tetravalent lanthanide ion. Wherein the matrix oxide semiconductor material is InSnZnO, and the positive quadrivalent lanthanide ion is Tb ⁴⁺ . The target material is prepared byThe preparation method comprises the following steps: the terbium oxide powder is further oxidized, is uniformly mixed with the matrix oxide semiconductor material powder after being ground, is sintered in a strong oxidizing atmosphere, is formed through cold isostatic pressing after being ground and mixed for the second time, and is sintered in the strong oxidizing atmosphere. The total content of Tb in different valence states in the target material is 5%, and all Tb can be controlled to be Tb by regulating the above-mentioned oxidation condition and sintering atmosphere ⁴⁺ 。

A transistor, as shown in fig. 10, is provided with: the semiconductor device includes a substrate 10, a gate electrode 11 on the substrate 10, a gate insulating layer 12 on the substrate 10 and the gate electrode 11, a channel layer 13 covering an upper surface of the gate insulating layer 12 and above the gate electrode 11, an etch stop layer 17 covering the channel layer, and a source electrode 14 and a drain electrode 15 spaced apart from each other and electrically connected to both ends of the channel layer 13 and the etch stop layer 14.

The substrate 10 is glass (containing a water oxygen barrier layer), a Mo/Al/Mo electrode is prepared on the substrate 10 by sputtering, the total thickness is 400nm, and the gate electrode 11 is formed by coating a photoresist, exposing, developing, and the like.

Preparation of SiN on the substrate 10 on which the gate electrode 11 is formed by Plasma Enhanced Chemical Vapor Deposition (PECVD) _x /SiO ₂ The stacked films were used as the gate insulating layer 12, and the total thickness was 320nm.

The channel layer 13 is made of tbinssnzno and is prepared by a sputtering method, and the thickness of the channel layer is 40nm. The specific manufacturing process of the channel layer 13 is as follows: the target material described in the present embodiment was mounted on a target position, and film-formed by sputtering and patterned by photolithography.

Preparing a layer of SiO with the thickness of 100nm on the substrate 10 with the channel layer 13 formed by adopting a PECVD method ₂ The thin film is patterned by dry etching to form an etching stopper layer 17.

The Mo/Al/Mo electrode is formed on the substrate 10 on which the etching stopper layer 17 is formed by using a sputtering method, the total thickness is 600nm, and the source electrode 14 and the drain electrode 15 are formed by using steps of coating a photoresist, exposing, developing, and the like.

After the device is prepared, annealing is carried out for 1h at 350 ℃ in the atmosphere.

In different proportions with respect to the raw materials prepared according to the above-mentioned processThin film transistor and comparative example, Δ V corresponding to gate bias test using LED white light irradiation plus-25V _th (V) and mobility, the results are shown in Table II.

TABLE II TFT device Performance (Tb) at different In/Sn/Zn ratios In TbInSnZnO ⁴⁺ The content is 5%)

It can be seen that the use of the additive containing Tb ⁴⁺ The transistor with the doped oxide semiconductor material as the channel layer can effectively improve the NBIS stability, and meanwhile, higher mobility is kept.

The oxide semiconductor film can be used as a channel layer material of a transistor. The oxide semiconductor film and the thin film transistor thereof are mainly used for active drive of organic light emitting display, liquid crystal display or electronic paper, and can also be used for integrated circuits.

Example 8.

An oxide semiconductor target material, which comprises a matrix oxide semiconductor material and positive quadrivalent terbium ion Tb ⁴⁺ . The host oxide semiconductor material is a mixture of three oxides of In, sn and Zn, wherein the ratio of In: sn: zn =77/10/10. The target material is prepared by the following method: the terbium oxide powder is further oxidized, is uniformly mixed with the matrix oxide semiconductor material powder after being ground, is sintered in a strong oxidizing atmosphere, is formed by cold isostatic pressing after being ground and mixed for the second time, and is sintered in the strong oxidizing atmosphere. The total content of Tb in different valence states in the target material is 5%, and Tb is controlled by regulating the above-mentioned oxidation condition and sintering atmosphere ⁴⁺ /Tb ³⁺ In the presence of a suitable solvent. A thin film transistor was manufactured by the same process as example 7. Adopting LED white light irradiation plus-25V grid bias voltage test to test corresponding delta V for the prepared thin film transistor _th (V) and mobility, the results are shown in Table III.

Tb different from Table III ⁴⁺ /Tb ³⁺ Proportional TFT device Performance

Tb ⁴⁺ /Tb ³⁺	Mobility (cm 2/Vs)	Δ Vth (V) under NBIS
			Tb ⁴⁺ /Tb ³⁺ ＝1/0	52.1	-0.8
Tb ⁴⁺ /Tb ³⁺ ＝10/1	48.5	-0.85
			Tb ⁴⁺ /Tb ³⁺ ＝5/1	46.2	-0.9
Tb ⁴⁺ /Tb ³⁺ ＝2/1	40.3	-1.05
			Tb ⁴⁺ /Tb ³⁺ ＝1/2	36.7	-2.32
Tb ⁴⁺ /Tb ³⁺ ＝1/10	24.9	-3.47
			Tb ⁴⁺ /Tb ³⁺ ＝1/20	18.9	-7.50

As can be seen, tb ⁴⁺ The introduction of (2) plays a major role in the NBIS stability of the device and can maintain good mobility of the device. Tb ⁴⁺ /Tb ³⁺ The higher the ratio of (a), the better the mobility and NBIS stability of the device.

Example 9.

An oxide semiconductor target comprising a matrix oxide semiconductor material and a positive tetravalent lanthanide ion. Wherein the host oxide semiconductor material is indium oxide (In) ₂ O ₃ ) The positive tetravalent lanthanide ion is positive tetravalent cerium (Ce) ⁴⁺ ). The target material is prepared by the following method: firstly, grinding Ce oxide, uniformly mixing with matrix oxide semiconductor material powder, sintering in a strong oxidizing atmosphere, grinding and mixing for the second time, forming by cold isostatic pressing, and sintering in the strong oxidizing atmosphere. The Ce content was 3%. Adjusting the oxidation condition and sintering atmosphere to obtain the Ce of the target material ⁴⁺ /Ce ³⁺ The ratio of (A) to (B) is controlled to be 1/0 (i.e., ce is not contained) ³⁺ ). For comparison, dysprosium (Dy) and ytterbium (Yb) -doped indium oxide were prepared under the same target preparation conditions, and Dy and Yb could not form positive quadrivalence under any conditions, and both the measured valence states were positive trivalence, so Dy was ⁴⁺ /Dy ³⁺ And Dy ⁴⁺ /Dy ³⁺ All are 0/1.

A thin film transistor was fabricated by the same process as in example 6, and the fabricated thin film transistor was subjected to a gate bias test of-20V plus white light from LED _th (V) and mobility, the results are shown in Table four. It can be seen that the NBIS stability of all three doped TFTs is poor.

Watch four

Ce. Dy and Yb content	Mobility (cm) ² /Vs)	Δ V under NBIS _th (V)
			0% (pure In) ₂ O ₃ )	39.5	-14.0
3％(Ce ⁴⁺ /Ce ³⁺ ＝1/0)	30.5	-12.8
			3％(Dy ⁴⁺ /Dy ³⁺ ＝0/1)	17.2	-13.4
3％(Yb ⁴⁺ /Yb ³⁺ ＝0/1)	16.9	-13.3

Example 10.

An oxide semiconductor target comprising a matrix oxide semiconductor material and a positive tetravalent lanthanide ion. Wherein the matrix oxide semiconductor material is indium oxide (In) ₂ O ₃ ) The positive tetravalent lanthanide ion is Pr ⁴⁺ . The target material is prepared by the following method: firstly, praseodymium oxide powder is mixed and oxidized, and is groundUniformly mixing with the matrix oxide semiconductor material powder, sintering in a strong oxidizing atmosphere, grinding and mixing for the second time, forming by cold isostatic pressing, and sintering in a strong oxidizing atmosphere. Two targets with different Pr doping amounts are prepared, and the Pr content is 3 percent and 7 percent respectively. Adjusting the oxidation condition and sintering atmosphere to obtain two kinds of Pr with different Pr contents ⁴⁺ /Pr ³⁺ The ratio of (A) to (B) is controlled to be 1/1.

FIG. 11 shows the reflection spectra of the target materials with different Pr doping amounts, and it can be seen that the target material without Pr doping (pure In) ₂ O ₃ ) Strong reflection in the wavelength range of about 400-1000nm, indicating very weak absorption in this wavelength range (reflectance + absorptance =1 can be approximated because the target is opaque); and In ₂ O ₃ Incorporation of 3% of Pr (Pr) ⁴⁺ /Pr ³⁺ = 1/1) the reflection of the target material in the range of 400-1000nm is relatively weak, which indicates that the absorption in the wavelength range is strong; in ₂ O ₃ Incorporation of 7% of Pr (Pr) ⁴⁺ /Pr ³⁺ The reflection of the target material of = 1/1) is improved in the range of 400-1000nm, which shows that the concentration quenching effect is generated at high Pr concentration. This is mainly due to Pr ⁴⁺ Or Pr ³⁺ Is caused by the f electron in (1). While the incorporation of Tb does not have this problem.

Therefore, the target preparation method can form the positive quadrivalent praseodymium on the target.

Example 11.

A transistor, as shown In FIG. 1, is prepared In the same manner as In example 6, except that the target material for the channel layer 13 of the thin film transistor is Pr-doped In example 10 ₂ O ₃ A target material.

FIGS. 12 and 13 show the difference based on Pr ⁴⁺ The transfer characteristics of the resulting Thin Film Transistors (TFTs) under NBIS (white light illumination of the LED plus a gate bias of-20V) are shown in Table five. It can be seen that the mobility was 18.9cm when 3% of Pr was doped ² Vs, NBIS lower threshold voltage shift amount (Δ V) _th ) is-4.1V, and has NBIS stability higher than that of pure In ₂ O ₃ TFT is improved; however, tb was added in the same concentration as the mixed solution ⁴⁺ In ₂ O ₃ TFComparison of T with Pr ⁴⁺ In ₂ O ₃ The mobility and NBIS stability of TFT are poor, and there is obvious hump effect in subthreshold region, i.e. current is turned on in advance, off-state current (I) _off ) Enlargement, mainly associated with oxygen vacancies or Pr ⁴⁺ The crystal contains one f electron, and is easily influenced by a crystal field to form a large number of defect energy levels, so that electron transportation is influenced, and mobility is reduced.

When 7% of Pr was doped, the mobility rapidly decreased to 9.2cm ² /Vs, NBIS lower threshold Voltage Shift amount (. DELTA.V) _th ) The positive drift is +0.5V in the first 100s, and the negative drift is-1.2V in the last 3500 s; when the gate voltage (V) _GS ) When the voltage is more than 5V, NBIS lower threshold voltage drift rule and V _GS The opposite is true below 5V. This suggests that two mechanisms work simultaneously when high concentration Pr is doped: firstly, the light absorption caused by concentration quenching is reduced, and the down-conversion effect is weakened; secondly, due to Pr ⁴⁺ The f electrons exist, and are split under the influence of a crystal field to cause a large number of electron traps, which are used as recombination mediators of ionized oxygen vacancy electrons to reduce the service life of photo-generated electrons, and are also used as traps of common carriers to capture the carriers at higher concentration, so that the threshold voltage is just floated at the beginning. In contrast, tb is doped ⁴⁺ In (2) of ₂ O ₃ The TFT does not have this phenomenon. In addition, pr down-converts green light upon absorption of blue light, and green light also has a partial effect on NBIS as shown in fig. 14 due to the upwarping of the interfacial band at negative gate voltages, which shifts the oxygen vacancy level upward.

Watch five

Thus, using Pr ⁴⁺ Doped In ₂ O ₃ The transistor as the channel layer has a limited improvement in NBIS stability of the device, and the mobility of the device is greatly reduced. Thus, pr doping does not meet the object of the present invention.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. An oxide semiconductor target, characterized in that: comprises a matrix oxide semiconductor material and a tetravalent lanthanide ion, wherein the matrix oxide semiconductor material contains at least one of five elements of In, zn, sn, ga and Cd, and the tetravalent lanthanide ion is a tetravalent terbium ion Tb ⁴⁺ Or praseodymium quaternary ⁴⁺ At least one of;

the positive tetravalent lanthanide ion is capable of orbital hybridization, the energy required for orbital hybridization transition is not higher than the energy of blue light, and the positive tetravalent lanthanide ion is converted to a non-radiative form after orbital hybridization transition.

2. The oxide semiconductor target according to claim 1, wherein: the positive tetravalent lanthanide ion is positive tetravalent terbium ion Tb ⁴⁺ ，Tb ⁴⁺ Ion number and Tb ³⁺ The ratio of the number of ions is greater than 0.1.

3. The oxide semiconductor target according to claim 2, wherein: tb ⁴⁺ Ion number and Tb ³⁺ The ratio of the number of ions is greater than 1.

4. The oxide semiconductor target according to claim 2, wherein: containing only Tb ⁴⁺ Does not contain Tb ³⁺ 。

5. The oxide semiconductor target according to any one of claims 1 to 4, wherein: the preparation method comprises the following steps of uniformly mixing oxide powder of elements corresponding to positive tetravalent lanthanide ions and matrix oxide semiconductor material powder, sintering in a strong oxidizing atmosphere, grinding and mixing for the second time, forming by cold isostatic pressing or hot pressing, and sintering in the strong oxidizing atmosphere to obtain the oxide semiconductor target.

6. An oxide semiconductor thin film, which is prepared by a physical vapor deposition method with a thickness of 3 to 200nm, wherein the oxide semiconductor target used for the physical vapor deposition is the oxide semiconductor target as defined in any one of claims 1 to 5.

7. A method for improving stability and mobility of a thin film transistor,

preparing an oxide semiconductor target material which comprises a matrix oxide semiconductor material and positive quadrivalent lanthanide ion serving as a functional ion, wherein the positive quadrivalent lanthanide ion is positive quadrivalent terbium ion Tb ⁴⁺ Or n-praseodymium Pr ⁴⁺ Functional ions can perform orbital hybridization, the energy required by orbital hybridization transition is not higher than that of blue light, and the functional ions are converted into a non-radiative form after orbital hybridization transition;

when the thin film transistor has illumination or illumination and negative grid bias voltage, the functional ions absorb blue light and even red and green light to realize orbital hybrid transition and convert into a non-radiative form; and the ionization of oxygen vacancies is prevented by absorbing illumination through the hybridization transition of functional ion orbitals, so that the serious lattice relaxation and the threshold voltage drift are avoided.

8. The method for improving stability and mobility of a thin film transistor according to claim 7, wherein the positive tetravalent lanthanide ion is Tb ⁴⁺ ，Tb ⁴⁺ Ion number and Tb ³⁺ The ratio of the number of ions is greater than 0.1.

9. A thin film transistor characterized in that a channel layer contains one or more oxide semiconductor layers, at least one of which is an oxide semiconductor thin film prepared by the method of any one of claims 6 to 8;

the thin film transistor is used as a driving back plate of display or used for an internal memory, a flash memory and a dynamic random access memory.