KR101368972B1 - Method for extracting subgap density of states of amorphous oxide semiconductor thin-film transistor using optical differential ideality factor and apparatus thereof - Google Patents

Abstract

A method for extracting state density in a band gap of an amorpous oxide semiconductor thin film transistor by using an optical differential ideality coefficient and a device thereof are provided. The method for extracting state density in a band gap of an amorpous oxide semiconductor thin film transistor includes a step of measuring a darkroom drain current from a darkroom according to a gate voltage and measuring a light reaction drain current according to the gate voltage by emitting light of a light source, a step of calculating a light reaction ideality coefficient and a darkroom ideality coefficient by using the light reaction drain current and the darkroom drain current, and a step of extracting the state density in the band gap of the thin film transistor based on the differentiation of the light reaction ideality coefficient and the darkroom ideality coefficient. The step of extracting the state density extracts genuine state density by de-embedding capacitance formed by free electrons. [Reference numerals] (AA) Start; (BB) End; (S310) Measure a darkroom drain current according to a gate voltage in a darkroom; (S320) Measure a light reaction drain current according to the gate voltage by emitting light of a light source; (S330) Calculate a darkroom ideality coefficient by using the darkroom drain current; (S340) Calculate a light reaction ideality coefficient by using the light reaction drain current; (S350) Calculate light reaction capacitance based on the differentiation of the light reaction ideality coefficient and the darkroom ideality coefficient; (S360) Extract state density from a band gap based on the light reaction capacitance

Description

Method for extracting subgap density of states of amorphous oxide semiconductor thin-film transistor using optical differential ideality factor and apparatus

The present invention is directed to the extraction of subgap density-of-states of amorphous oxide semiconductor thin film transistors (TFTs), specifically by optical electrons using optical differential ideality factors. The present invention relates to a method and apparatus for extracting a state density in a bandgap of an amorphous oxide semiconductor thin film transistor capable of extracting a state density in a bandgap de-embedded.

The present invention is derived from a study performed as a part of the Basic Research Project-Middle Researcher (Core Research) of the Ministry of Education, Science and Technology and the Ministry of Education, Science and Technology of the Korea Research Foundation. Development and Application of Integrated Thermo-Opto Electronic Characterization Platform for Semiconductor TFT].

Amorphous oxide semiconductor thin film transistors (TFTs) have advantages such as high carrier mobility, uniformity of thin films in a large area, and stability from a reliability point of view. Amorphous oxide semiconductor TFTs have been actively researched as an alternative to amorphous Si TFTs that are commercialized in display backplanes such as high resolution AM (Active Matrix) -LCD and AM-OLED (Organic Light-Emitting Diode) . Indeed, in the recent 3-4 years, a-IGZO (InGa-ZnO) TFT, which is an amorphous oxide semiconductor TFT, has been applied to various display pixel circuits and 3-D lamination circuits and proved its applicability.

Since the amorphous oxide semiconductor thin film transistor has a large influence on the state density (subgap DOS) existing in the bandgap, extraction of the state density in the bandgap plays a very important role in analyzing the characteristics of the device. In particular, as the scale decreases to improve the performance and the integration density of the amorphous oxide semiconductor thin film transistor, extracting the state density in the band gap is very important in the characteristics and performance of the active film.

Conventional methods of extracting the state density in the bandgap of an amorphous oxide semiconductor TFT include extraction using a capacitance-voltage (CV) characteristic, extraction using a photo-induced shift of a threshold voltage by using various wavelengths, , Numerical simulation-based fitting, and so on.

However, the conventional methods require a complicated calculation, or the reliability of the state density in the extracted band gap of the amorphous oxide semiconductor TFT due to the problem that the electrical properties drift due to the influence of light or temperature, heat, etc. There is this.

Therefore, there is a need for a method capable of extracting accurate state density in a bandgap without affecting complicated equations or external conditions.

Korea Patent Publication No. 10-1105273 (Registration date 2012.01.05)

IEEE Electron Device Lett., "Differential Ideality Factor Technique for Extraction of Subgap Density of States in Amorphous InGaZnO Thin-Film Transistors" (published Mar. 2012)

SUMMARY OF THE INVENTION The present invention was derived to solve the problems of the prior art as described above, and a method and apparatus for extracting state density in a bandgap of an amorphous oxide semiconductor thin film transistor capable of extracting state density in a bandgap using an optical differential ideal coefficient. The purpose is to provide.

Specifically, the present invention measures the drain current according to the irradiation of light, calculates each ideal factor using the measured drain current, and then calculates the band gap through the derivative of the difference between the two ideal coefficients calculated. By extracting the internal density, a complicated measurement process can be omitted, and the internal density of the bandgap independent of the threshold voltage can be extracted.

In addition, the present invention is a method of extracting the state density in the bandgap of the amorphous oxide semiconductor thin film transistor which can extract the state density in the bandgap simply and quickly through the derivative of the ideal coefficient using the drain current measured according to the irradiation of light and its It is an object to provide a device.

In addition, the present invention provides a method and apparatus for extracting a state density within a bandgap of an amorphous oxide semiconductor thin film transistor capable of extracting the state density within an intrinsic bandgap by de-embedding capacitance formed by free electrons. It aims to provide.

In order to achieve the above object, in the bandgap state density extraction method of the amorphous oxide semiconductor thin film transistor according to an embodiment of the present invention, in the bandgap state density extraction method of the amorphous oxide semiconductor thin film transistor, Measuring a dark room drain current according to a gate voltage of an amorphous oxide semiconductor thin film transistor, and measuring photoreaction drain current according to the gate voltage of the amorphous oxide semiconductor thin film transistor by irradiating light of a predetermined light source; Calculating a dark room ideal factor according to the gate voltage using the measured dark room drain current, and calculating a photo reaction abnormal coefficient according to the gate voltage using the measured photoreaction drain current. ; And extracting a state density within a band gap of the amorphous oxide semiconductor thin film transistor based on the calculated derivative of the dark room abnormality coefficient and the photoreaction abnormality coefficient.

The extracting of the state density in the bandgap may include a photoreaction capacitance formed at the state density in the bandgap by photoreaction by irradiation of light based on the derivative of the difference between the photoreaction anomaly and the darkroom abnormality coefficient. May be calculated and the state density in the band gap may be extracted based on the calculated photoreaction capacitance.

The dark room abnormality coefficient and the photoreaction abnormality coefficient may include capacitance formed by the density of states in the band gap and capacitance formed by free electrons.

The extracting the state density in the band gap may extract the state density in the intrinsic band gap of the amorphous oxide semiconductor thin film transistor by de-embedding the capacitance formed by the free electrons.

An apparatus for extracting a state density within a bandgap of an amorphous oxide semiconductor thin film transistor according to an exemplary embodiment of the present invention is a device for extracting a state density within a bandgap of an amorphous oxide semiconductor thin film transistor, wherein the gate voltage of the amorphous oxide semiconductor thin film transistor is dark in a dark room. A measurement unit configured to measure a dark room drain current according to the light source, and to measure a photoreaction drain current according to the gate voltage of the amorphous oxide semiconductor thin film transistor by irradiating light from a predetermined light source; A calculation unit calculating a dark room ideal factor according to the gate voltage using the measured dark room drain current, and calculating a photo reaction abnormal coefficient according to the gate voltage using the measured photoreaction drain current ; And an extraction unit for extracting a state density in a band gap of the amorphous oxide semiconductor thin film transistor based on the calculated derivative of the dark room abnormality coefficient and the photoreaction abnormality coefficient.

According to the present invention, the drain current is measured according to the presence or absence of light, the respective abnormal coefficients are calculated by using the measured drain current, and then the optical response by light irradiation is applied to the difference between the calculated two ideal coefficients. By calculating the photoreaction capacitance formed at the state density in the bandgap, and extracting the state density in the bandgap based on the calculated photoreaction capacitance, eliminating the complicated measurement process, the state density in the bandgap independent of the threshold voltage Can be extracted.

In addition, the present invention can simply and quickly extract the state density in the band gap through the derivative between the abnormal coefficients using the drain current measured according to the irradiation of light.

The present invention can extract the state density in the intrinsic bandgap of an amorphous oxide semiconductor TFT by de-embedding the capacitance formed by free electrons.

1 is a perspective view of an embodiment of an amorphous oxide semiconductor TFT.
FIG. 2 shows an equivalent model of capacitance for FIG. 1.
3 is an operation flowchart of a method for extracting a state density in a bandgap of an amorphous oxide semiconductor TFT according to an exemplary embodiment of the present invention.
4 shows an operation flowchart of an embodiment for step S360 shown in FIG.
5 shows an example of a characteristic curve of the drain current measured according to the gate voltage with or without light irradiation.
6 shows an example graph of the characteristic curve of the gate capacitance measured according to the gate voltage.
7 is a graph illustrating an example of an experimental value and a fitting value of an abnormal coefficient according to a gate voltage.
8 illustrates an exemplary diagram for explaining a difference between a state density extraction method in a bandgap and a state density extraction method in a bandgap according to the present invention.
9 shows an example graph of the density of states in a bandgap extracted by the method according to the present invention.
FIG. 10 shows a configuration of an apparatus for extracting a state density in a bandgap of an amorphous oxide semiconductor TFT according to an embodiment of the present invention.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings.

Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

However, the present invention is not limited to or limited by the embodiments. Like reference symbols in the drawings denote like elements.

Hereinafter, a method and apparatus for extracting state density in a bandgap of an amorphous oxide semiconductor thin film transistor using an optical differential ideal coefficient according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 10.

Amorphous oxide semiconducting TFTs are used as substitute devices due to their high carrier mobility, uniformity of thin films in a large area, and stability from a reliability point of view instead of a-Si TFTs, which are commercially available as switch or driving devices in display backplanes such as AMLCD and AMOLED Be in the spotlight.

In this amorphous oxide semiconductor TFT, it is very important to extract the state density in the bandgap which has a great influence on the electrical characteristics in the part of analyzing the characteristics of the device. May be affected by external environmental factors such as light, temperature, heat, etc., and may depend on the threshold voltage.

In the present invention, in extracting the state density in the band gap of an amorphous oxide semiconductor TFT, the effect of the factors caused by light, temperature, heat, etc. is eliminated by using the derivative of the difference of the respective abnormal coefficients calculated according to the irradiation of light. It is to accurately extract the state density in the bandgap which is independent of the threshold voltage and de-embedded the influence on the capacitance formed by the free electrons.

1 illustrates a perspective view of an embodiment of an amorphous oxide semiconductor TFT, and FIG. 2 illustrates an equivalent model of capacitance with respect to FIG. 1. In the present invention, an amorphous InGaZnO (a-IGZO) TFT is used as an amorphous oxide semiconductor TFT. An example of this is described.

1 and 2, the amorphous oxide semiconductor TFT includes electrodes (gate electrode, source electrode, and drain electrode) 120, 150 and 160 for applying driving power, a gate insulating layer 130, an amorphous oxide semiconductor An active layer 140, and a channel protective layer (ES)

The gate electrode 120 may be formed on a part of the substrate 110 and may overlap with the drain electrode 150 and the source electrode 160.

The gate insulating layer 130 is a layer for protecting the gate electrode 120 and electrically separating the gate electrode 120, the drain electrode 150, and the source electrode 160. The gate insulating layer 130 has a predetermined dielectric constant ε _OX . The material is formed by a predetermined thickness T _OX .

At this time, by a gate insulating layer 130 may be formed of a capacitance (C _OX), the capacitance formed (C _OX) may be obtained by using the physical structure of the gate insulating layer 130. That is, the capacitance C _OX formed by the gate insulating layer 130 may be obtained using the dielectric constant and thickness of the material used for the gate insulating layer 130. For example the ratio of the capacitance (C _OX) is the dielectric constant of the material (ε _OX) and thickness (T _OX) (ε _OX / T _OX ).

Of course, the gate insulating layer 130 is a stacked structure of two different insulating layers, for example, SiO 2 and SiN x, as shown in FIG. 1, and the first insulating layer 131 and the second insulating layer 132 are formed. ) May have a stacked structure, in which case the capacitance formed by the gate insulating layer is used for the dielectric constant (ε _OX1 ), the thickness (T _OX1 ), and the second insulating layer of the material used for the first insulating layer. It can be obtained using the dielectric constant (ε _OX2 ) and the thickness (T _OX2 ) of the material. That is, when the material used for the first insulating layer is SiO2, the dielectric constant (ε _SiO2 ) and thickness of _SiO2 (T _SiO2 ), and when the material used for the second insulating layer is SiNx, the dielectric constant (ε _SiNx ) and thickness of _SiNx Can be obtained using (T _SiNx ).

An amorphous oxide semiconductor (AOS) 140 is formed on the gate insulating layer 130 by a predetermined thickness T _IGZO using a material having a predetermined dielectric constant ε _IGZO .

In this case, as an example of the amorphous oxide semiconductor layer 140 may be a-IGZO.

The capacitance formed in the channel region of the amorphous oxide semiconductor layer 140 is present in the free electron capacitance C _FREE formed by the free carriers present in the conduction band and the state density in the band gap. Localized electron capacitance (C _LOC ) formed by localized electrons.

In addition, the channel region may further include a photoreaction capacitance (C _{LOC , ph} ) formed at a density of states in a bandgap by photoreaction by light irradiation.

In this case, the photoreaction capacitance C _{LOC, ph} refers to a capacitance formed by the charge excited from the trap in the bandgap by the photoreaction energy according to the irradiation of light.

The drain electrode 150 and the source electrode 160 are formed on the amorphous oxide semiconductor layer 140, and the drain electrode 150 and the source electrode 160 are formed to be spaced apart by a predetermined distance (L).

The channel protective layer 170 may have a channel or an active region exposed between the drain electrode 150 and the source electrode 160 to protect a channel or an active region exposed between the drain electrode 150 and the source electrode 160 At least.

1, the channel protection layer 170 may be formed between the amorphous oxide semiconductor layer 140 and the drain electrode 150 and between the source electrode 160 and the amorphous oxide semiconductor layer 140. In this case, the channel protection layer 170 may be an etch stopper layer (ESL) But it is not limited thereto and may be formed on a part of the upper portion of the exposed amorphous oxide semiconductor layer 140, the drain electrode 150 and the source electrode 160.

In addition, the gate electrode 120, the source electrode 150, the drain electrode 160, and the amorphous oxide semiconductor layer 140 may be formed to have a predetermined width W. The width of each component may vary depending on circumstances. It may be formed. For example, the gate electrode 120, the source electrode 150, and the drain electrode 160 may be formed to have the same width, and the amorphous oxide semiconductor layer 140 may be formed to have a different width.

In addition, although not shown in FIG. 1, a passivation layer may be formed on the source electrode 150, the drain electrode 160, and the channel passivation layer (ES) 170.

In the present invention, for each of the amorphous oxide semiconductor TFTs having the configuration and capacitance model shown in Figs. 1 and 2, each abnormal coefficient is calculated by using the drain current in the region before the threshold voltage among the drain currents measured according to the presence or absence of light irradiation. Calculates the photoresponse capacitance (C _{LOC , ph} ) through the derivative of the difference in each of the calculated ideal coefficients _, and forms the state density in the bandgap of the TFT by the free electrons based on the calculated photoresponse capacitance The method of extracting the density of states in the bandgap of the amorphous oxide semiconductor TFT according to the present invention by de-embedding and extracting the influence on the capacitance to be described will be described with reference to FIGS. 3 to 9.

3 is an operation flowchart of a method for extracting a state density in a bandgap of an amorphous oxide semiconductor TFT according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the method according to the present invention measures a drain current according to a gate voltage in the dark room (hereinafter referred to as “dark room drain current”) for an amorphous oxide semiconductor TFT, and measures light of a light source having a predetermined wavelength. Irradiation measures a drain current according to the gate voltage (hereinafter referred to as "photoreaction drain current") (S310 and S320).

For example, as shown in FIG. 5, the dark room drain current and the photoreaction drain current according to the gate voltage are measured. As can be seen in FIG. 5, the drain current values of the amorphous oxide semiconductor TFTs measured according to the presence or absence of light irradiation are different, and the photoreaction drain currents measured by irradiation with light have a higher value than the dark room drain current at the same gate voltage. Able to know.

Here, the drain current according to the gate voltage can be measured using a measuring means, for example, an Agilent 4156C semiconductor parameter analyzer, and can be measured using all measuring means capable of measuring the drain current.

When the darkroom drain current and the photoreaction drain current are measured in steps S310 and S320, the darkroom ideal factor is calculated using the measured darkroom drain current, and the photoreaction abnormality factor is calculated using the photoreaction drain current. S330, S340).

)는 게이트 전압에 따른 채널 전위(channel potential; V_CH)를 제어(V_CH=V_GS/

)하기 위한 제어가능 인자로 사용될 수 있다.In this case, the abnormality coefficient may be calculated using the drain current before the threshold voltage among the measured drain currents, and specifically, may be calculated using the drain current between the turn-on voltage and the threshold voltage. This ideal coefficient (

) Controls the channel potential (V _CH ) according to the gate voltage (V _CH = V _GS /

Can be used as a controllable factor.

For example, as in the example shown in FIG. 5, the abnormality coefficient uses a drain current measured according to a gate voltage between a turn-on voltage V _ON of 0 [V] and a threshold voltage V _T of 5.24 [V]. Is calculated.

Here, the dark room drain current (I _{D , dark} ) and the photoreaction drain current (I _{D , ph} ) between the turn-on voltage (V _ON ) and the threshold voltage (V _T ) are shown in Equations 1 and 2 below. Can be modeled as:

[Equation 1]

&Quot; (2) "

_dark와

_ph는 암실 이상계수와 광 반응 이상계수를 의미하고, V_DS는 드레인 전극과 소스 전극 사이에 인가되는 전압을 의미하며, I_D0는 게이트 전압이 문턱전압인 경우일 때의 드레인 전류를 의미한다. 게이트 전압이 문턱전압인 경우의 드레인 전류(I_D0)는 아래 <수학식 3>과 같이 나타낼 수 있다.
Here, V _th means a thermal voltage and is a constant value calculated using the operating temperature of the TFT, the Boltzmann constant, and the amount of electron charge.

_dark with

_ph denotes a dark room abnormality coefficient and a photoreaction abnormal coefficient, V _DS denotes a voltage applied between the drain electrode and the source electrode, and I _D0 denotes a drain current when the gate voltage is a threshold voltage. The drain current I _D0 when the gate voltage is the threshold voltage can be expressed by Equation 3 below.

&Quot; (3) &quot;

는

_dark와

_ph 중 어느 하나의 값을 가지게 되겠지만, 실제로 게이트 전압이 문턱전압인 경우에는 photovoltaic effect 에 의한 문턱 전압 shift 현상이 없기 때문에

=

_dark =

_ph 의 관계를 가지게 된다. Where μ _eff is the effective carrier mobility, and C _OX is the capacitance formed by the gate insulating layer, as described above, depending on the dielectric constant of the material used for the gate insulating layer and its formation thickness. Where W is the width of the source electrode and the drain electrode, and means the length between the gate electrode and the source electrode of L, when the gate voltage is the threshold voltage

The

_dark with

_It will have any value of _ph , but when the gate voltage is actually the threshold voltage, there is no threshold voltage shift caused by the photovoltaic effect.

=

_dark =

_It has a relation of _ph .

_dark)와 광 반응 이상계수(

_ph)는 아래 <수학식 4>, <수학식 5>와 같이 나타낼 수 있다.
Dark room abnormality coefficients described in Equations 1 and 2

_dark ) and photoreaction anomaly (

_ph ) can be expressed as Equation 4 and Equation 5 below.

&Quot; (4) &quot;

&Quot; (5) &quot;

Using the two ideal coefficients shown in equations (4) and (5), that is, the photoreaction capacitance formed by the state density in the bandgap by light irradiation of the light source, The photoreaction capacitance can be expressed by Equation 6 and Equation 7 below.

&Quot; (6) &quot;

&Quot; (7) &quot;

That is, the photoreaction capacitance C _{LOC, ph} may be calculated using the difference between the photoreaction abnormality coefficient and the dark room abnormality coefficient. Furthermore, the photoreaction capacitance may be calculated from the derivative of the difference between the photoreaction anomaly and the dark room anomaly, as described below.

As can be seen from the above Equation 4 to Equation 7, the present invention is de-embedded (de-) by the effect of the capacitance formed in the free electrons through the two ideal coefficients calculated in the drain current region where the gate voltage is less than the threshold voltage By embedding, it is intended to obtain a photoreaction capacitance (C _{LOC , ph} ) to extract the density of states in the intrinsic bandgap.

However, since each abnormal coefficient is dependent on the threshold voltage, the state density in the band gap extracted is also dependent on the threshold voltage, which may cause an important error in extracting the state density in the band gap. Therefore, in the present invention, in order to extract the state density in the band gap independent of the threshold voltage by removing the influence of the threshold voltage, a method of differentiating the dark room abnormality coefficient and the photoreaction abnormal coefficient is applied. The state density in the bandgap extracted in the present invention is the state density in the intrinsic bandgap by de-embedding the influence on the capacitance formed by the free electrons.

The dark room coefficient and photoreaction abnormal coefficient using the differential method can be expressed as Equation 8 and Equation 9 below.

&Quot; (8) &quot;

&Quot; (9) &quot;

Here, ΔV _GS refers to a voltage step, and may be a value small enough to guarantee a state density within a constant band gap.

_Dark)와 광 반응 이상계수(

_Photo_RED)를 피팅(fitting)함으로써, 수학식 8, 수학식 9와 같은 이상계수를 획득할 수 있다.As can be seen from Equations 8 and 9, the dark room and the photoreaction abnormal coefficients of the present invention are independent of the threshold voltage by a differential approach, as shown in FIG. 7. Likewise, experimentally measured darkroom anomaly (

_Dark) and photoreaction abnormal coefficient (

By fitting _Photo_RED), an ideal coefficient such as Equation 8 and Equation 9 can be obtained.

When the dark room coefficient and the photoreaction abnormal coefficient are calculated, the derivative of the difference between the calculated photoreaction abnormal coefficient and the dark room abnormal coefficient is calculated based on the photoresist capacitance (C _{LOC, ph} ) is calculated (S350).

&Quot; (10) &quot;

&Quot; (11) &quot;

는 에너지 레벨에 대한 표면 전위(surface potential)를 의미하고, V_FB는 플랫 밴드 전압(flat band voltage)을 의미한다.here,

Denotes surface potential for energy level, and V _FB denotes flat band voltage.

_Dark_fit,

_Photo_RED_fit)를 미분함으로써, 획득될 수 있다. 즉, 본 발명의 광 반응 커패시턴스는 광 조사 유무에 따른 드레인 전류를 측정하고, 측정된 드레인 전류 중 문턱전압 이전의 드레인 전류를 이용하여 암실 이상계수와 광 반응 이상계수를 각각 계산하며, 계산된 광 반응 이상계수와 암실 이상계수의 차이를 미분함으로써 획득되기 때문에 실험적으로 측정된 데이터만으로 획득될 수 있다.The differentiated darkroom and photoresponse coefficients are calculated from each of the fitted

_Dark_fit,

Can be obtained by differentiating _Photo_RED_fit). That is, the photoreaction capacitance of the present invention measures the drain current according to the presence or absence of light irradiation, calculates the dark room abnormality coefficient and the photoreaction abnormality coefficient by using the drain current before the threshold voltage of the measured drain current, respectively, Since it is obtained by differentiating the difference between the reaction abnormality coefficient and the darkroom abnormality coefficient, it can be obtained only by experimentally measured data.

As can be seen from Equations 4 and 5 described above, the photoresponse capacitance calculated in the present invention calculates an ideal coefficient in consideration of the influence on the capacitance formed by free electrons, and calculates the Since it is obtained based on the difference, the capacitance by the free electrons is in a de-embedded state. That is, the present invention can extract the state density in the band gap where the capacitance caused by free electrons is de-embedded using the photoreaction capacitance.

Based on the photoreaction capacitance calculated in step S350, the state density in the bandgap of the amorphous oxide semiconductor TFT, that is, the state density in the intrinsic bandgap, is extracted (S360).

Here, the state density in the band gap extracted based on the photoreaction capacitance may be expressed by Equation 12 below.

&Quot; (12) &quot;

As can be seen from Equations 11 and 12, the density of states in the band gap to be extracted in the present invention is not only the optical differential ideal coefficient, but also the thickness of the amorphous oxide semiconductor layer (T _IGZO ) and the thickness of the gate insulating layer (T _OX ). It can be seen that the extraction is based on physical structural parameters such as and permittivity (ε _OX ).

As shown in FIG. 8, the band gap state density (ODIFT_RED) extracted in the present invention has a capacitance (C) by free electrons included when extracting the band gap state density in a conventional differential ideal coefficient method (DIFT). _The state density in the intrinsic bandgap of the amorphous oxide semiconductor TFT can be extracted by de-embedding the component corresponding to _FREE ), that is, the hatched portion ΔC _FREE .

In addition, as shown in Figure 9, the state density in the bandgap according to the present invention extracted through the optical differential ideal coefficient is within the accurate bandgap compared to the extraction method (MFM) using the conventional capacitance-voltage (CV) characteristics The state density in the intrinsic bandgap or in the intrinsic bandgap is close to the state density in the intrinsic bandgap because the density of the state can be extracted and the capacitance formed by the free electrons included in the conventional ideal coefficient differential method (DIFT) is de-embedded. The density of states can be extracted.

In addition, since the state density in the band gap is the state density with respect to the energy level, the gate voltage should be converted into the surface potential (energy level), which will be described with reference to FIG. 4.

4 shows an operation flowchart of an embodiment for step S360 shown in FIG.

Referring to FIG. 4, in the extracting the state density in the band gap (S360), the capacitance according to the gate voltage is measured (S410).

Here, the capacitance can be measured using a measurement means, for example, an Agilent 4156C semiconductor parameter analyzer or an HP4284 LCR meter, and various corresponding measurement means can be utilized.

The surface potential is mapped to the gate voltage using the capacitance measured in step S410 (S420). That is, the relationship between the surface potential with respect to the gate voltage and the energy level is obtained with respect to the state density in the band gap.

)로 변환하는데, 게이트 전압에 따른 표면 전위는 아래 <수학식 13>에 의해 계산될 수 있다.
For example, as shown in the example illustrated in FIG. 6, the gate voltage is converted into a surface potential using a gate capacitance between the turn-on voltage V _ON and the threshold voltage V _T among the measured gate capacitances C _G.

), The surface potential according to the gate voltage can be calculated by Equation 13 below.

&Quot; (13) &quot;

Here, C _G (V _GS ) is a gate capacitance measured according to the gate voltage, and means a gate capacitance CV _dark measured in a dark room.

A state density in a band gap according to an energy level as shown in Equation 12 is extracted by using the surface potential for the energy level with respect to the gate voltage mapped in step S420 and the photoreaction capacitance calculated in step S350 (S430).

The state density in bandgap g _A (E) extracted for the bandgap state density extracted through the process of FIGS. 3 and 4, that is, the bandgap energy (E _V <E <E _C ), is given by Equation 14 Deep exponential and tail states can be modeled as superposition in exponential form, such as>. For example, as shown in FIG. 9, in the present invention, the band density state density (ODIFT) extracted by using the optical differential ideal coefficient is a band density state model (Model) modeled by Equation 14 below. It can be expressed as.

&Quot; (14) &quot;

Here, N _DA denotes a state density located in a deep state, k denotes a Boltzmann constant as a preset value, and N _TA denotes a state density located in a tail state. , kT _DA refers to the characteristic energy of the deep state (kT _TA) , kT _TA refers to the characteristic energy of the tail state (tail state).

As described above, the method according to the present invention calculates the dark room abnormality coefficient and the photoreaction abnormality coefficient using the drain current of the region before the threshold voltage among the drain currents measured according to the irradiation of light, and calculates the difference between the calculated two ideal coefficients. Calculate the photoreaction capacitance formed at the state density in the bandgap by photoreaction by irradiation of light through the differential, and the state density in the bandgap de-embedded the capacitance formed by the free electrons based on the calculated photoreaction capacitance. By extracting, the density of the state in the intrinsic bandgap of the amorphous oxide semiconductor TFT can be extracted, and the influence of light, temperature, or heat can be excluded, and the state in the bandgap is simple and fast without the complicated formula independent of the threshold voltage. The density can be extracted.

In addition, the present invention extracts the nonlinear slope below the threshold voltage caused by the non-uniform distribution of the density of states in the bandgap by extracting the state density in the bandgap independently of the threshold voltage Can have the advantage of being applicable to a TFT.

FIG. 10 shows a configuration of an apparatus for extracting a state density in a bandgap of an amorphous oxide semiconductor TFT according to an embodiment of the present invention.

Referring to FIG. 10, the apparatus 1000 according to the present invention includes a measuring unit 1010, a calculating unit 1020, a mapping unit 1030, and an extracting unit 1040.

The measurement unit 1010 measures the dark room drain current according to the gate voltage in the dark room with respect to the amorphous oxide semiconductor TFT, and irradiates light of a light source having a predetermined wavelength to measure the photoreaction drain current according to the gate voltage.

Here, the measuring unit 1010 may measure the drain current according to the gate voltage by using a measuring means, for example, an Agilent 4156C semiconductor parameter analyzer, as well as the gate using all measuring means capable of measuring the drain current. The drain current according to the voltage can be measured.

The calculation unit 1020 calculates the dark room abnormality coefficient according to the gate voltage using the measured dark room drain current, and calculates the photoreaction abnormality coefficient according to the gate voltage using the measured photoreaction drain current.

In this case, the calculation unit 1020 may calculate the dark room abnormality coefficient using the drain current of the region before the threshold voltage among the dark room drain current, and calculate the photoreaction abnormal coefficient using the drain current of the region before the threshold voltage among the photoreaction drain currents. Can be calculated

Further, the calculation unit 1020 may calculate the photoreaction capacitance formed at the state density in the bandgap by the photoreaction by irradiation of light based on the derivative of the difference between the calculated photoreaction abnormality coefficient and the darkroom abnormality coefficient.

The mapping unit 1030 maps the gate voltage to the surface potential with respect to the energy level.

That is, the mapping unit 1030 performs a function of converting the gate voltage to the surface potential for the energy level, and converts the gate voltage to the surface potential for the energy level by further considering physical structure parameters of the amorphous oxide semiconductor TFT. Can be.

The extraction unit 1040 extracts the state density in the band gap of the amorphous oxide semiconductor TFT based on the derivative of the dark room abnormality coefficient and the photoreaction abnormality coefficient calculated by the calculating unit 1020.

At this time, the extraction unit 1040 may extract the state density in the band gap based on the photoreaction capacitance calculated through the derivative of the difference between the photoreaction abnormality coefficient and the dark room abnormality coefficient.

Further, the extractor 1040 may extract the state density in the band gap by additionally considering the physical structural parameters of the amorphous oxide semiconductor TFT.

Of course, the extractor 1040 may extract the state density in the band gap according to the energy level by using the surface potential of the energy level according to the gate voltage mapped by the mapping unit 1030.

The state density in the band gap extracted by the extractor 1040 of the present invention may be the state density in the intrinsic band gap. The dark room abnormality coefficient and the photoreaction abnormality coefficient calculated by the calculation unit 1030 of the present invention are the capacitance formed by the state density in the bandgap, the capacitance formed by the free electrons, and the state density in the bandgap by light irradiation. Since the photoresist capacitance is formed, the photoresponse capacitance calculated by differentiating the difference between the two ideal coefficients is in a state of de-embedding the capacitance formed by the free electrons. That is, since the photoreaction capacitance used to extract the state density in the bandgap is a state of de-embedding the capacitance formed by the free electrons, the intrinsic bandgap in which the state density in the extracted bandgap is also de-embedded in the capacitance by the free electrons. It corresponds to my state density.

The state density extraction method in the bandgap of the amorphous oxide semiconductor thin film transistor according to the exemplary embodiment of the present invention may be implemented in the form of program instructions that may be executed by various computer means and may be recorded in a computer readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described by specific embodiments such as specific components and the like. For those skilled in the art, various modifications and variations are possible from these descriptions.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (6)

A method for extracting a state density in a bandgap of an amorphous oxide semiconductor thin film transistor,
The dark room drain current, which is a drain current according to the gate voltage of the amorphous oxide semiconductor thin film transistor, is measured in a dark room, and the photoreaction drain current which is a drain current according to the gate voltage of the amorphous oxide semiconductor thin film transistor by irradiating light of a predetermined light source. Measuring;
The darkroom abnormality coefficient which is an ideal coefficient according to the gate voltage by comparing a predetermined mathematical model of the darkroom drain current according to the gate voltage including the measured darkroom drain current according to the gate voltage and an ideality factor. Calculate a light and compare a predetermined mathematical model of the photoreaction drain current according to the gate voltage including the measured photoreaction drain current according to the gate voltage and an abnormality coefficient to be an ideal coefficient according to the gate voltage. Calculating a reaction abnormality coefficient; And
Extracting a state density in a band gap of the amorphous oxide semiconductor thin film transistor based on the calculated derivative of the dark room abnormality coefficient and the photoreaction abnormality coefficient
State density extraction method in the band gap of the amorphous oxide semiconductor thin film transistor comprising a. The method of claim 1,
Extracting the state density in the band gap
Calculating the photoreaction capacitance formed at the density of states in the bandgap by photoreaction by irradiation of the light based on the derivative of the difference between the photoreaction abnormality coefficient and the darkroom abnormality coefficient, and the calculated photoreaction capacitance Extracting the density of states in the band gap based on the method; extracting the density of states in the band gap of an amorphous oxide semiconductor thin film transistor. The method of claim 1,
The dark room abnormality coefficient and the photoreaction abnormality coefficient
And a capacitance formed by the state density within the band gap and a capacitance formed by the free electrons. The method of claim 1,
Extracting the state density in the band gap
A method for extracting a state density in a bandgap of an amorphous oxide semiconductor thin film transistor, characterized by extracting a state density in an intrinsic bandgap of the amorphous oxide semiconductor thin film transistor de-embedded with capacitance formed by free electrons.
In the band gap state density extraction apparatus of an amorphous oxide semiconductor thin film transistor,
The dark room drain current, which is a drain current according to the gate voltage of the amorphous oxide semiconductor thin film transistor, is measured in a dark room, and the photoreaction drain current which is a drain current according to the gate voltage of the amorphous oxide semiconductor thin film transistor by irradiating light of a predetermined light source. Measuring unit for measuring;
The darkroom abnormality coefficient which is an ideal coefficient according to the gate voltage by comparing a predetermined mathematical model of the darkroom drain current according to the gate voltage including the measured darkroom drain current according to the gate voltage and an ideality factor. Calculate and compare the photoreaction drain current according to the measured gate voltage with a predetermined mathematical model of the photoreaction drain current according to the gate voltage including an ideal coefficient to determine an ideal coefficient according to the gate voltage. A calculation unit for calculating a photo reaction abnormal coefficient; And
An extraction unit for extracting a state density in a band gap of the amorphous oxide semiconductor thin film transistor based on the calculated derivative of the dark room abnormality coefficient and the photoreaction abnormality coefficient
State density extraction apparatus in a band gap of the amorphous oxide semiconductor thin film transistor comprising a. 6. The method of claim 5,
The extracting unit
Calculating the photoreaction capacitance formed at the density of states in the bandgap by photoreaction by irradiation of the light based on the derivative of the difference between the photoreaction abnormality coefficient and the darkroom abnormality coefficient, and the calculated photoreaction capacitance And extracting the state density in the band gap based on the state density extracting device in the band gap of the amorphous oxide semiconductor thin film transistor.

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