KR101105273B1 - Method and apparatus for modeling drain-source current of amorphous oxide semiconductor thin-film transistor - Google Patents

Abstract

PURPOSE: A current modeling method and apparatus of an amorphous oxide semiconductor thin film transistor are provided to improve a current calculation speed by supplying an analytical current model. CONSTITUTION: Charge density which is restricted in state density within a band gap is calculated(S310). The charge density is approximated to a major carrier component in case voltage between gate-sources is less than threshold voltage and is over than the threshold voltage(S320). Total electric charge per unit area is calculated(S330). The mobility of a channel which depends on gate voltage is calculated(S340). A first current model and a second current model are created(S350). A total current model is created using the first current model and the second current model(S360).

Description

TECHNICAL AND MODEL MODELING METHOD OF Amorphous Oxide Semiconductor Thin Film Transistor TECHNICAL FIELD

The present invention relates to current modeling of an amorphous oxide semiconductor thin film transistor (TFT), and more particularly, an analytic current model based on subgap density-of-states (subgap DOS) in an amorphous oxide semiconductor TFT. The present invention relates to an amorphous oxide semiconductor thin film transistor that can provide a current modeling method and apparatus therefor.

Amorphous oxide semiconductor thin film transistors (TFTs) have advantages such as high carrier mobility, uniformity of the thin film at large areas, and stability in terms of reliability. Because of these advantages, amorphous oxide semiconductor TFTs are being actively researched as alternatives to amorphous Si TFTs that are commercially available in display backplanes such as high-resolution active matrix (LCD) and organic light-emitting diode (AM-OLED). It is becoming. In fact, in recent 3-4 years, a-IGZO (InGa-ZnO) TFT, which is an amorphous oxide semiconductor TFT, has been applied to various display pixel circuits or 3-D stacked circuits.

Since the amorphous oxide semiconductor TFT has a large electrical effect of the subgap DOS present in the bandgap, the current model should reflect the influence of the subgap DOS. In addition, when a circuit composed of TFTs performs low voltage operation, a current model below the threshold voltage and above is required because the current below the threshold voltage greatly affects the RC delay of the circuit.

However, the formula is complicated to reflect all of these points, and a method such as numerical iteration should be used to establish a current model in consideration of all the carrier components affecting the current of the amorphous oxide semiconductor TFT. In other words, by using the same method as the conventional numerical iteration, it takes a long time to calculate the current, and therefore, it is difficult to be applied to a model for predicting the performance of the circuit, for example, a spice simulation. .

Therefore, there is a need for an analytical current modeling technique that can be applied to a simulation model that can be used for circuit simulation by reducing the current calculation time.

Korean Registered Patent Publication No. 0938675 (Registration date 2010.01.18)

The present invention has been made to solve the above problems of the prior art, and an object thereof is to provide a current modeling method and apparatus capable of providing an analytical current model based on an amorphous oxide semiconductor TFT.

In addition, an object of the present invention is to provide a current modeling method and apparatus for an amorphous oxide semiconductor thin film transistor which can be applied to a circuit simulation model by improving the current calculation speed by providing an analytical current model.

In order to achieve the above object, the current modeling method of the amorphous oxide semiconductor thin film transistor according to an embodiment of the present invention includes the steps of calculating the charge density bound to the subgap DOS (bandgap DOS); Approximating the charge density present in the channel to the dominant carrier component for each of the gate-source voltages below and above the threshold voltage; Generate a first current model when the threshold voltage is lower than the threshold voltage and a second current model when the threshold voltage is higher than the threshold voltage based on information on the state density in the band gap, the approximated charge density, and information about a plurality of input parameters. Making; And generating a total current model using the first current model and the second current model.

Here, the state density in the bandgap includes a first state and a second state, and the charge density existing in the channel includes a first electron concentration bound to the first state and a second state bound to the second state. 2 may include electron concentration and free electron concentration present in the conduction band.

Furthermore, the method may further include calculating mobility of the channel by using the approximated charge density, and generating the first current model and the second current model further include the calculated mobility of the channel. In consideration of this, the first current model and the second current model may be generated.

The approximating may include approximating the charge density when the threshold voltage is lower than the second electron concentration and approximating the charge density when the threshold voltage is higher than the free electron concentration.

The plurality of parameters may include the width of the channel, the length of the channel, the thickness of the gate insulating layer, the capacitance of the gate insulating layer, the conduction band mobility, the effective state density located in the conduction band, the flat band voltage, and the bulk at thermal equilibrium. -Fermi voltage, effective state density at the conduction band minimum energy below the threshold voltage, effective characteristic energy below the threshold voltage, effective state density at the conduction band minimum energy above the threshold voltage, and effective characteristic above the threshold voltage. May include energy.

An apparatus for modeling a current of an amorphous oxide semiconductor thin film transistor according to an embodiment of the present invention includes an input unit for receiving information on a plurality of parameters; A calculation unit for calculating the charge density bound to the subgap DOS; An approximation unit for approximating the charge density existing in the channel as a dominant carrier component for each of the cases where the gate-source voltage is less than or equal to the threshold voltage; And a first current model when the threshold voltage is lower than the threshold voltage and a second current model when the threshold voltage is higher than the threshold voltage based on information on the state density in the band gap, the approximated charge density, and the received information about the plurality of parameters. And a current model generator for generating a total current model using the generated first current model and the second current model.

The calculator calculates a mobility of a channel by using the charge density approximated by the approximator, and the current model generator further considers the mobility of the channel calculated by the calculator to calculate the first current model. And the second current model.

The approximation unit may approximate the charge density when the threshold voltage is lower than the second electron concentration, and the charge density when the threshold voltage is higher than the threshold voltage to the free electron concentration.

According to the present invention, for the case where the gate-to-source voltage is less than or equal to the threshold voltage, each of them is approximated as a dominant carrier component, and the drain-source current model is represented by an analytical equation using the current. Speed up calculations to reduce computation time and enable faster simulation.

The current model of the present invention consists of parameters related to free electrons, mobility, and TFTs in the subgap DOS and conduction bands in the bandgap, and reflects the electrical characteristics of the amorphous oxide semiconductor TFT. have. In addition, current is calculated before and after the threshold voltage as a single integrated formula, which makes it easy to calculate the current and can be represented by an analytical current formula, so it can be represented by Technology Computer Aided Design (TCAD) or Simulation Program with Integrated. Circuit Emphasis) can be applied as a simulation current model. Therefore, in designing and producing circuits and systems based on amorphous oxide semiconductor TFTs, currents vary according to various process and layout conditions such as the density of states in the bandgap due to the element composition of the thin film, the type and thickness of the gate insulating film, and the TFT device structure. Model equations can be calculated quickly.

In addition, when it is applicable to TCAD or SPICE model from the current model of the present invention, it is possible to simulate the device and the circuit, so that the overall design of the optimized process, the device and the circuit is possible by predicting the performance of the circuit according to the process conditions or the device structure. .

Furthermore, the present invention can contribute to the improvement of mass production of the next-generation original technology because the circuit performance consisting of the oxide semiconductor TFT can be predicted and optimized.

In addition, the analytical current model that quickly calculates the current can be very useful as a model for circuit design because it can be added to the existing circuit design model and environment in the form of a macro-model.

1 shows a cross-sectional view and a perspective view of an embodiment of an amorphous oxide semiconductor TFT.
FIG. 2 shows an energy band diagram in the depth direction from the gate of FIG. 1 to the a-IGZO thin film used as the channel region of the TFT.
3 is a flowchart illustrating an operation of a current modeling method of an amorphous oxide semiconductor TFT according to an exemplary embodiment of the present invention.
Figure 4 shows an I _DS -V _GS graph of a logarithmic scale for comparing the measured value with the drain current calculated at a gate voltage below the threshold by the method according to the invention.
5 shows an I _DS -V _GS graph of a linear scale for comparing the measured value with the drain current calculated by the gate voltage above the threshold voltage according to the method of the present invention.
Figure 6 shows an I _DS -V _DS graph on a linear scale for comparing the calculated current and measured values when the voltage conditions are in the linear and saturation regions with the method according to the invention.
FIG. 7 is a graph showing main carrier concentrations according to gate voltage conditions in an amorphous oxide semiconductor TFT.
8 illustrates model parameters for calculating the drain current of FIGS. 4 to 6.
9 illustrates a configuration of a current modeling apparatus of an amorphous oxide semiconductor TFT according to an embodiment of the present invention.

Other objects and features of the present invention in addition to the above objects will be apparent from the description of the 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 describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

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

Hereinafter, a current modeling method and an apparatus of an amorphous oxide semiconductor thin film transistor according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 9.

Amorphous oxide semiconductor TFT is an alternative device due to stability in terms of high carrier mobility and uniformity and reliability of thin film in large area instead of a-Si TFT, which is commercially used as a switch or driving element in display backplanes such as AMLCD and AMOLED. Be in the spotlight.

In such an amorphous oxide semiconductor TFT, the drain current is determined by the subgap DOS present in the band gap and the free electrons present in the conduction band.

Here, the state density present in the band gap may include carrier density, field-effect mobility, threshold voltage, and sub-threshold swing in the thin film under specific voltage and current driving conditions. All electrical parameters, such as threshold swing, turn-on voltage, I _ON , I _ON / I _OFF , and capacitance, are determined. In addition, the density of states within the bandgap determines the stress time dependence, photo-sensitivity due to backlight, and temperature dependence under current / voltage stress, which are critical for TFT production. It is an important parameter. Therefore, in designing and mass-producing TFT-based circuits and systems, the density of states of amorphous oxide semiconductor thin films according to various process and layout conditions such as elemental composition and deposition conditions and thickness of thin films, type and thickness of gate insulating films, TFT device structure, etc. It is very important to measure quickly and easily.

Summary of the Invention The present invention aims to generate an analytical current model that can be applied to TCAD and SPICE simulation in consideration of the above-described state density in bandgap and parameters related to TFT and free electrons present in the conduction band.

1 is a cross-sectional view and a perspective view of an embodiment of an amorphous oxide semiconductor TFT. In the present invention, an example of an amorphous InGaZnO (a-IGZO) TFT as an amorphous oxide semiconductor TFT will be described below.

Here, W denotes a channel width, L denotes a channel length between a source and a drain, T _IGZO denotes an amorphous oxide semiconductor (AOS), for example, a thickness of an a-IGZO thin film, T _OX refers to the thickness of the gate insulator, and L _OV refers to the overlap length between the gate electrode and the source / drain electrodes.

FIG. 2 shows an energy band diagram in the depth direction from the gate of FIG. 1 to the a-IGZO thin film used as the channel region of the TFT.

Here, φ _S means surface potential, φ (x) means voltage in the depth direction (x), and φ _F0 denotes the bulk-Fermi voltage at thermal equilibrium. Where V _CH is the channel voltage that depends on the channel length direction y under a specific gate voltage and drain / source voltage, E _C is the conduction band minimum energy, and E _V is the appliance It means the valence band maximum energy, and E _Fm means the Fermi level of the gate electrode.

The channel voltage V _CH reflects that the Fermi level E _F is lowered to the quasi Fermi level E _Fn due to the applied drain voltage. Molybdenum (Mo) is used as the gate electrode, the drain electrode, and the source electrode. Etc. can be used.

3 is a flowchart illustrating an operation of a current modeling method of an amorphous oxide semiconductor TFT according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the current modeling method calculates the charge density bound to the state density within the bandgap because the electrical influence of the subgap DOS existing in the bandgap is large in the amorphous oxide semiconductor TFT (S310). .

The acceptor-like DOS [g _A (E)] of the amorphous oxide semiconductor TFT thin film is composed of acceptor-like deep states [g _DA (E)] and acceptor-like tail states [g _TA (E)]. 1>.

[Equation 1]

Here, N _DA denotes a density of state located in a deep state, k denotes a Boltzmann constant with a preset value, and N _TA denotes a tail state. KT _DA denotes a characteristic energy of a first state, and kT _TA denotes a characteristic energy of a second state (tail state).

The charge density per unit volume is calculated by applying a Poisson equation in the depth direction (x) from the gate insulator boundary to the channel region of the TFT.

Here, the charge density per unit volume is the electron concentration [n _deep (x)] bound to g _DA (E), the electron concentration [n _tail (x)] bound to g _TA (E), and the freedom present in the conduction band. Consisting of the electron concentration [n _free (x)], it can be expressed as shown in Equation 2.

[Equation 2]

Here, ε _IGZO denotes the dielectric constant of an amorphous oxide semiconductor thin film, for example, a-IGZO, and n _loc (x) is bound to g _A (E) as the sum of n _deep (x) and n _tail (x). Mean electron concentration.

The first electron concentration n _deep (x) and the second electron concentration n _tail (x) use respective states [g _DA (E), g _TA (E)] and Fermi-Dirac distribution function [f (E)]. Equation 3 and Equation 4 can be represented.

&Quot; (3) "

&Quot; (4) "

That is, n _deep (x) and n _tail (x), respectively g _DA (E) and g _TA (E) E is filled probability of Fermi-Dirac distribution function [f (E)] for multiplying E _V from E _C in By integrating up, it can be calculated.

n _free (x) may be represented as in Equation 5.

[Equation 5]

Here, N _C means the effective state density located in the conduction band.

Subsequently, in order to solve Equation 2 without numerical iteration, the dominant occupies the highest concentration of charge density for each of the gate voltage before and after the threshold voltage V _T. Approximation to a carrier component (S320).

Amorphous silicon (a-Si) because it has many g _A (E) in the band gap of the TFT when the DOS to be filled in the band gap increases _free n (x) is much smaller than n _loc (x). Therefore, in the voltage range below the threshold voltage, the charge density per unit volume is approximated to n _deep (x) among the n _loc (x) components, and in the voltage range after the threshold voltage, n among the n _loc (x) components can be approximated by _tail (x).

However, in the case of the amorphous oxide semiconductor TFT, it has a lower g _A (E) than the a-Si TFT, so that DOS to be filled in the band gap is relatively small, so n _free (x) can be ignored compared to n _loc (x). none. This is a graph showing the main carrier concentration according to the gate voltage condition shown in FIG. 7, in the case where the threshold voltage is lower than the threshold voltage, the electron concentration [n _tail (x)] trapped in g _TA (E) prevails, and the threshold voltage is higher than the threshold voltage. In this case, it can be seen that the free electron concentration [n _free (x)] in the conduction band is dominant. Therefore, in the range where the gate voltage is smaller than the threshold voltage, the charge density per unit volume [ρ (x)] can be approximated to n _tail (x) of n _loc (x) as shown in Equation 6, and the gate voltage is thresholded. In the case of near voltage, the charge density per unit volume can be approximated by the sum of n _tail (x) and n _free (x), as shown in Equation (7). In addition, in the range where the gate voltage is a large threshold voltage, the charge density per unit volume may be approximated to n _free (x) of ρ (x) as shown in Equation (8).

&Quot; (6) "

Here, V _FB means a flat band voltage.

[Equation 7]

[Equation 8]

In this case, n _eff (x) is an effective carrier density, and was introduced to reduce an error of a carrier concentration approximate for each gate voltage range, which can be expressed by Equation (9). Where N _eff represents the effective carrier density at the lowest energy of the conduction band. Therefore, n _eff1 (x) and n _eff2 (x) may be expressed as in Equation 10 and Equation 11.

[Equation 9]

[Equation 10]

Here, n _eff1 (x) means the effective carrier density n _eff (x) approximated in the gate voltage range below the threshold voltage, and kT _eff1 is the value of n _eff1 according to the depth direction potential φ (x) according to the externally applied voltage. Mean effective characteristic energy that governs dependency.

[Equation 11]

Here, n _eff2 (x) means the effective carrier density n _eff (x) approximated in the gate voltage range near and above the threshold voltage, and kT _eff2 is n according to the depth direction potential φ (x) according to the externally applied voltage. _The effective characteristic energy that governs the dependence of _eff2 .

When the charge density for the case of less than or equal to the threshold voltage is approximated to the main carrier component, the effective carrier density is determined using the approximated main carrier component, and the total charge per unit area is calculated using this (S330).

In the amorphous oxide semiconductor TFT, an electric field (E-field) in the channel depth direction may be represented by Equation 12 using Equations 2 and 9 above.

[Equation 12]

In addition, the free electron charge per unit area (Q _FREE (φ (x))) is integrated with Equation (5) in the depth direction, and then compared with the surface voltage [φ (x = 0) = φ _S ]. If the voltage [φ (x = T _IGZO ) = φ _B ] is negligible, it can be expressed as Equation 13.

[Equation 13]

Here, φ _B means a back voltage.

The total charge per unit area [Q _TOT (φ (x))] can be calculated by multiplying the electric field in the channel depth direction by the dielectric constant of the channel region, for example, the dielectric constant of the a-IGZO thin film. Can be represented.

[Equation 14]

When the total charge per unit area is calculated, the mobility [μ _CH (φ (x))] of the channel depending on the gate voltage is calculated (S340).

Here, the channel mobility can be calculated using the free electron charge per unit area [Q _FREE (φ (x))] and the total charge per unit area [Q _TOT (φ (x))]. Can be represented as:

[Equation 15]

Here, μ _CH means the effective mobility of the channel. In the amorphous oxide semiconductor TFT of the present invention, when the gate voltage is high, the free electron concentration is higher than the electron concentration trapped in g _A (E). Μ _CH is approximately equal to conduction band mobility ( _μBAND ).

When the channel mobility is calculated, the current model when the gate-to-source voltage is less than the threshold voltage using the values calculated by the above steps and information about the previously input parameters, that is, the values of each of the parameters, A first current model) and a current model (second current model) when the threshold voltage is greater than or equal to one are generated (S350).

Here, the input parameters include the width of the channel (W), the length of the channel (L), the thickness of the gate insulating layer (T _OX ), the capacitance of the gate insulating layer (C _ox ), the conduction band mobility (μ _BAND ), and the conduction band. Located effective state density (N _C ), flat band voltage (V _FB ), bulk-Fermi voltage (φ _F0 ) at thermal equilibrium, effective state density (N _eff1 ) at lowest conduction band below threshold voltage, threshold voltage Effective Characteristic Energy (kT _eff1 ) of Effective Carrier Density n _eff1 (x) _Below , Effective State Density (N _eff2 ) at Minimum _{Conduction Band} Above Threshold Voltage, Effective Carrier Density n _eff2 (x) _Above Threshold Voltage It may include the effective characteristic energy (kT _eff2 ) of.

The drain current reflecting the channel effective mobility calculated by step S340 is represented by Equation 16, and when the integral variable for the channel depth direction (x) axis is changed to the depth direction voltage, it is represented by Equation 17. have.

[Equation 16]

[Equation 17]

N _free (φ (x)) in Equation 5, electric field E _IGZO (φ (x)) in Equation 12 and channel mobility in Equation 15 [μ _CH (φ (x))] is calculated by reflecting in Equation 17, and when φ _B is negligible compared to φ _S , it can be expressed as Equation 18, and Equation 18 is a channel. Integrating from the source (y = 0) to the drain (y = L) in the longitudinal direction y can be expressed as Equation (19).

Equation 18

[Equation 19]

In order to calculate Equation 19, the Gaussian law should be applied at the boundary between the amorphous oxide semiconductor thin film and the gate insulating film, and the Gaussian law is shown in Equation 20.

[Equation 20]

Here, C _OX means the gate insulating film capacitance of the amorphous oxide semiconductor TFT, and C _OX is the maximum value (C _max = C _OX + C _OV [F]) and minimum value (C _min = C _OV [F] of the capacitance through the measurement. ]), And C _OV means the overlap capacitance between the gate electrode and the source / drain electrodes.

When E _IGZO (φ (x = 0) = φ _S ) shown in Equation 12 is applied to Equation 20, it can be expressed as Equation 21. In addition to <Equation 22> indicating the surface voltage relationship, <Equation 23> indicating the relationship between the channel voltage and the surface voltage can be obtained.

[Equation 21]

[Equation 22]

&Quot; (23) &quot;

Using Equation 22 and Equation 23, Equation 19 may be expressed as an analytical equation. Therefore, by reflecting <Equation 22> and <Equation 23> in <Equation 19>, <Equation 24> can be obtained, and by integrating the channel internal surface potential φ _S (y) from the source to the drain direction. Equation 25 showing the analytical equation for the drain current can be obtained.

&Quot; (24) &quot;

[Equation 25]

Here, φ _SS means the surface potential inside the channel at the source position, and φ _SD means the surface potential inside the channel at the drain position.

The current model of Equation 25 generated through the above process includes both the first current model when the gate-source voltage is less than the threshold voltage and the second current model that is greater than or equal to the threshold voltage.

When the first current model and the second current model are generated using Equation 25, the drain total current model I _{DS _ TOT} is generated using the first current model and the second current model (S360).

Here, the drain total current model may be expressed as Equation 26.

[Equation 26]

Here, I _DS (N _eff1 , kT _eff1 ) means the first current model calculated below the threshold voltage, and I _DS (N _eff2 , kT _eff2 ) means the second current model calculated above the threshold voltage.

As described above, the present invention represents the current model of the amorphous oxide semiconductor TFT by an analytical formula rather than a numerical repetition method, and the current calculated for the before and after threshold voltages is represented by one unified formula, so that the current calculation is convenient. It can be expressed as an analytical current formula and can be applied as a simulation current model.

4 to 6 show a result of comparing the drain current and the measured value calculated by the method according to the present invention, the model parameters for calculating the drain current is the same as FIG.

Among the model parameters shown in FIG. 8, W, L, T _OX and T _IGZO are the structural parameters of the TFT, and μ _BAND , N _C , φ _F0 are the parameters extracted by the physical and material engineering methods from the amorphous oxide semiconductor thin film material. The decision was made by reference. C _OX is the measured capacitance of the amorphous oxide semiconductor TFT, V _FB is the flat band voltage, and N _eff1 , kT _eff1 , N _eff2 , kT _eff2 are the parameters that are changed to match the calculated drain current and measured value. It corresponds to the effective characteristic energy of the effective state density and effective carrier concentration described.

Figure 4 shows an I _DS -V _GS graph of a logarithmic scale for comparing the measured value with the drain current calculated at a gate voltage below the threshold by the method according to the invention.

5 shows an I _DS -V _GS graph of a linear scale for comparing the measured value with the drain current calculated by the gate voltage above the threshold voltage according to the method of the present invention.

Figure 6 shows an I _DS -V _DS graph on a linear scale for comparing the calculated current and measured values when the voltage conditions are in the linear and saturation regions with the method according to the invention.

Here, the measured value may be measured using a measuring means, for example, an Agilent 4156C semiconductor parameter analyzer, as well as various measuring means corresponding thereto may be utilized.

4 to 6, it can be seen that the measured value when the gate-source voltage is less than the threshold voltage and the current calculated by the modeling method of the present invention match well with a constant slope 410. In addition, it can be seen that the measured value when the gate-source voltage is greater than or equal to the threshold voltage 510 and the current calculated by the modeling method of the present invention also coincide with the value.

As described above, since the modeling method of the present invention uses an integrated current model integrating the first current model when the threshold voltage is lower than the threshold voltage and the second current model when the threshold voltage is higher than the threshold voltage, However, even in the case of abnormality, it can be seen that the calculated current matches the measured value well.

Also, as shown in FIG. 6, it can be seen that the current and the measured value calculated according to the drain voltage match well in both the linear region and the saturation region by the modeling method of the present invention.

9 illustrates a configuration of a current modeling apparatus of an amorphous oxide semiconductor TFT according to an embodiment of the present invention.

9, the modeling apparatus 900 of the present invention includes an input unit 910, a calculator 920, an approximator 930, and a current model generator 940.

The input unit 910 receives information about a plurality of parameters.

Here, the plurality of input parameters include a channel width (W), a channel length (L), a thickness of the gate insulation layer (T _OX ), a capacitance of the gate insulation layer (C _ox ), and a conduction band mobility ( μ _BAND ), effective state density at conduction band (N _C ), flat band voltage (V _FB ), bulk-Fermi voltage (φ _F0 ) at thermal equilibrium, effective state density at conduction band minimum energy below threshold voltage (N _eff1 ), the effective characteristic energy of the effective carrier density below the threshold voltage (kT _eff1 ), the effective state density (N _eff2 ) of the minimum conduction band energy above the threshold voltage, and the effective carrier density above the threshold voltage Energy (kT _eff2 ).

The calculation unit 920 may calculate the charge density bound to the subgap DOS in the band gap, and calculate the total charge and channel mobility per unit area by using the value approximated by the approximation unit.

Here, the state density in the bandgap may include a deep state corresponding to the first state and a tail state corresponding to the second state, and the calculator 920 may calculate the state density in the bandgap using the above-described equations. subgap DOS), charge density per unit volume, total charge per channel area, and channel mobility.

The approximation unit 930 approximates the charge density present in the channel as a dominant carrier component for each of the gate-source voltages below and above the threshold voltage.

At this time, the charge density present in the channel is the first electron concentration bound in the first state of the subgap DOS, the second electron concentration bound in the second state of the subgap DOS, and the free electron concentration present in the conduction band. It may include.

The approximation unit 930 may approximate the charge density per unit volume to the second electron concentration when the gate voltage is less than the threshold voltage. If the gate voltage is near the threshold voltage, the approximation unit 930 may free the charge density per unit volume to the second electron concentration. The sum of the electron concentrations can be approximated, and the charge density per unit volume can be approximated to the free electron concentration in a range where the gate voltage is large.

The current model generator 940 is a first case in a case where the threshold voltage is less than the threshold voltage based on the charge density, the approximated charge density, and the information on the plurality of input parameters. A second current model is generated when the current model and the threshold voltage are higher than each other, and a total current model is generated using the generated first current model and the second current model.

In this case, the current model generator 940 may generate the first current model and the second current model by further considering the mobility of the channel calculated by the calculator 920.

As such, the modeling device of the present invention models an analytical current in consideration of parameters related to subgap DOS, free electrons, mobility, and TFT present in the conduction band and transfers the threshold voltage. The current calculations for and after are presented in one integrated formula, making current calculations convenient, speeding up current calculations, reducing computation time, and enabling fast simulation.

The current modeling method of the amorphous oxide semiconductor thin film transistor according to an 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, etc. alone or in combination. Program instructions recorded on the media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, 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 not only machine code generated by a compiler, but also 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 to which the present invention pertains, various modifications and variations are possible.

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 (11)

Calculating a charge density bound to a subgap DOS in a bandgap;
Approximating the charge density present in the channel to the dominant carrier component for each of the gate-source voltages below and above the threshold voltage;
Generate a first current model when the threshold voltage is lower than the threshold voltage and a second current model when the threshold voltage is higher than the threshold voltage based on information on the state density in the band gap, the approximated charge density, and information about a plurality of input parameters. Making; And
Generating a total current model using the first current model and the second current model
Current modeling method of the amorphous oxide semiconductor thin film transistor comprising a. The method of claim 1,
The density of states in the band gap
Including a first state and a second state,
The charge density present in the channel
A first electron concentration bound in the first state, a second electron concentration bound in the second state, and a free electron concentration present in a conduction band. Current modeling method. The method of claim 1,
Calculating mobility of a channel using the approximated charge density
Further comprising:
Generating the first current model and the second current model
And generating the first current model and the second current model in consideration of the calculated mobility of the channel.
The method of claim 2,
The approximation is
And approximating the charge density when the threshold voltage is lower than the second electron concentration, and approximating the charge density when the threshold voltage is higher than the threshold voltage to the free electron concentration. The method of claim 1,
The plurality of parameters
At the width of the channel, the length of the channel, the thickness of the gate insulation layer, the capacitance of the gate insulation layer, the conduction band mobility, the effective state density at the conduction band, the flat band voltage, the bulk-fermi voltage at thermal equilibrium, and below the threshold voltage. The effective state density at the lowest conduction band energy, the effective characteristic energy of the effective carrier density below the threshold voltage, the effective state density at the lowest conduction band energy above the threshold voltage, and the effective characteristic energy of the effective carrier density above the threshold voltage. A current modeling method for an amorphous oxide semiconductor thin film transistor comprising a. A computer-readable recording medium in which a program for executing the method of any one of claims 1 to 5 is recorded.
An input unit to receive information about a plurality of parameters;
A calculation unit for calculating the charge density bound to the subgap DOS;
An approximation unit for approximating the charge density existing in the channel as a dominant carrier component for each of the cases where the gate-source voltage is less than or equal to the threshold voltage; And
The first current model when the threshold voltage is lower than the threshold voltage and the second current model when the threshold voltage is higher than the threshold voltage are based on information on the state density in the band gap, the approximated charge density, and the received information about the plurality of parameters. A current model generator which generates a total current model by using the generated first current model and the second current model
Current modeling device for an amorphous oxide semiconductor thin film transistor comprising a. The method of claim 7, wherein
The density of states in the band gap
Including a first state and a second state,
The charge density present in the channel
A first electron concentration bound in the first state, a second electron concentration bound in the second state, and a free electron concentration present in a conduction band. Current modeling device. The method of claim 7, wherein
The calculation unit
The mobility of the channel is calculated using the charge density approximated by the approximation unit,
The current model generation unit
And the first current model and the second current model are generated in consideration of the mobility of the channel calculated by the calculation unit.
The method of claim 8,
The approximation unit
And approximating the charge density when the threshold voltage is less than the second electron concentration, and approximating the charge density when the threshold voltage is higher than the free electron concentration to the free electron concentration. The method of claim 7, wherein
The input unit
At the width of the channel, the length of the channel, the thickness of the gate insulation layer, the capacitance of the gate insulation layer, the conduction band mobility, the effective state density at the conduction band, the flat band voltage, the bulk-fermi voltage at thermal equilibrium, and below the threshold voltage. The effective state density at the lowest conduction band energy, the effective characteristic energy of the effective carrier density below the threshold voltage, the effective state density at the lowest conduction band energy above the threshold voltage, and the effective characteristic energy of the effective carrier density above the threshold voltage. An apparatus for modeling a current of an amorphous oxide semiconductor thin film transistor, characterized in that receiving information on the plurality of parameters, including.

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