PARAMETER EXTRACTION METHOD FOR QUASI-PHYSICAL LARGE-SIGNAL MODEL FOR MICROWAVE GALLIUM NITRIDE HIGH-ELECTRON-MOBILITY TRANSISTORS

Abstract

A parameter extraction method for quasi-physical large-signal model for microwave gallium nitride high-electron-mobility transistors (GaN HEMTs). The method includes: 1) acquiring a data set of parameters for a large-signal model for a plurality of different microwave transistors GaN HEMTs having the same size; 2) performing statistical analysis of physical parameters of the large-signal model and sub-models thereof: 3) characterizing the correlation between the physical parameters by factor analysis; and 4) predicting the output characteristics of the GaN HEMTs.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119 and the Paris Convention Treaty, this application claims foreign priority to Chinese Patent Application No. 202010154839.6 filed Mar. 6, 2020, the contents of which, including any intervening amendments thereto, are incorporated herein by reference. Inquiries from the public to applicants or assignees concerning this document or the related applications should be directed to: Matthias Scholl P. C., Attn.: Dr. Matthias Scholl Esq., 245 First Street, 18th Floor, Cambridge, Mass. 02142.

BACKGROUND

The disclosure relates to a parameter extraction method for quasi-physical large-signal model for microwave gallium nitride high-electron-mobility transistors (GaN HEMTs).

In the fabrication process of semiconductor devices, limited by the epitaxial growth, polarization, and unintentional doping of the semiconductor material, the process parameters tend to fluctuate, thus destroying the consistency of different batches or even the same batch of semiconductor devices, and adversely affecting the quality of the chip circuit. The statistical models of process parameters represent a mapping relationship between the process fluctuation and the output characteristic fluctuation of semiconductor devices, and can be used to assist the optimization and improvement of process parameters, guide the optimization design of chip circuits, effectively reduce the number of optimization iterations, and reduce the design cycle and cost.

Convectional statistical models of process parameters include technology computer aided design (TCAD)-based physical statistical models and empirical statistical models based on compact model theory. It is time-consuming for the TCAD-based physical statistical models to solve the semiconductor equation analytically, which can only meet the needs of the fluctuation of a single physical parameter, so it is difficult to apply to the simultaneous fluctuation of multiple physical parameters. The model equation of the empirical statistical models is derived from a pure mathematical formula and has no physical significance, so it cannot be used in the optimization design of process parameters and chip circuits of semiconductor devices.

SUMMARY

The disclosure provides a parameter extraction method for quasi-physical large-signal model for microwave gallium nitride high-electron-mobility transistors (GaN HEMTs). The method comprises: 1) acquiring a data set of parameters for a large-signal model for a plurality of different microwave transistors GaN HEMTs having the same size; 2) performing statistical analysis of physical parameters of the large-signal model and sub-models thereof; 3) characterizing the correlation between the physical parameters by factor analysis; and 4) predicting the output characteristics of the GaN HEMTs.

Specifically, the parameter extraction method for quasi-physical large-signal model for microwave GaN HEMTs comprises:

1) DC-IV Measurement of Multiple Batches of Microwave GaN HEMTs:

selecting multiple batches of microwave gallium nitride high-electron-mobility transistors (GaN HEMTs) intended to build a statistical model; measuring static DC-IV characteristics of each of the microwave GaN HEMTs at room temperature, thereby acquiring drain-source currents I_ds at different drain-source voltages V_ds and different gate-source voltages V_gs, where the gate-source voltages V_gs range from a pinch-off voltage thereof to 0 V, and the drain-source voltages V_ds range from 0 V to a maximum usable drain voltage of each microwave GaN HEMT, which is equal to 50% of a breakdown voltage thereof; the static DC-IV characteristics is measured by Power Device Analyzer/Curve Tracer;

2) Acquiring a Data Set of Parameters for the Statistical Model:

The statistical model to be built is a microwave GaN HEMT quasi-physical large-signal model satisfied with the following formula:

$\begin{array}{cc}{I}_{\mathrm{ds}}=\frac{I_{\max }{V}_{\mathrm{ds}}\left(1+\lambda V_{\mathrm{ds}}\right)}{\sqrt[\beta ]{{E_c^{\beta }\left(l_s+l_d\right)}^{\beta }+{\left(E_c{l}_g+V_{\mathrm{ds}}\right)}^{\beta }}};& \left(1\right)\\ n_s=0.5n_{\mathrm{smax}}·\tanh \left({\alpha }_3·{\left(V_{\mathrm{gs}}-V_{\mathrm{off}}\right)}^3+{\alpha }_2·{\left(V_{\mathrm{gs}}-V_{\mathrm{off}}\right)}^2+{\alpha }_1·\left(V_{\mathrm{gs}}-V_{\mathrm{off}}\right)+{\beta }_n\right)+0.5n_{\mathrm{smax}};& \left(2\right)\end{array}$

where I_max refers to the maximum drain-source current I_ds at different drain-source voltages V_ds and at different gate-source voltages V_gs and is measured by Power Device Analyzer/Curve Tracer; λ is the channel length modulation coefficient; β is the order of field-velocity relationship; E_c is the critical electric field strength; l_s and l_d refer to the lengths of the source and drain access regions, respectively; l_s is the gate length; n_s is the electron concentration: n_smax is the maximum electron areal density; V_off is the pinch-off voltage; and α₁, α₂, α₃, and β_n refer to the fitting parameters; l_s, l_d and l_g are measured by the SEM photograph of a certain GaN HEMT; V_off is regarded as the gate-source voltage V_gs when the corresponding l_max in the I_max−V_gs curve mentioned above is lower than 1 mA.

Formulas (1) and (2) are used to acquire a complete set of model parameters of each microwave GaN HEMT, as well as a maximum electron-saturation velocity v_max, a barrier layer thickness d, and fitting parameters a₀, a₁, b₀, b₁, and b₂ for a model for the critical electric field strength E_c: the maximum electron velocity v_max can be extracted by fitting the slope of the I_max−V_gs curve using the least square method: the barrier layer thickness d is extracted by the following formulas:

$\begin{array}{cc}d=\frac{{\varepsilon }_{\mathrm{AlGaN}}}{q\sigma }\left({\phi }_B-\Delta E-V_{\mathrm{off}}\right);& \left(3\right)\\ {\varepsilon }_{\mathrm{AlGaN}}=\left(10.4-0.3x\right){\varepsilon }_0;& \left(4\right)\\ {\phi }_B=1.3x+0.84;& \left(5\right)\\ E_g=6.13x+3.42\left(1-x\right)-x\left(1-x\right);& \left(6\right)\\ \Delta E=0.7\left(E_g-3.42\right);& \left(7\right)\end{array}$

• • where x refers to the aluminum mole fraction of the AlGaN/GaN HEMT; co is the permittivity of vacuum;

the extraction process is repeated same number of times for each microwave GaN HEMT, thereby acquiring a complete data set of the model parameters of the multiple batches of microwave GaN HEMTs: the mean value μ_i and standard deviation Q_i of each model parameter in the data set are both calculated, where i represents the i-th microwave GaN HEMT: the calculation method of mean and variance of each parameter are shown in the following formulas:

$\begin{array}{cc}d=\frac{{\varepsilon }_{\mathrm{AlGaN}}}{q\sigma }\left({\phi }_B-\Delta E-V_{\mathrm{off}}\right);& \left(8\right)\\ Q_i=\sqrt{\frac{\sum _{k=1}^N{\left(X_{\mathrm{ik}}-{\mu }_i\right)}^2}{N}};& \left(9\right)\end{array}$

where μ_i refers to the mean value of the i-th model parameter, Q_i refers to the standard deviation of the i-th model parameter, N represents the sample number, k is the i-th model parameter of the k-th sample.

3) Factor Analysis:

3.1) Standardization of Model Parameters:

The model parameters in the data set are arranged in a matrix form such that the data set containing k model parameters is arranged in a matrix with k columns, and each model parameter contains n observations (i.e., n microwave GaN HEMT) corresponding to n rows of the matrix; that is, the matrix has a dimension of n×k:

$\begin{array}{cc}x=\left[\begin{array}{cccc}{x}_{11}& x_{12}& \dots & x_{1k}\\ x_{21}& x_{22}& \dots & x_{2k}\\ ⋮& ⋮& ⋮& ⋮\\ x_{n1}& x_{n2}& \dots & x_{\mathrm{nk}}\end{array}\right];& \left(10\right)\end{array}$

The matrix is transformed into a standard matrix X:

$\begin{array}{cc}X=\left[\begin{array}{cccc}{X}_{11}& X_{12}& \dots & X_{1k}\\ X_{21}& X_{22}& \dots & X_{2k}\\ ⋮& ⋮& ⋮& ⋮\\ X_{n1}& X_{n2}& \dots & X_{\mathrm{nk}}\end{array}\right];& \left(11\right)\\ X_{\mathrm{ij}}=\frac{x_{\mathrm{ij}}-{\stackrel{\_}{x}}_j}{s_j},i=1,2,\dots ,n;j=1,2,\dots ,k;& \left(12\right)\end{array}$

where x_ij represents the i-th observation of the j-th model parameter: x_j is the mean value of the j-th model parameter; s_j is the standard deviation of the j-th model parameter;

3.2) Calculating Correlation Coefficient Matrix and Eigenvalues Thereof of the Standard Matrix X:

The standard matrix X is used in combination with Formula (13) to calculate each element of a correlation coefficient matrix.

$\begin{array}{cc}{r}_{\mathrm{ij}}=\frac{\sum _{k=1}^n\left(x_{\mathrm{ki}}-{\stackrel{\_}{x}}_i\right)\left(x_{\mathrm{kj}}-{\stackrel{\_}{x}}_j\right)}{\sqrt{\sum _{k=1}^n{\left(x_{\mathrm{ki}}-{\stackrel{\_}{x}}_i\right)}^2\sum _{k=1}^n{\left(x_{\mathrm{kj}}-{\stackrel{\_}{x}}_j\right)}^2}}i,j=1,2,\dots ,k;& \left(13\right)\end{array}$

The correlation coefficient matrix is used to calculate the eigenvalues λ_i, and the eigenvalues are sorted from largest to smallest, where i=1, 2, . . . , k;

3.3) Determination of the Number of Principle Components

The eigenvalues calculated in 3.2) are used to calculate the contribution rate and cumulative contribution rate of each principle component F_i, where the contribution rate refers to the percentage of an eigenvalue λ_i in all of the eigenvalues, and the eigenvalue λ_i corresponds to the principle component F_i.

$\begin{array}{cc}\mathrm{Contribution}\mathrm{rate}\mathrm{of}\mathrm{principle}\mathrm{component}{F}_i=\frac{{\lambda }_i}{\sum _{j=1}^k{\lambda }_j};& \left(14\right)\end{array}$

The larger contribution rate of the principle component Fi, the more the information related to the original data set in the principle component Fi; the cumulative contribution rate of the principle component Fi, represents the sum of the contribution rates of the top i-th principle components, and is satisfied with the following formula:

$\begin{array}{cc}\mathrm{Cumulative}\mathrm{contribution}\mathrm{rate}\mathrm{of}\mathrm{principle}\mathrm{component}{F}_i=\sum _{p=1}^i\frac{{\lambda }_p}{\sum _{j=1}^k{\lambda }_j};& \left(15\right)\end{array}$

Top p principle components having the maximum cumulative contribution rate, or top p principle components having the eigenvalues greater than or equal to 1 are selected.

3.4) Calculating Load Factor and Variance of Specific Factor:

The eigenvectors l₁, l₂, . . . , l_k are calculated for the corresponding eigenvalues obtained in 3.2). The k eigenvectors are normalized to obtain a combination W of columns of the normalized eigenvectors, that is, W=(W₁, W₂, . . . , W_k). The formula A=WΛ is used to calculate the factor loading matrix, where Λ is the diagonal matrix. The factor rotations are performed when the load factors are basically distributed around an average value. And the factor loading matrix of the top p principle components is calculated.

Formula (16) is used to calculate the specific variance:

$\begin{array}{cc}{\sigma }_i^2=1-\sum _{{}^{j=1}}^3{L}_{\mathrm{ij}}^2;& \left(16\right)\end{array}$

where σ_i is the standard deviation of the specific factors of the i-th model parameter; and L_ij is the load factor of the j-th principle component.

4) Statistical Characterization of Model Parameters:

According to the factor analysis theory, the common factors and the specific factors are used to predict each corresponding model parameter, and the following formula is satisfied:

$\begin{array}{cc}{X}_i={\mu }_i+Q_i\left(\underset{j=1}{\sum ^3}{L}_{\mathrm{ij}}{F}_j+{\varepsilon }_i\right);& \left(17\right)\end{array}$

where X_i is a parameter of the model I_d; μ_i and Q_i refer to the mean value and the standard deviation of the actually extracted model parameter X_i; L_ij is the load factor of the j-th principle components of the model parameter X_i; ε_i is the specific factor of the model parameter X_i, and obeys a normal distribution with zero mean: the common factors are independent of each other, with zero mean and a variance of 1;

5) Quasi-Physical Large-Signal Model:

The statistical distribution characteristics of each model parameter in 4) are substituted into a conventional large-signal model called Quasi-physical Zone Division model to obtain a complete quasi-physical statistical model for a device. The nonlinear harmonic balance method is used to solve the quasi-physical statistical model, thereby obtaining the large-signal output characteristics of the device.

Further, in 3.2), a method for calculating the eigenvectors λ_i is to solve |R−λE_k|=0 for the correlation coefficient matrix R, where i=1, 2, 3, . . . , k; and

E is the k-th order identity matrix;

$E_k=\left[\begin{array}{cccc}1& 0& \cdots & 0\\ 0& 1& \cdots & 0\\ ⋮& ⋮& \ddots & ⋮\\ 0& 0& \cdots & 1\end{array}\right];$

For |R−λE_k|=0, the expanded form of the determinant is as follows:

$R-\lambda E_k=\begin{array}{cccc}{r}_{11}-{\lambda }_1& r_{12}& \cdots & r_{1k}\\ r_{21}& r_{22}-{\lambda }_2& \cdots & r_{2k}\\ ⋮& ⋮& \ddots & ⋮\\ r_{k1}& r_{k2}& \cdots & r_{\mathrm{kk}}-{\lambda }_k\end{array}=0.$

The following advantages are associated with the disclosure: the parameter extraction method for quasi-physical large-signal model for microwave GaN HEMTs lays a foundation for optimization of the process parameters and product yield of semiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a parameter extraction method for quasi-physical large-signal model for microwave GaN HEMTs;

FIG. 2 shows the drain-source current Ids observed at different drain-source voltage Vds and different gate-source voltage Vgs;

FIG. 3 shows the transconductance g_m observed at different gate-source voltage Vgs and at a constant drain-source voltage Vds; and

FIG. 4 shows a comparison of the RF output characteristic of the device at different power under different external conditions.

DETAILED DESCRIPTION

To further illustrate the disclosure, embodiments detailing a parameter extraction method for quasi-physical large-signal model for microwave gallium nitride (GaN) high-electron-mobility transistors (HEMTs) are described below. It should be noted that the following embodiments are intended to describe and not to limit the disclosure.

Provided is a parameter extraction method for quasi-physical large-signal model for microwave gallium nitride high-electron-mobility transistors (GaN HEMTs), the method comprising:

1) DC-IV Measurement of Multiple Batches of Microwave GaN HEMTs:

Multiple batches of microwave GaN HEMTs are selected to build a statistical model; static DC-IV characteristics of each of the microwave GaN HEMTs are measured at room temperature; and the drain-source current I_ds at different drain-source voltages V_ds and different gate-source voltages V_gs is observed, where the gate-source voltage V_gs is scanned from pinch-off voltage to 0 V, and the drain-source voltage is scanned from 0 V to the maximum usable drain voltage (i.e. 50% breakdown voltage). The static DC-IV characteristics is measured by Power Device Analyzer/Curve Tracer.

2) Acquiring a Data Set of Parameters for the Statistical Model:

The statistical model to be built, is a microwave GaN HEMT quasi-physical large-signal model satisfied with the following formula

$\begin{array}{cc}{I}_{\mathrm{ds}}=\frac{I_{\max }{V}_{\mathrm{ds}}\left(1+\lambda V_{\mathrm{ds}}\right)}{\sqrt[\beta ]{{E_c^{\beta }\left(l_s+l_d\right)}^{\beta }+{\left(E_c{l}_g+V_{\mathrm{ds}}\right)}^{\beta }}};& \left(1\right)\end{array}$

where I_max refers to the maximum drain-source current I_ds at different drain-source voltages V_ds and gate-source voltages V_gs and is measured by Power Device Analyzer/Curve Tracer; λ is the channel length modulation coefficient; β is the order of field-velocity relationship; E_c is the critical electric field strength; l_s and l_d refer to the lengths of the source and drain access regions, respectively: l_g is the gate length; l_s, l_d and l_g are measured by the SEM photograph of a certain GaN HEMT; V_off is regarded as the gate-source voltage V_gs when the corresponding l_max in the I_max−V_gs curve mentioned above is lower than 1 mA; while for other model parameters above, they are all extracted using a Chinese patent titled “A method and system for parameter extraction of microwave GaN device nonlinear current model” (The application number is CN201810096978.0).

To accurately fit the I-V curves of all of devices, n_s(V_gs) is optimized as follows:

$\begin{array}{cc}{n}_s=0.5n_{\mathrm{smax}}·\tanh \left({\alpha }_3·{\left(V_{\mathrm{gs}}-V_{\mathrm{off}}\right)}^3+{\alpha }_2·{\left(V_{\mathrm{gs}}-I_{\mathrm{off}}\right)}^2+{\alpha }_1·\left(V_{\mathrm{gs}}-V_{\mathrm{off}}\right)+{\beta }_n\right)+0.5n_{\mathrm{smax}};& \left(2\right)\end{array}$

where, n_s is the electron concentration; n_smax is the maximum electron areal density; V_off is the pinch-off voltage; and α₁, α₂, α₃, and, β_n refer to the fitting parameters; V_off is regarded as the gate-source voltage V_gs when the corresponding I_max in the I_max−V_gs curve mentioned above is lower than 1 mA; While for other model parameters above, they are all extracted using I_max data mentioned above based on the method in a Chinese patent titled “A method and system for parameter extraction of microwave GaN device nonlinear current model” (The application number is CN201810096978.0).

Formula (1) and (2) are used to acquire a complete set of model parameters of each microwave GaN HEMT, as well as a maximum electron-saturation velocity v_max, a barrier layer thickness d, and fitting parameters a₀, a₁, b₀, b₁, and b₂ for a model for the critical electric field strength Ec; The maximum electron velocity v_max can be extracted by fitting the slope of the I_max−V_gs curve using the least square method; the barrier layer thickness d can be extracted by the following formulas; While for model parameters in critical electric field E_c model, they are all extracted using the drain-source current I_ds measured also by Power Device Analyzer/Curve Tracer (Keysight B1505A) based on the method in a Chinese patent titled “A method and system for parameter extraction of microwave GaN device nonlinear current model” (The application number is CN201810096978.0):

$\begin{array}{cc}d=\frac{{\varepsilon }_{\mathrm{AlGaN}}}{q\sigma }\left({\phi }_B-\Delta E-V_{\mathrm{off}}\right);& \left(3\right)\\ {\varepsilon }_{\mathrm{AlGaN}}=\left(10.4-0.3x\right){\varepsilon }_0;& \left(4\right)\\ {\phi }_B=1.3x+0.84;& \left(5\right)\\ E_g=6.13x+3.42\left(1-x\right)-x\left(1-x\right);& \left(6\right)\\ \Delta E=0.7\left(E_g-3.42\right);& \left(7\right)\end{array}$

where x refers to the aluminum mole fraction of the AlGaN/GaN HEMT: ε₀ is the permittivity of vacuum.

The extraction process is repeated same number of times for each microwave GaN HEMT, thereby acquiring a complete data set of the model parameters of the multiple batches of microwave GaN HEMTs; The mean value μ_i and standard deviation Q_i of each model parameter in the data set are both calculated, as shown in Table 1, where i represents the i-th microwave GaN HEMT. The calculation method of mean and variance of each parameter are shown in the following formulas:

$\begin{array}{cc}d=\frac{{\varepsilon }_{\mathrm{AlGaN}}}{q\sigma }\left({\phi }_B-\Delta E-V_{\mathrm{off}}\right);& \left(8\right)\\ Q_i=\sqrt{\frac{\sum _{k=1}^N{\left(X_{\mathrm{ik}}-{\mu }_i\right)}^2}{N}};& \left(9\right)\end{array}$

where μ_i refers to the mean value of the i-th model parameter, Q_i refers to the standard deviation of the i-th model parameter, N represents the sample number, k is the i-th model parameter of the k-th sample.

TABLE 1
Mean and standard deviation of each model
parameter extracted from measured data
	Parameter		Mean	Standard
	d	18.74	nm	0.60	nm
	vmax	1.53 × 105	m/s	0.03 × 105	m/s
	nsmax	8.42 × 1016	m−2	2.96 × 1015	m−2
	α1	2.32	0.13
	α2	−1.20	0.12
	α3	0.31	0.04
	βn	−1.59	0.02
	a0	1208.13	124.72
	a1	−788.87	123.24
	b0	1418.85	46.89
	b1	−64.08	2.22
	b2	0.75	0.03

3) Factor Analysis:

3.1) Standardization of Model Parameters:

The model parameters in the data set are arranged in matrix form such that the data set containing k model parameters is arranged in a matrix with k columns, and each model parameter contains n observations (i.e., n microwave GaN HEMT) corresponding to n rows of the matrix: that is, the matrix is a n×k matrix:

$\begin{array}{cc}x=\left[\begin{array}{cccc}{x}_{11}& x_{12}& \cdots & x_{1k}\\ x_{21}& x_{22}& \cdots & x_{2k}\\ ⋮& ⋮& \ddots & ⋮\\ x_{n1}& x_{n2}& \dots & x_{\mathrm{nk}}\end{array}\right].& \left(10\right)\end{array}$

The above matrix is transformed into a standard matrix X:

$\begin{array}{cc}X=\left[\begin{array}{cccc}{X}_{11}& X_{12}& \cdots & X_{1k}\\ X_{21}& X_{22}& \cdots & X_{2k}\\ ⋮& ⋮& ⋮& ⋮\\ X_{n1}& X_{n2}& \dots & X_{\mathrm{nk}}\end{array}\right];& \left(11\right)\\ X_{\mathrm{ij}}=\frac{x_{\mathrm{ij}}-{\stackrel{\_}{x}}_j}{s_j},i=1,2,\cdots ,n;j=1,2,\cdots ,k;& \left(12\right)\end{array}$

where x_ij represents the i-th observation of the j-th model parameter; x_j is the mean value of the j-th model parameter; s_j is the standard deviation of the j-th model parameter, as shown in Table 1.

3.2) Calculating correlation coefficient matrix and eigenvalues thereof of the matrix X:

The matrix X is used in combination with Formula (13) to calculate each element of a correlation coefficient matrix, and the results are shown in Table 2:

$\begin{array}{cc}{r}_{\mathrm{ij}}=\frac{\sum _{k=1}^n\left(x_{\mathrm{ki}}-{\stackrel{\_}{x}}_i\right)\left(x_{\mathrm{kj}}-{\stackrel{\_}{x}}_j\right)}{\sqrt{\sum _{k=1}^n{\left(x_{\mathrm{ki}}-{\stackrel{\_}{x}}_i\right)}^2\sum _{k=1}^n{\left(x_{\mathrm{kj}}-{\stackrel{\_}{x}}_j\right)}^2}}i,j=1,2,\cdots ,k;& \left(13\right)\end{array}$

TABLE 2
Correlation coefficient matrix of each model parameter
Original
variable	d	vmax	nsmax	α1	α2	α3	βn	a0	a1	b0	b1	b2
d	1
vmax	−0.66	1
nsmax	0.98	−0.61	1
α1	−0.72	0.09	−0.79	1
α2	0.77	−0.18	0.84	−0.99	1
α3	−0.89	0.38	−0.94	0.94	−0.97	1
βn	−0.06	0.57	0.03	−0.61	0.53	−0.33	1
a0	0.18	−0.74	0.13	0.41	−0.33	0.13	−0.82	1
a1	0.02	−0.50	−0.01	0.51	−0.44	0.27	−0.83	0.85	1
b0	0.21	−0.09	0.24	−0.32	0.33	−0.33	0.24	−0.22	−0.09	1
b1	0.16	0.25	0.16	−0.31	0.28	−0.21	0.24	−0.28	−0.41	−0.72	1
b2	−0.41	−0.20	−0.44	0.66	−0.64	0.56	−0.43	0.43	0.55	0.35	−0.89	1

The correlation coefficient matrix is used to calculate the eigenvalues λ_i, and the eigenvalues are then sorted from largest to smallest, where i=1, 2, . . . , k;

Specifically, a method for calculating the eigenvectors λ_i is to solve |R−λE_k|=0 for the correlation coefficient matrix R, where i=1, 2, 3, . . . , k; and E is the k-th order identity matrix;

$E_k=\left[\begin{array}{cccc}1& 0& \cdots & 0\\ 0& 1& \cdots & 0\\ ⋮& ⋮& \ddots & ⋮\\ 0& 0& \cdots & 1\end{array}\right].$

For |R−λE_k|=0, the expanded form of the determinant is as follows:

$R-\lambda E_k=\begin{array}{cccc}{r}_{11}-{\lambda }_1& r_{12}& \cdots & r_{1k}\\ r_{21}& r_{22}-{\lambda }_2& \cdots & r_{2k}\\ ⋮& ⋮& \ddots & ⋮\\ r_{k1}& r_{k2}& \cdots & r_{\mathrm{kk}}-{\lambda }_k\end{array}=0.$

3.3) Determination of the Number of Principle Components

The eigenvalues calculated in 3.2) are used to calculate the contribution rate and cumulative contribution rate of each principle component F_i, where the contribution rate refers to the percentage of an eigenvalue λ_i in all of the eigenvalues, and the eigenvalue λ_i corresponds to the principle component F_i.

$\begin{array}{cc}\mathrm{Contribution}\mathrm{rate}\mathrm{of}\mathrm{principle}\mathrm{component}{F}_i=\frac{{\lambda }_i}{\sum _{j=1}^k{\lambda }_j}.& \left(14\right)\end{array}$

The larger the contribution rate of the principle component F_i, the more the information related to the original data set in the principle component F_i; the cumulative contribution rate of the principle component F_i represents the sum of the contribution rates of the top i-th principle components, and is satisfied with the following formula:

$\begin{array}{cc}\mathrm{Cumulative}\mathrm{contribution}\mathrm{rate}\mathrm{of}\mathrm{principle}\mathrm{component}{F}_i=\sum _{p=1}^i\frac{{\lambda }_p}{\sum _{j=1}^k{\lambda }_j}.& \left(15\right)\end{array}$

The contribution rate and cumulate contribution rate of each principle component are calculated as shown in Table 3.

TABLE 3
Contribution rate of each principle component
and cumulate contribution rates
	Principle component
	F1	F2	F3	F4	. . .	F12
Contribution	47.03	30.49	17.22	2.34	. . .	3.68 × 10−4
rate (%)
Cumulate	47.03	77.52	94.74	97.08	. . .	100
contribution
rate (%)

The top p principle components are selected so that the cumulate contribution rate is above 85% or the eigenvalue is greater than or equal to 1; referring to Table 3, the top 3 principle components of the data set of the I_ds model parameter has a variance of 94.74%, illustrating that the data set can be explained with three variances independent of each other.

3.4) Calculating Load Factor and Variance of Specific Factor:

The eigenvectors l₁, l₂, . . . , l_k are calculated for the corresponding eigenvalues obtained in 3.2). The k eigenvectors are normalized to obtain a combination W of columns of the normalized eigenvectors, that is, W=(W₁, W₂, . . . , W_k). The formula A=WΛ is used to calculate the factor loading matrix, where Λ is the diagonal matrix. It is necessary to perform factor rotations when the load factors are basically distributed around an average value. And the factor loading matrix of the top p principle components is calculated. The number of the principle components determined in 3) is 3, which are used to calculate the loading factor matrix as shown in Table 4.

TABLE 4
Factor loading matrix
	F1	F2	F3
	d	0.9515	0.2730	−0.0662
	vmax	−0.4960	−0.7442	−0.1602
	nsmax	0.9812	0.1770	−0.0359
	α1	−0.8864	0.4576	0.0358
	α2	0.9257	−0.3722	−0.0221
	α3	−0.9872	0.1482	0.0020
	βn	0.2054	−0.9380	0.0419
	a0	−0.0146	0.8705	0.0613
	a1	−0.1583	0.8079	0.1835
	b0	0.3163	−0.1749	0.8688
	b1	0.1803	−0.2596	−0.9463
	b2	−0.5037	0.4196	0.7312

Since only three principle components are used to explain the statistical distribution and leads to severe information loss, the specific factors are introduced for a minimum information loss.

Formula (16) is used to calculate the variance of the specific factors:

$\begin{array}{cc}{\sigma }_i^2=1-\sum _{j=1}^3{L}_{\mathrm{ij}}^2;& \left(16\right)\end{array}$

where σ_i is the standard deviation of the specific factor of the i-h model parameter; and L_ij is the load factor of the j-th principle component. And the results are shown in Table 5.

TABLE 5
Variance of specific factors of corresponding model parameter
Original Variance of
variable specific factors
d        0.0155
vmax     0.1244
nsmax    0.0052
α1       0.0550
α2       0.0143
α3       0.0872
βn       0.0760
a0       0.0382
a1       0.0883
b0       0.1144
b1       0.0050
b2       0.0353

4) Statistical Characterization of Model Parameters:

According to the factor analysis theory, the common factors and the specific factors are used to predict each corresponding model parameter, and the following formula is satisfied:

$\begin{array}{cc}{X}_i={\mu }_i+Q_i\left(\sum _{j=1}^3{L}_{\mathrm{ij}}{F}_j+{\varepsilon }_i\right);& \left(17\right)\end{array}$

where X_i is a parameter of the model I_ss; μ_i and Q_i refer to the mean value and the standard deviation of the actually extracted model parameter X_i; L_ij is the load factor of the j_th principle components of the model parameter X_i; ε_i is the specific factor of the model parameter X_i, and obeys a normal distribution with zero mean. The common factors are independent of each other, with a zero mean and a variance of 1.

The mean value μ_i and standard deviation σ_i of model parameters in Table 1, the factor loading matrix L_ij in Table 4, the variance e, of each model parameter in Table 5, and the random numbers from the standard normal distribution N(0, 1) are substituted into Formula (17), thereby obtaining statistical characteristics for characterizing the model parameters.

5) Quasi-Physical Large-Signal Model:

The statistical distribution characteristics of each model parameter in 4) are substituted into a conventional large-signal model called Quasi-physical Zone Division model (Reported in Z. Wen, Y. Xu, Y. Chen, H. Tao, C. Ren, H. Lu, Z. Wang, W. Zheng, B. Zhang, T. Chen, T. Gao and R. Xu, “A Quasi-Physical Compact Large-Signal Model for AlGaN/GaN HEMTs,” IEEE Transactions on Microwave Theory and Techniques, vol. 65, no. 12, pp. 5113-5122, December 2017.) to obtain a complete quasi-physical statistical model for a device. The nonlinear harmonic balance method is used to solve the quasi-physical statistical model, thereby obtaining the large-signal output characteristics of the device.

In the embodiment of the disclosure, the output characteristic of the device includes DC characteristic and RF output characteristic. Referring to FIG. 2, the DC characteristic is determined by the drain-source current I_ds at one or two gate-source voltage V_gs and different drain-source V_gs, and the transconductance g, at different gate-source voltage V_gs and at a constant drain-source voltage V_ds. The RF output characteristic is determined by output power (Pout), gain (Gain), and power-added efficiency (PAE) at different input power when the device has constant input impedance and output impedance, and is operated at a specific frequency and in fixed bias point. Referring to FIG. 4, the dotted line represents the results simulated by the model, and the solid line represents the results plotted with measured data.

It will be obvious to those skilled in the art that changes and modifications may be made, and therefore, the aim in the appended claims is to cover all such changes and modifications.

Claims

1. A method, comprising: 1) selecting multiple batches of microwave gallium nitride high-electron-mobility transistors (GaN HEMTs) intended to build a statistical model: measuring static DC-IV characteristics of each of the microwave GaN HEMTs at room temperature, thereby acquiring drain-source currents Ids at different drain-source voltages Vds and different gate-source voltages Vgs, where the gate-source voltages Vgs range from a pinch-off voltage thereof to 0 V, and the drain-source voltages Vds range from 0 V to a maximum usable drain voltage of each microwave GaN HEMT, which is equal to 50% of a breakdown voltage thereof;2) building a microwave GaN HEMT quasi-physical large-signal model satisfying the following formulas:

2. The method of claim 1, wherein in 3.2), calculating the eigenvectors λi comprises solving the equation |R−λEk|=0, where i=1, 2, 3, . . . , k; and E is a k-th order identity matrix;