JP2002280571A - GaN TYPE HEMT SIMULATOR - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a conventional equivalent circuit model is incapable of clearing a difference between an intrinsic transconductance of a GaN type HEMT measured in a DC and that measured by RE and a relation with physical factors causing the difference and hence it is impossible to effectively execute simulation applied to the analysis of element characteristics and the optimization of a device structure. SOLUTION: A simulator incorporates a GaN type HEMT equipment circuit model comprising a parallel circuit of a first capacitance Cdr and second resistance Rdr is provided at a drain node and a parallel circuit of a second capacitance Csr and fourth resistance Rsr is provided at a source node in an equivalent circuit model of a compound semiconductor FET.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a GaN-based HEMT.
And a high-frequency simulation device incorporating the equivalent circuit model.

[0002]

2. Description of the Related Art A semiconductor device using GaN, which is a semiconductor having a wide band gap, can operate at a high frequency equal to or higher than that of a semiconductor device using GaAs, and can perform an operation requiring high breakdown voltage characteristics. Therefore, it has attracted attention as a semiconductor material for high-frequency power devices having a high power density.

Among field effect transistors using GaN-based materials, HEMTs (High Electron Mobility Transistors) in which an electron supply layer is made of AlGaN are:
There is an advantage that the two-dimensional electron concentration can be increased as compared with a GaAs HEMT, and therefore, it is extremely promising as a high-frequency power transistor.

[0004] When the device structure is optimized according to the use of the HEMT using the above-mentioned GaN-based material, or when integrated to form an MMIC (Micro-wave Monolithic Integrated).
In the case of a circuit, it is effective to design using a simulation, but for that purpose, an equivalent circuit model that can accurately reproduce the characteristics of a HEMT using a GaN-based material is required.

However, an HEM using a GaN-based material
T is different from the conventional field effect transistor using a compound semiconductor such as GaAs, and the intrinsic transconductance measured by DC is significantly different from the intrinsic transconductance measured by RF measurement. Therefore, the equivalent circuit model of the conventional GaAs field effect transistor is used as it is. However, there is a problem that the characteristics of the HEMT using the GaN-based material cannot be accurately reproduced in the simulation.

Regarding the problem of reproducibility, an equivalent circuit model for RF measurement is described in “2000 IEEE MTT-S Digest, WE2B-5, June
11-16, 2000 ", this model measures S-parameters under approximately 100 voltage conditions,
It is necessary to extract the FET parameters, calculate the difference from the value obtained by the DC measurement, and perform the simulation by incorporating the calculation result. Therefore, this model requires a great deal of time and effort to perform parameter extraction.

Furthermore, this model does not clarify the difference between the intrinsic transconductance measured by DC measurement and the intrinsic transconductance measured by RF measurement, and the relationship between physical factors that cause the difference. And it is very difficult to apply to optimization of device structure.

[0008]

As described above, in the conventional equivalent circuit model, the HEMT using a GaN-based material
The difference between the intrinsic transconductance measured by the C measurement and the intrinsic transconductance measured by the RF measurement and the relationship with the physical element that causes the difference cannot be clarified, and there is a problem that the simulation cannot be executed efficiently.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and there is provided a high-frequency circuit simulation apparatus incorporating a GaN-based HEMT equivalent circuit model capable of accurately and easily reproducing both DC characteristics and RF characteristics. The purpose is to provide.

[0010]

According to the present invention, there is provided a drain node corresponding to a drain electrode of a GaN-based HEMT, a source node corresponding to a source electrode of the GaN-based HEMT, GaN-based HE
A gate node corresponding to the gate electrode of the MT;
a first current source corresponding to a drain current of the aN HEMT, a first inductance and a first capacitance connected in series between the drain node and the first current source;
And a first resistor, a second resistor connected in parallel with the first capacitor, a second inductance connected in series between the source node and the first current source, 2
And a third resistor connected in parallel with the second capacitor, a third inductor connected to the gate node, and a series connection including a fifth resistor. A second current source corresponding to the gate-drain current of the GaN-based HEMT connected between the series connection of the third inductance and the fifth resistor and the drain end of the first current source And a third capacitor connected in parallel to the second current source, a third inductance, and a series connection of a fifth resistor and a source connected to the first current source. A third current source corresponding to a gate-source current of the GaN-based HEMT; a series connection including a fourth capacitor and a sixth resistor connected in parallel to the third current source; Fifth connected in parallel with one current source
And a series connection including a sixth capacitor and a seventh resistor connected in parallel to the first current source.
Provided is a simulation device incorporating an equivalent circuit model of a system HEMT.

In the simulation apparatus having this configuration, D
Both the C characteristic and the RF characteristic can be accurately and easily reproduced.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a general GaN-based HEMT has a sectional structure as shown in FIG. That is, a substrate 1 made of sapphire or SiC is provided.
An undoped GaN electron storage layer 2 is formed thereon as a buffer layer, and an undoped AlGaN spacer layer 3 having a thickness of several nm and an n-type Al
The GaN electron supply layer 4 has a thickness of several tens of nm, and the undoped AlGaN cap layer 5 has a thickness of several nm.

The gate electrode 6 is formed on the AlGaN cap layer 5 to obtain a high Schottky barrier, and the source electrode 7 and the drain electrode 8 are removed from the AlGaN cap layer 5 to obtain an ohmic contact with low contact resistance. It is formed on the n-type AlGaN electron supply layer 4 thus formed.

In order to examine an equivalent circuit model from the element structure of the GaN-based HEMT having such a configuration, the gate electrode 6
A plurality of evaluation samples having a gate width of 200 μm having different distances between the gate electrode 6 and the source electrode 7 and different distances between the gate electrode 6 and the drain electrode 8 were prepared.
A current was passed under the three conditions of only the drain electrode 8, the gate electrode 6 to the source electrode 7, and only the gate electrode 6 to the drain electrode 8, and the resistance value for each electrode interval was calculated from the measurement result of the gate current by DC measurement.

FIG. 3 shows a straight line obtained by plotting the calculated resistance value with a solid square mark and obtaining a parameter value by the least square method assuming that the resistance value is a linear expression with the electrode interval as a variable. . Looking at the resistance depending on the electrode spacing from FIG. 3, it is 2.1 Ω / μm.
This resistance was in good agreement with the resistance calculated from the sheet resistance of the wafer used for the evaluation sample, 420 Ω / □.
The resistance value that does not depend on the electrode interval is 21Ω.

Further, the distance between the electrodes is 2.1 μm and 1.6 μm.
The S-parameters of the sample were measured, and the values of the source resistance obtained at 5 GHz were plotted with hollow square marks in FIG.
It was about half of the resistance value calculated from the measurement. 3 to D
It has been found that the parasitic resistance on the source side obtained by the C measurement largely contributes to the impedance independent of the electrode interval.

From these results, the present inventor has found that GaN
In the system HEMT, the equivalent circuit model shown in FIG. 1 was created by considering that the contact portion of the ohmic electrode with respect to the two-dimensional electron layer includes a capacitance. (Embodiment) FIG. 1 shows an equivalent circuit model of a GaN-based HEMT according to the present invention. In FIG. 1, first, each parameter is considered in a path from the drain electrode 8 to the source electrode. A parallel connection circuit of a capacitance Cdr for an RF current and a resistance Rdr for a DC current is connected to the drain electrode 8 via an inductance Ld.

A drain current Id is connected as a current source from a connection point between the capacitance Cdr and the resistor Rdr via a drain-side distributed resistor Rdd. The source-side resistor Rsd is connected between a parallel connection circuit of the capacitance Csr for the RF current and the resistor Rsr for the DC current on the source electrode 7 side, and the drain current Id.

Further, a source electrode 7 side inductance Ls is connected from the source electrode 7 to a connection point between the capacitance Csr and the resistor Rsr. Note that, at both ends of the current source indicating the drain current Id, the capacitance Cds of the transistor intrinsic portion between the source and the drain, and the DC with the GaN electron storage layer 2
A series circuit of the cut capacitance Crf and the RF output resistor Rcf is connected in parallel.

Next, each parameter viewed from the gate electrode 6 will be described. The gate electrode 6 has a gate inductance L
g and the resistor Rg are connected in series. From the resistance Rg,
A gate-drain current Igd is connected as a current source between the drain side of the current source indicating the drain current Id,
The gate-source current Igs is connected as a current source to a source side of the current source indicating the drain current Id.

The gate-drain current Igd is connected in parallel with a gate-drain capacitance Cgd, and the gate-source current Igs is a series circuit of a gate-source capacitance Cgs and a gate current resistance Ri. Connected in parallel.

When the transconductance of the GaN-based HEMT was calculated by a simulation device incorporating the above-described equivalent circuit model, it was in good agreement with the value obtained by the S-parameter measurement as shown by the broken curve in FIG.
Also, a simulation with an error of 5% or less can be realized for the S parameter value and the output characteristic at 1.9 GHz.
It was confirmed that the measured value of the GaN-based HEMT could be reproduced well.

FIG. 1 shows an example in which an inductor, a parallel circuit of a capacitor and a resistor, and a resistor are connected in order from the drain node to the current source Id corresponding to the drain current. The same effect can be exhibited even if it is switched. Similarly, a diagram in which a resistor, a parallel circuit of a resistor and a capacitor, and an inductor are connected in order from the current source Id to the source node is shown. However, the same effect can be obtained by changing the order of these three elements.

Although a parallel circuit of a capacitor and a resistor is introduced between the drain node and the current source Id in FIG. 1, a circuit in which this is connected in series may be used. If connected in series, connect a resistor in parallel with this circuit,
Further, a circuit in which an inductor is connected in series to this parallel circuit can be used. Similarly, between the source node and the current source Id, a circuit in which a capacitor and a resistor are connected in series, a resistor is connected in parallel with this circuit, and an inductor is connected in series with this parallel circuit can be used.

[0025]

As described above in detail, according to the present invention, there is provided a high-frequency circuit simulation apparatus incorporating a GaN-based HEMT equivalent circuit model capable of accurately and easily reproducing both DC characteristics and RF characteristics. Obtainable. Further, since each circuit element of the GaN-based HEMT equivalent circuit model is associated with a structural physical element of the GaN-based HEMT, it is easy to optimize the device structure and design the MMIC according to the application. A high-frequency circuit simulation device can be obtained.

[Brief description of the drawings]

FIG. 1 shows a GaN-based HEMT according to an embodiment of the present invention.
FIG.

FIG. 2 is a structural sectional view of a GaN-based HEMT.

FIG. 3 is a diagram showing a change in resistance value with respect to an electrode interval.

FIG. 4 is a diagram showing the reproducibility of a simulation according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... GaN electron storage layer 3 ... AlGaN spacer layer 4 ... n-type AlGaN electron supply layer 5 ... AlGaN cap layer 6 ... Gate electrode 7 ... Source electrode 8 ... Drain electrode Ld, Ls, Lg ... Inductance Cdr, Csr, Cds: Capacitance Rdr, Rsr, Rg, Ri: Resistance Rdd, Rsd: Resistance Id: Drain current Crf: DC cut capacitance Rcf: RF output resistance Igd: Gate-drain current Igs: Gate-source current Cgd: Gate-drain Capacitance Cgs: Capacitance between gate and source

Claims (3)

[Claims] A drain node corresponding to a drain electrode of the GaN-based HEMT; and a source node corresponding to a source electrode of the GaN-based HEMT.
A node and a gate corresponding to the gate electrode of the GaN-based HEMT.
A first current source corresponding to a drain current of the GaN-based HEMT; a first inductance and a first capacitance connected in series between the drain node and the first current source; And a first resistor; a second resistor connected in parallel with the first capacitor; a second inductance connected in series between the source node and the first current source; And a third resistor connected in parallel with the second capacitor, a third inductor connected to the gate node, and a fifth resistor connected in series. And a second current corresponding to a gate-drain current of the GaN-based HEMT connected between a series connection of the third inductance and the fifth resistor and a drain end of the first current source. A second current source; A third capacitor connected to the GaN-based HEMT connected between a series connection of the third inductance and the fifth resistor and a source terminal of the first current source. A third current source corresponding to a current, a series connection including a fourth capacitor and a sixth resistor connected in parallel to the third current source, and a parallel connection to the first current source The GaN-based HEMT having a fifth capacitor and a series connection including a sixth capacitor and a seventh resistor connected in parallel to the first current source
Simulation device incorporating the equivalent circuit model of 2. A GaN-based HEM in which the second resistor is connected in parallel to a series connection of the first capacitor and the first resistor.
2. The simulation device according to claim 1, wherein an equivalent circuit model of T is incorporated. 3. A GaN-based HEM wherein the fourth resistor is connected in parallel to a series connection of the second capacitor and the third resistor.
2. The simulation device according to claim 1, wherein an equivalent circuit model of T is incorporated.