CN102565650B - Measurement system and method for transconductance frequency dispersion characteristic of GaN HEMT device - Google Patents

Abstract

The invention relates to a system and a method for measuring transconductance frequency dispersion characteristics of a GaNHEMT device, and belongs to the technical field of integrated circuits. The measuring system comprises a first direct current power supply, a second direct current power supply, an alternating current signal providing device, a capacitor, an inductor, a resistor, a first voltmeter and a second voltmeter; the drain electrode is connected with the resistor, the resistor is connected with the first direct current power supply, and the first voltage meter and the resistor are connected in parallel; the grid is connected with the second voltmeter in parallel, the capacitor is connected between the grid and the alternating current signal supply device, and the inductor is connected between the grid and the second direct current power supply. The frequency dispersion characteristic measured by the measuring system can infer the surface state of the device and the number of traps, and further judge the quality of materials and devices; meanwhile, a transconductance curve containing the frequency dispersion characteristic can accurately represent the direct current characteristic of the device, is related to the extraction of frequency dispersion parameters in the model, and is significant for establishing the device model.

Description

A measurement system and method for transconductance dispersion characteristics of GaN HEMT devices

technical field

The invention relates to a measurement system and method for the transconductance dispersion characteristic of a GaN HEMT device, in particular to a measurement system and method for the transconductance low-frequency scattering characteristic of a GaN HEMT device, and belongs to the technical field of integrated circuits.

Background technique

Since the GaN material is a new material, the material is still in the development and research stage, and its epitaxial growth is also in the immature stage, so dislocations or faults will be introduced during the growth process, which will introduce impurities or defects into the material itself. , At the same time, interface states will be introduced at the interface of different materials of the device, and there are defects such as traps inside the material, so that deep trap levels will be generated in the energy band, and they will generate carriers in the device channel The process of capture and release will affect the change of the source-drain current, which will also affect the power characteristics of the device, and have a great impact on the electrical characteristics of the entire device.

The trap effect will bring many adverse effects, which will lead to a great reduction in the current and power of the device. Since the time factor of the energy level corresponding to the trap is mostly between microseconds and milliseconds, that is to say, most of these traps can only respond to AC signals below 1MHz, and will not change with higher frequency signals. Because the trap's charging and discharging process cannot keep up with the rate of change of the higher frequency signal, the trap exhibits essentially no state change at very high frequencies. Therefore, the number of traps in the device can be judged by measuring the low-frequency response of the transconductance of the GaN HEMT device, and then the quality of the material and the reliability and stability of the device process can be judged, so it can characterize the quality of the material and the device from a macro perspective. At the same time, because the trap effect needs to be considered in the process of establishing the large signal model, some parameters related to the trap effect can be extracted through the measurement of the low-frequency scattering characteristics of the transconductance, which is also very useful for the establishment of the large signal model of GaN HEMT devices. significance. To sum up, it is very important to accurately measure the frequency scattering characteristics of GaN HEMT devices.

Contents of the invention

The purpose of the present invention is based on the dispersion characteristics can be used for the evaluation of the device material quality and device performance, while the low frequency (below 1MHz) scattering characteristics of the transconductance also provides important data for the establishment of the device model, and because the device surface and The trap effect in the material mainly responds to signals within 1MHz. Therefore, in order to study the influence of low-frequency signals on the transconductance characteristics of GaN HEMT devices, a measurement system and method for the transconductance dispersion characteristics of GaN HEMT devices are provided. 

The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a measurement system of GaN HEMT device transconductance dispersion characteristic comprises a first DC power supply, a second DC power supply, an AC signal providing device, a capacitor, an inductance, a resistance, a first voltage table and a second voltmeter, the GaN HEMT device includes a gate, a drain and a source; the source of the GaN HEMT device is grounded, the drain of the GaN HEMT device is connected to a resistor, and the resistor is connected to the first connected to a DC power supply, the first DC power supply is used to provide a forward bias voltage for the drain of the GaN HEMT device, the first voltmeter is connected in parallel with the resistor, and the first voltmeter is used to measure the two resistors terminal voltage; the gate of the GaN HEMT device is connected in parallel with a second voltmeter, and the second voltmeter is used to monitor the gate-source voltage of the GaN HEMT device, and the capacitor is connected between the gate of the GaN HEMT device and Between the AC signal providing device, the AC signal providing device is used to provide an AC signal for the grid of the GaN HEMT device, and the inductance is connected between the grid of the GaN HEMT device and the second DC power supply, and the second DC The power supply is used to negatively bias the gate of the GaN HEMT device.

On the basis of the above technical solutions, the present invention can also be improved as follows.

Further, the amplitude of the AC signal provided by the AC signal providing device is less than 250mV, and the frequency of the AC signal is between 10 Hz and 1 MHz.

The present invention also provides a technical solution for solving the above-mentioned technical problems as follows: a method for measuring the transconductance dispersion characteristics of a GaN HEMT device comprises the following steps:

1) Adjust the AC signal supply device to provide AC signals of different frequencies, and monitor the first voltmeter connected in parallel with the resistor R and the second voltmeter connected in parallel with the gate of the GaN HEMT device, and record the AC signals of different frequencies The reading V _R of the first voltmeter and the reading V _gs of the second voltmeter under the signal;

2) Use the formula I _R = V _R /R to calculate the current I _R flowing through the resistor under AC signals of different frequencies. This current I _R is equal to the drain-source current I _ds of the GaN HEMT device, thereby obtaining the drain-source of the GaN HEMT device The relationship between current and AC signal frequency;

3) Calculate the transconductance of the GaN HEMT device corresponding to the drain-source current I _ds of different GaN HEMT devices by the formula gm=I _ds /V _gs , so as to obtain the relationship between the transconductance of the GaN HEMT device and the AC signal frequency.

The beneficial effects of the present invention are: the measurement data of the GaN HEMT device transconductance characteristic obtained by the measurement system of the GaN HEMT device transconductance dispersion characteristic of the present invention, because the dispersion characteristic of the GaN HEMT device transconductance is related to the trap effect of the device, The number of surface states and traps of GaN devices can be qualitatively inferred from the severity of dispersion characteristics, and then the quality of materials and devices can be judged; the measurement data can evaluate the quality of epitaxial material growth, and monitor the degree of process consistency and stability , which qualitatively reflects the performance of materials and devices from a macroscopic perspective; at the same time, the dispersion characteristics reflect the delay characteristics of an output signal relative to the input signal, and the transconductance curve including the dispersion characteristics can accurately characterize the DC characteristics of the device, and can be extracted Some parameters related to the trap in the large signal model also provide the necessary data for the establishment of the device model, and the model including the frequency scattering parameters can more accurately reflect the actual characteristics of the device.

Description of drawings

Fig. 1 is the structural representation of the measurement system of GaN HEMT device transconductance dispersion characteristic of the embodiment of the present invention;

FIG. 2 is a graph showing the variation of transconductance and AC signal frequency of a GaN HEMT device according to an embodiment of the present invention.

Detailed ways

The principles and features of the present invention are described below in conjunction with the accompanying drawings, and the examples given are only used to explain the present invention, and are not intended to limit the scope of the present invention.

FIG. 1 is a schematic structural diagram of a measurement system for transconductance dispersion characteristics of a GaN HEMT device according to an embodiment of the present invention. As shown in Figure 1, the measurement system of the GaN HEMT device transconductance dispersion characteristic comprises a first DC power supply 103, a second DC power supply 108, an AC signal providing device 106, a capacitor 105, an inductance 107, a resistor 101, a first A voltmeter 102 and a second voltmeter 104, the GaN HEMT device 100 includes a gate, a drain and a source; the source of the GaN HEMT device 100 is grounded, and the drain of the GaN HEMT device 100 is connected to a resistor 101 , the resistor 101 is connected to a first DC power supply 103, the first DC power supply 103 is used to provide a forward bias voltage for the drain of the GaN HEMT device 100, and the first voltmeter 102 is connected to the resistor 101 In parallel, the first voltmeter 102 is used to measure the voltage across the resistor 101; the gate of the GaN HEMT device 100 is connected in parallel with a second voltmeter 104, and the second voltmeter 104 is used to measure the GaN HEMT device 100 The gate-source voltage of the GaN HEMT device 100 is monitored, and the capacitor 105 is connected between the gate of the GaN HEMT device 100 and the AC signal providing device 106, and the AC signal providing device 106 is used to provide an AC signal for the gate of the GaN HEMT device 100, The inductor 107 is connected between the gate of the GaN HEMT device 100 and the second DC power supply 108, and the second DC power supply 108 is used to provide a negative bias voltage for the gate of the GaN HEMT device 100. Since it is necessary to add DC and AC signal excitation to the gate at the same time, it is necessary to use a capacitor to couple the AC signal in and prevent the interference of the DC power supply. The DC power supply also needs to use an inductor to isolate the AC signal. The external resistance connected to the drain can play a role in stabilizing the GaN HEMT device. In this embodiment, the resistance is selected to be equivalent to the output resistance Rds of the drain, which is generally greater than 50 ohms, so 100 ohms or 200 ohms are selected. , but the Rds of different devices is slightly different, so it needs to be selected according to the actual situation. The larger the inductance and capacitance, the better, so the better the isolation effect, that is, choose the largest inductance and capacitance that can be found. In this embodiment, the capacitance is several hundred uF, and the inductance is a self-made inductance coil.

In this embodiment, the GaN HEMT device is placed on a Cascade summit 9000 probe station during measurement, and two signals in the HP6624A power supply are used to provide bias voltages to the gate and drain of the GaN HEMT device, wherein , the gate provides a negative bias voltage, and the drain provides a forward bias voltage. The AC signal supply device is an Agilent 33220A function generator, which provides an AC signal for the grid, with an amplitude of 250mV, and manually adjusts the frequency change, and adopts capacitive coupling to enter the grid to prevent the DC signal from interfering with it. The DC bias is connected to the grid in series with the inductor to prevent the AC signal from interfering with the DC source. Use the second voltmeter to monitor the gate-source voltage V _gs , connect a resistor in series to the drain, and connect the first voltmeter in parallel at both ends, so that the current can be monitored by I _R =V _R /R, and then by calculating gm =I _ds /V _gs =I _R /V _gs , the frequency of each AC signal corresponds to different V _gs and I _R , so different gm values are obtained, so that the corresponding relationship between transconductance and frequency can be obtained, and also It is the frequency scattering characteristic of the transconductance. The grid voltage can also be changed, so that the corresponding dispersion characteristics under different grid voltages can be obtained.

FIG. 2 is a graph showing the variation of transconductance and AC signal frequency of a GaN HEMT device according to an embodiment of the present invention. As shown in Figure 2, it can be seen that the transconductance value is slightly larger at low frequencies close to the DC state. As the frequency increases, the transconductance gradually decreases, and it reaches the minimum near 1MHz. If the frequency increases further, the transconductance The transconductance will basically not change, because the trap at this time can no longer keep up with the change rate of the high-frequency signal, and the transconductance will not continue to decrease as the frequency continues to increase.

The high-purity growth conditions of compound semiconductor materials such as GaN materials are still in the process of continuous development, so their interface characteristics are more complex than those of traditional semiconductors, and due to the unique physical properties of GaN materials, there will be or doping at the interface or inside the material Other unnecessary defects, so there will be surface states on the surface of the device, and defects will be introduced inside, which will lead to the existence of many traps in GaN HEMT devices. These traps will cause many bad effects, including gate delay, drain delay, and current collapse. , frequency scattering and other effects. The transconductance frequency scattering effect here can be used to evaluate the growth quality of the material, monitor the purity and accuracy of the process, and analyze the physical characteristic parameters of the device.

The measurement system of the GaN HEMT device transconductance dispersion characteristic of the present invention measures the variation relationship of the device transconductance with the frequency, and can analyze and compare the devices according to the severity of the transconductance variation with the frequency, and the variation of the transconductance of the device with the frequency. The growth of the material, the influence of different process flows on the device characteristics, and the required parameter extraction data are provided for the GaN HEMT device model. The introduction of the dispersion parameter enables the device model to better simulate nonlinear characteristics. Practice has proved that the measurement of transconductance dispersion characteristics of GaN HEMT devices provides a great guiding role for the research on related work of HEMT devices. This measurement method is also applicable to the measurement of transconductance dispersion characteristics of GaAs HEMT and other HEMT devices affected by the trap effect.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (3)

1. A measurement system of GaN HEMT device transconductance dispersion characteristic, it is characterized in that, described measurement system comprises a first DC power supply, a second DC power supply, an AC signal providing device, a capacitor, an inductance, a resistance, a first voltage table and a second voltmeter, the GaN HEMT device includes a gate, a drain and a source; the source of the GaN HEMT device is grounded, the drain of the GaN HEMT device is connected to a resistor, and the resistor is connected to the first connected to a DC power supply, the first DC power supply is used to provide a forward bias voltage for the drain of the GaN HEMT device, the first voltmeter is connected in parallel with the resistor, and the first voltmeter is used to measure the two resistors terminal voltage; the gate of the GaN HEMT device is connected in parallel with a second voltmeter, and the second voltmeter is used to monitor the gate-source voltage of the GaN HEMT device, and the capacitor is connected between the gate of the GaN HEMT device and Between the AC signal providing device, the AC signal providing device is used to provide an AC signal for the grid of the GaN HEMT device, and the inductance is connected between the grid of the GaN HEMT device and the second DC power supply, and the second DC The power supply is used to negatively bias the gate of the GaN HEMT device. 2. The measurement system of the GaN HEMT device transconductance dispersion characteristic according to claim 1, wherein the amplitude of the AC signal provided by the AC signal providing device is less than 250mV, and the frequency of the AC signal is between 10Hz～1MHz . 3. a method for measuring the GaN HEMT device transconductance dispersion characteristic based on the measurement system of the GaN HEMT device transconductance dispersion characteristic according to claim 1, it is characterized in that, the measurement method comprises the following steps: 1) Adjust the AC signal supply device to provide AC signals of different frequencies, and monitor the first voltmeter connected in parallel with the resistor, and the second voltmeter connected in parallel with the gate of the GaN HEMT device, and record the AC signals of different frequencies respectively Under the reading _VR of the first voltmeter and the reading V _gs of the second voltmeter; 2) Use the formula I _R = V _R /R to calculate the current I _R flowing through the resistor under AC signals of different frequencies. This current I _R is equal to the drain-source current I _ds of the GaN HEMT device, thereby obtaining the drain-source of the GaN HEMT device The relationship between current and AC signal frequency; 3) Calculate the transconductance of the GaN HEMT device corresponding to the drain-source current I _ds of different GaN HEMT devices by the formula gm=I _ds /V _gs , so as to obtain the relationship between the transconductance of the GaN HEMT device and the AC signal frequency.

Images