A method for testing transfer characteristic curves of silicon carbide MOSFETs under bipolar switching stress

Abstract

The present invention discloses a method for testing the transfer characteristic curve of a silicon carbide MOSFET under bipolar switch stress, the method being as follows: S1: setting switch stress parameters: switching frequency f, duty cycle d, positive bias voltage V CC , negative bias voltage V EE and gate resistance R; S2: Based on OTF technology, the transfer characteristic curve is extracted using a silicon carbide MOSFET transfer characteristic curve extraction circuit. The transfer characteristic curves during the transition from positive voltage to negative voltage and the transfer characteristic curve during the transition from negative voltage to positive voltage are extracted; S3: The two extracted transfer characteristic curves are plotted on the same coordinate axis, and the closed graph formed by the two is used to characterize and accurately measure the hysteresis characteristics of the transfer characteristic curves. This method effectively solves the problems of traditional extraction techniques, such as the complex preprocessing required before extracting the transfer characteristic curve and the measurement delay during the extraction process, significantly improving measurement accuracy.

Description

Technical Field

[0001] The present invention belongs to the field of reliability assessment and relates to a method for testing a transfer characteristic curve of a silicon carbide MOSFET, and in particular to a method for testing a transfer characteristic curve of a silicon carbide MOSFET under bipolar switch stress. Background Art

[0002] Silicon carbide (SiC) MOSFETs have been widely used to replace silicon (Si) MOSFETs in high-temperature, high-power electronic applications due to their excellent performance. However, due to the higher interface defect density in the gate oxide of SiC MOSFETs, their stability and reliability are more prominent. When subjected to a positive voltage, interface defects can lead to electron capture, thereby reducing the electric field in the channel; when subjected to a negative voltage, these defects can release electrons, resulting in an increase in the channel electric field. Therefore, compared with the transfer characteristic curve obtained during the transition from positive voltage to negative voltage, the transfer characteristic curve obtained during the transition from negative voltage to positive voltage exhibits a leftward shift. This unique phenomenon is often referred to as the transfer characteristic curve hysteresis.

[0003] The hysteresis of the transfer characteristic curve reflects the level of interface defect density and can serve as an important indicator for evaluating device health. It also significantly affects its speed, oscillation, and other characteristics during high-speed switching, making it a key parameter in silicon carbide MOSFET applications. Therefore, accurate extraction of the transfer characteristic curve is of great significance. Summary of the Invention

[0004] The present invention provides a method for testing the transfer characteristic curve of a silicon carbide MOSFET under bipolar switch stress. This method can effectively solve the problems of traditional extraction technology, such as the need for complex preprocessing before extracting the transfer characteristic curve and the measurement delay during the extraction process, and significantly improve measurement accuracy.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A circuit for testing transfer characteristic curves of a silicon carbide MOSFET under bipolar switching stress includes a gate driver IC, a microcontroller, a DC-DC power supply module, an adjustable variable resistor, and a non-inductive resistor, wherein:

[0007] The gate driver IC is used to provide a driving signal for the device under test;

[0008] The microcontroller is used to generate a PWM signal with adjustable switching frequency and duty cycle, and the PWM signal is input to the non-inverting input terminal of the gate drive IC through the PCB wire;

[0009] The DC-DC power supply module is used to apply positive bias voltage and negative bias voltage to the device under test. The positive bias voltage is connected to the V CC The negative bias voltage is connected to the gate driver IC's V EE Department;

[0010] The adjustable resistor is connected to OUT+ and OUT- of the gate driver IC as a gate drive resistor, and is used to adjust the gate drive resistance;

[0011] The non-inductive resistor is used for the load, and a DC-DC power supply module is used to provide a bus voltage to the load end.

[0012] A method for testing a transfer characteristic curve of a silicon carbide MOSFET under bipolar switching stress comprises the following steps:

[0013] Step S1: Set the switch stress parameters, which include the switching frequency f (Hz), duty cycle d (%), positive bias voltage V CC (V), negative bias voltage V EE (V) and gate resistance R (Ω);

[0014] Step S2: Based on the on-the-fly (OTF) technology, the transfer characteristic curve extraction circuit of the silicon carbide MOSFET is used to extract the transfer characteristic curve during the transition from positive voltage to negative voltage (Down) and the transfer characteristic curve during the transition from negative voltage to positive voltage (Up);

[0015] Step S3: Plotting the two transfer characteristic curves extracted in step S2 on the same coordinate axis, and using the closed graph formed by the two to represent and accurately measure the hysteresis characteristics of the transfer characteristic curves.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The transfer characteristic curve of silicon carbide MOSFET is intrinsically linked to its practical application. However, complex preprocessing operations and measurement delays make accurate extraction of the transfer characteristic curve difficult. The present invention uses an OTF technique to extract the transfer characteristic curve of silicon carbide MOSFET. Under continuous bipolar switching stress, the transfer characteristic curve can be extracted with zero measurement delay based on synchronous sampling technology. This ensures that the charge in interface defects can be released in time during the switching cycle, thereby improving test accuracy. In addition, the transfer characteristic curve can be directly extracted without any preprocessing operations, simplifying the control and extraction process.

[0018] 2. The present invention can plot the transfer characteristic curve (Down) during the transition from positive voltage to negative voltage and the transfer characteristic curve (Up) during the transition from negative voltage to positive voltage on the same coordinate axis. The closed figure enclosed by the two can significantly observe the change in the hysteresis characteristics of the transfer characteristic curve.

[0019] 3. The present invention proposes a transfer characteristic curve test circuit for silicon carbide MOSFET under bipolar switching stress. During the test process, an oscilloscope is used to synchronously sample the gate-source voltage of the device under test and the current flowing through the load resistor to achieve accurate transfer characteristic curve extraction and analysis.

[0020] 4. Compared with the traditional method, the present invention does not require pre-processing operations and eliminates measurement delays, thereby improving the stability of the gate oxide layer charging state, thereby significantly improving the accuracy of transfer characteristic curve extraction.

[0021] 5. The present invention can significantly improve the accuracy of transfer characteristic curve extraction and lay the foundation for online monitoring and health management. It can provide strong support for the extraction and online monitoring of silicon carbide MOSFET transfer characteristic curves, and help in the selection and application of silicon carbide MOSFET devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram comparing OTF technology and traditional technology;

[0023] Figure 2 This is the schematic diagram of the measurement circuit principle;

[0024] Figure 3 is the transfer characteristic curve under different switching frequencies and duty cycles;

[0025] Figure 4 is the transfer characteristic curve under different switching speeds;

[0026] Figure 5 is the transfer characteristic curve under different positive bias voltages;

[0027] Figure 6 Transfer characteristic curves under different negative bias voltages. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below with reference to the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0029] Traditional extraction methods require complex preprocessing and measurement delays, which makes it difficult to accurately extract the transfer characteristic curve under bipolar switching stress. To this end, the present invention provides a method for testing the transfer characteristic curve of silicon carbide MOSFET under bipolar switching stress, such as Figure 1 As shown in the figure, this method uses OTF technology to extract the transfer characteristic curve. This method can achieve zero measurement delay transfer characteristic curve extraction under continuous bipolar switching stress based on synchronous sampling technology. During the switching cycle, the charge in the interface defects can be released back to the channel in a timely manner, improving the accuracy of the test data. During the extraction process, an oscilloscope is used to synchronously sample the gate-source voltage of the device under test and the current flowing through the load resistor to achieve accurate data recording and analysis. The specific steps are as follows:

[0030] Step S1: Set the switch stress parameters, which include the switching frequency f (Hz), duty cycle d (%), positive bias voltage V CC (V), negative bias voltage V EE (V) and gate resistance R (Ω).

[0031] Step S2: Based on the on-the-fly (OTF) technology, the transfer characteristic curve is extracted using the silicon carbide MOSFET transfer characteristic curve extraction circuit to extract the transfer characteristic curve during the transition from positive voltage to negative voltage (Down) and the transfer characteristic curve during the transition from negative voltage to positive voltage (Up).

[0032] like Figure 2 As shown in FIG, the SiC MOSFET transfer characteristic curve extraction circuit includes a gate driver IC, a microcontroller, a DC-DC power supply module, an adjustable variable resistor, and a non-inductive resistor, where:

[0033] The gate driver IC is used to provide a driving signal for the device under test;

[0034] The microcontroller is used to generate a PWM signal with adjustable switching frequency and duty cycle, and the PWM signal is input to the non-inverting input terminal of the gate drive IC through the PCB wire;

[0035] The DC-DC power supply module is used to apply positive bias voltage and negative bias voltage to the device under test. The positive bias voltage is connected to the V CC The negative bias voltage is connected to the gate driver IC's V EE Department;

[0036] The adjustable resistor is connected to OUT+ and OUT- of the gate driver IC as a gate drive resistor, and is used to adjust the gate drive resistance;

[0037] The non-inductive resistor is used for the load, and a DC-DC power supply module is used to provide a bus voltage to the load end.

[0038] The specific extraction steps are as follows:

[0039] Step S21: using a gate driver IC to provide a drive signal to the device under test;

[0040] Step S22: Using a microcontroller to generate a PWM signal with adjustable switching frequency and duty cycle, the PWM signal is input to the non-inverting input terminal of the gate driver IC via a PCB conductor;

[0041] Step S23: Use a DC-DC power supply module to provide positive bias voltage and negative bias voltage, where the positive bias voltage can be adjusted from +5V to +20V, and the negative bias voltage can be adjusted from -5V to -10V. Connect the positive bias voltage to the V pin of the gate driver IC. CC The negative bias voltage is connected to the gate driver IC's V EE At this point, the circuit can flexibly adjust the gate-source voltage amplitude;

[0042] Step S24: Using a 0Ω-1kΩ adjustable resistor as a gate drive resistor and connecting it to OUT+ and OUT- of the gate drive IC respectively, so that the circuit can flexibly adjust the gate drive resistance;

[0043] Step S25: Select a 5Ω non-inductive resistor and a heat sink as the load resistor, and use a DC-DC power module to provide a 3.3V voltage to the bus;

[0044] Step S26: Place the device under test (heat-generating component) on the back of the circuit board and use copper cladding and windowing to increase heat dissipation. Minimize loop inductance during wiring to reduce parasitic parameters and prevent oscillation.

[0045] Step S27: The heating component operates under a continuous pulse width modulation (PWM) signal, and an oscilloscope is used to synchronously sample the gate-source voltage of the heating component and the current flowing through the load resistor, thereby obtaining a transfer characteristic curve (Down) during the transition from positive voltage to negative voltage and a transfer characteristic curve (Up) during the transition from negative voltage to positive voltage;

[0046] Step S3: Plotting the two transfer characteristic curves extracted in step S2 on the same coordinate axis, and using the closed graph formed by the two to represent and accurately measure the hysteresis characteristics of the transfer characteristic curves.

[0047] Example:

[0048] In order to ensure the reliability of the measurement results, this embodiment selects two representative silicon carbide MOSFETs as experimental test devices: one is a planar gate (DUT.P) and the other is a trench gate (DUT.T). Set the bipolar switch stress configuration: the switching frequency is 1kHz, the duty cycle is 50%, the positive bias voltage is +20V, the negative bias voltage is -10V, and the gate resistance is 200Ω. Modify the bipolar switch stress configuration by controlling the variables, extract the transfer characteristic curve (Down) during the transition from positive voltage to negative voltage and the transfer characteristic curve (Up) during the transition from negative voltage to positive voltage, draw the above two transfer characteristic curves on the same coordinate axis, and use the closed graph enclosed by the two to characterize the change in the hysteresis characteristics of the transfer characteristic curve. The specific steps are as follows:

[0049] Step S1: Measure at different switching frequencies (1kHz, 10kHz, 100kHz). Figure 3 As shown, the lower the frequency, the more obvious the hysteresis characteristic.

[0050] Step S2: Measure at different duty cycles (10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%). Figure 3 As shown in Figure 2, the higher the duty cycle, the more obvious the hysteresis characteristic.

[0051] Step S3: Measure under different gate resistances (10Ω, 50Ω, 100Ω, 150Ω, 250Ω, 300Ω, 350Ω). Figure 4 As shown, the higher the gate resistance, the more obvious the hysteresis characteristic.

[0052] Step S4: Measure at different positive bias voltages (+5V, +10V, +15V, +20V). Figure 5 As shown in Figure 2, the higher the positive bias voltage amplitude, the more obvious the hysteresis characteristic.

[0053] Step S5: Measure under different negative bias voltages (-5V, -8V, -10V). Figure 6 As shown in Figure 2, the higher the negative bias voltage amplitude, the more obvious the hysteresis characteristic.

[0054] In summary, the OTF technique effectively achieves zero-measurement-delay transfer curve extraction under continuous bipolar switching stress based on synchronous sampling, without the need for additional preprocessing. This significantly reduces undetected interface defects during extraction and reveals significant hysteresis. Significant hysteresis in the transfer curve can be observed by increasing the amplitude of the positive and negative bias voltages, reducing the switching frequency, and selecting a slightly larger gate resistor.

Claims

1. A method for testing the transfer characteristic curve of a silicon carbide MOSFET under bipolar switching stress, characterized in that The method comprises the following steps: Step S1: Setting the switch stress parameters, which include the switching frequency f, duty cycle d, and positive bias voltage V CC , negative bias voltage V EE and gate resistance R; Step S2: Based on the OTF technology, a transfer characteristic curve test circuit of a silicon carbide MOSFET is used to extract a transfer characteristic curve, and a transfer characteristic curve during a transition from a positive voltage to a negative voltage and a transfer characteristic curve during a transition from a negative voltage to a positive voltage are extracted; The test circuit includes a gate drive IC, a microcontroller, a DC-DC power supply module, an adjustable variable resistor and a non-inductive resistor, wherein: The gate driver IC is used to provide a driving signal for the device under test; The microcontroller is used to generate a PWM signal with adjustable switching frequency and duty cycle, and the PWM signal is input to the non-inverting input terminal of the gate drive IC through the PCB wire; The DC-DC power supply module is used to apply positive bias voltage and negative bias voltage to the device under test. The positive bias voltage is connected to the V CC The negative bias voltage is connected to the gate driver IC's V EE Department; The adjustable resistor is connected to OUT+ and OUT- of the gate driver IC as a gate drive resistor, and is used to adjust the gate drive resistance; The non-inductive resistor is used for the load, and a DC-DC power supply module is used to provide a bus voltage to the load end; The specific steps are as follows: Step S21: using a gate driver IC to provide a drive signal to the device under test; Step S22: Using a microcontroller to generate a PWM signal with adjustable switching frequency and duty cycle, the PWM signal is input to the non-inverting input terminal of the gate driver IC via a PCB conductor; Step S23: Use the DC-DC power supply module to provide positive bias voltage and negative bias voltage, and connect the positive bias voltage to the V CC The negative bias voltage is connected to the gate driver IC's V EE At this point, the circuit can flexibly adjust the gate-source voltage amplitude; Step S24: Using an adjustable rheostat as a gate drive resistor and connecting it to OUT+ and OUT- of the gate drive IC respectively, so that the circuit can flexibly adjust the gate drive resistance; Step S25: Select a non-inductive resistor and a heat sink as the load resistor, and use a DC-DC power module to provide a 3.3V voltage to the bus; Step S26: placing the device under test on the back of the circuit board and adopting copper cladding and window opening to increase heat dissipation, and minimizing loop inductance during wiring to reduce parasitic parameters and prevent oscillation; Step S27: The device under test operates under a continuous pulse width modulation signal, and an oscilloscope is used to synchronously sample the gate-source voltage of the heating component and the current flowing through the load resistor, thereby obtaining a transfer characteristic curve during a transition from a positive voltage to a negative voltage and a transfer characteristic curve during a transition from a negative voltage to a positive voltage; Step S3: Plotting the two transfer characteristic curves extracted in step S2 on the same coordinate axis, and using the closed graph formed by the two to represent and accurately measure the hysteresis characteristics of the transfer characteristic curves.

Images