Alternating current time-dependent breakdown effect characterization system and method applied to MOSFET (Metal Oxide Semiconductor Field Effect Transistor) device

Abstract

The invention discloses an alternating current time-dependent breakdown effect characterization system and method applied to an MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) device. The system comprises an arbitrary waveform generator, a broadband amplifier, a broadband combiner, a broadband bias device, a high-speed input probe, a high-speed output probe, a source measurement unit and a system control unit, according to the method, any waveform generating the alternating current TDDB effect can be accurately controlled, a TDDB stress current track is accurately represented, and a solid foundation is laid for accurately extracting breakdown time, so that ultrahigh-frequency TDDB alternating current characteristic representation is realized, and the test sensitivity is high. In addition, cooperative and unified control can be completed by means of communication equipment, and the accuracy of a test result is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of characterization and testing of semiconductor MOSFET device reliability, and specifically relates to a characterization technology for time-dependent breakdown effects of high-performance electronic devices, especially metal oxide semiconductor field effect transistors (MOSFETs) devices under AC stress. Background Art

[0002] In the past few decades, with the development of CMOS integrated circuit technology, the size of the most core unit in the circuit - metal oxide semiconductor field effect transistors (MOSFETs) has been gradually reduced in accordance with Moore's Law, from micrometers (μm) to nanometers, and the density and performance of transistor devices have been continuously improved. One of the important indicators for measuring transistor reliability is the time-dependent breakdown effect (TDDB) of the gate dielectric. TDDB refers to the process in which the gate dielectric breaks down due to the long-term bias voltage applied to the gate of the transistor. Before the breakdown, the electrical characteristics of the transistor degrade, such as threshold voltage drift, saturation current and transconductance reduction. After the breakdown, the gate loses the ability to control the channel, that is, the device fails. In order to achieve higher integration density and lower power dissipation, it is necessary to continuously reduce the size of the device and reduce the operating voltage of the device, which forces the gate oxide layer to maintain the controllability and driveability of the gate to be continuously thinned. However, ultra-thin oxide not only leads to an increase in gate leakage current, but also makes the device more susceptible to TDDB. Therefore, it is of great significance to accurately evaluate and characterize the time-dependent breakdown effect of MOSFET devices.

[0003] The traditional characteristics of the time-dependent breakdown effect are thickness dependence, temperature dependence, and voltage dependence. As the operating frequency in actual circuits increases, the frequency dependence of the time-dependent breakdown effect has also been gradually studied and explored. For example, in silicon dioxide and high-k material MOSFET devices, TDDB has obvious frequency dependence, and the device life shows a significant gain under stress characterization at ultra-high frequencies. Studying the AC TDDB characteristics of MOSFET devices can more accurately evaluate the device life, so the AC TDDB characterization technology needs to be proposed and improved.

[0004] The characterization method of dielectric time-dependent breakdown (TDDB) is to apply a constant voltage to the gate, and use the time point corresponding to the sudden increase in gate oxide leakage current as the failure time to determine the breakdown of the device. Traditional TDDB characterization applies a DC voltage to the gate, and the breakdown time obtained by extrapolating the breakdown time under the nominal voltage will seriously underestimate the life of the device. At present, some on-the-fly or fast AC TDDB measurement technologies can perform MHz-level characterization. Experiments have proved the life gain of TDDB frequency dependence, but it seems that the frequency gain margin has not yet been reached. The experimental characterization requires high-frequency and large-amplitude AC signals, which are restricted by the hardware equipment for semiconductor characterization and analysis. There is currently no direct commercial instrument. In addition, the TDDB breakdown phenomenon occurs instantly. The conventional "test-stress-test" process only measures the leakage current during the test phase, and does not measure during the stress process, which makes it difficult to accurately record the breakdown time. This is also the difficulty and problem of current AC TDDB characterization. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies in the prior art and provide an AC time-dependent breakdown effect testing system and method for MOSFET devices, which directly measures and accurately extracts the real-time changes of the stress current trajectory, accurately captures the breakdown time from the real-time changes, and realizes the AC TDDB life characterization of MOSFET devices in the high-frequency range.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] According to a first aspect of the present specification, there is provided an AC time-dependent breakdown effect characterization system applied to a MOSFET device, the system comprising an arbitrary waveform generator, a wideband amplifier, a wideband combiner, a wideband bias device, a high-speed input probe, a high-speed output probe, a source measurement unit and a system control unit;

[0008] The arbitrary waveform generator has a multi-channel synchronous replication output function, the first channel generates an AC voltage signal whose level and time can be precisely controlled, and the remaining channels generate AC voltage signals with the same shape and phase as the first channel and synchronized with the clock; the AC voltage signals generated by each channel are respectively input into different wide-band amplifiers to obtain amplitude gain, and the AC voltage signals of each channel after amplification have the same shape and phase and completely synchronized with the clock, and are respectively connected to the input ends of the wide-band combiner;

[0009] The broadband combiner combines multiple input signals into one signal and outputs it to the broadband bias device;

[0010] The wide-band bias device superimposes a DC voltage on the input AC voltage signal to meet the amplitude requirement of the stress voltage required by the MOSFET device under test, thereby forming an AC TDDB gate voltage stress signal;

[0011] The high-speed input probe inputs the AC TDDB gate voltage stress signal to the gate of the MOSFET device under test; after the drain, source and substrate of the MOSFET device under test are connected to the same end, the high-speed output probe collects the response current signal and inputs it to the source measurement unit;

[0012] The source measurement unit is used to monitor the response current signal and feed back the signal to the system control unit in real time;

[0013] The response current signal received by the system control unit is the sum of the drain, source and substrate currents of the MOSFET device under test. The amplitude of the response current signal is the same as the gate leakage current signal but the phase is opposite. By characterizing the amplitude of the response current signal, the change trajectory of the gate leakage current over time under the AC TDDB gate pressure stress signal is obtained to determine whether time-dependent breakdown occurs and record the occurrence time.

[0014] Further, the wide-band amplifier is used to gain the peak-to-peak value of the AC voltage signal generated by a single channel of the arbitrary waveform generator and to keep the high-frequency signal edge from being excessively distorted;

[0015] The wideband combiner has multiple input ends and one output end. When the phases of each input signal are the same and the clocks are synchronized, the output signal is the superposition of each input signal, which is used to further increase the amplitude of the AC voltage signal and improve the noise of the high and low level signal waveforms and the overshoot of the rising edge signal.

[0016] Furthermore, the arbitrary waveform generator is used to generate stress voltage signals with different frequencies, duty cycles, polarities, and controllable time and amplitude.

[0017] Furthermore, the high-speed input probe is a "ground-signal-ground" radio frequency probe capable of automatic heat dissipation, and a 100Ω resistor is connected between the "ground-signal" terminals on both sides; the high-speed output probe is a "ground-signal-ground" radio frequency probe capable of automatic heat dissipation.

[0018] Furthermore, the MOSFET device under test includes a transistor, a metal-oxide-semiconductor MOS capacitor component in the transistor, and other capacitor components containing a dielectric in the transistor.

[0019] Furthermore, the drain, source and substrate of the MOSFET device under test are connected to the same end through layout structure design or test cables.

[0020] Furthermore, all connecting transmission cables in the system are millimeter wave cables, and their maximum bandwidth needs to ensure the integrity of signal transmission.

[0021] Furthermore, the system control unit is a computer that can accurately control the arbitrary waveform generator and the source measurement unit through instructions and has data calculation and processing capabilities.

[0022] According to a second aspect of the present specification, there is provided a method for characterizing the AC time-dependent breakdown effect using the system described in the first aspect, the method comprising the following steps:

[0023] Step 1: Perform a pre-breakdown test on the MOSFET device to exclude devices that will instantly break down;

[0024] Step 2: Configure the AC TDDB gate voltage stress signal V gstress ;

[0025] Step 3: Implement the measurement phase and apply the AC TDDB gate voltage stress signal V gstres The gate of the MOSFET device under test is connected to the gate of the MOSFET device under test, and the response current signal I of the MOSFET device under test at the zero point is monitored at the same time. avg,0 As the initial state quantity;

[0026] Step 4: Continue to apply AC TDDB gate voltage stress signal V gstres The gate of the MOSFET device under test is used to monitor the response current signal I at every predetermined interval. sum And calculate the average current value I avg ;

[0027] Step 5: According to the initial state quantity I avg,0 Determine the average current value I avg Whether the failure standard is reached, if the failure standard is reached, the test is terminated and the breakdown time is recorded; otherwise, steps 4 and 5 are repeated until the failure standard is reached.

[0028] Furthermore, the average current value I avg With V gstress The response current signal I at high level high 、V gstress The response current signal I at low level low and V gstress The specific calculation relationship is I avg =DF*I high +(1-DF)*I low .

[0029] The beneficial effects of the present invention are as follows: First, the present invention can accurately control any waveform that produces the AC TDDB effect, and innovatively combines a wideband amplifier, a wideband combiner, and a wideband bias device to achieve a high-frequency, large-amplitude GHz signal that can characterize the ultra-high frequency (close to GHz) TDDB AC characteristics. Second, the present invention adopts a dynamic monitoring average current method to directly measure and accurately extract the real-time changes of the stress current trajectory, from which the breakdown time is accurately captured, and the test sensitivity is high. Third, the present invention can use communication equipment to complete coordinated and unified control to ensure the accuracy of the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the structure of a system for characterizing the AC time-dependent breakdown effect of a MOSFET device provided in an embodiment of the present invention.

[0031] Figure 2 A circuit diagram of an AC time-dependent breakdown effect characterization system provided by an embodiment of the present invention.

[0032] Figure 3 Based on Figure 2 A waveform diagram of the process in which an AC voltage signal generated by an arbitrary waveform generator of an AC time-dependent breakdown effect characterization system used in an embodiment changes to an AC TDDB gate voltage stress signal.

[0033] Figure 4 A schematic flow chart of a method for characterizing the AC time-dependent breakdown effect provided in an embodiment of the present invention.

[0034] Figure 5 This is a comparison diagram of gate leakage current trajectories under 500MHz AC and DC TDDB stresses measured by the present invention. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] like Figure 1As shown, the present invention provides an AC time-dependent breakdown effect characterization system for MOSFET devices, comprising an arbitrary waveform generator 101, a broadband amplifier 102, a broadband combiner 103, a broadband bias device 104, a high-speed input probe 105, a high-speed output probe 107, a source measurement unit 108 and a system control unit 109; the arbitrary waveform generator 101 has a multi-channel synchronous replication output function, the first channel generates an AC voltage signal whose level and time can be precisely controlled, and the remaining channels generate AC voltage signals with the same shape and phase as the first channel and synchronized with the clock; the AC voltage signal generated by each channel is respectively input to each broadband amplifier 102 to obtain amplitude gain, and each amplified AC voltage signal has the same shape and phase and is completely synchronized with the clock, and is respectively connected to each input end of the broadband combiner 103; the broadband combiner 103 combines multiple input signals into one channel and outputs it to the broadband bias device 104; the broadband bias device 104 generates an AC voltage signal on the input AC voltage signal. A DC voltage is superimposed to meet the amplitude requirement of the stress voltage required by the MOSFET device under test, thereby forming an AC TDDB gate voltage stress signal; a high-speed input probe 105 inputs the TDDB gate voltage stress signal to the gate G of the MOSFET device under test 106; the drain D, source S, and substrate B of the MOSFET device under test 106 are connected to the same end through a layout structure design or a test cable, and a response current signal collected at this end is input to a source measurement unit 108 through a high-speed output probe 107. The source measurement unit 108 is used to monitor the response current signal and feed it back to the system control unit 109 in real time; the response current signal received by the system control unit 109 is the sum of the drain, source, and substrate currents of the MOSFET device under test 106, and the amplitude of the response current signal is the same as the gate leakage current signal but the phase is opposite. By characterizing the amplitude of the response current signal, the change trajectory of the gate leakage current over time under the AC TDDB gate voltage stress signal is obtained, and it is determined whether time-dependent breakdown occurs and the occurrence time is recorded.

[0037] Figure 2 A circuit diagram of an AC time-dependent breakdown effect characterization system provided by an embodiment of the present invention. Figure 3 Given based on Figure 2Schematic diagram of the waveform of the process of the AC voltage signal generated by the arbitrary waveform generator of the AC time-destruction effect characterization system used in the embodiment changing to the AC TDDB gate voltage stress signal. In this embodiment, the three channels of the arbitrary waveform generator 101 respectively generate periodic square wave signals 201, 202, and 203, and the waveforms generated by the three channels have exactly the same shape and phase and are clock-synchronized; the three signals are respectively input into three wide-band amplifiers 102 to obtain amplitude gain, and each of the AC voltage signals 204, 205, and 206 after amplification still maintains the same shape and phase and is clock-synchronized. The wide-band amplifier 102 is mainly used to gain the peak-to-peak value of the AC voltage signal generated by a single channel of the arbitrary waveform generator, and to keep the high-frequency signal edge from being excessively distorted; the wide-band combiner 103 has multiple input terminals and an output terminal. When the clock of each input signal is synchronized, the output signal is the superposition of each input signal, which is used to further increase the amplitude of the AC voltage signal and improve the high and low The noise of the level signal waveform and the rising edge signal overshoot; in the embodiment, the wideband combiner 103 uses three input terminals to combine the three input AC voltage signals 204, 205, and 206 into one AC voltage signal 207. Since the three signals have the same phase and clock synchronization, the combined signal 207 is the superposition of 204, 205, and 206, which further increases the amplitude of the AC voltage signal; although the peak-to-peak value of the AC voltage signal 207 after amplification and combination meets the AC TDDB characteristic characterization requirements, its amplitude range is still not satisfied. The wideband bias device 104 superimposes a DC voltage on the input AC voltage signal 207, thereby meeting the amplitude requirement of the stress voltage required by the MOSFET device 106 under test, and forming an AC TDDB gate voltage stress signal 208, recorded as V gstress . The high-speed input probe 105 is a "ground-signal-ground" radio frequency probe capable of automatic heat dissipation. A 100Ω resistor is connected between the "ground-signal" terminals on both sides to ensure that the radio frequency probe terminal impedance is 50Ω, thereby shortening the reflection path length when a high-speed signal is reflected at the gate of the MOSFET device 106 under test; the high-speed output probe 107 is a "ground-signal-ground" radio frequency probe capable of automatic heat dissipation. The MOSFET device 106 under test includes but is not limited to transistors, metal-oxide-semiconductor MOS capacitor components in transistors, and other capacitor components containing dielectrics in transistors. All connecting transmission cables in the circuit configuration are millimeter wave cables, and their maximum bandwidth is required to ensure the integrity of signal transmission. The source measurement unit 108 is an instrument that can output voltage or current and measure voltage and / or current at the same time. In this embodiment, it is used to monitor the response current signal 209, and the response current signal 209 is recorded as I sum Since the drain, source, and substrate of the MOSFET device 106 under test are connected to the same end through layout structure design or test cables, the response current signal I sumIt is the sum of the drain, source, and substrate currents. Its amplitude is the same as the gate leakage current signal but its phase is opposite. It is characterized by the response current signal I sum The gate leakage current can be obtained in the AC TDDB gate voltage stress signal V gstress The time-varying trajectory is recorded to determine whether a time-varying breakdown occurs and the time of occurrence is recorded. The system control unit 109 is a computer that can accurately control the arbitrary waveform generator 101 and the source measurement unit 108 through instructions and has data calculation and processing capabilities. In order to reduce system noise, a common ground is established in the entire system.

[0038] Figure 4 An optional flow chart of a method for characterizing the AC time-dependent breakdown effect provided by an embodiment of the present invention includes the following steps:

[0039] Step S301, pre-breakdown test;

[0040] A constant DC voltage is applied to the gate G of the MOSFET device 106 under test, and the gate leakage current is monitored. If the device under test breaks down immediately after the DC voltage is applied, it is excluded and the next device is selected for AC TDDB characterization. The amplitude of the DC voltage is equal to the operating voltage of the device under test and is much smaller than the AC TDDB gate voltage stress signal V gstress The purpose of this pre-breakdown test is to screen and exclude devices that will break down instantly, so as to avoid errors caused by process manufacturing and other reasons in the characterization of the AC TDDB effect.

[0041] Step S302: Configure the AC TDDB gate voltage stress signal V gstress ;

[0042] Here, the AC TDDB gate voltage stress signal V gstress Peak-to-peak value, high level value V high and low level value V low The size is selected according to the operating voltage of the MOSFET device under test. It should be able to cause the TDDB effect on the device under test and the characterization time should be appropriate. The characterization time is usually not less than V gstress The measurement cycle does not need to be too long, but it does not need to be too long to waste measurement resources.

[0043] Step S303: Applying an AC TDDB gate voltage stress signal V gstres At the same time, the source measurement unit monitors the response current signal I of the MOSFET device under test at the zero point. avg,0 As the initial state quantity;

[0044] The source measurement unit usually takes several microseconds or even milliseconds to complete a measurement and then output a voltage or current value; when the AC TDDB gate voltage stress signal V gstressWhen the frequency reaches the megahertz level, that is, each cycle does not exceed 1 microsecond, the source measurement unit will respond to the current signal I sum With the AC TDDB gate voltage stress signal V gstress The source measurement unit changes according to the monitored response current signal I sum Calculate the average current value I avg As the final output value, the average current value I avg With V gstress The response current signal I at high level high 、V gstress The response current signal I at low level low and V gstress The specific calculation relationship is I avg =DF*I high +(1-DF)*I low In this embodiment, a square wave signal with a duty cycle DF of 50% is selected, I avg =0.5*I high +0.5*I low .

[0045] Step S304: Continue to apply the AC TDDB gate voltage stress signal V gstres The gate of the MOSFET device under test is used to monitor the response current signal I at every predetermined interval. sum And calculate the average current value I avg Here, the interval time should be no less than the time length for the source measurement unit to complete a measurement, and no greater than the time resolution represented by the TDDB. In this embodiment, the selected interval time is 0.5 seconds, that is, the source measurement unit monitors the response current signal once every 0.5 seconds.

[0046] Step S305: According to the initial state quantity I avg,0 Judgment I avg If the failure standard is reached, the test is terminated and the breakdown time is recorded; otherwise, steps S304 and S305 are repeated until the failure standard is reached. avg More than I avg,0 The failure standard is 100 times or more. The failure standard can be changed according to the actual measurement situation.

[0047] Figure 5 The gate leakage current measured by the AC time-dependent breakdown effect characterization system of the present invention changes with time under the AC TDDB gate voltage stress signal, and is compared with the DC time-dependent breakdown test result. In this embodiment, an AC TDDB gate voltage stress signal V is applied to an nMOSFET device. gstress, frequency is 500MHz, duty cycle is 50%, amplitude is from 0V to 3.6V; for AC voltage stress, effective stress time = applied V gstress Total duration*duty cycle; Apply a DC TDDB gate voltage stress signal V' to another nMOSFET device gstress , the amplitude is constant at 3.6V; for DC voltage stress, the effective stress time = applied V' gstress Total time. Obviously, the breakdown time of the present invention under high-frequency AC time-dependent breakdown stress is much longer than that under DC stress, and this AC stress is closer to the AC working state of the MOSFET constantly switching in the actual circuit. The present invention can more accurately evaluate the time-dependent breakdown life and obtain a larger reliability life window for circuit design.

[0048] The above embodiments are merely examples of the present invention. Although the best embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the best embodiments and drawings.

Claims

1. A system for characterizing the AC time-dependent breakdown effect of MOSFET devices. It is characterized in that The system includes an arbitrary waveform generator, a wideband amplifier, a wideband combiner, a wideband bias device, a high-speed input probe, a high-speed output probe, a source measurement unit and a system control unit; The arbitrary waveform generator has a multi-channel synchronous replication output function, the first channel generates an AC voltage signal whose level and time can be precisely controlled, and the remaining channels generate AC voltage signals with the same shape and phase as the first channel and synchronized with the clock; the AC voltage signals generated by each channel are respectively input into different wide-band amplifiers to obtain amplitude gain, and the AC voltage signals of each channel after amplification have the same shape and phase and completely synchronized with the clock, and are respectively connected to the input ends of the wide-band combiner; The broadband combiner combines multiple input signals into one signal and outputs it to the broadband bias device; The wide-band bias device superimposes a DC voltage on the input AC voltage signal to meet the amplitude requirement of the stress voltage required by the MOSFET device under test, thereby forming an AC TDDB gate voltage stress signal; The high-speed input probe inputs the AC TDDB gate voltage stress signal to the gate of the MOSFET device under test; after the drain, source and substrate of the MOSFET device under test are connected to the same end, the high-speed output probe collects the response current signal and inputs it to the source measurement unit; The source measurement unit is used to monitor the response current signal and feed back the signal to the system control unit in real time; The response current signal received by the system control unit is the sum of the drain, source and substrate currents of the MOSFET device under test. The amplitude of the response current signal is the same as the gate leakage current signal but the phase is opposite. By characterizing the amplitude of the response current signal, the change trajectory of the gate leakage current over time under the AC TDDB gate pressure stress signal is obtained to determine whether time-dependent breakdown occurs and record the occurrence time.

2. The AC time-dependent breakdown effect characterization system for MOSFET devices according to claim 1, It is characterized in that The wideband amplifier is used to increase the peak-to-peak value of the AC voltage signal generated by a single channel of the arbitrary waveform generator and to keep the high-frequency signal edge from being excessively distorted; The wideband combiner has multiple input ends and one output end. When the phases of each input signal are the same and the clocks are synchronized, the output signal is the superposition of each input signal, which is used to further increase the amplitude of the AC voltage signal and improve the noise of the high and low level signal waveforms and the overshoot of the rising edge signal.

3. The AC time-dependent breakdown effect characterization system for MOSFET devices according to claim 1, It is characterized in that The arbitrary waveform generator is used to generate stress voltage signals with different frequencies, duty cycles, polarities, and controllable time and amplitude.

4. The AC time-dependent breakdown effect characterization system for MOSFET devices according to claim 1, It is characterized in that The high-speed input probe is a "ground-signal-ground" radio frequency probe capable of automatic heat dissipation, with a 100Ω resistor connected between the "ground-signal" terminals on both sides; the high-speed output probe is a "ground-signal-ground" radio frequency probe capable of automatic heat dissipation.

5. The AC time-dependent breakdown effect characterization system for MOSFET devices according to claim 1, It is characterized in that The MOSFET device under test includes a transistor, a metal-oxide-semiconductor MOS capacitor component in the transistor, and other capacitor components containing a dielectric in the transistor.

6. The AC time-dependent breakdown effect characterization system for MOSFET devices according to claim 1, It is characterized in that The drain, source and substrate of the MOSFET device under test are connected to the same end through layout structure design or test cables.

7. The AC time-dependent breakdown effect characterization system for MOSFET devices according to claim 1, It is characterized in that All connecting transmission cables in the system are millimeter wave cables, and their maximum bandwidth is required to ensure the integrity of signal transmission.

8. The AC time-dependent breakdown effect characterization system for MOSFET devices according to claim 1, It is characterized in that The system control unit is a computer that can accurately control the arbitrary waveform generator and the source measurement unit through instructions and has data calculation and processing capabilities.

9. A method for characterizing the time-dependent breakdown effect of an alternating current using the system according to any one of claims 1 to 8, It is characterized in that The following steps are involved: Step 1: Perform a pre-breakdown test on the MOSFET device to exclude devices that will instantly break down; Step 2: Configure the AC TDDB gate voltage stress signal V gstress ; Step 3: Implement the measurement phase and apply the AC TDDB gate voltage stress signal V gstres The gate of the MOSFET device under test is connected to the gate of the MOSFET device under test, and the response current signal I of the MOSFET device under test at the zero point is monitored at the same time. avg,0 As the initial state quantity; Step 4: Continue to apply AC TDDB gate voltage stress signal V gstres The gate of the MOSFET device under test is used to monitor the response current signal I at every predetermined interval. sum And calculate the average current value I avg ; Step 5: According to the initial state quantity I avg,0 Determine the average current value I avg Whether the failure standard is reached, if the failure standard is reached, the test is terminated and the breakdown time is recorded; otherwise, steps 4 and 5 are repeated until the failure standard is reached.

10. The method for characterizing the AC breakdown effect over time according to claim 9, It is characterized in that The average current value I avg With V gstress The response current signal I at high level high 、V gstress The response current signal I at low level low and V gstress The specific calculation relationship is I avg =DF*I high +(1-DF)*I low .

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