Accurate measurement method for p-GaN HEMT transient threshold voltage change

Abstract

The invention discloses a method for accurately measuring transient threshold voltage change of a p-GaN HEMT (High Electron Mobility Transistor). The method can be used for measuring the transient threshold voltage change of a p-GaN HEMT device under electrical bias. Before grid voltage bias application and transient threshold voltage test, a test for introducing transient voltage change to sampling current is designed and added, and the test condition is consistent with the test condition of a threshold voltage transient curve. And after actual measurement of the transient threshold voltage curve is completed, factors additionally introduced by the part are removed from the actual measurement curve. According to the method, the influence of the collected current on the change of the transient threshold voltage can be corrected, so that the accurate change quantity of the threshold voltage along with the time can be obtained, and the threshold voltage drift and trap action conditions of the p-GaN HEMT device under the electrical bias can be correctly evaluated.

Description

Technical Field

[0001] The invention relates to accurate measurement of transient threshold voltage change of p-GaN HEMT, and belongs to the field of electrical characteristic testing and reliability of power semiconductor devices. Background Art

[0002] Enhanced-mode GaN-based devices have a wide range of applications in the field of power switches, among which Schottky-type p-GaN HEMT has lower switching losses and smaller gate leakage current, achieving widespread commercial applications. However, the gate structure of p-GaN HEMT is more complex, and the trap effect under the gate voltage causes the device threshold voltage to drift, which may lead to reduced switching efficiency and reduced device operation stability, posing serious risks to the reliability of p-GaN HEMT devices and related systems.

[0003] At present, the threshold voltage drift of p-GaN HEMT under positive gate voltage has been widely studied, and a variety of threshold voltage test technologies have also been developed. The device threshold voltage can be obtained by reading the gate-source voltage under a constant drain-source current (for example, 1 mA) using the transfer characteristics; when the gate-source voltage and drain-source voltage are equal, the device threshold voltage can also be obtained by applying a constant sampling current to the drain-source end of the device. These two methods can conveniently and quickly obtain the static threshold voltage value of the device, but the transient change of the threshold voltage over time under electrical stress still needs to be further characterized. The pulse transfer characteristics can be used to obtain the change of the threshold voltage of p-GaN HEMT under electrical bias over time. This test method requires setting the pulse duty cycle, so the threshold voltage obtained over time is in the form of a scatter plot rather than a continuous curve change. In addition, keeping the gate and drain of the device short-circuited and applying a constant sampling current can obtain the transient threshold voltage change. This method can obtain a continuous threshold voltage change curve. However, in the actual test process, the constant sampling current applied may cause trap filling and cause voltage changes. This additional transient change is included in the measured transient voltage curve, which brings errors to the measured curve. Therefore, it is necessary to develop accurate and non-destructive p-GaN HEMT threshold voltage transient testing technology.

[0004] The technology of the present invention proposes a correction method for the measurement error in the transient change test of the threshold voltage of p-GaN HEMT, evaluates the transient voltage change caused by the trap effect under the condition of applying the sampling current, and removes the additional influence introduced by this part from the transient voltage curve of the p-GaN HEMT under the gate voltage stress, so as to obtain a more accurate transient threshold voltage change of the p-GaN HEMT, and provide technical means for the accurate analysis of the internal trap effect and trap-related parameters of the p-GaN HEMT. This method can be applied to the transient threshold voltage test of p-GaN HEMT devices from different manufacturers, and has a good application basis. Summary of the invention

[0005] The change of the transient threshold voltage of p-GaN HEMT under gate voltage is usually characterized by the transient voltage change caused by the sampling current after the gate and drain of the device are short-circuited. However, during the test, the sampling current applied to the p-GaN HEMT will also cause the internal trap effect. The measured transient threshold voltage curve includes the influence of the threshold voltage change under the gate voltage and the additional voltage change introduced by the sampling current. Based on the measured curve, further analysis shows that there may be errors in the trap parameters inside the p-GaN HEMT under gate voltage. In order to solve this problem, we designed and added the test and evaluation of transient voltage change under sampling current before the traditional gate voltage application and threshold voltage test, and eliminated this test result from the final measured threshold voltage transient curve to obtain an accurate p-GaN HEMT transient threshold voltage change curve, and analyzed to obtain accurate information related to traps.

[0006] The technical solution adopted by the present invention is a method for accurately measuring the transient threshold voltage change of a p-GaN HEMT. The implementation process of the method is as follows: Step 1). The p-GaN HEMT device under test is placed in a temperature chamber at 303 K. First, a gate-drain voltage VGD is applied between the gate and drain of the device, and a test current Isense is applied between the source and drain of the device; wherein the gate-drain voltage VGD is 0 V, and the range of the test current Isense is 0.1 mA≤Isense≤20 mA. Monitor the change of the drain-source voltage VSD of the device under test over time and record the transient curve as VSD1, and the test time is tm1. After completing the VSD1 test for a time of tm1, keep the device under test in an unpowered state for 10 minutes; wherein the range of the test time tm1 is 100 s≤tm1≤1000 s, and the range of the transient curve VSD1 is 0.1 V≤VSD1≤10 V.

[0007] Step 2). After 10 minutes of rest, apply a filling voltage VGD_F between the gate and drain of the device, while keeping the source and drain of the device short-circuited, that is, VSD=0 V. At this time, the voltage between the gate and drain of the device under test is equal to the voltage between the source and drain, so the filling voltage between the gate and source is VGS_F=VGD_F, and the filling time is tf. Among them, the range of the filling voltage VGD_F is 1V≤VGD_F≤10 V; the range of the filling time tf is 10 ms≤tm1≤1000 s. After the filling time tf is completed, a gate-drain test voltage VGD_M of 0 V is applied between the gate and drain of the device, and a test current Isense is applied between the source and drain of the device; monitor the change of the drain-source voltage VSD of the device under test over time and record the transient curve as VSD2, and the test time is tm2. Among them, the range of VSD2 is 0.1 V≤VSD2≤10 V, and the range of tm2 is 100 s≤tm2≤1000 s. At this time, the change of VSD over time is the measured change of the threshold voltage of the device under test over time ΔVTH_measured, where the range of ΔVTH_measured is 0 V≤ΔVTH_measured≤5 V.

[0008] Step 3). After completing the test time tm2, compare the transient curves VSD1 and VSD2 of the drain-source voltage over time. The transient curve VSD1 obtained during the tm1 test time reflects the impact of 0 V VGD and 1 mA Isense applied to the device on VSD. This test condition is consistent with the 0 V VGD_M and 1 mA Isense applied to the device during tm2. The voltage difference between VSD1 and VSD2 at the same sampling time point is VSD1-VSD2, where the difference in the corresponding sampling time of VSD1 and VSD2 is less than 2 ms, which is the same sampling time point. The transient curve VSD2 obtained in the test phase after the filling voltage is applied includes the impact of the test conditions, so ΔVTH_actual=VSD2-VSD1 represents the actual transient curve change caused by the filling voltage, where the range of ΔVTH_actual is 0 V≤ΔVTH_actual≤9.9 V.

[0009] Step 4). Change the filling time tf and repeat steps 1) to 3) to obtain the corresponding transient threshold voltage change. The Bayesian iteration technique can be used to further construct the time constant spectrum and differential amplitude spectrum, from which the trap time constant and amplitude information contained in the threshold voltage change can be extracted. The absolute amplitude of the trap represents the exact contribution of N traps to the threshold voltage change, where 1≤N≤8; the sum of the absolute amplitudes of the N traps is the actual threshold voltage transient change ΔVTH_actual.

[0010] The present invention proposes and corrects the influence of applying a sampling current on the measured transient voltage curve during the transient threshold voltage test of a p-GaN HEMT. The method can accurately obtain the transient change curve of the threshold voltage of a p-GaN HEMT under electrical stress, and accurately evaluate the change of the threshold voltage of a p-GaN HEMT under different voltage biases. The beneficial effects of the present invention are: the test technology described in the present invention is convenient and fast, and the test conditions are simple. On the basis of the existing p-GaN HEMT threshold voltage test method, an accurate transient threshold voltage test technology is proposed, which provides an effective technical means for the electrical characteristics test and reliability evaluation of p-GaN HEMT. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 : The transient threshold voltage test timing diagram involved in the present invention.

[0012] Figure 2 : The measured threshold voltage transient curve and the accurate threshold voltage transient curve after processing.

[0013] Figure 3 : Accurate threshold voltage transient change curve under different filling time and the threshold voltage change caused by each trap. DETAILED DESCRIPTION

[0014] The following is a more detailed description of the accurate measurement of the transient threshold voltage change of p-GaN HEMT in conjunction with the accompanying drawings and specific embodiments. The p-GaN HEMT produced by EPC is selected as the device under test, the model is EPC2007C, and its maximum operating voltage is 100 V and the maximum operating current is 6 A. The method involved in the present invention includes the following steps: Step 1: Place the p-GaN HEMT device under test in a temperature chamber at 303 K. First, apply a gate-drain voltage VGD of 0 V between the gate and drain of the device, and apply a test current Isense of 1 mA between the source and drain of the device. Monitor the change of the drain-source voltage VSD of the device under test over time and record the transient curve as VSD1. The test time tm1 is 500 s. After completing the 500 s VSD1 test, keep the device under test unpowered for 10 minutes.

[0015] Step 2: After 10 minutes of rest, apply a 5 V fill voltage VGD_F between the gate and drain of the device, while keeping the source and drain of the device short-circuited, that is, VSD=0 V. At this time, the voltage between the gate and drain of the device under test is equal to the voltage between the source and drain, so the gate-source fill voltage VGS_F=VGD_F=5 V, and the fill time tf is 30 s. After the 30 s fill time tf is completed, a 0 V gate-drain test voltage VGD_M is applied between the gate and drain of the device, and a 1 mA test current Isense is applied between the source and drain of the device; monitor the change of the drain-source voltage VSD of the device under test over time and record the transient curve as VSD2. The test time tm2 is 500 s. At this time, the change of VSD over time is the measured change of the threshold voltage of the device under test over time ΔVTH_measured. The test timing is as follows: Figure 1 shown.

[0016] Step 3: After completing the test time tm2 of 500 s, compare the transient curves VSD1 and VSD2 of the drain-source voltage changing with time. The transient curve VSD1 obtained during the test time tm1 reflects the impact of 0 V VGD and 1 mA Isense applied to the device on VSD. This test condition is consistent with the 0 V VGD_M and 1 mA Isense applied to the device during tm2. The voltage difference between VSD1 and VSD2 at the same sampling time point is VSD1-VSD2, where the difference in the corresponding sampling time of VSD1 and VSD2 is less than 2 ms, which is the same sampling time point. The transient curve VSD2 obtained in the test phase after removing the fill voltage includes the influence of the test conditions, so ΔVTH_actual=VSD2-VSD1 represents the actual transient curve change caused by the fill voltage. The results are shown in Figure 2 As shown. Under the fill voltage condition of VGS_F=VGD_F=5 V, the threshold voltage change corresponding to VSD2 obtained after the tm2 test time is ΔVTH_measured; the threshold voltage change corresponding to the removal of VSD1 introduced during the tm1 test time is ΔVTH_actual.

[0017] Step 4: The filling time tf is changed to 50 ms, 100 ms, 200 ms, 1 s, 5 s, 30 s and 300 s in sequence, and steps 1 to 3 are repeated to obtain the corresponding transient threshold voltage changes as shown in Figure 3The Bayesian iteration technique can be used to further construct the time constant spectrum and differential amplitude spectrum, from which the trap time constant and amplitude information contained in the threshold voltage change can be extracted. The absolute amplitude of the trap represents the exact contribution of the three traps to the threshold voltage change, and the sum of the absolute amplitudes of the three traps is the actual threshold voltage transient change ΔVTH_actual.

Claims

1. A method for accurately measuring the transient threshold voltage change of a p-GaN HEMT, characterized in that: Step 1) The p-GaN HEMT device under test is placed in a temperature box at a temperature of 303 K; first, a gate-drain voltage VGD of 0 V is applied between the gate and the drain of the p-GaN HEMT device under test, and a test current Isense is applied between the source and the drain of the device; the change of the drain-source voltage VSD of the p-GaN HEMT device under test over time is monitored and the transient curve is recorded as VSD1, and the test time is tm1; after completing the VSD1 test of time tm1, the p-GaN HEMT device under test is kept in an unpowered state and left for 10 minutes; Step 2) After 10 minutes of rest, a filling voltage VGD_F is applied between the gate and drain of the device, while the source and drain of the p-GaN HEMT device under test are kept short-circuited, that is, VSD=0 V; at this time, the voltage between the gate and drain of the p-GaN HEMT device under test is equal to the voltage between the source and drain, so the gate-source filling voltage VGS_F=VGD_F, and the filling time is tf; after the filling time tf is completed, a gate-drain test voltage VGD_M of 0 V is applied between the gate and drain of the device, and a test current Isense is applied between the source and drain of the p-GaN HEMT device under test; the change of the drain-source voltage VSD of the p-GaN HEMT device under test over time is monitored and the transient curve is recorded as VSD2, and the test time is tm2; at this time, the change of VSD over time is the measured change of the threshold voltage of the p-GaN HEMT device under test over time ΔVTH_measured; Step 3) After the test time tm2 is completed, compare the transient curves VSD1 and VSD2 of the drain-source voltage changing with time; the transient curve VSD1 obtained during the test time tm1 reflects the influence of 0 V VGD and 1 mA Isense applied to the p-GaN HEMT device under test on VSD, and this test condition is consistent with the 0 V VGD_M and 1 mA Isense applied to the p-GaN HEMT device under test during the tm2 time; the voltage difference between VSD1 and VSD2 at the same sampling time point is VSD1-VSD2, where the difference between the corresponding sampling times of VSD1 and VSD2 is less than 2 ms, which is the same sampling time point; the transient curve VSD2 obtained in the test phase after the filling voltage is applied includes the influence of the test conditions, so VSD2-VSD1 represents the actual transient curve change ΔVTH_actual caused by the filling voltage; Step 4) Change the filling time tf and repeat steps 1) to 3) to obtain the corresponding transient threshold voltage change; use Bayesian iteration to construct the time constant spectrum and differential amplitude spectrum, and extract the trap time constant and amplitude information contained in the threshold voltage change; the absolute amplitude of the trap represents the accurate contribution of N traps to the threshold voltage change; the sum of the absolute amplitudes of the N traps is the actual threshold voltage transient change ΔVTH_actual.

2. The method for accurately measuring the transient threshold voltage change of a p-GaN HEMT according to claim 1, characterized in that: In the VSD1 test phase described in step 1), the gate-drain voltage VGD of the p-GaN HEMT device under test is 0 V, and the range of the test current Isense is 0.1 mA≤Isense≤20 mA, the range of the test time tm1 is 100 s≤tm1≤1000 s, and the range of the transient curve VSD1 is 0.1 V≤VSD1≤10 V.

3. The method for accurately measuring the transient threshold voltage change of a p-GaN HEMT according to claim 1, characterized in that: In step 2), the range of the filling voltage VGD_F is 1 V≤VGD_F≤10 V, and the drain and source of the p-GaN HEMT device under test are short-circuited to ensure that VGD_F=VGS_F is the gate filling voltage applied to the device; the range of the filling time tf is 10 ms≤tm1≤1000 s.

4. The method for accurately measuring the transient threshold voltage change of a p-GaN HEMT according to claim 1, characterized in that: In step 2), during the VSD2 test, the range of VSD2 is 0.1 V≤VSD2≤10 V, the range of tm2 is 100 s≤tm2≤1000 s, and the range of ΔVTH_measured is 0 V≤ΔVTH_measured≤5 V.

5. The method for accurately measuring the transient threshold voltage change of a p-GaN HEMT according to claim 1, characterized in that: The sampling current Isense applied during the test of VSD1 and VSD2 is the same, the test time tm1=tm2, and the voltage difference at the same sampling time point is VSD1-VSD2, where the difference between the corresponding sampling times of VSD1 and VSD2 is less than 2 ms, which means they are at the same sampling time point.

6. The method for accurately measuring the transient threshold voltage change of a p-GaN HEMT according to claim 1, characterized in that: ΔVTH_actual=VSD2-VSD1 is the transient curve change ΔVTH_actual actually caused by the fill voltage, where the range of ΔVTH_actual is 0 V≤ΔVTH_actual≤9.9V.

7. The method for accurately measuring the transient threshold voltage change of a p-GaN HEMT according to claim 1, characterized in that: The accurate contribution of the N traps to the threshold voltage change is the absolute amplitude of the trap obtained using the differential amplitude spectrum, where 1≤N≤8; the sum of the absolute amplitudes of the N traps is the actual threshold voltage transient change ΔVTH_actual.

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