CN114325286A

CN114325286A - SiC MOSFET power cycle test circuit and control method thereof

Info

Publication number: CN114325286A
Application number: CN202111683278.XA
Authority: CN
Inventors: 罗皓泽; 吴强; 陈宏�; 崔瑞杰; 康建龙; 严辉强
Original assignee: ZJU Hangzhou Global Scientific and Technological Innovation Center
Current assignee: ZJU Hangzhou Global Scientific and Technological Innovation Center
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2022-04-12

Abstract

The invention discloses a SiC MOSFET power cycle test circuit and a control method thereof, wherein the test circuit comprises a bypass switch AS and a load current source I_loadDevice under test Q_{1_1}～Q_{m_n}Branch diode D₁～D_mDriving resistance R_{1_1}～R_{m_n}Switch S_{1_1}～S_{m_n}And IS_{1_1}～IS_{m_n}Small current source I_{1_1}～I_{m_n}. The control method adopts a round-robin junction temperature measuring method, and monitors the junction temperature and the threshold voltage of one device on a branch in each power cycle test period, thereby solving the problem of measurement result error caused by the difference of junction temperature measuring sequences of the devices on a serial branch. The circuit structure provided by the invention can realize on-line monitoring of the threshold voltage and temperature of the device to be tested in the power cycle test of the SiC MOSFET, and the method for measuring the threshold voltage does not need to add an additional current source and is simple to realize. The control method can realize the ultimate temperature (highest) of each tested device on the serial branchJunction temperature and lowest junction temperature).

Description

SiC MOSFET power cycle test circuit and control method thereof

Technical Field

The invention belongs to the field of power semiconductor device testing, and particularly relates to a SiC MOSFET power cycle testing circuit and a control method thereof.

Background

Third generation semiconductor power devices, represented by SiC MOSFETs, have found wide application due to their excellent performance. Meanwhile, the reliability problem is also receiving more and more attention. Power cycling is a widely used method of accelerated burn-in testing that accelerates the burn-in of a device by intermittently passing a power current through the device under test.

SiC MOSFETs have a unique threshold voltage shift phenomenon due to their immature gate oxide process. Therefore, in order to explore the degradation characteristics of the SiC MOSFET chip, it is important to realize online monitoring of the threshold voltage of the SiC MOSFET chip in a power cycle test. In addition, the lifetime of the power device is mainly affected by temperature. In the power cycle test, the maximum value of junction temperature fluctuation and junction temperature swing of the power device are focused. Therefore, in SiC MOSFET power cycling tests, it is important to achieve on-line accurate measurement of device junction temperature and device threshold voltage.

In view of this, the invention provides a SiC MOSFET power cycle test circuit and a control method thereof, which can realize accurate measurement of the threshold voltage and junction temperature of each tested SiC MOSFET.

Disclosure of Invention

The invention provides a novel SiC MOSFET power cycle test circuit and a control method thereof, which can realize on-line monitoring of threshold voltage and temperature of the SiC MOSFET in power cycle test.

The technical scheme of the invention is as follows:

the invention provides a novel SiC MOSFET power cycle test circuit and a control method thereof, which can realize the on-line measurement of threshold voltage and junction temperature in power cycle test and specifically comprises the following characteristics:

the circuit structure comprises a bypass switch AS, a load current source I_loadN × m devices under test Q_{1_1}～Q_{m_n}M branch diodes D₁～D_mN × m driving resistors R_{1_1}～R_{m_n}N × m switches S_{1_1}～S_{m_n}And n x m current source series switches IS_{1_1}～IS_{m_n}Small current source I of n x m_{1_1}～I_{m_n}. The test circuit comprises m test branches, an auxiliary switch bypass and a load current source branch. Each test branch includes a diode and n tested SiC MOSFET devices. n and m can be freely selected according to test requirements. The m test branches are numbered as branch 1, and branch 2 to branch m in sequence. One diode per test branch, D_iRepresenting diodes in series on branch i. Each test branch has n tested SiC MOSFETs. Q_{i_j}Representing the jth device under test on the ith branch. Each device under test has a driving resistor, R, connected in series on its gate_{i_j}Represents Q_{i_j}And the driving resistor is connected in series on the grid. A switch is connected between the gate and the drain of each device under test, wherein S_{i_j}Represents Q_{i_j}A switch connected between the gate and the drain. A branch circuit formed by connecting a switch and a small current source in series is connected between the drain electrode and the source electrode of each tested device, wherein I_{i_j}Represents Q_{i_j}Current source in parallel drain and source branches, IS_{i_j}Represents Q_{i_j}Switches in the drain and source legs. The drain and the source of each tested device on the same branch are connected in sequence to form a branch.

The provided threshold voltage online measurement method is characterized in that: to Q_{i_j}When measuring the threshold voltage, Q is measured_{i_j}Is set to a forward drive voltage, Q_{i_j}Switch S between gate and drain_{i_j}Closed, current source series switch IS_{i_j}And (5) disconnecting. The driving voltage of other tested devices on the same branch is negative driving voltage, and the switch connected between the grid and the drain and the switch connected with the current source in series are all disconnected. Q_{i_j}Positive driving voltage and kiloohm driving resistance pair Q_{i_j}Injecting a small current in milliampere level. Measurement of Q_{i_j}The gate-source voltage or the drain-source voltage can be obtainedA threshold voltage.

The device junction temperature on-line measurement method is characterized by comprising the following steps: to Q_{i_j}And during junction temperature measurement, the grid driving voltage of all the tested devices on the branch circuit is negative driving voltage. The switches between the gates and drains of all the devices under test on the branches are open. Q_{i_j}Control switch IS with series current sources_{i_j}And when the current source is closed, the other current source series switches on the branch are all opened. Measurement of Q_{i_j}The voltage drop between the source and the drain is obtained by using the preset calibrated negative pressure Q during turn-off_{i_j}Body diode at low current I_{i_j}The relationship between the injection pressure drop and the temperature can be obtained_{i_j}The temperature of (2).

The control method of the power cycle test circuit is characterized in that the power circuit I_loadThe current flows through the m parallel branches and the bypass AS in sequence, and the power supply always works in a current source mode. The measurements of the limit temperature (highest and lowest), the cooling curve and the threshold voltage are done for one device on each series branch at each power cycle test period. And completing one complete measurement of the junction temperature and the threshold voltage of n devices on the serial branch in n power cycle test periods.

In summary, the invention provides a new SiC MOSFET power cycle test circuit and a control method thereof, which can realize online measurement of threshold voltage and junction temperature in power cycle test. The circuit provided ingeniously utilizes the driving voltage and the grid driving resistor to realize small current injection, realizes the online measurement of the threshold voltage, and does not need to add an additional current source circuit. The control method for measuring the junction temperature of the SiC MOSFET device in the power cycle test by adopting the round-robin mode solves the problem that the measurement result is inaccurate due to the difference of the sequence when each device on a serial branch measures the highest/lowest junction temperature in one test period in the power cycle test of the SiC MOSFET.

Based on the technical method, the invention has the following beneficial technical effects:

(1) the invention provides a brand-new test circuit topological structure aiming at the power cycle test of the SiC MOSFET, the proposed circuit structure can realize the on-line measurement of the threshold voltage and the junction temperature of the SiC MOSFET in the power cycle test, and can better explore the failure rule of the SiC MOSFET in the power cycle test.

(2) The circuit provided by the invention ingeniously utilizes the driving voltage and the driving resistor to inject small current, and realizes the on-line monitoring of the threshold voltage in the power cycle test. The implementation is easy without additional current sources.

(2) The control method provided by the invention solves the problem that the measurement result is inaccurate due to the difference of the sequence when each device on the serial branch measures the highest/lowest junction temperature in one test period in the power cycle test of the SiC MOSFET, and can realize the accurate measurement of the limit temperature of the device in the power cycle test.

Drawings

FIG. 1 is a circuit configuration diagram of a power cycle test of a SiC MOSFET according to an exemplary embodiment;

FIG. 2 is a current path of an injection current in a threshold voltage test without a branch diode according to an embodiment;

FIG. 3 is a graph illustrating the variation of device junction temperature during a power cycle test period according to an exemplary embodiment;

FIG. 4 is a circuit operating state of the branch heating stage according to the embodiment;

FIG. 5 illustrates the circuit operating state during the bypass cooling phase according to an exemplary embodiment;

FIG. 6 is a heating switching sequence of each branch according to the embodiment;

FIG. 7 shows the circuit operating state when Q1 performs threshold voltage measurement according to the embodiment;

FIG. 8 illustrates an exemplary embodiment of a device for measuring junction temperature in a circuit operating state;

fig. 9 illustrates an exemplary embodiment of the operation of a circuit in which multiple devices in a series branch simultaneously perform junction temperature measurements;

FIG. 10 illustrates an example of a problem with measuring the highest junction temperature for different devices during a power cycle test cycle;

fig. 11 is a control method for measuring junction temperatures of devices in a serial branch in a polling manner according to an embodiment;

Detailed Description

In order to explain the present invention in more detail, the present invention will be further explained in detail with reference to the drawings and examples.

Each power cycle test cycle includes a heating phase and a cooling phase. In the heating phase, the power current I_loadThe junction temperature of the device rises when the current flows through the device; in the cooling phase, the device is in an off state and the device junction temperature drops. Fig. 1 shows a circuit structure diagram for power cycle testing of a SiC MOSFET according to the present invention. The proposed circuit arrangement comprises m test branches and an auxiliary switch bypass and a load current source branch. Each test branch includes a diode and n tested SiC MOSFET devices. n and m can be freely selected according to test requirements. The bypass is an auxiliary branch that can be used to adjust the cooling time in the power cycle. The bypass AS may be an IGBT, a relay, or the like, and fig. 1 illustrates an IGBT AS an example. I is_loadIs a load current source that provides a stable current output during power cycling for heating the device under test. A total of m test branches, each having a diode, D₁、D₂···D_m，D_iRepresenting diodes in series on branch i. There are n SiC MOSFETs under test on each test branch, thus totaling n × m devices under test. Q_{i_j}Representing the jth device under test on the ith branch. Each device under test has a driving resistor, R, connected in series on its gate_{i_j}Represents Q_{i_j}And the driving resistor is connected in series on the grid. A switch is connected between the gate and the drain of each device under test, wherein S_{i_j}Represents Q_{i_j}A switch connected between the gate and the drain. The switch may be an electronic switch or the like. A branch circuit formed by connecting a switch and a small current source in series is connected between the drain electrode and the source electrode of each tested device, wherein I_{i_j}Represents Q_{i_j}Current source in the drain and source branches, IS_{i_j}Represents Q_{i_j}Switches in the drain and source legs. The drain and the source of each tested device on the same branch are connected in sequence to form a branch.

The on-line measurement method of the threshold voltage mostly adopts a small current injection method. The gate-source voltage can be measured to obtain the threshold voltage by short-circuiting the gate and the drain and injecting a small current of a mA level. Fig. 2 illustrates a problem in measuring the threshold voltage without adding a branch series diode, taking n-2 and m-2 as an example. Fig. 2(a) and (b) show the current paths existing in branch 1 for threshold voltage measurements by the upper and lower officers using the low current injection method, respectively. At the moment, two devices of the branch circuit 1 are switched off and are in a cooling state; branch 2 with two devices on and power current I_loadFlowing through and being in a heating state. When a small current is injected on the upper or lower tube of the illustrated branch 1, there is an undesired path 2 in addition to the desired path 1, which affects the measurement of the threshold voltage. By using the scheme shown in figure 1, diodes (D) are added to each branch₁～D_m) The path 2 can be blocked, and the accuracy of the threshold voltage on-line measurement is ensured.

Fig. 3 shows the device junction temperature fluctuation during a power cycle test period. During the heating phase, the device junction temperature rises, and during the cooling phase, the device junction temperature falls. The measurement of the junction temperature of the device and the measurement of the threshold voltage are arranged in the cooling phase of the power cycle test of the device. Among them, the junction temperature measurement focuses on the highest junction temperature and the lowest junction temperature. The highest junction temperature can be measured by a cooling curve of the device and obtained by compensation by a root t method.

Figure 4 shows the circuit operating state when the bypass heating state is illustrated. In this stage Q₁～Q_nThe driving voltage being high, Q₁～Q_nIs located in the guideOn state, load current I_loadThe current flows through, and the device junction temperature rises. Electronic switch S in the branch of the figure₁～S_nAnd IS₁～IS_nRemain open.

Fig. 5 shows the circuit operating state when the bypass cooling state is illustrated. In this stage Q₁～Q_nThe drive voltage is negative gate bias, Q₁～Q_nIn the off state, load current I_loadFlowing through the other branch, the junction temperature drop of the devices of the branch is illustrated. Electronic switch S in the branch of the figure₁～S_nAnd IS₁～IS_nRemain open.

Fig. 6 shows the switching of the heating sequence of each branch of the embodiment. Each branch has heating time T₁Bypass heating time of T₂Then each branch heating time is T₁Cooling time is (n-l) T₁+T₂。T₁And T₂Can be freely selected according to the test requirements. The current is switched between each branch and the bypass, and the power supply always works in a constant current source mode, so that the potential service life influence on the service life of the power supply caused by frequent switching between constant voltage/constant current working modes is avoided. Each power cycle test period including a heating phase T₁And a cooling stage (n-1) T₁+T₂So that a complete power cycle test period T ═ nT₁+T₂。

FIG. 7 shows Q in the branch of the diagram₁The operating state of the circuit when the threshold voltage measurement is performed. The threshold voltage measurement is arranged in the cooling phase of the test device. At this time, the load current I_loadFlows through the other branch. Grid voltage of other devices on the branch circuit is kept to be negative pressure, and the branch circuit is ensured to be switched off. Q1 is used for measuring threshold voltage with positive voltage V_gAnd is generally 15V to 20V. And closes a switch connected between the gate and drain of Q1, shorting the gate and drain. Positive pressure V_gAnd kiloohm driving resistor R₁Will generate a mA level small current to be injected into Q₁Drain electrode, measurement Q₁The gate-source voltage or the drain-source voltage can be used to obtain the threshold voltage. The magnitude of the injected small current can be calculated by the following equationObtaining:

wherein I_injectThe magnitude of the small current source injected for the measurement of the threshold voltage. R_gFor the gate drive resistor at Q_{i_j}Upper corresponding resistance R_{i_j}. The adjustment of the magnitude of the injection current can be realized by adjusting the driving resistor according to the test requirement. The dotted line in fig. 7 is a path for injecting a small current for the measurement threshold.

In the power cycle test of the SiC MOSFET, junction temperature extraction is mostly carried out by utilizing the linear relation between the voltage drop and the temperature of a body diode under small current. In the on-line test, a mA-level small current is injected into a body diode of the device to be tested in the turn-off state, and the source-drain voltage V of the device to be tested is measured_SDAnd combining the relationship between the diode drop and the temperature obtained by calibration in advance to obtain the temperature of the tested device. In pair Q_{i_j}When junction temperature measurement is carried out, the grid voltage V of the junction temperature measurement device_gIs under-pressure, thereby ensuring reliable shut-off of the device under test. S_{i_j}Disconnection, IS_{i_j}Closed, at this time a small current source I_{i_j}Implantation may be achieved. Fig. 8 shows the operation of the circuit illustrating the branch Qi for junction temperature measurement. At this time, the load current I_loadThrough other open branches or bypasses, the illustrated branches being in a cooled state. Q₁～Q_nOn the switch S₁～S_nOpen, switch IS₁～IS_i-1Open, switch IS_iClosed, switch IS_i+1～IS_nAnd (5) disconnecting. Grid voltage of all devices on the branch circuit is negative pressure, and the branch circuit is guaranteed to be turned off. Q_iConnected small current source I_iTo Q_iThe body diode injects and the current path is shown as the thin dashed line in fig. 8.

But the devices under test on the same branch cannot make simultaneous junction temperature measurements. Fig. 9 illustrates the problem of junction temperature measurement performed simultaneously for all devices of the illustrated branch. At this time, the load current I_loadThrough other open branches or bypasses, shownIn the cold state. When junction temperature measurement is carried out by all device graphs on the graph branch, Q₁～Q_nOn the switch S₁～S_nOpen, switch IS₁～IS_nAnd (5) closing. Instead of injecting the body diode of each SiC MOSFET under test, each current source would then form a current path through the remaining open branch as shown by the dotted line in fig. 9. Therefore, the junction temperature measurements cannot be made simultaneously for each device under test on the same branch.

Therefore, junction temperature measurements for different devices under test on the same branch cannot be made simultaneously. It is also not advisable to sequentially measure junction temperatures of each device on the same series branch in the same power cycle test period. As shown in fig. 10, at t₁～t₂Within a time period to Q₁Making the highest junction temperature measurement at t₂～t₃Within a time period to Q₁At t, making the highest junction temperature measurement_k～t_k+1Within a time period to Q_nThe highest junction temperature measurement is made. Due to different measurement sequences of all devices on the same serial branch, the error of the highest junction temperature measured by the devices at the later positions is larger.

The round robin thermometry control strategy shown in FIG. 11 is therefore presented. And carrying out junction temperature measurement on one tested device on each series branch in each power cycle test period, and completing n tested devices Q on the series branch shown in the figure 4 by spending n power cycle test periods₁、Q₂...Q_nA junction temperature measurement. As shown in FIG. 11, at t₀～t₀+ T for the first device under test (Q) in the m test branches_{1_1}～Q_{m_1}) Junction temperature and threshold voltage measurements are made; at t₀+T～t₀+2T of the power cycle test period, for the second device under test (Q) in the m test branches_{1_2}～Q_{m_2}) Junction temperature and threshold voltage measurements are made … and so on. To t₀And when the voltage is + nT, completely measuring n tested devices on the serial branch at one time. And then returning to the first device of each branch to measure the junction temperature and the threshold voltage. I.e. a complete temperature measurement period ofn power cycle test periods. The control method solves the problem that the measurement result is inaccurate due to the difference of the sequence when each device on the serial branch measures the highest/lowest junction temperature in one test period in the power cycle test of the SiC MOSFET.

The embodiments described above are presented to enable a person having ordinary skill in the art to make and use the invention. It will be readily apparent to those skilled in the art that various modifications to the above-described embodiments may be made, and the generic principles defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications to the present invention based on the disclosure of the present invention within the protection scope of the present invention.

Claims

1. A SiC MOSFET power cycle test circuit and a control method thereof can realize the online accurate measurement of the threshold voltage and the limit temperature (the highest junction temperature and the lowest junction temperature) of the SiC MOSFET in the power cycle test.

2. The test circuit topology of claim 1, wherein: the test circuit comprises a bypass switch AS, a load current source I_loadN × m devices under test Q_{1_1}～Q_{m_n}M branch diodes D₁～D_mN × m driving resistors R_{1_1}～R_{m_n}N × m switches S_{1_1}～S_{m_n}And n x m current source series switches IS_{1_1}～IS_{m_n}Small current source I of n x m_{1_1}～I_{m_n}. The test circuit comprises m test branches, an auxiliary switch bypass and a load current source branch. Each test branch includes a diode and n tested SiC MOSFET devices. n and m can be freely selected according to test requirements. The m test branches are numbered as branch 1, and branch 2 to branch m in sequence. One diode per test branch, D_iRepresenting diodes in series on branch i. Each test branch has n tested SiC MOSFETs. Q_{i_j}Indicating the jth measured branch on the ith branchA device. Each device under test has a driving resistor, R, connected in series on its gate_{i_j}Represents Q_{i_j}And the driving resistor is connected in series on the grid. A switch is connected between the gate and the drain of each device under test, wherein S_{i_j}Represents Q_{i_j}A switch connected between the gate and the drain. A branch circuit formed by connecting a switch and a small current source in series is connected between the drain electrode and the source electrode of each tested device, wherein I_{i_j}Represents Q_{i_j}Current source in parallel drain and source branches, IS_{i_j}Represents Q_{i_j}Switches in the drain and source legs. The drain and the source of each tested device on the same branch are connected in sequence to form a branch.

3. The online threshold voltage measurement method according to claim 1, wherein: to Q_ijWhen measuring the threshold voltage, Q is measured_{i_j}Is set to a forward drive voltage, Q_{i_j}Switch S between gate and drain_{i_j}Closed, current source series switch IS_{i_j}And (5) disconnecting. The driving voltage of other tested devices on the same branch is negative driving voltage, and the switch connected between the grid and the drain and the switch connected with the current source in series are all disconnected. Q_{i_j}Positive driving voltage and dry ohm level driving resistance pair Q_{i_j}Injecting a small current in milliampere level. Measurement of Q_{i_j}The gate-source voltage or the drain-source voltage can be used to obtain the threshold voltage.

4. The device-under-test junction temperature on-line measurement method according to claim 1, wherein: to Q_{i_j}And during junction temperature measurement, the grid driving voltage of all the tested devices on the branch circuit is negative driving voltage. The switches between the gates and drains of all the devices under test on the branches are open. Q_{i_j}Control switch IS with series current sources_{i_j}And when the current source is closed, the other current source series switches on the branch are all opened. Measurement of Q_{i_j}The voltage drop between the source and the drain is obtained by using the preset calibrated negative pressure Q during turn-off_{i_j}Body diode at low current I_{i_j}The relationship between the injection pressure drop and the temperature can be obtained_{i_j}Temperature of。

5. The method of claim 1 wherein the power circuit I is a power cycle test circuit_loadThe current flows through the m parallel branches and the bypass AS in sequence, and the power supply always works in a current source mode. The measurements of the limit temperature (highest and lowest), the cooling curve and the threshold voltage are done for one device on each series branch at each power cycle test period. And completing one complete measurement of the junction temperature and the threshold voltage of n devices on the serial branch in n power cycle test periods.