A method and circuit for online monitoring of junction temperature

Abstract

This invention provides a method and circuit for online junction temperature monitoring, belonging to the field of HTRB testing technology for MOSFETs. It includes a high-voltage bias blocking circuit and a monitoring circuit; by closing multiple switches, the high-voltage bias blocking circuit and the monitoring circuit are controlled to conduct independently; when the high-voltage bias blocking circuit is conducting, the high-voltage bias on the MOSFET under test is cut off, and the monitoring circuit is activated within a few hundred microseconds to introduce test current for junction temperature monitoring. This invention fills the gap in online junction temperature testing technology for HTRB testing in the market; it ensures the accuracy of junction temperature extraction; it can safely monitor the sample junction temperature within 1ms of high-voltage bias cutoff, ensuring the timeliness of junction temperature testing; it isolates the high-voltage bias of the device, only detecting the voltage drop of several hundred millivolts when the test current flows through the device, ensuring the accuracy of junction temperature extraction.

Description

Technical Field

[0001] This invention relates to the field of HTRB testing technology for MOSFETs, and more particularly to a method and circuit for online monitoring of junction temperature during HTRB testing of MOSFETs. Background Technology

[0002] High-temperature reverse bias (HTRB) testing is used to assess the lifetime of MOSFET chips. HTRB testing mainly focuses on the migration of ionic contaminants related to production under temperature and field conditions. This migration increases surface charge, leakage current, and threshold voltage degradation. The difference in the coefficient of thermal expansion (CTEs) of the MOSFET assembly process and assembly materials has a significant impact on the integrity of the passivation layer, making the device susceptible to external contaminants and causing increased leakage current.

[0003] The principle of HTRB testing is as follows: Figure 1 As shown in the figure, the MOSFET is the sample under test, placed in a high-temperature environment, and 0V or negative gate bias is applied to keep the sample in a blocking state. The constant voltage source provides a bias voltage of ≥ 0.8 VDSmax. During the test, the leakage current of the sample is monitored in real time through the sampling resistor. For a detailed description of the test, refer to IEC 60747-8.

[0004] HTRB is a targeted test that focuses on failures in and around the chip. It requires the chip to reach its maximum junction temperature, but the case temperature can be lower than the maximum junction temperature.

[0005] At high temperatures, device leakage current increases, leading to device heating and consequently raising the chip junction temperature. If the test environment temperature is not set properly, the device junction temperature may exceed the maximum junction temperature during HTRB testing, resulting in failures with unspecified failure mechanisms and affecting the accuracy of the test. Accurately measuring the chip junction temperature during HTRB testing and confirming that the chip is aging at a reasonable junction temperature is a key technical challenge of HTRB testing.

[0006] The existing technology solution is to calculate the sample power based on the voltage drop and leakage current across the sample, and then substitute these values ​​into the following formula to calculate the chip junction temperature:

[0007]

[0008]

[0009] In the formula,

[0010] R ja The steady-state junction-to-ring thermal resistance is a known quantity;

[0011] R jc For steady-state junction-shell thermal resistance;

[0012] T a The ambient temperature;

[0013] T c Shell temperature;

[0014] P This represents real-time power.

[0015] The existing technology has at least the following shortcomings:

[0016] 1. HTRB is usually performed in a high-temperature chamber with air cooling. The heat dissipation environment differs significantly from the standard thermal resistance test conditions. Therefore, substituting the junction-case or junction-ring thermal resistance under standard test conditions into the formula to calculate the chip junction temperature will introduce a large error. Summary of the Invention

[0017] To address the technical problems existing in the prior art, this invention provides a method and circuit for online monitoring of junction temperature, including a high-voltage bias blocking circuit and a monitoring circuit. The two ends of the monitoring circuit are respectively connected to the collector and emitter of the MOSFET under test. The high-voltage bias blocking circuit includes a first switch, a second switch, a third switch, and a fourth switch. The high-voltage bias blocking circuit and the monitoring circuit are controlled to conduct by closing or opening the first, second, third, and fourth switches. When the high-voltage bias blocking circuit is on, the high-voltage bias applied by the HTRB test is clamped in the low-voltage range, and the high-voltage bias on the MOSFET under test is cut off. After cutting off the high-voltage bias on the MOSFET under test, the monitoring circuit is turned on within a few hundred microseconds to introduce the test circuit. The current is used for junction temperature monitoring. The monitoring circuit includes a first MOSFET, a first Schottky diode, a second Schottky diode, a third Schottky diode, a Zener diode, a first resistor, a second resistor, and a first capacitor. The first and second Schottky diodes are connected in parallel, and then connected in series with the circuit formed by the parallel connection of the Zener diode and the second resistor. One end of the series circuit, point C, is grounded, and the other end, point D, is connected to the emitter of the first MOSFET. Points D and C are respectively connected to the differential probe of an oscilloscope. The collector of the first MOSFET is connected to the third Schottky diode. One end of the first capacitor is connected to the gate of the first MOSFET, and the other end of the first capacitor is grounded. The gate of the first MOSFET is also connected in series with the first resistor and then connected to a constant voltage source. The circuit for online junction temperature monitoring provided by this invention fills the gap in online junction temperature testing technology for HTRB tests in the market. It guides operators to adjust the test environment temperature based on the measured junction temperature, ensuring that the sample is not subjected to overstress (exceeding the maximum junction temperature) conditions, thus preventing additional failure mechanisms and test failure. By calculating the junction temperature through online measured electrical parameters, the accuracy of junction temperature extraction is guaranteed. Through a fast relay combined with a test protection circuit, the high-voltage bias on the sample is quickly cut off during the HTRB test before the test current source is introduced. With appropriate device selection, safe monitoring of the sample junction temperature can be achieved within 1ms of high-voltage bias cutoff, ensuring the timeliness of the junction temperature test. This invention uses a high-voltage bias blocking circuit to isolate the high-voltage bias of the device, only detecting the voltage drop of several hundred millivolts when the test current flows through the device, ensuring the accuracy of junction temperature extraction.

[0018] This invention provides a circuit for online monitoring of junction temperature, including a high-voltage bias blocking circuit and a monitoring circuit; the two ends of the monitoring circuit are respectively connected to the collector and emitter of the MOSFET under test; the high-voltage bias blocking circuit includes a first switch, a second switch, a third switch and a fourth switch; by closing or opening the first switch, the second switch, the third switch and the fourth switch, the high-voltage bias blocking circuit and the monitoring circuit are controlled to be turned on respectively.

[0019] When the high-voltage bias blocking circuit is turned on, the high-voltage bias applied by the HTRB test is clamped in the low-voltage range, and the high-voltage bias on the MOSFET under test is cut off. After the high-voltage bias on the MOSFET under test is cut off, the monitoring circuit is turned on within a hundred microseconds to introduce the test current and monitor the junction temperature.

[0020] The monitoring circuit includes a first MOSFET, a first Schottky diode, a second Schottky diode, a third Schottky diode, a Zener diode, a first resistor, a second resistor, and a first capacitor. The first and second Schottky diodes are connected in parallel, and then connected in series with the circuit formed by the parallel connection of the Zener diode and the second resistor. One end of the series circuit, point C, is grounded, and the other end, point D, is connected to the emitter of the first MOSFET. Points D and C are respectively connected to the differential probe of an oscilloscope. The collector of the first MOSFET is connected to the third Schottky diode. One end of the first capacitor is connected to the gate of the first MOSFET, and the other end of the first capacitor is grounded. The gate of the first MOSFET is also connected in series with the first resistor and then connected to a constant voltage source.

[0021] Preferably, the collector of the MOSFET under test is connected to a first switch, and the emitter of the MOSFET under test is connected to a second switch; a third switch is also connected between the first switch and the collector of the MOSFET under test, and a fourth switch is also connected between the second switch and the emitter of the MOSFET under test; when both the first and second switches are closed and both the third and fourth switches are open, the high-voltage bias blocking circuit is turned on, and the monitoring circuit is turned off; when both the first and second switches are open and both the third and fourth switches are closed, the monitoring circuit is turned on, and the high-voltage bias blocking circuit is turned off.

[0022] Preferably, the collector of the MOSFET under test is also connected to the first terminal of the first switch, the second terminal of the first switch is connected to the first constant current source, and the emitter of the MOSFET under test is also connected to the first terminal of the second switch; the first terminal of the third switch is also connected between the first terminal of the first switch and the collector of the MOSFET under test, the first terminal of the fourth switch is also connected between the first terminal of the second switch and the emitter of the MOSFET under test, and a second constant current source is provided between the second terminals of the third switch and the second terminals of the fourth switch.

[0023] Preferably, a sampling resistor is also provided between the second switch and the MOSFET to be tested.

[0024] Preferably, the second terminal of the first switch is connected to the positive terminal of the first constant current source, and the second terminal of the second switch and the negative terminal of the first constant current source are both grounded.

[0025] Preferably, the second terminal of the third switch and the negative terminal of the second constant current source are both grounded.

[0026] Preferably, a 0V or negative bias gate voltage is applied to the MOSFET under test.

[0027] Preferably, an oscilloscope is used for measurement in the monitoring loop.

[0028] Preferably, the breakdown voltage of the Zener diode is less than 8V.

[0029] This invention provides a method for online monitoring of junction temperature, employing any of the above-described online junction temperature monitoring circuits, comprising the following steps:

[0030] Step 1: Disconnect the third and fourth switches, and close the first and second switches to put the MOSFET sample under test in a high-voltage bias state. The gate voltage of the first MOSFET is limited to the threshold voltage, the Zener diode is broken down, and the voltage at point D monitored is the breakdown voltage of the Zener diode.

[0031] Step 2: Disconnect the first and second switches, and close the third and fourth switches to enter the junction temperature test stage of the MOSFET sample under test. The third Schottky diode reverse blocks, and the first MOSFET turns on. The voltage at point D monitored is the voltage drop of the MOSFET sample under test under the test current. Based on this voltage drop value, the chip junction temperature is calculated.

[0032] Preferably, the voltage at point D is introduced into a voltage follower circuit, the output of the voltage follower circuit is sent to an optocoupler isolation circuit, the output of the optocoupler isolation circuit is used as a comparator input, and the comparator output is connected to a controller.

[0033] The signal flow in step 2 is as follows: When the controller receives the junction temperature test command, it first sends a control signal, which is electrically isolated through the optocoupler isolation circuit, and controls the relay K1 to open. At this time, the voltage in the sample MOSFET output capacitor discharges through the monitoring circuit. When the voltage at point D drops to <0.5V, the comparator output reverses and is input to the controller. The controller sends a control signal, which is electrically isolated through the optocoupler isolation circuit, and controls the relay K2 to close, switching the circuit to the junction temperature test circuit and entering the junction temperature test stage.

[0034] This invention derives the chip junction temperature based on electrical methods, using the forward voltage drop of the MOSFET's body diode under low current as a temperature-sensitive parameter, and calibrates the equivalent relationship between forward voltage and junction temperature.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects:

[0036] 1. The circuit for online junction temperature monitoring provided by this invention fills the gap in the market for online junction temperature testing technology in HTRB testing;

[0037] 2. This invention can guide operators to adjust the test environment temperature according to the measured junction temperature, ensuring that the sample is tested under non-overstress (exceeding the maximum junction temperature) conditions. It solves the defects of junction temperature monitoring in HTRB tests and avoids test failure caused by excessive junction temperature during the test leading to additional failure mechanisms.

[0038] 3. This invention calculates the junction temperature by measuring electrical parameters online, which solves the problem of large errors in the existing technology of deriving the junction temperature by shell temperature or ambient temperature, and ensures the accuracy of the junction temperature extraction;

[0039] 4. This invention uses a fast relay combined with a monitoring circuit to quickly cut off the high voltage bias on the sample during HTRB testing and then introduce the test current source. With proper device selection, this invention can safely monitor the sample junction temperature within 1ms of the high voltage bias being cut off, ensuring the timeliness of the junction temperature test.

[0040] 5. This invention uses a high-voltage bias blocking circuit to isolate the high-voltage bias of the device, and only detects the voltage drop of several hundred millivolts when the test current flows through the device, thus ensuring the accuracy of junction temperature extraction. Attached Figure Description

[0041] Figure 1 This is the schematic diagram of the HTRB experimental circuit.

[0042] Figure 2 This is a schematic diagram of the switching state of the high-voltage bias blocking circuit when it is turned on in an online junction temperature monitoring circuit according to an embodiment of the present invention.

[0043] Figure 3 This is a schematic diagram of the switching state of the monitoring loop when it is turned on in an online junction temperature monitoring circuit according to an embodiment of the present invention.

[0044] Figure 4 This is a schematic diagram of a monitoring loop circuit according to an embodiment of the present invention;

[0045] Figure 5 This is a schematic diagram of the voltage change at point D in an online junction temperature monitoring circuit according to an embodiment of the present invention during the high voltage bias stage and the junction temperature test stage. K1 includes a first switch K1-1 and a second switch K1-2, and K2 includes a third switch K2-1 and a fourth switch K2-2.

[0046] In the diagram, K1-1 is the first switch; K1-2 is the second switch; K2-1 is the third switch; and K2-2 is the fourth switch. K1-1 and K1-2 are switches for spring relays or high-frequency relays K1, and K2-1 and K2-2 are switches for spring relays or high-frequency relays K2. Detailed Implementation

[0047] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0048] This invention provides a circuit for online monitoring of junction temperature, including a high-voltage bias blocking circuit and a monitoring circuit; the two ends of the monitoring circuit are respectively connected to the collector and emitter of the MOSFET under test; the connection point between the monitoring circuit and the collector of the MOSFET under test is point A; the high-voltage bias blocking circuit includes a first switch, a second switch, a third switch, and a fourth switch; by closing or opening the first switch, the second switch, the third switch, and the fourth switch, the high-voltage bias blocking circuit and the monitoring circuit are controlled to be turned on respectively.

[0049] When the high-voltage bias blocking circuit is turned on, the high-voltage bias applied by the HTRB test is clamped in the low-voltage range, and the high-voltage bias on the MOSFET under test is cut off. After the high-voltage bias on the MOSFET under test is cut off, the monitoring circuit is turned on within a hundred microseconds to introduce the test current and monitor the junction temperature.

[0050] The monitoring circuit includes a first MOSFET, a first Schottky diode, a second Schottky diode, a third Schottky diode, a Zener diode, a first resistor, a second resistor, and a first capacitor. The first and second Schottky diodes are connected in parallel, and then connected in series with the circuit formed by the parallel connection of the Zener diode and the second resistor. One end of the series circuit, point C, is grounded, and the other end, point D, is connected to the emitter of the first MOSFET. Point D is the voltage monitoring point. Points D and C are respectively connected to the differential probe of an oscilloscope. The collector of the first MOSFET is connected to the third Schottky diode. One end of the first capacitor is connected to the gate of the first MOSFET, and the other end of the first capacitor is grounded. The gate of the first MOSFET is also connected in series with the first resistor and then connected to a constant voltage source. HTRB testing is usually performed in a high-temperature chamber. The test circuit and constant current power supply module need to be placed outside the chamber. According to the temperature characteristics of the MOSFET internal diode, a voltage drop of tens of millivolts can introduce a chip junction temperature deviation of more than 10°C. Therefore, in order to accurately measure the voltage drop of the MOSFET internal diode, the MOSFET internal diode voltage drop sampling four-wire method is used for measurement. The two measurement terminals A and C of the test circuit are as close as possible to the collector-emitter of the MOSFET sample under test.

[0051] In the experiment, the bias voltage of the sample under the blocking state is as high as hundreds of volts or even thousands of volts, while the forward voltage drop of the body diode under the test current is only hundreds of millivolts. Measuring low voltage in the voltage range of hundreds of volts has very low accuracy. This paper proposes a method to isolate the high voltage bias of the device and only detect the voltage drop of hundreds of millivolts when the test current flows through the device, thus ensuring the accuracy of junction temperature extraction.

[0052] The first switch K1-1 and the second switch K1-2 are switches for spring relays or high-frequency relays K1, and the third switch K2-1 and the fourth switch K2-2 are switches for spring relays or high-frequency relays K2. The spring relays or high-frequency relays have an operating time of less than 100 microseconds, which meets the requirements of the present invention for rapid switching.

[0053] According to a specific embodiment of the present invention, the collector of the MOSFET under test is connected to a first switch, and the emitter of the MOSFET under test is connected to a second switch; a third switch is also connected between the first switch and the collector of the MOSFET under test, and a fourth switch is also connected between the second switch and the emitter of the MOSFET under test, with the connection point between the fourth switch and the emitter of the MOSFET under test being point B; when both the first and second switches are closed and both the third and fourth switches are open, the high-voltage bias blocking circuit is turned on, and the monitoring circuit is turned off; when both the first and second switches are open and both the third and fourth switches are closed, the monitoring circuit is turned on, and the high-voltage bias blocking circuit is turned off.

[0054] According to a specific embodiment of the present invention, the collector of the MOSFET under test is also connected to the first terminal of the first switch, the second terminal of the first switch is connected to the first constant current source, and the emitter of the MOSFET under test is also connected to the first terminal of the second switch; the first terminal of the third switch is also connected between the first terminal of the first switch and the collector of the MOSFET under test, and the first terminal of the fourth switch is also connected between the first terminal of the second switch and the emitter of the MOSFET under test; a second constant current source is provided between the second terminals of the third switch and the second terminals of the fourth switch.

[0055] According to one specific embodiment of the present invention, a sampling resistor is further provided between the second switch and the MOSFET to be tested.

[0056] According to a specific embodiment of the present invention, the second terminal of the first switch is connected to the positive terminal of the first constant current source, and the second terminal of the second switch and the negative terminal of the first constant current source are both grounded.

[0057] According to a specific embodiment of the present invention, the second terminal of the third switch and the negative terminal of the second constant current source are both grounded.

[0058] According to one specific embodiment of the present invention, a 0V or negative bias gate voltage is applied to the MOSFET under test.

[0059] According to one specific embodiment of the present invention, an oscilloscope is used for measurement in the monitoring loop.

[0060] According to one specific embodiment of the present invention, the breakdown voltage of the Zener diode is less than 8V.

[0061] This invention provides a method for online monitoring of junction temperature, employing any of the above-described online junction temperature monitoring circuits, comprising the following steps:

[0062] Step 1: Disconnect the third and fourth switches, and close the first and second switches to put the MOSFET sample under test in a high-voltage bias state. The gate voltage of the first MOSFET is limited to the threshold voltage. The first MOSFET shares most of the bias high voltage, and the Zener diode is broken down. The voltage at point D monitored is the breakdown voltage of the Zener diode.

[0063] Step 2: Disconnect the first and second switches, and close the third and fourth switches to enter the junction temperature test stage of the MOSFET sample under test. The test current is injected into the MOSFET sample under test from point B. Since D4 reverse blocks, the test current will not flow through the test protection circuit. The third Schottky diode reverse blocks, and the first MOSFET is turned on. The voltage at point D monitored is the voltage drop of the MOSFET sample under test under the test current. Based on this voltage drop value, the chip junction temperature is calculated.

[0064] According to a specific embodiment of the present invention, the voltage at point D is introduced into a voltage follower circuit, the output of which is sent to an optocoupler isolation circuit. The output of the optocoupler isolation circuit serves as a comparator input, and the comparator output is connected to a controller. This method ensures that the high-voltage bias on the sample is removed before introducing the test current. The voltage at point D is also used to confirm the on / off timing of relays K1 and K2.

[0065] The signal flow in step 2 is as follows: When the controller receives the junction temperature test command, it first sends a control signal, which is electrically isolated through the optocoupler isolation circuit, and controls the relay K1 to open. At this time, the voltage in the sample MOSFET output capacitor discharges through the monitoring circuit. When the voltage at point D drops to <0.5V, the comparator output reverses and is input to the controller. The controller sends a control signal, which is electrically isolated through the optocoupler isolation circuit, and controls the relay K2 to close, switching the circuit to the junction temperature test circuit and entering the junction temperature test stage.

[0066] Example 1

[0067] According to a specific embodiment of the present invention, the circuit for online monitoring of junction temperature will be described in detail.

[0068] This invention provides a circuit for online monitoring of junction temperature, including a high-voltage bias blocking circuit and a monitoring circuit; the two ends of the monitoring circuit are respectively connected to the collector and emitter of the MOSFET under test; the connection point between the monitoring circuit and the collector of the MOSFET under test is point A; the high-voltage bias blocking circuit includes a first switch, a second switch, a third switch, and a fourth switch; by closing or opening the first switch, the second switch, the third switch, and the fourth switch, the high-voltage bias blocking circuit and the monitoring circuit are controlled to be turned on respectively.

[0069] When the high-voltage bias blocking circuit is turned on, the high-voltage bias applied by the HTRB test is clamped in the low-voltage range, and the high-voltage bias on the MOSFET under test is cut off. After the high-voltage bias on the MOSFET under test is cut off, the monitoring circuit is turned on within a hundred microseconds to introduce the test current and monitor the junction temperature.

[0070] The monitoring circuit includes a first MOSFET, a first Schottky diode, a second Schottky diode, a third Schottky diode, a Zener diode, a first resistor, a second resistor, and a first capacitor. The first and second Schottky diodes are connected in parallel, and then connected in series with the circuit formed by the parallel connection of the Zener diode and the second resistor. One end of the series circuit, point C, is grounded, and the other end, point D, is connected to the emitter of the first MOSFET. Point D is the voltage monitoring point. Points D and C are respectively connected to the differential probe of an oscilloscope. The collector of the first MOSFET is connected to the third Schottky diode. One end of the first capacitor is connected to the gate of the first MOSFET, and the other end of the first capacitor is grounded. The gate of the first MOSFET is also connected in series with the first resistor and then connected to a constant voltage source.

[0071] Example 2

[0072] According to a specific embodiment of the present invention, the circuit for online monitoring of junction temperature will be described in detail.

[0073] This invention provides a circuit for online monitoring of junction temperature, including a high-voltage bias blocking circuit and a monitoring circuit; the two ends of the monitoring circuit are respectively connected to the collector and emitter of the MOSFET under test; the connection point between the monitoring circuit and the collector of the MOSFET under test is point A; the high-voltage bias blocking circuit includes a first switch, a second switch, a third switch, and a fourth switch; by closing or opening the first switch, the second switch, the third switch, and the fourth switch, the high-voltage bias blocking circuit and the monitoring circuit are controlled to be turned on respectively.

[0074] When the high-voltage bias blocking circuit is turned on, the high-voltage bias applied by the HTRB test is clamped in the low-voltage range, and the high-voltage bias on the MOSFET under test is cut off. After the high-voltage bias on the MOSFET under test is cut off, the monitoring circuit is turned on within a hundred microseconds to introduce the test current and monitor the junction temperature.

[0075] The monitoring circuit includes a first MOSFET, a first Schottky diode, a second Schottky diode, a third Schottky diode, a Zener diode, a first resistor, a second resistor, and a first capacitor. The first and second Schottky diodes are connected in parallel, and then connected in series with the circuit formed by the parallel connection of the Zener diode and the second resistor. One end of the series circuit, point C, is grounded, and the other end, point D, is connected to the emitter of the first MOSFET. Point D is the voltage monitoring point. Points D and C are respectively connected to the differential probe of an oscilloscope. The collector of the first MOSFET is connected to the third Schottky diode. One end of the first capacitor is connected to the gate of the first MOSFET, and the other end of the first capacitor is grounded. The gate of the first MOSFET is also connected in series with the first resistor and then connected to a constant voltage source.

[0076] The collector of the MOSFET under test is connected to a first switch, and the emitter of the MOSFET under test is connected to a second switch. A third switch is also connected between the first switch and the collector of the MOSFET under test, and a fourth switch is also connected between the second switch and the emitter of the MOSFET under test. When both the first and second switches are closed and both the third and fourth switches are open, the high-voltage bias blocking circuit is turned on, and the monitoring circuit is turned off. When both the first and second switches are open and both the third and fourth switches are closed, the monitoring circuit is turned on, and the high-voltage bias blocking circuit is turned off.

[0077] The collector of the MOSFET under test is also connected to the first terminal of the first switch, the second terminal of the first switch is connected to the first constant current source, and the emitter of the MOSFET under test is also connected to the first terminal of the second switch. The first terminal of the third switch is also connected between the first terminal of the first switch and the collector of the MOSFET under test, and the first terminal of the fourth switch is also connected between the first terminal of the second switch and the emitter of the MOSFET under test. A second constant current source is provided between the second terminals of the third switch and the second terminals of the fourth switch.

[0078] A sampling resistor is also set between the second switch and the MOSFET to be tested.

[0079] The second terminal of the first switch is connected to the positive terminal of the first constant current source, and the second terminal of the second switch and the negative terminal of the first constant current source are both grounded.

[0080] The second terminal of the third switch and the negative terminal of the second constant current source are both grounded.

[0081] Apply a 0V or negative bias gate voltage to the MOSFET under test.

[0082] An oscilloscope was used to perform measurements in the monitoring loop.

[0083] The breakdown voltage of the Zener diode is less than 8V.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A circuit for online monitoring of junction temperature, characterized in that, It includes a high-voltage bias blocking circuit and a monitoring circuit; the two ends of the monitoring circuit are respectively connected to the collector and emitter of the MOSFET under test; the high-voltage bias blocking circuit includes a first switch, a second switch, a third switch and a fourth switch; by closing or opening the first switch, the second switch, the third switch and the fourth switch, the high-voltage bias blocking circuit and the monitoring circuit are controlled to be turned on respectively. When the high-voltage bias blocking circuit is turned on, the high-voltage bias applied by the HTRB test is clamped in the low-voltage range, and the high-voltage bias on the MOSFET under test is cut off. After the high-voltage bias on the MOSFET under test is cut off, the monitoring circuit is turned on within a hundred microseconds to introduce the test current and monitor the junction temperature. The monitoring circuit includes a first MOSFET, a first Schottky diode, a second Schottky diode, a third Schottky diode, a Zener diode, a first resistor, a second resistor, and a first capacitor. The first and second Schottky diodes are connected in parallel, and then connected in series with the circuit formed by the parallel connection of the Zener diode and the second resistor. One end (point C) of the series circuit is grounded, and the other end (point D) is connected to the emitter of the first MOSFET. Points D and C are respectively connected to the differential probe of an oscilloscope. The collector of the first MOSFET is connected to the third Schottky diode. One end of the first capacitor is connected to the gate of the first MOSFET, and the other end of the first capacitor is grounded. The gate of the first MOSFET is also connected in series with the first resistor and then connected to a constant voltage source. The collector of the MOSFET under test is connected to a first switch, and the emitter of the MOSFET under test is connected to a second switch. A third switch is also connected between the first switch and the collector of the MOSFET under test, and a fourth switch is also connected between the second switch and the emitter of the MOSFET under test. When both the first and second switches are closed and both the third and fourth switches are open, the high-voltage bias blocking circuit is turned on, and the monitoring circuit is turned off. When both the first and second switches are open and both the third and fourth switches are closed, the monitoring circuit is turned on, and the high-voltage bias blocking circuit is turned off.

2. The circuit for online junction temperature monitoring according to claim 1, characterized in that, The collector of the MOSFET under test is also connected to the first terminal of the first switch, the second terminal of the first switch is connected to the first constant current source, and the emitter of the MOSFET under test is also connected to the first terminal of the second switch. The first terminal of the third switch is also connected between the first terminal of the first switch and the collector of the MOSFET under test, and the first terminal of the fourth switch is also connected between the first terminal of the second switch and the emitter of the MOSFET under test. A second constant current source is provided between the second terminals of the third switch and the second terminals of the fourth switch.

3. The circuit for online junction temperature monitoring according to claim 2, characterized in that, A sampling resistor is also set between the second switch and the MOSFET to be tested.

4. The circuit for online junction temperature monitoring according to claim 2, characterized in that, The second terminal of the first switch is connected to the positive terminal of the first constant current source, and the second terminal of the second switch and the negative terminal of the first constant current source are both grounded.

5. The circuit for online junction temperature monitoring according to claim 2, characterized in that, The second terminal of the third switch and the negative terminal of the second constant current source are both grounded.

6. The circuit for online junction temperature monitoring according to claim 1, characterized in that, Apply a 0V or negative bias gate voltage to the MOSFET under test.

7. The circuit for online junction temperature monitoring according to claim 1, characterized in that, The breakdown voltage of the Zener diode is less than 8V.

8. A method for online monitoring of junction temperature, characterized in that, The circuit for online junction temperature monitoring according to any one of claims 1-7 includes the following steps: Step 1: Disconnect the third and fourth switches, and close the first and second switches to put the MOSFET sample under test in a high-voltage bias state. The gate voltage of the first MOSFET is limited to the threshold voltage, the Zener diode is broken down, and the voltage at point D monitored is the breakdown voltage of the Zener diode. Step 2: Disconnect the first and second switches, and close the third and fourth switches to enter the junction temperature test stage of the MOSFET sample under test. The third Schottky diode reverse blocks, and the first MOSFET turns on. The voltage at point D monitored is the voltage drop of the MOSFET sample under test under the test current. Based on this voltage drop value, the chip junction temperature is calculated.

9. The method for online monitoring of junction temperature according to claim 8, characterized in that, The voltage at point D is introduced into a voltage follower circuit, the output of which is sent to an optocoupler isolation circuit. The output of the optocoupler isolation circuit is used as a comparator input, and the comparator output is connected to a controller.

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