Method and system for repairing threshold drift of silicon carbide MOS tube based on dynamic electric field

Abstract

The present invention discloses a method and system for repairing threshold drift of silicon carbide MOS tube based on dynamic electric field, the method comprising: real-time monitoring of threshold voltage of SiC MOSFET; judging whether threshold voltage drift occurs, and if drift occurs, starting dynamic electric field repair operation: connecting power supply with adjustable voltage output to gate of SiC MOSFET, and constructing control circuit to accurately control timing and amplitude of power supply output voltage; adjusting parameters of dynamic electric field, including electric field strength, frequency and action time, according to the drift of threshold voltage, until threshold voltage does not drift. The present invention solves the problem that silicon carbide MOSFET is prone to threshold drift, lacks stability and affects device performance, reliability and life, and provides real-time repair for dynamic aging and degradation of device.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and in particular to a method and system for repairing threshold drift of a silicon carbide MOS tube based on a dynamic electric field. Background Art

[0002] Silicon carbide MOSFET has been widely used in the field of power electronics due to its high withstand voltage, low on-resistance, high frequency and other characteristics. However, due to the interface defects and trap effects of the gate oxide layer, SiC MOSFET is prone to threshold drift problems in long-term operation, which seriously affects the performance and reliability of the device and limits its promotion in some applications with high stability requirements. Traditional silicon carbide MOSFET threshold drift prevention methods often focus on various optimization measures at the design level and the construction of corresponding protection mechanisms, but these methods have limitations and cannot provide real-time repair for dynamic aging and degradation of devices.

[0003] Existing research has comprehensively analyzed the causes of threshold voltage instability and reviewed various solutions, but most of them are theoretical discussions and general method summaries, lacking specific repair methods with strong pertinence and operability. Specifically, the defects in the current solutions for SiC MOSFET threshold drift stability include:

[0004] 1. Methods to improve the quality of the oxide layer, such as optimizing the oxidation process, can suppress the threshold voltage drift at the design level, but these processes have high requirements, are difficult to implement, and will increase manufacturing costs. Even if the quality of the oxide layer is optimized, it is difficult to completely eliminate the threshold voltage drift. Because intrinsic factors such as the high interface state density at the interface between silicon carbide and silicon dioxide still exist, the degree of drift can only be reduced to a certain extent, which is a static adjustment and difficult to adapt to dynamic changes.

[0005] 2. The special gate drive circuit designed to solve the threshold voltage drift problem will greatly increase the complexity of the entire system. This not only increases the difficulty of design and debugging, but also may reduce the reliability of the system. Once the circuit fails, the difficulty of troubleshooting and repairing the problem will also increase accordingly. It is also a static architecture that lacks flexibility and cannot be flexibly changed according to the real-time status of the device.

[0006] 3. The monitoring and protection circuit mainly takes protective measures when it detects that the threshold voltage drift exceeds a certain limit, but this method is passive protection and cannot actively repair the threshold voltage drift that has occurred. For application scenarios with extremely high reliability requirements and no performance degradation is allowed, it may not meet the needs. In addition, this method requires additional sensors, detection circuits, and data processing units, which will increase the cost, volume, and power consumption of the system. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] Based on the above problems, the present invention provides a method and system for repairing threshold drift of silicon carbide MOS tubes based on dynamic electric field, which solves the problem that silicon carbide MOSFET is prone to threshold drift and lacks stability, thus affecting device performance, reliability and life, and provides real-time repair for dynamic aging and degradation of devices.

[0009] (II) Technical solution

[0010] Based on the above technical problems, the present invention provides a method for repairing threshold drift of silicon carbide MOS tube based on dynamic electric field, comprising:

[0011] S1, real-time monitoring of the threshold voltage of SiC MOSFET;

[0012] S2, determine whether the threshold voltage drifts, if so, proceed to step S3, otherwise, return to step S1;

[0013] S3, starting the dynamic electric field repair operation: connecting a power supply with adjustable voltage output to the gate of the SiC MOSFET, and constructing a control circuit to control the timing and amplitude of the output voltage of the power supply;

[0014] S4, according to the drift of threshold voltage Δ V th , adjust the parameters of the dynamic electric field, including the electric field strength, frequency and action time, until the threshold voltage does not drift.

[0015] Furthermore, the S1 includes: connecting a threshold voltage monitoring circuit between the gate and source of the SiC MOSFET, and using the collected real-time voltage value as V gs (t), calculate the real-time value of the threshold voltage V th (t);

[0016] I d =β ( V gs -V th ) 2 (1+ λV ds )

[0017] In the formula, I d is the drain current; β is the transconductance parameter; V th is the threshold voltage;V gs is the gate-source voltage; V ds is the drain-source voltage; l is the channel length modulation factor.

[0018] Furthermore, S2 includes: monitoring the threshold voltage in real time V th (t) comparing with a preset threshold voltage standard range; if it is not within the preset threshold voltage standard range, determining that the threshold voltage has drifted, and entering step S3; otherwise, determining that the threshold voltage has not drifted, and returning to step S1 to continue monitoring the threshold voltage.

[0019] Further, in S4, the parameters of the dynamic electric field are adjusted, including the electric field strength, frequency and action time, including: if the threshold voltage drift Δ V th Too large, indicating that the current electric field strength is insufficient to adjust the trap charge density. Increase the electric field strength according to the following formula E s :

[0020] ;

[0021] If the interaction between carriers and traps is found to be poor, adjust the frequency according to the following formula f :

[0022] ;

[0023] Adjust the action time according to the following formula and the actual threshold voltage stabilization time: t :

[0024] ;

[0025] in, is the rate of change of the trapped charge density, k 1 is a proportionality constant related to the material properties and the nature of the trap, k 2 is a coefficient related to the oxide layer structure and carrier scattering mechanism, x eff is the effective motion range of carriers in the oxide layer, m is the carrier mobility, V th0 is the initial threshold voltage, V th∞ is the threshold voltage that stabilizes after a sufficient period of time, t is the time constant.

[0026] Furthermore, the actual threshold voltage stabilization time is determined according to the following method: defining the threshold voltage stability Δ V stab , when | V th (t)- V th∞ |≤Δ V stab When the threshold voltage is considered to be stable, the action time is t That’s the effective repair time.

[0027] The present invention also discloses a system for repairing threshold drift of silicon carbide MOS tube based on dynamic electric field, comprising:

[0028] at least one processor; and at least one memory in communication with the processor, wherein:

[0029] The memory stores program instructions that can be executed by the processor, and the processor can execute the method by calling the program instructions.

[0030] The present invention also discloses a non-transitory computer-readable storage medium, wherein the non-transitory computer-readable storage medium stores computer instructions, wherein the computer instructions enable the computer to execute the method.

[0031] (III) Beneficial effects

[0032] The above technical solution of the present invention has the following advantages:

[0033] (1) The present invention measures the initial threshold voltage of the silicon carbide MOSFET device to be repaired, determines the appropriate dynamic electric field strength, frequency and action time parameters according to its drift condition, and places the device between the electrodes of an electric field generating device to apply a dynamic electric field for repair. According to the drift amount of the threshold voltage, the electric field parameters are dynamically adjusted using the formula for the relationship between the threshold voltage change and the electric field strength, the formula for the rate of change of the trap charge density, the formula for the relationship between the frequency and the carrier movement, and the formula for the change of the threshold voltage over time, to ensure the repair effect, until the threshold voltage is stabilized within a preset range, and then the application of the dynamic electric field is stopped, so as to achieve effective repair of the instability of the threshold drift of the silicon carbide MOSFET and ensure the stability of the threshold voltage of the silicon carbide MOSFET, thereby achieving real-time repair of the dynamic aging and degradation of the device;

[0034] (2) The present invention effectively repairs the instability of the threshold drift of silicon carbide MOSFET based on the dynamic electric field, which can effectively solve the threshold drift problem of silicon carbide MOSFET and overcome many defects existing in existing solutions, such as passive protection is difficult to repair, poor adaptability, and high cost. It is of great significance to improve the stability and reliability of silicon carbide MOSFET in the fields of power electronics, and provides a strong guarantee for its wider and more stable application. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0036] Figure 1 This is a flow chart of a method for repairing threshold drift of a silicon carbide MOS tube based on a dynamic electric field according to an embodiment of the present invention;

[0037] Figure 2 Schematic diagram of a SiC NMOSFET device according to an embodiment of the present invention;

[0038] Figure 3 FIG. 4 is a defect distribution space diagram of the SiC NMOSFET according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0040] The embodiment of the present invention is a method and system for repairing threshold drift of silicon carbide MOS tube based on dynamic electric field, including real-time monitoring of threshold voltage of SiC MOSFET, judging whether threshold voltage drift occurs, dynamic electric field repair operation and dynamic electric field parameter adjustment, such as Figure 1 As shown, Figure 2 Taking SiC NMOSFET as an example, the following steps are included:

[0041] S1. Real-time monitoring of the threshold voltage of SiC MOSFET: A threshold voltage monitoring circuit is connected between the gate and source of SiC MOSFET. The real-time voltage value collected is used as V gs (t), calculate the real-time value of the threshold voltage V th (t);

[0042] A threshold voltage monitoring circuit is connected between the gate and source of the SiC MOSFET. Assume that the real-time voltage value collected by the monitoring circuit is V gs(t), according to the threshold voltage characteristic formula of MOSFET:

[0043] I d =β ( V gs -V th ) 2 (1+ λV ds ) (1)

[0044] In the formula, I d is the drain current; β is the transconductance parameter; V th is the threshold voltage; V gs is the gate-source voltage; V ds is the drain-source voltage; l is the channel length modulation coefficient. I d , β , V ds and l Under these conditions, by measuring V gs (t) Indirectly obtain the real-time value of the threshold voltage V th (t).

[0045] S2, determine whether the threshold voltage drifts, if so, proceed to step S3, otherwise, return to step S1; specifically, the threshold voltage monitored in real time V th (t) comparing with a preset threshold voltage standard range; if the threshold voltage is not within the preset threshold voltage standard range, determining that the threshold voltage has drifted, and proceeding to step S3; otherwise, determining that the threshold voltage has not drifted, and returning to step S1 to continue monitoring the threshold voltage;

[0046] The preset threshold voltage standard range is [ V thmin ，V thmax ]. The threshold voltage monitored in real time V th (t) is compared with this range. If V th (t)< V thmin or V th (t)> V thmax, then it is determined that the threshold voltage has drifted; if V thmin ≤ V th (t)≤ V thmax , it is determined that the threshold voltage has not drifted.

[0047] cause V th The microscopic essential factors of drift are mainly SiC / SiO2 interface traps, oxide traps, fixed charges and mobile ions, such as Figure 3 As shown in Figure 2, the traps include interface traps, near-interface traps, and oxide traps. However, interface traps and near-interface traps are considered to be the main causes of V th The main cause of drift. V th The quantitative relationship between drift and trap-type defects is as follows:

[0048] (2)

[0049] (3)

[0050] In the formula, f ms is the work function difference, X sic is the electron affinity of SiC, E g is the bandgap width, Q ot is the oxide layer charge, Q it is the interface state charge, n i is the intrinsic carrier concentration, e s is the dielectric constant of SiC, C ox is the unit oxide capacitance, N A is the doping concentration in the channel region, q is the electron charge, k is the Boltzmann constant, T is the Kelvin temperature.

[0051] Interface state trap charge ( Q it ) The calculation formula is related to the interface state density and the Fermi level position, and is usually expressed as:

[0052] (4)

[0053] In the formula, Dit ( E ) is the interface state density, which represents the number of interface states per unit area and per unit energy; f ( E ) is the Fermi distribution function, which represents the probability of an interface state being occupied and is given by:

[0054] (5)

[0055] in, E F is the Fermi level, E 1 and E 2 represents the interface state density D it ( E ) is within the valid range of .

[0056] Interface state density D it ( E ) is often extracted through capacitance-voltage (CV) characteristic measurements, based on differences in flat-band voltage drift or high-frequency / quasi-static capacitance, using the formula:

[0057] (6)

[0058] In the formula, Δ V is the measured voltage change, Δ E is the energy range corresponding to the interface state charge (related to the semiconductor Fermi level or the conduction band bottom position).

[0059] Oxide layer trapped charge Q ot It can be expressed as:

[0060] (7)

[0061] In the formula, N ot ( x ) is the trap state density in the oxide layer, i.e., the number of traps per unit volume; f ot ( x ) is the trap filling factor, indicating the depth x The probability that the trap state is filled (range 0 to 1); t ox is the oxide layer thickness.

[0062] In addition, the physical mechanism followed by the oxide layer traps in SiC MOSFETs causing device instability is the charge trapping tunneling model. According to the tunneling theory of quantum mechanics, the tunneling probability is related to factors such as the shape and height of the barrier and the energy of the electron. According to the WKB (Wentzel-Kramers-Brillouin) approximation of quantum mechanics, the tunneling probability can be expressed as:

[0063] (8)

[0064] in, E total is the electron energy, m ＊ is the electron mass, h is the reduced Planck constant, f b is the barrier height, F ox is the oxide layer electric field, e is the electron charge. This formula shows that the tunneling probability is related to the electric field strength and the potential barrier height. As the electric field strength increases, the tunneling probability increases exponentially; the higher the potential barrier height, the lower the tunneling probability.

[0065] The charge capture probability is related to the properties of the traps (such as trap density, capture cross section) and the carrier flux. Assume that the carrier (electron or hole) velocity is v , the concentration is n , then the carrier flux is:

[0066] f = nv (9)

[0067] The probability of a carrier being trapped per unit time P c It can be expressed as:

[0068] P c = s t v N t (10)

[0069] in, s t is the capture cross section of the trap, which represents the effective area of ​​the trap to capture carriers; N t is the trap density, i.e. the number of traps per unit volume. This means that the higher the trap density, the larger the capture cross section, and the faster the carrier velocity, the higher the charge capture probability.

[0070] In the charge trapping tunneling model, it is necessary to consider the process in which the carrier first tunnels to a certain area and then is captured by the trap. Assume that the carrier tunneling probability is T FN , the charge capture probability is P c , then the total oxide layer charge capture tunneling probability P total is the product of the two:

[0071] (11)

[0072] In summary, the threshold drift of SiC MOSFET is mainly affected by the interface state charge and the oxide layer charge, and the electric field is the key factor in the process of capturing / releasing the charge by the interface state trap and the oxide layer trap. Therefore, applying a dynamic electric field to repair the threshold voltage drift problem of SiC MOSFET has a feasible theoretical basis.

[0073] S3, start the dynamic electric field repair operation:

[0074] When it is determined that the threshold voltage has drifted, the dynamic electric field repair operation is initiated: a power supply with adjustable voltage output is connected to the gate of the SiC MOSFET, and a control circuit is built to accurately control the timing and amplitude of the power supply output voltage to achieve the generation of a dynamic electric field.

[0075] S4, according to the drift of threshold voltage Δ V th , adjust the parameters of the dynamic electric field, including the electric field strength, frequency and action time, until the threshold voltage does not drift, that is, the threshold voltage returns to the preset threshold voltage standard range.

[0076] In the dynamic electric field repair process, the role of the electric field strength is to promote the redistribution of charges in the trap, thereby changing the threshold voltage. Under the action of the dynamic electric field, the rate of change of the trap charge density is proportional to the electric field strength, expressed as:

[0077] (12)

[0078] in, is the rate of change of the trapped charge density, E s is the electric field strength, k 1 is a proportionality constant related to the material properties and the nature of the trap.

[0079] Since the dynamic electric field is alternating, the frequency f It will affect the distance that the carriers move in one cycle, and the speed of the carriers in the dynamic electric field is related to the electric field strength. Es and carrier mobility m about, that is v = μE s In addition, the effective range of carrier movement in the oxide layer is x eff It will affect the probability of interaction between carriers and traps, thus affecting the repair effect. This range is related to the frequency and is defined as

[0080] (13)

[0081] in, k 2 It is a coefficient related to the oxide layer structure and carrier scattering mechanism.

[0082] At the same time, the change of threshold voltage is a time-varying process, and under the action of dynamic electric field, the change of threshold voltage conforms to the exponential law:

[0083] (14)

[0084] in V th (t) Yes t The threshold voltage at the moment; V th0 is the initial threshold voltage; V th∞ It is the threshold voltage that stabilizes after a sufficient period of time; t It is a time constant and is related to factors such as material properties, electric field strength and frequency.

[0085] when t →∞, V th (t) → V th∞ In the actual repair process, a threshold voltage stability Δ V stab . When | V th (t)- V th∞ |≤Δ V stab When the threshold voltage is considered to be stable, the action time is t This is the effective repair time. It can be determined experimentally under different electric field strengths and frequencies. t and Δ V stab , thereby establishing a quantitative relationship between action time and repair effect.

[0086] Therefore, the threshold voltage change of the device is monitored in real time during the repair process. When the threshold voltage is stable within the preset range, the dynamic electric field is stopped. If it is found that the threshold voltage has not reached the expected stable state, that is, according to the drift of the threshold voltage Δ V th , further adjust the parameters of the dynamic electric field. For example, if Δ V th If it is too large, it means that the current electric field strength is insufficient to adjust the trap charge density. It can be appropriately increased according to formula (12). E s If the interaction between carriers and traps is not good, the frequency can be adjusted by referring to formula (13). f At the same time, according to formula (14) and the actual threshold voltage stabilization time, adjust the action time t Through continuous monitoring and dynamic adjustment based on formulas, it is ensured that the threshold voltage can be stabilized within an acceptable range, thus effectively repairing the instability of the threshold drift of SiC MOSFET.

[0087] The threshold voltage is continuously monitored, and when the threshold voltage returns to the preset standard range, the dynamic electric field repair operation is stopped. During the entire repair process, the threshold voltage is continuously monitored according to the method of step S1. V th ( t ) ,like V thmin ≤ V th (t)≤ V thmax , the dynamic electric field repair operation is stopped, and the silicon carbide MOSFET returns to normal working state.

[0088] Finally, it should be noted that the above method can be converted into software program instructions, which can be implemented by running a system including a processor and a memory, or by computer instructions stored in a non-transitory computer-readable storage medium. The above integrated unit implemented in the form of a software functional unit can be stored in a computer-readable storage medium. The above software functional unit is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor to perform some steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk and other media that can store program code.

[0089] In summary, the above method and system for repairing threshold drift of silicon carbide MOS tube based on dynamic electric field have the following beneficial effects:

[0090] (1) The present invention measures the initial threshold voltage of the silicon carbide MOSFET device to be repaired, determines the appropriate dynamic electric field strength, frequency and action time parameters according to its drift condition, and places the device between the electrodes of an electric field generating device to apply a dynamic electric field for repair. According to the drift amount of the threshold voltage, the electric field parameters are dynamically adjusted using the formula for the relationship between the threshold voltage change and the electric field strength, the formula for the rate of change of the trap charge density, the formula for the relationship between the frequency and the carrier movement, and the formula for the change of the threshold voltage over time, to ensure the repair effect, until the threshold voltage is stabilized within a preset range, and then the application of the dynamic electric field is stopped, so as to achieve effective repair of the instability of the threshold drift of the silicon carbide MOSFET and ensure the stability of the threshold voltage of the silicon carbide MOSFET, thereby achieving real-time repair of the dynamic aging and degradation of the device;

[0091] (2) The present invention effectively repairs the instability of the threshold drift of silicon carbide MOSFET based on the dynamic electric field, which can effectively solve the threshold drift problem of silicon carbide MOSFET and overcome many defects existing in existing solutions, such as passive protection is difficult to repair, poor adaptability, and high cost. It is of great significance to improve the stability and reliability of silicon carbide MOSFET in the fields of power electronics, and provides a strong guarantee for its wider and more stable application.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the embodiments of the present invention are described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations shall fall within the scope defined by the appended claims.

Claims

1. A method for repairing threshold drift of silicon carbide MOS tube based on dynamic electric field, The invention is characterized by comprising: S1, real-time monitoring of the threshold voltage of SiC MOSFET; S2, determine whether the threshold voltage drifts, if so, proceed to step S3, otherwise, return to step S1; S3, start the dynamic electric field repair operation: connect a power supply with adjustable voltage output to the gate of the SiC MOSFET, and construct a control circuit to control the timing and amplitude of the output voltage of the power supply; S4, according to the drift amount Δ of the threshold voltage V th , adjusting the parameters of the dynamic electric field, including the electric field strength, frequency and action time, until the threshold voltage does not drift; If the threshold voltage drift Δ V th If the electric field strength exceeds the set threshold, it indicates that the current electric field strength is insufficient to adjust the trap charge density. The electric field strength is increased according to the following formula. Es : ; If the interaction between carriers and traps is found to be poor, adjust the frequency according to the following formula f : ; Adjust the action time according to the following formula and the actual threshold voltage stabilization time: t : ;in, is the rate of change of the trapped charge density, k 1 is a proportionality constant related to the material properties and the trap properties, k 2 is a coefficient related to the oxide layer structure and carrier scattering mechanism, x eff is the effective motion range of carriers in the oxide layer, μ is the carrier mobility, V th0 is the initial threshold voltage, V th∞ is the threshold voltage that stabilizes after a sufficient period of time, is a time constant, and the actual threshold voltage stabilization time is determined according to the following method: Define the threshold voltage stability Δ V stab , when | V th (t)- V th∞ |≤Δ V stab When the threshold voltage is considered to be stable, the action time is t That’s the effective repair time.

2. The method for repairing threshold drift of silicon carbide MOS tube based on dynamic electric field according to claim 1, characterized in that: The S1 includes: connecting a threshold voltage monitoring circuit between the gate and source of the SiC MOSFET, and using the collected real-time voltage value as Vg (t), calculate the real-time value of the threshold voltage V th (t); In the formula, I d is the drain current; β is the transconductance parameter; V th is the threshold voltage; V gs is the gate-source voltage; V ds is the drain-source voltage; λ is the channel length modulation factor.

3. The method for repairing threshold drift of silicon carbide MOS tube based on dynamic electric field according to claim 1, characterized in that: The S2 includes: monitoring the threshold voltage in real time V th ( t ) is compared with a preset threshold voltage standard range. If it is not within the preset threshold voltage standard range, it is determined that the threshold voltage has drifted and the process goes to step S3. Otherwise, it is determined that the threshold voltage has not drifted and the process goes back to step S1 to continue monitoring the threshold voltage.

4. A system for repairing threshold drift of silicon carbide MOS tubes based on dynamic electric field, The invention is characterized by comprising: at least one processor; and at least one memory in communication with the processor, wherein: The memory stores program instructions that can be executed by the processor, and the processor can execute the method according to any one of claims 1 to 3 by calling the program instructions.

5. A non-transitory computer-readable storage medium, characterized in that: The non-transitory computer-readable storage medium stores computer instructions, which enable the computer to execute the method according to any one of claims 1 to 3.

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