Drift region gradient doped SiC-TVS device

Abstract

The invention discloses a SiC-TVS device with gradient doping in a drift region. The SiC-TVS device comprises a SiC substrate layer; the drift region is arranged on the SiC substrate layer, and the drift region comprises a first layer of SiC drift region to an nth layer of SiC drift region which are sequentially stacked from bottom to top and have different doping concentrations; the emitter region is arranged in the nth layer of SiC drift region; comprising an emitting electrode and two base electrodes which are in contact with each other, the emitting electrode is arranged on the emitting region, the two base electrodes are arranged on the nth layer of SiC drift region located on the two sides of the emitting electrode respectively, the emitting electrode and the emitting region are in ohmic contact, and the base electrodes and the nth layer of SiC drift region are in Schottky contact; and the positive electrode is arranged on the lower surface of the SiC substrate layer, and the positive electrode is in ohmic contact with the SiC substrate layer. The clamping response speed of the TVS device is improved, the response time is shortened, the maximum peak electric field intensity in the device is reduced, and the working reliability of the device is improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a SiC-TVS device with gradient doping in the drift region. Background Technology

[0002] Electronic equipment may encounter various overvoltage surges during operation, such as lightning, electrostatic discharge, and switching power supply noise. These overvoltage surges can cause electronic equipment to malfunction, operate incorrectly, or even be damaged. Transient Voltage Suppressor (TVS) is a commonly used protective device, widely used in electrical equipment, aerospace, and military equipment due to its advantages such as fast response, precise voltage control, and low leakage current. When a circuit is subjected to a transient overvoltage surge, the TVS connected in parallel to the circuit can quickly change from high impedance to low impedance, absorbing the surge power and clamping the voltage across its terminals to a predetermined value, thereby protecting the circuit.

[0003] Currently, the research and commercialization of silicon (Si)-based TVS devices are quite mature. However, technological advancements have placed higher demands on TVS devices. Silicon-based TVS devices are no longer suitable for high-temperature, high-pressure, and strong radiation environments. Compared to silicon, silicon carbide (SiC) materials possess a wider bandgap, a higher critical electric field, and higher thermal conductivity. TVS devices fabricated using SiC exhibit advantages such as low leakage current, good heat dissipation, and high voltage resistance, enabling SiC-based TVS devices to operate in harsh environments such as high pressure, high temperature, and strong radiation.

[0004] In EMP (Electromagnetic Pulse) protection applications, the rise time of EMP signals is typically on the order of nanoseconds or picoseconds, thus requiring TVS devices to have a correspondingly fast response time. For NPN punch-through SiC-TVS devices, the TVS operates when the reverse-biased N+ / P- junction is connected to the depletion region of the forward-biased P- / N+ junction. However, due to the minority carrier injection phenomenon in the forward-biased junction, the depletion propagation of the reverse-biased junction is hindered, resulting in a slower clamping response speed and an inability to achieve a nanosecond-level fast response, thus limiting the use of punch-through TVS devices in EMP protection applications. Therefore, when protecting precision devices that are sensitive to overvoltage surges, TVS devices are required to have a correspondingly fast response time. Furthermore, since the operation of punch-through TVS devices is based on the base region punch-through effect, if the peak electric field of the reverse-biased junction is too large during operation, there is a risk of premature breakdown, and it can also induce leakage current at the device edge.

[0005] Therefore, providing a TVS device that can improve clamping response speed, shorten TVS response time, and reduce the peak electric field intensity inside the device has become an urgent problem to be solved. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a SiC-TVS device with gradient doping in the drift region.

[0007] The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a SiC-TVS device with gradient doping in the drift region, the SiC-TVS device comprising: SiC substrate layer; A drift region is disposed on the SiC substrate layer. The drift region includes a first SiC drift region to an nth SiC drift region stacked sequentially from bottom to top. The doping concentrations of the first SiC drift region to the nth SiC drift region are different, and n≥2. The emission region is disposed within the nth SiC drift region and extends from the upper surface of the nth SiC drift region into the nth drift region; The device includes a negative electrode consisting of an emitter and two base electrodes that are in contact with each other. The emitter is disposed on the emitter region, and the two base electrodes are respectively disposed on the nth SiC drift region located on both sides of the emitter. The emitter and the emitter region are in ohmic contact, and the base electrodes and the nth SiC drift region are in Schottky contact. A positive electrode is disposed on the lower surface of the SiC substrate, and the positive electrode and the SiC substrate are in ohmic contact.

[0008] In one embodiment of the present invention, the SiC drift regions from the first layer to the nth layer are all of the first doping type, and the doping concentration of the SiC drift regions from the first layer to the nth layer gradually increases.

[0009] In one embodiment of the present invention, the SiC drift regions from the first layer to the nth layer are all uniformly doped.

[0010] In one embodiment of the present invention, the SiC drift regions from the first layer to the nth layer are all gradient doped with Gaussian tail structures.

[0011] In one embodiment of the present invention, the doping type of both the SiC substrate and the emitter region is the second doping type, and the doping types of the first doping type and the second doping type are opposite.

[0012] In one embodiment of the present invention, the doping concentration of the SiC substrate is lower than the doping concentration of the emitter region. In one embodiment of the present invention, the doping concentration of the nth SiC drift region is less than the doping concentration of the SiC substrate layer. In one embodiment of the present invention, the thickness of the SiC drift region in the nth layer is greater than the depth of the emitter region. In one embodiment of the present invention, 2≤n≤6. In one embodiment of the present invention, the materials of the negative electrode and the positive electrode include one of Ni and Ti.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a SiC-TVS device with a gradient-doped drift region. When the device is turned on for clamping, the peak electric field strength at its reverse-biased junction is reduced, meaning the maximum peak electric field strength inside the device is lowered. This reduces the risk of premature breakdown, decreases high-field-induced edge leakage current, and improves device reliability. Furthermore, the use of a SiC-TVS device with a gradient-doped drift region enhances the clamping response speed of the TVS device, shortening the response time and providing better protection for circuits connected in parallel with the TVS.

[0014] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0015] Figure 1 A schematic diagram of the structure of a SiC-TVS device with gradient doping in the drift region provided by the present invention; Figure 2 Dynamic response time diagrams of three different TVS devices with different structures provided by the present invention; Figure 3 Longitudinal electric field intensity diagrams for three different TVS devices with different structures provided by the present invention; Figure 4 A schematic diagram of another SiC-TVS device with gradient doping in the drift region provided by the present invention; Figure 5 Another dynamic response time diagram for the three different TVS devices provided by this invention; Figure 6 Another longitudinal electric field intensity diagram for the three different structures of TVS devices provided by this invention. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0017] Example 1 Traditional punch-through TVS devices have a response time in the microsecond range, which is too slow and too long. Traditional punch-through TVS devices cannot meet the requirement of effectively protecting the back-end circuit under EMP signals with nanosecond-level rising edges.

[0018] Please see Figure 1 , Figure 1 This is a schematic diagram of a SiC-TVS device with gradient doping in the drift region provided by the present invention. The present invention provides a SiC-TVS device with gradient doping in the drift region, which includes: SiC substrate layer 20; Drift region 30 is disposed on SiC substrate layer 20. Drift region 30 includes SiC drift region 301 to SiC drift region 30n stacked sequentially from bottom to top. The doping concentration of SiC drift region 301 to SiC drift region 30n is different, and n≥2. The emission region 40 is disposed within the nth SiC drift region 30n and extends from the upper surface of the nth SiC drift region 30n into the nth drift region 30. The negative electrode 50 includes an emitter 501 and two bases 502 that are in contact with each other. The emitter 501 is disposed on the emitter region 40, and the two bases 502 are respectively disposed on the nth SiC drift region 30n located on both sides of the emitter 501. The emitter 501 and the emitter region 40 are in ohmic contact, and the bases 502 and the nth SiC drift region 30n are in Schottky contact. The positive electrode 10 is disposed on the lower surface of the SiC substrate 20, and there is an ohmic contact between the positive electrode 10 and the SiC substrate 20.

[0019] Specifically, the SiC-TVS device in this embodiment includes a SiC substrate 20, a drift region 30, a positive electrode 10, and a negative electrode 50. The SiC substrate 20 and the drift region 30 are made of the same material, SiC. The drift region 30 includes n layers of SiC drift regions, which are stacked sequentially from the first SiC drift region 301 to the nth SiC drift region 30n on the SiC substrate 20 from bottom to top. That is, the first SiC drift region 301 is located on the SiC substrate 20, and the nth SiC drift region 30n is located on the top layer. The doping concentrations of the n SiC drift regions are different from each other. The negative electrode 50 includes a... Figure 1The device comprises a horizontally connected emitter 501 and two bases 502. The emitter 501 is located on the emitter region 40 within the nth SiC drift region 30n. The two bases 502 are located on either side of the emitter 501 and on the nth SiC drift region 30n exposed at both ends. The contact between the emitter 501 and the emitter region 40 is an ohmic contact, and the contact between the bases 502 and the drift region 30 is a Schottky contact. The positive electrode 10 is located below the SiC substrate 20, and the contact between the positive electrode 10 and the SiC substrate 20 is an ohmic contact. Compared to the uniformly doped base open-circuit structure and the base-emitter short-circuit structure, this embodiment uses a SiC-TVS device with gradient doping in the drift region. When the device is turned on for clamping, the peak electric field intensity at its reverse-biased junction is reduced, i.e., the maximum peak electric field intensity inside the device is reduced, thereby reducing the risk of premature breakdown, reducing high-field induced edge leakage current, and improving the reliability of the device. This embodiment uses a SiC-TVS device with gradient doping in the drift region, which can improve the clamping response speed of the TVS device, shorten the response time, and is more conducive to protecting the circuit connected in parallel with the TVS.

[0020] Optionally, the doping types of the first SiC drift region 301 to the nth SiC drift region 30n are the same, all being the first doping type, and the doping concentration of the first SiC drift region 301 to the nth SiC drift region 30n gradually increases, with the doping concentration of the first SiC drift region 301 being N. P1 The doping concentration of the second SiC drift region 302 is N. P2 The doping concentration up to the nth SiC drift region 30n is N Pn Then N is sufficient. Pn >N Pn-1 >...N P2 >N P1 .

[0021] This embodiment increases the doping concentration in the drift region near the emitter junction (the PN junction formed at the junction of emitter region 40 and emitter 501 is the emitter junction), thereby reducing the resistance in this region and lowering the voltage drop generated by carriers flowing through the drift region to the electrode during conduction. This reduces the forward bias amplitude of the forward bias junction, decreases the number of minority carriers injected into the base region by the forward bias junction, and thus reduces the recombination rate in the drift region. This improves the clamping response speed of the TVS device, shortens the response time, and is more beneficial for protecting circuits connected in parallel with the TVS.

[0022] In an optional embodiment, the doping concentration inside the i-th SiC drift region 30i has two forms, 1≤i≤n.

[0023] In the first form, all SiC drift regions from the first layer 301 to the nth layer 30n are uniformly doped. That is, for the i-th layer SiC drift region 30i, the doping concentration is consistent from its edge to its interior, which is uniform doping. This doping method can be achieved through epitaxial growth, i.e., uniformly doped SiC drift regions from the first layer 301 to the nth layer 30n are grown sequentially using epitaxial growth.

[0024] In the second form, all SiC drift regions from the first layer 301 to the nth layer 30n are characterized by a gradient doping structure with a Gaussian tail. The Gaussian tail structure gradually transitions from the doping concentration at the top of the i-th SiC drift region 30i to the bottom of the (i+1)-th SiC drift region 30i+1, and finally to the doping concentration within the (i+1)-th SiC drift region 30i+1. In other words, the interior of each SiC drift region is uniformly doped, while the doping concentration at both the top and bottom gradually increases. This doping method is formed through ion implantation.

[0025] Optionally, the SiC substrate 20 and the emitter region 40 are both doped with the second doping type, and the first doping type and the second doping type are opposite. That is, when the first doping type is n-type, the second doping type is p-type, and when the second doping type is n-type, the first doping type is p-type.

[0026] Optionally, the doping concentration of the SiC substrate layer 20 is lower than the doping concentration of the emitter region 40, and the doping concentration of the nth SiC drift region 30n is lower than the doping concentration of the SiC substrate layer 20.

[0027] Optionally, the thickness of the nth SiC drift region 30n is greater than the depth of the emitter region 40, i.e. Figure 1 The T shown n >T N .

[0028] Alternatively, 2 ≤ n ≤ 6.

[0029] Optionally, the materials of the negative electrode 50 and the positive electrode 10 include one of Ni and Ti.

[0030] This invention reduces the resistance of the drift region by increasing the doping concentration near the emitter junction, thereby reducing the voltage drop generated by carriers flowing through the drift region to the electrode during conduction. This reduces the forward bias amplitude of the forward bias junction, decreases the number of minority carriers injected into the base region, and consequently reduces the recombination rate in the drift region. This improves the clamping response speed of the TVS device, shortens the response time, and is more beneficial for protecting circuits connected in parallel with the TVS.

[0031] Compared to the base open-circuit structure and the base-emitter short-circuit structure with uniform doping in the drift region, the SiC-TVS with gradient doping in the drift region of this invention will reduce the peak electric field intensity at the reverse bias junction when the device is turned on to perform clamping function. That is, the maximum peak electric field intensity inside the device is reduced, thereby reducing the risk of premature breakdown, reducing the high field-induced edge leakage current, and improving the reliability of the device.

[0032] Example 2 like Figure 1 As shown, this invention provides an implementation example of a SiC-TVS device with gradient doping in the drift region, where n=2, and the specific parameters are as follows: The SiC substrate layer 20 is N-type doped with a doping concentration of 5 × 10¹⁸ cm⁻³.

[0033] The second drift region 302 is p-type doped with a doping concentration of 4 × 10⁻⁶. 16 cm -3 Thickness T2 = 1.3 μm.

[0034] Emitter region 40 is N-type doped with a doping concentration of 1 × 10⁻⁶. 19 cm -3 Its thickness T N =0.8μm, its width W N =1μm.

[0035] The first SiC drift region 301 is p-type doped with a doping concentration of 4.92 × 10⁻⁶. 15 cm -3 Its thickness T1 = 5.5 μm.

[0036] The positive electrode 10 is made of nickel, a metallic material, deposited on the lower surface of the SiC substrate 20. The contact between the metallic nickel and the lower surface of the SiC substrate 20 is an ohmic contact.

[0037] The negative electrode 50 is made of nickel, which is deposited on the upper surface of the device. The contact between the nickel metal and the upper surface of the emitter region 40 is an ohmic contact, and the contact between the nickel metal and the upper surface of the drift region 30 is a Schottky contact.

[0038] Simulation verification of the SiC-TVS device provided in this embodiment two: Based on the SiC-TVS device with the specific parameters described in Embodiment 2, simulation verification was performed using simulation software. The simulation results are as follows: Figure 2 and Figure 3 As shown. The signal source used for dynamic characteristic simulation is a 10 / 1000μs pulse signal with a peak voltage of 1000V.

[0039] Figure 2The dynamic response time diagrams are shown for a traditional TVS device with an open base structure, a traditional TVS device with a short base and emitter structure, and the SiC-TVS device provided in Embodiment 2. Figure 2 It can be seen that (1) the traditional open-base TVS device has the longest response time, reaching 2μs; (2) the traditional base and emitter short-circuit TVS device and the SiC-TVS device provided in this embodiment 2 have faster response times, both reaching the ns level; (3) the SiC-TVS device provided in this embodiment 2 has the fastest response time, reaching 2.9ns; compared with the 4.8ns response time of the traditional base and emitter short-circuit TVS device, the response time of the device provided in this embodiment 2 is shortened by 40%.

[0040] Figure 3 The diagrams show the longitudinal electric field intensity of a conventional TVS device with an open base, a conventional TVS device with a short base and emitter, and the SiC-TVS device provided in this embodiment. Figure 3 It can be seen that (1) the peak electric field of the traditional TVS device with open base and the traditional TVS device with short base and emitter reaches 1.12 × 10⁻⁶. 6 V / cm and 1.11×10 6 V / cm; (2) The peak electric field of the SiC-TVS device provided in this embodiment is 8.5×10 V / cm; 5 V / cm, compared to the other two structures, the peak electric field is reduced by 24%.

[0041] Example 3 like Figure 4 As shown, this invention also provides an embodiment of a SiC-TVS device with gradient doping in the drift region, where n=4, and the specific parameters are as follows: The first SiC drift region P1 is p-type doped with a doping concentration of 1.3 × 10⁻⁶. 14 cm -3 Thickness T p1 It is 1.5μm.

[0042] The second SiC drift region P2 is p-type doped with a doping concentration of 6.9 × 10⁻⁶. 14 cm -3 Thickness T p2 It is 1.5μm.

[0043] The third SiC drift region P3 is p-type doped with a doping concentration of 3.7 × 10⁻⁶. 15 cm -3 Thickness T p3 It is 1.5μm.

[0044] The fourth SiC drift region P4 is p-type doped with a doping concentration of 2 × 10⁻⁶. 16 cm -3 Thickness T p4 It is 2.3 μm.

[0045] Simulation verification of the SiC-TVS device provided in this embodiment three: Based on the SiC-TVS device with the specific parameters described in Embodiment 3, simulation verification was performed using simulation software. The simulation results are as follows: Figure 5 and Figure 6 As shown. The signal source used for dynamic characteristic simulation is a 10 / 1000μs pulse signal with a peak voltage of 1000V.

[0046] Depend on Figure 5 As can be seen, the SiC-TVS device provided in this embodiment 3 has the fastest response speed, with a response time of 2.3ns. Compared with the response speed of the traditional TVS device with open base structure, it is an order of magnitude improvement. Compared with the 4.8ns response time of the traditional TVS device with short base and emitter structure, the response time of the SiC-TVS device provided in this embodiment 3 is shortened by 48%.

[0047] Depend on Figure 6 It can be seen that the SiC-TVS device provided in this embodiment has the smallest peak electric field strength of 6.83 × 10⁻⁶. 5 V / cm. The peak electric field of traditional TVS devices with open base and short base / emitter structures reaches 1.12 × 10⁻⁶ V / cm. 6 V / cm and 1.11×10 6 V / cm. The peak electric field of the SiC-TVS device provided in this embodiment is reduced by 38%.

[0048] It should be noted that the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention.

[0049] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0050] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings and the disclosure in carrying out the claimed invention. In the description of the invention, the word "comprising" does not exclude other components or steps, "a" or "an" does not exclude a plurality, and "a plurality" means two or more, unless otherwise explicitly specified. Furthermore, while different embodiments may describe certain measures, this does not mean that these measures cannot be combined to produce good results.

[0051] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0052] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0053] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A SiC-TVS device with gradient doping in the drift region, characterized in that, The SiC-TVS device includes: SiC substrate layer; A drift region is disposed on the SiC substrate layer. The drift region includes a first SiC drift region to an nth SiC drift region stacked sequentially from bottom to top. The doping concentrations of the first SiC drift region to the nth SiC drift region are different, and n≥2. The emission region is disposed within the nth SiC drift region and extends from the upper surface of the nth SiC drift region into the nth drift region; The device includes a negative electrode consisting of an emitter and two base electrodes that are in contact with each other. The emitter is disposed on the emitter region, and the two base electrodes are respectively disposed on the nth SiC drift region located on both sides of the emitter. The emitter and the emitter region are in ohmic contact, and the base electrodes and the nth SiC drift region are in Schottky contact. A positive electrode is disposed on the lower surface of the SiC substrate, and the positive electrode and the SiC substrate are in ohmic contact.

2. The SiC-TVS device according to claim 1, characterized in that, The SiC drift regions from the first layer to the nth layer are all of the first doping type, and the doping concentration of the SiC drift regions from the first layer to the nth layer gradually increases.

3. The SiC-TVS device according to claim 2, characterized in that, The SiC drift regions from the first layer to the nth layer are all uniformly doped.

4. The SiC-TVS device according to claim 2, characterized in that, The SiC drift regions from the first layer to the nth layer are all gradient doped with Gaussian tail structures.

5. The SiC-TVS device according to claim 2, characterized in that, Both the SiC substrate and the emitter region are doped with the second doping type, and the first doping type and the second doping type are opposite in type.

6. The SiC-TVS device according to claim 5, characterized in that, The doping concentration of the SiC substrate is lower than that of the emitter region.

7. The SiC-TVS device according to claim 6, characterized in that, The doping concentration of the SiC drift region in the nth layer is less than the doping concentration of the SiC substrate layer.

8. The SiC-TVS device according to claim 1, characterized in that, The thickness of the SiC drift region in the nth layer is greater than the depth of the emitter region.

9. The SiC-TVS device according to claim 1, characterized in that, 2≤n≤6。 10. The SiC-TVS device according to claim 1, characterized in that, The materials of the negative electrode and the positive electrode include one of Ni and Ti.

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