Bidirectional TVS diode and preparation method thereof

Abstract

The invention discloses a bidirectional TVS diode and a preparation method thereof, the bidirectional TVS diode comprises a first N-type layer, a second N-type layer and a P-type layer located between the first N-type layer and the second N-type layer, a first depletion region is formed at the interface position of the P-type layer and the first N-type layer, a second depletion region is formed at the interface position of the P-type layer and the second N-type layer, and the first depletion region and the second depletion region are located at the interface position of the P-type layer and the second N-type layer. A neutral region is formed between the first depletion region and the second depletion region, and when the voltage difference between the two ends of the bidirectional TVS diode is smaller than the breakdown voltage of the bidirectional TVS diode, the distance between the interface of the first depletion region and the neutral region and the surface of the side, away from the P-type layer, of the first N-type layer is 18-22 microns. And the distance between the interface of the second depletion region and the neutral region and the surface of one side, far away from the P-type layer, of the second N-type region is 18-22 microns. The invention provides a bidirectional TVS (Transient Voltage Suppressor) diode with a deep junction structure, which can realize more excellent transient surge protection capability.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, specifically relating to a bidirectional TVS diode and its fabrication method. Background Technology

[0002] Transient voltage suppressor (TVS) diodes are widely used, high-efficiency circuit protection devices. Their main characteristic is that, under reverse application conditions, when subjected to a high-energy, large-pulse voltage, they can clamp the voltage to a predetermined level, effectively protecting delicate components in electronic circuits from damage caused by various surge pulses. Bidirectional TVS diodes are one type of widely used TVS diode, capable of operating under both forward and reverse voltages, exhibiting the same avalanche breakdown and clamping characteristics in both directions.

[0003] Existing bidirectional TVS diodes fabricated using single-crystal bipolar processes employ N-type single-crystal substrates with a thickness exceeding 300 μm as the raw material. These diodes cannot generate conductivity modulation effects during current conduction, resulting in high resistance and high clamping voltage at breakdown. Furthermore, the high resistance at breakdown leads to severe heating in the bidirectional TVS diode, reducing its surge withstand capability.

[0004] Therefore, to address the aforementioned technical problems, it is necessary to provide a bidirectional TVS diode and its fabrication method. Summary of the Invention

[0005] The purpose of this invention is to provide a bidirectional TVS diode and its fabrication method, which can improve the performance of the bidirectional TVS diode.

[0006] To achieve the above objectives, an embodiment of the present invention provides the following technical solution:

[0007] A bidirectional TVS diode includes a first N-type layer and a second N-type layer, and a P-type layer located between the first N-type layer and the second N-type layer. A first depletion region is formed at the interface between the P-type layer and the first N-type layer, and a second depletion region is formed at the interface between the P-type layer and the second N-type layer. A neutral region is formed between the first depletion region and the second depletion region. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage, the distance between the interface between the first depletion region and the neutral region and the surface of the first N-type layer away from the P-type layer is 18 μm to 22 μm, and the distance between the interface between the second depletion region and the neutral region and the surface of the second N-type region away from the P-type layer is 18 μm to 22 μm.

[0008] In one embodiment, when the voltage difference across the bidirectional TVS diode is greater than or equal to its breakdown voltage, electrons in the first N-type layer or the second N-type layer enter the neutral region, exciting the conductivity modulation effect in the neutral region.

[0009] In one embodiment, the sum of the thicknesses of the first N-type layer, the second N-type layer, and the P-type layer is 180 μm to 220 μm.

[0010] In one embodiment, the sum of the thicknesses of the first N-type layer, the second N-type layer, and the P-type layer is 220 μm. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage, the ratio of the neutral region to the sum of the thicknesses of the first N-type layer, the second N-type layer, and the P-type layer is 0.80 to 0.83.

[0011] In one embodiment, the doping concentration of the first N-type layer is greater than the doping concentration of the P-type layer, and the doping concentration of the second N-type layer is greater than the doping concentration of the P-type layer.

[0012] In one embodiment, the operating voltage of the bidirectional TVS diode is 12V~15V, and the breakdown voltage of the bidirectional TVS diode is greater than the operating voltage of the bidirectional TVS diode.

[0013] In one embodiment, the bidirectional TVS diode has a mesa structure, and the resistivity of the P-type layer is 0.045 Ω·cm to 0.05 Ω·cm; or,

[0014] The bidirectional TVS diode has a planar structure, and the resistivity of the P-type layer is 0.035 Ω·cm ~ 0.04 Ω·cm.

[0015] Another embodiment of the present invention provides the following technical solution:

[0016] A method for fabricating a bidirectional TVS diode, the method comprising the following steps:

[0017] A P-type substrate is provided, the P-type substrate including a first surface and a second surface disposed opposite to each other;

[0018] A first N-type layer and a second N-type layer are diffused and formed on the first surface and the second surface, respectively. A P-type layer is formed between the first N-type layer and the second N-type layer. A first depletion region is formed at the interface between the P-type layer and the first N-type layer. A second depletion region is formed at the interface between the P-type layer and the second N-type layer. A neutral region is formed between the first depletion region and the second depletion region. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage, the distance between the interface between the first depletion region and the neutral region and the first surface is 18 μm to 22 μm, and the distance between the interface between the second depletion region and the neutral region and the second surface is 18 μm to 22 μm.

[0019] In one embodiment, a first N-type layer and a second N-type layer are formed by pre-diffusion and secondary diffusion on a first surface and a second surface, respectively, wherein the diffusion temperature in the secondary diffusion is greater than or equal to 1250°C.

[0020] In one embodiment, in the step of forming a first N-type layer and a second N-type layer by diffusion on a first surface and a second surface, respectively, liquid phosphorus oxychloride is used as a dopant source.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The bidirectional TVS diode of the present invention has a deep junction structure, which further reduces the thickness of the neutral region when the voltage difference across the bidirectional TVS diode is less than its breakdown voltage. This makes it easier to excite the conductivity modulation effect of the neutral region when the voltage difference across its terminals is greater than or equal to its breakdown voltage, and it still has excellent surge protection capability when its size is small. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the bidirectional TVS diode in Embodiment 1 of the present invention.

[0025] Explanation of key figure labels:

[0026] 101 - P-type layer, 201 - first N-type layer, 202 - second layer, 301 - first passivation layer, 302 - second passivation layer, 401 - first electrode, 402 - second electrode. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0028] The present invention discloses a bidirectional TVS diode, which includes a first N-type layer and a second N-type layer, and a P-type layer located between the first N-type layer and the second N-type layer. A first depletion region is formed at the interface between the P-type layer and the first N-type layer, and a second depletion region is formed at the interface between the P-type layer and the second N-type layer. A neutral region is formed between the first depletion region and the second depletion region. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage, the distance between the interface of the first depletion region and the neutral region and the surface of the first N-type layer away from the P-type layer is 18μm to 22μm, and the distance between the interface of the second depletion region and the neutral region and the surface of the second N-type layer away from the P-type layer is 18μm to 22μm.

[0029] The present invention also discloses a method for manufacturing a bidirectional TVS diode, which includes the following steps:

[0030] Provide a P-type substrate, which includes a first surface and a second surface arranged oppositely;

[0031] Diffuse and form a first N-type layer and a second N-type layer on the first surface and the second surface respectively. A P-type layer is formed between the first N-type layer and the second N-type layer. A first depletion region is formed at the interface between the P-type layer and the first N-type layer, and a second depletion region is formed at the interface between the P-type layer and the second N-type layer. A neutral region is formed between the first depletion region and the second depletion region. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage, the distance between the interface of the first depletion region and the neutral region and the first surface is 18μm to 22μm, and the distance between the interface of the second depletion region and the neutral region and the second surface is 18μm to 22μm.

[0032] The following further illustrates the present invention with specific examples.

[0033] Example 1:

[0034] Refer Figure 1 As shown, the bidirectional TVS diode in this embodiment includes a first N-type layer 201 and a second N-type layer 202, and a P-type layer 101 located between the first N-type layer 201 and the second N-type layer 202. A first depletion region 11 is formed at the interface between the P-type layer 101 and the first N-type layer 201, and a second depletion region 12 is formed at the interface between the P-type layer 101 and the second N-type layer 202. A neutral region 13 is formed between the first depletion region 11 and the second depletion region 12. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage, the distance between the interface of the first depletion region 11 and the neutral region 13 and the surface of the first N-type layer 201 away from the P-type layer 101 is 18μm to 22μm, and the distance between the interface of the second depletion region 12 and the neutral region 13 and the surface of the second N-type layer 202 away from the P-type layer 101 is 18μm to 22μm.

[0035] Furthermore, when the voltage difference across the bidirectional TVS diode is greater than or equal to its breakdown voltage, electrons in the first N-type layer 201 or the second N-type layer 202 enter the neutral region, exciting the conductivity modulation effect in the neutral region.

[0036] Specifically, the bidirectional TVS diode in this embodiment is integrated into the circuit for overvoltage protection. When a surge pulse voltage occurs in the circuit and reaches its breakdown voltage, the bidirectional TVS diode undergoes avalanche breakdown. Under the action of the electric field, a large number of electrons in the first N-type layer or the second N-type layer will be injected into the neutral region. Since the bidirectional TVS diode needs to maintain electrical neutrality throughout, the same number and concentration of holes will accumulate in the neutral region. When the electron injection reaches the same level as the hole concentration in the neutral region, the additional accumulated hole concentration is equivalent to the hole doping concentration in the neutral region, resulting in a decrease in the resistance of the neutral region and a significant increase in the conductivity, thus achieving conduction. This shunts and clamps the surge voltage, thereby protecting other components in the circuit from damage by the instantaneous surge pulse voltage.

[0037] More specifically, to achieve conductivity modulation in the neutral region, the concentration of minority carriers (i.e., electrons) accumulated in the neutral region must reach a certain value. The accumulation of minority carriers is directly related to their lifetime and the time it takes for them to drift through the neutral region. Therefore, to excite the conductivity modulation effect in the neutral region under the influence of an electric field, it is necessary to increase the lifetime of minority carriers in the neutral region while reducing the time it takes for them to drift through it. Specific control methods are as follows:

[0038] 1. By reducing the doping concentration of the P-type layer, i.e. controlling the resistivity of the P-type layer, the number of recombination centers of minority carriers in the neutral region can be controlled. The fewer the recombination centers, the longer the minority carrier lifetime.

[0039] 2. Reduce the time it takes for minority carriers to drift through the neutral region by decreasing the thickness of the neutral region.

[0040] It should be understood that a bidirectional TVS diode can be viewed as consisting of two "back-to-back" PN junctions. In a PN junction, when the P-type and N-type layers are in contact, a depletion region is formed at the interface between the P-type and N-type layers due to the diffusion and drift of charge carriers (electrons and holes). This depletion region is affected by the applied voltage. For a bidirectional TVS diode, when no voltage is applied, or when the voltage difference across it is less than its breakdown voltage (equivalent to an open circuit), the thickness of the neutral region is the same as in the initial state.

[0041] Compared to conventional bidirectional TVS diodes, the junction depth of the bidirectional TVS diode in this embodiment (i.e., the distance between the interface of the first depletion region and the neutral region and the surface of the first N-type layer away from the P-type layer, or the distance between the interface of the second depletion region and the neutral region and the surface of the second N-type region away from the P-type layer) is deeper, resulting in a thinner neutral region in the initial state.

[0042] Furthermore, in this embodiment, the sum of the thicknesses of the first N-type layer 201, the second N-type layer 202, and the P-type layer 101 is 180μm~220μm.

[0043] It should be understood that when the junction depth reaches its limit, the smaller the sum of the thicknesses of the first N-type layer, the second N-type layer, and the P-type layer, the smaller the thickness of the neutral region in the initial state. Then, when the voltage difference across it is greater than or equal to its breakdown voltage, it is easier to excite the conductivity modulation effect of the neutral region. However, if the sum of the thicknesses of the first N-type layer, the second N-type layer, and the P-type layer is too small, it will be detrimental to the fabrication of bidirectional TVS diodes and they are prone to breakage during the production process.

[0044] Preferably, in this embodiment, the sum of the thicknesses of the first N-type layer 201, the second N-type layer 202, and the P-type layer 101 is 220 μm. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage (i.e., the initial state), the ratio of the neutral region 13 to the sum of the thicknesses of the first N-type layer 201, the second N-type layer 202, and the P-type layer 101 is 0.80 to 0.83.

[0045] Furthermore, the doping concentration of the first N-type layer 201 is greater than that of the P-type layer 101, and the doping concentration of the second N-type layer 202 is greater than that of the P-type layer 101.

[0046] When a bidirectional TVS diode is integrated into a circuit for circuit protection, one PN junction is forward-biased and the other is reverse-biased. In this embodiment, the first N-type layer is electrically connected to the positive terminal of the power supply, and the second N-type layer is electrically connected to the negative terminal of the power supply. At this time, the thickness of the depletion region (first depletion region) in the reverse-biased PN junction satisfies the formula... , where N A For the acceptor doping concentration of the P-type layer, N D V represents the donor doping concentration of the first N-type layer. bi For the built-in potential, ϵ s V is the dielectric constant, q is the electron charge, and V is the dielectric constant. RThis is the reverse bias voltage. As shown in the formula above, when the concentration difference across the junction in a reverse-biased PN junction is large, the thickness of the depletion region is dominated by the side with the lower doping concentration. Therefore, in this embodiment, by increasing the concentrations of the first N-type layer and the second N-type layer, the concentration difference across the PN junction is increased. The thickness of the first depletion region is dominated by the P-type region, causing a transient surge pulse in the circuit. When the voltage difference across the bidirectional TVS diode exceeds its breakdown voltage, the first depletion region will further extend into the neutral region, further reducing the thickness of the neutral region and promoting the excitation of the conductivity modulation effect in the neutral region. Simultaneously, in a forward-biased PN junction, electrons in the second N-type layer will enter the neutral region under the influence of the electric field. Due to the increased doping concentration of the second N-type layer, the number of electrons injected into the neutral region will also increase, significantly promoting the excitation of the conductivity modulation effect in the neutral region.

[0047] It should be understood that the bidirectional TVS diode in this embodiment also includes:

[0048] The electrodes include a first electrode 401 disposed on the surface of the first N-type diffusion region 201 and a second electrode 402 disposed on the surface of the second N-type diffusion region 202;

[0049] The passivation layer includes a first passivation layer 301 disposed on the outer periphery of the first N-type diffusion region 201 and a second passivation layer 302 disposed on the outer periphery of the second N-type diffusion region 202.

[0050] The fabrication method of the bidirectional TVS diode in this embodiment includes the following steps:

[0051] S1. A P-type substrate is provided, the P-type substrate including a first surface and a second surface disposed opposite to each other.

[0052] In this embodiment, a P-type single-crystal substrate is directly used as the raw material to fabricate a bidirectional TVS diode. Compared with an N-type single-crystal substrate, under the same doping concentration, the minority carrier lifetime and minority carrier diffusion length of the P-type single-crystal substrate are significantly better.

[0053] S2. A first N-type layer and a second N-type layer are diffused to form on the first surface and the second surface, respectively. A P-type layer is formed between the first N-type layer and the second N-type layer. A first depletion region is formed at the interface between the P-type layer and the first N-type layer. A second depletion region is formed at the interface between the P-type layer and the second N-type layer. A neutral region is formed between the first depletion region and the second depletion region. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage, the distance between the interface between the first depletion region and the neutral region and the first surface is 18μm to 22μm, and the distance between the interface between the second depletion region and the neutral region and the second surface is 18μm to 22μm.

[0054] It should be understood that the sum of the thicknesses of the first N-type layer, the second N-type layer, and the P-type layer is equal to the thickness of the P-type single crystal substrate.

[0055] In this embodiment, a high-concentration liquid doping source is used, preferably liquid phosphorus oxychloride, to increase the concentration of the first N-type layer and the second N-type layer, increase the concentration difference between the P-type layer and the N-type layer, and facilitate the preparation of a deep junction structure.

[0056] Specifically, in this embodiment, pre-diffusion and secondary diffusion are used to diffuse on the first surface and the second surface respectively to form a first N-type layer and a second N-type layer. In the secondary diffusion, the diffusion temperature is controlled to be greater than or equal to 1250°C.

[0057] In this embodiment, the diffusion temperature of the secondary diffusion is increased from the conventional 1100℃ to 1250℃, which is beneficial for preparing a deep junction structure, thereby reducing the thickness of the neutral region in the initial state.

[0058] More specifically, when the diffusion temperature of the secondary diffusion is 1250℃, the diffusion time must be greater than or equal to 3h; when the diffusion temperature of the secondary diffusion is 1275℃, the diffusion time must be greater than or equal to 2h to ensure the preparation of a deep junction structure.

[0059] It should be understood that the fabrication process of the bidirectional TVS diode in this embodiment also includes other conventional steps, which will not be described in detail here.

[0060] In this embodiment, by increasing the diffusion temperature of the secondary diffusion and using liquid phosphorus oxychloride as a doping source, the doping concentration of the N-type layer can be increased while increasing the junction depth, thereby increasing the concentration difference between the P-type and N-type layers. When the voltage difference across the bidirectional TVS diode is greater than or equal to its breakdown voltage, the excitation of the conductivity modulation effect in the neutral region is promoted.

[0061] Example 2:

[0062] The structure and fabrication method of the bidirectional TVS diode in this embodiment are roughly the same as those in Embodiment 1. The difference is that the bidirectional TVS diode in this embodiment is a planar structure. Since the junction depth and junction termination technology of the planar structure bidirectional TVS diode are different from those of the mesa structure, the resistivity of its P-type layer should also be adjusted accordingly.

[0063] Specifically, in this embodiment, the operating voltage of the bidirectional TVS diode is the same as that in Embodiment 1, which is 12V ~ 15V, and the resistivity of the P-type layer is 0.035Ω·cm ~ 0.04Ω·cm.

[0064] Comparative Example 1:

[0065] The bidirectional TVS diode in this comparative example uses a 250μm thick P-type single crystal substrate as raw material and is prepared using a conventional diffusion process. A conventional gaseous doping source is used during diffusion, and the diffusion temperature for secondary diffusion is set to 1100℃.

[0066] The bidirectional TVS diode in this comparative example can also induce a conductance modulation effect in the neutral region when the voltage difference across its terminals is greater than or equal to its breakdown voltage, exhibiting good surge current carrying capacity. However, compared to the bidirectional TVS diode in Example 1, it uses thicker materials and has a shallower junction depth, resulting in a thicker neutral region in its initial state. Given limited package size (requiring the bidirectional TVS diode to be less than or equal to 1.4mm*1.4mm) and higher requirements for surge current carrying capacity in the circuit, the bidirectional TVS diode in this comparative example will not meet the requirements.

[0067] The maximum peak current (Imax) measured by the bidirectional TVS diode in Example 1 and Comparative Example 1 under an 8 / 20μs surge test waveform. pp ) and limit clamping voltage (V c As shown in Table 1. Among them, the bidirectional TVS diode in Comparative Example 1 and the bidirectional TVS diode in Example 1 both have a size of 1.4mm*1.4mm, which has a very small package size.

[0068] Comparative Example 1 Example 1 Test voltage (V) 550 1050 <![CDATA[Limit I pp (A)]]> 252 552 <![CDATA[Limit V c (V)]]> 28 37.6

[0069] As shown in Table 1, the bidirectional TVS diode in Comparative Example 1 fails when the test voltage exceeds 550V, and its maximum peak current withstand capability is 252A. However, the bidirectional TVS diode in Example 1 does not fail under a test voltage of 1050V, and compared with Comparative Example 1, its maximum peak current withstand capability exceeds 500A, proving that the bidirectional TVS diode in Example 1 has superior surge protection capability.

[0070] As can be seen from the above technical solution, the present invention has the following beneficial effects:

[0071] The bidirectional TVS diode of the present invention has a deep junction structure, which further reduces the thickness of the neutral region in the initial state. This makes it easier to excite the conductivity modulation effect of the neutral region when the voltage difference across its two ends is greater than or equal to its breakdown voltage. Even with its small size, it still has excellent surge protection capability.

[0072] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0073] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A bidirectional TVS diode, characterized in that, The bidirectional TVS diode includes a first N-type layer and a second N-type layer, and a P-type layer located between the first N-type layer and the second N-type layer. A first depletion region is formed at the interface between the P-type layer and the first N-type layer, and a second depletion region is formed at the interface between the P-type layer and the second N-type layer. A neutral region is formed between the first depletion region and the second depletion region. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage, the distance between the interface between the first depletion region and the neutral region and the surface of the first N-type layer away from the P-type layer is 18μm to 22μm, and the distance between the interface between the second depletion region and the neutral region and the surface of the second N-type region away from the P-type layer is 18μm to 22μm.

2. The bidirectional TVS diode according to claim 1, characterized in that, When the voltage difference across the bidirectional TVS diode is greater than or equal to its breakdown voltage, electrons in the first N-type layer or the second N-type layer enter the neutral region, exciting the conductivity modulation effect in the neutral region.

3. The bidirectional TVS diode according to claim 1, characterized in that, The sum of the thicknesses of the first N-type layer, the second N-type layer, and the P-type layer is 180 μm to 220 μm.

4. The bidirectional TVS diode according to claim 1, characterized in that, The sum of the thicknesses of the first N-type layer, the second N-type layer, and the P-type layer is 220 μm. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage, the ratio of the neutral region to the sum of the thicknesses of the first N-type layer, the second N-type layer, and the P-type layer is 0.80 to 0.

83.

5. The bidirectional TVS diode according to claim 1, characterized in that, The doping concentration of the first N-type layer is greater than that of the P-type layer, and the doping concentration of the second N-type layer is greater than that of the P-type layer.

6. The bidirectional TVS diode according to claim 1, characterized in that, The operating voltage of the bidirectional TVS diode is 12V~15V, and the breakdown voltage of the bidirectional TVS diode is greater than the operating voltage of the bidirectional TVS diode.

7. The bidirectional TVS diode according to claim 6, characterized in that, The bidirectional TVS diode has a mesa structure, and the resistivity of the P-type layer is 0.045 Ω·cm ~ 0.05 Ω·cm; or, The bidirectional TVS diode has a planar structure, and the resistivity of the P-type layer is 0.035 Ω·cm ~ 0.04 Ω·cm.

8. A method for fabricating a bidirectional TVS diode, characterized in that, The preparation method includes the following steps: A P-type substrate is provided, the P-type substrate including a first surface and a second surface disposed opposite to each other; A first N-type layer and a second N-type layer are diffused and formed on the first surface and the second surface, respectively. A P-type layer is formed between the first N-type layer and the second N-type layer. A first depletion region is formed at the interface between the P-type layer and the first N-type layer. A second depletion region is formed at the interface between the P-type layer and the second N-type layer. A neutral region is formed between the first depletion region and the second depletion region. When the voltage difference across the bidirectional TVS diode is less than its breakdown voltage, the distance between the interface between the first depletion region and the neutral region and the first surface is 18 μm to 22 μm, and the distance between the interface between the second depletion region and the neutral region and the second surface is 18 μm to 22 μm.

9. The method for fabricating a bidirectional TVS diode according to claim 8, characterized in that, A first N-type layer and a second N-type layer are formed by pre-diffusion and secondary diffusion on the first and second surfaces, respectively, wherein the diffusion temperature in the secondary diffusion is greater than or equal to 1250°C.

10. The method for fabricating a bidirectional TVS diode according to claim 8, characterized in that, In the step of forming a first N-type layer and a second N-type layer by diffusion on the first surface and the second surface respectively, liquid phosphorus oxychloride is used as a doping source.

Images