Transient voltage absorbing element and transient voltage absorbing circuit

Abstract

A transient voltage absorbing element (11) is connected in shunt between a signal line (SL) in which inductors (La, Lb) are connected in series and a reference potential. A first path (1) connected in shunt between the signal line (SL) and the reference potential is provided with a diode (BD) including a first floating capacitance, a first parasitic inductor (L1), and a first parasitic resistance (R1) which are connected in series. A second path (2) connected in shunt between the signal line (SL) and the reference potential is provided with a second floating capacitance (C2), a second parasitic inductor (L2), and a second parasitic resistance (R2) which are connected in series. The capacitance of the paths formed between the signal line (SL) and the reference potential has a frequency dependency such that the capacitance of the paths is smaller in the frequency band of a signal propagating in the signal line (SL) than in the frequency bands other than the frequency band of the signal.

Description

[Technical field]

[0001] The present invention relates to a transient voltage absorbing element that absorbs surges such as transient abnormal voltages caused by ESD (electrostatic discharge) and lightning surges and switching surges, and to a transient voltage absorbing circuit that includes the same and protects electronic devices. [Background technology]

[0002] In general, when a transient voltage absorbing element is inserted between a transmission line and ground, high frequency signals leak to the ground due to the stray capacitance of the transient voltage absorbing element, deteriorating the transmission characteristics of the transmission line.

[0003] Patent Document 1 discloses a transient voltage absorbing circuit that utilizes a mutual induction element or the like to suppress the influence of a stray capacitance component of a transient voltage absorbing element.

[0004] Patent Document 2 shows a transient voltage absorption circuit in which a series LC filter is formed using the floating capacitance of a diode, the frequency band of the input signal is included in the pass band of the filter, and the main frequency of the surge is included in the attenuation band of the filter. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-156846 A [Patent Document 2] JP 2010-57332 A Summary of the Invention [Problem to be solved by the invention]

[0006] 20 is a circuit diagram of a conventional transient voltage absorption circuit. This transient voltage absorption circuit includes a first terminal T1, a second terminal T2, a third terminal T3, and a signal line SL that exists between the first terminal T1 and the second terminal T2. The third terminal T3 is connected to a reference potential such as ground. Inductors La and Lb are connected in series to the signal line SL, and a diode BD serving as a transient voltage absorption element is connected in shunt between the signal line SL and the third terminal T3 (reference potential). The diode BD serving as a transient voltage absorption element has a floating capacitance.

[0007] Fig. 21 is a diagram showing the frequency characteristics of the transmission coefficient S21 of the transient voltage absorption circuit shown in Fig. 20. In Fig. 21, characteristic curve A shows the frequency dependence of the transient voltage absorption circuit when the stray capacitance is 0.1 pF, characteristic curve B shows the stray capacitance is 0.3 pF, and characteristic curve C shows the stray capacitance is 0.5 pF. Here, the 20 GHz band is the frequency band of frequencies that are desired to pass. Of course, "20 GHz" here is just one example.

[0008] Thus, in order to suppress the deterioration of the transmission characteristics in the high frequency band of the transmission line, it is important to reduce the stray capacitance of the transient voltage absorbing element. However, there is a trade-off between the tolerance of the transient voltage absorbing element against the applied voltage and the stray capacitance of the transient voltage absorbing element. For example, when a diode is used as a transient voltage absorbing element, it is possible to reduce the stray capacitance without reducing the tolerance by adjusting the doping amount of the PN junction that forms the diode. However, when the doping amount is fixed to a certain value by the breakdown voltage or dynamic resistance determined by the product specifications, it is necessary to reduce the area of ​​the PN junction in order to reduce the capacitance value of the above-mentioned stray capacitance consisting of the depletion layer of the diode, which causes a problem that the tolerance of the transient voltage absorbing element itself is reduced.

[0009] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a transient voltage absorbing circuit which improves the transient voltage absorbing function of a transient voltage absorbing element without degrading the high frequency passing characteristics of a transmission line. [Means for solving the problem]

[0010] (A) One example of a transient voltage absorption element according to the present disclosure is a transient voltage absorption element connected in shunt between a signal line having an inductor connected in series with a reference potential, wherein the capacitance of a path formed between the signal line and the reference potential is frequency dependent, and the capacitance of the path is smaller in a frequency band of a signal propagating through the signal line than in frequency bands other than the frequency band of the signal.

[0011] (B) A transient voltage absorption element as an example of the present disclosure is a transient voltage absorption element connected in shunt between a signal line to which an inductor is connected in series and a reference potential, the transient voltage absorption element including a first floating capacitance, a first parasitic inductor, and a first parasitic resistance connected in series in a first path connected in shunt between the signal line and the reference potential, and a second floating capacitance, a second parasitic inductor, and a second parasitic resistance connected in series in a second path connected in shunt between the signal line and the reference potential, the first parasitic impedance due to the first parasitic inductor and the first parasitic resistance and the second parasitic impedance due to the second parasitic inductor and the second parasitic resistance are different in a frequency band of a signal propagating through the signal line, and an influence of the first floating capacitance inserted in the first path or the second floating capacitance inserted in the second path which has a higher parasitic impedance in the frequency band of the signal, between the first parasitic impedance and the second parasitic impedance, is suppressed.

[0012] (C) A transient voltage absorption circuit as an example of the present disclosure is characterized in that it is composed of a transient voltage absorption element connected in shunt between a signal line and a reference potential, and an inductor connected in series to the signal line, and the capacitance of a path formed between the signal line and the reference potential is frequency dependent, and the capacitive capacitance of the path is smaller in the frequency band of a signal propagating through the signal line than in frequency bands other than the frequency band of the signal.

[0013] (D) A transient voltage absorption circuit as an example of the present disclosure includes a transient voltage absorption element connected in shunt between a signal line and a reference potential, and an inductor connected in series to the signal line, and a first path connected in shunt between the signal line and the reference potential includes a first stray capacitance, a first parasitic inductor, and a first parasitic resistance connected in series, The second path connected with a shunt between the signal line and the reference potential includes a second floating capacitance, a second parasitic inductor, and a second parasitic resistance connected in series, and a first parasitic impedance due to the first parasitic inductor and the first parasitic resistance and a second parasitic impedance due to the second parasitic inductor and the second parasitic resistance in the frequency band of the signal propagating through the signal line are different, and an influence of the first floating capacitance inserted in the first path or the second floating capacitance inserted in the second path which is the higher parasitic impedance in the frequency band of the signal out of the first parasitic impedance and the second parasitic impedance is suppressed. Effect of the Invention

[0014] According to the present invention, a transient voltage absorbing circuit is obtained in which the surge absorbing function of the transient voltage absorbing element is improved without degrading the high frequency passing characteristics of the transmission line. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a circuit diagram of a transient voltage absorbing circuit 101 according to the first embodiment. [Diagram 2] FIG. 2 is a circuit diagram of a specific example of the configuration of the transient voltage absorbing circuit 101 shown in FIG. [Diagram 3] 3A is a diagram showing the frequency dependence of the capacitance of the stray capacitance (occurring between the signal line SL and the third terminal T3 (reference potential) of the transient voltage absorbing circuit 101) of the transient voltage absorbing element 11. FIG. 3B is a diagram showing the frequency dependence of the impedance of the transient voltage absorbing element 11. [Figure 4] FIG. 4 is a plan view of the transient voltage absorbing element 11. As shown in FIG. [Diagram 5] FIG. 5 is a cross-sectional view of a portion XX in FIG. [Figure 6] FIG. 6 is a circuit diagram of the transient voltage absorbing element 11 shown in FIG. [Figure 7] FIG. 7 is a plan view of a transient voltage absorbing element 11 different from the example shown in FIG. [Figure 8] FIG. 8 is a diagram showing the frequency dependency of the impedance due to the stray capacitance of the transient voltage absorbing element 11. In FIG. [Figure 9] FIG. 9 is a diagram showing the frequency characteristic of the transmission coefficient S21 of the transient voltage absorbing circuit 101. As shown in FIG. [Figure 10] FIG. 10 is a perspective view of a transient voltage absorbing element 12 according to the second embodiment. [Figure 11] FIG. 11 is a plan view of the pattern of conductors that conduct to the diodes of the transient voltage absorbing element 12. As shown in FIG. [Figure 12] FIG. 12 is a diagram showing the electric field strength at various points of a conductor as viewed from the rear surface, expressed by shading. [Figure 13] FIG. 13 is a cross-sectional view of a transient voltage absorbing element 13 according to the third embodiment. [Figure 14] FIG. 14 is a circuit diagram of a transient voltage absorbing circuit 103 including a transient voltage absorbing element 13. As shown in FIG. [Figure 15] 15(A) and 15(B) are cross-sectional views of a transient voltage absorbing element 14 according to the fourth embodiment. [Figure 16] FIG. 16 is a circuit diagram of a transient voltage absorbing circuit 105 according to the fifth embodiment. [Figure 17] FIG. 17 is a cross-sectional view of a transient voltage absorbing element 16 according to the sixth embodiment. [Figure 18] 18A is a circuit diagram of a transient voltage absorbing circuit 106 including a transient voltage absorbing element 16. FIG 18B is a circuit diagram of a transient voltage absorbing circuit including the transient voltage absorbing element 11 shown in FIG. [Figure 19] FIG. 19 is a circuit diagram of a transient voltage absorbing circuit 107 according to the seventh embodiment. [Figure 20] FIG. 20 is a circuit diagram of a conventional transient voltage absorbing circuit. [Figure 21] FIG. 21 is a diagram showing the frequency characteristic of the transmission coefficient S21 of the transient voltage absorbing circuit shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, several specific examples will be given with reference to the drawings to show several embodiments for carrying out the present invention. In each drawing, the same reference numerals are given to the same parts. In consideration of the ease of explanation or understanding of the main points, the embodiments are shown divided into several embodiments for convenience of explanation, but partial replacement or combination of the configurations shown in different embodiments is possible. In the second and subsequent embodiments, the description of matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar actions and effects due to similar configurations will not be mentioned in each embodiment.

[0017] First Embodiment 1 is a circuit diagram of a transient voltage absorbing circuit 101 according to a first embodiment. This transient voltage absorbing circuit 101 includes a first terminal T1, a second terminal T2, a third terminal T3, and a signal line SL that exists between the first terminal T1 and the second terminal T2. The third terminal T3 is connected to a reference potential such as the ground. Inductors La and Lb are connected in series to the signal line SL, and a transient voltage absorbing element 11 is connected in shunt between the signal line SL and the third terminal T3 (reference potential).

[0018] The transient voltage absorbing element 11 is a two-terminal element and includes a diode between its terminals as a main component. The transient voltage absorbing element 11 also includes a first stray capacitance C1, a first parasitic inductor L1, a first parasitic resistance R1, a second stray capacitance C2, a second parasitic inductor L2, and a second parasitic resistance R2 as parasitic components.

[0019] As will be shown later, the diode consists of two diodes connected in series with their forward directions reversed.

[0020] Inductors La and Lb are inductance components included in signal line SL, and in FIG. 1, inductors La and Lb are illustrated as circuit elements.

[0021] The transient voltage absorption circuit 101 constitutes a low-pass filter with inductors La and Lb and the stray capacitance component of the transient voltage absorption element 11.

[0022] The transient voltage absorption element 11 includes a first path 1 shunt-connected between the signal line SL and the third terminal T3, and a second path 2 shunt-connected between the signal line SL and the third terminal T3. The first path 1 includes a first stray capacitance C1, a first parasitic inductor L1, and a first parasitic resistor R1 connected in series. The second path 2 includes a second stray capacitance C2, a second parasitic inductor L2, and a second parasitic resistor R2 connected in series.

[0023] In FIG. 1, the parasitic impedance due to the first parasitic inductor L1 and the first parasitic resistor R1 is represented by the first parasitic impedance Z1P, and the parasitic impedance due to the second parasitic inductor L2 and the second parasitic resistor R2 is represented by the second parasitic impedance Z2P. In the frequency band of the communication signal, if the value of the first parasitic impedance Z1P is represented by Z1P and the value of the second parasitic impedance Z2P is represented by Z2P, they are in the relationship of Z1P > Z2P or Z1P < Z2P. Thus, the resonance frequencies of the first path 1 and the second path 2 are different.

[0024] FIG. 2 is a circuit diagram of a specific configuration example of the transient voltage absorption circuit 101 shown in FIG. 1. The transient voltage absorption circuit 101 includes a diode BD connected in series with the forward directions opposite to each other. The diode BD has a stray capacitance caused by the diode, such as its depletion layer capacitance and the stray capacitance generated between the wirings that conduct to the BD diode. The first stray capacitance C1 of the transient voltage absorption circuit 101 shown in FIG. 1 constitutes the stray capacitance caused by the diode BD. The second stray capacitance C2 of the transient voltage absorption circuit 101 shown in FIG. 1 is a stray capacitance other than the depletion layer capacitance of the diode.

[0025] FIG. 3(A) is a diagram showing the frequency dependence of the capacitance of the stray capacitance (occurring between the signal line SL and the third terminal T3 (reference potential) of the transient voltage absorbing circuit 101) of the transient voltage absorbing element 11. FIG. 3(B) is a diagram showing the frequency dependence of the impedance of the transient voltage absorbing element 11. The characteristic curve A in FIG. 3(A) and FIG. 3(B) shows the characteristics of the transient voltage absorbing element 11 according to this embodiment, and the characteristic curve B in FIG. 3(A) and FIG. 3(B) shows the characteristics of a transient voltage absorbing element whose stray capacitance does not have frequency dependence. The stray capacitance of the transient voltage absorbing element 11 according to this embodiment is 0.38 pF at 1 GHz and 0.15 pF at 40 GHz.

[0026] The capacitance value on the vertical axis of FIG. 3(A) is a value converted from the imaginary part of the S parameter of the transient voltage absorbing element 11. In a frequency band lower than the frequency band of the communication signal propagating through the signal line SL, the transient voltage absorbing element 11 is capacitive, so the value converted from the imaginary part of the S parameter is a capacitance value, but in a frequency range higher than the resonant frequency of the transient voltage absorbing element 11, the transient voltage absorbing element 11 is inductive. In FIG. 3(A), the resonant frequency band is from 10 GHz to 20 GHz, and in this frequency band, the capacitance converted from the imaginary part of the S parameter is the lowest. The frequency band of the communication signal is from 10 GHz to 20 GHz. In FIG. 3(A), it appears as if the capacitance value increases again in a frequency band higher than the frequency band of the communication signal, but this is because the imaginary part of the S parameter increases again due to the inductance components of the parasitic inductors L1 and L2 in a region higher than the frequency band of such a communication signal.

[0027] Fig. 4 is a plan view of the transient voltage absorption element 11. Fig. 5 is a cross-sectional view of the XX portion in Fig. 4. The transient voltage absorption element 11 includes a semiconductor substrate portion. The semiconductor substrate portion includes a semiconductor substrate Sub, an epitaxial layer Epi, a trench TR, an insulator Ins1, and conductors Cond11, Cond12, and Cond13. The trench TR is formed from the epitaxial layer Epi to the semiconductor substrate Sub.

[0028] The semiconductor substrate Sub may be made of, for example, Si or GaAs. The epitaxial layer Epi is, for example, an N-type epitaxial layer formed on the semiconductor substrate Sub, and the insulator Ins1 may be made of, for example, SiO2 or SiN. The conductors Cond11, Cond12, and Cond13 may be made of, for example, Al or Cu.

[0029] A stray capacitance Cp of the diode is generated between the p+ region and the n+ region (depletion layer of the diode). A stray capacitance Cg is formed between the conductor Cond11 and the conductor Cond12, which are conductive to the diode, and between the conductor Cond13 and the conductor Cond12. In addition, a stray capacitance Cs is formed between the conductors Cond11, Cond12, and Cond13 of the wiring layer and the semiconductor substrate portion.

[0030] For example, the first stray capacitance C1 shown in Fig. 1 corresponds to a composite capacitance of the stray capacitance Cp of the depletion layer of the diode BD shown in Fig. 2 and the stray capacitance Cg between the conductors. Also, for example, the second stray capacitance C2 corresponds to the stray capacitance Cs formed between the conductors Cond11, Cond12, Cond13 and the semiconductor substrate Sub.

[0031] FIG. 6 is a circuit diagram of the transient voltage absorption element 11 shown in FIG. 4. The dashed arrows in FIG. 4 indicate the path and direction of the current flowing through the transient voltage absorption element 11. That is, when a positive potential is applied to the conductor Cond11 on the left end in FIG. 4 and a voltage exceeding the forward voltage is applied to each diode, the current flows through the path [Cond11]→[p+]→[n+]→[Cond12]→[p+]→[n+]→[Cond13]. Also, when a positive potential is applied to the conductor Cond13 on the right end in FIG. 4 and a voltage exceeding the forward voltage is applied to each diode, the current flows through the path [Cond13]→[p+]→[n+]→[Cond12]→[p+]→[n+]→[Cond11].

[0032] FIG. 7 is a plan view of a transient voltage absorption element 11 different from the example shown in FIG. 4. The positional relationship between the n+ region and the p+ region is different from the example shown in FIG. 4. In this example, when a positive potential is applied to the conductor Cond11 at the left end in FIG. 7 and a voltage exceeding the forward voltage is applied to each diode, a current flows through the path [Cond11]→[p+]→[n+]→[Cond12]→[p+]→[n+]→[Cond13]. When a positive potential is applied to the conductor Cond13 at the right end in FIG. 7 and a voltage exceeding the forward voltage is applied to each diode, a current flows through the path [Cond13]→[p+]→[n+]→[Cond12]→[p+]→[n+]→[Cond11].

[0033] Fig. 8 is a diagram showing the frequency dependence of the impedance due to the stray capacitance of the transient voltage absorption element 11. In Fig. 8, the horizontal axis is frequency and the vertical axis is impedance. Characteristic curve Z1 in Fig. 8 shows the frequency dependence of the impedance of the first path 1 in Fig. 1, and characteristic curve Z2 shows the frequency dependence of the impedance of the second path 2 in Fig. 1. Characteristic curve Z1 / / Z2 shows the frequency dependence of the impedance of the transient voltage absorption element 11.

[0034] In the example of FIG. 8, range A represents the frequency range from 1 GHz to 5.4 GHz, range B represents the frequency range from 5.4 GHz to 18 GHz, and range C represents the frequency range from 18 GHz to 50 GHz.

[0035] In FIG. 8, in range A (low frequency), the combined capacitance of the first stray capacitance C1 of the first path 1 of the transient voltage absorbing element 11 and the second stray capacitance C2 of the second path 2 is visible (appears). In range B (mid frequency), the first path 1 resonates (approaches the resonant frequency), and the characteristics of the first parasitic resistance R1 become dominant. In range C (high frequency), the impedance of the second stray capacitance C2 falls below the impedance of the first stray capacitance C1, and the characteristics of the second stray capacitance C2 become dominant. In other words, since the stray capacitance of the transient voltage absorbing element 11 is smaller in the high frequency range C than in range A and range B, the resonance point of the low-pass filter shifts to a higher frequency than in the transient voltage absorbing circuit of the conventional configuration.

[0036] When the impedance of the first parasitic impedance Z1P due to the first parasitic inductor L1 and the first parasitic resistor R1 is represented by Z1P, and the impedance of the second parasitic impedance Z2P due to the second parasitic inductor L2 and the second parasitic resistor R2 is represented by Z2P, when Z1P > Z2P, the influence of the first stray capacitance C1 in FIG. 1 is suppressed in range B. In the example shown in FIG. 2, the combined capacitance of the stray capacitance Cp of the depletion layer of the diode BD and the stray capacitance Cg between the conductors conducting to the diode is substantially invisible. In addition, when Z1P < Z2P, the influence of the second stray capacitance C2 in FIG. 1 is suppressed in range B. That is, in the example shown in FIG. 2, the stray capacitance Cs is substantially invisible between the conductors conducting to the diode and the semiconductor substrate Sub.

[0037] Fig. 9 is a diagram showing the frequency characteristic of the transmission coefficient S21 of the transient voltage absorption circuit 101. In Fig. 9, characteristic curve A shows the characteristic of the transient voltage absorption circuit 101 according to this embodiment. Characteristic curve B is a comparative example, and shows the characteristic when the first parasitic impedance Z1P and the second parasitic impedance Z2P shown in Fig. 1 are 0, or when the impedances of the first parasitic impedance Z1P and the second parasitic impedance Z2P are equal, and corresponds in terms of capacitive characteristic to characteristic B in Figs. 3(A) and 3(B).

[0038] In the example shown in Fig. 9, the communication signal propagating through the signal line SL is shunted to the third terminal T3 (reference potential) at around 20 GHz. In this example, the signal power drops to about -5 dB at 20 GHz. In contrast, the transient voltage absorption circuit 101 according to this embodiment has a low capacitance at around 20 GHz, as shown by characteristic A in Figs. 3(A) and 3(B). For this reason, as shown in Fig. 9, the resonance point of the low-pass filter shifts to a higher frequency than that of the transient voltage absorption circuit of the conventional configuration. As a result, the signal power transmitted through the signal line SL drops only to about -0.5 dB at 20 GHz.

[0039] Second Embodiment In the second embodiment, the overall structure of the transient voltage absorbing element and the electric field strength of the transient voltage absorbing element with respect to frequency are illustrated.

[0040] Fig. 10 is a perspective view of a transient voltage absorption element 12 according to the second embodiment. However, the part above the pattern of the conductor that is conductive to the diode is not shown. The transient voltage absorption element 12 shown in Fig. 10 includes a semiconductor substrate Sub, an N-type epitaxial layer Epi, an insulator Ins1, and conductors Cond11, Cond12, and Cond13. The basic configuration of these is the same as that shown in Fig. 5.

[0041] Fig. 11 is a plan view of a conductor pattern that is conductive to a diode of the transient voltage absorption element 12. A plurality of p+ regions are surrounded by n+ regions. The plurality of p+ regions on the left side of Fig. 11 are conductive to conductor Cond11, and the plurality of n+ regions on the left side are conductive to conductor Cond12. Also, the n+ region on the right side of Fig. 11 is conductive to conductor Cond12, and the p+ region on the right side is conductive to conductor Cond13.

[0042] In the second embodiment, when the impedance of the first parasitic impedance Z1P shown in Fig. 2 is represented by Z1P, and the impedance of the second parasitic impedance Z2P due to the second parasitic inductor L2 and the second parasitic resistor R2 is represented by Z2P, Z1P < Z2P. The second stray capacitance C2 is mainly the stray capacitance Cs generated between the conductor conducting to the diode shown in Fig. 5 and the semiconductor substrate part. The stray capacitance of the diode BD shown in Fig. 2 is mainly the combined capacitance of the stray capacitance Cp of the depletion layer of the diode shown in Fig. 5 and the stray capacitance Cg between the conductors conducting to the diode.

[0043] FIG. 12 is a diagram showing the electric field strength of each part of the conductor viewed from the back side by using shading. The upper part of FIG. 12 shows the electric field strength at 1 MHz, and the lower part of FIG. 12 shows the electric field strength at 10 GHz. At 1 MHz, the electric field strength at the center of the conductor Cond11 is 3.1e6 V / m, and at 10 GHz, the electric field strength at the center of the conductor Cond11 is 4.5e5 V / m. That is, the electric field strength at 10 GHz is reduced by about 85% compared to 1 MHz. In other words, even if the stray capacitance Cs generated between the conductors Cond11 and Cond13 shown in FIG. 5 and the semiconductor substrate part is large, since the relationship Z1P < Z2P holds, the stray capacitance Cs (the second stray capacitance C2 shown in FIG. 2) becomes invisible (its influence is suppressed) in the frequency band of the communication signal, and the decrease in the signal strength of the communication signal is suppressed.

[0044] The floating capacitance Cs generated in the conductor Cond12 is a floating capacitance generated between the midpoints of the series capacitance of the floating capacitance Cp-Cp of the depletion layer formed by the two diodes connected in series, and the series capacitance of the floating capacitance Cs-Cs formed by the conductor Cond11 and the conductor Cond13, so there is no potential difference applied to the floating capacitance Cs generated between these midpoints. Therefore, as shown in FIG. 12, substantially no electric field is generated in the conductor Cond12. However, due to the presence of another path such as the parasitic capacitance due to the Cu wiring formed on the upper part, a small electric field is generated. However, even if such an electric field is generated, such an electric field can be attenuated depending on the parasitic impedance generated in the path.

[0045] Here, the intentional difference in the capacitance components of the transient voltage absorbing element between the low frequency band to be absorbed and the high frequency band of the communication signal to be propagated will be considered as follows.

[0046] The "low frequency band" refers to the measurement frequency of the TVS data sheet, which is 1 MHz and is specified in JISC5101-12019, section 4.7. The high frequency band is the frequency band of communication signals, for example, 10 GHz. As shown in the example in Figure 12, if the electric field strength of the conductor conducting to the diode is 50% or less, it can be considered that there is an intentional difference as mentioned above.

[0047] Third embodiment In the third embodiment, the overall structure of the transient voltage absorbing element is illustrated. Fig. 13 is a cross-sectional view of the transient voltage absorbing element 13 according to the third embodiment. Fig. 14 is a circuit diagram of a transient voltage absorbing circuit 103 including the transient voltage absorbing element 13.

[0048] The transient voltage absorption element 13 is composed of a semiconductor substrate portion and a rewiring portion. The semiconductor substrate portion includes a semiconductor substrate Sub, an epitaxial layer Epi, a trench TR, an insulator Ins1, and conductors Cond11, Cond12, and Cond13. The rewiring portion includes insulators Ins2, Ins3, Ins4, and Ins5, a conductor Cond2, and a pad Pad.

[0049] The epitaxial layer Epi is formed on the surface of the semiconductor substrate Sub. A p+ region and an n+ region are formed on the surface of the epitaxial layer Epi. An insulator Ins1 is formed on the surface of the epitaxial layer Epi. Conductors Cond11, Cond12, and Cond13 are formed from the surface of the epitaxial layer Epi to the p+ region and n+ region. In addition, a trench TR is formed from the insulator Ins1 to the semiconductor substrate Sub.

[0050] The rewiring portion has a conductor Cond2 formed therein, which is electrically connected to the conductors Cond11 and Cond13. A pad Pad is formed on the conductor Cond2 in the uppermost layer.

[0051] The semiconductor substrate Sub may be made of, for example, Si or GaAs. The epitaxial layer Epi is, for example, an N-type epitaxial layer formed on the semiconductor substrate Sub, and the insulators Ins1, Ins2, Ins3, Ins4, and Ins5 may be made of, for example, SiO2, SiN, or solder resist depending on the locations where they are formed. The conductors Cond11, Cond12, and Cond13 may be made of, for example, Al or Cu.

[0052] The pad Pad may be composed of a plurality of layers of electrode-forming conductors. That is, the pad Pad may include, for example, a base layer and a surface layer, and may further include an adhesive layer between the base layer and the surface layer. For example, the base layer may be made of Ni, Cr or an alloy thereof, the adhesive layer may be made of Ti or W, and the surface layer may be made of Au or other precious metals.

[0053] As shown in Fig. 13, floating capacitances Cp1 and Cp2 are formed in the depletion layer formed at the interface between the N-type epitaxial layer Epi and the p+ region. A floating capacitance Cg1 is formed between the conductor Cond11 and the conductor Cond12, and a floating capacitance Cg2 is formed between the conductor Cond12 and the conductor Cond13. Floating capacitances Cs1, Cs2, and Cs3 are formed between the conductor Cond11, Cond12, and Cond13 and the epitaxial layer Epi, and a floating capacitance Cs4 is formed between the conductor Cond2 and the epitaxial layer Epi. A floating capacitance Cg3 is formed between the conductor Cond2 and the conductor Cond2.

[0054] The transient voltage absorbing circuit 103 shown in FIG. 14 includes a first terminal T1, a second terminal T2, a third terminal T3, and a signal line SL between the first terminal T1 and the second terminal T2. The third terminal T3 is connected to a reference potential such as ground. Inductors La and Lb are connected in series to the signal line SL, and a transient voltage absorbing element 12 is connected in shunt between the signal line SL and the third terminal T3 (reference potential). In this example, the transient voltage absorbing circuit 103 includes a capacitor Cc connected in parallel to the inductors La and Lb. In this way, the capacitor Cc is provided between the first terminal T1 and the second terminal T2, and the capacitor Cc constitutes a high-pass filter. Note that in FIG. 14, the parasitic inductors L1 and L2 and the parasitic resistors R1 and R2 shown in FIG. 1 are omitted.

[0055] 14, the first stray capacitance C1 is a capacitor formed by the stray capacitances Cp1, Cp2, Cg1, Cg2, Cg3, etc. shown in FIG 13. The second stray capacitance C2 is a capacitor formed by the stray capacitances Cs1, Cs2, Cs3, Cs4, etc. shown in FIG 13.

[0056] As shown in this embodiment, the stray capacitance formed between the signal line SL and the third terminal T3 (reference potential) may be formed in the rewiring portion.

[0057] Fourth embodiment In the fourth embodiment, a transient voltage absorbing element including an inductive element for reducing the stray capacitance of the transient voltage absorbing element will be illustrated.

[0058] Figures 15(A) and 15(B) are cross-sectional views of a transient voltage absorption element 14 according to a fourth embodiment. The transient voltage absorption element 14 shown in Figures 15(A) and 15(B) includes an inductive element Lc for reducing the capacitive nature of the first path in the communication frequency band, in a redistribution layer formed on the surface of a semiconductor substrate.

[0059] In both of the examples shown in Fig. 15(A) and Fig. 15(B), an inductive element Lc is formed by a Cu wiring formed in the redistribution layer. In addition, a stray capacitance Cs is formed between this Cu wiring and the semiconductor substrate. The inductive element Lc and the stray capacitance of the diode form a T-type low-pass filter, so that the resonant frequency of the filter can be changed by changing the inductance of the inductive element.

[0060] In the example shown in FIG. 15(B), the stray capacitance generated between the inductive element Lc and the semiconductor substrate is large, but in the example shown in FIG. 15(A), the Cu wiring constituting the inductive element Lc is a via conductor, and the stray capacitance Cs generated between the inductive element Lc and the semiconductor substrate can be relatively small. In addition, this embodiment has the effect that the stray capacitance Cs does not change even if the inductive element Lc is increased or decreased. In other words, the balance between the left and right inductive elements Lc can be changed without changing the stray capacitance Cs. For example, it is better to change the inductance of the left and right inductive elements Lc according to the ESR (equivalent series resistance component) contained in the left and right inductive elements Lc.

[0061] Fifth embodiment In the fifth embodiment, a configuration of a transient voltage absorbing circuit 105 having an inductance or an element other than an inductance component in a signal line will be illustrated.

[0062] FIG. 16 is a circuit diagram of a transient voltage absorbing circuit 105 according to a fifth embodiment. The transient voltage absorbing circuit 105 includes a first terminal T1, a second terminal T2, a third terminal T3, and a signal line SL between the first terminal T1 and the second terminal T2. The third terminal T3 is connected to a reference potential such as ground. Inductors La and Lb are connected in series to the signal line SL, and a transient voltage absorbing element 15 is connected in shunt between the signal line SL and the third terminal T3 (reference potential). A resistor or a resistance component Rb is configured in the signal line SL. In this example, a capacitor Cc is connected in parallel to the inductors La and Lb. Note that in FIG. 16, the parasitic inductors L1 and L2 and the parasitic resistors R1 and R2 shown in FIG. 1 are omitted.

[0063] The transient voltage absorbing circuit 105 according to this embodiment differs from the transient voltage absorbing circuit 103 shown in Fig. 14 in that a resistor or a resistive component Rb is configured. In the transient voltage absorbing circuit 105 of this embodiment, a resistive component Rb is provided on one side across the connection point of the transient voltage absorbing element 15 between the signal line SL and the third terminal T3 (reference potential). In the case of such a circuit configuration, the inductance of the inductors La, Lb connected in series to the signal line SL is changed. In other words, when the inductances of the inductors La, Lb are different, the value of the resistive component Rb may be determined accordingly.

[0064] Sixth Embodiment In the sixth embodiment, a location where stray capacitance occurs due to a trench in a transient voltage absorbing element will be illustrated.

[0065] Fig. 17 is a cross-sectional view of a transient voltage absorbing element 16 according to a sixth embodiment. Fig. 18(A) is a circuit diagram of a transient voltage absorbing circuit 106 including the transient voltage absorbing element 16. Fig. 18(B) is a circuit diagram of a transient voltage absorbing circuit including the transient voltage absorbing element 11 shown in Fig. 5.

[0066] In the example shown in FIG. 17, the transient voltage absorption element 16 includes a semiconductor substrate Sub, an N-type epitaxial layer Epi, and an insulator Ins1. The epitaxial layer Epi is formed on the surface of the semiconductor substrate Sub. A p+ region and an n+ region are formed on the surface of the epitaxial layer Epi. An insulator Ins1 is formed on the surface of the epitaxial layer Epi. Conductors Cond11, Cond12, and Cond13 are formed from the surface of the insulator Ins1 to the p+ region and the n+ region. In addition, a trench TR is formed from the insulator Ins1 to the semiconductor substrate Sub.

[0067] In Fig. 18(A), capacitors C1a and C1b are two capacitors connected in series to represent the stray capacitance caused by the double trench. In Fig. 18(B), a first stray capacitance C1 is one capacitor to represent the stray capacitance caused by the single trench. Thus, compared to the example shown in Fig. 5, in the transient voltage absorption element 15 shown in Fig. 18(A), the epitaxial layer Epi of each diode is isolated by a double trench, so that the stray capacitance caused by the trench can be reduced.

[0068] Seventh embodiment In the seventh embodiment, a transient voltage absorbing element that can be represented by a circuit having three paths between a signal line and a reference potential will be illustrated.

[0069] 19 is a circuit diagram of a transient voltage absorbing circuit 107 according to a seventh embodiment. This transient voltage absorbing circuit 107 includes a first terminal T1, a second terminal T2, a third terminal T3, and a signal line SL that exists between the first terminal T1 and the second terminal T2. The third terminal T3 is connected to a reference potential such as the ground. Inductors La and Lb are connected in series to the signal line SL, and a transient voltage absorbing element 17 is connected in shunt between the signal line SL and the third terminal T3 (reference potential).

[0070] The transient voltage absorbing element 17 is a two-terminal element and includes a diode between its terminals as a main part. The transient voltage absorbing element 17 includes a first path 1 connected to a shunt between the signal line SL and the third terminal T3, a second path 2 connected to a shunt between the signal line SL and the third terminal T3, and a third path 3 connected to a shunt between the signal line SL and the third terminal T3. The first path 1 includes a first stray capacitance C1, a first parasitic inductor L1, and a first parasitic resistance R1, which are connected in series. The second path 2 includes a second stray capacitance C2, a second parasitic inductor L2, and a second parasitic resistance R2, which are connected in series. The third path 3 includes a third stray capacitance C3, a third parasitic inductor L3, and a third parasitic resistance R3, which are connected in series. The parasitic impedance due to the first parasitic inductor L1 and the first parasitic resistor R1 is represented as the first parasitic impedance Z1P, the parasitic impedance due to the second parasitic inductor L2 and the second parasitic resistor R2 is represented as the second parasitic impedance Z2P, and the parasitic impedance due to the third parasitic inductor L3 and the third parasitic resistor R3 is represented as the third parasitic impedance Z3P.

[0071] The basic structure of the transient voltage absorbing element 17 is as shown in FIG. 5 and FIG. 13, but the seventh embodiment can be said to be a representation of these in the form of an equivalent circuit having three paths.

[0072] The diode is composed of two diodes connected in series with their forward directions reversed to each other. For example, the second stray capacitance C2 is mainly the stray capacitance Cp of the diode. For example, the first stray capacitance C1 is mainly the stray capacitance Cg generated between the conductor Cond11 and the conductor Cond12, which are conductive to the diode, and between the conductor Cond13 and the conductor Cond12. For example, the third stray capacitance C3 is mainly the stray capacitance Cs generated between the conductors Cond11, Cond12, and Cond13 of the wiring layer and the semiconductor substrate Sub.

[0073] The first parasitic inductor L1 and the first parasitic resistance R1 are parasitic inductors and parasitic resistances that occur in the current path that flows through the stray capacitance Cg. The second parasitic inductor L2 and the second parasitic resistance R2 are parasitic inductors and parasitic resistances that occur in the current path that flows through the diode. The third parasitic inductor L3 and the third parasitic resistance R3 are parasitic inductors and parasitic resistances that occur in the current path that flows through the stray capacitance Cs.

[0074] In the example shown in Figure 1, the combined capacitance of the stray capacitance Cg occurring between conductor Cond11 and conductor Cond12 and between conductor Cond13 and conductor Cond12 and the stray capacitance Cp of the diode is represented by the first stray capacitance C1, so that it can be represented by a circuit having two paths between the signal line SL and the third terminal T3. However, if the stray capacitance Cg occurring between conductor Cond11 and conductor Cond12 and between conductor Cond13 and conductor Cond12 is represented by being separated from the stray capacitance formed by the depletion layer of the diode, the transient voltage absorption element 17 can be represented by a circuit having three paths between the signal line SL and the third terminal T3 as shown in Figure 19.

[0075] The impedances of the first parasitic impedance Z1P, the second parasitic impedance Z2P, and the third parasitic impedance Z3P differ depending on the frequency of the signal or noise propagating through the signal line SL. Therefore, due to the magnitude relationship of the first parasitic impedance Z1P of the transient absorption element 17, the large parasitic impedance gradually disappears from the connected stray capacitance. For example, if the relationship Z3P > Z1P and Z3P > Z2P exists in the frequency band of the communication signal, the influence of the third stray capacitance can be most effectively suppressed in that frequency band. Also, for example, if the relationship Z3P > Z2P > Z1P exists in a certain frequency band, the influence of the third stray capacitance C3 can be most effectively suppressed in that frequency band, and the influence of the second stray capacitance C2 can be next most effectively suppressed.

[0076] Although the example shown in FIG. 19 shows a circuit having three paths 1, 2, and 3, the number of paths that can be represented is not limited to three.

[0077] Finally, the present invention is not limited to the above-described embodiments. Appropriate modifications and changes are possible by those skilled in the art. The scope of the present invention is indicated by the claims, not the above-described embodiments. Furthermore, the scope of the present invention includes modifications and changes from the embodiments within the scope of the claims and the equivalent scope. [Explanation of symbols]

[0078] BD: Diode C1: First floating capacitance C11, C12: Floating capacitance C1a, C1b...capacitor Cond11, Cond12, Cond13...Conductors C2: Second stray capacitance C21, C22, C23, C24, C25...stray capacitance C3: Third stray capacitance Cc: Capacitor Cp, Cp1, Cp2...stray capacitance Cg, Cg1, Cg2, Cg3...stray capacitance Cs, Cs1, Cs2, Cs3, Cs4...stray capacitance L1: First parasitic inductor L2: Second parasitic inductor L3: Third parasitic inductor La, Lb…Inductor Lc: Inductive element Epi: N-type epitaxial layer Ins1, Ins2, Ins3, Ins4, Ins5...insulators R1…first parasitic resistance R2…Second parasitic resistance R3…Third parasitic resistance Rb…resistance component Sub: Semiconductor substrate SL: Signal line SR1, SR2, SRT...Solder resist film T1: First terminal T2: Second terminal T3: Third terminal TR…Trench Z1P: First parasitic impedance Z2P: Second parasitic impedance 1...First route 2...Second route 3…Third Route 11-17: Transient voltage absorbing elements 101, 102, 103, 104, 105, 106, 107...Transient voltage absorption circuit

Claims

1. A transient voltage absorbing element connected in shunt between a signal line with an inductor connected in series and a reference potential, a capacitance of a path formed between the signal line and the reference potential has frequency dependence, and the capacitance of the path is smaller in a frequency band of a signal propagating through the signal line than in a frequency band other than the frequency band of the signal; Transient voltage absorbing element.

2. A transient voltage absorbing element connected in shunt between a signal line with an inductor connected in series and a reference potential, a first path connected in shunt between the signal line and the reference potential, the first path including a first stray capacitance, a first parasitic inductor, and a first parasitic resistance connected in series; a second path connected in shunt between the signal line and the reference potential, the second path including a second stray capacitance, a second parasitic inductor, and a second parasitic resistance connected in series; a first parasitic impedance due to the first parasitic inductor and the first parasitic resistance is different from a second parasitic impedance due to the second parasitic inductor and the second parasitic resistance in a frequency band of a signal propagating through the signal line, an influence of the first stray capacitance inserted in the first path or the second stray capacitance inserted in the second path, which is a higher parasitic impedance in the frequency band of the signal, is suppressed; Transient voltage absorbing element.

3. the first stray capacitance or the second stray capacitance includes a stray capacitance caused by a diode formed in a semiconductor substrate portion; The transient voltage absorbing element according to claim 2 .

4. Among the first stray capacitance and the second stray capacitance, a stray capacitance other than a stray capacitance caused by the diode includes a stray capacitance generated between a wiring of a wiring layer and a semiconductor substrate portion. The transient voltage absorbing element according to claim 3 .

5. A transient voltage absorbing element connected in shunt between a signal line with an inductor connected in series and a reference potential, a first path connected in shunt between the signal line and the reference potential, the first path including a first stray capacitance, a first parasitic inductor, and a first parasitic resistance connected in series; a second path connected in shunt between the signal line and the reference potential, the second path including a second stray capacitance, a second parasitic inductor, and a second parasitic resistance connected in series; a third path connected in shunt between the signal line and the reference potential, the third path including a third stray capacitance, a third parasitic inductor, and a third parasitic resistance connected in series; the first stray capacitance includes stray capacitance occurring between wirings in a wiring layer, the second stray capacitance includes a stray capacitance generated in a depletion layer of a diode, the third stray capacitance includes a stray capacitance occurring between a wiring of the wiring layer and a semiconductor substrate portion; Transient voltage absorbing element.

6. A transient voltage absorbing element connected in shunt between a signal line and a reference potential, and an inductor connected in series with the signal line; a capacitance of a path formed between the signal line and the reference potential has frequency dependence, and the capacitance of the path is smaller in a frequency band of a signal propagating through the signal line than in a frequency band other than the frequency band of the signal; Transient voltage absorption circuit.

7. A transient voltage absorbing element connected in shunt between a signal line and a reference potential, and an inductor connected in series with the signal line; a first path connected in shunt between the signal line and the reference potential, the first path including a first stray capacitance, a first parasitic inductor, and a first parasitic resistance connected in series; a second path connected in shunt between the signal line and the reference potential, the second path including a second stray capacitance, a second parasitic inductor, and a second parasitic resistance connected in series; a first parasitic impedance due to the first parasitic inductor and the first parasitic resistance is different from a second parasitic impedance due to the second parasitic inductor and the second parasitic resistance in a frequency band of a signal propagating through the signal line, an influence of the first stray capacitance inserted in the first path or the second stray capacitance inserted in the second path, which is a higher parasitic impedance in the frequency band of the signal, is suppressed; Transient voltage absorption circuit.

8. the first stray capacitance or the second stray capacitance includes a stray capacitance caused by a diode formed in a semiconductor substrate portion, Among the first stray capacitance and the second stray capacitance, the stray capacitance other than the stray capacitance caused by the diode includes a stray capacitance generated between a wiring of a wiring layer and a semiconductor substrate portion.

8. The transient voltage absorption circuit of claim 7.

9. a capacitor connected in parallel with the inductor; A transient voltage absorption circuit according to any one of claims 6 to 8.

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