Optical receiver

Abstract

An optical receiver (1) according to one embodiment of the present invention comprises a transimpedance amplifier (22) that has: a first pad (22b); and a second pad (22c) and third pad (22v) that are provided on an insulation layer (22j), connected to a cathode wiring layer (22f) via a first via (22g), and positioned on both sides of the first pad (22b), the second pad (22c) being connected to a first cathode pad (20d) of a light reception element (20) and the third pad (22v) being connected to a second cathode pad (20v) of the light reception element (20). The light reception element (20) is connected to: an anode pad (20c) mounted on the transimpedance amplifier (22), provided on a surface facing the transimpedance amplifier (22), and connected to an anode electrode via an anode wiring pattern; and the first cathode pad (20d) and second cathode pad (20v), which are connected to a cathode electrode via a cathode wiring pattern and positioned on both sides of the anode pad (20c).

Description

[Technical Field]

[0001] The present disclosure relates to optical receivers. This application claims priority from Japanese Application No. 2021-010186 filed on January 26, 2021, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] Patent Document 1 describes an optical receiver equipped with a photodiode, a transimpedance amplifier, a differential output circuit, and an averaging circuit. The photodiode generates a photocurrent, and the transimpedance amplifier converts the photocurrent from the photodiode into a received signal, which is a voltage signal. The averaging circuit provides the average value of the received signal as a reference voltage to the differential output circuit. The differential output circuit generates a differential signal based on the received signal from the transimpedance amplifier and the reference voltage from the averaging circuit. The transimpedance amplifier has a gain variable means that passively changes the conversion gain of the transimpedance amplifier according to the magnitude of the photocurrent. The time constant of the averaging circuit is variable according to an electrical control signal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-274032 Summary of the Invention

[0004] An optical receiver according to one embodiment includes a light-receiving element having an anode pad connected to an anode electrode via an anode wiring pattern, and first and second cathode pads connected to a cathode electrode via the cathode wiring pattern and positioned on either side of the anode pad. The optical receiver also includes a cathode wiring layer that supplies a cathode potential to the cathode pad of the light-receiving element, an insulating layer having the cathode wiring layer therein, a first pad provided on the insulating layer and connected to the anode pad of the light-receiving element, and a transimpedance amplifier having a second pad provided on the insulating layer, connected to the cathode wiring layer via a first via, positioned on either side of the first pad, connected to the first cathode pad of the light-receiving element, and connected to the second cathode pad of the light-receiving element. The light receiving element is mounted on the transimpedance amplifier, and is connected to an anode pad that is provided on the surface facing the transimpedance amplifier and is connected to the anode electrode via an anode wiring pattern, and to a first cathode pad and a second cathode pad that are connected to the cathode electrode via a cathode wiring pattern and are positioned on either side of the anode pad. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a plan view schematically showing the internal structure of an optical receiver. [Figure 2] FIG. 2 is a schematic longitudinal sectional view of an optical receiver. [Figure 3] FIG. 3 is an enlarged perspective view of the periphery of the light receiving element and the transimpedance amplifier of the optical receiver. [Figure 4] FIG. 4 is a diagram schematically illustrating a light receiving element and a transimpedance amplifier in the optical receiver according to the first embodiment. [Figure 5] FIG. 5 is a diagram schematically illustrating the transimpedance amplifier of FIG. [Figure 6] FIG. 6 is a schematic cross-sectional view of a transimpedance amplifier and a light receiving element. [Figure 7]FIG. 7 is a schematic cross-sectional view of a transimpedance amplifier and a light receiving element. [Figure 8] FIG. 8 is a schematic cross-sectional view of a transimpedance amplifier and a light receiving element according to the second embodiment. [Figure 9] FIG. 9 is a schematic cross-sectional view of a transimpedance amplifier and a light receiving element according to the third embodiment. [Figure 10] FIG. 10 is a diagram showing an equivalent circuit of the transimpedance amplifier and the light receiving element. [Figure 11] FIG. 11 is a schematic cross-sectional view of the transimpedance amplifier and the light receiving element according to the first embodiment. [Figure 12] FIG. 12 is a schematic cross-sectional view of a transimpedance amplifier and a light receiving element according to the second embodiment. [Figure 13] FIG. 13 is a graph showing the resonance frequency in the transimpedance amplifier and the light receiving element of the first embodiment. [Figure 14] FIG. 14 is a graph showing the resonance frequency in the transimpedance amplifier and the light receiving element of the second embodiment. [Figure 15] FIG. 15 is a schematic cross-sectional view of a transimpedance amplifier and a light receiving element according to a third embodiment. [Figure 16] FIG. 16 is a schematic cross-sectional view of a transimpedance amplifier and a light receiving element according to a fourth embodiment. [Figure 17] FIG. 17 is a graph showing the resonance frequency in the transimpedance amplifier and the light receiving element according to the third embodiment. [Figure 18] FIG. 18 is a graph showing the resonance frequency in the transimpedance amplifier and the light receiving element according to the fourth embodiment. [Figure 19] FIG. 19 is a diagram illustrating a transimpedance amplifier and a light receiving element according to a fifth embodiment. [Figure 20] FIG. 20 is a schematic cross-sectional view of a transimpedance amplifier and a light receiving element according to a fifth embodiment. [Figure 21]FIG. 21 is a schematic cross-sectional view of a transimpedance amplifier and a light receiving element according to a fifth embodiment. [Figure 22] FIG. 22 is a graph showing the resonance frequency in the transimpedance amplifier and the light receiving element of the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0006] It is desirable to shift the resonant frequency caused by the parasitic capacitance or inductance between a light-receiving element (photodiode) and a transimpedance amplifier to a higher frequency. A known method for shifting the resonant frequency to a higher frequency is to arrange multiple wires in parallel between the light-receiving element and the transimpedance amplifier. However, the method of arranging multiple wires in parallel may not be sufficient to shift the resonant frequency to a higher frequency. Therefore, it is desirable to further shift the resonant frequency caused by the parasitic capacitance or inductance to a higher frequency.

[0007] An object of the present disclosure is to provide an optical receiver capable of shifting the resonant frequency caused by parasitic capacitance or inductance to the higher frequency side.

[0008] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. An optical receiver according to one embodiment includes a light-receiving element having an anode pad connected to an anode electrode via an anode wiring pattern, and first and second cathode pads connected to a cathode electrode via a cathode wiring pattern and positioned on either side of the anode pad. The optical receiver also includes a cathode wiring layer that supplies a cathode potential to the cathode pad of the light-receiving element, an insulating layer having the cathode wiring layer therein, a first pad provided on the insulating layer and connected to the anode pad of the light-receiving element, and a transimpedance amplifier having a second pad provided on the insulating layer, connected to the cathode wiring layer via a first via, positioned on either side of the first pad, connected to the first cathode pad of the light-receiving element, and connected to the second cathode pad of the light-receiving element. The light receiving element is mounted on the transimpedance amplifier, and is connected to an anode pad that is provided on the surface facing the transimpedance amplifier and is connected to the anode electrode via an anode wiring pattern, and to a first cathode pad and a second cathode pad that are connected to the cathode electrode via a cathode wiring pattern and are positioned on either side of the anode pad.

[0009] In this optical receiver, the transimpedance amplifier includes a cathode wiring layer, a first pad, a second pad, and a third pad. The photodetector includes an anode pad, a first cathode pad, and a second cathode pad. The photodetector is mounted on the transimpedance amplifier. The second and third pads of the transimpedance amplifier are arranged on either side of the first pad. The first and second cathode pads of the photodetector are arranged on either side of the anode pad. The first pad of the transimpedance amplifier is connected to the anode pad of the photodetector. The second pad of the transimpedance amplifier is connected to the first cathode pad of the photodetector. The third pad of the transimpedance amplifier is connected to the second cathode pad of the photodetector. With the above configuration, the resonant frequency caused by parasitic capacitance or inductance can be shifted to a higher frequency. For example, the frequency of the resonant circuit present in the RF current path between the photodetector and the transimpedance amplifier can be set to 100 GHz or higher.

[0010] The first pad of the transimpedance amplifier may be connected to the anode pad of the light receiving element via a columnar member or protrusion, the second pad of the transimpedance amplifier may be connected to the first cathode pad of the light receiving element via a columnar member or protrusion, and the third pad of the transimpedance amplifier may be connected to the second cathode pad of the light receiving element via a columnar member or protrusion.

[0011] The transimpedance amplifier may further include a ground layer connected to a reference potential. The ground layer of the transimpedance amplifier may be connected to the cathode wiring layer of the transimpedance amplifier via a capacitor.

[0012] The optical receiver according to one aspect may further include a backside ground provided on the backside of the transimpedance amplifier and connected to a reference potential. The ground layer of the transimpedance amplifier is provided on the backside of the cathode wiring layer and is connected to the backside ground through a TSV (Through Silicon Via) 22m. Alternatively, it may be connected to the rear surface ground via a DSV (Deep Silicon Via) 22p.

[0013] The light-receiving element may include a cathode relay pad connected between the cathode electrode and the first cathode pad via a cathode wiring pattern. The transimpedance amplifier may include a relay pad connected to the cathode wiring layer on the surface of the insulating layer via a second via and disposed at a position corresponding to the cathode relay pad of the light-receiving element, spaced apart from the second pad and the third pad. The relay pad of the transimpedance amplifier may be connected to the cathode relay pad of the light-receiving element via a first columnar member.

[0014] A back surface metal layer may be provided on the back surface of the light receiving element.

[0015] The cathode wiring layer may surround the first pad, and the cathode electrode and cathode wiring may be disposed on both sides of the anode electrode and anode wiring. In this case, the cathode electrode and cathode wiring surround the anode electrode and anode wiring from both sides, so that the magnetic fields generated by the currents flowing through the light receiving elements cancel each other out. This makes it difficult for the magnetic field to leak outside the cathode wiring, and reduces crosstalk due to electromagnetic coupling to other lanes.

[0016] [Details of the embodiments of the present disclosure] Specific examples of optical receivers according to embodiments will be described below with reference to the drawings. The present disclosure is not limited to the following examples, but is intended to include all modifications set forth in the claims and within the scope equivalent to the claims. In the description of the drawings, identical or corresponding elements are given the same reference numerals, and redundant description will be omitted as appropriate. The drawings may be partially simplified or exaggerated to facilitate understanding, and the dimensional ratios and the like are not limited to those shown in the drawings.

[0017] (First embodiment) A schematic configuration of an exemplary optical receiver 1 will be described with reference to FIG. 1. The configuration of an optical receiver according to the present disclosure is not limited to the configuration of the optical receiver 1 described below. FIG. 1 is a plan view of the internal structure of the optical receiver 1 with the lid of the package removed. FIG. 2 is a schematic vertical cross-sectional view of the optical receiver 1. The exemplary optical receiver 1 is used as a ROSA (Receiver Optical Sub Assembly) of an optical transceiver. The optical receiver 1 includes a package 11. The package 11 The optical fiber optic optical fiber 10 has a metal side wall 11a and a metal bottom plate 11b. The bottom plate 11b extends along a plane defined by a first direction A1 and a second direction A2 intersecting the first direction A1. The side wall 11a includes a side wall 11aa and a side wall 11ab extending along a plane intersecting the first direction A1. The side wall 11aa and the side wall 11ab are aligned along the first direction A1. An opening on the side wall 11a opposite the bottom plate 11b is sealed by a lid (not shown). An opening is formed in the side wall 11aa. A bushing 12 is provided in the opening of the side wall 11aa. A receptacle of the optical receiver 1 is fixed via the bushing 12. An optical window 13, for example, is disposed inside the bushing 12.

[0018] The optical receiver 1 further includes an optical axis converter 14 that converts the optical axis of input light L, an optical demultiplexer 15 that demultiplexes the light L, and multiple lenses 16 onto which each light beam demultiplexed by the optical demultiplexer 15 is incident. The optical axis converter 14 has, for example, a pair of mirrors 14b. The light L is incident on one of the pair of mirrors 14b along a first direction A1. The optical axis of the light L incident on one mirror 14b is bent 90 degrees, reflected in a third direction A3, and incident on the other mirror 14b. The optical axis of the light L incident on the other mirror 14b is bent 90 degrees, reflected in the first direction A1, and incident on the optical demultiplexer 15. The light L is, for example, multiplexed signal light having multiple signal light components. The optical demultiplexer 15 demultiplexes the light L, which is multiplexed signal light, into each of the multiple signal light components. The light beams demultiplexed by the optical demultiplexer 15 are incident on each of the plurality of lenses 16 .

[0019] The optical receiver 1 further includes a feedthrough 17, a plurality of photodetectors 20, and a TIA (transimpedance amplifier) ​​22. The feedthrough 17 is disposed on the side wall 11ab and is electrically connected to an external circuit. A portion of the feedthrough 17 located outside the side wall 11ab is provided with a plurality of terminals 17a for electrical connection to the external circuit. A portion of the feedthrough 17 located inside the side wall 11ab is provided with a plurality of terminals for electrical connection to the TIA 22. The plurality of terminals inside the side wall 11ab and the plurality of terminals 17a outside the side wall 11ab are short-circuited to each other by wiring embedded inside the feedthrough 17.

[0020] 3 is an enlarged perspective view of the multiple lenses 16, multiple photodetectors 20, and TIA 22 of the optical receiver 1. The multiple lenses 16 are arranged between the optical demultiplexer 15 and the multiple photodetectors 20. The multiple lenses 16 are aligned along the second direction A2. Each of the multiple lenses 16 focuses a respective one of the multiple signal light components output from the optical demultiplexer 15 and guides the focused light to each of the multiple photodetectors 20. The optical receiver 1 further includes, for example, a substrate 21 on which the TIA 22 and capacitor 24 are mounted. The substrate 21 is arranged on the bottom plate 11b of the package 11.

[0021] A plurality of photodetectors 20 are mounted on the TIA 22. The photodetectors 20 are arranged on the TIA 22 along the second direction A2. As an example, four photodetectors 20 are provided. However, the number of photodetectors 20 is not particularly limited. The photodetectors 20 are semiconductor elements that convert corresponding signal light components into electrical signals. The photodetectors 20 are optically coupled to the optical splitter 15 via a lens 16. The signal light components from the lens 16 are input to, for example, a side surface of the photodetector 20. The photodetector 20 is, for example, a waveguide-type photodetector. The photodetector 20 is electrically connected to the TIA 22. The TIA 22 is disposed between the photodetector 20 and the feedthrough 17 and converts the current signal from the photodetector 20 into a voltage signal. The TIA 22 is electrically connected to the wiring of the feedthrough 17 via, for example, a bonding wire (not shown). The voltage signal output from the TIA 22 is output to the outside of the optical receiver 1 via the feedthrough 17 .

[0022] 4, the photodetector 20 and the TIA 22 are flip-chip bonded (FCB: Flip Chip Bonding). 3, and is the surface facing the surface 22d of the TIA 22. An anode pad 20c, a first cathode pad 20d, and a second cathode pad 20v are provided on the surface 20b of the light receiving element 20. On the surface 20b of the light receiving element 20, the first cathode pad 20d and the second cathode pad 20v are disposed on both sides of the anode pad 20c. The light receiving element 20 is mounted so that the surface 20b of the light receiving element 20 faces the surface 22d of the TIA 22, as indicated by the arrow in the figure.

[0023] For example, a first cathode pad 20d and a second cathode pad 20v are arranged along the second direction A2. An anode pad 20c is disposed between the first cathode pad 20d and the second cathode pad 20v arranged along the second direction A2. As a specific example, one anode pad 20c and at least three or more cathode pads including the first cathode pad 20d and the second cathode pad 20v are provided on the surface metal of the surface 20b, which is the flip-chip connection surface of the light-receiving element 20. The anode pad 20c is connected to the anode electrode of the light-receiving element 20 via an anode wiring pattern 20f. The first cathode pad 20d and the second cathode pad 20v are each connected to the cathode electrode of the light-receiving element 20 via a cathode wiring pattern 20g. FIG. 4 shows an example in which the light-receiving element 20 has one anode pad 20c, a first cathode pad 20d, a second cathode pad 20v, and two cathode pads 20w.

[0024] FIG. 5 is a diagram illustrating the layout of a TIA 22 on which a light-receiving element 20 is mounted. As illustrated in FIGS. 4 and 5, the TIA 22 includes a first pad 22b, a second pad 22c, and a third pad 22v. For example, the second pad 22c and the third pad 22v are aligned along the second direction A2. The first pad 22b is positioned between the second pad 22c and the third pad 22v aligned along the second direction A2. The second pad 22c and the third pad 22v of the TIA 22 are positioned on either side of the first pad 22b. For example, the TIA 22 includes only pads formed of a surface metal. The TIA 22 does not include any metal other than the pads on the surface 22d facing the light-receiving element 20. FIG. 5 illustrates an example in which the TIA 22 includes a first pad 22b, a second pad 22c, a third pad 22v, and two pads 22w. As will be described in detail later, a cathode wiring layer 22f is provided inside the TIA 22.

[0025] 6 shows a cross section of the light receiving element 20 and the TIA 22 taken along the first direction A1 (line A1-A1) in FIG. 5. FIG. 7 shows a cross section of the light receiving element 20 and the TIA 22 taken along the second direction A2 (line A2-A2) in FIG. 5. As shown in FIGS. 6 and 7, the first pad 22b of the TIA 22 is connected to the anode pad 20c of the light receiving element 20. The second pad 22c and the third pad 22v of the TIA 22 are connected to the first cathode pad 20d and the second cathode pad 20v of the light receiving element 20, respectively.

[0026] The first pad 22b of the TIA 22 is connected to an anode wiring layer 22x inside the TIA 22 via a via 22y. The anode wiring layer 22x supplies an anode potential. The second pad 22c and the third pad 22v of the TIA 22 are each connected to a cathode wiring layer 22f of the TIA 22 via a via 22g (first via). The cathode wiring layer 22f supplies a cathode potential. The anode wiring layer 22x and the cathode wiring layer 22f are provided in an insulating layer 22j. The first pad 22b, the second pad 22c, and the third pad 22v are provided on the insulating layer 22j. The cathode wiring layer 22f of the TIA 22 is connected to a ground layer 22h of the TIA 22 via a capacitance (capacitor).

[0027] (Second embodiment) An optical receiver according to the second embodiment will now be described. Part of the configuration of the optical receiver according to the second embodiment overlaps with part of the configuration of the optical receiver 1 according to the first embodiment. Therefore, in the following, parts that overlap with the above-mentioned explanation, including the configuration of the optical receiver 1, will be assigned the same reference numerals and explanations thereof will be omitted as appropriate.

[0028] 8 shows a side view of the light receiving element 20A and the TIA 22A according to the second embodiment as viewed in the first direction A1. As shown in FIG. 8, the ground layer 22h of the TIA 22A is connected to a back surface ground 22k of the TIA 22A via a TSV (Through Silicon Via). The TSV is configured to be connected from the back surface ground 22k of the TIA 22A to the ground layer 22h through a via 22m. The cathode wiring layer 22f is connected to the ground layer 22h through a capacitance (capacitor). The light receiving element 20A and the TIA 22A are connected through a pillar 25 (a columnar member). The height of the pillar 25 is, for example, 20 μm or less. The light receiving element 20A and the TIA 22A may be connected through a bump.

[0029] (Third embodiment) 9 shows a side view of a light receiving element 20B and a TIA 22B according to the third embodiment, viewed along the first direction A1. As shown in FIG. 9, a ground layer 22h of the TIA 22B is connected to a heavily doped substrate 22z of the TIA 22B via a deep silicon via (DSV). The DSV is connected from the heavily doped substrate 22z of the TIA 22B to an insulating layer 22j via a via 22p.

[0030] FIG. 10 shows an electrical equivalent circuit of the RF current path between the photodetector and the TIA. FIG. 10 shows an equivalent circuit when the photodetector and the TIA are FCBed. "Port 1" in FIG. 10 indicates the part established between the anode (A) and cathode (C) of the photodetector. "Port 2" indicates the part established between the input (IN) and TIA_GND of the TIA. For example, the RF current of the photodetector 20 flows from the anode of the photodetector through the input of the TIA to TIA_GND, and then capacitively couples to VPDx (x is a natural number), which is the cathode bias supply terminal of the TIA. The RF current then flows from VPDx through the pillar and returns to the cathode (C) of the photodetector.

[0031] As mentioned above, the pillars are formed between the photodetector and the TIA pad. Therefore, if a pad larger than the pillar is formed on the TIA, parasitic capacitance occurs between the photodetector and the TIA, and the pillar inductance and capacitance form a parallel resonant circuit. If this inductance is several tens of pH and the capacitance is several tens of fF, resonance occurs around 80 GHz, blocking the RF current path. For the TIA, if the VIA inductance is large, a series resonant circuit is formed with the parasitic capacitance Ccg generated by the cathode and ground. At the resonant frequency determined by these values, the original photodetector current is shunted into the RF path, resulting in loss. The optical receivers according to the first to third embodiments described above can solve the aforementioned problems and enable resonant frequencies of 100 GHz or higher.

[0032] The following describes the effects and advantages of the optical receivers according to the first to third embodiments. As illustrated in FIG. 7, in the optical receiver 1, the TIA 22 includes a cathode wiring layer 22f, a first pad 22b, a second pad 22c, and a third pad 22v. The light-receiving element 20 includes an anode pad 20c, a first cathode pad 20d, and a second cathode pad 20v. The light-receiving element 20 is mounted on the TIA 22. In the TIA 22, the second pad 22c and the third pad 22v are disposed on both sides of the first pad 22b. In the light-receiving element 20, the first cathode pad 20d and the second cathode pad 20v are disposed on both sides of the anode pad 20c. The first pad 22b of the TIA 22 is connected to the anode pad 20c of the light-receiving element 20. The second pad 22c of the TIA 22 is connected to the first cathode pad 20d of the light-receiving element 20. The third pad 22v of the TIA 22 is connected to the second cathode pad 20v of the light receiving element 20. With the above configuration, the resonant frequency caused by parasitic capacitance or inductance can be shifted to a higher frequency. For example, the frequency of the resonant circuit present in the RF current path between the light receiving element 20 and the TIA 22 can be set to 100 GHz or higher.

[0033] The first pad 22b of the TIA 22 may be connected to the anode pad 20c of the light receiving element 20 via a pillar 25 or a bump. The second pad 22c of the TIA 22 may be connected to the first cathode pad 20d of the light receiving element 20 via a pillar 25 or a bump. The third pad 22v of the TIA 22 may be connected to the second cathode pad 20v of the light receiving element 20 via a pillar 25 or a bump.

[0034] The TIA 22 may further include a ground layer 22h having a reference potential. The ground layer 22h of the TIA 22 may be connected to the cathode wiring layer 22f of the TIA 22 via a capacitance (capacitor).

[0035] 8 and 9, the optical receiver 1 may further include a back surface ground 22k provided on the back surface of the TIA 22A (TIA 22B) having a reference potential. The ground layer 22h of the TIA 22A may be provided on the back surface side of the cathode wiring layer 22f, and may be connected to the back surface ground 22k via a TSV or DSV.

[0036] A back surface metal layer may be provided on the back surface of the light receiving element 20.

[0037] As shown in Figures 4 and 5, the cathode wiring layer 22f (cathode wiring) may surround the first pad 22b. The first cathode pad 20d (cathode electrode), the second cathode pad 20v (cathode electrode), and the cathode wiring pattern 20g (cathode wiring) may surround the anode pad 20c (anode electrode) and the anode wiring pattern 20f (anode wiring) from both sides. In this case, the cathode electrode and cathode wiring surround the anode electrode and anode wiring from both sides, so that magnetic fields generated by currents flowing through the light-receiving element 20 cancel each other out. This makes it difficult for the magnetic field to leak outside the cathode wiring, thereby reducing crosstalk due to electromagnetic coupling to other lanes.

[0038] Next, examples of optical receivers according to the present disclosure will be described. Note that the present disclosure is not limited to the examples described below. An optical receiver 1C according to a first embodiment and an optical receiver 1D according to a second embodiment will be described with reference to FIGS. 11 and 12.

[0039] As shown in FIG. 11, the optical receiver 1C according to the first embodiment includes a TIA 22C and a photodetector 20C mounted on a substrate 30. The substrate 30 is made of CuW (copper tungsten). The TIA 22C is made of Si (silicon). A conductive silver paste 26 is interposed between the substrate 30 and the TIA 22C. A pad 30b is provided on the substrate 30. The pad 30b and a pad 22q connected to a ground layer 22h of the TIA 22C are connected to each other by a bonding wire X. A back surface metal 20j is provided on a back surface 20h of the photodetector 20C opposite to the surface 20b facing the TIA 22C.

[0040] 11 and 12, the optical receiver 1D according to the second embodiment is different from the optical receiver 1C according to the first embodiment in that it includes a light-receiving element 20D that does not have a back surface metal 20j on the back surface 20h. Examples of resonance frequencies in the optical receiver 1C according to the first embodiment and the optical receiver 1D according to the second embodiment are shown in FIGS.

[0041] Fig. 13 is a graph showing the resonance frequency of the optical receiver 1C according to Example 1 for each channel of the light receiving element. Fig. 14 is a graph showing the resonance frequency of the optical receiver 1D according to Example 2 for each channel of the light receiving element. As shown in Figs. 13 and 14, in Example 2 which does not have the back surface metal 20j, it was found that the resonance frequency (resonance point) shifts slightly to the high frequency side (approximately 85 GHz) compared to Example 1 which has the back surface metal 20j.

[0042] An optical receiver 1E according to a third embodiment and an optical receiver 1F according to a fourth embodiment will be described with reference to FIGS. 15 and 16. The optical receiver 1E according to the third embodiment includes a TIA 22E and a photodetector 20E mounted on a substrate 30. The TIA 22E has a plurality of vias 22t formed therein, extending along the stacking direction of the photodetector 20E. A silicon nitride (SiN) 27 is interposed between the photodetector 20E and the TIA 22E. A back surface metal 20j is provided on a back surface 20h of the photodetector 20E, which is opposite to a surface 20b facing the TIA 22E. The optical receiver 1F according to the fourth embodiment differs from the optical receiver 1E according to the third embodiment in that the optical receiver 1F includes a photodetector 20F that does not have a back surface metal 20j on the back surface 20h.

[0043] FIG. 17 is a graph showing the resonance frequency of the optical receiver 1E according to Example 3 for each channel of the light receiving element. FIG. 18 is a graph showing the resonance frequency of the optical receiver 1F according to Example 4 for each channel of the light receiving element. As shown in FIGS. 17 and 18, in Examples 3 and 4 in which a plurality of vias 22t extending along the stacking direction are formed, it was found that the resonance frequency can be increased to about 100 GHz. In Example 4, which does not have the back surface metal 20j, it was found that the resonance frequency can be shifted further to the high frequency side (about 130 GHz) compared to Example 3 in which the back surface metal 20j is provided.

[0044] Next, an optical receiver 1G according to a fifth embodiment will be described with reference to Figs. 19 to 21. As shown in Fig. 19, the optical receiver 1G includes a photodetector 20G and a TIA 22G. The photodetector 20G and the TIA 22G are FCB-connected. The photodetector 20G has an anode pad 20c, a first cathode pad 20d, and a second cathode pad 20v provided on a surface 20b facing the TIA 22G.

[0045] The anode pad 20c is connected to the anode electrode of the light receiving element 20 via an anode wiring pattern 20f. The light receiving element 20G includes a cathode relay pad 20p connected between the cathode electrode of the light receiving element 20G and the first cathode pad 20d via a cathode wiring pattern 20g. The TIA 22G includes a cathode wiring layer 22f therein.

[0046] FIG. 20 shows a cross-sectional view of the light-receiving element 20G and the TIA 22G taken along the first direction A1 (line A1'-A1') in FIG. 19. FIG. 21 shows a cross-sectional view of the light-receiving element 20G and the TIA 22G taken along the second direction A2 (line A2'-A2') in FIG. 19. As shown in FIGS. 19 to 21, the TIA 22G is connected to the cathode wiring layer 22f on the surface of the insulating layer 22j through a via 22r (second via). The TIA 22G includes a relay pad 22s disposed at a position corresponding to the cathode relay pad 20p of the light-receiving element 20G and spaced apart from the second pad 22c and the third pad 22v. The relay pad 22s of the TIA 22G is connected to the cathode relay pad 20p of the light-receiving element 20G via a pillar 29.

[0047] As described above, the light-receiving element 20G according to the fifth embodiment may include a cathode relay pad 20p connected between the cathode electrode and the first cathode pad 20d via the cathode wiring pattern 20g. The TIA 22 includes a relay pad 22s connected to the cathode wiring layer 22f on the surface of the insulating layer 22j via the via 22r and disposed at a position corresponding to the cathode relay pad 20p of the light-receiving element 20, spaced apart from the second pad 22c and the third pad 22v. The relay pad 22s of the TIA 22G may be connected to the cathode relay pad 20p of the light-receiving element 20 via a pillar 29.

[0048] Fig. 22 is a graph showing the resonant frequency for each channel of the optical receiver 1G according to Example 5. As shown in Fig. 22, in the optical receiver 1G according to Example 5 including the photodetector 20G and the TIA 22G connected to each other at four cathode pads, it was found that the resonant frequency could be shifted further to the higher frequency side, to about 160 GHz.

[0049] Various embodiments and examples of the optical receiver according to the present disclosure have been described above. However, the present invention is not limited to the above-described embodiments. In other words, those skilled in the art will readily recognize that various modifications and variations are possible within the scope of the claims. For example, the shape, size, number, material, and arrangement of each component of the optical receiver are not limited to those described above and can be modified as appropriate. [Explanation of symbols]

[0050] 1, 1C, 1D, 1E, 1F, 1G...Optical receiver 11...Package 11a, 11aa, 11ab…side wall 11b…Bottom plate 12...Bush 13...Optical window 14...Optical axis converter 14b...Mirror 15...Optical demultiplexer 16...Lens 17...Feedthrough 17a...Terminal 20, 20A, 20B, 20C, 20D, 20E, 20F, 20G...Photodetector 20b...side 20c...Anode pad (anode electrode) 20d...First cathode pad (cathode electrode) 20f...Anode wiring pattern (anode wiring) 20g...Cathode wiring pattern (cathode wiring) 20h...Back side 20j…back side metal 20p...Cathode relay pad 20v...Second cathode pad (cathode electrode) 20w...Cathode pad (cathode electrode) 21... Circuit board 22, 22A, 22B, 22C, 22E, 22G...TIA (Transimpedance Amplifier) 22b...First pad 22c...2nd pad 22d…Surface 22f...Cathode wiring layer 22g...Via (first via) 22h: Ground layer 22j...insulating layer 22k...back ground 22m...Beer 22p…Beer 22q...Pad 22r...Via (second via) 22s...Relay pad 22t...Beer 22v...3rd pad 22w...pad 24...Capacitor 25...Pillar 26...Silver paste 29...Pillar 30...Substrate 30b...pad A1…first direction A2…Second direction X...Bonding wire

Claims

1. anode electrode, Anode wiring pattern, an anode pad connected to the anode electrode via the anode wiring pattern; a cathode electrode, Cathode wiring pattern, and a first cathode pad and a second cathode pad connected to the cathode electrode via the cathode wiring pattern and disposed at positions sandwiching the anode pad; a light receiving element having a cathode wiring layer that supplies a cathode potential to the first cathode pad and the second cathode pad of the light receiving element; an insulating layer having the cathode wiring layer therein; a first pad provided on the insulating layer and connected to the anode pad of the light receiving element; a second pad provided on the insulating layer, connected to the cathode wiring layer through a first via, and disposed at positions sandwiching the first pad, the second pad being connected to the first cathode pad of the light receiving element; and a third pad connected to the second cathode pad of the light receiving element; a transimpedance amplifier having Equipped with the anode pad of the light receiving element provided on a surface facing the transimpedance amplifier is connected to the first pad of the transimpedance amplifier; the first cathode pad of the light receiving element is connected to the second pad of the transimpedance amplifier; the second cathode pad of the light receiving element is connected to the third pad of the transimpedance amplifier; a rear surface ground provided on a rear surface of the transimpedance amplifier and connected to a reference potential; a ground layer of the transimpedance amplifier is provided on the back surface side of the cathode wiring layer and is connected to the back surface ground via a TSV (Through Silicon Via) or a DSV (Deep Silicon Via); Optical receiver.

2. the first pad of the transimpedance amplifier is connected to the anode pad of the light receiving element via a columnar member or a protrusion; the second pad of the transimpedance amplifier is connected to the first cathode pad of the light receiving element via a columnar member or a protrusion; the third pad of the transimpedance amplifier is connected to the second cathode pad of the light receiving element via a columnar member or a protrusion; 2. The optical receiver of claim 1.

3. anode electrode, Anode wiring pattern, an anode pad connected to the anode electrode via the anode wiring pattern; a cathode electrode, Cathode wiring pattern, and a first cathode pad and a second cathode pad connected to the cathode electrode via the cathode wiring pattern and disposed at positions sandwiching the anode pad; a light receiving element having a cathode wiring layer that supplies a cathode potential to the first cathode pad and the second cathode pad of the light receiving element; an insulating layer having the cathode wiring layer therein; a first pad provided on the insulating layer and connected to the anode pad of the light receiving element; a second pad provided on the insulating layer, connected to the cathode wiring layer through a first via, and disposed at positions sandwiching the first pad, the second pad being connected to the first cathode pad of the light receiving element; and a third pad connected to the second cathode pad of the light receiving element; a transimpedance amplifier having Equipped with the anode pad of the light receiving element provided on a surface facing the transimpedance amplifier is connected to the first pad of the transimpedance amplifier; the first cathode pad of the light receiving element is connected to the second pad of the transimpedance amplifier; the second cathode pad of the light receiving element is connected to the third pad of the transimpedance amplifier; a rear surface ground provided on a rear surface of the transimpedance amplifier and connected to a reference potential; the transimpedance amplifier further includes a ground plane connected to a reference potential; the ground layer of the transimpedance amplifier is connected to the cathode wiring layer of the transimpedance amplifier via a capacitor; Optical receiver.

4. the light receiving element includes a cathode relay pad connected between the cathode electrode and the first cathode pad via the cathode wiring pattern; the transimpedance amplifier includes a relay pad that is connected to the cathode wiring layer on the surface of the insulating layer through a second via, and that is disposed at a position corresponding to the cathode relay pad of the light receiving element and spaced apart from each of the second pad and the third pad; the relay pad of the transimpedance amplifier is connected to the cathode relay pad of the light receiving element via a first columnar member; 4. An optical receiver according to claim 1.

5. A back surface metal layer is provided on the back surface of the light receiving element.

5. An optical receiver according to claim 1.

6. the cathode wiring layer surrounds the first pad, the cathode electrode and the cathode wiring pattern are disposed on both sides of the anode electrode and the anode wiring pattern; 6. An optical receiver according to claim 1.

7. anode electrode, Anode wiring pattern, an anode pad connected to the anode electrode via the anode wiring pattern; a cathode electrode, Cathode wiring pattern, and a first cathode pad and a second cathode pad connected to the cathode electrode via the cathode wiring pattern and disposed at positions sandwiching the anode pad; a light receiving element having a cathode wiring layer that supplies a cathode potential to the first cathode pad and the second cathode pad of the light receiving element; an insulating layer having the cathode wiring layer therein; a first pad provided on the insulating layer and connected to the anode pad of the light receiving element; a second pad provided on the insulating layer, connected to the cathode wiring layer through a first via, and disposed at positions sandwiching the first pad, the second pad being connected to the first cathode pad of the light receiving element; and a third pad connected to the second cathode pad of the light receiving element; a transimpedance amplifier having Equipped with the anode pad of the light receiving element provided on a surface facing the transimpedance amplifier is connected to the first pad of the transimpedance amplifier; the first cathode pad of the light receiving element is connected to the second pad of the transimpedance amplifier; the second cathode pad of the light receiving element is connected to the third pad of the transimpedance amplifier; a rear surface ground provided on a rear surface of the transimpedance amplifier and connected to a reference potential; the cathode wiring layer surrounds the first pad, the cathode electrode and the cathode wiring pattern are disposed on both sides of the anode electrode and the anode wiring pattern; Optical receiver.

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