Optical module and method for manufacturing same

Abstract

Provided are: an optical module capable of suppressing high frequency oscillations and operating stably; and a method of manufacturing the same. An optical module according to the present disclosure includes: either a driver IC chip and a modulator chip or a TIA chip and a receiver chip that are integrated in the same package having an RF terrace connected to an RF interface; wires that connect the driver IC chip and the modulator chip or the TIA chip and the receiver chip, and the driver IC chip and the RF terrace or the TIA chip and the RF terrace, respectively, a plurality of the wires being installed at each connection point; and a lid that serves as a cover part disposed at a position facing the driver IC chip and the modulator chip or the TIA chip and the receiver chip. The vertical distance from the surface of the driver IC chip or the surface of the TIA chip to the surface of the lid is less than half a wavelength dependent on the atmosphere in the package at a frequency of 0.7 times the operating baud rate.

Description

Optical module and manufacturing method thereof

[0001] The present disclosure relates to an optical module and a method for manufacturing the same.

[0002] In order to meet the increasing demand for communication traffic, high-speed optical modulators and optical receivers compatible with advanced optical modulation methods are required. In the optical modulators and optical receivers used in early 100G digital coherent communication systems, each component was packaged and mounted on a printed circuit board (PCB). For example, in the case of an optical modulator, the driver IC and optical modulator chip were individually packaged, and the packaged ICs and chips were mounted on the PCB. In the case of an optical receiver, the transimpedance amplifier (TIA) and optical receiver chip were individually packaged and mounted on the PCB as separate components.

[0003] In digital coherent communication systems exceeding 400 Gbps, which are experiencing ever-increasing speeds, optical modulators and optical receivers are also required to have wider bandwidths to handle signals of 40 GHz and above, necessitating reduced high-frequency loss and miniaturization. In the case of optical modulators, the driver IC and optical modulator chip are now integrated into a single package as an optical module. In the case of optical receivers, the TIA and optical receiver chip are now integrated into a single optical module. Regarding the signal format for inputting and outputting baseband signals, a shift from single-ended to differential designs has become common as one means of achieving higher speeds, smaller size, and lower power consumption. Currently, device development is underway to achieve 800 Gbps and 1 Tbps (128 GBd operation).

[0004] The Optical Internetworking Forum (OIF) has standardized an optical transmitter in which a driver IC and an optical modulator are mounted in an integrated package under the name High-Bandwidth Coherent Driver Modulator (HB-CDM). Non-Patent Document 1 specifies various types of modules, including their physical configurations and interface specifications. On the receiving side, a TIA and an optical receiver are mounted in an integrated package, also known as a High-Bandwidth Intradyne Coherent Receiver (HB-ICR).

[0005] As described above, in the current demand for wider bandwidth digital coherent communication systems, the driver IC, TIA, etc. are integrated into the same package as the optical device, which makes the mounting state extremely complicated, and there is a problem that it is much more difficult to always achieve stable operation within the entire operating frequency band than when the driver IC, TIA, etc. are individually packaged. Specifically, depending on the mounting state, an event such as oscillation occurs within the required frequency band, which may cause deterioration of the characteristics of the optical module (optical modulator module and optical receiver module).

[0006] OIF, Implementation Agreement for the High Bandwidth Coherent Driver Modulator (HB-CDM), [online], July 15, 2021, [Retrieved January 20, 2023], Internet <URL: https: / / www.oiforum.com / wp-content / uploads / OIF-HB-CDM-02.0.pdf>. A.L.M.T. Corporation, Heatsink Material Properties List, [online], June 4, 2018, Internet <URL: https: / / www.allied-material.co.jp / dcms_media / other / t52nn.pdf>. J. Ozaki et al., “Over-85-GHz-bandwidth InP-based Coherent Driver Modulator Capable of 1-Tb / s / λ-class Operation,” IEEE / OSA Journal of Lightwave Technology, vol. 41, issue 11, pp. 3290-3296 (2023).

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and its purpose is to propose an optical module in which a driver IC and an optical modulator chip, or a TIA and an optical receiver chip, are mounted adjacent to each other in the same package, which suppresses oscillation of high-frequency characteristics and can operate stably, and a method for manufacturing the same.

[0008] In response to the above-described problems, the present disclosure provides an optical module comprising either a driver IC chip and a modulator chip, or a TIA chip and a receiver chip, integrated in the same package having an RF terrace connected to an RF interface; wires connecting the driver IC chip and the modulator chip, or the TIA chip and the receiver chip, and the driver IC chip and the RF terrace, or the TIA chip and the RF terrace, and each being installed at a plurality of connection points; and a lid serving as a cover portion arranged in a position facing the driver IC chip and the modulator chip, or the TIA chip and the receiver chip, wherein the vertical distance from the surface of the driver IC chip or the surface of the TIA chip to the surface of the lid is less than 1 / 2 the wavelength corresponding to the atmosphere inside the package at a frequency 0.7 times the operating baud rate.

[0009] 1A and 1B are side cross-sectional views schematically showing the structure of an optical module 100 according to the present disclosure; FIG. 1C is a diagram schematically showing the structure of an optical module 200 according to the present disclosure; FIG. 1D is a side cross-sectional view schematically showing the configuration of an optical module 300 according to the present disclosure, where (a) is a side cross-sectional view and (b) is a top view of a driver IC chip 101 installed on a metal block 106; FIG. 1E is a side cross-sectional view schematically showing the structure of an optical module 400 according to the present disclosure. A prototype HB-CDM capable of 160 GBd-class operation, equipped with a driver IC chip 101 and a modulator chip 102, was fabricated, and the thickness of the lid 110 was changed to adjust the distance between the surface of the driver IC chip 101 and the surface of the lid 110, thereby making the distance less than half the wavelength at the maximum frequency, thereby confirming the effect of suppressing oscillation.

[0010] Various embodiments of the present disclosure will be described in detail below with reference to the drawings. The same or similar reference numerals indicate the same or similar elements, and redundant description may be omitted. Numerical values ​​are for illustrative purposes and are not intended to limit the technical scope of the present disclosure. Furthermore, the following description is an example, and some configurations may be omitted or modified, or additional configurations may be added, as long as they do not deviate from the gist of one embodiment of the present disclosure.

[0011] In the following description, the optical module according to the present disclosure is described as an HB-CDM in which a driver IC chip and a modulator chip are mounted in a single package. However, this is for illustrative purposes only, and the optical module according to the present disclosure may be an optical module having the same or a similar configuration (for example, an optical receiver module (e.g., HB-ICR) in which the driver IC chip is replaced with a TIA and the modulator chip is replaced with a receiver chip, or an optical transmitter / receiver module (e.g., IC-TROSA)).

[0012] FIG. 1 is a side cross-sectional view schematically illustrating the structure of an optical module 100 according to the present disclosure. As shown in FIG. 1 , the optical module 100 has a configuration in which a driver IC chip 101, a modulator chip 102, a Peltier element 103, and an optical mounting member 104 are mounted in a package 105. The optical module 100 also includes an RF terrace 109 connected to a radio frequency (RF) signal interface (e.g., a flexible printed circuit board), and a lid 110 serving as a cover for the optical module 100, formed in a position facing the top surfaces of the driver IC chip 101 and the modulator chip 102. The driver IC and the modulator chip 102, and the driver IC and the RF terrace 109, are connected by wires 108. The package 105 is hermetically sealed. 1, the lid 110 is depicted as being divided into a thin plate portion 110a disposed on the outside and a thick plate portion 110b disposed on the inside, but this is merely an example, and the thin plate portion 110a and the thick plate portion 110b may be integrally molded. Furthermore, the thick plate portion 110b may be a single layer (a single-sheet structure) as shown in FIG. 1, or may be a multi-layer structure (a structure including an additional metal block for thickness adjustment).

[0013] As shown in FIG. 1 , the driver IC chip 101 may be mounted on a metal block 106 or on a package 105 made of a ceramic material (dielectric material). However, for stable operation of the driver IC chip 101, it is important to stabilize the ground plane of the driver IC chip 101. Therefore, from the viewpoint of stabilizing the ground potential, it is desirable to mount the driver IC chip 101 on the metal block 106. In addition, since the driver IC chip 101 generates a large amount of heat, it is also desirable to mount it on the metal block 106 from the viewpoint of heat dissipation. The material of the metal block 106 may be, for example, CuW. Furthermore, the metal block 106 is mounted in the package 105 by soldering, and the driver IC chip 101 is mounted on the metal block 106 using a conductive paste, low-temperature solder, or the like. These bonding aids are suitable as mounting aids because they reduce the thermal load on the driver IC chip 101 and have excellent thermal conductivity.

[0014] The modulator chip 102 uses InP and therefore requires temperature control. For this reason, the modulator chip 102 is mounted on a Peltier element 103, allowing for temperature control. As shown in FIG. 1 , the optical module 100 may include a substrate 107 between the Peltier element 103 and the modulator chip 102. The substrate 107 may be made of AlN and configured to carry DC wiring for the modulator chip 102. The substrate 107 may also include alignment marks for mounting the optical mounting member 104. Alternatively, the optical module 100 may not include the substrate 107. In such a case, wiring a similar metal pattern on the top surface of the Peltier element 103 (the surface to which the modulator chip 102 is connected) achieves the same functionality. Furthermore, such a configuration that does not include a substrate 107 reduces the number of contact points between elements and the number of components, which leads to reduced thermal resistance and ultimately reduces the power consumption of the Peltier element 103.

[0015] As described above, AlN is used for the substrate 107. This is because AlN has a linear expansion coefficient similar to that of InP used in the modulator chip 102, thereby providing excellent material matching, such as suppressing thermal stress caused by differences in thermal expansion coefficients (see, for example, Non-Patent Document 2). Therefore, it is desirable to use AlN for the upper surface of the Peltier element 103, regardless of whether or not the substrate 107 is present. Accordingly, it is also desirable to use AlN for the lower surface of the Peltier element 103 (the surface that contacts the package 105). This is due to deformation (warping) caused by the application of temperature when the Peltier element 103 is fixed to the package 105 by soldering. Specifically, a high temperature of 200°C or higher is applied to the Peltier element 103 during the soldering process. If the upper and lower surfaces of the Peltier element 103 are made of different ceramic materials, the Peltier element 103 may be fixed in a warped state. Furthermore, if other components are formed in this warped state, the warping can increase optical loss. Therefore, it is desirable that both the upper and lower surfaces of the Peltier element 103 are made of AlN.

[0016] The Peltier element 103 and substrate 107, or the Peltier element 103 and modulator chip 102, need to be mounted using a material with excellent thermal conductivity (for example, solder or conductive paste), similar to the driver IC chip 101 and metal block 106. This is because if they are fixed using a bonding aid with low thermal conductivity, the power consumption of the Peltier element 103 increases due to an increase in thermal resistance.

[0017] The optical mounting members 104 may be, for example, lenses. In FIG. 1 , two optical mounting members 104 (optical mounting members 104 a and 104 b ) are depicted as being mounted on the substrate 107, but all of the optical mounting members 104 do not necessarily need to be mounted on the substrate 107. However, it is desirable that the optical mounting members 104 be mounted on the same member as the modulator chip 102 so that the optical mounting members 104 can adapt to warping and other distortions that may occur during various operations. Furthermore, when all of the optical mounting members 104 are mounted on the Peltier element 103, the optical mounting members 104 are maintained at a constant temperature, thereby suppressing fluctuations in the optical mounting members 104 due to temperature dependency, thereby achieving the effect of stabilizing the optical characteristics regardless of temperature.

[0018] The optical module 100 according to the present disclosure having such a configuration includes additional components for suppressing oscillation in the high frequency characteristics described above. The configuration will be described in detail below.

[0019] (Distance between Driver IC and Lid) The following describes the positional relationship of each component when considering high-frequency characteristics. The vertical distance from the surface of the driver IC chip 101 to the surface of the lid 110 (corresponding to the vertical distance from the surface of the driver IC chip 101 to the surface of the thick plate portion 110b facing the driver IC 101 in the embodiment shown in FIG. 1) must be less than half the wavelength corresponding to the atmosphere inside the package 105 at a frequency 0.7 times the operating baud rate in order to prevent oscillation within the required frequency band. 0.7 times the operating baud rate is a value that generally indicates the frequency band required to operate at that baud rate. Since the operation of the driver IC chip 101 is particularly prone to become unstable in higher frequency ranges, it is important to consider the state at maximum frequency.

[0020] For example, assuming 128 GBd operation, a frequency 0.7 times the operating baud rate is approximately 90 GHz. If the atmosphere inside the package 105 is air, the relative dielectric constant is approximately 1. Therefore, when a 90 GHz signal is converted into a wavelength, the signal wavelength is approximately 3.33 mm. From the above perspective, the optical module 100 must be configured so that this wavelength does not coincide with the structural cavity resonance frequency. Cavity resonance generally occurs when the length of the space (cavity) is an integer multiple of λ / 2, resulting in a standing wave. If the length coincides with the resonant wavelength, resonance occurs within the space, resulting in oscillation with high-frequency characteristics. Therefore, to suppress this cavity resonance, the length of the space (cavity) must be less than half the spatial wavelength, thereby suppressing the occurrence of resonance across the entire frequency band. This is because if the length of the space (cavity) is less than half the wavelength at the maximum frequency, it is possible to ensure that all frequencies below that length are less than half the wavelength. Ideally, the entire length of the entire space within the package 105 should be less than half the wavelength at the maximum frequency. However, this is difficult in reality, so it is sufficient to simply set the length of the portion that contributes most to the generation of resonance to half the wavelength at the maximum frequency. This most contributing portion is the vertical distance from the surface of the driver IC chip 101 to the surface of the lid 110. Because the driver IC chip 101 contains factors that can cause unstable operation and has the function of amplifying high-frequency signals, it is most important that the portion of the driver IC chip 101 that most affects the characteristics satisfies this condition. Therefore, since the electromagnetic field distribution is also radiated upward from the driver IC chip 101, it is sufficient that the vertical distance from the surface of the driver IC chip 101 to the lid 110 is less than half the wavelength at the maximum frequency. However, the vertical distance between the entire surface of the driver IC 101 and the surface of the lid 110 installed above it must all be less than half the wavelength at the maximum frequency.

[0021] In this manner, in the optical module 100 according to the present disclosure, the driver IC chip 101 and the lid 110 are closely spaced in the vertical direction, thereby preventing cavity resonance within the required frequency band (the vertical distance from the driver IC chip 101 to the surface of the lid 110 must be an integer multiple of λ / 2 throughout the required frequency band). In FIG. 1 , the thick plate portion 110b of the lid 110 is depicted as extending to positions facing not only the driver IC chip 101 but also the modulator chip 102 and the optical mounting member 104. However, as in the optical module 200 shown in FIG. 2 , the thick plate portion 110b of the lid 110 may be formed only in the portion corresponding to the driver IC chip 101, which is a space requiring particular attention. For example, if the optical mounting member 104 is positioned higher than the surface of the driver IC chip 101, interference between the thick plate portion 110b of the lid 110 and the optical mounting member 104 may occur in the optical module 100. In that case, the configuration of the optical module 200 is useful. Furthermore, if there is a possibility that the thick plate portion 110b of the lid 110 may interfere with another member (for example, the optical mounting member 104), the thick plate portion 110b of the lid 110 may have a structure in which the interfering portion is thin.

[0022] (Distance between the driver IC and the modulator chip, and between the driver IC and the RF terrace) In order to realize a wideband optical modulator, it is extremely important to reduce the distance between the RF terrace 109 and the driver IC chip 101, and between the driver IC chip 101 and the modulator chip 102, as much as possible, and to suppress the inductance of the connecting wires 108. Considering the impact on high-frequency characteristics, it is particularly important to suppress the inductance of the wires 108b connecting the driver IC chip 101 and the modulator chip 102, and it is important to consider the mounting positional relationship of this part (see, for example, Non-Patent Document 3). For example, the distance and height difference between the driver IC chip 101 and the modulator chip 102 must be 100 μm or less. On the other hand, the distance and height difference between the driver IC chip 101 and the RF terrace 109 have a smaller impact on characteristics than the former, so both the distance and height difference can be tolerated up to 200 μm or less.

[0023] (Wire Configuration and Bonding Procedure) Because FIG. 1 is a side cross-sectional view, it appears that there is only one wire 108a, one wire 108b, but from the perspective of suppressing the inductance of the wire 108, there may be multiple wires 108a, one wire 108b. For example, if two or more wires are connected to each signal line PAD, it is possible to effectively reduce wire inductance. Note that the height difference values ​​listed above are based on the assumption that all wires 108 are ball wires and that there are two or more wires 108a, one wire 108b per signal line. If there is only one wire 108a, one wire 108b, the wire inductance will be large, making it difficult to realize an optical module requiring speeds of 128 GBd or more.

[0024] Considering the loop shape of the wire 108, it is best to launch the wire 108 from a lower position to a higher position during bonding in order to minimize the length of the wire 108. Furthermore, in drivers that achieve operation of 128 GBd or higher, as shown in Non-Patent Document 3, driver ICs fabricated with SiGe BiCMOS are used. These SiGe BiCMOS driver ICs typically use Al electrode pads, and Au wires are typically used for the wires. Furthermore, Au electrode pads are also typically used for modulator chips and optical communication devices. That is, the connection between the driver IC chip 101 and the wire 108 is not an Au-Au bond, but an Au-Al dissimilar material connection. Care must be taken when forming the wire 108 to suppress aging and environmental degradation at the Au-Al dissimilar material connection and ensure long-term reliability. Specifically, it is known that a large amount of Au is desirable to ensure long-term stability for the connection portion with the Al electrode pad of the driver IC chip 101. Therefore, it is desirable to insert the wire 108 on the driver IC chip 101 side having the Al electrode pad in the first bonding step, which forms a ball in bonding, and then perform bonding on the modulator chip 102 or RF terrace 109 side as the second bonding step.

[0025] From the viewpoint of mounting in this manner, it is desirable that the driver IC chip 101 be mounted so that it is lower than the modulator chip 102 and the RF terrace 109. Furthermore, the ball thickness in the first bonding of the wire 108 is about 50 μm, and taking into consideration the shape adjustment of the wire 108, it is desirable that the height differences between the driver IC chip 101 and the modulator chip 102 and between the driver IC chip 101 and the RF terrace 109 are both about 50 to 100 μm.

[0026] However, the bonding procedure is not limited to the above. In the connection between the driver IC chip 101 and the modulator chip 102 and between the driver IC chip 101 and the RF terrace 109 using the wire 108, the driver IC chip 101 side may be second-bonded, and first-bonded on the modulator chip 102 and the RF terrace 109 side. When bonding using this procedure, it is desirable to form a ball-on-wire shape on the driver IC chip 101 side. That is, a ball is formed on the driver IC chip 101 side in advance, and then the wire 108 is struck on the ball formed on the driver IC chip 101 in the second bonding. This makes it possible to ensure the reliability of the connection even when the driver IC chip 101 side is second-bonded. Furthermore, when bonding using this procedure, in order to minimize the length of the wire 108, balls are formed on all of the driver IC chip 101, the modulator chip 102, and the RF terrace, so there is no need to consider the height of the ball, and it is desirable that these heights are approximately the same.

[0027] (Formation of Metal Pillars) As described above, from the viewpoint of suppressing oscillations in the high-frequency characteristics due to instability of the driver IC chip 101, it is extremely important to manage the vertical distance from the surface of the driver IC chip 101, which is fixed to the package 105 by seam welding, to the surface of the lid 110. To operate the driver IC chip 101 at high speed, it may be difficult to achieve absolute stability (k-factor > 1) in both the differential and common-mode characteristics across all frequency bands and under any load conditions. In such cases, oscillations may occur in the high-frequency characteristics due to ground instability caused by, for example, the inductance of the wires 108 during mounting. To avoid ground instability and ensure the stability of the driver IC chip 101, it is possible to reduce inductance by grounding the driver IC chip 101 with as many wires as possible and to minimize the length of the ground wires from the driver IC chip 101.

[0028] FIG. 3 is a schematic diagram illustrating the configuration of an optical module 300 according to the present disclosure. In addition to the configuration of the optical module 100 described above, the optical module 300 according to this embodiment includes a metal pillar 301 disposed on the metal block 106 and adjacent to the driver IC chip 101, and a ground wire 302 connecting the metal pillar 301 to the driver IC chip 101. While FIG. 2 depicts four metal pillars 301 and four ground wires 302, this is for illustrative purposes only, and any number may be arranged depending on the design. Furthermore, the metal pillar 301 may be made of, for example, Au-plated CuW to ensure connectivity with Au wires. Since heat dissipation and consistency of material constants are not required for this part, it is of course acceptable to use other metals as the base material.

[0029] As described above, in order to suppress oscillation in the high-frequency characteristics (stabilize the ground potential of the driver IC 101), it is desirable to shorten the length of the ground wire 302 from the driver IC chip 101. From the perspective of minimizing the length of the ground wire 302, it is desirable to install a metal pillar 301 on the metal block 106 so that it is higher than the driver IC chip 101. This is because, if the metal pillar 301 is struck down (or if the driver and the metal block are the same height), the length will be longer by the thickness of the ball if a ball wire is used. For the reasons described above, it is desirable to perform first bonding on the driver IC chip 101 side. However, as with the RF connection portion described above, second bonding may also be performed on the driver IC chip 101. In such a case, it is desirable to perform a bonding procedure in which a ball is formed on the driver IC chip 101 in advance and the ground wire 302 is struck on the ball during second bonding. Note that, if such second bonding is performed on the driver IC chip 101 side, it is desirable that the height of the surface of the pad arranged on the top surface of the driver IC chip 101 and the top surface of the metal pillar 301 are approximately the same.

[0030] Another method for suppressing oscillation in the high-frequency characteristics is to provide a ground pad on the RF terrace 109 disposed adjacent to the driver IC chip 101. However, while the configuration described above allows the driver IC chip 101 and the metal pillar 301 to be disposed very close to each other, at a distance of 100 μm or less, the configuration described below requires the RF terrace 109 to be positioned closer to the driver IC chip 101. To achieve this, the driver IC chip 101 is inserted into the package 105 later. Therefore, considering tolerances and workability during mounting, this configuration has the disadvantage of being more difficult to position closer than a configuration in which the metal pillar 301 is formed. Therefore, the configuration in which the metal pillar 301 is formed is preferable from the viewpoint of minimizing the length of the ground wire 302.

[0031] (Formation of Radio Wave Absorber) FIG. 4 is a side cross-sectional view schematically illustrating the structure of an optical module 400 according to the present disclosure. As shown in FIG. 4, the optical module 400 includes, in addition to the components of the optical module 100, a radio wave absorber 401 formed on the lid 110. Note that FIG. 4 depicts a configuration in which the radio wave absorber 401 is formed on the thick plate portion 110b of the lid 110, but this is intended as an example and is not limited to the configuration shown in FIG. 4. As described above, the thick plate portion 110 may be configured with multiple layers, and additional metal blocks may be further disposed to adjust the thickness. In such a configuration, the radio wave absorber 401 is formed on the additional metal block.

[0032] From the perspective of more efficiently suppressing oscillation in high-frequency characteristics, if a frequency prone to oscillation is identified, it is effective to absorb radio waves in the frequency band where there is a risk of oscillation. The radio wave absorber 401 is configured to absorb radio waves in such a frequency band where there is a risk of oscillation. In addition, the radio wave absorber 401 can also be configured to absorb light having the same wavelength as the signal light. The signal light here may be, for example, the 1.55 μm or 1.3 μm band often used as signal light in optical communications. The radio wave absorber 401 configured in this manner can also absorb stray light generated by the modulator chip 102 and the optical mounting member 104. This prevents the stray light from reflecting off the surface of the lid 110 and interfering with the signal light, thereby degrading the optical characteristics of the optical module. From a similar perspective, it is desirable that the ceramic members of the package 105 are also configured to absorb signal light.

[0033] (Verification Test) Figure 5 shows the results of a prototype HB-CDM capable of 160 GBd-class operation, which is actually equipped with a driver IC chip 101 and a modulator chip 102. By changing the thickness of the lid 110, the vertical distance from the surface of the driver IC chip 101 to the surface of the lid 110 was adjusted to be less than half the wavelength at the maximum frequency, and the oscillation suppression effect was confirmed. In the prototype HB-CDM, the driver IC chip 101 installed inside had a k-factor, which indicates driver stability, of less than 1 at 80 to 90 GHz, based on high-frequency measurement data of the driver IC chip 101 alone. In other words, it is known that the driver IC chip 101 is not absolutely stable, and if it becomes unstable due to the mounting state or the like, there is a very high risk of oscillation at frequencies of 80 to 90 GHz where k-factor is less than 1.

[0034] As shown in Figure 5, when the vertical distance from the surface of the driver IC chip 101 to the lid 110 is 1.78 mm, it can be confirmed that oscillation occurs at a frequency of 84 GHz. When converted to a wavelength, 84 GHz is approximately 3.57 mm, assuming a relative dielectric constant of 1. Half this wavelength is approximately 1.785 mm, which is equivalent to the vertical distance from the surface of the driver IC chip 101 to the lid 110 of 1.78 mm, and it can be seen that this closely matches the cavity resonance frequency between the surface of the driver IC chip 101 and the surface of the lid 110. Since the prototype HB-CDM is intended for 160 GBd-class operation, the cavity resonance frequency must be set to 160 GHz x 0.7 = 112 GHz or higher. When the relative dielectric constant is 1, 112 GHz is equivalent to a wavelength of approximately 2.68 mm. Therefore, half the wavelength is approximately 1.34 mm, and it is necessary to make the vertical distance from the surface of the driver IC chip 101 to the surface of the lid 110 shorter than this. As shown in the figure, it was confirmed that oscillation was clearly suppressed when the vertical distance from the surface of the driver IC chip 101 to the lid 110 was 1.34 mm.

[0035] In this verification, the shape of the package 105 was fixed, and the thickness of the lid 110 was changed for the study. However, in practice, the thickness of the lid 110 may be fixed and the distance between the driver IC chip and the lid 110 may be adjusted by adjusting the thickness of the package 105. However, if the shape of the package 105 is predetermined, it is effective to adjust the distance between the driver IC chip and the lid 110 by adjusting the thickness of the lid 110, as described above. For example, because the package 105 requires complex routing of RF wiring, DC wiring, and the like, the number of layers and thickness required are predetermined to a certain extent, and it is often impossible to adjust the thickness to the desired level. Furthermore, since the lid 110 is less expensive and more readily available than the package 105, it can be said that it is easier to adjust the distance between the driver IC chip 101 and the lid 110 using the lid 110.

[0036] The above explanation has focused on optical modulator modules, such as HB-CDM, in which an InP modulator chip and a driver IC chip are mounted in the same package. However, the modulator chip does not necessarily have to be an InP modulator chip; it may be a Si modulator or an LN modulator. Furthermore, as mentioned above, the present effect can also be achieved with optical receiver modules such as HB-ICR, in which a TIA and a receiver chip are mounted in the same package, or with IC-TROSA or COSA modules, in which a modulator chip and a driver, a receiver chip and a TIA, and both transmitter and receiver are mounted. Furthermore, since the effect is independent of the number of channels, optical implementation, and package configuration of the optical module, these can have any configuration. In configurations that do not use an InP modulator, the Peltier element 103 and hermetic sealing described above are not necessarily required.

[0037] As described above, the optical module and manufacturing method thereof according to the present disclosure can provide a stable, wideband optical module without oscillation of high-frequency characteristics within a required frequency band. Such an optical module is expected to be applied to high-speed optical communication systems as digital coherent systems.

[0038] REFERENCE SIGNS LIST 100 Optical module 101 Driver IC chip 102 Modulator chip 103 Peltier element 104 Optical mounting member 104a, b Optical mounting member 105 Package 106 Metal block 107 Substrate 108 Wire 108a, b Wire 109 RF terrace 110 Lid 110a Thin plate portion 110b Thick plate portion 200 Optical module 300 Optical module 301 Metal pillar 302 Ground wire 400 Optical module 401 Radio wave absorber

Claims

1. An optical module comprising: a driver IC chip and a modulator chip, or a TIA chip and a receiver chip, integrated in the same package having an RF terrace connected to an RF interface; wires connecting the driver IC chip and the modulator chip, or the TIA chip and the receiver chip, and the driver IC chip and the RF terrace, or the TIA chip and the RF terrace, and each of the wires is installed at each connection point; and a lid serving as a cover portion, disposed at a position facing the driver IC chip and the modulator chip, or the TIA chip and the receiver chip; wherein the vertical distance from the surface of the driver IC chip or the surface of the TIA chip to the surface of the lid is less than 1 / 2 the wavelength corresponding to the atmosphere inside the package at a frequency 0.7 times the operating baud rate.

2. The optical module according to claim 1, wherein the lid is configured such that the vertical distance from the surface of the driver IC chip or the surface of the TIA chip to the surface of the lid only in the portion corresponding to the driver IC chip or the TIA chip is less than 1 / 2 the wavelength corresponding to the atmosphere inside the package at a frequency 0.7 times the operating baud rate.

3. The optical module according to claim 1, wherein the driver IC chip is mounted so that its height is the same as or lower than the heights of the modulator chip and the RF terrace, or the TIA chip is mounted so that its height is the same as or lower than the heights of the receiver chip and the RF terrace.

4. An optical module as described in claim 1, wherein the electrode PAD of the driver IC chip or the TIA chip is Al, the electrode PAD of the modulator chip or the receiver chip and the RF terrace is Au, the wire is an Au ball wire, the distance between the driver IC chip and the modulator chip or the distance between the TIA chip and the receiver chip is 100 μm or less, the height difference between the electrode PAD surface of the driver IC chip and the electrode PAD surface of the modulator chip or the height difference between the electrode PAD surface of the TIA chip and the electrode PAD surface of the receiver chip is within 100 μm, and the distance and height difference between the PAD surface of the RF terrace and the electrode PAD surface of the driver IC chip or the distance and height difference between the PAD surface of the RF terrace and the electrode PAD surface of the TIA chip are both within 200 μm.

5. The optical module described in claim 1, further comprising: a metal block arranged between the driver IC chip or the TIA chip and the package; a metal pillar arranged on the metal block so as to be electrically connected to the metal block; and a ground wire connecting the metal pillar and the driver IC chip or the TIA chip, wherein the height of the driver IC chip or the TIA chip is mounted so as to be the same as or lower than the height of the metal pillar.

6. The optical module according to claim 1, further comprising an electromagnetic wave absorber formed on the lid and configured to absorb light having the same wavelength as electromagnetic waves and signal light in a frequency band in which there is a predicted risk of oscillation.

7. A method for manufacturing an optical module as described in claim 2, wherein the height of the driver IC chip is lower than that of the modulator chip and the RF terrace, or the height of the TIA chip is lower than that of the receiver chip and the RF terrace, comprising bonding the wire, wherein bonding the wire comprises: first bonding to the top surface of the driver IC chip or the TIA chip; and then second bonding to the top surfaces of each of the modulator chip or the receiver chip and the RF terrace.

8. A method for manufacturing an optical module as described in claim 2, wherein the height of the driver IC chip is the same as that of the modulator chip and the RF terrace, or the height of the TIA chip is the same as that of the receiver chip and the RF terrace, comprising bonding the wire, wherein bonding the wire comprises: first bonding to the top surface of each of the modulator chip or the receiver chip and the RF terrace; and then second bonding onto a ball previously formed on the top surface of the driver IC chip or the TIA chip.

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