JP4734310B2 - Chip carrier for semiconductor optical device, optical module, and optical transceiver - Google Patents

Description

  The present invention relates to a chip carrier on which a semiconductor optical device or the like is mounted, an optical module using the chip carrier, and an optical transceiver.

  In general, an optical module includes a chip carrier on which a semiconductor optical element such as a semiconductor laser diode (hereinafter referred to as an LD) or an optical modulator and a chip capacitor are soldered, a power supply terminal, an input signal terminal, a ground terminal, It is formed by incorporating it into a package having optical output fiber connector terminals and the like. A dielectric or semiconductor substrate is used for the chip carrier, and the semiconductor optical device is fixed to the ground metal coating formed on the surface thereof by soldering, and between the high frequency transmission line and the like formed on the same substrate surface. Are connected by wire bonding.

  With recent high-speed operation of semiconductor optical devices, good high-frequency characteristics are also required for chip carriers. A configuration example of a chip carrier for the purpose of improving high-frequency characteristics includes a combination of a conductive base substrate on which a semiconductor optical device is mounted and a dielectric or semiconductor substrate on which a high-frequency transmission line and a terminating resistor are arranged. Is disclosed in Patent Document 1.

Japanese Patent Laid-Open No. 10-275957 (section 4, FIG. 6)

  In a typical chip carrier using only a dielectric or semiconductor substrate, it is not easy to obtain good characteristics in a high frequency range of 20 GHz or higher.

  Further, a chip carrier as disclosed in Patent Document 1 in which a conductive base substrate and a high-frequency transmission substrate are separately provided has a relatively good high-frequency characteristic, but its manufacturing cost is high due to its structure. In addition, there is a problem that the mounting process takes time.

  The problem to be solved by the present invention is to provide a chip carrier having excellent high frequency characteristics and low cost, and an optical module and an optical transceiver incorporating the chip carrier.

  In order to solve the above-described problems, reducing the inductance of the chip carrier is an effective means. That is, a high-frequency transmission line and a ground metal coating are disposed on a dielectric or semiconductor substrate whose back is metal-coated, and the metal coating on the front surface and the metal coating on the back are electrically connected by a metal via hole. In the connected chip carrier, a part or the whole of the side surface of the chip carrier was coated with metal, and the metal-coated portion on the surface of the dielectric or semiconductor substrate and the back surface were electrically connected.

  Further, as another means for reducing the inductance of the chip carrier, shortening the distance between the modulator semiconductor optical element mounted on the chip carrier and the via hole of the chip carrier is also an effective means. In the present invention, the via hole is arranged when the position of the via hole is closest to the modulator part semiconductor optical device, that is, immediately below the modulator part semiconductor optical element.

  By using the chip carrier of the present invention, it is possible to provide a low-cost chip carrier, an optical module incorporating the same, and an optical transceiver without deteriorating the frequency characteristics of an optical semiconductor optical device that operates at high speed. It is.

  Specific examples relating to the present invention will be described in detail below.

  FIG. 1 is a view showing an upper surface (a) and a side surface (b) of a chip carrier 100 according to a first embodiment of the present invention. The chip carrier 100 uses a substrate 101 made of a dielectric such as alumina (AlN) or a semiconductor such as silicon (Si). On the substrate 101, a high-frequency transmission line 102, a ground metal coating 103 on which a semiconductor optical element is mounted, and a termination resistor 104 are formed. A semiconductor optical device 110 is bonded onto the ground metal coating 103 by solder. In the present embodiment, a description will be given on the assumption that an external modulation laser in which a semiconductor laser 111 and an external modulator 112 are combined is used as the semiconductor optical device 110.

  In the present embodiment, the high-frequency transmission line 102 is a microstrip line, and in order to improve high-frequency characteristics, the signal input unit 130 on the left side of the drawing is a coplanar line sandwiched between the transmission lines 102 and the ground conductors 131 and 132, and from there In the region 140 to the vicinity of the center, the back surface (not shown) of the substrate 101 is metal-coated for grounding so that the transmission line 102 is a microstrip line. In this embodiment, since the entire back surface is covered with metal, particularly the region 130 is referred to as a grounded coplanar line. In addition, the ground metal cover 103 is electrically connected to the metal cover on the back surface of the ground metal 131 and 132 for the coplanar lines by via holes 105, and the ground is strengthened. Reference numeral 104 denotes a termination resistor.

  In the present invention, in order to further strengthen the ground, the whole or a part (120) of the side surface of the substrate 101 is metal-coated, and the metal coating portion 103 on the substrate surface is electrically connected to the metal coating portion on the back surface. It is. Of the four side surfaces 150 to 153 of the chip carrier as shown in FIG. 4, it is most effective to metallize the side surface 150 located closest to the modulator unit 112 directly related to the high frequency operation.

  In order to confirm the effect of the present invention, the optical response characteristics of the chip carrier of this embodiment (when the side surface 150 is entirely covered with metal) by an actual machine is shown in FIG. The optical response means the ratio of the output light intensity to the high-frequency signal intensity input to the modulator unit. For comparison, the characteristics when the metal coating on the side surface is not performed are also shown in FIG.

  When the metal coating on the side surface is not performed (FIG. 2B), the characteristics are rapidly deteriorated and resonance is generated in the vicinity of 35 GHz. On the other hand, when the side surface 150 is entirely covered with metal (FIG. 2 (a)), no rapid characteristic deterioration or resonance occurs, and a −3 dB optical response can be obtained even at about 40 GHz. High frequency characteristics are realized.

  FIG. 3 is an equivalent circuit when an external modulation type laser is mounted on a chip carrier. Here, Z0 (301) is the characteristic impedance of the high-frequency transmission line 102, 50Ω, Rt (309) is the resistance of the terminating resistor 104, L1 (302) is the inductance of the bonding wire 108, and L2 (303) is the bonding wire 109. Rm (304) is the internal resistance of the modulator unit 112, Cm (305) is the parasitic capacitance of the modulator unit 112, Rc (306) is the resistance of the chip carrier 100, and Cc (307) is the capacitance of the chip carrier 100 , Lc (308) is the inductance of the chip carrier 100.

  Since the laser unit 111 of the external modulation type laser is DC drive and can be ignored in the analysis of the high frequency characteristics, only the modulator unit is shown in the equivalent circuit in FIG.

  The sudden characteristic deterioration and resonance near 35 GHz observed in FIG. 2B are caused by series resonance between the parasitic capacitance Cm of the modulator unit 112 and the inductance Lc 308 of the chip carrier 100. Here, the resonance frequency fr is given by (Equation 1).

この直列共振周波数をより高周波側へシフトさせて特性の向上を図るには、変調器部の寄生容量（Ｃｍ）を低減する、あるいは、チップキャリアのインダクタンス（Ｌｃ）を低減する必要がある。しかし、前者の変調器部の容量低減は、光のオンオフの比である消光比の低下など素子特性の劣化を引き起こす可能性がある。このため、後者のチップキャリアのインダクタンス低減が有力な手段と考えられる。

In order to improve the characteristics by shifting the series resonance frequency to a higher frequency side, it is necessary to reduce the parasitic capacitance (Cm) of the modulator section or reduce the inductance (Lc) of the chip carrier. However, the former reduction in the capacity of the modulator section may cause deterioration in device characteristics such as a reduction in the extinction ratio, which is the ratio of light on / off. For this reason, it is considered that reducing the inductance of the latter chip carrier is an effective means.

  In the configuration of FIG. 1, the side surface of the chip carrier is metal-coated to enhance grounding, thereby reducing the inductance Lc of the chip carrier and sufficiently increasing the series resonance frequency. It is considered that good photoresponse characteristics without sudden characteristic deterioration and resonance are obtained.

  Note that the characteristics also differ depending on the size of the region of the side surface to be coated with metal. FIG. 5 shows that when the side surface 150 of the chip carrier closest to the modulator section 112 is metal-coated, 1/10, 1/5, 1/3, 1/2, and the entire surface of the side area are covered. It is the simulation result which analyzed the frequency characteristic (transfer characteristic) at the time of using the model of FIG.

  From the simulation results of FIG. 5, it can be seen that the frequency characteristics are improved when the metal coating area is increased. In particular, in the region of 40 GHz or more, it can be seen that if the metal coating area is set to 1/3 or more, substantially the same characteristics as those obtained when the entire surface is metal-coated can be obtained.

  FIG. 6 is a structural diagram of an LD module 600 incorporating the chip carrier 100 of this embodiment. A high frequency signal for modulation 630 from the outside is supplied to the semiconductor optical device 110 on the chip carrier 100 via the relay substrate 602. Similarly, a DC power source 640 for driving the semiconductor optical device 110 is supplied via the relay substrate 603. Laser light 610 from the semiconductor optical device 110 is condensed by a condensing lens 601 and transmitted to an optical transmission fiber 620 connected to the outside. A monitoring photodiode 604 is mounted to monitor the light output state of the semiconductor optical device 110.

  FIG. 7 shows optical response characteristics of the actual device when the side surface of the chip carrier 100 is metal-coated in the LD module shown in FIG. The metal coating was applied to the entire side surface closest to the modulator portion 111112 of the semiconductor optical device 110. For comparison, the optical response characteristics of an LD module equipped with a chip carrier that does not have a side metal coating are also shown. From this evaluation result, it was confirmed that the optical response characteristic was improved by about 10 GHz by metallizing the side surface of the chip carrier.

  As described above, according to the present embodiment, there is no abrupt deterioration of characteristics by simply metallizing the side surface of a conventional inexpensive chip carrier composed only of a dielectric or a semiconductor substrate, and a high frequency range. Therefore, it is possible to provide a chip carrier excellent in frequency characteristics that can obtain good frequency characteristics with a high gain and that is inexpensive and easy in work process, and an optical module and an optical transmitter using the chip carrier.

  In this embodiment, the case where an external modulation laser is used as the semiconductor optical element has been described as an example. However, the same effect can be expected when a direct modulation laser having no external modulator is used. In this case, the side surface closest to the position where the directly modulated laser is mounted on the chip carrier is coated with metal.

  The present invention is not limited to the shape and pattern of the components on the chip carrier. For example, in this embodiment, the high-frequency transmission line has a pattern in which a microstrip line grounded coplanar line and a microstrip line are combined. The same effect can be obtained only in the case of a line that does not attenuate a high-frequency signal (generally a 50Ω line) or only in the case of a microstrip line.

  Further, in this embodiment, a chip carrier is shown in which a high-frequency signal and a direct current are individually supplied to the element via a wire 108 and a wire 109, respectively. The same effect can be obtained for a chip carrier that is supplied to the device together with a direct current.

  From the above-described embodiments, it has been found that it is effective to reduce the inductance in order to improve the high frequency characteristics of the chip carrier. Here, as another means for reducing the inductance, it is conceivable to shorten the distance between the modulator section 112 of the external modulation laser 110 mounted on the chip carrier and the via hole of the chip carrier. In order to make them closest to each other, as shown in FIG. 8, a via hole 105 </ b> A may be disposed immediately below the modulator unit 112.

  FIG. 9 shows a simulation result obtained by analyzing the frequency characteristics in the case where the via hole 105A is arranged immediately below the modulator unit 112 shown in FIG. 8 using the model shown in FIG. Compared to the case where the side surface of the chip carrier described in the first embodiment is coated with metal, the gain in the high frequency band is small, but good characteristics are obtained that do not cause a sudden decrease in gain or resonance. I understand that.

  However, by disposing the via hole directly under the element, the flatness between the via hole portion and the surrounding dielectric or semiconductor substrate may be deteriorated, and the adhesion during soldering of the element may be lowered. In addition, due to the difference in the thermal expansion coefficient between the via hole portion and the substrate, the semiconductor optical device is stressed and there is a possibility that the reliability is lowered. Therefore, these measures, for example, reinforcement of soldering, etc. are separately taken as necessary.

  As described above, according to the present embodiment, in an inexpensive chip carrier composed of a conventional dielectric or semiconductor substrate, a good frequency characteristic without sudden characteristic deterioration or resonance can be obtained by simply changing the position of the via hole. Therefore, it is possible to provide a chip carrier excellent in frequency characteristics that is inexpensive and easy in work process, and an optical module and an optical transmitter using the chip carrier. The present embodiment is not limited to the shape and pattern of the components on the chip carrier as in the first embodiment.

  Further, by combining the first embodiment with the present embodiment, that is, by coating the side surface of the chip carrier with a metal and providing a via hole directly under the semiconductor optical device component that operates at high frequency, the high frequency characteristics can be further improved. I can expect.

  In this embodiment, the case where an external modulation laser is used as the semiconductor optical element has been described as an example. However, the same effect can be expected when a direct modulation laser having no external modulator is used. In this case, the via hole is arranged immediately below the position where the directly modulated laser is mounted on the chip carrier.

  Although the first and second embodiments have been described using the light emitting elements, the present invention is not limited to this, and a photodiode (PD) or avalanche photodiode (APD) is used. It is also effective for a chip carrier of a light receiving element such as), an optical module using the chip carrier, and an optical receiver.

  Further, the chip carrier of the present invention is not limited to the semiconductor optical device. If the factor that degrades the high frequency characteristics is due to the parasitic capacitance of the element, that is, a capacitive element having a capacitor structure such as a transistor, improvement of the high frequency characteristics can be expected by using the chip carrier of the present invention. .

It is a figure explaining the chip carrier structure of the present invention. It is a figure explaining the characteristic by the chip carrier of the present invention. It is a figure which shows the equivalent circuit of the chip carrier of this invention. It is a figure explaining the chip carrier structure of the present invention. It is a figure explaining the characteristic by the chip carrier of the present invention. It is a figure explaining LD module structure of the present invention. It is a figure explaining the characteristic by LD module of the present invention. It is a figure explaining the chip carrier structure of the present invention. It is a figure explaining the characteristic by the chip carrier of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Chip carrier, 101 ... Dielectric or semiconductor substrate, 102 ... High frequency transmission line, 103 ... Metal coating part for grounding, 104 ... Terminating resistor, 105 ... Via hole, 106- DESCRIPTION OF SYMBOLS 108 ... Wire, 110 ... External modulation type laser, 111 ... Semiconductor laser, 112 ... External modulator, 120 ... Side metal coating, 150-153 ... Side surface of chip carrier, 600 ... Optical module, 601 ... Condensing lens, 602 to 603 ... Relay substrate, 604 ... PD for monitoring

Claims (3)

A chip carrier in which the back surface of the substrate is metal-coated, and a semiconductor laser element provided with a modulator portion is bonded to the metal-coated portion formed on the surface of the substrate by bonding with a first solder;
The metal cover part on the substrate surface and the metal cover part on the back surface are connected by a metallic via hole penetrating the substrate,
The via hole is formed under the modulator portion of the semiconductor laser element,
Wherein the semiconductor optical element and the metallization on the substrate surface, the chip carrier adhesion of the first two by the solder at the second solder is characterized in that it is reinforced. An optical module incorporating a chip carrier equipped with a semiconductor laser element having a modulator section ,
In the chip carrier, the back surface of the substrate is metal-coated, and the semiconductor laser element is mounted on the metal-coated portion formed on the surface of the substrate by being bonded with a first solder,
The metal cover part on the substrate surface and the metal cover part on the back surface are connected by a metallic via hole penetrating the substrate,
The via hole is formed under the modulator portion of the semiconductor laser element,
Wherein the semiconductor optical element and the metallization on the substrate surface, the optical module adhesion of the first two by the solder at the second solder is characterized in that it is reinforced.   An optical transceiver comprising the optical module according to claim 2 mounted thereon.

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