阅读说明：本技术 马赫-曾德尔调制器 (Mach-Zehnder modulator ) 是由 河野直哉 渡边昌崇 于 2019-06-26 设计创作，主要内容包括：本发明涉及一种马赫-曾德尔调制器,其包括：第一电阻元件和第二电阻元件,其均具有第一接触区域和第二接触区域,第一电阻元件的第一接触区域和第二接触区域沿第一轴线的方向排列,第二电阻元件的第一接触区域和第二接触区域沿第二轴线的方向排列；共用导体,其将第一电阻元件和第二电阻元件的各第一接触区域彼此连接在一起；第一波导结构和第二波导结构,其均包括沿与第一轴线和第二轴线交叉的第三轴线的方向延伸的波导部分；第一信号导体,其连接至第一波导结构的波导部以及第一电阻元件的第二接触区域；以及第二信号导体,其连接至第二波导结构的波导部以及第二电阻元件的第二接触区域。(The present invention relates to a Mach-Zehnder modulator, comprising: a first resistive element and a second resistive element each having a first contact region and a second contact region, the first contact region and the second contact region of the first resistive element being aligned in a direction of a first axis, the first contact region and the second contact region of the second resistive element being aligned in a direction of a second axis; a common conductor connecting the respective first contact regions of the first and second resistance elements to each other; a first waveguide structure and a second waveguide structure each including a waveguide portion extending in a direction of a third axis intersecting the first axis and the second axis; a first signal conductor connected to the waveguide portion of the first waveguide structure and the second contact region of the first resistive element; and a second signal conductor connected to the waveguide portion of the second waveguide structure and the second contact region of the second resistive element.)

1. A mach-zehnder modulator comprising:

a first resistive element having a first contact region and a second contact region, the first and second contact regions of the first resistive element being aligned along a direction of a first axis;

a second resistive element having a first contact region and a second contact region, the first and second contact regions of the second resistive element being aligned along a direction of a second axis;

a common conductor in contact with the first contact region of the first resistive element and the first contact region of the second resistive element to connect the first resistive element and the second resistive element to each other;

a first waveguide structure including a waveguide portion extending in a direction of a third axis intersecting the first axis and the second axis;

a second waveguide structure including a waveguide portion extending in a direction of the third axis;

a first signal conductor connected to the waveguide portion of the first waveguide structure and the second contact region of the first resistive element; and

a second signal conductor connected to the waveguide portion of the second waveguide structure and the second contact region of the second resistive element.

2. A mach-zehnder modulator according to claim 1, further comprising a reference potential conductor extending along at least one of the first signal conductor and the second signal conductor.

3. A mach-zehnder modulator according to claim 1 or 2, further comprising:

a semiconductor stage portion on which the first resistance element and the second resistance element are mounted; and

a buried region in which the first waveguide structure and the second waveguide structure are buried, the first resistive element and the second resistive element being arranged in the buried region.

4. A mach-zehnder modulator according to any one of claims 1 to 3, further comprising a conductive semiconductor layer connecting the first waveguide structure and the second waveguide structure to each other.

Technical Field

The present invention relates to a Mach-Zehnder (Mach-Zehnder) modulator.

Background

U.S. patent No.9069223, which is referred to as patent document 1, discloses a mach-zehnder modulator.

Disclosure of Invention

A mach-zehnder modulator according to an aspect of an embodiment includes: a first resistive element having a first contact region and a second contact region, the first and second contact regions of the first resistive element being aligned along a direction of a first axis; a second resistive element having a first contact region and a second contact region, the first and second contact regions of the second resistive element being aligned along a direction of a second axis; a common conductor in contact with the first contact region of the first resistive element and the first contact region of the second resistive element to connect the first resistive element and the second resistive element to each other; a first waveguide structure including a waveguide portion extending in a direction of a third axis intersecting the first axis and the second axis; a second waveguide structure including a waveguide portion extending in a direction of the third axis; a first signal conductor connected to the waveguide portion of the first waveguide structure and the second contact region of the first resistive element; and a second signal conductor connected to the waveguide portion of the second waveguide structure and the second contact region of the second resistive element.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the accompanying drawings.

Fig. 1 is a schematic diagram showing a mach-zehnder modulator according to an example of the embodiment.

Fig. 2A is a cross-sectional view taken along a line IIa-IIa shown in fig. 1 illustrating a mach-zehnder modulator according to an example of the embodiment.

Fig. 2B is a cross-sectional view taken along line IIb-IIb shown in fig. 1 showing a mach-zehnder modulator according to an example of the embodiment.

Fig. 2C is a cross-sectional view taken along line IIc-IIc shown in fig. 1 illustrating a mach-zehnder modulator according to an example of an embodiment.

Fig. 3 is a schematic diagram showing such a mach-zehnder modulator: which includes a first resistive element and a second resistive element arranged in an arrangement direction different from that of the first resistive element and the second resistive element of the mach-zehnder modulator according to the example of the embodiment.

Fig. 4A is a graph showing a simulated EO response.

Fig. 4B is a graph showing simulated reflection characteristics of the differential mode.

Fig. 5A is a plan view showing the shape of the resistive layer for the first resistive element and the second resistive element.

Fig. 5B is a plan view showing the shape of the resistive layer for the first resistive element and the second resistive element.

Fig. 6A is a schematic diagram showing main steps in a method for manufacturing a mach-zehnder modulator according to an example of the embodiment.

Fig. 6B is a schematic diagram illustrating major steps in a method according to an example of an embodiment.

Fig. 6C is a schematic diagram illustrating major steps in a method according to an example of an embodiment.

Fig. 7A is a schematic diagram illustrating major steps in a method according to an example of an embodiment.

Fig. 7B is a schematic diagram illustrating major steps in a method according to an example of an embodiment.

Fig. 7C is a schematic diagram illustrating major steps in a method according to an example of an embodiment.

Fig. 8A is a schematic diagram illustrating major steps in a method according to an example of an embodiment.

Fig. 8B is a schematic diagram illustrating major steps in a method according to an example of an embodiment.

Fig. 8C is a schematic diagram illustrating major steps in a method according to an example of an embodiment.

Detailed Description

The mach-zehnder modulator in patent document 1 is designed to operate in response to a differential signal that propagates on a pair of signal conductors in a semiconductor device. The semiconductor device receives a differential signal from an external driving circuit at its input electrode pad. Specifically, the differential signal thus received is applied to a pair of branch waveguides of the mach-zehnder modulator through a pair of signal conductors. A pair of signal conductors from the input pad electrodes extend toward the output electrode pads, which are connected to respective external resistive elements in the terminator by bonding wires. This connection via the bond wires creates parasitic inductance between the semiconductor device and the external resistive element of the terminator. Combining the resistive element of such a terminator with a semiconductor device removes the bond wires of the electrical connection between the signal conductors of the semiconductor device and the resistive element of the terminator.

The inventors' teachings reveal that integrating the resistive element with the semiconductor device may cause new signal reflections in the semiconductor device.

It would be desirable to provide a mach-zehnder modulator that reduces signal reflections resulting from the integration of the resistive elements of the terminator with the mach-zehnder modulator.

A description will be given below of an example according to the embodiment.

The mach-zehnder modulator according to the example includes: (a) a first resistive element having a first contact region and a second contact region, the first contact region and the second contact region of the first resistive element being aligned in a direction of the first axis; (b) a second resistive element having a first contact region and a second contact region, the first contact region and the second contact region of the second resistive element being aligned along a direction of a second axis; (c) a common conductor in contact with the first contact region of the first resistance element and the first contact region of the second resistance element to connect the first resistance element and the second resistance element to each other; (d) a first waveguide structure including a waveguide portion extending in a direction of a third axis intersecting the first axis and the second axis; (e) a second waveguide structure including a waveguide portion extending in a direction of a third axis; (f) a first signal conductor connected to the waveguide portion of the first waveguide structure and the second contact region of the first resistive element; and (g) a second signal conductor connected to the waveguide portion of the second waveguide structure and the second contact region of the second resistive element.

A mach-zehnder modulator that allows the first and second branch waveguide structures to receive differential signals propagating on the first and second signal conductors, respectively, is integrated with the first and second resistive elements. The first and second resistive elements are connected to the first and second signal conductors and oriented in respective directions along first and second axes that intersect the third axis. The orientation of the first resistive element allows a first component of the differential signal on the first signal conductor to propagate through the first and second contact regions of the first resistive element aligned in the direction of the first axis, and the orientation of the second resistive element allows a second component of the differential signal on the second signal conductor to propagate through the first and second contact regions of the second resistive element aligned in the direction of the second axis. The first and second resistive elements so oriented may terminate the differential mode component of the differential signal such that the common conductor has a remaining component that includes primarily common mode.

The mach-zehnder modulator according to an example of embodiment further includes a reference potential conductor extending along at least one of the first signal conductor and the second signal conductor.

The mach-zehnder modulator allows the reference potential conductor to provide a ground plane for the first signal conductor and the second signal conductor.

The mach-zehnder modulator according to an example of the embodiment further includes: a semiconductor stage (stage) on which a first resistance element and a second resistance element are mounted; and a buried region in which the first waveguide structure and the second waveguide structure are buried, the first resistance element and the second resistance element being arranged in the buried region.

The Mach-Zehnder modulator is provided with a semiconductor mesa in which heat can be dissipated to the substrate for the first resistance element and the second resistance element. The semiconductor mesa may separate the first and second resistance elements from the conductive semiconductor layer to prevent a tight electrical coupling between the conductive semiconductor layer and the first and second resistance elements.

The mach-zehnder modulator according to an example of embodiment further includes a conductive semiconductor layer connecting the first waveguide structure and the second waveguide structure to each other.

The mach-zehnder modulator provides the first branch waveguide structure and the second branch waveguide structure with a common conductive semiconductor layer shared by these waveguide structures.

The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, which are shown by way of example. A mach-zehnder modulator and a method of manufacturing the mach-zehnder modulator according to an example of the present embodiment will be described below with reference to the drawings. To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.

Fig. 1 is a schematic diagram showing a mach-zehnder modulator according to an example of the present embodiment. Fig. 2A is a cross-sectional view taken along a line IIa-IIa in fig. 1 showing a mach-zehnder modulator according to an example of the embodiment. Fig. 2B is a cross-sectional view taken along line IIb-IIb in fig. 1 showing a mach-zehnder modulator according to an example of the embodiment. Fig. 2C is a cross-sectional view taken along line IIc-IIc in fig. 1 showing a mach-zehnder modulator according to an example of the embodiment.

The mach-zehnder modulator 11 includes a first resistive element 13, a second resistive element 15, a common conductor 17, a first branch waveguide structure 19, a second branch waveguide structure 21, a first signal conductor 23, and a second signal conductor 25. The first resistance element 13 has a first contact region 13a and a second contact region 13b, and is arranged on the semiconductor substrate 27. The first contact region 13a and the second contact region 13b are aligned in the direction of the first axis Ax 1. The second resistance element 15 has a first contact region 15a and a second contact region 15b and is arranged on the semiconductor substrate 27. The first contact region 15a and the second contact region 15b are aligned in the direction of the second axis Ax 2. The common conductor 17 is arranged on the semiconductor substrate 27 and is in contact with both the first contact region 13a of the first resistance element 13 and the first contact region 15a of the second resistance element 15 to connect the first resistance element 13 and the second resistance element 15 to each other. The first branch waveguide structure 19 includes waveguide portions extending in the direction of a third axis Ax3, the third axis Ax3 intersecting the first axis Ax1 and the second axis Ax 2. The second branch waveguide structure 21 includes a waveguide portion extending in the direction of the third axis Ax 3. The first signal conductor 23 is in contact with the second contact region 13b of the first resistive element 13 and connects the waveguide portion of the first branch waveguide structure 19 with the first resistive element 13. The second signal conductor 25 is in contact with the second contact region 15b of the second resistive element 15 and connects the waveguide portion of the second branch waveguide structure 21 with the second resistive element 15.

The mach-zehnder modulator 11, which allows the first and second branch waveguide structures 19, 21 to receive respective components of the differential signal SDIF on the first and second signal conductors 23, 25, is combined with the first and second resistive elements 13, 15. The first resistance element 13 is connected to the first signal conductor 23 at the second contact region 13b and extends from the second contact region 13b in the direction of a first axis Ax1 intersecting the third axis Ax3, and the second resistance element 15 is connected to the second signal conductor 25 at the second contact region 15b and extends from the second contact region 15b in the direction of a second axis Ax2 intersecting the third axis Ax 3. Specifically, the first resistive element 13 receives the first signal component S1 of the differential signal SDIF from the first signal conductor 23 at the second contact region 13b, and the first signal component S1 thus received propagates from the second contact region 13b toward the first contact region 13a to reach the common conductor 17, and the first contact region 13a and the second contact region 13b are arranged on the first axis Ax1 to define the flow direction of the first signal component S1. The second resistive element 15 receives the second signal component S2 of the differential signal SDIF from the second signal conductor 25 at the second contact region 15b, and the second signal component S2 thus received propagates from the second contact region 15b to the first contact region 15a to reach the common conductor 17, and the first contact region 15a and the second contact region 15b are arranged on the second axis Ax2 to define the flow direction of the second signal component S2. The arrangement of the first resistive element 13 and the second resistive element 15 results in the first signal component S1 and the second signal component S2 propagating in opposite directions to reach the common conductor 17. Propagating in the opposite direction can terminate the differential mode to produce a remaining component on the common conductor 17, and this remaining component comprises mainly the common mode.

Referring to fig. 1, the optical transmitter 44 includes a mach-zehnder modulator 11 and a driver 42. The mach-zehnder modulator 11 includes a divider (divider)29 and a combiner (merger) 31. The splitter 29 is connected at its input port to the input waveguide 33 and at its output port to each of the first branch waveguide structure 19 and the second branch waveguide structure 21. The combiner 31 is connected at its output port to an output waveguide 35 and at its input port to both the first branch waveguide structure 19 and the second branch waveguide structure 21. The distributor 29, the first branch waveguide structure 19, the second branch waveguide structure 21, and the combiner 31 are arranged on the main surface 27a of the semiconductor substrate 27 of the mach-zehnder modulator 11.

A first signal conductor 23 and a second signal conductor 25 are connected to the top surface of the first branch waveguide structure 19 and the top surface of the second branch waveguide structure 21, respectively.

The mach-zehnder modulator 11 also includes a conductive semiconductor layer 39. The conductive semiconductor layer 39 is mounted with the first branch waveguide structure 19, the second branch waveguide structure 21, the divider 29, and the combiner 31, and connects the bottom of the first branch waveguide structure 19 and the bottom of the second branch waveguide structure 21 to each other. The conductive semiconductor layer 39 is disposed on the main surface 27a of the semiconductor substrate 27 of the mach-zehnder modulator 11. In this example, the conductive semiconductor layer 39 may be connected to a metal conductor 43 to receive a bias voltage from an external bias voltage source BEXT.

The mach-zehnder modulator 11 also includes at least one reference potential conductor 37. The reference potential conductor 37 may extend along at least one of the first signal conductor 23 and the second signal conductor 25. In the present example, a single reference potential conductor 37 arranged between the waveguide of the first branch waveguide structure 19 and the waveguide of the second branch waveguide structure 21 extends along both the first signal conductor 23 and the second signal conductor 25. The reference potential conductor 37 creates a ground plane in the differential signal line of the mach-zehnder modulator 11. The differential signal line is provided with first and second signal conductors 23 and 25 and a reference potential conductor 37.

The first signal conductor 23, the reference potential conductor 37, and the second signal conductor 25 are connected to the driver 42 at their respective input terminals. The first signal conductor 23 and the second signal conductor 25 terminate at their respective other ends opposite to the input end. Specifically, the first signal conductor 23 and the second signal conductor 25 extend in the direction of the third axis Ax3 so as to be periodically connected with the first branch waveguide structure 19 and the second branch waveguide structure 21, respectively, and then reach the first resistive element 13 and the second resistive element 15, which are integrated with the mach-zehnder modulator 11, respectively, the first resistive element 13 and the second resistive element 15.

Referring to fig. 2A, each of the first and second branch waveguide structures 19 and 21 includes a semiconductor mesa MS disposed on the conductive semiconductor layer 39. The semiconductor mesa MS includes a semiconductor laminate 47. Specifically, the semiconductor laminate 47 includes a first conductivity type semiconductor region 47a, a core layer 47b, and a second conductivity type semiconductor region 47 c. The first conductivity type semiconductor region 47a, the core layer 47b, and the second conductivity type semiconductor region 47c are arranged in a direction of an axis intersecting the main surface 27a of the semiconductor substrate 27. The first signal conductor 23 may include a first lower metal layer 24a and a first upper metal layer 24b, and the second signal conductor 25 may include a second lower metal layer 26a and a second upper metal layer 26 b. The first lower metal layer 24a contacts the second conductive type semiconductor region 47c of the first branch waveguide structure 19, and the second lower metal layer 26a contacts the second conductive type semiconductor region 47c of the second branch waveguide structure 21.

The mach-zehnder modulator 11 includes a buried region 49, and the first branch waveguide structure 19 and the second branch waveguide structure 21 are buried in the buried region 49. In the present embodiment, the embedded region 49 includes a first inorganic insulating film 51a, a second inorganic insulating film 51b, a third inorganic insulating film 51c, a first embedded resin body 53a, and a second embedded resin body 53 b. The first inorganic insulating film 51a covers the main surface 27a of the semiconductor substrate 27, the conductive semiconductor layer 39, the first branch waveguide structure 19, and the second branch waveguide structure 21. The first embedded resin body 53a covers the first inorganic insulating film 51a, the first branch waveguide structure 19, and the second branch waveguide structure 21. The second inorganic insulating film 51b covers the first embedded resin body 53 a. The second embedded resin body 53b covers the second inorganic insulating film 51 b. The third inorganic insulating film 51c covers the second embedded resin body 53 b. The first signal conductor 23, the second signal conductor 25, and the reference potential conductor 37 are arranged on the third inorganic insulating film 51 c. The first lower metal layer 24a and the second lower metal layer 26a are disposed in the respective openings of the second inorganic insulating film 51b and the first embedded resin body 53a, and the first upper metal layer 24b and the second upper metal layer 26b are connected to the first lower metal layer 24a and the second lower metal layer 26a through the openings of the third inorganic insulating film 51c and the openings of the second embedded resin body 53 b.

Referring to fig. 2B, the mach-zehnder modulator 11 further includes a semiconductor stage ST. In the present embodiment, the semiconductor stage portion ST is mounted with the first resistance element 13 and the second resistance element 15. The mach-zehnder modulator 11 provides a heat radiation path to the semiconductor substrate 27 via the semiconductor stage ST for the first resistance element 13 and the second resistance element 15 arranged on the semiconductor stage ST.

The mach-zehnder modulator 11 may include another conductive semiconductor layer 41 mounted with the semiconductor mesa ST. The further conductive semiconductor layer 41 is separated from the conductive semiconductor layer 39. This separation can prevent the first resistance element 13 and the second resistance element 15 mounted on the semiconductor mesa portion ST from being electrically coupled with the conductive semiconductor layer 39.

In the present embodiment, the first resistance element 13 and the second resistance element 15 are arranged in the buried region 49. Specifically, the first resistance element 13 and the second resistance element 15 are provided on the first inorganic insulating film 51a, and the first inorganic insulating film 51a covers the semiconductor stage portion ST. The first resistance element 13, the second resistance element 15, and the first inorganic insulating film 51a are embedded with the first embedded resin body 53 a. The second inorganic insulating film 51b is disposed on the first resistance element 13, the second resistance element 15, and the first buried resin body 53a so as to cover them.

The common conductor 17 includes a third lower metal layer 28a, and the third lower metal layer 28a is disposed in the second inorganic insulating film 51b and the opening 30a of the first buried resin body 53a to be in contact with the first contact region 13a of the first resistance element 13 and the first contact region 15a of the second resistance element 15.

The first signal conductor 23 and the second signal conductor 25 include a fourth lower metal layer 28b and a fifth lower metal layer 28c, respectively, and the fourth lower metal layer 28b and the fifth lower metal layer 28c are arranged in the second inorganic insulating film 51b and the openings 30b and 30c in the first buried resin body 53a, respectively. Specifically, the fourth lower metal layer 28b and the fifth lower metal layer 28c are in contact with the second contact region 13b of the first resistance element 13 and the second contact region 15b of the second resistance element 15, respectively.

In the mach-zehnder modulator 11 according to the present embodiment, the reference potential conductor 37 is arranged on the buried region 49 so as to cross the first and second resistance elements 13 and 15 and the common conductor 17, wherein the first and second resistance elements 13 and 15 and the common conductor 17 are separated from the reference potential conductor 37 by the buried region 49. The first resistance element 13 and the second resistance element 15 are designed with approximately the same resistance value and approximately the same dimensions, wherein the resistance value may be in the range of 25 to 50ohm, for example. The mach-zehnder modulator 11 is provided with a virtual ground plane having zero amplitude in a region between the second contact region 13b of the first resistance element 13 and the second contact region 15b of the second resistance element 15.

Referring to fig. 1, the mach-zehnder modulator 11 according to the present embodiment has the first resistance element 13 and the second resistance element 15 oriented in respective directions opposite to each other, and specifically, the first resistance element 13 and the second resistance element 15 are aligned in the directions of the first axis Ax1 and the second axis Ax2, respectively. This arrangement of the first and second resistive elements 13 and 15 can reduce reflection of the differential mode in the mach-zehnder modulator 11.

In the mach-zehnder modulator 11 according to the present embodiment, the second contact region 13b of the first resistive element 13 may be spaced apart from the second contact region 15b of the second resistive element 15 by 200 micrometers or less. A distance within this range may provide mach-zehnder modulator 11 with a reduction in reflection of the common mode in the metal body connecting together first contact region 13a of first resistive element 13 and first contact region 15a of second resistive element 15. Specifically, the first resistive element 13 and the second resistive element 15 are oriented such that the respective electrical signals from the first signal conductor 23 and the second signal conductor 25 propagate in opposite directions in the first resistive element 13 and the second resistive element 15. In order to make this arrangement possible (orientation of the first resistive element 13 and the second resistive element 15), the first signal conductor 23 may be bent near the second contact area 13b of the first resistive element 13, and the second signal conductor 25 may be bent near the second contact area 15b of the second resistive element 15.

The semiconductor mesa ST may be provided with a semiconductor laminate 47, the semiconductor laminate 47 having a structure similar to the first and second branch waveguide structures 19 and 21.

Referring to fig. 2C, the reference potential conductor 37 extends on the top surface of the buried region 49, and the common conductor 17 extends within the buried region 49. If desired, to allow a portion of common conductor 17 to extend over buried region 49, common conductor 17 may use both a lower metal layer and an upper metal layer that vary from a lower metal layer to an upper metal layer, or both a lower metal layer and an upper metal layer that vary from an upper metal layer to a lower metal layer. In the present embodiment, the common conductor 17 and the reference potential conductor 37 are arranged in a direction perpendicular to the axis of the main surface 27a of the semiconductor substrate 27 to provide a crossing (crossing) above or below. The embedded region 49 (specifically, the third inorganic insulating film 51c and the second embedded resin body 53b) can separate the reference potential conductor 37 from the common conductor 17. The mach-zehnder modulator 11 allows the common conductor 17 to extend along the reference potential conductor 37 below the reference potential conductor 37 and to be arranged in the buried region 49, thereby matching the transmission line associated with the common conductor 17 with the common-mode impedance. In the present embodiment, the common conductor 17 and the reference potential conductor 37 extend in parallel to the common mode terminator 45 to be grounded there. The reference potential conductor 37 may extend within the buried region 49 if possible, so that the common conductor 17 may be arranged on the buried region 49 and the reference potential conductor 37, thereby forming a transmission line with respect to the common conductor 17.

The transmission line is effective to reduce reflection of a common mode in the mach-zehnder modulator 11 including the common conductor 17, the common conductor 17 connecting the other end of the first resistive element 13 and the other end of the second resistive element 15 together, and having a length exceeding 300 μm.

(examples)

Exemplary Mach-Zehnder modulator according to this embodiment

First resistance element 13: NiCr, NiCrSi, CuNi or TaN having a thickness of 50nm and dimensions of 50X 50 microns

Second resistance element 15: NiCr, NiCrSi, CuNi or TaN having a thickness of 50nm and dimensions of 50X 50 microns

Semiconductor laminate 47 for use in first and second branch waveguide structures

First conductivity type semiconductor region 47 a: n-type InP with a thickness of 0.5 microns

Core layer 47 b: AlGaInAs-based multiple quantum well with thickness of 0.5 micron

Second conductivity type semiconductor region 47 c: p-type InP with a thickness of 0.5 microns

Conductive semiconductor layer 39: n-type InP with a thickness of 1 micron

First embedded resin body 53a and second embedded resin body 53 b: benzocyclobutene (BCB)

First inorganic insulating film 51 a: silicon oxide with a thickness of 100nm

Second inorganic insulating film 51 b: silicon oxide with a thickness of 200nm

Third inorganic insulating film 51 c: silicon oxide with a thickness of 200nm

Common conductor 17: gold with a thickness of 2 microns

First signal conductor 23 and second signal conductor 25: gold having a thickness of 5 microns and a width of 100 microns

Reference potential conductor 37: gold having a thickness of 5 microns and a width of 10 microns

Fig. 3 is a schematic diagram showing a mach-zehnder modulator 1 including a first resistive element 2 and a second resistive element 3. The first resistance element 2 and the second resistance element 3 are arranged in a different manner from the arrangement of the first resistance element 13 and the second resistance element 15 in the mach-zehnder modulator according to the present embodiment.

The mach-zehnder modulator 1 is provided with a connecting conductor 4, a first branch waveguide structure 5, a second branch waveguide structure 6, a first signal conductor 7, and a second signal conductor 8 in addition to the first resistance element 2 and the second resistance element 3. The first branch waveguide structure 5 has a waveguide portion extending in the direction of the third axis Ax 3. The second branch waveguide structure 6 has a waveguide portion extending in the direction of the third axis Ax 3. The connection conductor 4 is in contact with the first contact area 2a of the first resistance element 2 and the first contact area 3a of the second resistance element 3. The first signal conductor 7 is connected to the waveguide portion of the first branch waveguide structure 5 and is in contact with the second contact region 2b of the first resistive element 2. The second signal conductor 8 is connected to the waveguide portion of the second branch waveguide structure 6, and is in contact with the second contact region 3b of the second resistance element 3. The first resistance element 2 and the second resistance element 3 extend in the direction of the third axis Ax 3.

The EO response and reflectance properties in the differential mode were calculated using a simulation model. The simulation model of the mach-zehnder modulator 1 is the same as that of the mach-zehnder modulator 11 except for the arrangement of the first and second resistance elements 2 and 3 and the arrangement of the reference potential conductor, the first signal conductor, and the second signal conductor.

Fig. 4A is a graph showing a simulated EO response, and fig. 4B is a graph showing a simulated reflection in a differential mode. Comparison of the EO response CEO of mach-zehnder modulator 1 with the EO response DEO of mach-zehnder modulator 11 shows that the EO response CEO of mach-zehnder modulator 1 exhibits greater fluctuation than the EO response DEO of mach-zehnder modulator 11 over a modulation frequency range up to 40 GHz. The reflection characteristic DDR of the mach-zehnder modulator 11 in the differential mode is smaller than the reflection characteristic CDR of the mach-zehnder modulator 1 in the modulation frequency range up to 40 GHz.

Fig. 5A and 5B are plan views showing the shape of a resistive layer applied to a first resistive element and a second resistive element.

Referring to fig. 5A, the first resistance element 13 and the second resistance element 15 are made of a resistance layer 60. In this example, the resistive layer 60 includes a first portion 60a, a second portion 60b, a third portion 60c, a fourth portion 60d, and a fifth portion 60 e. Specifically, the first portion 60a is connected to the first signal conductor 23; the second portion 60b is connected to the second signal conductor 25; the third portion 60c is connected to the common conductor 17; the fourth portion 60d is disposed between the first portion 60a and the third portion 60 c; and the fifth portion 60e is disposed between the second portion 60b and the third portion 60 c. The first, fourth and third portions 60a, 60d, 60c of the resistive layer 60 are arranged to form a first resistive element 13, and the second, fifth and third portions 60b, 60e, 60c of the resistive layer 60 are arranged to form a second resistive element 15. In the resistive layer 60, the first portion 60a and the third portion 60c may be provided with the second contact region 13b and the first contact region 13a, respectively. In the resistive layer 60, the second portion 60b and the third portion 60c may be provided with a second contact region 15b and a first contact region 15a, respectively.

Specifically, the first, fourth and third portions 60a, 60d, 60c of the resistive layer 60 are aligned in the direction of the first axis Ax1, and the second, fifth and third portions 60b, 60e, 60c of the resistive layer 60 are aligned in the direction of the second axis Ax 2.

The resistive layer 60 is designed such that: the first, fourth and third portions 60a, 60d, 60c of the resistive layer 60 are symmetrically arranged with respect to the third axis Ax3 with respect to the second, fifth and third portions 60b, 60e, 60c of the resistive layer 60.

The mach-zehnder modulator 11 may be provided with a single connection resistance layer 60 having both the first resistance element 13 and the second resistance element 15. The single-connection resistive layer 60 is provided with a first portion 60a, a second portion 60b, and a third portion 60c between the first portion 60a and the second portion 60b to reduce differential mode reflection.

In the present embodiment, the first portion 60a, the fourth portion 60d, the third portion 60c, the fifth portion 60e, and the second portion 60b of the resistive layer 60 may be arranged in a row.

Referring to fig. 5B, the first resistance element 13 and the second resistance element 15 are provided by a first resistance layer 61 and a second resistance layer 62, respectively. Specifically, the first resistive layer 61 includes a first portion 61a, a second portion 61b, and a third portion 61 c. The first portion 61a and the second portion 61b are connected to the first signal conductor 23 and the common conductor 27, respectively, and the third portion 61c is arranged between the first portion 61a and the second portion 61 b. The second resistive layer 62 includes a first portion 62a, a second portion 62b, and a third portion 62 c. The first portion 62a and the second portion 62b are connected to the second signal conductor 25 and the common conductor 17, respectively, and the third portion 62c is arranged between the first portion 62a and the second portion 62 b.

The first portion 61a, the third portion 61c, and the second portion 61b of the first resistance layer 61 are sequentially arranged to form the first resistance element 13. The first resistive layer 61 provides the first and second portions 61a and 61b with the second and first contact areas 13b and 13a, respectively. The first portion 62a, the third portion 62c, and the second portion 62b of the second resistance layer 62 are sequentially arranged to form the second resistance element 15. The second resistive layer 62 provides the first and second portions 62a and 62b with the second and first contact areas 15b and 15a, respectively.

Specifically, the first portion 61a, the third portion 61c, and the second portion 61b are aligned in the direction of the first axis Ax1 to form the first resistive layer 61, and the first portion 62a, the third portion 62c, and the second portion 62b are aligned in the direction of the second axis Ax2 to form the second resistive layer 62.

The first and second resistance layers 61 and 62 are designed such that the first, third and second portions 61a, 61c and 61b and the first, third and second portions 62a, 62c and 62b are arranged symmetrically about the third axis Ax3, so that the first and second resistance layers 61 and 62 are also arranged symmetrically about the third axis Ax 3.

The connection of the resistive layers (specifically, the first resistive layer 61 and the second resistive layer 62) patterned to be separated from each other to the common conductor 17 can reduce the reflection of the differential mode.

In the present embodiment, the first resistive layer 61 and the second resistive layer 62, specifically, the first portion 61a, the third portion 61c, and the second portion 61b and the second portion 62b, the third portion 62c, and the first portion 62a are arranged in a row.

Fig. 6A, 6B and 6C, 7A, 7B and 7C, and 8A, 8B and 8C are schematic diagrams respectively showing main steps in a method for manufacturing a mach-zehnder modulator according to the present embodiment. A description will be given of a manufacturing method according to an embodiment with reference to fig. 6A to 8C.

Referring to fig. 6A, the method includes a method for preparing a semiconductor product SP. The semiconductor product SP is provided with a first branch waveguide structure 19, a second branch waveguide structure 21, a semiconductor mesa ST, and conductive semiconductor layers 39 and 41. The first and second branch waveguide structures 19 and 21, the semiconductor mesa ST, and the conductive semiconductor layers 39 and 41 are disposed on the wafer W.

The semiconductor product SP can be produced as follows. The semiconductor laminated region for optical waveguide is grown on the wafer W by a growth method such as MOCVD. The semiconductor laminated region is formed by growing films for the conductive semiconductor layers 39 and 41, the first conductivity type semiconductor region 47a, the core layer 47b, and the second conductivity type semiconductor region 47c on the wafer W to prepare an epitaxial (epi) substrate. Performing photolithography on the epitaxial substrate may form a mask having a pattern defining shapes of the semiconductor mesa and the waveguide structure. The mask is used to etch the epitaxial substrate, thereby manufacturing the semiconductor product SP.

Referring to fig. 6B, the method includes a step for forming an inorganic insulating film on the semiconductor product SP. Specifically, the first inorganic insulating film 51a is formed on the semiconductor product SP. The first inorganic insulating film 51a may include, for example, a silicon-based inorganic insulator, and is grown by, for example, chemical vapor deposition.

Referring to fig. 6C, the method includes a step for forming a resistive layer 60 on the semiconductor mesa ST. The resistive layer 60 is formed by depositing and patterning the semiconductor product SP to obtain a first substrate product SP 1. The resistive layer 60 includes a thin film made of a resistive material such as NiCr, NiCrSi, CuNi, or TaN. The resistive layer 60 is formed by, for example, sputtering and lift-off process (lift-off).

Referring to fig. 7A, the method includes a step of forming a resin body for the first embedded resin body 53a in the first substrate product SP 1. Specifically, a BCB resin is applied to the wafer W to form the first embedded resin body 53 a. The BCB resin thus coated is cured to form a cured resin body, which is hereinafter referred to as a resin body for the first embedded resin body 53 a. The resin body for the first buried resin body 53a is buried with the first and second branch waveguide structures 19 and 21, the resistive layer 60, the semiconductor mesa ST, and the conductive semiconductor layers 39 and 41.

Referring to fig. 7B, the method includes forming contact holes in a resin body to manufacture a first buried resin body 53 a. Specifically, photolithography and etching are performed on the resin body to form openings 54a, 54b, and 54c leading to the resistive layer 60 (and openings 54d and 54e leading to the first branch waveguide structure 19 and the second branch waveguide structure 21 of the mach-zehnder modulator) in the resin body, thereby providing the first embedded resin body 53 a.

After the first buried resin body 53a is provided with these openings, a second inorganic insulating film 51b is deposited on the wafer W so as to cover the entire top surface of the first buried resin body 53 a. The second inorganic insulating film 51b covers the top surface of the first buried resin body 53a and the side and bottom surfaces of the openings 54a, 54b, 54c, 54d, and 54 e. The second inorganic insulating film 51b may include, for example, a silicon-based inorganic insulator, and is grown by, for example, chemical vapor deposition.

Further, performing photolithography and etching on the second inorganic insulating film 51b may remove the second inorganic insulating film 51b at the bottom of the opening of the first buried resin body 53a, so that the resistive layer 60 is exposed at the openings 54a, 54b, 54c, 54d, and 54e of the first buried resin body 53 a.

Referring to fig. 7C, the method includes a step for depositing a metal material on the wafer W to manufacture a lower metal film. Lower metal films (for preparing the metal layers 28a, 28b, 28c, 24a, and 26a) are formed in the openings (the respective openings 54a, 54b, 54c, 54d, and 54e) of the first buried resin body 53 a.

Referring to fig. 8A, the method includes a step of forming a resin body for the second embedded resin body 53b on the wafer W. Specifically, after the lower metal layers (28a, 28b, 28c, 24a, and 26a) are produced by patterning the lower metal film, the second embedded resin body 53b is formed on the wafer W. To form the second embedded resin body 53b, BCB resin is coated on the wafer W, and the BCB resin thus coated is cured to form a cured resin body, which is hereinafter referred to as a resin body for the second embedded resin body 53 b. The resin body for the second embedded resin body 53b is embedded with the lower metal layers (28a, 28b, 28c, 24a, and 26a), the first embedded resin body 53a, and the second inorganic insulating film 51 b.

Referring to fig. 8B, the method includes a step of forming a contact hole in the resin body for the second embedded resin body 53B. Specifically, performing photolithography and etching on the resin body for the second embedded resin body 53b may form openings (56b, 56c, 56d, and 56e) in the resin body for the second embedded resin body 53b, which may reach the lower metal layers (28b, 28c, 24a, and 26a), respectively.

After the second buried resin body 53b having these openings is formed, a third inorganic insulating film 51c is deposited on the entire top surface of the wafer W so as to cover the second buried resin body 53 b. The third inorganic insulating film 51c covers the top surface of the second buried resin body 53b and the side surfaces and the bottom surfaces of the openings 56b, 56c, 56d, and 56 e. The third inorganic insulating film 51c includes, for example, a silicon-based inorganic insulator, and may be grown by, for example, chemical vapor deposition.

The third inorganic insulating film 51c is subjected to photolithography and etching to remove the third inorganic insulating film 51c at the bottoms of the openings (56b, 56c, 56d, and 56e) of the second buried resin body 53b, so that the lower metal layers (28b, 28c, 24a, and 26a) are exposed at the openings (56b, 56c, 56d, and 56e) of the second buried resin body 53b, respectively.

Referring to fig. 8C, the method includes the step of depositing metal films for the first upper metal layer 24b and the second upper metal layer 26 b. Performing photo-etching and film deposition on the third inorganic insulating film 51c makes it possible to fabricate a metal film as a patterned metal film (hereinafter referred to as a first upper metal layer 24b and a second upper metal layer 26b) on the third inorganic insulating film 51c to fabricate the first signal conductor 23, the second signal conductor 25, and the reference potential conductor 37. Specifically, a metal film is deposited on the third inorganic insulating film 51c and in the openings (54b and 54d and 54c and 54e) of the second buried resin body 53b, and is patterned by a lift-off process.

These steps complete the mach-zehnder modulator 11.

The mach-zehnder modulator 11 drives the first branch waveguide structure 19 and the second branch waveguide structure 21 using differential signals propagating on the first signal conductor 23 and the second signal conductor 25. The first signal conductor 23 and the second signal conductor 25 are connected to respective one ends of the first resistive element 13 and the second resistive element 15 as built-in terminators. The first resistance element 13 and the second resistance element 15 are arranged in opposite directions so as to be connected to a common conductor 17 at their respective other ends, thereby terminating the differential signal.

The mach-zehnder modulator 11 is provided with a conductive semiconductor layer 39, and the conductive semiconductor layer 39 is biased by an external power source and is connected to the first branch waveguide structure 19 and the second branch waveguide structure 21.

For transmitting the differential signal to the branch waveguide, the mach-zehnder modulator 11 may use a transmission line including the first signal conductor 23 and the second signal conductor 25 and the reference potential conductor 37 between the first signal conductor 23 and the second signal conductor 25. If desired, the mach-zehnder modulator 11 may be provided with additional first and second additional reference potential conductors extending outside the first and second signal conductors 23, 25 to form transmission lines.

The above-described embodiments may provide a mach-zehnder modulator that may reduce signal reflections caused by a built-in termination resistance element.

Having described and illustrated the principles of the invention in its preferred embodiments, it should be apparent to those skilled in the art that the invention may be modified in arrangement and detail without departing from such principles. We therefore claim all modifications and variations that fall within the spirit and scope of the appended claims.

This application claims priority from japanese patent application No.2018-121839, filed on 27.6.2018, which is incorporated herein by reference in its entirety.