JP4369219B2 - Matrix optical switch - Google Patents

Description

  The present invention relates to a matrix optical switch used for setting or switching an optical path in an optical communication system or the like, and is particularly effective when applied to a large-scale matrix type.

  The optical path is switched at the intersection of the optical waveguides by enclosing the refractive index matching liquid equal to the optical waveguide in the gap provided at the intersection of the optical waveguides that intersect each other and moving this refractive index matching liquid within the gap. Various optical switches have been proposed so far.

  For example, in Japanese Patent Application Laid-Open No. 9-133932, m optical waveguides that do not intersect with each other and n optical waveguides that do not intersect with each other intersect each other, and the optical axis of the optical waveguide is predetermined at each intersection. A gap having an angled wall surface, an optically transparent liquid having a refractive index approximate to the refractive index of the optical waveguide enclosed in a part of the gap, and means for generating heat near the gap. And an optical switch that switches the optical path by moving the liquid in the gap by generating heat from the heating means.

  Japanese Patent Laid-Open No. 10-73775 discloses a method for assembling an optical switch proposed in the above publication. Specifically, as shown in FIG. 2, a silica-based optical waveguide layer 32 is formed on a silicon substrate 31, and a metal having a relatively high resistance such as titanium or chromium is formed on the optical waveguide layer 32. After a thin film and a metal thin film having a low resistance such as gold are deposited by a sputtering method, a vacuum evaporation method, or the like, and after manufacturing the electric heater 36, the electric wiring 35, and the slit by a technique combining photolithography and dry etching, etc. Then, a silicon layer is deposited thereon, and a silicon layer and a substrate 37 made of Pyrex glass (“Pyrex” is a registered trademark and is a representative product of silicoborate glass to which boron oxide is added) and an anode When the gap 34 is formed at the intersection of the optical waveguide 33 by bonding and bonding the slits with the substrate 37, the optical waveguide layer 32 or the substrate 37 has a bonding surface. After the refractive index matching liquid 41 is accurately injected into the gap 34 from the injection port 40 of the injection line 39 formed in advance by a pressure control method or the like, the injection port 40 is closed with an epoxy resin or the like. By doing so, the optical switch as described above is obtained. Reference numeral 38 denotes a bypass duct.

JP-A-9-133932 Japanese Patent Laid-Open No. 10-73775

  When the conventional optical switch as described above is applied to a large-scale matrix type optical switch, there are the following problems.

  In the optical switch described above, at least two electric heaters 36 are required to move the refractive index matching liquid 41 in one element, that is, one air gap 34, in the air gap 34, and these electric heaters 36 are independent of each other. In order to supply electric power, at least three electric wires are required. For this reason, when n elements are arranged in a row, 2n + 1 electric wirings 35 are required even if the ground of each electric heater 36 is shared. Furthermore, when n elements are arranged in m rows (n × m), (2n + 1) × m electrical wirings 35 are required.

When a matrix type optical switch is mounted on an electric circuit board on which a drive circuit for the electric heater 36 is mounted, the electric wiring 35 of the optical switch and the electric wiring on the electric circuit board can be connected by a technique such as wire bonding. As described above, since the electrical wiring 35 of the optical switch needs to be developed on the end face of the optical waveguide layer 32 of the optical switch, the electrical wiring 35 must be disposed with a necessary and sufficient gap between elements. For this reason, the size of the optical switch becomes very large, and it becomes difficult to manufacture the electrical wiring 35 and the like by a technique combining photolithography and dry etching.

  In the 8 × 8 scale matrix optical switch, the wiring is stacked in two layers, the vertical direction is the first layer, the horizontal direction is the second layer, and electrical wiring is used to insert a heater at the intersection. Driving the target heater with a total of 24 wires with the wires as GND can be incomplete. Incomplete means that the current flows in addition to the target heater because the wiring is assembled in a mesh.

  As a method of eliminating this unnecessary sneak current, it is effective to connect a rectifier, that is, a diode in series with a heater (Japanese Patent Laid-Open No. 2001-311888). Further, it is conceivable to further reduce wiring by incorporating a memory circuit (flip-flop circuit) using a thin film transistor used in the manufacture of a liquid crystal display and a heater drive circuit (current switch) for each heater.

  In an 8 × 8 scale matrix optical switch, in addition to the power supply line and the GND line (ground line), at least 24 lines are required for specifying the matrix. In the diode array vertical and horizontal specified lines, the heater drive current flows, so the appropriate thickness is required, but in the array using transistors, the matrix specification is a logic circuit, so almost no current flows and the wiring resistance A high-density polysilicon wiring may be used, and a thin wire is sufficient. Of course, it is inevitable that the number of wiring layers is two or more in both the diode array and the transistor array.

  Although it seems that it is possible to build these semiconductor elements in a planar optical circuit with an example of a liquid crystal display, the driving current of the liquid crystal display is extremely low, less than a microampere, whereas the matrix targeted by the present invention is The heater driving current in the optical switch has a current amount of several tens of milliamperes and 4 digits or more. Polysilicon and amorphous silicon deposited on the glass surface layer are not current capacities that can be realized in a small area of about 100 microns square. Therefore, the technique using the thin film transistor cannot be applied to the matrix optical switch at all.

  It is relatively easy to fabricate the above diode array and transistor array on a silicon substrate by a technique similar to a normal IC. However, when the heater is built at the same time, the heat conductivity of silicon is about an order of magnitude higher than that of quartz glass of a planar optical circuit, so the heat of the heater is taken away by the silicon substrate. Therefore, in order to drive the optical switch, it is necessary not only to increase the current flowing to the heater than when it is covered with glass, but also to cause a malfunction of the semiconductor element. There was a problem that it could not be formed. It is also difficult to closely bond these semiconductor elements to a planar optical circuit while maintaining a fine structure such as a groove and an injection path.

  Accordingly, an object of the present invention is to provide a matrix optical switch that can be reduced in size and power even in a large-scale matrix type.

In the configuration of the present invention that solves the above-described problems, a liquid having a predetermined optical characteristic is sealed in a gap provided at an intersection of optical waveguides that cross each other, and power is supplied to an electric heater provided in the vicinity of the gap. In a matrix-type optical switch having a plurality of elements in a row direction and a column direction that move the liquid in the gap by switching the optical path by heating the liquid in the intersecting portion of the optical waveguide.
A silicon layer is deposited on the surface of a planar optical circuit substrate having a gap provided at the intersection of optical waveguides that intersect each other formed on a silicon substrate, and the silicoborate glass plate is anodically bonded to the silicon layer. A substrate,
An electric heater and a semiconductor element substrate on which an electric circuit for energizing the heater is formed on a silicon substrate are bonded and fixed ,
FETs are connected in series to each electric heater, and one end of a series circuit terminal composed of the electric heater and FET is connected to a first electric wiring formed in a grid shape to which a positive voltage is applied. And the other end of the terminals of the series circuit is connected to a second electrical wiring formed in a grid connected to the ground potential,
Furthermore, it has a heat insulating structure between the electric heater and the semiconductor element substrate side,
When viewed in a plan view, the first electrical wiring and the second electrical wiring surround the electric heater, and when viewed in a plan view, the gap is electrically separated. It is characterized by being surrounded by a pair of electric heaters .

Further, according to the configuration of the present invention, a liquid having a predetermined optical characteristic is sealed in a gap provided at the intersection of the optical waveguides that cross each other, and the liquid is heated by supplying power to an electric heater provided in the vicinity of the gap. In the matrix-type optical switch having a plurality of elements in the row direction and the column direction that move the liquid in the gap and switch the optical path at the intersection of the optical waveguides.
A substrate in which a bonding silicon layer is deposited on the surface of a planar optical circuit substrate having a gap provided at an intersection of optical waveguides that intersect with each other formed on a silicon substrate;
On the surface of the semiconductor element substrate on which an electric heater and an electric circuit for energizing the heater are formed on a silicon substrate , a layer made of any one of silicon, aluminum, chromium, and titanium and a layer of bonding borosilicate glass The substrate deposited in this order is fixed in close contact with the bonding silicon borosilicate glass layer and the bonding silicon layer by anodic bonding,
FETs are connected in series to each electric heater, and one end of a series circuit terminal composed of the electric heater and FET is connected to a first electric wiring formed in a grid shape to which a positive voltage is applied. And the other end of the terminals of the series circuit is connected to a second electrical wiring formed in a grid connected to the ground potential,
Furthermore, it has a heat insulating structure between the electric heater and the semiconductor element substrate side,
When viewed in a plan view, the first electrical wiring and the second electrical wiring surround the electric heater, and when viewed in a plan view, the gap is electrically separated. It is characterized by being surrounded by a pair of electric heaters.

  The structure of the present invention is a heat insulating structure comprising a polyimide film having a thickness of 2000 mm or more, a thermal decomposition temperature of 350 ° C. or more, and a heat transfer coefficient of 0.2 W / mK or less between the electric heater and the semiconductor element substrate side. It is characterized by having.

  The structure of the present invention is characterized in that it has a heat insulating structure in which a quartz layer having a thickness of 5 μm or more is partially embedded between the electric heater and the semiconductor element substrate side.

  According to the present invention, the liquid having predetermined optical characteristics enclosed in the intersecting portions of the optical waveguides that intersect with each other is heated and moved by the electric heater, thereby having a plurality of elements for switching the optical path in the row direction and the column direction. The matrix type optical switch can be reduced in size, power consumption, and productivity.

  The best mode for carrying out the present invention will be described below with reference to examples.

  FIGS. 1A and 1B are structural views showing a matrix optical switch according to Embodiment 1 of the present invention. Although only one element is shown in the sectional view of FIG. 1A, a plurality of elements are integrated in the depth direction. FIG. 1B is a schematic structural diagram showing the circuit configuration of the semiconductor element substrate in a plan view.

  In the first embodiment, the substrate I and the semiconductor element substrate II are bonded and fixed with an adhesive 17. In addition, the electric heater 4 of the semiconductor element substrate II is aligned and bonded and fixed above the groove 3 of the substrate I so as to be disposed in close proximity.

  The substrate I has a planar optical circuit substrate Ia. In the planar optical circuit board Ia, the optical waveguide 1 is formed so as to intersect on the silicon substrate 8, and a groove (gap) 3 is formed at the intersecting portion. A bonding silicon layer 9 is deposited on the surface of the planar optical circuit board Ia, and the Pyrex plate 7 is anodically bonded in close contact with the bonding silicon layer 9. In the groove 3, a refractive index matching liquid (oil) L that moves in the groove is sealed. This refractive index matching liquid L has a refractive index equal to the refractive index of the core 2.

  In the semiconductor element substrate II, an electric heater 4 and an electric circuit for energizing the electric heater 4 are formed on an FET substrate (silicon substrate) 12. As this electric circuit, there are an FET (field effect transistor) 13, a drain electrode wiring 14, a gate electrode wiring 15, a source electrode wiring 16, a first electric wiring 5-1 and a second electric wiring 5-2. . The semiconductor element substrate II includes an insulating layer 6, a heat insulating layer 18, and a silica insulating layer 19. The electrical wiring 5-1 and the electrical wiring 5-2 are electrically insulated while being spaced apart in the vertical direction. A positive voltage is applied to one of the electrical wirings 5-1 and 5-2, and the other is connected to the ground potential.

  More specifically, as shown in FIG. 1B, each electric heater 4 has an FET 13 connected in series. Moreover, among the terminals of the FET 13, the heater side terminal is connected to the first electric wiring 5-1 formed in a grid pattern, and the non-heater side terminal is the second electric wiring 5-2 formed in a grid pattern. It is connected to the. That is, the series circuit formed by connecting the electric heater 4 and the FET 13 in series has one end connected to the first electric wiring 5-1 and the other end connected to the second electric wiring 5-1. Thus, by forming the electric wirings 5-1 and 5-2 in a lattice shape, the electric resistance in the electric wirings 5-1 and 5-2, and thus the voltage drop in the electric wiring 5-1 and 5-2 is reduced. The voltage can be applied to each FET 13 and the electric heater 4 evenly, and the amount of heat generated by each electric heater 4 is equalized. In addition, since the electric wirings 5-1 and 5-2 are in a lattice shape, the electric wirings 5-1 and 5-2 surround the electric heater 4 without overlapping with the electric heater 4 when viewed in a plan view. Therefore, heat transfer from the electric heater 4 to the electric wirings 5-1 and 5-2 can be suppressed, and the heat generated by the electric heater 4 can be used efficiently. When the FET 13 is turned on, a current flows through the electric heater 4 to generate heat, and when the FET 13 is turned off, the current is cut off and heating of the electric heater 4 is stopped.

  As shown in FIG. 1A, the electric heater 4 is positioned above the groove 3 when viewed in the vertical direction. However, when viewed in plan as shown in FIG. It is surrounded by a pair of (two) separated electric heaters 4 (one electric heater 4 is arranged on the right side and the other electric heater 4 is arranged on the left side in the longitudinal direction of the groove 3). For this reason, the pair of electric heaters 4 are alternately operated (heat generation) to give a local temperature gradient to the refractive index matching liquid L sealed in the groove 3, and the refractive index is obtained by utilizing the surface tension due to the temperature difference. The matching liquid L can be moved in the groove 3. Thus, the optical switch operation can be performed by moving the refractive index matching liquid L in the groove 3. As a result, when light propagation is possible in one of the optical waveguides 1 and 1 that intersect each other at the position of the groove 3, light is blocked in the other optical waveguide 1 that intersects with this.

  Further, the gate electrode wiring 15 of the FET 13 is connected to a driver circuit for selecting the heater 4 to be driven by a fine wiring (not shown). Further, between the electric heater 4 and the semiconductor element substrate side, there is a heat insulating structure (heat insulating layer) 18 made of a polyimide film having a thickness of 1 μm, a thermal decomposition temperature of 350 ° C. or more, and a thermoelectric conductivity of 0.2 W / mK. Is formed.

  FIG. 3 is a diagram showing the relationship between the thickness of the heat insulating layer and the rising temperature of the electric heater. When the electric heater is formed directly on the silicon substrate, the heat of the electric heater is taken away by the silicon substrate because the thermal conductivity of silicon is about an order of magnitude higher than that of the quartz glass of the planar optical circuit. For this reason, the temperature rise of the electric heater is greatly different from the case where it is covered with quartz glass, which is insufficient for operating the optical switch.

  In order to drive the optical switch, it is only necessary to increase the current flowing to the electric heater as compared with the case where it is covered with glass. For this purpose, the FET element and the wiring must be enlarged, and the semiconductor element itself Since a rise in temperature may cause a malfunction, a problem that a semiconductor element cannot be formed in the vicinity of the heater occurs.

  In order to avoid this, in the first embodiment, by providing the heat insulating layer 18 between the electric heater 4 and the semiconductor element substrate side, the switching operation can be performed with a current equal to or less than that in the case of being covered with quartz glass. It can be made possible. Further, heat insulation by a thin film is possible, and multilayer wiring can be easily formed. When the film thickness is large, a step is generated at the time of formation, which causes a problem of wiring breakage or insulation failure.

  In Example 1, the Pyrex plate 7 is bonded to the surface of the planar optical circuit Ia by anodic bonding to form a sealed groove structure on the planar optical circuit side, and the substrate I and the semiconductor element substrate II are bonded to each other. Separately, the adhesive 17 is used. A silicon layer 9 for anodic bonding is deposited on the surface of the planar optical circuit Ia, and a thin Pyrex (pyrex plate 7) is stacked on the silicon layer 9 for anodic bonding. After the anodic bonding is completed, the surface is further ground and polished to reduce the thickness of the Pyrex to 10 μm or less.

  An optical switch is configured by closely fixing the semiconductor element substrate II on the Pyrex plate 7 with an adhesive 17. In Example 1, since heating and voltage application are not performed on the semiconductor element (FET 13) in the manufacturing process, it is possible to avoid damaging the semiconductor element in the manufacturing process.

  FIG. 4 is a sectional view showing a matrix optical switch according to Embodiment 2 of the present invention. Similarly to Example 1, Example 2 also shows only one element in the cross-sectional view, but a plurality of elements are integrated in the depth direction.

In the second embodiment, the planar optical circuit substrate III and the semiconductor element substrate IV are closely attached and fixed by anodic bonding. The circuit configuration of the semiconductor element substrate IV is substantially the same as that of the semiconductor element substrate II of the first embodiment.
The second embodiment differs from the first embodiment in two points: a heat insulating structure (heat insulating layer 18A) between the electric heater 4 and the semiconductor element substrate IV, and a method of fixing the planar optical circuit substrate III and the semiconductor element substrate IV. It is. For this reason, the same parts as those in the first embodiment are denoted by the same reference numerals, the description of the overlapping parts is omitted, and different parts are mainly described.

  First, regarding the heat insulation structure between the electric heater 4 and the semiconductor element substrate IV, after forming the semiconductor element, the heater forming portion is etched to form a recess, and quartz glass is deposited by sputtering over 5 μm, and then the surface is polished. Then, after flattening, wiring and a heater are formed. In this manner, the heat insulating layer 18A is formed by depositing, polishing, and planarizing the quartz glass.

  Next, a method for fixing the planar optical circuit substrate III and the semiconductor element substrate IV will be described. In the second embodiment, a bonding silicon layer 9 having a thickness of about 1 μm is deposited for bonding on the surface layer of the planar optical circuit substrate III before the semiconductor element substrate IV is firmly fixed.

  On the semiconductor element substrate IV, as in the first embodiment, an array of heaters and a circuit for individually controlling the heaters by FETs are formed. The surface of the semiconductor element substrate IV is embedded with a silica insulating layer 19, and a silicon layer 20 and a Pyrex glass 21 for bonding are sequentially deposited thereon. The silicon layer 20 under the Pyrex glass 21 functions as an electrode for the Pyrex glass 21 when anodic bonding is performed. The thickness of the Pyrex glass 21 layer on the surface of the semiconductor element substrate IV is several μm.

  Then, the layer of Pyrex glass 21 for anodic bonding on the semiconductor element substrate IV side and the silicon layer 9 for bonding on the planar optical circuit board III side are brought into close contact with each other and heated to a temperature of several hundred degrees C. The cathode is electrically contacted with the electrode silicon layer 20 and the anode is electrically contacted with the bonding silicon layer 9 on the planar optical circuit board III side to apply a voltage to perform anodic bonding.

In this configuration, since the semiconductor element substrate IV side serves as a cathode, sodium ions inside the Pyrex glass 21 are accelerated to the semiconductor element substrate IV side by an electric field. However, in the configuration of the present invention, the silicon layer 20 is sandwiched between the Pyrex glass 21 and the semiconductor element, and the potential of sodium ions is the anode. Since the potential of the silicon layer 20 serving as the lower electrode of the Pyrex glass 21 is the highest, the accelerated sodium ions are captured by the silicon layer 20 and penetrate through the underlying silica insulating layer 19 and diffuse to the semiconductor element. Can be prevented.

  When the semiconductor element substrate IV is brought into contact with the anode together with the silicon layer 20 serving as the electrode to have the same potential, the electric field inside the semiconductor is shielded from the outside and becomes completely the same potential, so that the penetration of sodium can be prevented more reliably. .

  Note that the silicon layer 20 serving as an electrode may be replaced with another metal material. For example, metals with high adhesion to glass, such as aluminum, chromium, and titanium, are suitable for this purpose.

Sectional drawing which shows the matrix optical switch which concerns on Example 1 of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram illustrating a planar configuration of a circuit formed on a semiconductor element substrate of a matrix optical switch according to Embodiment 1 of the present invention. The schematic structure figure showing an example of the conventional optical switch. The characteristic view which shows the relationship between the thickness of a heat insulation film | membrane, and the raise temperature of a heater. FIG. 5 is a schematic structural diagram showing a matrix optical switch according to Embodiment 2 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical waveguide 2 Core 3 Groove 4 Electric heater 5-1 1st electric wiring 5-2 2nd electric wiring 6 Insulating layer 7 Pyrex board 8 Silicon substrate 9 Bonding silicon layer 12 FET substrate 13 FET
14 Drain electrode wiring 15 Gate electrode wiring 16 Source electrode wiring 17 Adhesive 18, 18A Thermal insulation layer 19 Silica insulating layer 20 Silicon layer 21 Pyrex glass for bonding 31 Silicon substrate 32 Quartz-based optical waveguide layer 33 Optical waveguide 34 Void 35 Electrical wiring 36 Electric heater 37 Pyrex glass substrate 38 Detour pipe 39 Injection pipe 40 Inlet 41 Refractive index matching liquid I Substrate Ia Planar optical circuit board II Semiconductor element substrate III Planar optical circuit board IV Semiconductor element substrate L Refractive index matching liquid

Claims (4)

A liquid having a predetermined optical characteristic is sealed in a gap provided at the intersection of the optical waveguides that cross each other, and the liquid is heated by supplying power to an electric heater provided in the vicinity of the gap. In a matrix-type optical switch that has a plurality of elements in a row direction and a column direction that are moved in the gap and switch an optical path at the intersection of the optical waveguides,
A silicon layer is deposited on the surface of a planar optical circuit substrate having a gap provided at the intersection of optical waveguides that intersect each other formed on a silicon substrate, and the silicoborate glass plate is anodically bonded to the silicon layer. A substrate,
An electric heater and a semiconductor element substrate on which an electric circuit for energizing the heater is formed on a silicon substrate are bonded and fixed,
FETs are connected in series to each electric heater, and one end of a series circuit terminal composed of the electric heater and FET is connected to a first electric wiring formed in a grid shape to which a positive voltage is applied. And the other end of the terminals of the series circuit is connected to a second electrical wiring formed in a grid connected to the ground potential,
Furthermore, it has a heat insulating structure between the electric heater and the semiconductor element substrate side,
When viewed in a plan view, the first electrical wiring and the second electrical wiring surround the electric heater, and when viewed in a plan view, the gap is electrically separated. A matrix optical switch surrounded by a pair of electric heaters. A liquid having a predetermined optical characteristic is sealed in a gap provided at the intersection of the optical waveguides that cross each other, and the liquid is heated by supplying power to an electric heater provided in the vicinity of the gap. In a matrix-type optical switch that has a plurality of elements in a row direction and a column direction that are moved in the gap and switch an optical path at the intersection of the optical waveguides,
A substrate in which a bonding silicon layer is deposited on the surface of a planar optical circuit substrate having a gap provided at an intersection of optical waveguides that intersect with each other formed on a silicon substrate;
On the surface of the semiconductor element substrate on which an electric heater and an electric circuit for energizing the heater are formed on a silicon substrate , a layer made of any one of silicon, aluminum, chromium, and titanium and a layer of bonding borosilicate glass The substrate deposited in this order is fixed in close contact with the bonding silicon borosilicate glass layer and the bonding silicon layer by anodic bonding,
FETs are connected in series to each electric heater, and one end of a series circuit terminal composed of the electric heater and FET is connected to a first electric wiring formed in a grid shape to which a positive voltage is applied. And the other end of the terminals of the series circuit is connected to a second electrical wiring formed in a grid connected to the ground potential,
Furthermore, it has a heat insulating structure between the electric heater and the semiconductor element substrate side,
When viewed in a plan view, the first electrical wiring and the second electrical wiring surround the electric heater, and when viewed in a plan view, the gap is electrically separated. A matrix optical switch surrounded by a pair of electric heaters.   A heat insulating structure made of a polyimide film having a thickness of 2000 mm or more, a thermal decomposition temperature of 350 ° C or more, and a heat transfer coefficient of 0.2 W / mK or less is provided between the electric heater and the semiconductor element substrate side. The matrix optical switch according to claim 1 or 2.   3. The matrix optical switch according to claim 1, wherein the matrix optical switch has a heat insulating structure in which a quartz layer having a thickness of 5 μm or more is partially embedded between the electric heater and the semiconductor element substrate side.

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