Photoelectric devices

Abstract

An optoelectronic device is disclosed. The optoelectronic device includes: a rib waveguide disposed on a substrate of the device, the rib waveguide including a ridge portion and a plate portion; a heater disposed within the plate portion; a thermal isolation groove adjacent to the rib waveguide and extending into the substrate of the device; and a thermal isolation cavity within the substrate, the thermal isolation cavity being directly connected to the thermal isolation groove and extending between at least the rib waveguide and the substrate across at least a portion of the width of the rib waveguide.

Description

Technical Field

[0001] Embodiments of the present invention relate to an optoelectronic device, and in particular to an optoelectronic device including or being a thermally efficient phase shifter comprising a thermal isolation trench and a cavity. Background Art

[0002] Highly efficient phase shifters are important building blocks for photonic integrated circuits in a variety of applications. For example, optical switches and optical phase arrays often contain tens or hundreds of phase shifters. The operating principle of thermo-optic phase shifters is that the refractive index of a material depends on temperature. The degree to which the refractive index of a material changes in response to temperature changes is classified by the following thermo-optic coefficients: .

[0003] Therefore, given the relatively large number of phase shifters required, it is desirable to minimize the power consumption of the phase shifters. Thermo-optical phase shifters can be made very efficient (phase shift of approximately <1mW). However, there is a trade-off between efficiency and speed for this type of phase shifter. Good thermal isolation improves efficiency while significantly reducing speed. Typically, speed is an important performance metric for phase shifters.

[0004] For example, Fang, Qing et al. "Ultralow power silicon photonics thermo-optic switch with suspended arms IEEE Photon, Technol. Letter. 23.8 (2011): 525-527 demonstrates a highly efficient thermo-optical heater (0.49 mW / ).

[0005] The heater and thermal isolation design then need to be optimized to meet both efficiency and speed requirements. Summary of the invention

[0006] Thus, in a first aspect, embodiments of the present invention provide an optoelectronic device comprising:

[0007] a rib waveguide disposed on a substrate of the device, the rib waveguide comprising a ridge portion and a plate portion;

[0008] a heater disposed within the plate portion;

[0009] a thermal isolation trench adjacent to the rib waveguide and extending into the substrate of the device; and

[0010] A thermal isolation cavity within the substrate is directly connected to the thermal isolation trench and extends between the rib waveguide and the substrate across at least a portion of the width of the rib waveguide.

[0011] Because the heater and the rib waveguide can be (to a large extent) thermally decoupled from the surrounding devices, such an optoelectronic device delivers significant thermal efficiency. The thermal isolation grooves can provide thermal isolation in the horizontal direction (i.e., in the same plane as the waveguide and the plate), while the thermal isolation cavity can provide thermal isolation in the vertical direction (i.e., perpendicular to the plate). For example, embodiments of the present invention can be implemented using between 1 mW and 20 mW and a 10% to 90% response time (i.e., the time it takes for the power output of the device to increase from 10% to 90% of the total change in amplitude between the peaks and valleys of the voltage output curve) between 10 μs and 50 μs. Phase shift.

[0012] The optional features of the invention will now be described. These may be applied alone or in combination with any aspect of the invention.

[0013] The rib waveguide may be a ridge waveguide, as it comprises only the ridge portion and no slab portion.The optoelectronic device may be a phase shifter.The optoelectronic device may be an electro-absorption modulator or a photodiode, comprising a phase shifting or phase tuning capability.

[0014] The length of the heater as measured in a direction parallel to the guiding direction of the waveguide may be between 50 μm and 500 μm. The length of the or each thermal isolation trench as measured in a direction parallel to the guiding direction of the waveguide may be between 0.5 L h With 1.0L h Between, where L h is the length of the heater as measured in the guiding direction of the waveguide.

[0015] The thermal isolation trench may be positioned on a side of the heater opposite the ridge portion.

[0016] The device may further include a second thermal isolation trench disposed on a side of the rib waveguide opposite to the first thermal isolation trench. The second thermal isolation trench may be connected to the thermal isolation cavity such that an overhanging portion of the rib waveguide between the first thermal isolation trench and the second thermal isolation trench does not directly abut the substrate.

[0017] The or each thermal isolation trench may be fluidly connected to the thermal isolation cavity.

[0018] The or each thermal isolation trench and the thermal isolation cavity may be filled with a connected insulator.

[0019] The thermal isolation cavity may have a semicircular cross section as viewed along the guiding direction of the rib waveguide.The thermal isolation cavity may be formed by two partially overlapping regions, each of which has a semicircular cross section as viewed along the guiding direction of the rib waveguide.

[0020] The optoelectronic device may further include a third thermal isolation groove, the third thermal isolation groove being spaced apart from the first thermal isolation groove in a direction parallel to the guiding direction of the waveguide, the third thermal isolation groove extending into the substrate. The thermal isolation cavity may extend from the first thermal isolation groove to the third thermal isolation groove between the plate portion of the waveguide and the substrate. The optoelectronic device may include a fourth thermal isolation groove, the fourth thermal isolation groove being spaced apart from the first thermal isolation groove in a direction parallel to the guiding direction of the waveguide, the fourth thermal isolation groove extending into the substrate and positioned on a side of the rib waveguide opposite to the third thermal isolation groove. The thermal isolation cavity may extend from the second thermal isolation groove to the fourth thermal isolation groove between the plate portion of the waveguide and the substrate.

[0021] There may be gaps between pairs of thermal isolation grooves on the same side of the rib waveguide. The length of the gaps between the pairs of thermal isolation grooves may be between 5 μm and 20 μm. There may be an array of pairs of thermal isolation grooves, wherein a pair of thermal isolation grooves are disposed on opposite sides of the rib waveguide. There may be a plurality of thermal isolation cavities, wherein one thermal isolation cavity is associated with each pair of thermal isolation grooves of the array of thermal isolation grooves.

[0022] In a second aspect, embodiments of the present invention provide a method of forming an optoelectronic device, the method comprising the steps of:

[0023] disposing a rib waveguide on a substrate of the device, the rib waveguide comprising a ridge portion and a plate portion;

[0024] providing a heater disposed within the plate portion;

[0025] etching a thermal isolation trench into the substrate, the trench being adjacent to the rib waveguide;

[0026] The device is exposed to an etching liquid, thereby etching a thermal isolation cavity in the substrate, the thermal isolation cavity extending from the thermal isolation trench between the rib waveguide and the substrate and directly connected to the thermal isolation trench across at least the width of the rib waveguide.

[0027] The method may include any one or any combination of the following optional features, as long as they are compatible.

[0028] The etching liquid may be any one of etching gas, etching liquid or etching steam. The etching liquid may be etching gas. The etching gas may be XeF2.

[0029] The thermal isolation trench may be positioned on a side of the heater opposite the ridge portion.

[0030] The method may further include etching a second thermal isolation trench into the substrate of the device, the second thermal isolation trench on a side of the ridge portion opposite the first thermal isolation trench. The thermal isolation cavity within the substrate may extend from the first thermal isolation trench to the second thermal isolation trench.

[0031] The method may further include etching a third thermal isolation trench at a position spaced apart from the first thermal isolation trench in a direction parallel to the guiding direction of the rib waveguide.

[0032] The method may further include etching a fourth thermal isolation trench at a position spaced apart from the first thermal isolation trench in a direction parallel to the guiding direction of the rib waveguide and on a side of the rib waveguide opposite to the first thermal isolation trench. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0034] Figure 1 A top view showing an optoelectronic device according to an embodiment of the present invention;

[0035] Figure 2 Shown is a view taken along line A-A' Figure 1 A cross-sectional view of an optoelectronic device;

[0036] Figure 3 Shown is a view taken along line BB′ Figure 1 A cross-sectional view of an optoelectronic device;

[0037] Figure 4 A top view showing an optoelectronic device according to an embodiment of the present invention;

[0038] Figure 5A and Figure 5B The thermal response time measurement results of the doped Si heater with undercut and without undercut are shown respectively;

[0039] Fig. 6A and Figure 6B Graphs of transient response time versus power, and ratio of groove length to heater length are shown, respectively;

[0040] Figure 7is a graph of power consumption versus response time; and

[0041] Figure 8 is a top view of a photovoltaic device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying drawings. Other aspects and embodiments will be apparent to those skilled in the art.

[0043] Figure 1 A top view of an optoelectronic device 100 according to an embodiment of the present invention is shown. The device includes a silicon rib waveguide 101 formed by a ridge portion 102 and a plate portion 103. The waveguide guides light in a guiding direction (in this example, along the x-axis). The waveguide is located on the upper surface of a substrate 104, which is primarily formed of silicon and is coated with SiO2 on the upper surface. The waveguide itself is also coated with SiO2 on the upper surface and sidewall surfaces, and is coated with a buried oxide layer (the buried oxide layer may also be formed of SiO2) on the lower surface (defining the boundary between the waveguide and the substrate or the waveguide and the thermal isolation cavity, discussed below). The ridge portion is in a direction perpendicular to the guiding direction of the waveguide ( Figure 1 The width of the plate portion measured in the z direction in the ridge portion may be about 3 μm. The width of the plate portion measured in the same direction may total about 38 μm, and may have two regions (on either side of the ridge portion), one region having a width of about 21 μm (containing the heater) and another region having a width of about 17 μm.

[0044] The heater 105 is adjacent to the ridge portion 102 and is located within a portion of the plate portion 103. The heater is formed by doping a portion of the plate with a dopant (in this example, an n-type dopant), and in this example, the width of the heater is 4 μm. The heater is connected and terminated to a first electrical interface 106 and a second interface electrode 107, respectively, which connect the heater to a first aluminum electrode 108 and a second aluminum electrode 109, respectively. The electrodes can be generally square in shape and have dimensions of 100 μm × 100 μm. Passing current from the first electrode to the second electrode causes the heater to heat the waveguide 101 and, therefore, phase shift the light passing through the waveguide.

[0045] The thermal isolation grooves 110 and 111 are located adjacent to the rib waveguide 101. The thermal isolation grooves define the ends (in the z direction) of the area of ​​the plate portion of the rib waveguide. Figure 2 Discussing in more detail, the thermal isolation trench forms a connection with a thermal isolation cavity extending below the rib waveguide such that a portion of the rib waveguide is lifted through the cavity. Can be heater length function of the heater length and is typically less than the heater length.

[0046] Figure 2 Shown is a view taken along line A-A' Figure 1 1 is a cross-sectional view of an optoelectronic device 100 of the present invention. Like features are indicated by like reference numerals. As can be seen from this view, each of the thermal isolation grooves 110 and 111 is connected to a thermal isolation cavity 201 extending below the rib waveguide 102. The thermal isolation cavity 201 is formed by two partially overlapping semicircular gaps 201a and 201b. Therefore, the cavity takes the shape of two partially overlapping semicircular prisms, which extend in a direction parallel to the guiding direction of the waveguide. Due to the isotropic etching technology used to form the cavity, the cavity body takes this shape. When the thermal isolation grooves 110 and 111 are connected to the thermal isolation cavity and the thermal isolation cavity 201 extends across the width of the rib waveguide, a portion of the rib waveguide is physically isolated from the surrounding substrate.

[0047] Figure 3 Shown is a view taken along line BB′ Figure 1 1 is a cross-sectional view of an optoelectronic device 100 of the present invention. Like features are indicated by like reference numerals. This view better illustrates the electrical connection made between the heater 105 and the first electrode 108. The heater extends from the plate portion of the rib waveguide in a direction away from the ridge portion to make electrical contact with the connecting portion of the aluminum electrode 108. The connecting portion of the aluminum electrode extends through the silicon dioxide layer to make electrical contact with the heater 105. A similar connection is made in the second electrical interface 107 between the second portion of the heater 105 and the second aluminum electrode 109.

[0048] Figure 4 4 shows a top view of an optoelectronic device 400 according to an embodiment of the present invention. Figure 1 The illustrated apparatus 100 shares many features and therefore like features are indicated by like reference numerals. Figure 1 Compared to the device 100 of the rib waveguide 102, the device 400 includes six thermal isolation grooves. On the first side of the rib waveguide, thermal isolation grooves 401a, 401b and 401c are provided. These grooves are spaced apart in the guiding direction, leaving a gap of length G between each groove. Similarly, on the second side of the rib waveguide, thermal isolation grooves 402a, 402b and 402c are provided. These grooves are also spaced apart in the guiding direction, leaving a gap of length G between each groove. Multiple pairs of thermal isolation grooves 401a and 402a, 401b and 402b, and 401c and 402c can be mirror images of each other along a line intercepted in the center of the rib waveguide 102. As previously described, each thermal isolation groove is connected to a thermal isolation cavity ( Figure 2Such a structure may provide increased stability and strength compared to a thermal isolation trench extending the same distance without a gap, since the "bridge" formed by the gap provides further support for the rib waveguide 101.

[0049] Figure 5A and Figure 5B is a graph showing the transient response of two thermo-optic phase shifters, one without an undercut / thermal isolation cavity ( Figure 5A ) and a thermo-optical phase shifter with undercut / thermally isolated cavity ( Figure 5B ). In both graphs, the dashed line indicates the voltage applied to the phase shifter electrodes. The solid line corresponds to the voltage read out from an oscilloscope channel connected to a photodetector downstream of the phase shifter. Essentially, the voltage is proportional to the photocurrent generated in the photodetector, which is proportional to the optical power from the phase shifter. As can be seen, the transient response (shown in the x-axis of both graphs) of the device without undercut / thermal isolation cavity is substantially longer than that of the device with undercut / thermal isolation cavity. Figure 5A The devices in the example have transient response times of the order of hundreds of microseconds, while Figure 5B The device has a transient response time of approximately a few microseconds.

[0050] Fig. 6A is a plot of heater length versus rise time for various devices: a device with a trench and a single thermal isolation cavity (Ntr = 1), a device with a trench and an array of thermal isolation cavities (Ntr>1), and those without trenches and without any cavities. 10% to 90% Rise Time Ratio shows a negative correlation and a linear relationship. The data from various heater lengths (200 μm, 500 μm, 800 μm) were plotted together and aligned well on a linear curve. Therefore, the length of the heater may not be considered a determining factor in transient time or efficiency. The ratio of trench length to heater length (D / L) is Figure 6B is shown in the graph.

[0051] Figure 7 is a graph of power consumption versus response time for four photovoltaic devices. The three on the left have the thermal isolation features (grooves and cavities) discussed above, while the device on the right does not include any thermal isolation features. The undercut length (length of the or each groove) of the device with undercut is equal to the length of the heater. The response time is defined as the sum of the 10% to 90% rise and fall times. yes The electrical power consumed by the phase shift. The graph illustrates that there is a trade-off between the speed and efficiency of the heater.

[0052] Figure 8A top view of a variant optoelectronic device 700 according to an embodiment of the present invention is shown. Figure 8 The device 700 shown is an electro-absorption modulator and includes a SiGe rib waveguide adjacent to a slab portion, the SiGe rib waveguide including a p-doped region on a first side of the rib waveguide and an n-doped region on a second, opposite side. This provides a pin junction or a pn junction, wherein the SiGe rib includes a doped sidewall. A heater is disposed above the n-doped region, but is preferably electrically isolated from the n-doped region. In this example, the heater can be used to tune the electro-absorption modulator to improve efficiency.

[0053] The device 700 includes four thermal isolation grooves: 701, 702, 703 and 704. These grooves are respectively located in the corners of the plate of the waveguide. The grooves are connected by one or more thermal isolation cavities extending under the plate and ridge portion of the waveguide. The structure of the thermal isolation cavity is similar to Figure 2 The structure shown is similar. Depending on the extent of etching, there may be two thermal isolation cavities, each connecting multiple pairs of thermal isolation trenches on opposite sides of the waveguide. If the extent of etching is sufficient, there may be a single thermal isolation cavity connecting all four thermal isolation trenches.

[0054] A method of manufacturing the device discussed above includes a first step of providing a rib waveguide on a substrate of an SOI wafer. The rib waveguide includes a ridge portion and a plate portion. A heater is also provided, which is provided in the plate portion. These steps can be performed in situ, or a wafer that already includes the rib waveguide and the heater can be provided.

[0055] Subsequently, one or more thermal isolation grooves are etched into the substrate. This etching can be performed via photolithography. The grooves are formed adjacent to the rib waveguides and can distinguish the area of ​​the plate portion. Next, the etched device is exposed to an etching liquid that isotropically etches the thermal isolation cavity in the substrate of the device. This cavity extends from each of the thermal isolation grooves and is directly connected to each of the thermal isolation grooves. In the example shown above, etching is performed until the thermal isolation grooves are fluidically connected via the thermal isolation cavity. The etchant in this example is an etching gas including XeF2. However, the etchant can be an etching liquid or an etching vapor. The etchant can be in a plasma phase.

[0056] Although the present invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when this disclosure is given. Therefore, the exemplary embodiments of the present invention set forth above are considered to be illustrative rather than restrictive. Various changes may be made to the described embodiments without departing from the spirit and scope of the present invention.

Claims

1. A photoelectric device comprising: a rib waveguide disposed on a substrate of the device, the rib waveguide comprising a ridge portion and a plate portion; a heater disposed within the plate portion; a first thermal isolation trench adjacent to the rib waveguide and extending into the substrate of the device; as well as A thermal isolation cavity within the substrate is directly connected to the first thermal isolation trench and extends between at least the rib waveguide and the substrate across at least a portion of the width of the rib waveguide. 2 . The photovoltaic device of claim 1 , wherein the heat isolation groove is positioned on a side of the heater opposite to the ridge portion.

3. The optoelectronic device according to claim 1 or claim 2, further comprising a second thermal isolation trench, the second thermal isolation trench being disposed on a side of the rib waveguide opposite to the first thermal isolation trench.

4. The optoelectronic device of claim 3, wherein the second thermal isolation trench is connected to the thermal isolation cavity such that an overhanging portion of the rib waveguide between the first thermal isolation trench and the second thermal isolation trench does not directly abut the substrate. 5 . The optoelectronic device of claim 3 , wherein each of the thermal isolation trenches is fluidly connected to the thermal isolation cavity. 6 . The photovoltaic device of claim 3 , wherein each of the thermal isolation trenches and the thermal isolation cavity are filled with a connected insulator. 7 . The optoelectronic device of claim 1 , wherein the thermal isolation cavity has a semicircular cross-section as viewed along a guiding direction of the rib-shaped waveguide.

8. The optoelectronic device of claim 7, wherein the thermal isolation cavity is formed by two partially overlapping regions, each of the two partially overlapping regions having a semicircular cross-section as viewed along the guiding direction of the rib waveguide.

9. The optoelectronic device of claim 3, further comprising a third thermal isolation trench spaced apart from the first thermal isolation trench in a direction parallel to a guiding direction of the rib waveguide, the third thermal isolation trench extending into the substrate.

10. The optoelectronic device of claim 9, wherein the thermal isolation cavity extends between the plate portion of the waveguide and the substrate from the first thermal isolation trench to the third thermal isolation trench.

11. The optoelectronic device of claim 10 , further comprising a fourth thermal isolation groove, the fourth thermal isolation groove being spaced apart from the first thermal isolation groove in the direction parallel to the guiding direction of the waveguide, the fourth thermal isolation groove extending into the substrate and being positioned on a side of the rib waveguide opposite to the third thermal isolation groove.

12. The optoelectronic device of claim 11, wherein the thermal isolation cavity extends between the plate portion of the waveguide and the substrate from the second thermal isolation trench to the fourth thermal isolation trench.

13. A method of forming an optoelectronic device comprising the steps of: disposing a rib waveguide on a substrate of the device, the rib waveguide comprising a ridge portion and a plate portion; providing a heater disposed within the plate portion; etching a first thermal isolation trench into the substrate, the trench being adjacent to the rib waveguide; The device is exposed to an etching liquid, thereby etching a thermal isolation cavity in the substrate, the thermal isolation cavity extending from the thermal isolation trench between the rib waveguide and the substrate and directly connected to the thermal isolation trench across at least the width of the rib waveguide.

14. The method of claim 13, wherein the etching liquid is any one of etching gas, etching liquid or etching vapor. The method of claim 13 , wherein the etching liquid is an etching gas.

16. The method of claim 15, wherein the etching gas is XeF2.

17. The method of any one of claims 13-16, wherein the thermal isolation groove is positioned on a side of the heater opposite the ridge portion.

18. The method according to any one of claims 13 to 16, further comprising the steps of: A second thermal isolation trench is etched into the substrate of the device, the second thermal isolation trench being located on a side of the ridge portion opposite the first thermal isolation trench. 19 . The method of claim 18 , wherein the thermal isolation cavity in the substrate extends from the first thermal isolation trench to the second thermal isolation trench.

20. The method of claim 17, further comprising the step of etching a third thermal isolation trench at a position spaced apart from the first thermal isolation trench in a direction parallel to a guiding direction of the rib waveguide.

21. The method of claim 17, further comprising the step of etching a fourth thermal isolation trench at a position spaced apart from the first thermal isolation trench in a direction parallel to a guiding direction of the rib waveguide and on a side of the rib waveguide opposite to the first thermal isolation trench.

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