Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
  • G02B6/122—Basic optical elements, e.g. light-guiding paths
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
  • G02B6/122—Basic optical elements, e.g. light-guiding paths
  • G02B6/1225—Basic optical elements, e.g. light-guiding paths comprising photonic band-gap structures or photonic lattices
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/24—Coupling light guides
  • G02B6/42—Coupling light guides with opto-electronic elements
  • G02B6/43—Arrangements comprising a plurality of opto-electronic elements and associated optical interconnections

Definitions

• the present invention relates generally to the transmission of data at the silicon level, and relates more specifically to a wave guide seamlessly integrated with a semiconductor light source of a different technology for conducting light generated by the semiconductor light source.
• a wave guide seamlessly integrated with a semiconductor light source of a different technology for conducting light generated by the semiconductor light source.
• information is processed and transmitted electrically over small metallic wires that interconnect silicon-based devices, such as transistors and/or other electrical components.
• transmitting electricity over wires is subject to certain limitations, including limited transmission speeds, electromagnetic interferences, etc.
• One potential solution to overcome some of the limitations of electrical transmission is to utilize pulsed light to carry information over an optical network.
• Figure 1 depicts an example of a model for generating light from a bipolar transistor, where E is the emitter, C is the collector, B is the base, and SUB is the measure of substrate current. Details of such an embodiment are described, for instance, in J.H. Klootwijk, J. W. Slotboom, M.S. Peter, Photo Carrier Generation in Bipolar
• the present invention addresses the above-mentioned problems, as well as others by providing an integrated optical wave guide for conducting light generated by a semiconductor light source.
• the invention provides a seamlessly integrated hybrid optical network device, comprising: a semiconductor light source mounted in a cavity in a silicon substrate, wherein the semiconductor light source can be biased into an avalanche condition to emit photons, and wherein the semiconductor light source is fabricated from a non-silicon material; and a photonic bandgap (PBG) structure seamlessly integrated with the semiconductor light source to act as an optical wave guide for the photons emitted by the semiconductor light source, wherein the PBG structure is etched directly in the silicon substrate.
• PBG photonic bandgap
• the invention provides a method of fabricating a seamlessly integrated hybrid optical network device, comprising: providing a silicon substrate; etching a cavity in the silicon substrate; etching a photonic bandgap (PBG) structure in the silicon substrate proximate the cavity; and placing a non-silicon semiconductor light source in the cavity, wherein the semiconductor light source can be biased into an avalanche condition to emit photons.
• PBG photonic bandgap
• the invention provides a seamlessly integrated optical network, comprising: a non-silicon semiconductor light source mounted in a silicon substrate that can be biased into an avalanche condition to emit photon pulses; a photonic bandgap (PBG) structure fabricated in the silicon substrate and seamlessly integrated with the semiconductor light source in the silicon substrate that acts as an optical wave guide for the photon pulses generated by the semiconductor light source; and a receiving device realized proximate a distal end of the optical wave guide for receiving the photon pulses generated by the semiconductor light source.
• PBG photonic bandgap
• Figure 1 depicts a bipolar transistor reverse biased into an avalanche condition to emit photons in accordance with the present invention.
• Figure 2 depicts a first step for forming an optical network device in accordance with the present invention.
• Figure 3 depicts a side view of an optical network device in accordance with the present invention.
• Figure 4 depicts a silicon based optical network in accordance with the present invention.
• Figure 5 depicts four cross-sectional micrographs of exemplary photonic band gap (PBG) structures in a silicon wafer after dry etching with a mask.
• PBG photonic band gap
• the present invention provides a seamlessly integrated optical network comprising an optical wave guide structure that is combined with a semiconductor light source, resulting in a low-current density light source with a seamlessly integrated optical wave guide.
• the optical network comprises an optical wave guide structure etched into a silicon substrate and a light emitting device formed from a semiconductor material that resides in a cavity etched proximate the optical wave guide structure.
• the present invention utilizes "photonic bandgap" (PBG) structures to act as optical wave guides for light generated by the semiconductor light source.
• the PBG structures comprise corrugated channel-cage structures, which may for example be dry-etched in a silicon substrate.
• PBG structures are implemented as two- dimensional (2D) crystals consisting of parallel cylinders (or elements) that can be readily realized at submicron lengths.
• 2D two- dimensional
• 3D three-dimensional
• a combined etching is performed to form both a cavity 41 and a PBG structure 22 in a silicon (e.g., BICMOS or CMOS) substrate 11.
• a silicon e.g., BICMOS or CMOS
• corrugated channel-cage elements i.e., the photonic bandgap (PBG) structures
• PBG photonic bandgap
• a semiconductor light source 10 - in this case a bipolar device - formed from a different (e.g., non-silicon based) technology is placed into the cavity 41.
• the semiconductor light source is fabricated from a material that is not purely silicon (Si), but is instead fabricated from a "non-silicon" material.
• exemplary materials for the "non-silicon" semiconductor light sources include, e.g., SiGe, SiGeC, InP, GaAs, etc. (Accordingly, the term "non-silicon" as used herein should be interpreted to include silicon compounds.)
• the result is a hybrid optical network device 20 in which compound materials forming a semiconductor light source 10 are seamlessly integrated with a silicon-based optical waveguide 22.
• a specific wavelength (or different wavelengths) can be achieved that will be conducted by the PBG structure 22.
• the designer can select a desired light wavelength by using a material having properties to achieve the desired light wavelength.
• an interconnect layer 46 can be added.
• a light source e.g., of infrared light having a wavelength ⁇ ⁇ 1 ⁇ m, is provided using a hybrid combination of semiconductor light sources and PBG structures, which are seamlessly integrated to form an optical network device 20 in, e.g., lightly doped silicon.
• an optical network 13 that includes a plurality of devices 10, 27a-d that communicate optically within a silicon substrate 11.
• Optical communication is achieved with the optical network device 20 described above in Figure 3 formed into silicon substrate 11.
• Device 20 includes: (1) a non-silicon semiconductor light source 10, in this case a bipolar transistor, capable of emitting a light beam 12, i.e., photon beam, from a base-collector junction, and (2) a PBG structure 22 having a plurality of PBG elements 14 that defines a wave guide channel 16.
• the light beam 12 can be "bent" and split through the wave guide channel 16, thereby allowing the light source to be directed to any point in the silicon substrate 11.
• PBG elements 14 can therefore be strategically located as needed throughout the silicon substrate 11 to create any desired wave guide configuration. Possible configurations may include wave guides channels with beam splitters to achieve multiple branches, configurations for achieving polarization and/or filtering, channels that interconnect devices internally within the silicon substrate 11, channels that interconnect devices with external devices, etc.
• the wave guide is connected to a set of receiving devices 27a-d (e.g., photo-diodes) that receive pulsed light from the semiconductor light source 10.
• Control over the network 13 can be provided by control system 29, which may include, e.g., a microprocessor or other logic that dictates when light should be transmitted from the semiconductor light source. Control system 29 may reside within the silicon substrate 11 and/or externally to the substrate.
• semiconductor light source 10 may be fabricated with a reflective material 25 (e.g., a 'A l-coating) on one or more surfaces to block photon emission and thereby cause the light beam 12 to be directed out of only a single surface. Furthermore, the reflective material 25 could be selectively placed to define an optical window 24 through which the light source will be focused.
• PBG Structure Figure 5 depicts four cross-sectional micrographs of exemplary photonic band gap
• PBG PBG structures in a silicon wafer after dry etching with a mask.
• Each cylinder element essentially comprises a "pore" through the silicon.
• the mask hole diameter and pitch are (a) 2 ⁇ m and, 10 ⁇ m, (b) 1.5 ⁇ m and 3.5 ⁇ m, (c) and (d) 3 ⁇ m and 5 ⁇ m.
• the particular diameter and pitch of the PBG structure 22 can vary according to the particular application.
• the PBG structure 22 could be fabricated with a wet chemical etch process.
• the pores in the PBG structure 22 have a round cross section and are arranged in a square or hexagonal array to make the structure suitable for guiding polarized light and non-polarized light, respectively.
• Exemplary pore diameters are of the order of 1 ⁇ m, and the pitch a between the pores is only slightly larger.
• the wavelength ⁇ can be tailored by setting the pitch a, the relationship being: a/ ⁇ - 0.2 to 0.5. This implies that a complete wavelength range can be covered from the near to the far infrared, e.g., 0.8 ⁇ m (GaAs bandgap) and 1.1 (Si bandgap) to -100 ⁇ m.
• Typical characteristic pore diameter and pitch values for a PBG structure can be, depending on the wavelength of the light to be guided, of the order of 300 nm (for visible light guiding) to a few ⁇ m (for infrared light guiding). Any methodology may be employed to realize the PBG structure 22.
• One way of manufacturing the PBG structure is by electrochemical etching, e.g. photo-electrochemical etching of lightly n-doped silicon, with the silicon wafer connected as the anode. By varying the photo-irradiation intensity of the wafer backside, i.e., the current density, during the electrochemical etching the pore radius can be changed periodically.
• the pore array that makes up the PBG structure 22 could also be realized by using dry etching, i.e., reactive ion etching (RIE).
• RIE reactive ion etching
• the PBG structure 22 could be realized with the corrugated pillars remaining, thus creating the inverse structure of an array of pillars instead of pores.
• One dry-etching technique for making the necessary corrugated pore array structures involves the so-called "Bosch process.” This process is a dry-etching process enabling high aspect ratio trenches and pores. Etching is done in SF 6 chemistry whereas passivation is done in C 4 F 8 chemistry. By changing the process parameters such that one alternatively enters and leaves the process window from anisotropic into isotropic etching, these corrugated structures can be made.
• the silicon etch process is based on plasma etching where rapidly switching of etching and passivation chemistry enables the formation pores, trenches, etc.
• An exemplary process may use the following steps: (1) Etching and passivation as in the Bosch process, until the desired depth of the first corrugation. (2) Step 1 ends with an etch cycle. This is required since the passivation polymer on the bottom of the pore has to be removed in order to enable the next isotropic etching step, (3) Isotropic etching by using SF 6 /O 2 chemistry.
• the platen power bias voltage on the chuck supporting the wafer
• the process switches to the next step, starting this time with a passivation cycle; this to cover and protect the complete structure etched thus far with a passivation layer.
• the process resumes step 1 again and can be repeated several times.
• the optical wave guide may consist of a high refractive index core with a lower refractive index cladding.
• Typical combinations that can be use include: TiO2 core and SiO2 cladding; Si3N4 core and SiO2 cladding; SiON core and SiO2 cladding; PMMA core and Cr cladding; Poly Si core and SiO2 cladding; and InGaAsP core and InP cladding.
• Semiconductor light source As noted, the semiconductor light source 10 can be fabricated from any non-silicon material suitable for providing the desired wavelength. Examples include SiGe, SiGeC, InP, and GaAs. It should be also noted that the non-silicon material could be mounted in any suitable type of silicon substrate, including an active substrate such as CMOS, high-speed SiGe, SiGeC, BiCMOS, etc.
• One exemplary method starts with a high-resistivity wafer having a thermal oxide layer e.g. 1 ⁇ m.
• a thick resist mask e.g., lO ⁇ m
• the silicon is etched to the depth of the light- emitting device that will be placed in the cavity. Dry etching of cavities with nearly perfect sidewall slopes is possible using the BoschTM process in a commercially available etcher.
• the next step is the placement and the gluing of the bipolar device in the cavity, using, e.g., an organic polymer glue, such as benzo cyclobutane (BCB).
• BCB benzo cyclobutane

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• Semiconductor Lasers (AREA)

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• 2005
  • 2005-01-22 JP JP2006550437A patent/JP2007519049A/ja active Pending
  • 2005-01-22 WO PCT/IB2005/050260 patent/WO2005071452A1/en not_active Application Discontinuation
  • 2005-01-22 CN CNA2005800028701A patent/CN1910487A/zh active Pending
  • 2005-01-22 KR KR1020067014759A patent/KR20060132658A/ko not_active Application Discontinuation
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