Patent Application
20240377661
At high frequencies or high data rates, electrical transmission is reaching its limit due to high energy loss over long distances. As such, electrical chips that depend on long distance transmission are turning to optical transmission. Such electrical chips may, for example, include switch chips or system-on-chip (SoC) chips. Such SoC chips may, for example, include application-specific integrated circuit (ASIC) chips, central processing unit (CPU) chips, graphics processing unit (GPU) chips, and so on.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The present disclosure provides many different embodiments, or examples, for implementing different features of this disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
An optical module may comprise a waveguide and a photodetector. The waveguide passes an optical signal to the photodetector, which generates an electrical signal based on the optical signal. Conventionally, some photodetectors designed to function with both optical circuits and electronic circuits use a flip-chip method of integration, where optical circuits and electronic circuits are fabricated on separate chips before the circuits are bonded together using solder bumps. However, the flip-chip method of integration depends on precise alignment between the chips being bonded in order to effectively pass signals between the two chips. Chips used in flip-chip bonding additionally have a minimum area to support the coupling and separation of individual solder bumps. Therefore, a single chip solution is desirable to reduce the area used by the photodetector, enhance the flexibility of designs, and mitigate the risks associated with misalignment between chips.
Various embodiments of the present disclosure relate to an optical module comprising a photodetector integrated into a ribbed waveguide. In some embodiments, the optical module comprises the ribbed waveguide, where a portion of the ribbed waveguide is divided into a P-type region and an N-type region. The P-type region and the N-type region form a PN junction approximate to a center of the ribbed waveguide. Further, a biasing circuit is coupled to first and second protrusions extending from the P-type region and the N-type region, respectively. The biasing circuit reverse biases the PN junction, widening a depletion region proximate to the center of the ribbed waveguide. Due to the photoelectric effect, photons traveling through the ribbed waveguide may enter the depletion region and generate carriers. The carriers generated in the depletion region are prevented from recombining by the electric field present across the PN junction, which then pulls the carriers towards separate protrusions (e.g., the first and second protrusions) and into the biasing circuit, creating a measurable current.
The integration of a photodetector into the ribbed waveguide increases the flexibility of designs utilizing both photonic and electronic circuits. For example, a device that uses photonic circuits for high speed and/or long distance communications between different chips may convert the photonic signal to an electronic signal without using more than one chip, mitigating or removing issues related to chip bonding, alignment, and minimum space requirements.
A first-doping-type region 112 extends from the first protrusion 104c to the rib 104b, and a second-doping-type region 114 extends from the second protrusion 104d to the rib 104b. In some embodiments, the first-doping-type region 112 is a P-type region and the second-doping-type region 114 is an N-type region. In other embodiments, the first-doping-type region 112 is an N-type region and the second-doping-type region 114 is a P-type region. The first-doping-type region 112 and the second-doping-type region 114 form a PN junction 113 extending through the slab 104a and the rib 104b. In some embodiments, the PN junction 113 is approximately at a midpoint between outer sidewalls of the rib 104b and/or at a center between the first protrusion 104c and the second protrusion 104d.
A semiconductor region 110 is on the PN junction 113. In some embodiments, the semiconductor region 110 may be regarded as a semiconductor cap or the like. The ribbed waveguide 104 comprises a first semiconductor material, such as monocrystalline silicon or the like. The semiconductor region 110 comprises a second semiconductor material, such as germanium (Ge), or a III-V semiconductor material, such as gallium arsenide (GaAs), indium arsenide (InAs), gallium nitride (GaN), indium phosphide (InP), or the like. The second semiconductor material has a higher absorption coefficient for target radiation than the first semiconductor material and may, for example, have a higher electron mobility and/or differing bandgap energies relative to the first semiconductor material. In some embodiments, the semiconductor region 110 is devoid of a P-type doping and an N-type doping, whereby the semiconductor region 110 may be regarded as intrinsic.
The use of the second semiconductor material in the semiconductor region 110 may increase the quantum efficiency of the photodetector 101 over the desired range of wavelengths. For example, use of germanium or silicon germanium for the semiconductor region 110 may improve quantum efficiency for near infrared radiation due to a narrow bandgap relative to silicon. This increase in the quantum efficiency leads to a proportional increase in the electronic output signal of the photodetector 101 for the same photonic input signal. An increased output signal reduces the effect of noise on the output, which in turn may result in less errors and a more accurate data transfer between the photonic and electronic circuits.
In some embodiments, the semiconductor region 110 corresponds to a free carrier concentration modulation peak of the photodetector 101. Further, in some embodiments, a location at both a height-wise center of the ribbed waveguide 104 and a width-wise center of the ribbed waveguide 104 corresponds to a peak of a photoelectric field during use of the photodetector 101. Therefore, because a bottom surface of the semiconductor region 110 is elevated relative to a top surface of the ribbed waveguide 104, the carrier modulation peak is above the peak of the photodetector field in some embodiments.
A first heavily doped region 116 is in the first protrusion 104c. The first heavily doped region 116 has the same doping type as the first-doping-type region 112, but has a greater concentration of dopants. A second heavily doped region 118 is in the second protrusion 104d. The second heavily doped region 118 has the same doping type as the second-doping-type region 114, but has a greater concentration of dopants. In some embodiments, the first-doping-type region 112 and the second-doping-type region 114 have doping concentrations approximately between 2e16 to 9e18 atoms/cm3, approximately between 2015 to 9e17 atoms/cm3, approximately between 2e17 to 9e19 atoms/cm3, or the like. In further embodiments, the first heavily doped region 116 and the second heavily doped region 118 have doping concentrations approximately between 1e18 and 9e20 atoms/cm3, approximately between 1e17 and 9c19 atoms/cm3, approximately between 1e19 and 9c21 atoms/cm3, or the like. In some embodiments, the first heavily doped region 116 and the first-doping-type region 112 overlap in a portion of the slab 104a. The second-doping-type region 114 and the second heavily doped region 118 may also overlap in a portion of the slab 104a.
Contacts 120 are coupled to the first protrusion 104c, the second protrusion 104d, and the semiconductor region 110. The contacts 120 connect the first protrusion 104c, the second protrusion 104d, and the semiconductor region 110 to a wire layer 122.
The integration of the photodetector 101 into a single chip capable of holding a photonic circuit and an electronic circuit increases the flexibility of designs utilizing both photonic and electronic circuits, mitigating or removing issues related to chip bonding, alignment, and minimum area requirements of bonded chips.
The optical coupler 202 is coupled to the ribbed waveguide 104 by a strip waveguide 204 and a transition waveguide 206. The optical coupler 202 may, for example, be a grating coupler, an edge coupler, or the like. At the transition waveguide 206, a width of the transition waveguide 206 increases from a width of the strip waveguide 204 to a width of the rib 104b of the ribbed waveguide 104. Further, the slab 104a transitions from having a width of the strip waveguide 204 to having a width of the ribbed waveguide 104. One or more additional photonic circuit components (e.g., a power spreader, a Mach-Zehnder modulator (MZM), or the like) may, for example, be coupled to the strip waveguide 204 or the ribbed waveguide 104.
The PN junction 113 is at the rib 104b, formed by the first-doping-type region 112 and the second-doping-type region 114. The first-doping-type region 112 and the second-doping-type region 114 extend from the PN junction 113 respectively to the first protrusion 104c and the second protrusion 104d. Further, the first protrusion 104c and the second protrusion 104d respectively accommodate the first heavily doped region 116 and the second heavily doped region 118. Focusing on
Photons entering the ribbed waveguide 104 may be represented by an electromagnetic field traveling along the ribbed waveguide 104. The magnitude of the electromagnetic field is highest near the center of the ribbed waveguide 104. The square of the magnitude of the electromagnetic field is proportional to the number of photons concentrated in that position. Therefore, the highest concentration of photons in the ribbed waveguide 104 is at the center of the ribbed waveguide 104, which is approximately at a width-wise center of the rib 104b and is approximately at a height-wise center of the ribbed waveguide 104. Efforts to increase the efficiency of carrier generation (e.g., quantum efficiency) are therefore focused on the center of the ribbed waveguide as described hereafter with regard to
As shown in the cross-sectional view 300a of
During use of the photodetector 101, electromagnetic field traveling along the ribbed waveguide 104 may enter the semiconductor region 110. As noted above, the second semiconductor material of the semiconductor region 110 may have a higher absorption coefficient for incident radiation than the first semiconductor material and may therefore enhance quantum efficiency. In other words, the second semiconductor material increases the number of carriers generated and converted to photoelectric current. Because the semiconductor region 110 is implanted into the rib 104b, the semiconductor region 110 overlaps with a center of the ribbed waveguide 104. Further, because the concentration of photons is highest towards the center of the ribbed waveguide 104, greater quantum efficiency is achieved.
In some embodiments, the semiconductor region 110 corresponds to a free carrier concentration modulation peak of the photodetector 101. Further, in some embodiments, the center of the ribbed waveguide 104 corresponds to a peak of a photoelectric field during use of the photodetector 101. Therefore, because the semiconductor region 110 is at the center of the ribbed waveguide 104, the carrier modulation peak is coincident with the peak of the photodetector field in some embodiments.
As shown in the cross-sectional view 300b of
As shown in the cross-sectional view 300c of
As shown in the cross-sectional view 300d of
As shown in the cross-sectional view 300e of
The first-doping-type region 112 is in the upper slab 104e and extends to an upper boundary of the semiconductor region 110, and the second-doping-type region 114 is in the lower slab 104f and extends to a lower boundary of the semiconductor region 110. The first-doping-type region 112, the semiconductor region 110, and the second-doping-type region 114 together result in a PIN junction or the like.
In some embodiments, a fill layer 302 separates the upper slab 104e from the insulative layer 106. In some embodiments, the fill layer 302 is or comprises silicon oxide and/or the like. In some embodiments, the upper slab 104c is or comprises polysilicon and/or the like, whereas the lower slab 104f is or comprises monocrystalline silicon and/or the like.
The semiconductor region 110 is directly between the first-doping-type region 112 and the second-doping-type region 114 in a center of the ribbed waveguide 104. The greatest concentration of photons passes through the ribbed waveguide 104 at the position of the semiconductor region 110, so an increase to the quantum efficiency of the photodetector 101 at this point results in a greater change in quantum efficiency. The semiconductor region 110 may be either implanted or deposited before formation of the upper slab 104c.
As shown in the cross-sectional view 300f of
As shown in the cross-sectional view 300g of
As shown in the cross-sectional view 300h of
As shown in the cross-sectional view 300i of
As shown in the cross-sectional view 300j of
In some embodiments, the rib 104b has a first width W1 approximately between 300 and 2000 nanometers, approximately between 200 and 1500 nanometers, approximately between 400 and 2500 nanometers, or within another suitable range. In some embodiments, the first protrusion 104c has a second width W2 approximately between 120 and 200 percent of the first width W1. In some embodiments, the second protrusion 104d has a third width W3 approximately between 120 and 200 percent of the first width W1. In some embodiments, a first portion of the slab 104a extending between the first protrusion 104c and the rib 104b has a fourth width W4 approximately between 100 and 200 percent of the first width W1. In some embodiments, a second portion of the slab 104a extending between the second protrusion 104d and the rib 104b has a fifth width W5 approximately between 100 and 200 percent of the first width W1. In some embodiments, a distance D1 between the semiconductor region 110 and the second heavily doped region 118 is approximately between 35 and 99 percent of the fifth width W5. In some embodiments, the semiconductor region 110 has a sixth width W6 approximately between 100 and 350 percent of the first width W1.
In some embodiments, the first heavily doped region 116 has a seventh width W7 approximately between 150 and 230 percent of the first width W1. In some embodiments, the first heavily doped region 116 extends past sidewalls of the first protrusion 104c. In some embodiments, the second heavily doped region 118 has an eighth width W8 approximately between 150 and 230 percent of the first width W1. In some embodiments, the second heavily doped region 118 extends past sidewalls of the second protrusion 104d. In some embodiments, the first-doping-type region 112 outside of the first heavily doped region 116 has a ninth width W9 approximately between 50 and 100 percent of a combination of the first width W1, the second width W2, and the fourth width W4. In some embodiments, the second-doping-type region 114 outside of the second heavily doped region 118 has a tenth width W10 approximately between 50 and 100 percent of a combination of the first width W1, the second width W2, and the fourth width W4. The first-doping-type region 112 and the first heavily doped region 116 overlap by approximately 100 nanometers, 120 nanometers, 150 nanometers, or the like. The second-doping-type region 114 and the second heavily doped region 118 overlap by approximately 100 nanometers, 120 nanometers, 150 nanometers, or the like.
In some embodiments, the distance from an upper surface of the rib 104b to a bottom surface of the slab 104a has a first height approximately between 50 and 1000 nanometers, approximately between 40 and 800 nanometers, approximately between 60 and 1200 nanometers, or within another suitable range. In some embodiments, the rib 104b has a second height H2 approximately between 10 and 90 percent of the first height H1. In some embodiments, the semiconductor region has a third height H3 approximately between 1 and 50 percent of the second height H2. In some embodiments, the slab 104a has a fourth height H4 approximately between 10 and 90 percent of the first height H1. In some embodiments, the insulative layer 106 has a fifth height approximately between 2000 and 5000 nanometers, approximately between 1800 and 4500 nanometers, approximately between 2200 and 5500 nanometers, or within another suitable range.
In some embodiments, the ribbed waveguides 104 extending through the array of photodetectors 101a-101d terminate at the central region 601. The photonic signals that pass through the array of photodetectors 101a-101d may, for example, be absorbed in the central region 601. In some embodiments, the central region 601 has a semiconductor cap (not shown) that is configured to absorb the remainder of the photonic signals in the central region 601.
The central region 601 may have a polygonal shape (e.g., a diamond shape, a pentagon shape, etc.). The photodetectors 101a-101d are evenly spaced around the central region 601. In some embodiments, the photodetectors 101a-101d are coupled to the vertices of the polygonal shape. By coupling the array of photodetectors 101a-101d to the central region 601, the area normally used to absorb the photonic signals output from individual photodetectors in a column array is reduced, increasing the space efficiency of the design. Additionally, embodiments comprising one or more additional photodetectors coupled to the central region 601 will not (or will minimally) increase the area taken by the array, increasing flexibility in the number of photodetectors used and the scalability of the design.
As shown in
Amplitude modulation or frequency modulation may, for example, be used to encode the information from the individual photodetectors 101a-101d into one or more digital signals. In some embodiments, a clock signal is used to add delays to individual output signals from the individual photodetectors 101a-101d, such that each photodetector has a different delay amount. In some embodiments, modulators 602a-602d alter the amplitudes and/or frequencies of the photonic signals 130 to be different from one another. The amplitudes of the photonic signals 130 are proportionate to the output current of the photodetectors 101a-101d, as the number of carriers generated is proportional to the number of photons entering the depletion region. Because the individual first protrusions 104c are coupled to the first pad 124 and because the individual second protrusions 104d are coupled to the second pad 126, the electrical signals from the array of photodetectors 101a-101d may add and/or combine into an output signal.
In some embodiments, the modulators 602a-602d may be coupled to a fourth pad 604. An electric signal from the fourth pad 604 may be used to control the modulators 602a-602d. In some embodiments, attenuators 606 may be coupled to the ribbed waveguides 104 to further control the amplitude of the photonic signals 130. The attenuators 606 may be controlled by signals received from a fifth pad 608. In some embodiments, the positioning of the plurality of pads 124, 126, 128, 604, and 608 may vary from what is shown in
Because the individual photodetectors 101a-101d share the same set of pads, space efficiency is enhanced. Less area is wasted on pads. Further, the pitch between photodetectors may be reduced. Accordingly, there may be more photodetectors per given area than would otherwise be possible (e.g., with a layout like that of
With reference to
As illustrated by a cross-sectional view 700 of
As illustrated by a cross-sectional view 800 of
As illustrated by a cross-sectional view 900 of
As illustrated by a cross-sectional view 1000 of
As illustrated by a cross-sectional view 1100 of
As illustrated by a cross-sectional view 1200 of
As illustrated by a cross-sectional view 1300 of
As illustrated by a cross-sectional view 1400 of
As illustrated by a cross-sectional view 1500 of
As illustrated by a cross-sectional view 1600 of
As illustrated by a cross-sectional view 1700 of
As illustrated by a cross-sectional view 1800 of
As illustrated by a cross-sectional view 1900 of
As illustrated by a cross-sectional view 2000 of
With reference to
At 2102, a semiconductor layer is patterned to form a first waveguide on a substrate. See, for example,
At 2104, the first waveguide is doped to form a first PN junction. See, for example,
At 2106, a first semiconductor region is formed on the first PN junction using one or both of an implantation process and a deposition process, wherein the semiconductor layer comprises a first semiconductor material and the first semiconductor region comprises a second semiconductor material different from the first semiconductor material. See, for example,
While the block diagram 2100 of
In some embodiments, the present disclosure provides an optical module, including: a waveguide including a rib and further including a first protrusion and a second protrusion respectively on opposite sides of the rib; a photodetector comprising a PN junction in the rib; and a semiconductor region on the PN junction, where the waveguide comprises a first semiconductor material, and the semiconductor region comprises a second semiconductor material different from the first semiconductor material.
In some embodiments, the present disclosure provides another optical module, including: waveguides arranged around and ending at a central region; photodetectors integrated into the waveguides around the central region; a first pad coupled to N-type regions of the photodetectors; and a second pad coupled to P-type regions of the photodetectors.
In some embodiments, the present disclosure provides a method for forming an optical module, including: patterning a semiconductor layer to form a first waveguide in the semiconductor layer; doping the first waveguide to form a first PN junction; forming a first semiconductor region on the first PN junction using one of an implantation process or a deposition process, wherein the semiconductor layer comprises a first semiconductor material and the first semiconductor region comprises a second semiconductor material different from the first semiconductor material.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.
