This invention relates to the field of electro-optical logic circuits and techniques and, more particularly, to such circuits and techniques that employ light-emitting transistors and/or transistor lasers.
As computing grows increasingly more complex and performance goals escalate with the implementation of multi-core strategies and massively parallel computing, building blocks are needed that can perform at higher speeds, continue to scale with integrable components to achieve economies of scale, and satisfy the demand for interconnect speeds between each computing component and blocks of transistors. As the demand for lower power consumption (e.g., longer battery life) increases, copper interconnects are becoming more and more complex, and are expected to hit a stumbling block as increasing peripheral power (e.g., that consumed in pre-amplifier circuitry) will no longer meet the requirements for better performance at lower power. Photonics could provide the solution to both enabling massively parallel computing, and solving the problem of copper interconnects, thus ensuring that computing technology continues to grow and scale successfully. However, prior attempts at devising optical logic have encountered serious limitations. For example, two prior types of solution that have been proposed for all optical logic gates are based on: (1) Laser-PNPN thyristor switch, and (2) Laser-phototransistor. Both solutions have major disadvantages that could not be overcome. The major issue with a laser-photothyristor implementation is that the PNPN-thyristor has an extremely slow switching speed, typically in the MHz range. This fundamental limitation is owing to the saturated nature of PNPN switch operation. Once turned on, the PNPN device accumulates large quantities of charges in its base, and can take a long time just to turn off again. This sets a fundamental limit to the speed of the laser-photothyristor solution. Regarding a proposed all optical logic gate based on a laser-phototransistor, a key issue is that the solution requires a complex layer structure comprising layers of crystal growth to form a laser on top of a phototransistor, or vice versa. This results in very complex device fabrication. The manufacturing process has low yields and low repeatability, negating the possibility for very large scale integration.
The transistor has been the fundamental building block of electronic integrated circuits. In addition to its logic and switching capability, the transistor is also the ‘precursor’ to various circuit blocks because essential components such as amplifiers, resistors, varactors, and diodes can be fabricated from transistor structures. The transistor therefore enables the integration of multiple components on an integrated circuit or chip for logic, switching and various circuit applications.
A part of the background hereof lies in the development of heterojunction bipolar transistors which operate as light-emitting transistors and transistor lasers. Reference can be made for example, to U.S. Pat. Nos. 7,091,082, 7,286,583, 7,354,780, 7,535,034 and 7,693,195; U.S. Patent Application Publication Numbers US2005/0040432, US2005/0054172, US2008/0240173, US2009/0134939, and US2010/0034228; and to PCT International Patent Publication Numbers WO/2005/020287 and WO/2006/093883. Reference can also be made to the following publications: Light-Emitting Transistor: Light Emission From InGaP/GaAs Heterojunction Bipolar Transistors, M. Feng, N. Holonyak, Jr., and W. Hafez, Appl. Phys. Lett. 84, 151 (2004); Quantum-Well-Base Heterojunction Bipolar Light-Emitting Transistor, M. Feng, N. Holonyak, Jr., and R. Chan, Appl. Phys. Lett. 84, 1952 (2004); Type-II GaAsSb/InP Heterojunction Bipolar Light-Emitting Transistor, M. Feng, N. Holonyak, Jr., B. Chu-Kung, G. Walter, and R. Chan, Appl. Phys. Lett. 84, 4792 (2004); Laser Operation Of A Heterojunction Bipolar Light-Emitting Transistor, G. Walter, N. Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. Lett. 85, 4768 (2004); Microwave Operation And Modulation Of A Transistor Laser, R. Chan, M. Feng, N. Holonyak, Jr., and G. Walter, Appl. Phys. Lett. 86, 131114 (2005); Room Temperature Continuous Wave Operation Of A Heterojunction Bipolar Transistor Laser, M. Feng, N. Holonyak, Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, 131103 (2005); Visible Spectrum Light-Emitting Transistors, F. Dixon, R. Chan, G. Walter, N. Holonyak, Jr., M. Feng, X. B. Zhang, J. H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 88, 012108 (2006); The Transistor Laser, N. Holonyak and M Feng, Spectrum, IEEE Volume 43, Issue 2, February 2006; Signal Mixing In A Multiple Input Transistor Laser Near Threshold, M. Feng, N. Holonyak, Jr., R. Chan, A. James, and G. Walter, Appl. Phys. Lett. 88, 063509 (2006); and Collector Current Map Of Gain And Stimulated Recombination On The Base Quantum Well Transitions Of A Transistor Laser, R. Chan, N. Holonyak, Jr., A. James, and G. Walter, Appl. Phys. Lett. 88, 14508 (2006); Collector Breakdown In The Heterojunction Bipolar Transistor Laser, G. Walter, A. James, N. Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. Lett. 88, 232105 (2006); High-Speed (/spl ges/1 GHz) Electrical And Optical Adding, Mixing, And Processing Of Square-Wave Signals With A Transistor Laser, M. Feng, N. Holonyak, Jr., R. Chan, A. James, and G. Walter, Photonics Technology Letters, IEEE Volume: 18 Issue: 11 (2006); Graded-Base InGaN/GaN Heterojunction Bipolar Light-Emitting Transistors, B. F. Chu-Kung et al., Appl. Phys. Lett. 89, 082108 (2006); Carrier Lifetime And Modulation Bandwidth Of A Quantum Well AlGaAs/InGaP/GaAs/InGaAs Transistor Laser, M. Feng, N. Holonyak, Jr., A. James, K. Cimino, G. Walter, and R. Chan, Appl. Phys. Lett. 89, 113504 (2006); Chirp In A Transistor Laser, Franz-Keldysh Reduction of The Linewidth Enhancement, G. Walter, A. James, N. Holonyak, Jr., and M. Feng, Appl. Phys. Lett. 90, 091109 (2007); Photon-Assisted Breakdown, Negative Resistance, And Switching In A Quantum-Well Transistor Laser, A. James, G. Walter, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 90, 152109 (2007); Franz-Keldysh Photon-Assisted Voltage-Operated Switching of a Transistor Laser, A. James, N. Holonyak, M. Feng, and G. Walter, Photonics Technology Letters, IEEE Volume: 19 Issue: 9 (2007); Experimental Determination Of The Effective Minority Carrier Lifetime In The Operation Of A Quantum-Well n-p-n Heterojunction Bipolar Light-Emitting Transistor Of Varying Base Quantum-Well Design And Doping; H. W. Then, M. Feng, N. Holonyak, Jr., and C. H. Wu, Appl. Phys. Lett. 91, 033505 (2007); Charge Control Analysis Of Transistor Laser Operation, M. Feng, N. Holonyak, Jr., H. W. Then, and G. Walter, Appl. Phys. Lett. 91, 053501 (2007); Optical Bandwidth Enhancement By Operation And Modulation Of The First Excited State Of A Transistor Laser, H. W. Then, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 91, 183505 (2007); Modulation Of High Current Gain (β>49) Light-Emitting InGaN/GaN Heterojunction Bipolar Transistors, B. F. Chu-Kung, C. H. Wu, G. Walter, M. Feng, N. Holonyak, Jr., T. Chung, J.-H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 91, 232114 (2007); Collector Characteristics And The Differential Optical Gain Of A Quantum-Well Transistor Laser, H. W. Then, G. Walter, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 91, 243508 (2007); Transistor Laser With Emission Wavelength at 1544 nm, F. Dixon, M. Feng, N. Holonyak, Jr., Yong Huang, X. B. Zhang, J. H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 93, 021111 (2008); Optical Bandwidth Enhancement Of Heterojunction Bipolar Transistor Laser Operation With An Auxiliary Base Signal, H. W. Then, G. Walter, M. Feng, and N. Holonyak, Jr. Appl. Phys. Lett. 93, 163504 (2008). Bandwidth extension by trade-off of electrical and optical gain in a transistor laser, Three-terminal control, H. W. Then, M. Feng, and N. Holonyak, Jr. Appl. Phys. Lett.94, 013509 (2009). Tunnel Junction Transistor Laser, M. Feng, N. Holonyak, Jr., H. W. Then, C. H. Wu, and G. Walter Appl. Phys. Lett 94, 041118 (2009); Electrical-Optical Signal Mixing And Multiplication (2→22 GHz) With A Tunnel Junction Transistor Laser, H. W. Then, C. H. Wu, G. Walter, M. Feng, and N. Holonyak, Jr. Appl. Phys. Lett. 94, 101114 (2009); Scaling Of Light Emitting Transistor For Multigigahertz Optical Bandwidth, C. H. Wu, G. Walter, H. W. Then, M. Feng, and N. Holonyak, Jr. Appl. Phys. Lett. 94, 171101 (2009); Device Performance Of Light Emitting Transistors With C-Doped And Zn-Doped Base Layers; Huang, Y.; Ryou, J.-H.; Dupuis, R. D.; Dixon, F.; Holonyak, N.; Feng, M.; Indium Phosphide & Related Materials, 2009; Tilted-Charge High Speed (7 GHz) Light Emitting Diode, G. Walter, C. H. Wu, H. W. Then, M. Feng, and N. Holonyak, Jr. Appl. Phys. Lett. 94, 231125 (2009); 4.3 GHz Optical Bandwidth Light Emitting Transistor, G. Walter, C. H. Wu, H. W. Then, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 94, 241101 (2009) Received: 29 Jan. 2009; accepted: 17 Apr. 2009; published online: 15 Jun. 2009. Resonance-Free Frequency Response Of A Semiconductor Laser, M. Feng, H. W. Then, N. Holonyak, Jr., G. Walter, and A. James, Appl. Phys. Lett. 95, 033509 (2009).
It is among the objectives here to achieve improvements in electro-optical logic functions and circuits, by advantageously utilizing light-emitting transistors, transistor lasers, and related structures for implementing NOR functions and other logic functions needed for high speed opto-electronic systems and methods.
The advent of the light-emitting transistor and transistor laser allows the integration of the transistor and laser as a single component or device, adding a natural photonic component to integrated circuits. The light-emitting transistor and transistor laser, due to its direct-gap (III-V semiconductor) structure, possesses a major advantage over its purely electrical cousin: it has the capability of processing (receive, transform and transmit) both electrical and optical signals. For example, besides performing its usual electrical signal processing functions, a light-emitting transistor can convey its output signal via either an electrical output or, where desired, it can propagate the output signals in the form of an optical signal, thereby allowing near lossless, high-speed optical signal transmission (e.g. in optical waveguides) over distances unreachable by copper interconnects.
By adding a ‘third’ optical dimension, the light-emitting transistor can provide a new scalable and integrable building block for massive arrays that can be addressed simultaneously instead of by the usual multiplexed approach. This enables information to be processed and transmitted simultaneously. Arrays of optical switches and logic gates made from light-emitting transistors can thus, for example, provide the building blocks for constructing a very large scale parallel integrated optical network and logic functions for massively parallel computing.
A form of the invention hereof comprises a universal electro-optical NOR gate based on the light-emitting transistor (LET) or transistor laser (TL), from which all other logic functions may be constructed. The optical NOR gate can, for example, form a building block for a larger optical based network to support massive parallel computing. Moreover, due to its inherent transistor structure, the same device or component can be fabricated into electrical logic building blocks for computing and for other traditional (electronic) information processing functions as well. Moreover, all the required components for integrated circuits can be fabricated on a single epitaxial structure for the light-emitting transistor, thus facilitating integration on a very large scale and driving economies of scale.
In accordance with an embodiment of the invention, a method is set forth for implementing an electro-optical logic function, such as a NOR function, responsive to first and second logical inputs, comprising the following steps: providing, as an output stage, a light-emitting transistor having an electrical input port and an optical output port; and providing, as an input stage, a circuit for receiving said first and second logical inputs and producing a control signal that is coupled with the electrical input port of said output stage. In one embodiment, at least one of said logical inputs is an optical input, and the step of providing, as an input stage, a circuit for receiving said first and second logical inputs, comprises providing an electro-optical circuit for receiving said first and second logical inputs. In this embodiment, the step of providing, as an input stage, an electro-optical circuit, comprises providing an electro-optical circuit that includes a phototransistor, which can preferably be a light-emitting transistor configured as a phototransistor. The output stage light-emitting transistor and the light emitting transistor configured as a phototransistor can advantageously have a substantially common semiconductor layer structure.
In an embodiment of the method of the invention, the step of providing said electro-optical circuit comprises providing a circuit that further includes a light-emitting transistor configured as a resistor, and further comprises arranging said light-emitting transistor configured as a resistor and said light-emitting transistor configured as a phototransistor in a biased series arrangement, such that the signal level at a terminal of said resistor depends on whether a logical input signal is being received by said phototransistor. In this embodiment, the step of producing a control signal comprises producing a voltage applied as the collector voltage of the light-emitting transistor of the output stage. The recited light-emitting transistors can comprise transistor lasers and/or tunnel junction transistor lasers. Also, other logical functions can be implemented.
As will also be described, a bistable latch function is implemented by combining first and second NOR gate functions in accordance with an embodiment of the invention. In an embodiment thereof, each of said NOR gate functions is adapted to receive, as one of its inputs, a signal derived from the output of the other NOR gate function.
In accordance with a further embodiment of the invention, a method is set forth for implementing a universal electro-optical logic function responsive to plural logical inputs, comprising the following steps: providing, on a common substrate, first, second, and third transistor structures having substantially common semiconductor layering; configuring said third transistor structure as a light-emitting transistor output stage having an electrical input port, an electrical output port, and an optical output port; configuring said first transistor structure to operate as a resistor; configuring said second transistor structure to operate as a phototransistor; and providing, as an input stage, an electro-optical circuit that includes said configured first and second transistor structures, for receiving a plurality of logical inputs and producing a control signal that is coupled with the electrical input port of said output stage.
Further features and advantages of the invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.
In an embodiment hereof, in constructing a NOR gate from a light-emitting transistor, both its electrical and optical functionalities are utilized. A light-emitting transistor laser with a collector tunnel junction design (see e.g. U.S. Patent Application Publication No. US2010/0085995) is employed in this example for illustration. Its electrical and optical properties are shown in
If an optical signal of a particular strength (power) is incident on TL0, TL0 will switch to a low impedance state and a current will be conducted through TL1. Consequently, the potential at A will be raised sufficiently to switch off TL2, thus rendering its output a logic “0”. The output logic “0” case is shown
The table of
Operation of the bistable latch of the
Priority is claimed from U.S. Provisional Patent Application Ser. No. 61/401,501, filed Aug. 13, 2010, and said U.S. Provisional Patent Application is incorporated herein by reference.
Number | Date | Country | |
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61401501 | Aug 2010 | US |