Xuliang Han

All ink-jet-printed carbon nanotube thin-film transistor on a polyimide substrate with an ultrahigh operating frequency of over 5 GHz

We report a flexible carbon nanotube (CNT) thin-film transistor (TFT) fabricated solely by ink-jet printing technology. The TFT is top gate configured, consisting of source and drain electrodes, a carrier transport layer based on an ultrapure, high-density (>1000 CNTs/μm2) CNT thin film, an ion-gel gate dielectric layer, and a poly(3,4-ethylenedioxythiophene) top gate electrode. All the TFT elements are ink-jet printed at room temperature on a polyimide substrate without involving any photolithography patterning or surface pretreatment steps. This CNT-TFT exhibits a high operating frequency of over 5 GHz and an on-off ratio of over 100. Such an all-ink-jet-printed process eliminates the need for lithography, vacuum processing, and metallization procedures and thus provides a promising technology for low-cost, high-throughput fabrication of large-area high-speed flexible electronic circuits on virtually any desired flexible substrate.

An 8-Gb/s optical backplane bus based on microchannel interconnects: design, fabrication, and performance measurements

We describe the characteristics of a microchannel-based optical backplane including signal-to-noise ratio (SNR), interconnect distances, and data transfer rates. The backplane employs 250 /spl mu/m-spacing two-dimensional (2-D) vertical cavity surface emitting lasers (VCSELs) and a microlens array to implement 500 /spl mu/m-, 750 /spl mu/m-, and 1-mm optical beam arrays. By integrating the transmitter and a multiplexed polymeric hologram as a deflector/beam-splitter for the guided-wave optical backplane, the result demonstrates a multibus line architecture and its high-speed characteristics. Maximum interconnect distances of 6 cm and 14 cm can be achieved to satisfy 10/sup -12/ bit error rate (BER) using 2/spl times/2 beams of 500 /spl mu/m- and 1 mm-spacing array devices. The total data transfer rate of the developed backplane has shown 8 Gb/s from eye diagram measurements.

Accurate diffraction efficiency control for multiplexed volume holographic gratings

We report the method of accurate diffraction efficiency control for multiplexed volume holographic gratings in dry photopolymer films (DuPont HRF-600). Based on the experimental evaluations of the grating formation characteristics in dry photopolymer films, we present the way to develop the practical recording schedules for the fabrication of holographic gratings under accurate diffraction efficiency control. Using this method, we obtained single holographic gratings with the desired diffraction efficiency (variation 2.5%) and high-efficiency equal-strength (47%/ 47%) double holographic gratings. As a practical application, we demonstrated the centralized optical backplane architecture with uniform fanouts using the single and equal-strength double holographic gratings we recorded.

An optical centralized shared-bus architecture demonstrator for microprocessor-to-memory interconnects

An architecture demonstrator of an innovative interconnect scheme called the optical centralized shared-bus is presented. This architecture retains the advantages of shared-bus topology while at the same time specifying a uniform interface between the electrical and the optical backplane layers in contrast to other proposed architectures. For the first time, a fanout equalized optical backplane bus is demonstrated. In this architecture demonstrator, the data paths required for the microprocessor-to-memory interconnects are provided by the optical centralized shared-bus. The optoelectronic interface modules are optimized to support data rates up to 1.25 Gb/s. The objective of this microprocessor-to-memory interconnects demonstration is to ensure the feasibility of applying this innovative architecture in real systems.

Crosstalk and interconnection distance considerations for board-to-board optical interconnects using 2-D VCSEL and microlens array

We describe the design and experimental characterization of a substrate-mode optical backplane using 0.5-, 0.75- and 1-mm spacing two-dimensional (2-D) optical beam arrays. The system uses arrays of multiplexed holograms to implement free space board-to-board interconnects, and employs 250-/spl mu/m pitch 2-D vertical-cavity surface-emitting lasers (VCSEL) and microlens array as a transmitter to provide 0.5- to 1-mm spacing 2-D beam array, operating at 850 nm. By comparing the optical beam properties at the detector plane including the spot size and power uniformity of the optical beam array, as well as signal-to-noise ratio (SNR), the maximum interconnect distances are justified. Furthermore, we point out the improvement of the throughput that can be achieved by 2D crosstalk analysis within the same design concept. The results of crosstalk analysis obtained here can be used for application to the standard five-board free-space optical backplane system.

A method for rebroadcasting signals in an optical backplane bus system

A guided-wave optical backplane bus system intended for use in high-performance board-to-board interconnects is described. Its multiplexed polymeric holograms can implement optical signal broadcast between boards so that all boards share common optical channels. By introducing an active coupler to the doubly multiplexed hologram at the center board, signals received from any board can be rebroadcast to all other boards. We describe the design concepts for a centralized optical backplane and the resulting performance and assembly advantages over previously developed guided-wave and free-space optical backplane bus systems used for broadcasting signals. These advantages include equalized fan-out power, increased interconnect distance, and simpler fabrication.

All-Printed Thin-Film Transistor Based on Purified Single-Walled Carbon Nanotubes with Linear Response

We report an all-printed thin-film transistor (TFT) on a polyimide substrate with linear transconductance response. The TFT is based on our purified single-walled carbon nanotube (SWCNT) solution that is primarily consists of semiconducting carbon nanotubes (CNTs) with low metal impurities. The all-printed TFT exhibits a high ON/OFF ratio of around 103 and bias-independent transconductance over a certain gate bias range. Such bias-independent transconductance property is different from that of conventional metal-oxide-semiconductor field-effect transistors (MOSFETs) due to the special band structure and the one-dimensional (1D) quantum confined density of state (DOS) of CNTs. The bias-independent transconductance promises modulation linearity for analog electronics.

15-gb/s bit-interleaved optical backplane bus using volume photopolymer holograms

A 15-Gb/s bit-interleaved optical backplane bus interconnection is experimentally demonstrated in a three-board system based on optical backplane using volume photopolymer holograms. During upstream data transferring, bit pulses from each daughter board are superposed to form an interleaved sequence while for downstream data transferring, the data broadcast from the central board are time-division demultiplexed locally at each daughter board, and only the destined bits are stored respectively. In this way, slow electronic chips can be coordinated to generate a high aggregated bandwidth to relieve wiring congestion. Both nonreturn-to-zero and return-to-zero signaling modes based on vertical-cavity surface-emitting laser sources and pulse lasers are independently employed to implement 2.5- and 15-Gb/s operations. This optical bus architecture also provides a secure and reliable data storage method at 850 nm with a bit-error rate better than 10-12

Demonstration of the centralized optical backplane architecture in a three-board microprocessor-to-memory interconnect system

Abstract A prototype of a novel interconnection architecture called the centralized optical backplane (COB) was experimentally demonstrated in a three-board microprocessor-to-memory interconnect system. COB keeps the advantages of bus architecture while at the same time providing uniform optical signal fan-outs. In the prototype, the required connectivity for the microprocessor-to-memory interconnect was achieved by using a COB. The optoelectronic interface modules were optimized to support high-speed processing elements at data rates up to 1.25 Gbps . This demonstration illustrates the conceptual design of the COB and its feasibility in real systems.

A flexible thin-film transistor with high field-effect mobility by using carbon nanotubes

This paper describes a flexible thin-film transistor (TFT) fabricated on a standard transparency fdm. The carrier transport layer of this TFT is a high-density ultrapure carbon nanotube (CNT) film formed by using an electronic-grade CNT solution from Brewer Science, Inc. This CINT-TFT demonstrates a high field-effect mobility of ~ 48,000 cm2/Vs and a large current-carrying capacity of > 35 mA. Such a device would become a critical building block of next-generation low-cost large-area high-speed flexible electronics.