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A CMOS-based light modulator for contactless data transfer: theory and concept

Silicon Photonics VI, 2011

A new technique pertaining to the optical contactless chip-to-board communication using a commercially available CMOS technology is under development. The main concept is to use mid-IR light from a small LED which will enter an IC from the underside, impinge upon one or more pn-junctions and be reflected by a metallic sheet so that it falls on an external, discrete photodetector. After propagation through the doped semiconductor, the light undergoes attenuation due to free carrier absorption. By varying the reverse bias across the pn-junction(s), the depletion region widths are changed and therefore modulation of light intensity can be achieved. Through this scheme, data readout can be realized optically, thus alleviating the need for galvanic contacts (most notably wirebonds).

A CMOS-based light modulator for contactless data transfer: theory and concept

2011

ABSTRACT A new technique pertaining to the optical contactless chip-to-board communication using a commercially available CMOS technology is under development. The main concept is to use mid-IR light from a small LED which will enter an IC from the underside, impinge upon one or more pn-junctions and be reflected by a metallic sheet so that it falls on an external, discrete photodetector. After propagation through the doped semiconductor, the light undergoes attenuation due to free carrier absorption.

CMOS Integration of Capacitive, Optical, and Electrical Interconnects

2007 IEEE International Interconnect Technology Conferencee, 2007

We present a 90nm test chip integrating proximity communication, optics using external lasers and photodiodes, and CML electronics on a single CMOS chip which can route data at multi-Gb/s rates through any combination of its three interconnect interfaces. A robust and flexible unclocked datapath allows independent timing and margin characterization of each path. Motivation Proximity communication provides a high-bandwidth, highdensity channel between two chips. Test results show far lower per-pin power, latency, and area costs when compared to traditional solder balls [2][3]. However, because this technique relies on capacitive coupling between two chips placed faceto-face, it only works if the chips are in very close proximity. In contrast, optical networks provide a proven communication technology for larger distances, ranging from backplanes to wide-area-networks [4]. Systems that integrate many multi-chip packages together can benefit from both communication technologies: they can use proximity communication within each package for very high bandwidth and low power data transfers, and they can communicate between packages using optical networks. In addition, such a system would likely require high-speed electrical channels for system I/O, testing, and configuration. To explore this diverse three-way marriage of optics, proximity communication, and high-speed electrical I/O, we built a CMOS test chip in the ST Microelectronics 90nm process integrating all three. In this paper, we discuss interface requirements, floorplanning, and test results from this chip.

Hybrid Integration of End-to-End Optical Interconnects on Printed Circuit Boards

IEEE Transactions on Components and Packaging Technologies, 2007

This paper discusses the integration of an end-to-end optical interconnect testbed on printed circuit boards using inexpensive off-the-shelf, bare die, optoelectronic components. We developed a process for efficient and simultaneous in-plane optical coupling between edge emitting laser and waveguides, and between photodetector and waveguide. We demonstrated an optically smooth buffer layer separating the printed circuit layer from the optical transport layer. The demonstrated radically new optical interconnect technology, which we refer to as interface optical coupling, is able to efficiently and simultaneously form optical interfaces between waveguides, lasers and photodetectors by photolithographic technique, thereby eliminating the need for micro-lenses and manual alignment. The measured laser to waveguide coupling efficiency is 45% and measured waveguide to photodetector coupling is 35%. The optical link is demonstrated to operate at 10 Gbps. Index Terms-Chip-to-chip, embedded devices, optical communication, optical integration, optical interconnect, polymer waveguide, printed circuit boards (PCBs), system-on-package (SOP). I. INTRODUCTION A S THE digital processor continues to scale down and the processing speed increases as predicted by Moore's law, the signal transport by electrical interconnection on printed circuit boards (PCBs) becomes a limiting factor for further improvement of a digital system due to its complexity in system layout, power consumption, electromagnetic interference, etc [1]. Optical interconnect is a promising solution in routing and distributing data at bit rate in multi-gigabits to above 10 Gpbs in distance less than 50 cm. In recent years, a number of chip-tochip optical interconnect technologies have been demonstrated, including thin film device optoelectronics [2], embedded active and passive component integration [3], [4], hybrid packaging of electronic and optical component [5], [6], optical board technique [7], [8], etc.

Optical I/O for Chip-to-Chip Interconnects on CMOS Platform

Optical Fiber Communication Conference/National Fiber Optic Engineers Conference 2011, 2011

Optical devices on a CMOS die and package for terabit computing are discussed. 200Gbps transmission is accomplished with a 1x10 VCSEL array. CMOS backend compatible modulators and photodetectors are demonstrated at 40Gbps for on-die integration.

Optical interconnect for on-chip data communication

2006

It is believed that the concept of integrated optical interconnect is a potential technological solution to alleviate some of the ever more pressing issues involved in exchanging data between cores in SoC architectures (inter-line crosstalk, latency, global throughput, connectivity and power consumption). This abstract summarises work carried out in the framework of the EU-funded PICMOS project on the quantitative comparison of optical interconnect to electrical interconnect in the context of on-chip data communication.

Optical Chip-to-Chip Link System by Using Optical Wiring Method for Reducing EMI

IEEE Transactions on Advanced Packaging, 2000

This paper describes a new optical link system which consists of a metal optical bench, a module printed circuit board, a driver/receiver integrated circuit, a vertical-cavity surface-emitting laser/photo diode (VCSEL/PD) array, and an optical link block with plastic optical fibers for reducing electromagnetic interference (EMI) noise. For the optical interconnection between the light-sources and detectors, an optical wiring method whose distinctive features include the absence of EMI noise and easy assembly is proposed. The results clearly demonstrate that the use of an optical wiring method can provide robust, cost-effective assembly and easy-repair. We successfully achieved a 4.5 Gb/s data transmission rate without EMI problems.

Optical interconnections on electrical boards using embedded active optoelectronic components

IEEE Journal of Selected Topics in Quantum Electronics, 2003

Significant opportunities are emerging for optical interconnections at the board, module, and chip level if compact, low loss, high data rate optical interconnections can be integrated into these electrical interconnection systems. This paper describes an integration process for creating optical interconnections which can be integrated in a postprocessing format onto standard boards, modules, and integrated circuits. These optical interconnections utilize active thin-film optoelectronic components embedded in waveguides, which are integrated onto or into the interconnection substrate, thus providing an electrical output on the substrate from an optical interconnection. These embedded optical interconnections are reported herein using BCB (Benzocyclobutene) polymer optical waveguides in two different formats, as well as a third waveguide structure using a BCB cladding with an Ultem core. All of these waveguides were fabricated with InGaAs-based thin-film inverted metal-semiconductor-metal (I-MSM) photodetectors embedded in the waveguide layer, thus eliminating the need for beam turning elements at the output of the waveguide. These embedded interconnections have been fabricated and tested, and the coupling efficiency of the optical signals from the waveguides to the embedded photodetectors was estimated from these measurements. These measurement-based estimates are then compared to theoretical models of the coupling efficiency. Using the theoretical coupling efficiency model, variable coupling can be engineered into the interconnect design, thus enabling partial coupling for arrays of photodetectors embedded in waveguide interconnections.

A novel bidirectional CMOS transceiver for chip-to-chip optical interconnects

IEEE Photonics Technology Letters, 2000

A novel bidirectional complementary metal-oxide-semiconductor (CMOS) transceiver for chip-to-chip optical interconnects operating at 2.5 Gb/s is proposed, which shares the common block of a receiver and a transmitter on a single chip. The share of the common block of two circuits makes it possible to save 55% or 20% of power dissipation, depending on the operating mode. The chip in 0.18m CMOS technology occupies an area of 0.82 0.82 mm 2 , 70% of the total area of a typical unshared transceiver chip. The transmitting and receiving modes of operation show 3-dB bandwidths of 2.2 and 2.4 GHz and electrical isolations of 28 and 40 dB, respectively.