integrated circuits An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

, optical interconnects refers to any system of transmitting signals from one part of an integrated circuit to another using light. Optical interconnects have been the topic of study due to the high latency and power consumption incurred by conventional metal interconnects in transmitting electrical signals over long distances, such as in interconnects classed as '' global interconnects''. The

International Technology Roadmap for Semiconductors The International Technology Roadmap for Semiconductors (ITRS) is a set of documents that was coordinated and organized by Semiconductor Research Corporation and produced by a group of experts in the semiconductor industry. These experts were rep ...

(ITRS) has highlighted interconnect scaling as a problem for the semiconductor industry. In electrical interconnects, nonlinear

signal A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...

s (e.g. digital signals) are transmitted by copper wires conventionally, and these electrical wires all have resistance and

capacitance Capacitance is the ability of an object to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are two closely related ...

which severely limits the rise time of signals when the dimension of the wires are scaled down. Optical solution are used to transmit signals through long distances to substitute interconnection between dies within the

integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

(IC) package. In order to control the optical signals inside the small IC package properly,

microelectromechanical system MEMS (micro-electromechanical systems) is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size (i.e., 0.001 to 0.1 mm), and MEMS devices ...

(MEMS) technology can be used to integrate the optical components (i.e.

optical waveguide An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber waveguides, transparent dielectric waveguides made of plastic and glass, liquid ligh ...

s, optical fibers,

lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...

mirror A mirror, also known as a looking glass, is an object that Reflection (physics), reflects an image. Light that bounces off a mirror forms an image of whatever is in front of it, which is then focused through the lens of the eye or a camera ...

s, optical

actuators An actuator is a component of a machine that produces force, torque, or displacement, when an electrical, pneumatic or hydraulic input is supplied to it in a system (called an actuating system). The effect is usually produced in a controlled way. ...

, optical

sensors A sensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal. In the broadest definition, a sensor is a devi ...

etc.) and the electronic parts together effectively.

Problems of the current interconnect in the package

Conventional physical metal wires possess both resistance and

, limiting the rise time of signals. Bits of information will overlap with each other when the frequency of signal is increased to a certain level.David A. B. Miller, ‘Rationale and Challenges for Optical Interconnects to Electronic Chips’, Proceedings of the IEEE, Vol. 88, No. 6, June 2000

Benefits of using optical interconnection

Optical interconnections can provide benefits over conventional metal wires which include: # More predictable timing # Reduction of power and area for clock distribution # Distance independence of performance of optical interconnects # No frequency-dependent Cross-talk # Architectural advantages # Reducing power dissipation in interconnects # Voltage isolation # Density of interconnects # Reducing the wiring layers # Chips could be tested in a non-contact optical test set # Benefits of short optical pulses

Challenges for optical interconnect

However, there are still many technical challenges in implementing dense optical interconnects to silicon CMOS chips. These challenges are listed as below:R.K. Dokania and A.B. Apsel, "Analysis of Challenges for On-Chip Optical Interconnects", ACM Proceedings of Great Lakes Symposium on VLSI, May 10–12, 2009, Boston # Receiver circuits and low-capacitance integration of

photodetectors Photodetectors, also called photosensors, are devices that detect light or other forms of electromagnetic radiation and convert it into an electrical signal. They are essential in a wide range of applications, from digital imaging and optical c ...

# Evolutionary improvement in optoelectronic devices # Absence of appropriate practical optomechanical technology # Integration technologies # Polarization control # Temperature dependencies and process variation # Losses and errors # Testability # Packaging

References

{{reflist Integrated circuits

Problems of the current interconnect in the package

Benefits of using optical interconnection

Challenges for optical interconnect

See also

References