Electronics and Optics on One Chip Getting Light out of Silicon


Reading time ( words)

Electronics and light don't go well together on a standard 'CMOS' chip. Researcher Satadal Dutta of the University of Twente succeeded in introducing a light connection into the heart of a semiconductor chip. In this way, two circuits can communicate. Or: the worlds of electronics and photonics are connected.

What is particularly attractive about Dutta's solution is that no special materials or manufacturing processes are needed: the light comes from silicon. The light source, detector and the light channel can be made using the technology that is used to make the electronic circuits. Fully optical circuits are available nowadays, but they use materials like indium phosphide and gallium arsenide, which can't easily be combined with the CMOS chip processes used for semiconductor chips you'll find in today's smartphones, for example.

Avalanche LED

The alternative would be: make a LED out of silicon. And that's the problem: silicon only emits a tiny amount of infrared light, while a detector made out of silicon needs visible light. They are talking and listening at different wavelengths. Dutta therefore chooses a remarkable way out: connect the LED reverse. At low voltages, there's no current, but at a voltage that is high enough, there will be a small current that amplifies itself like an avalanche. In this 'avalanche mode', the LED will transmit visible light. Using the same process, the light detector, as well as the light channel in-between can be made. Thanks to the special comb structure that Dutta designed, the light source gets more uniform and energy efficient.

Isolation

An optical link on a chip is a good way to 'galvanically' isolate two circuits from each other. This is often necessary in cases where one circuit is a low-voltage and low-current one, while the other is a high-power circuit. They should be connected, but not by conducting wires, for reasons of safety. A classic transformer is an option then, but an optical connection is often used as well. Until now, this is a separate 'optocoupler', which is large and has a limited bit rate. Dutta's new solution is much more compact as an alternative: it total, it is just a few tens of microns and it offers the protection that's needed. Compared to optical channels in full-optical circuits, the energy consumption is relatively high, as there is quite some scattering of light. On the other hand: designing the electronics around the optical link in an efficient way, the amount of light needed for a successful connection, can be kept to a minimum.

Connecting worlds

All-optical circuits may become the 'new electronics', predictions say. In the transition from electronic to optic circuits, hybrid circuits, like the one Dutta designed, could play an important role.

Satadal Dutta (1990, Barrackpore, India) did his PhD research in the Semiconductor Components group of Prof Jurriaan Schmitz, together with the Integrated Circuit Design group of Prof. Bram Nauta. Dutta defended his thesis 'Avalanche-mode silicon LEDs for monolithic optical coupling in CMOS technology' on 8 November. It was supported financially by NWO-TTW in The Netherlands and by NXP Semiconductors.

Share


Suggested Items

Beyond Scaling: An Electronics Resurgence Initiative

06/05/2017 | DARPA
The Department of Defense’s proposed FY 2018 budget includes a $75 million allocation for DARPA in support of a new, public-private “electronics resurgence” initiative. The initiative seeks to undergird a new era of electronics in which advances in performance will be catalyzed not just by continued component miniaturization but also by radically new microsystem materials, designs, and architectures.

Today’s MilAero Options, Part 1: 'Pride Goeth Before...'

04/12/2016 | Marc Carter
Historians, with their 20/20 hindsight, often write about the inevitable decline and fall of kingdoms, empires, religions, organizations, governments, and all the other permanent structures we humans build.

Stretchable Inks: Changing the Wearables Market and the Landscape of Manufacturing

05/13/2015 | Barry Matties, I-Connect007
I-Connect007 Publisher Barry Matties and DuPont’s Steven Willoughby and Michael Burrows spoke recently and discussed new material for wearable electronics: stretchable inks. Wearable electronics is a fast growing sector of the electronics industry that is inspiring new and exciting products, as well as changing the requirements for becoming an electronics manufacturer.



Copyright © 2018 I-Connect007. All rights reserved.