Electro-Optic Platform for Free Space CMOS Photonics
Completed Project (2009-2013)
Research Team: Alexandru Serb (PhD thesis), Konstantin Nikolic, Timothy Constandinou
Collaborators: DNA Electronics Ltd.
Funding: Engineering and Physical Sciences Research Council (EPSRC) EP/G070466/1
With the recent surge in the demand for lab-on-chip applications, the requirement for a low-cost integration of different technologies, in particular CMOS/MEMS and microfluidics has become crucial. Economies-of-scale especially driven by the semiconductor industry favour solutions based on unmodified commercial processes. The constraints dictated by the varying range of physical dimensions of the different components make wafer-level integration too costly for low-cost mass manufacture. A common technique is therefore to integrate these components at die-level; however, this brings on its own challenges. For example, to package a lab-on-chip system for chemical sensing requires careful encapsulation of delicate bond wires and the engineering of a robust seal for fluidic isolation. This presents a question on reliability but also a bottleneck in scalability, i.e. for mass manufacture.
This research has proposed a radically different approach to solving this interconnect problem. Instead of connecting fine wires between the chip and package, the concept of a truly contactless CMOS lab-on-chip (i.e. zero bond wires) has been put forward. Specifically, this project has explored the feasibility of developing a fully optical link (i.e. delivering power to a chip and communicating data to/from) with the constraint of utilizing only unmodified, commercially available CMOS technology and no wired off-chip components. The concept put forward involves utilizing an external light source (eg. LED), passing this through a CMOS chip (in free space) and detecting the remaining light using an external photodetector. By implementing an optical modulator on-chip using simple pn-junctions, the absorption in the optical path can be controlled and thus data can be encoded and communicated to the external photodetector. The chip can be powered through a simple solar cell arrangement (using an on-chip photodiode).
- Demonstrating the world’s first implementation of a free-space optical modulator in unmodified, commercially available CMOS technology. This is significant because silicon is an indirect bandgap material and therefore light sources cannot be efficiently integrated.
- Investigating the effect of free carrier absorption in silicon CMOS technology, the key parameters (eg. doping concentration, device topology and structure, optical wavelength, alignment, etc) and compared performance at three different process nodes (specifically 0.13, 0.18 and 0.35 micron).
- Developing an optoelectronic test platform (i.e. laboratory apparatus) for a free space optical link between discrete (external) devices (i.e. light source and detector) and an integrated circuit based modulator. Specific features include: (1) multiple light sources (eg. infrared/visible-light lasers/LEDs/incandescent sources), (2) precise alignment and positioning, (3) continuous-time or phase-locked detection.
- Prototyping several integrated devices, circuits and systems for optical scavenging (parasitic pn-junction photodiode structures) and power management (charge pumps, regulators, bias references) to provide a stable on-chip power supply towards developing truly contactless CMOS chips.
- Securing the background intellectual property to this invention.
Ongoing and future research will concentrate on further optimizing the structures that have already been developed towards the monolithic integration in commercial lab-on-chip platforms.
- Serb, A., Nikolic, K., & Constandinou, T. G. (2011). A CMOS-based light modulator for contactless data transfer: theory and concept. In SPIE OPTO (pp. 794317-794317).
- Nikolic, K., Serb, A., & Constandinou, T. G. (2011). An Optical Modulator in Unmodified, Commercially Available CMOS Technology. Photonics Technology Letters, IEEE, 23(16), 1115-1117.
- Serb, A., Nikolic, K., & Constandinou, T. G. (2011). Feasibility of an electro-optic link for bondpad-less CMOS lab-on-chips. In Biomedical Circuits and Systems Conference (BioCAS), 2011 IEEE (pp. 353-356).
- Luan, S., Eftekhar, A., Murphy, O. H., & Constandinou, T. G. (2011). Towards an inductively coupled power/data link for bondpad-less silicon chips. In Circuits and Systems (ISCAS), 2011 IEEE International Symposium on (pp. 2597-2600). IEEE.
- Nikolic, K., Constandinou, T., & Toumazou, C. (2011). U.S. Patent Application 13/576,216.
- Garner, D. M., Bai, H., Georgiou, P., Constandinou, T. G., Reed, S., Shepherd, L. M., ... & Toumazou, C. (2010). A multichannel DNA SoC for rapid point-of-care gene detection. In 2010 IEEE International Solid-State Circuits Conference-(ISSCC).