Single molecule sensing using nano-field effect transistors: device & circuit aspects

With significant progress in CMOS process technology, we are now able to manufacture nano-scale Field-Effect Transistors (FETs) down to 7 nm. This has opened doors not just for better computing but also for areas like bio-sensing for proteins and DNA.

While semiconductor nanowire devices have already been demonstrated as highly sensitive detectors for charged molecules, recently a new device has been proposed, which is the symbiotic combination of a nanopore and a nanoscaled field effect transistor, where the FET detects the presence and the motion of single molecules that are passing through the pore. An important innovation lies in the large-scale integration of nanoscale transistors for analyzing biological systems, which could provide for massive parallelization and deliver a more complete view of a biological system at a reasonable cost. However, there are several challenges open that still need to be tackled to achieve such a large-scale bio-electronic sensor chip. 

In this PhD thesis, the student will investigate initially existing nano-sized field effect transistors, bioFETs and nanopore FETs, for their ability to sense and analyze single biomolecules in electrolytic environments. Novel designs using advanced nodes will be investigated, and the design will be steered using on the one hand experimental observations from the 1^st generation devices, including e.g. noise and required bandwidth, and on the other hand considerations from the surrounding read-out circuitry. The interactions between technology, device and circuit have a determining influence on the final system performance and will be explored in this thesis. This includes device-level modifications such as surface coatings, but also the interaction between the device and the circuit. The conjunction of technology and device design with array circuit layout and architecture and read-out ampifier design will influence the sensor bandwidth as well as the sensor array density and attainable parallelism, crucial parameters of sensor chip performance. Based on experimental data, compact models will be generated in collaboration with circuit design experts. This model will be used to theoretically explore different biasing schemes and measurement strategies, e.g. using ac-biasing. 

As this topic requires in-depth understanding of both the experimental biosensor device properties and of the circuit requirements, the work involves both working in the “labs”, such as cleanroom, bio-chemistry labs and on electrical characterization tools and modeling and simulation using e.g. TCAD tools.

Imec is soliciting enthusiastic PhD candidates to advance single molecule electrical sensing technology, approaching the problem both from the experimental side and from a higher, circuit level.