When bio-Nanotechnology meets Microelectronics

During the last years, material science was focusing on the exploration of the material characteristics at nanoscale. To completely exploit the ultra-small dimension and high sensitivity of these materials, researchers addressed the development of nanodevices including only a single nanostructured element, such as nanowires (NWs), nanotubes, molecules or nanoparticles. These nanomaterials can also be considered the basis for a new generation of bio-sensors able to interact with gas, molecules (e.g., DNA molecules) or other bio-substances at nanoscale. To electrically connect the nano-element, we use planar gold nanogaps (<10nm) organized in arrays and obtained through electromigration process controlled by a full custom PCB-based modular system. During first experiments, monolayers of conductive Thiophene molecules have been self-assembled onto the nanogap resulting in a gold-molecules-gold molecular junction. Even functionalized NWs can be placed in the nanogap using dielectrophoresis. The I/V characteristic of a Metal- Molecular-Metal junction shows that a plausible resistance is in the range 10MΩ – 10GΩ but it strongly depends on the size of NWs or on the type, the number and the length of bonded molecules on the nanogap. Basically, these new generation sensors rely on changes of electrical properties (R, C) of nanodevices that have to be converted into electrical signals with an ad-hoc interfacing circuit fabricated in a standard low-cost technology. The CMOS process satisfies these requirements. The design of the read-out circuit has to garantee: – large R and C read-out range, due to process variation of nanodevices; – high SNR, to measure ultra-low current flowing through molecular nanodevices; – low power consumption to support high densitity integration of nanosensors organized in array; A quasi-digital Resistance to time-domain converter (e.g., Resistance-to-Frequency(R2F), Resistance-to-Time(R2T), PWM) can be an adaptive and effective solution. The proposed R2F converter shows low measurement error (<1%) within the 50kΩ – 3GΩ range and consumes 142μW. Moreover, the last R2T prototype consumes only 8.5μW, it has higher linearity in the whole range with maximum measurement error of 0.8%.