Optimal amplification of signals in the nano-ampere range
The academic community in Europe has established itself at the forefront of nanotechnology research. The Information Society Technologies Programme has played an important role in stimulating innovation in this field. The Nanomass II project, which built on the progress made during the original Nanomass project, is a perfect example. Nanomass II was coordinated by the Universitat Autonoma de Barcelona. Scientists with its Department of Electronic Engineering oversaw the development of the new mass sensor. One of the issues that had to be resolved was the proper handling of the electrical signal produced by the nanocantilevers that form the heart of the sensor. Two different approaches were implemented in an effort to minimise the capacitance caused by the interface between the nanocantilever's transducer and the circuitry. The circuitry was based on Complementary metal–oxide–semiconductor (CMOS) technology. Tests with a current amplifier indicated that it could effectively eliminate parasitic capacitance when a virtual grounding technique was employed. In the case of a buffer amplifier, it was advantageous to produce its polarisation capacitance using the same nanolithographical process as for the transducer. The effect of autopolarisation was also investigated. Both amplifiers proved capable of accurately measuring currents in the range of 10-100 nanoamperes within a bandwidth of one megahertz. Finally, the usefulness of the sensor was enhanced with the inclusion of phase detection circuitry.
