NEMSIC: Hybrid Nano-Electro-Mechanical / Integrated Circuit Systems for Sensing and Power Management Applications

To detect a carcinogen, a pharmaceutically active compound or toxic gases in the environment within seconds thanks to a handheld device: a revolution that may be made possible through the integration of so-called NEMS, miniaturised electromechanical structures in which at least one dimension is of nanometre scale, on an electronic chip.
The devices envisaged in the framework of the FP7 STREP project NEMSIC, coordinated by Prof. A.M. Ionescu at EPFL and including a broad European partnership, are some tens of nanometre thick and one micrometre long and will include both the sensors and the electronics necessary for data analysis.
At the heart of the "intelligent sensor" is a suspended nano-wire which is excited to vibrate at a particular frequency - its resonance frequency. The wire is chemically or biologically functionalised to make it selective for target molecules like carcinogens. Binding of target molecules leads to an increase in the mass of of the wire which in turn will change its resonance frequency and vibrate at a lower frequency (think of a violin: the thicker the string the lower the tone). Apart from the resonance frequency, the shape of the resonance curve (its quality factor) is also expected to change (see Figure 1).

The NEMSIC silicon nanowires have advanced local information processing capabilities as compared to traditional NEM resonators...

...being realized like vibrating gate or a vibrating body transistors (see Figure 2). Therefore, the resulting signal is amplified and can be easily interfaced with the external world. The project proposes the realization of the first active vibrating sensor structures with very low power consumption.
This device is, for example, expected to detect a single specific cancerous molecule; it will also allow environmental monitoring to detect carbon, nitride or sulphur oxide. The data will be analysed and made available in a few seconds. NEMSIC sees other future applications in drug screening and DNA detection.

NEMSIC is a very challenging project, which requires the development of innovative technologies...

...among which the two most important ones are:
• The demonstration of a fabrication platform on silicon for vibrating and switchable NEMS structures with dimensions smaller than 100 nanometres that will enable sensing performances and miniaturisation beyond any actual system, and
• The compatibility of this platform with standard electronics for data analysis and presentation.
In the beginning, the project will develop new principles and key technologies for “intelligent” sensors based on NEMS towards environmental monitoring and for detection of specific bio-molecules. Techniques for immobilizing chemical species and bio-molecules will also be studied and in parallel simulation tools will be developed to support the technology.

A NEMSIC core activity is studying the compatibility of the NEMS devices with the electronics circuits...

...especially conceived for reading of the sensing values will be developed in two fabrication processes, allowing for optimization of the characteristics measured in the first step. Also great attention will be given to reliability and metrology of both NEMS and electronics circuits.
In parallel, NEMSIC will develop an advanced technology platform at CEA-LETI that will allow for the fabrication of advanced NEMS that are compatible with silicon ICs. A very aggressive technology will be developed by the project in order to reach a feature size of 50 nanometres or less. In Figure 2 an example of such extremely small feature size is shown in a typical series of three suspended nano-wires, which can show excellent performances in terms of sensitivity, stiffness and in miniaturization potential, in addition to the high frequency vibration capability. Figure 3 shows another possible architecture of a suspended bent nano-wire that can be realized with the technology provided by the project partners.
The surface of these nanostructures will be functionalised to become sensible to specific gases or bio-molecules as well as to combine them with the appropriate electronics for powering, reading and storing.

The scientific innovation potential of the project is extremely high...

...the final device may have a very low cost, may be used in a portable system and may also be multi-functional, for gas detection.
Moreover, NEMISIC will explore for supplementary functionality of the fabricated NEM-FETs as CMOS-compatible power management switches, enabling subthreshold power savings.
The project objective for 2011 is to fabricate the sensors and the electronic circuit as well as to understand the sensitivity and resolution limits; a possible industrialisation is estimated to be possible within 3 to 5 years.